Journal articles: 'Cytokinin degradation'

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Avalbaev, A. M., K. A. Somov, R. A. Yuldashev, and F. M. Shakirova. "Cytokinin oxidase is key enzyme of cytokinin degradation." Biochemistry (Moscow) 77, no. 12 (December 2012): 1354–61. http://dx.doi.org/10.1134/s0006297912120024.

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Frébortová, Jitka, and Ivo Frébort. "Biochemical and Structural Aspects of Cytokinin Biosynthesis and Degradation in Bacteria." Microorganisms 9, no. 6 (June 16, 2021): 1314. http://dx.doi.org/10.3390/microorganisms9061314.

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It has been known for quite some time that cytokinins, hormones typical of plants, are also produced and metabolized in bacteria. Most bacteria can only form the tRNA-bound cytokinins, but there are examples of plant-associated bacteria, both pathogenic and beneficial, that actively synthesize cytokinins to interact with their host. Similar to plants, bacteria produce diverse cytokinin metabolites, employing corresponding metabolic pathways. The identification of genes encoding the enzymes involved in cytokinin biosynthesis and metabolism facilitated their detailed characterization based on both classical enzyme assays and structural approaches. This review summarizes the present knowledge on key enzymes involved in cytokinin biosynthesis, modifications, and degradation in bacteria, and discusses their catalytic properties in relation to the presence of specific amino acid residues and protein structure.

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Nedvěd, Daniel, Petr Hošek, Petr Klíma, and Klára Hoyerová. "Differential Subcellular Distribution of Cytokinins: How Does Membrane Transport Fit into the Big Picture?" International Journal of Molecular Sciences 22, no. 7 (March 26, 2021): 3428. http://dx.doi.org/10.3390/ijms22073428.

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Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of “equilibrative nucleoside transporters” and “purine permeases”, which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

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Chen, CM, G. Jin, BR Andersen, and JR Ertl. "Modulation of Plant Gene Expression by Cytokinins." Functional Plant Biology 20, no. 5 (1993): 609. http://dx.doi.org/10.1071/pp9930609.

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Cytokinins play important roles in plant growth and development. They regulate the synthesis or degradation of proteins and nucleic acids. Specific mRNAs and proteins are up- and down-regulated by the hormones. Regulation of plant gene expression by cytokinins is at the levels of transcription and post-transcription. Expression of a single gene can be modulated by the interaction of two hormones since the levels of cytokinin-enhanced nitrate reductase transcript are reduced by abscisic acid. Relatively high-affinity cytokinin-binding proteins have been isolated, but the physiological role of the binding proteins remains unknown. Examination of X-ray crystal structures of cytokinin molecules indicates that correct stereochemical conformation is required for a biologically active cytokinin. Using available genetic, immunological, biochemical and recombinant DNA techniques, some questions regarding the mechanisms of cytokinin action may be answered in the near future.

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Frebort, I., M. Kowalska, T. Hluska, J. Frebortova, and P. Galuszka. "Evolution of cytokinin biosynthesis and degradation." Journal of Experimental Botany 62, no. 8 (February 14, 2011): 2431–52. http://dx.doi.org/10.1093/jxb/err004.

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Berková, Veronika, Michaela Kameniarová, Vladěna Ondrisková, Miroslav Berka, Simona Menšíková, Romana Kopecká, Markéta Luklová, et al. "Arabidopsis Response to Inhibitor of Cytokinin Degradation INCYDE: Modulations of Cytokinin Signaling and Plant Proteome." Plants 9, no. 11 (November 13, 2020): 1563. http://dx.doi.org/10.3390/plants9111563.

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Cytokinins are multifaceted plant hormones that play crucial roles in plant interactions with the environment. Modulations in cytokinin metabolism and signaling have been successfully used for elevating plant tolerance to biotic and abiotic stressors. Here, we analyzed Arabidopsis thaliana response to INhibitor of CYtokinin DEgradation (INCYDE), a potent inhibitor of cytokinin dehydrogenase. We found that at low nanomolar concentration, the effect of INCYCE on seedling growth and development was not significantly different from that of trans-Zeatin treatment. However, an alteration in the spatial distribution of cytokinin signaling was found at low micromolar concentrations, and proteomics analysis revealed a significant impact on the molecular level. An in-depth proteome analysis of an early (24 h) response and a dose-dependent response after 168 h highlighted the effects on primary and secondary metabolism, including alterations in ribosomal subunits, RNA metabolism, modulations of proteins associated with chromatin, and the flavonoid and phenylpropanoid biosynthetic pathway. The observed attenuation in stress-response mechanisms, including abscisic acid signaling and the metabolism of jasmonates, could explain previously reported positive effects of INCYDE under mild stress conditions.

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Werner, T., I. Köllmer, I. Bartrina, K. Holst, and T. Schmülling. "New Insights into the Biology of Cytokinin Degradation." Plant Biology 8, no. 3 (May 2006): 371–81. http://dx.doi.org/10.1055/s-2006-923928.

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Acheampong, Atiako Kwame, Carly Shanks, Chia-Yi Cheng, G. Eric Schaller, Yasin Dagdas, and Joseph J. Kieber. "EXO70D isoforms mediate selective autophagic degradation of type-A ARR proteins to regulate cytokinin sensitivity." Proceedings of the National Academy of Sciences 117, no. 43 (October 13, 2020): 27034–43. http://dx.doi.org/10.1073/pnas.2013161117.

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The phytohormone cytokinin influences many aspects of plant growth and development, several of which also involve the cellular process of autophagy, including leaf senescence, nutrient remobilization, and developmental transitions. The Arabidopsis type-A response regulators (type-A ARR) are negative regulators of cytokinin signaling that are transcriptionally induced in response to cytokinin. Here, we describe a mechanistic link between cytokinin signaling and autophagy, demonstrating that plants modulate cytokinin sensitivity through autophagic regulation of type-A ARR proteins. Type-A ARR proteins were degraded by autophagy in an AUTOPHAGY-RELATED (ATG)5-dependent manner, and this degradation is promoted by phosphorylation on a conserved aspartate in the receiver domain of the type-A ARRs. EXO70D family members interacted with type-A ARR proteins, likely in a phosphorylation-dependent manner, and recruited them to autophagosomes via interaction of the EXO70D AIM with the core autophagy protein, ATG8. Consistently, loss-of-function exo70D1,2,3 mutants exhibited compromised targeting of type-A ARRs to autophagic vesicles, have elevated levels of type-A ARR proteins, and are hyposensitive to cytokinin. Disruption of both type-A ARRs and EXO70D1,2,3 compromised survival in carbon-deficient conditions, suggesting interaction between autophagy and cytokinin responsiveness in response to stress. These results indicate that the EXO70D proteins act as selective autophagy receptors to target type-A ARR cargos for autophagic degradation, demonstrating modulation of cytokinin signaling by selective autophagy.

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Frébortová, Jitka. "Function of plant defense secondary metabolite in cytokinin degradation." Plant Signaling & Behavior 5, no. 5 (May 2010): 523–25. http://dx.doi.org/10.4161/psb.10965.

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Chi, Wei, Jing Li, Baoye He, Xin Chai, Xiumei Xu, Xuwu Sun, Jingjing Jiang, et al. "DEG9, a serine protease, modulates cytokinin and light signaling by regulating the level of ARABIDOPSIS RESPONSE REGULATOR 4." Proceedings of the National Academy of Sciences 113, no. 25 (June 6, 2016): E3568—E3576. http://dx.doi.org/10.1073/pnas.1601724113.

