Добірка наукової літератури з теми "Thylakoid pigment"

Biochemical and spectroscopic studies on the effects of high temperatures (45-47� C) over a 1 h period on the protein composition, fluorescence and photochemical activities of the barley thylakoid membrane were made. Photosystem II (PS II) activity decreased as expected, and photosystem I (PS I) activity also unexpectedly decreased. Our data support previous conclusions that the decrease in PS I activity is largely due to inactivation (or loss) of a component between the two photosystems. A two-dimensional electrophoretic system permitted first the separation of the thylakoid pigment-protein complexes of unstressed and stressed plants, followed by a determination of their subunit composition. The changes in the protein composition of each pigment-protein complex in response to elevated temperatures were monitored. Heat changed the quaternary structure of PS II and resulted in removal of the oxygen-evolving enhancer proteins from the thylakoid, but did essentially no damage to the PS I complex. The PS II core complex dissociated from a dimeric form to a monomeric one, and the major LHC II component (LHC IIb) changed from a trimeric to a monomeric form. The pigments that are lost from thylakoids during heat stress are mainly removed from the PS II pigment-proteins.

Light is the driving force of photosynthesis. Plants adapt to rapid changes in irradiance, quality and duration of the light environment by modulating the composition of the thylakoid membranes to make the best use of the available light energy. Each chloroplast contains a large amount of thylakoid membranes some of which may be arranged as stacks (granal thylakoids) and others as unstacked sacks (stromal thylakoids). Shaded chloroplasts develop more thylakoid surface area as compared to those growing in full sunlight. Conversion of sun-type chloroplasts to those of shade-types can occur quickly, when sun plants are shaded. However, the response mechanism of chloroplasts to changes in light levels is yet to be understood. Reports in the literature showed that plants grown in red light developed more grana compared to those grown under blue light and a pigment detection system has been postulated. While, other models propose that overall energy flux changes within the chloroplast induce sun/shade response.

Ice algae have successfully adapted to the extreme environmental conditions in the Antarctic, however the underlying mechanisms involved in the regulation and response of thylakoid membranes and chloroplast to low-temperature stress are still not well understood. In this study, changes in pigment concentrations, lipids, fatty acids and pigment protein complexes in thylakoid membranes and chloroplast after exposure to low temperature conditions were investigated using the Antarctic ice algae Chlamydomonas sp. ICE-L. Results showed that the chloroplasts of Chlamydomonas sp. ICE-L are distributed throughout the cell except in the nuclear region in the form of thylakoid lamellas which exists in the gap between organelles and the starch granules. Also, the structure of mitochondria has no obvious change after cold stress. Concentrations of Chl a, Chl b, monogalactosyl diacylglycerol, digalactosyl diacylglycerol and fatty acids were also observed to exhibit changes with temperature, suggesting possible adaptations to cold environments. The light harvesting complex, lutein and β-carotene played an important role for adaptation of ICE-L, and increasing of monogalactosyl diacylglycerol and digalactosyl diacylglycerol improved the overall degree of unsaturation of thylakoid membranes, thereby maintaining liquidity of thylakoid membranes. The pigments, lipids, fatty acids and pigment-protein complexes maintained the stability of the thylakoid membranes and the normal physiological function of Chlamydomonas sp. ICE-L.

Pigment photobleaching was performed in thylakoid membranes of Hordeum vulgare (wild type, mutant Chlorina f2, Norfluranzon treated seedlings) and in pigment-protein complexes (CP-I and LHCP) isolated from H. vulgare and Chlamydomonas reinhardtii. Multiphasic kinetics were obtained in all of the above cases. Energy transfer towards pigments absorbing at longer wavelength is postulated as a general protection mechanism against photobleaching. This mechanism explains a substantial bleaching of carotenoids and a faster bleaching of chlorophyll aggregates, absorbing at long wavelength. These conclusions were valid for isolated complexes as well as for thylakoid membranes, although membranes were less sensitive to light.