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Cytokinin is an essential phytohormone that controls various biological processes in plants. A number of response regulators are known to be important for cytokinin signal transduction. ARABIDOPSIS RESPONSE REGULATOR 4 (ARR4) mediates the cross-talk between light and cytokinin signaling through modulation of the activity of phytochrome B. However, the mechanism that regulates the activity and stability of ARR4 is unknown. Here we identify an ATP-independent serine protease, degradation of periplasmic proteins 9 (DEG9), which localizes to the nucleus and regulates the stability of ARR4. Biochemical evidence shows that DEG9 interacts with ARR4, thereby targeting ARR4 for degradation, which suggests that DEG9 regulates the stability of ARR4. Moreover, genetic evidence shows that DEG9 acts upstream of ARR4 and regulates the activity of ARR4 in cytokinin and light-signaling pathways. This study thus identifies a role for a ubiquitin-independent selective protein proteolysis in the regulation of the stability of plant signaling components.

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Mercure, Eric W., Carol A. Auer, and Mark H. Brand. "Understanding the Role of Cytokinins in Tissue Proliferation of Rhododendron `Montego'." HortScience 32, no. 3 (June 1997): 447B—447. http://dx.doi.org/10.21273/hortsci.32.3.447b.

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Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons propagated in vitro. However, TP of Rhododendron `Montego' is observed initially in in vitro shoot cultures and it is characterized by the formation of multiple shoots with small leaves and nodal tumors. The formation of shoots in `Montego' TP (TP+) shoot cultures occurs without the presence of exogenous cytokinin in the medium, unlike normal `Montego' (TP–) shoot cultures, which require cytokinin for shoot growth. Structural studies have shown that tumors are composed of many adventitious buds and parenchyma cells, suggesting that TP is a result of abnormal cytokinin regulation that is controlling tumor and shoot formation. Two approaches are being used to determine if differences in cytokinin concentration and/or metabolism exist between TP+ and TP– shoot cultures. In the first approach, shoot cultures are grown in vitro for 1 week in the presence of tritiated isopentenyladenine (iP). Cytokinin uptake and metabolism are analyzed using HPLC and other analytical methods. Experiments suggest that extensive degradation and N-glucoside conjugation occur in TP+ and TP– shoots, resulting in the removal of most of the exogenous iP. In the second approach, the levels of endogenous cytokinins such as iP, isopentenyladenosine, zeatin, and zeatin riboside, are being measured in TP+ tumors and shoots and in TP– shoots by an ELISA method.

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Wang, Jian, D. S. Letham, Edwina Cornish, K. Wei, C. H. Hocart, M. Michael, and K. R. Stevenson. "Studies of Cytokinin Action and Metabolism Using Tobacco Plants Expressing either the ipt or the GUS Gene Controlled by a Chalcone Synthase Promoter. IIipt and GUS Gene Expression, Cytokinin Levels and Metabolism." Functional Plant Biology 24, no. 5 (1997): 673. http://dx.doi.org/10.1071/pp96102.

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The expression of GUS and ipt genes under control of a chalcone synthase (chs) promoter (PCHS) has been determined in tobacco (Nicotiana tabacum L.) plants and related to the development of plants expressing the chimaeric PCHS -ipt gene. GUS gene expression, which served as a model for the expression of the ipt gene, was highest in the internal phloem tissue of stems, in mature leaf laminae and in the upper part of corollas when fully open. Expression of the PCHS -ipt gene was assessed by quantifying the cytokinins produced, by determining incorporation of [3H]adenine into cytokinins and by quantifying ipt mRNA. Results from these studies were in general agreement with those based on expression of the PCHS -GUS gene. The chs promoter controlled expression of the ipt gene with some degree of tissue and temporal specificity. Expression of the ipt gene markedly elevated the cytokinin level in mature leaf laminae and the upper stems of flowering plants. The former was associated with retardation of leaf senescence and increased rates of transpiration due to changes in number, size and aperture of stomata, while the latter was associated with development of lateral shoots. In shoot tip cultures, 2-fold elevations in endogenous cytokinin level caused clear changes in development and this is discussed in relation to current concepts concerning the hormonal control of plant development. Using the transgenic tobacco tissues, it was shown that cis-zeatin is a substrate for cytokinin oxidase, that cis-zeatin is not converted to trans-zeatin in these tissues and that the endogenous cytokinin level influences the level of cytokinin oxidase activity in tissue and the rate of degradation of exogenous zeatin riboside to adenosine.

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Di Mambro, Riccardo, Micol De Ruvo, Elena Pacifici, Elena Salvi, Rosangela Sozzani, Philip N. Benfey, Wolfgang Busch, et al. "Auxin minimum triggers the developmental switch from cell division to cell differentiation in the Arabidopsis root." Proceedings of the National Academy of Sciences 114, no. 36 (August 22, 2017): E7641—E7649. http://dx.doi.org/10.1073/pnas.1705833114.

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In multicellular organisms, a stringent control of the transition between cell division and differentiation is crucial for correct tissue and organ development. In the Arabidopsis root, the boundary between dividing and differentiating cells is positioned by the antagonistic interaction of the hormones auxin and cytokinin. Cytokinin affects polar auxin transport, but how this impacts the positional information required to establish this tissue boundary, is still unknown. By combining computational modeling with molecular genetics, we show that boundary formation is dependent on cytokinin’s control on auxin polar transport and degradation. The regulation of both processes shapes the auxin profile in a well-defined auxin minimum. This auxin minimum positions the boundary between dividing and differentiating cells, acting as a trigger for this developmental transition, thus controlling meristem size.

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Laila, Rawnak, Arif Hasan Khan Robin, Jong-In Park, Gopal Saha, Hoy-Taek Kim, Md Abdul Kayum, and Ill-Sup Nou. "Expression and Role of Response Regulating, Biosynthetic and Degrading Genes for Cytokinin Signaling during Clubroot Disease Development." International Journal of Molecular Sciences 21, no. 11 (May 29, 2020): 3896. http://dx.doi.org/10.3390/ijms21113896.

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The obligate biotroph Plasmodiophora brassicae causes clubroot disease in oilseeds and vegetables of the Brassicaceae family, and cytokinins play a vital role in clubroot formation. In this study, we examined the expression patterns of 17 cytokinin-related genes involved in the biosynthesis, signaling, and degradation in Chinese cabbage inoculated with the Korean pathotype group 4 isolate of P. brassicae, Seosan. This isolate produced the most severe clubroot symptoms in Chinese cabbage cultivar “Bullam-3-ho” compared to three other Korean geographical isolates investigated. BrIPT1, a cytokinin biosynthesis gene, was induced on Day 1 and Day 28 in infected root tissues and the upregulation of this biosynthetic gene coincided with the higher expression of the response regulators BrRR1, on both Days and BrRR6 on Day 1 and 3. BrRR3 and 4 genes were also induced during gall enlargement on Day 35 in leaf tissues. The BrRR4 gene, which positively interact with phytochrome B, was consistently induced in leaf tissues on Day 1, 3, and 14 in the inoculated plants. The cytokinin degrading gene BrCKX3-6 were induced on Day 14, before gall initiation. BrCKX2,3,6 were induced until Day 28 and their expression was downregulated on Day 35. This insight improves our current understanding of the role of cytokinin signaling genes in clubroot disease development.

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Grant, Jan E., Annu Ninan, Natalia Cripps-Guazzone, Martin Shaw, Jiancheng Song, Ivan Petřík, Ondřej Novák, Mechthild Tegeder, and Paula E. Jameson. "Concurrent overexpression of amino acid permease AAP1(3a) and SUT1 sucrose transporter in pea resulted in increased seed number and changed cytokinin and protein levels." Functional Plant Biology 48, no. 9 (2021): 889. http://dx.doi.org/10.1071/fp21011.