Understanding the light-harvesting properties of algae and higher plants are a fundamental topic in photosynthesis research. Much oceanographic research has focused on characterizing the in vivo chlorophyll-specific absorption coefficient, a*ph (λ) in phytoplankton because it serves as an input variable for bio-optical modeling of photosynthesis using remote sensing instrumentation such as moorings, drifters, and satellites. Values of a*ph (λ) vary spectrally and the magnitude depends on accessory pigments, photo-protective pigments, and pigment packaging effects. Several studies have shown that the contribution of cellular characteristics to a*ph(λ) varies with growth conditions including temperature, light, and nutrients. It has been shown that a*ph (λ) values in Phaeocystis vary predictably at 4°C over light intensities under light limitation. Phaeocystis demonstrated significant pigment package effects that depended on single cell diameter and thylakoid membrane stacking. Using thick sections obtained from fixed and embedded cultures of colonial P. antarctica, we calculated tomographic reconstructions of individual chloroplasts under light-limiting conditions for net photosynthesis in order to gain an understanding of the continuity of thylakoid membranes and understand the spatial relationship between the pyrenoid, the starch containing organelle, and thylakoid membranes.

The thylakoid membranes of higher plant chloroplasts contain at least two major pigment protein complexes, photosystem I (PSI), and photosystem II (PSII). The mature apoprotein of these complexes (involved in the initial reactions of photosynthesis) bind specific chlorophylls (Chl) and specific carotenoids in an unknown manner. It has been suggested, however, that the synthesis of pigments is normally coordinated with that of apoproteins. We have examined the effect of gabaculine (3-amino-2, 3-dihydrobenzoic acid) on granal thylakoid stacking as well as pigment and apoprotein accumulations for PSI and PSII in wheat.Gabaculine (0.5mM) was applied with nutrient solution to 6.5 day-old wheat seedlings maintained in a growth chamber at 23C. One seedling lot grown under continuous light (400 μmol photons s-1 m-2) possessed green primary leaves at time of treatment whereas another seedling lot, dark grown, possessed only etiolated primary leaves. Twelve hours after treatment, the etiolated seedlings were transferred into continuous light. The primary and secondary leaves were subsequently harvested from 14 day-old seedlings of both lots.

Eleven proteins belonging to photosystem II (PSII) bind photosynthetic pigments in the form of thylakoid membrane-associated pigment-protein complexes. Five of them (PsbA, PsbB, PsbC, PsbD and PsbS) are assigned to PSII core complex while the remaining six (Lhcb1, Lhcb2, Lhcb3, Lhcb4, Lhcb5 and Lhcb6) constitute, along with their pigments, functional complexes situated more distantly with regard to P680 - the photochemical center of PSII. The main function of the pigment-binding proteins is to harvest solar energy and deliver it, in the form of excitation energy, ultimately to P680 although individual pigment-proteins may be engaged in other photosynthesis-related processes as well. The aim of this review is to present the current state of knowledge regarding the structure, functions and degradation of this family of proteins.

Biological membranes were originally described as a fluid mosaic with uniform distribution of proteins and lipids. Later, heterogeneous membrane areas were found in many membrane systems including cyanobacterial thylakoids. In fact, cyanobacterial pigment–protein complexes (photosystems, phycobilisomes) form a heterogeneous mosaic of thylakoid membrane microdomains (MDs) restricting protein mobility. The trafficking of membrane proteins is one of the key factors for long-term survival under stress conditions, for instance during exposure to photoinhibitory light conditions. However, the mobility of unbound ‘free’ proteins in thylakoid membrane is poorly characterized. In this work, we assessed the maximal diffusional ability of a small, unbound thylakoid membrane protein by semi-single molecule FCS (fluorescence correlation spectroscopy) method in the cyanobacterium Synechocystis sp. PCC6803. We utilized a GFP-tagged variant of the cytochrome b6f subunit PetC1 (PetC1-GFP), which was not assembled in the b6f complex due to the presence of the tag. Subsequent FCS measurements have identified a very fast diffusion of the PetC1-GFP protein in the thylakoid membrane (D = 0.14 − 2.95 µm2s−1). This means that the mobility of PetC1-GFP was comparable with that of free lipids and was 50–500 times higher in comparison to the mobility of proteins (e.g., IsiA, LHCII—light-harvesting complexes of PSII) naturally associated with larger thylakoid membrane complexes like photosystems. Our results thus demonstrate the ability of free thylakoid-membrane proteins to move very fast, revealing the crucial role of protein–protein interactions in the mobility restrictions for large thylakoid protein complexes.