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Using pea as our model crop, we sought to understand the regulatory control over the import of sugars and amino acids into the developing seeds and its importance for seed yield and quality. Transgenic peas simultaneously overexpressing a sucrose transporter and an amino acid transporter were developed. Pod walls, seed coats, and cotyledons were analysed separately, as well as leaves subtending developing pods. Sucrose, starch, protein, free amino acids, and endogenous cytokinins were measured during development. Temporal gene expression analyses (RT-qPCR) of amino acid (AAP), sucrose (SUT), and SWEET transporter family members, and those from cell wall invertase, cytokinin biosynthetic (IPT) and degradation (CKX) gene families indicated a strong effect of the transgenes on gene expression. In seed coats of the double transgenics, increased content and prolonged presence of cytokinin was particularly noticeable. The transgenes effectively promoted transition of young sink leaves into source leaves. We suggest the increased flux of sucrose and amino acids from source to sink, along with increased interaction between cytokinin and cell wall invertase in developing seed coats led to enhanced sink activity, resulting in higher cotyledon sucrose at process pea harvest, and increased seed number and protein content at maturity.

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Steiner, Evyatar, Monica Rojas Triana, Sivan Kubasi, Shula Blum, Javier Paz-Ares, Vicente Rubio, and David Weiss. "KISS ME DEADLY F-box proteins modulate cytokinin responses by targeting the transcription factor TCP14 for degradation." Plant Physiology 185, no. 4 (January 29, 2021): 1495–99. http://dx.doi.org/10.1093/plphys/kiab033.

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Zubo, Yan O., and G. Eric Schaller. "Role of the Cytokinin-Activated Type-B Response Regulators in Hormone Crosstalk." Plants 9, no. 2 (January 30, 2020): 166. http://dx.doi.org/10.3390/plants9020166.

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Cytokinin is an important phytohormone that employs a multistep phosphorelay to transduce the signal from receptors to the nucleus, culminating in activation of type-B response regulators which function as transcription factors. Recent chromatin immunoprecipitation-sequencing (ChIP-seq) studies have identified targets of type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) and integrated these into the cytokinin-activated transcriptional network. Primary targets of the type-B ARRs are enriched for genes involved in hormonal regulation, emphasizing the extensive crosstalk that can occur between cytokinin, auxin, abscisic acid, brassinosteroids, gibberellic acid, ethylene, jasmonic acid, and salicylic acid. Examination of hormone-related targets reveals multiple regulatory points including biosynthesis, degradation/inactivation, transport, and signal transduction. Here, we consider this early response to cytokinin in terms of the hormones involved, points of regulatory crosstalk, and physiological significance.

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Avilez-Montalvo, Johny R., Ana O. Quintana-Escobar, Hugo A. Méndez-Hernández, Víctor Aguilar-Hernández, Ligia Brito-Argáez, Rosa M. Galaz-Ávalos, Miguel A. Uc-Chuc, and Víctor M. Loyola-Vargas. "Auxin-Cytokinin Cross Talk in Somatic Embryogenesis of Coffea canephora." Plants 11, no. 15 (August 2, 2022): 2013. http://dx.doi.org/10.3390/plants11152013.

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Cytokinins (CK) are plant growth regulators involved in multiple physiological processes in plants. One less studied aspect is CK homeostasis (HM). The primary genes related to HM are involved in biosynthesis (IPT), degradation (CKX), and signaling (ARR). This paper demonstrates the effect of auxin (Aux) and CK and their cross talk in a Coffea canephora embryogenic system. The transcriptome and RT-qPCR suggest that Aux in pre-treatment represses biosynthesis, degradation, and signal CK genes. However, in the induction, there is an increase of genes implicated in the CK perception/signal, indicating perhaps, as in other species, Aux is repressing CK, and CK are inducing per se genes involved in its HM. This is reflected in the endogenous concentration of CK; pharmacology experiments helped study the effect of each plant growth regulator in our SE system. We conclude that the Aux–CK balance is crucial to directing somatic embryogenesis in C. canephora.

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Leuendorf, Jan Erik, and Thomas Schmülling. "Meeting at the DNA: Specifying Cytokinin Responses through Transcription Factor Complex Formation." Plants 10, no. 7 (July 16, 2021): 1458. http://dx.doi.org/10.3390/plants10071458.

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Cytokinin is a plant hormone regulating numerous biological processes. Its diverse functions are realized through the expression control of specific target genes. The transcription of the immediate early cytokinin target genes is regulated by type-B response regulator proteins (RRBs), which are transcription factors (TFs) of the Myb family. RRB activity is controlled by phosphorylation and protein degradation. Here, we focus on another step of regulation, the interaction of RRBs among each other or with other TFs to form active or repressive TF complexes. Several examples in Arabidopsis thaliana illustrate that RRBs form homodimers or complexes with other TFs to specify the cytokinin response. This increases the variability of the output response and provides opportunities of crosstalk between the cytokinin signaling pathway and other cellular signaling pathways. We propose that a targeted approach is required to uncover the full extent and impact of RRB interaction with other TFs.

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Alonso-Díaz, Alejandro, Santosh B. Satbhai, Roger de Pedro-Jové, Hannah M. Berry, Christian Göschl, Cristiana T. Argueso, Ondrej Novak, Wolfgang Busch, Marc Valls, and Núria S. Coll. "A genome-wide association study reveals cytokinin as a major component in the root defense responses against Ralstonia solanacearum." Journal of Experimental Botany 72, no. 7 (January 21, 2021): 2727–40. http://dx.doi.org/10.1093/jxb/eraa610.

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Abstract Bacterial wilt caused by the soil-borne pathogen Ralstonia solancearum is economically devastating, with no effective methods to fight the disease. This pathogen invades plants through their roots and colonizes their xylem, clogging the vasculature and causing rapid wilting. Key to preventing colonization are the early defense responses triggered in the host’s root upon infection, which remain mostly unknown. Here, we have taken advantage of a high-throughput in vitro infection system to screen natural variability associated with the root growth inhibition phenotype caused by R. solanacearum in Arabidopsis during the first hours of infection. To analyze the genetic determinants of this trait, we have performed a genome-wide association study, identifying allelic variation at several loci related to cytokinin metabolism, including genes responsible for biosynthesis and degradation of cytokinin. Further, our data clearly demonstrate that cytokinin signaling is induced early during the infection process and cytokinin contributes to immunity against R. solanacearum. This study highlights a new role for cytokinin in root immunity, paving the way for future research that will help in understanding the mechanisms underpinning root defenses.

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Gasparis, Przyborowski, Kała, and Nadolska-Orczyk. "Knockout of the HvCKX1 or HvCKX3 Gene in Barley (Hordeum vulgare L.) by RNA-Guided Cas9 Nuclease Affects the Regulation of Cytokinin Metabolism and Root Morphology." Cells 8, no. 8 (July 26, 2019): 782. http://dx.doi.org/10.3390/cells8080782.

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Barley is among four of the most important cereal crops with respect to global production. Increasing barley yields to desired levels can be achieved by the genetic manipulation of cytokinin content. Cytokinins are plant hormones that regulate many developmental processes and have a strong influence on grain yield. Cytokinin homeostasis is regulated by members of several multigene families. CKX genes encode the cytokinin oxidase/dehydrogenase enzyme, which catalyzes the irreversible degradation of cytokinin. Several recent studies have demonstrated that the RNAi-based silencing of CKX genes leads to increased grain yields in some crop species. To assess the possibility of increasing the grain yield of barley by knocking out CKX genes, we used an RNA-guided Cas9 system to generate ckx1 and ckx3 mutant lines with knockout mutations in the HvCKX1 and HvCKX3 genes, respectively. Homozygous, transgene-free mutant lines were subsequently selected and analyzed. A significant decrease in CKX enzyme activity was observed in the spikes of the ckx1 lines, while in the ckx3 lines, the activity remained at a similar level to that in the control plants. Despite these differences, no changes in grain yield were observed in either mutant line. In turn, differences in CKX activity in the roots between the ckx1 and ckx3 mutants were reflected via root morphology. The decreased CKX activity in the ckx1 lines corresponded to greater root length, increased surface area, and greater numbers of root hairs, while the increased CKX activity in the ckx3 mutants gave the opposite results. RNA-seq analysis of the spike and root transcriptomes revealed an altered regulation of genes controlling cytokinin metabolism and signaling, as well as other genes that are important during seed development, such as those that encode nutrient transporters. The observed changes suggest that the knockout of a single CKX gene in barley may be not sufficient for disrupting cytokinin homeostasis or increasing grain yields.

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Veselova, Svetlana V., Tatyana V. Nuzhnaya, Guzel F. Burkhanova, Sergey D. Rumyantsev, Elza K. Khusnutdinova, and Igor V. Maksimov. "Ethylene-Cytokinin Interaction Determines Early Defense Response of Wheat against Stagonospora nodorum Berk." Biomolecules 11, no. 2 (January 28, 2021): 174. http://dx.doi.org/10.3390/biom11020174.

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Ethylene, salicylic acid (SA), and jasmonic acid are the key phytohormones involved in plant immunity, and other plant hormones have been demonstrated to interact with them. The classic phytohormone cytokinins are important participants of plant defense signaling. Crosstalk between ethylene and cytokinins has not been sufficiently studied as an aspect of plant immunity and is addressed in the present research. We compared expression of the genes responsible for hormonal metabolism and signaling in wheat cultivars differing in resistance to Stagonospora nodorum in response to their infection with fungal isolates, whose virulence depends on the presence of the necrotrophic effector SnTox3. Furthermore, we studied the action of the exogenous cytokinins, ethephon (2-chloroethylphosphonic acid, ethylene-releasing agent) and 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) on infected plants. Wheat susceptibility was shown to develop due to suppression of reactive oxygen species production and decreased content of active cytokinins brought about by SnTox3-mediated activation of the ethylene signaling pathway. SnTox3 decreased cytokinin content most quickly by its activated glucosylation in an ethylene-dependent manner and, furthermore, by oxidative degradation and inhibition of biosynthesis in ethylene-dependent and ethylene-independent manners. Exogenous zeatin application enhanced wheat resistance against S. nodorum through inhibition of the ethylene signaling pathway and upregulation of SA-dependent genes. Thus, ethylene inhibited triggering of SA-dependent resistance mechanism, at least in part, by suppression of the cytokinin signaling pathway.

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Flinn, Barry S., David T. Webb, and William Newcomb. "Morphometric analysis of reserve substances and ultrastructural changes during caulogenic determination and loss of competence of Eastern White pine (Pinus strobus) cotyledons in vitro." Canadian Journal of Botany 67, no. 3 (March 1, 1989): 779–89. http://dx.doi.org/10.1139/b89-105.

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Lipid, starch, and protein reserves were monitored cytochemically and, along with certain ultrastructural changes, were quantified morphometrically during adventitious shoot determination or loss of competence in cotyledons from cultured Pinus strobus zygotic embryos. Initial expiants were rich in lipid, which declined during culture. There was more lipid retention in explants on cytokinin medium by day 5 than on basal medium. However, by day 7, five- and six-celled clusters showed greater lipid utilization than most other cells on cytokinin, which may have indicated a shift towards shoot determination in these cells. Except for an initially greater retention on cytokinin, a similar pattern for storage protein degradation was observed in both treatments. Starch levels increased during culture, but did not differ between treatments during the first 7 days. Vacuolation increased during culture and was greater on basal medium than on cytokinin. Relative nuclear size also increased, but was greater on cytokinin. Relative mitochondrial area increased during culture, except in noncluster cells on basal medium. While few differences were noted between cell types within each treatment, distinct differences in nuclear size, vacuolation, and lipid content existed between cells on cytokinin and basal medium. These coincided with the timing of caulogenic determination in cytokinin-treated expiants. The loss of lipid reserves, as well as ultrastructural changes associated with the maturation of cells on basal medium, was associated with the loss of competence.

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Duan, Jingbo, Hong Yu, Kun Yuan, Zhigang Liao, Xiangbing Meng, Yanhui Jing, Guifu Liu, Jinfang Chu, and Jiayang Li. "Strigolactone promotes cytokinin degradation through transcriptional activation ofCYTOKININ OXIDASE/DEHYDROGENASE 9in rice." Proceedings of the National Academy of Sciences 116, no. 28 (June 24, 2019): 14319–24. http://dx.doi.org/10.1073/pnas.1810980116.

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Strigolactones (SLs), a group of terpenoid lactones derived from carotenoids, are plant hormones that control numerous aspects of plant development. Although the framework of SL signaling that the repressor DWARF 53 (D53) could be SL-dependently degraded via the SL receptor D14 and F-box protein D3 has been established, the downstream response genes to SLs remain to be elucidated. Here we show that the cytokinin (CK) content is dramatically increased in shoot bases of the rice SL signaling mutantd53. By examining transcript levels of all the CK metabolism-related genes after treatment with SL analog GR24, we identifiedCYTOKININ OXIDASE/DEHYDROGENASE 9(OsCKX9) as a primary response gene significantly up-regulated within 1 h of treatment in the wild type but not ind53. We also found that OsCKX9 functions as a cytosolic and nuclear dual-localized CK catabolic enzyme, and that the overexpression ofOsCKX9suppresses the browning ofd53calli. Both the CRISPR/Cas9-generatedOsCKX9mutants andOsCKX9-overexpressing transgenic plants showed significant increases in tiller number and decreases in plant height and panicle size, suggesting that the homeostasis ofOsCKX9plays a critical role in regulating rice shoot architecture. Moreover, we identified the CK-inducible rice type-A response regulatorOsRR5as the secondary SL-responsive gene, whose expression is significantly repressed after 4 h of GR24 treatment in the wild type but not inosckx9. These findings reveal a comprehensive plant hormone cross-talk in which SL can induce the expression ofOsCKX9to down-regulate CK content, which in turn triggers the response of downstream genes.

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Jain, V., W. Kaiser, and S. C. Huber. "Cytokinin Inhibits the Proteasome-Mediated Degradation of Carbonylated Proteins in Arabidopsis Leaves." Plant and Cell Physiology 49, no. 5 (March 11, 2008): 843–52. http://dx.doi.org/10.1093/pcp/pcn060.

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FRÉBORTOVÁ, Jitka, Marco W. FRAAIJE, Petr GALUSZKA, Marek ŠEBELA, Pavel PEČ, Jan HRBÁČ, Ondřej NOVÁK, Kristin D. BILYEU, James T. ENGLISH, and Ivo FRÉBORT. "Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors." Biochemical Journal 380, no. 1 (May 15, 2004): 121–30. http://dx.doi.org/10.1042/bj20031813.

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The catalytic reaction of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was studied in detail using the recombinant flavoenzyme from maize. Determination of the redox potential of the covalently linked flavin cofactor revealed a relatively high potential dictating the type of electron acceptor that can be used by the enzyme. Using 2,6-dichlorophenol indophenol, 2,3-dimethoxy-5-methyl-1,4-benzoquinone or 1,4-naphthoquinone as electron acceptor, turnover rates with N6-(2-isopentenyl)adenine of approx. 150 s−1 could be obtained. This suggests that the natural electron acceptor of the enzyme is quite probably a p-quinone or similar compound. By using the stopped-flow technique, it was found that the enzyme is rapidly reduced by N6-(2-isopentenyl)adenine (kred=950 s−1). Re-oxidation of the reduced enzyme by molecular oxygen is too slow to be of physiological relevance, confirming its classification as a dehydrogenase. Furthermore, it was established for the first time that the enzyme is capable of degrading aromatic cytokinins, although at low reaction rates. As a result, the enzyme displays a dual catalytic mode for oxidative degradation of cytokinins: a low-rate and low-substrate specificity reaction with oxygen as the electron acceptor, and high activity and strict specificity for isopentenyladenine and analogous cytokinins with some specific electron acceptors.