AbstractThe present work investigates the effect of α-, β- and γ-cyclodextrins (CD), i.e., α-CD, β- CD and γ-CD, on the oxygen evolution activity, the protein content and the uv-vis spectroscopic characteristics of thylakoid membranes. To study the pH-dependence, the thylakoids were incubated with the cyclodextrins at 273 K for a period of 10 min in the pH range from 5.5 to 9.0. To study the temperature-dependence the membranes were incubated at 273 and 293 K at pH 6.5, that is, the pH which induces a maximal oxygen evolution in the thylakoid preparations. The major observations are: (i) a stimulation of oxygen evolution in thylakoids incubated with α- and β-CD either in acidic or alkaline conditions, (ii) a low inhibitory effect induced by γ-CD on oxygen evolution, (iii) a significant decrease of the stimulatory effect of α- and β-CD on oxygen evolution as the incubation temperature is raised from 273 to 293 K, (iv) the apparent inability of the cyclodextrins to change the protein contents of the thylakoids, and (v) a significant CD-induced red-shift from 681 to 683 nm observed in the absorption and second derivative spectra of the thylakoid membranes treated with β-CD. First, it was found that the temperature effect described here is in accord with the general trend of the chemical effect of various cyclodextrins, i.e., the increase of the CD efficiency with decreasing temperature. Secondly, the CD effect is related to the size of the inner cavity diameter of the cyclodextrin molecules. An important conclusion in this work is that the molecular targets of the cyclodextrins are not limited to the thylakoid lipids as was described previously [Rawyler A. and Siegenthaler P.A. (1996) Biochim. Biophys. Acta 1278, 89-97], but are located as well in other molecular species exposed at the stromal side of the thylakoid membrane. In particular, the CD-induced red-shift from 681 to 683 nm in the absorption and second derivative spectra of the thylakoid membranes indicates that the cyclodextrins targets might be either the exposed heme macrocycle in cytochrome b559, or the chlorophylls and pheophytins in the pigment-proteins of the photosystems I and II.

Suji (Pleomele angustifolia) is one kind of Indonesian typical plants which can be used as natural green food coloring agent. The susceptibility of natural pigment to external environment forces the protection in order to prolong its shelf life. Encapsulation has been known in the art of food preparation to provide protection for several ingredients including food coloring agent. The objective of this study was to observe the method for isolation and encapsulation of thylakoid, and to investigate the stability and characteristics of thylakoid of suji leaves encapsulated in maltodextrin during dark storage at 30 °C, 45 °C, and 60 °C. The degradation of the encapsulated pigments was identified through chromametric analysis which resulted in the increase of L* (lightness), a* (redness), and b* (yellowness) values. In addition, it was also indicated by the decrease of total chlorophyll (TC) which was determined using spectrophotometer. Chromatography analysis confirmed the presence of four major peaks in the fresh encapsulated thylakoid powder and five major peaks in the encapsulated thylakoid powder stored at the highest temperature (60 °C), with Chl a as the dominant pigments in both powder. The vivid green powder was able to preserve its color without any obvious change to an untrained eye up to 60 d of storage at 30 °C, becoming a promising ingredient to replace the synthetic colorants.