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Frébortová, Jitka, Ondřej Novák, Ivo Frébort, and Radek Jorda. "Degradation of cytokinins by maize cytokinin dehydrogenase is mediated by free radicals generated by enzymatic oxidation of natural benzoxazinones." Plant Journal 61, no. 3 (February 2010): 467–81. http://dx.doi.org/10.1111/j.1365-313x.2009.04071.x.

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van Voorthuizen, Matthew J., Jaroslav Nisler, Jiancheng Song, Lukáš Spíchal, and Paula E. Jameson. "Targeting Cytokinin Homeostasis in Rapid Cycling Brassica rapa with Plant Growth Regulators INCYDE and TD-K." Plants 10, no. 1 (December 25, 2020): 39. http://dx.doi.org/10.3390/plants10010039.

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Modifying the cytokinin content in plants is a means of improving plant productivity. Here, we report the development and biological activity of compound TD-K (1-(furan-2-ylmethyl)-3-(1,2,3-thiadiazol-5-yl)urea)which is related to thidiazuron. TD-K—which exhibited extremely high antisenescence activity in the wheat leaf bioassay—and INCYDE (2-chloro-6-(3-methoxyphenyl)aminopurine)—a plant growth regulator reported to inhibit cytokinin oxidase/dehydrogenase (CKX), an enzyme involved in the degradation of the plant hormone cytokinin—were selected for investigation of their effects on the model plant Rapid Cycling Brassica rapa (RCBr). We monitored the expression of BrCKX and isopentenyl transferase (BrIPT), which codes for the key cytokinin biosynthesis enzyme, in developing leaves following INCYDE and TD-K application. Growth room experiments revealed that INCYDE increased RCBr seed yield per plant, but only when applied multiple times and when grown in 5 mM KNO3. Expression in control leaves showed transient, high levels of expression of BrCKX and BrIPT at true leaf appearance. Following INCYDE application, there was a rapid and strong upregulation of BrCKX3, and a transient downregulation of BrIPT1 and BrIPT3. Interestingly, the upregulation of BrCKX3 persisted in a milder form throughout the course of the experiment (16 days). TD-K also upregulated BrCKX3. However, in contrast to INCYDE, this effect disappeared after two days. These results suggest that both compounds (CKX inhibitor and cytokinin TD-K) influenced cytokinin homeostasis in RCBr leaves, but with different mechanisms.

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Kim, H. J., Y. H. Chiang, J. J. Kieber, and G. E. Schaller. "SCFKMD controls cytokinin signaling by regulating the degradation of type-B response regulators." Proceedings of the National Academy of Sciences 110, no. 24 (May 29, 2013): 10028–33. http://dx.doi.org/10.1073/pnas.1300403110.

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Ramireddy, Eswarayya, Hilde Nelissen, Jan Erik Leuendorf, Mieke Van Lijsebettens, Dirk Inzé, and Thomas Schmülling. "Root engineering in maize by increasing cytokinin degradation causes enhanced root growth and leaf mineral enrichment." Plant Molecular Biology 106, no. 6 (July 17, 2021): 555–67. http://dx.doi.org/10.1007/s11103-021-01173-5.

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Abstract Key message Root-specific expression of a cytokinin-degrading CKX gene in maize roots causes formation of a larger root system leading to higher element content in shoot organs. Abstract The size and architecture of the root system is functionally relevant for the access to water and soil nutrients. A great number of mostly unknown genes are involved in regulating root architecture complicating targeted breeding of plants with a larger root system. Here, we have explored whether root-specific degradation of the hormone cytokinin, which is a negative regulator of root growth, can be used to genetically engineer maize (Zea mays L.) plants with a larger root system. Root-specific expression of a CYTOKININ OXIDASE/DEHYDROGENASE (CKX) gene of Arabidopsis caused the formation of up to 46% more root dry weight while shoot growth of these transgenic lines was similar as in non-transgenic control plants. The concentration of several elements, in particular of those with low soil mobility (K, P, Mo, Zn), was increased in leaves of transgenic lines. In kernels, the changes in concentration of most elements were less pronounced, but the concentrations of Cu, Mn and Zn were significantly increased in at least one of the three independent lines. Our data illustrate the potential of an increased root system as part of efforts towards achieving biofortification. Taken together, this work has shown that root-specific expression of a CKX gene can be used to engineer the root system of maize and alter shoot element composition.

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Liu, Yang, Xun Wang, Xiaofei Wang, Wensheng Gao, and Chunxiang You. "Identification and Functional Characterization of Apple MdCKX5.2 in Root Development and Abiotic Stress Tolerance." Horticulturae 8, no. 1 (January 10, 2022): 62. http://dx.doi.org/10.3390/horticulturae8010062.

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Cytokinin oxidase/dehydrogenases (CKXs) are the key enzymes in cytokinin degradation and have been widely studied in model plants. Little is known about apple’s (Malus×domestica) CKX genes. Here, using genome-wide analysis, we identified 10 MdCKX genes in apple. The phylogenetics, chromosome locations, and genome structures were then tested. Expression analysis showed that MdCKX genes had different expression profiles in apple, pointing to the different roles. Meanwhile, relative expression analysis showed that these genes have different expression patterns in response to several exogenous cytokinin factors, including trans-zeatin (ZT), thidiazuron (TDZ), and N6-furfuryladenine (KT). Finally, we introduced the MdCKX5.2 gene into Arabidopsis to evaluate its functions, and the results suggested the transgenic Arabidopsis displayed phenotypes related to promoting primary root and lateral root development, response to exogenous ZT, and conferring to drought and salt tolerant. Taken together, our results provide insights on the possible application of the MdCKX5.2 gene for molecular breeding in apples.

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Wei, Wei, Junichi Inaba, Yan Zhao, Joseph D. Mowery, and Rosemarie Hammond. "Phytoplasma Infection Blocks Starch Breakdown and Triggers Chloroplast Degradation, Leading to Premature Leaf Senescence, Sucrose Reallocation, and Spatiotemporal Redistribution of Phytohormones." International Journal of Molecular Sciences 23, no. 3 (February 5, 2022): 1810. http://dx.doi.org/10.3390/ijms23031810.