碩士
國立臺灣大學
植物學研究所
88
The present study is try to describe the changes in non-leaf green tissue of cotyledons of black bean（Glycine max. L. Merrilx）during seed ripening、desiccation and germination, including the changes in plastids morphology、thylakoid stacking、photosynthetic pigments and the compositions of pigment-protein complexes. During seeds ripening, guard mother cells appeared in the cotyledons. After germination, the stomatal feature and distribution of the adaxial and abaxial regions of cotyledons are very different. There are more stomata on the adaxial region. The plastids of cotyledons of developing seeds in the pods are quite different. They are plastids with irregular shape. Some of them are with only one starch grain and some with aggregate starch grains. All of them have grana stacking without stromal lamelle connecting. In dry seeds, there are more compact thylakoid stacking without flatted grana in the plastids. After imbibition, the thylakoid stacking of grana become looser and multi-direction orientated. After seed germination and seedling exposed to light, there are crystal-shape prolamellar bodies in plastid, from which thylakoids extended to growth and stackness becoming grana. The chlorophyll a/b ratio of the cotyledons of the seeds in the pods was low down between 1.7 and 2.1; after germinaiton, it became 2.8. The changing patterns of contents of total chlorophylls and porphyrins of cotyledons were similar. They decayed during seed ripening and desiccation, and enriched rapidly after germination. In each developmental stages, the mole fraction of three porphyrins revealed periodical fluctuation. The changing pattern of protoporphyrin IX was different from those of Mg-protoporphyrin IX and protochlorophyllide. HPLC profile of xanthophylls showed that the contents of lutein were the highest in cotyledons at all stages of seed. The epioxidation index of seed cotyledons in the pods is about 0.1 lower than that ones after germination. Similar thylakoid protein pattern of mature cotyledons and leaves were revealed by SDS-PAGE gradient gel electrophoresis. In Thornber system electrophoresis, the cotyledons of imbibition seed was deficient CPI pigment-protein complex, and only with CPII. In MARS system electrophoresis, it was deficient A1、AB1 and AB2, and only with AB3. After seed germination and seedling exposed to light, all pigment-protein complexes were recoveried and were similar with the pattern of leaves. This indicated that a phenomenon of pigment-protein complex cycle ( PPCC ) specifically belongs to non-leaf green tissues. Immunocytochemical studies revealed that the colloidal-golds of LHCII b protein were specifically located in grana of cotyledons. This indicated that there are relationship between LHCII b protein and thylakoid stacking.