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Witches’-broom (WB, excessive initiation, and outgrowth of axillary buds) is one of the remarkable symptoms in plants caused by phytoplasmas, minute wall-less intracellular bacteria. In healthy plants, axillary bud initiation and outgrowth are regulated by an intricate interplay of nutrients (such as sugars), hormones, and environmental factors. However, how these factors are involved in the induction of WB by phytoplasma is poorly understood. We postulated that the WB symptom is a manifestation of the pathologically induced redistribution of sugar and phytohormones. Employing potato purple top phytoplasma and its alternative host tomato (Solanum lycopersicum), sugar metabolism and transportation, and the spatiotemporal distribution of phytohormones were investigated. A transmission electron microscopy (TEM) analysis revealed that starch breakdown was inhibited, resulting in the degradation of damaged chloroplasts, and in turn, premature leaf senescence. In the infected source leaves, two marker genes encoding asparagine synthetase (Sl-ASN) and trehalose-6-phosphate synthase (Sl-TPS) that induce early leaf senescence were significantly up-regulated. However, the key gibberellin biosynthesis gene that encodes ent-kaurene synthase (Sl-KS) was suppressed. The assessment of sugar content in various infected tissues (mature leaves, stems, roots, and leaf axils) indicated that sucrose transportation through phloem was impeded, leading to sucrose reallocation into the leaf axils. Excessive callose deposition and the resulting reduction in sieve pore size revealed by aniline blue staining and TEM provided additional evidence to support impaired sugar transport. In addition, a spatiotemporal distribution study of cytokinin and auxin using reporter lines detected a cytokinin signal in leaf axils where the axillary buds initiated. However, the auxin responsive signal was rarely present in such leaf axils, but at the tips of the newly elongated buds. These results suggested that redistributed sucrose as well as cytokinin in leaf axils triggered the axillary bud initiation, and auxin played a role in the bud elongation. The expression profiles of genes encoding squamosa promoter-binding proteins (Sl-SBP1), and BRANCHED1 (Sl-BRC1a and Sl-BRC1b) that control axillary bud release, as determined by quantitative reverse transcription (qRT)-PCR, indicated their roles in WB induction. However, their interactions with sugars and cytokinins require further study. Our findings provide a comprehensive insight into the mechanisms by which phytoplasmas induce WB along with leaf chlorosis, little leaf, and stunted growth.

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Brinegar, A. Chris, Anne Stevens, and J. Eugene Fox. "Biosynthesis and Degradation of a Wheat Embryo Cytokinin-Binding Protein during Embryogenesis and Germination." Plant Physiology 79, no. 3 (November 1, 1985): 706–10. http://dx.doi.org/10.1104/pp.79.3.706.

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34

Mantilla, Gunther, Gabriel Antonio Lorenzo, and Libertad Mascarini. "Hormonal endogenous changes in response to the exogenous 6-benzylaminopurine application in pre- and post-harvesting lilium flower stalks." Ornamental Horticulture 27, no. 3 (September 2021): 357–64. http://dx.doi.org/10.1590/2447-536x.v27i3.2337.

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Abstract Phyto-hormones play a key role in regulating plant responses to stress. Cytokines are a type of phyto-hormones involved in the regulation of many important biological processes related to growth, development, and response to environmental variables. The exogenous application of cytokines increases the possibility of delaying senescence; however, this is a physiological process, and, under certain conditions, degradation processes may be triggered. The effect of 6-bencilaminopurine application and the endogenous hormonal changes involved in lilies floral stalks after their cutting were studied. In order to improve vase life and quality of Lilium longiflorum ‘Brindisi’ flower stalks, they were sprayed with 6-BAP, at a concentration of 300 ppm at pre-harvest, post-harvest, and pre- and post-harvest stages. After that, they were compared to non-sprayed control stalks. The application of 6-BAP caused endogenous hormonal changes in abscisic acid and cytokinin levels, and the most effective treatment was pre-harvest spraying. This treatment proved to be an appropriate method to improve the stalk tolerance to post-harvest stress as it delayed the appearance of senescence symptoms and reduced the speed of chlorophyll degradation with differences of up to 10% with respect to untreated stalks. In addition, the opening of flowers was delayed by up to 2 days, although there were no significant differences in total vase life.

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Taverner, Elizabeth A., David S. Letham, Jian Wang, and Edwina Cornish. "Inhibition of carnation petal inrolling by growth retardants and cytokinins." Functional Plant Biology 27, no. 4 (2000): 357. http://dx.doi.org/10.1071/pp99093.

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Excised carnation petals induced to senescence by ethrel (an ethylene-releasing compound) exhibited morphological changes that closely resembled those of senescing petalsin situ in cut flowers. The sensitivity of the excised petals to ethylene was reduced by exogenous cytokinin and this type of hormonal interaction in the control of plant development is discussed. Using the excised petals, a number of known and potential growth inhibitors were compared for ability to prevent petal inrolling induced by ethrel. Cycloheximide and 6-methylpurine were the most effective and inhibited inrolling almost completely, but purine, purine riboside, lauric acid, L-azetidine-2-carboxylic acid and n-decyl alcohol were also very effective. All these compounds were considerably more effective than any cytokinin tested. When supplied through the transpiration stream to short-stemmed carnations, cycloheximide, 6-methylpurine and purine inhibited inrolling nearly completely and the flowers finally senesced by water loss. 6-Methylpurine inhibited ethylene production in cut flowers and RNA synthesis in excised petals very markedly. Degradation of exogenous zeatin riboside by cytokinin oxidase, and the level of activity of the enzyme in petals, were reduced by 6-methylpurine. These biochemical changes probably account for the strong inhibition of inrolling induced by this compound.

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Gemrotová, Markéta, Manoj G. Kulkarni, Wendy A. Stirk, Miroslav Strnad, Johannes Van Staden, and Lukáš Spíchal. "Seedlings of medicinal plants treated with either a cytokinin antagonist (PI-55) or an inhibitor of cytokinin degradation (INCYDE) are protected against the negative effects of cadmium." Plant Growth Regulation 71, no. 2 (April 18, 2013): 137–45. http://dx.doi.org/10.1007/s10725-013-9813-8.

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Larriba, Eduardo, Ana Belén Sánchez-García, María Salud Justamante, Cristina Martínez-Andújar, Alfonso Albacete, and José Manuel Pérez-Pérez. "Dynamic Hormone Gradients Regulate Wound-Induced de novo Organ Formation in Tomato Hypocotyl Explants." International Journal of Molecular Sciences 22, no. 21 (October 31, 2021): 11843. http://dx.doi.org/10.3390/ijms222111843.

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Plants have a remarkable regenerative capacity, which allows them to survive tissue damage after biotic and abiotic stresses. In this study, we use Solanum lycopersicum ‘Micro-Tom’ explants as a model to investigate wound-induced de novo organ formation, as these explants can regenerate the missing structures without the exogenous application of plant hormones. Here, we performed simultaneous targeted profiling of 22 phytohormone-related metabolites during de novo organ formation and found that endogenous hormone levels dynamically changed after root and shoot excision, according to region-specific patterns. Our results indicate that a defined temporal window of high auxin-to-cytokinin accumulation in the basal region of the explants was required for adventitious root formation and that was dependent on a concerted regulation of polar auxin transport through the hypocotyl, of local induction of auxin biosynthesis, and of local inhibition of auxin degradation. In the apical region, though, a minimum of auxin-to-cytokinin ratio is established shortly after wounding both by decreasing active auxin levels and by draining auxin via its basipetal transport and internalization. Cross-validation with transcriptomic data highlighted the main hormonal gradients involved in wound-induced de novo organ formation in tomato hypocotyl explants.

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Rivero, R. M., J. Gimeno, A. Van Deynze, H. Walia, and E. Blumwald. "Enhanced Cytokinin Synthesis in Tobacco Plants Expressing PSARK::IPT Prevents the Degradation of Photosynthetic Protein Complexes During Drought." Plant and Cell Physiology 51, no. 11 (September 24, 2010): 1929–41. http://dx.doi.org/10.1093/pcp/pcq143.

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Holst, Kerstin, Thomas Schmülling, and Tomáš Werner. "Enhanced cytokinin degradation in leaf primordia of transgenic Arabidopsis plants reduces leaf size and shoot organ primordia formation." Journal of Plant Physiology 168, no. 12 (August 2011): 1328–34. http://dx.doi.org/10.1016/j.jplph.2011.03.003.

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Moriyama, Ayane, Chiho Yamaguchi, Shinichi Enoki, Yoshinao Aoki, and Shunji Suzuki. "Crosstalk Pathway between Trehalose Metabolism and Cytokinin Degradation for the Determination of the Number of Berries per Bunch in Grapes." Cells 9, no. 11 (October 29, 2020): 2378. http://dx.doi.org/10.3390/cells9112378.

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In grapes, the number of flowers per inflorescence determines the compactness of grape bunches. Grape cultivars with tight bunches and thin-skinned berries easily undergo berry splitting, especially in growing areas with heavy rainfall during the grapevine growing season, such as Japan. We report herein that grape cytokinin oxidase/dehydrogenase 5 (VvCKX5) determines the number of berries per inflorescence in grapes. The number of berries per bunch was inversely proportional to the VvCKX5 expression level in juvenile inflorescences among the cultivars tested. VvCKX5 overexpression drastically decreased the number of flower buds per inflorescence in Arabidopsis plants, suggesting that VvCKX5 might be one of the negative regulators of the number of flowers per inflorescence in grapes. Similarly, the overexpression of grape sister of ramose 3 (VvSRA), which encodes trehalose 6-phosphate phosphatase that catalyzes the conversion of trehalose-6-phosphate into trehalose, upregulated AtCKX7 expression in Arabidopsis plants, leading to a decrease in the number of flower buds per Arabidopsis inflorescence. VvCKX5 gene expression was upregulated in grapevine cultured cells and juvenile grape inflorescences treated with trehalose. Finally, injecting trehalose into swelling buds nearing bud break using a microsyringe decreased the number of berries per bunch by half. VvCKX5 overexpression in Arabidopsis plants had no effect on the number of secondary inflorescences from the main inflorescence, and similarly trehalose did not affect pedicel branching on grapevine inflorescences, suggesting that VvCKX5, as well as VvSRA-mediated trehalose metabolism, regulates flower formation but not inflorescence branching. These findings may provide new information on the crosstalk between VvSRA-mediated trehalose metabolism and VvCKX-mediated cytokinin degradation for determining the number of berries per bunch. Furthermore, this study is expected to contribute to the development of innovative cultivation techniques for loosening tight bunches.

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Kučerová, Zuzana, Marek Rác, Jaromír Mikulík, Ondřej Plíhal, Pavel Pospíšil, Magdaléna Bryksová, Michaela Sedlářová, Karel Doležal, and Martina Špundová. "The Anti-Senescence Activity of Cytokinin Arabinosides in Wheat and Arabidopsis Is Negatively Correlated with Ethylene Production." International Journal of Molecular Sciences 21, no. 21 (October 30, 2020): 8109. http://dx.doi.org/10.3390/ijms21218109.

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Leaf senescence, accompanied by chlorophyll breakdown, chloroplast degradation and inhibition of photosynthesis, can be suppressed by an exogenous application of cytokinins. Two aromatic cytokinin arabinosides (6-benzylamino-9-β-d-arabinofuranosylpurines; BAPAs), 3-hydroxy- (3OHBAPA) and 3-methoxy- (3MeOBAPA) derivatives, have recently been found to possess high anti-senescence activity. Interestingly, their effect on the maintenance of chlorophyll content and maximal quantum yield of photosystem II (PSII) in detached dark-adapted leaves differed quantitatively in wheat (Triticum aestivum L. cv. Aranka) and Arabidopsis (Arabidopsisthaliana L. (Col-0)). In this work, we have found that the anti-senescence effects of 3OHBAPA and 3MeOBAPA in wheat and Arabidopsis also differ in other parameters, including the maintenance of carotenoid content and chloroplasts, rate of reduction of primary electron acceptor of PSII (QA) as well as electron transport behind QA, and partitioning of absorbed light energy in light-adapted leaves. In wheat, 3OHBAPA had a higher protective effect than 3MeOBAPA, whereas in Arabidopsis, 3MeOBAPA was the more efficient derivative. We have found that the different anti-senescent activity of 3OHBAPA and 3MeOBAPA was coupled to different ethylene production in the treated leaves: the lower the ethylene production, the higher the anti-senescence activity. 3OHBAPA and 3MeOBAPA also efficiently protected the senescing leaves of wheat and Arabidopsis against oxidative damage induced by both H2O2 and high-light treatment, which could also be connected with the low level of ethylene production.

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Patel, Ruby, and Archana Mankad. "ESTIMATION OF PROTEIN METABOLITES DURING POSTHARVEST SHELF LIFE OF TITHONIA ROTUNDIFOLIA BLAKE." International Association of Biologicals and Computational Digest 1, no. 1 (May 2, 2022): 88–91. http://dx.doi.org/10.56588/iabcd.v1i1.21.

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Senescence has a specialized meaning in plant biology, which is part of a cloud of terms mentioning generally to the process or condition of growing old. Many physiological changes takes place during senescence like Chlorophyll degradation; change in pigmentation; decrease the starch content, RNA and protein; DNA molecules are degraded by the enzyme DNase; growth promoting hormones such as cytokinin decrease; the deteriorative hormones such as ethylene and abscisic acid (ABA) content are increases. Post harvest shelf life of cut flower is dependent on the water balance, level and supply of carbohydrates and susceptibility towards growth retarding hormone like ethylene which leads to senescence. Beside carbohydrate metabolism, protein metabolism is also known to be associated with the senescence process and programmed cell death (PCD). During senescence degradation of protein may occur and make free amino acids. Proteins play important role during senescence. During present study it was observed that the total protein content decreased during course of time under cut conditions of flower. This may be due to less reserve in cut condition.

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Aremu, Adeyemi O., Nqobile A. Masondo, Taofik O. Sunmonu, Manoj G. Kulkarni, Marek Zatloukal, Lukáš Spichal, Karel Doležal, and Johannes Van Staden. "A novel inhibitor of cytokinin degradation (INCYDE) influences the biochemical parameters and photosynthetic apparatus in NaCl-stressed tomato plants." Planta 240, no. 4 (August 5, 2014): 877–89. http://dx.doi.org/10.1007/s00425-014-2126-y.

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Jiang, Shuang, Haishan An, Jun Luo, Xiaoqing Wang, Chunhui Shi, and Fanjie Xu. "Comparative Analysis of Transcriptomes to Identify Genes Associated with Fruit Size in the Early Stage of Fruit Development in Pyrus pyrifolia." International Journal of Molecular Sciences 19, no. 8 (August 9, 2018): 2342. http://dx.doi.org/10.3390/ijms19082342.

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Pear (Pyrus L.) is an important commercial fruit in the world. The fruit size is one of the important characters in fruit quality. The previous research reported that the fruit size of pear was mainly caused by the number of cell in about 40 days after blossom (DAB) in nature. However, studies about the mechanisms underlying cell division in young fruit development are very limited in pear. Two pear accessions codenamed ‘GH59B’ with big fruit and ‘GH81S’ with small fruit in three stages were sampled and the RNA-seq high-throughput sequencing was used to evaluate changes of gene transcription levels in the early stage of fruit development. The difference of cell size among two samples was little in 40 DAB, implying that the difference of the fruit size was caused by the number of the cell. More than 274,517,982 high quality reads from six libraries of fruit development were sequenced. A total of 797 differentially expressed genes (DEGs) were identified. Three cytokinin dehydrogenase genes and two gibberellin 2-beta-dioxygenase gene were identified in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to zeatin and gibberellin. Their expression was upregulated at 20 DAB in ‘GH81S’ and at 30 DAB in ‘GH59B’, suggesting that the small fruit size might be related to the early degradation of cytokinin and gibberellin inducing a short period of cell division. A total of 38 DEGs of transcription factors were found and 23 DEGs including NAC, ERF and bHLH transcription factors were highly related with cytokinin dehydrogenase and gibberellin dioxygenase genes. Altogether, the results of the present study provide information from a comprehensive gene expression analysis and insight into the molecular mechanism underlying the difference of fruit size in Pyrus pyrifolia.