Le condizioni ambientali cui sono esposte le piante variano in continuazione, in particolare per quanto riguarda quantità e qualità della luce incidente. Essendo organismi sessili, le piante hanno evoluto una serie di meccanismi atti a rispondere a queste continue variazioni, allo scopo di assorbire efficientemente la luce quando questa è limitante e di evitare la fotoinibizione in condizioni di alta luce. Diversi lavori sperimentali hanno studiato e descritto le modificazioni funzionali che avvengono nelle piante quando esse si adattano a crescere in condizioni di luce limitante o eccessiva. In particolare, cambiamenti nell’intensità dell’irraggiamento attivano molte risposte molecolari a livello del cloroplasto, che si possono distinguere in risposte a breve o a lungo termine sulla base del tempo necessario alla loro piena attivazione. Le risposte a lungo termine, che coinvolgono il cloroplasto in risposta a variazioni nella disponibilità di luce, sono collettivamente conosciute come acclimatazione, e consistono nella sintesi e degradazione selettiva di componenti funzionali dell’organello, al fine di ottimizzarne l’efficienza fotosintetica. La regolazione del turnover proteico è un meccanismo fondamentale che permette un controllo preciso del tipo e della quantità delle specie proteiche presenti nella cellula, determinando quindi i processi metabolici attivi. Nonostante la risposta di acclimatazione sia stata ampiamente studiata e descritta, i meccanismi molecolari che sono alla base della stessa non sono ancora ben definiti. Lo scopo di questa tesi è quello approfondire la conoscenza di questo processo, studiando da un lato i meccanismi molecolari coinvolti, e dall’altro la cinetica degli eventi di acclimatazione nella specie modello Arabidopsis thaliana. Sono stati testati diversi approcci analitici, allo scopo di misurare il tasso di turnover dei complessi fotosintetici, in piante esposte sia a bassa che ad alta luce. Tra tutti i complessi fotosintetici, solo per la subunità D1 del PSII è stato misurato il tempo di vita con precisione, mentre mancano indicazioni in letteratura sul tempo di vita degli altri complessi pigmento-proteina quali PSI, LHCI e LHCII. Lo studio del turnover del supercomplesso LHCII è di particolare interesse, in quanto LHCII è soggetto a una forte regolazione in seguito a variazioni nell’intensità della luce incidente, allo scopo di modulare la taglia funzionale di antenna. In un primo approccio siamo ricorsi ad esperimenti di pulse-chase utilizzando isotopi sia radioattivi che non-radioattivi. Le prove in cui è stato utilizzato 35S, sia come Na2SO4 che come metionina, hanno evidenziato come la foglia ricicli attivamente lo zolfo, oltre ad immagazzinarlo, probabilmente nel vacuolo, e questo fenomeno falsa la misura del turnover, sovrastimandolo. Per superare questo inconveniente abbiamo utilizzato l’acqua deuterata, che entra rapidamente nei compartimenti cellulari equilibrandosi con l’ambiente acquoso, permettendo quindi una più affidabile misura dei tempi di vita. In questo caso, l’efficienza di marcatura si è rivelata essere molto bassa per le proteine di membrana, e non ha permesso quindi di ottenere una buona stima del tasso di turnover, anche utilizzando una tecnica analitica molto sensibile quale la spettrometria di massa. Nel complesso, questi risultati confermano che la misura del tasso di turnover di LHCII è un obiettivo tutt’altro che banale, reso tale probabilmente dal lungo tempo di vita del complesso quando stabilizzato nella membrana tilacoidale. Siamo ricorsi quindi ad una differente strategia, volta a determinare la composizione dei complessi LHC in diverse condizioni di luce. A questo scopo le singole subunità LHC, clonate e purificate, verranno utilizzate come standard interno in un esperimento di spettrometria di massa, per confrontare la composizione dei tilacoidi di piante acclimatate a bassa o alta luce e determinare quale delle subunità LHC è regolata in risposta all’acclimatazione. Il clonaggio e le prove di espressione sono state svolte in questa tesi. Tra i meccanismi molecolari responsabili dell’adattamento all’intensità di luce, è stato approfondito il ruolo della degradazione delle clorofille nella riorganizzazione dell’apparato fotosintetico in seguito ad esposizione ad alta luce. Utilizzando mutanti che mancano di enzimi per la degradazione della clorofilla (nolnyc e pph) abbiamo evidenziato come lo stesso pathway di degradazione agisca non solo durante la senescenza fogliare, come precedentemente descritto, ma anche durante l’acclimatazione. Infatti, entrambi i mutanti mostravano un blocco nella regolazione della composizione dei fotosistemi, e questo indica che la rimozione delle clorofille è un evento fondamentale per la riorganizzazione dell’apparato fotosintetico. Nonostante ciò, il catabolismo delle clorofille non appare indispensabile alla fotoprotezione dei cloroplasti, visto che entrambi i mutanti mantengono una buona resa quantica del PSII durante il trattamento con alta luce. Oltre al ruolo delle clorofille, è stata approfondita la funzione delle xantofille nella modulazione della stabilità dei complessi fotosintetici. Oltre a confermare la loro importanza nella stabilizzazione dei complessi LHCII, è stato dimostrato come il contenuto di xantofille abbia un ruolo nella modulazione del contenuto relativo di PSI, rispetto al PSII: abbiamo stabilito una correlazione positiva tra il rapporto xantofille/carotenoidi e il rapporto PSI/PSII, all’interno di un ampio range di valori. Il risultato è stato ottenuto analizzando piante wild type con diverso rapporto xantofille/carotenoidi, regolato dall’intensità della luce di crescita. Inoltre, è stato studiato un mutante privo di xantofille (nox), incapace di crescere in terra a causa della completa mancanza di PSI. Questi risultati dimostrano che le xantofille