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Guan, Chunmei, Xingchun Wang, Jian Feng, Sulei Hong, Yan Liang, Bo Ren, and Jianru Zuo. "Cytokinin Antagonizes Abscisic Acid-Mediated Inhibition of Cotyledon Greening by Promoting the Degradation of ABSCISIC ACID INSENSITIVE5 Protein in Arabidopsis." Plant Physiology 164, no. 3 (January 17, 2014): 1515–26. http://dx.doi.org/10.1104/pp.113.234740.

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Berka, Miroslav, Romana Kopecká, Veronika Berková, Břetislav Brzobohatý, and Martin Černý. "Regulation of heat shock proteins 70 and their role in plant immunity." Journal of Experimental Botany 73, no. 7 (January 12, 2022): 1894–909. http://dx.doi.org/10.1093/jxb/erab549.

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Abstract Heat shock proteins 70 (HSP70s) are steadily gaining more attention in the field of plant biotic interactions. Though their regulation and activity in plants are much less well characterized than are those of their counterparts in mammals, accumulating evidence indicates that the role of HSP70-mediated defense mechanisms in plant cells is indispensable. In this review, we summarize current knowledge of HSP70 post-translational control in plants. We comment on the phytohormonal regulation of HSP70 expression and protein abundance, and identify a prominent role for cytokinin in HSP70 control. We outline HSP70s’ subcellular localizations, chaperone activity, and chaperone-mediated protein degradation. We focus on the role of HSP70s in plant pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity, and discuss the contribution of different HSP70 subfamilies to plant defense against pathogens.

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Monden, Kota, Mikiko Kojima, Yumiko Takebayashi, Takamasa Suzuki, Tsuyoshi Nakagawa, Hitoshi Sakakibara, and Takushi Hachiya. "Root-specific Reduction of Cytokinin Perception Enhances Shoot Growth in Arabidopsis thaliana." Plant and Cell Physiology 63, no. 4 (February 2, 2022): 484–93. http://dx.doi.org/10.1093/pcp/pcac013.

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Abstract Previous studies suggest that root-derived cytokinins (CKs) contribute to shoot growth via long-distance transport; therefore, we hypothesized that an increase in root-derived CKs enhances shoot growth. To verify this, we grafted Arabidopsis Col-0 (wild type, WT) scion onto rootstock originated from WT or a double-knockout mutant of CK receptors Arabidopsis histidine kinase 2 (AHK2) and AHK3 (ahk2-5 ahk3-7; ahk23) because this mutant overaccumulates CKs in the body probably due to feedback homeostasis regulation. The grafted plants (scion/rootstock: WT/WT and WT/ahk23) were grown in vermiculite pots or solid media for vegetative growth and biochemical analysis. The root-specific deficiency of AHK2 and AHK3 increased root concentrations of trans-zeatin (tZ)-type and N6-(Δ2-isopentenyl) adenine (iP)-type CKs, induced CK biosynthesis genes and repressed CK degradation genes in the root. The WT/ahk23 plants had significantly larger shoot weight, rosette diameter and leaves area than did the WT/WT plants. Shoot concentrations of tZ-type CKs showed increasing trends in the WT/ahk23 plants. Moreover, the root-specific deficiency of AHK2 and AHK3 enhanced shoot growth in the WT scion more strongly than in the ahk23 scion, suggesting that shoot growth enhancement could occur through increased shoot perception of CKs. In the WT/ahk23 shoots compared with the WT/WT shoots, however, induction of most of CK-inducible response regulator genes was not statistically significant. Thus we suggest that the root-specific reduction of CK perception enhances shoot growth only partly by increasing the amount of root-derived tZ-type CKs and their perception by shoots. The unknown mechanism(s) distinct from CK signaling would also be involved in the shoot growth enhancement.

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Ramireddy, Eswarayya, Seyed A. Hosseini, Kai Eggert, Sabine Gillandt, Heike Gnad, Nicolaus von Wirén, and Thomas Schmülling. "Root Engineering in Barley: Increasing Cytokinin Degradation Produces a Larger Root System, Mineral Enrichment in the Shoot and Improved Drought Tolerance." Plant Physiology 177, no. 3 (June 5, 2018): 1078–95. http://dx.doi.org/10.1104/pp.18.00199.

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Wang, Qi, Yanchun Zhu, Xiao Zou, Fengfeng Li, Jialiang Zhang, Ziyi Kang, Xuefei Li, Changxi Yin, and Yongjun Lin. "Nitrogen Deficiency-Induced Decrease in Cytokinins Content Promotes Rice Seminal Root Growth by Promoting Root Meristem Cell Proliferation and Cell Elongation." Cells 9, no. 4 (April 9, 2020): 916. http://dx.doi.org/10.3390/cells9040916.

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Rice (Oryza sativa L.) seedlings grown under nitrogen (N) deficiency conditions show a foraging response characterized by increased root length. However, the mechanism underlying this developmental plasticity is still poorly understood. In this study, the mechanism by which N deficiency influences rice seminal root growth was investigated. The results demonstrated that compared with the control (1 mM N) treatment, N deficiency treatments strongly promoted seminal root growth. However, the N deficiency-induced growth was negated by the application of zeatin, which is a type of cytokinin (CK). Moreover, the promotion of rice seminal root growth was correlated with a decrease in CK content, which was due to the N deficiency-mediated inhibition of CK biosynthesis through the down-regulation of CK biosynthesis genes and an enhancement of CK degradation through the up-regulation of CK degradation genes. In addition, the N deficiency-induced decrease in CK content not only enhanced the root meristem cell proliferation rate by increasing the meristem cell number via the down-regulation of OsIAA3 and up-regulation of root-expressed OsPLTs, but also promoted root cell elongation by up-regulating cell elongation-related genes, including root-specific OsXTHs and OsEXPs. Taken together, our data suggest that an N deficiency-induced decrease in CK content promotes the seminal root growth of rice seedlings by promoting root meristem cell proliferation and cell elongation.

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Veerasamy, Mahalaxmi, Yali He, and Bingru Huang. "Leaf Senescence and Protein Metabolism in Creeping Bentgrass Exposed to Heat Stress and Treated with Cytokinins." Journal of the American Society for Horticultural Science 132, no. 4 (July 2007): 467–72. http://dx.doi.org/10.21273/jashs.132.4.467.

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Abstract:

Heat stress induces leaf senescence and causes changes in protein metabolism. The objective of this study was to investigate effects of exogenous application of a synthetic form of cytokinin, zeatin riboside (ZR), on protein metabolism associated with leaf senescence under heat stress for a cool-season grass species. Creeping bentgrass (Agrostis stolonifera L.) (cv. Penncross) plants were exposed to optimum temperature control (20/15 °C, day/night) and heat stress (35/30 °C) in growth chambers. Before heat stress treatments, foliage was sprayed with 10 μmol ZR or water (untreated) for 3 days and then once per week during 35 days of heat stress. Leaf chlorophyll content, photochemical efficiency (Fv/Fm), and soluble protein content declined, whereas protease activity increased during heat stress. Treatments with ZR helped maintain higher leaf chlorophyll content, Fv/Fm, and soluble protein content under heat stress. Protease activity in ZR-treated plants was lower than that of untreated plants. Zeatin riboside-treated plants had less severe degradation of ribulose-1,5-bisphosphate carboxylase proteins than untreated plants exposed to heat stress. In addition, ZR treatment upregulated the expression of 32- and 57-kDa proteins under heat stress conditions. These results demonstrated that the exogenous application of ZR ameliorated the negative effects of heat stress, as manifested by suppression or delay of leaf senescence. Cytokinins may have helped to alleviate heat stress injury, probably by slowing down the action of protease and by induction or upregulation of heat-shock proteins.

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Journal articles on the topic 'Cytokinin degradation'

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