hanno un ruolo fondamentale nella biogenesi del PSI e sono quindi necessarie alla crescita autotrofica. L’ultima parte del lavoro di tesi aveva l’obiettivo di individuare nuove subunità proteiche coinvolte nell’ottimizzazione della risposta di acclimatazione all’alta luce. Diversi prodotti genici sono stati selezionati in base all’annotazione, che riportava la presenza di domini simili a subunità del complesso ubiquitina/proteasoma, e una localizzazione cloroplastica. Tra i geni analizzati, tre sono stati selezionati in base al fenotipo di maggior suscettibilità alla fotoinibizione: AT2G22890, AT4G27030 and AT4G32250. I primi due geni codificano per isoforme di una desaturasi degli acidi grassi (FAD4), e questo suggerisce un ruolo chiave della biosintesi dei lipidi nella risposta allo stress foto-ossidativo. Il terzo gene identificato codifica per una protein chinasi, localizzata nell’envelope del cloroplasto, la cui assenza provoca una marcata fotoinibizione del PSII quando la pianta è esposta ad alta luce. Nel genoma di Arabidopsis non esistono geni omologhi a questo, ma si trovano ortologhi in altre specie di piante, indicando che questa funzione è stata probabilmente conservata durante l’evoluzione. Possiamo ipotizzare che questa subunità sia coinvolta nella trasduzione del segnale di stress dal cloroplasto al nucleo, o regoli l’import di proteine nel cloroplasto, oppure partecipi alla fosforilazione di proteine stromatiche target.
Plants continually experience fluctuations in the conditions of their environment, particularly in the quantity and quality of incident light. Since devoid of motility, plants have evolved a plethora of molecular mechanisms aimed to accommodate changes in irradiance, in order to enable efficient light harvesting in limited light while avoiding photoinhibition under excess light. A number of works have investigated the modifications occurring in various plant species when grown under limiting or excess irradiances. In particular, changes in light intensity elicit major responses at the level of chloroplast, which can be distinguished in short- and long-term response based on their timescale of activation. In particular the long-term responses to irradiance at the chloroplast level are known as acclimation, and consist in the selective synthesis and degradation of functional components in order to optimize the photosynthetic efficiency. Regulation of proteins turnover is surely involved in acclimation: it allows a fine tuning of the proteins quality and quantity, thus defining the metabolic processes active in the cell. However, the regulatory mechanisms which underlie the molecular rearrangement of chloroplast, in particular those elicited during acclimation to excess light, are still poorly defined. This thesis is aimed at gaining new insight on timing and factors affecting turnover of pigment-binding complexes, and how these modulate the acclimatory response in Arabidopsis thaliana leaves. Several efforts have been made in order to measure the turnover rate of photosynthetic complexes, both in low and high light conditions. Indeed, with the exception of D1 subunits, whose turnover rate has been assessed accurately, no information are available regarding the half-life of the other chlorophyll-binding complexes, such as PSI, LHCI and LHCII. The turnover of LHCII complexes is of particular interest, since degradation of this antenna is triggered by the high light response and represents a strategy to regulate the PSII functional antenna size. As first trials, both radioactive and non-radioactive pulse-chase experiments were performed. Pulse-chase with 35S, supplied either as Na2SO4 or methionine, showed that the plant cell actively recycles sulphur, as well as stores it probably in the vacuole, thus it leads to an over-estimation of protein turnover rate. A second approach resorted to deuterium oxide as a labelling system, coupled to a mass spectrometry analysis. 2H2O is totally invasive, rapidly equilibrates with the water environment, and therefore does not distort turnover rate estimation due to over-labelling of the system. In this case, a too low labelling efficiency was reached, thus making the assessment of turnover rate unreliable even with a very sensitive techniques such as mass spectrometry. Altogether, these results confirmed that determination of LHCII turnover rate was an hard task, indeed efficient labelling cannot be achieved by means of a classic pulse-chase approach, due to the long half-life of these complexes. A different strategy was thus pursued, namely purification of recombinant LHC isoforms to be used as internal standards in an mass-spectrometry analysis, in order to evaluate LHC abundance in thylakoids from low- vs. high-light acclimated plants and to assess which subunits are regulated during acclamatory responses. Both cloning and expression trials were carried out in this thesis work. Regarding the molecular mechanisms underlying acclimation, the role of chlorophylls degradation pathway on the high light dependent re-organization of the photosynthetic machinery was studied. By analyzing mutants devoid of chlorophylls catabolism enzymes (nolnyc and pph), we assessed that these enzymes are responsible for chlorophylls degradation not only during senescence, as previously shown, but even upon exposure to high light conditions. Both mutants were less effective than the wild type in regulating photosystems composition and abundance once challenged with HL, thus indicating that chlorophylls removal is one of the early events triggering acclimation of the photosynthetic apparatus. Nevertheless, chlorophylls catabolism was shown not essential for acclimation, since both mutants were effective in preserving PSII quantum yield in high light. In addition to chlorophylls, the function of xanthophylls in the structural stability of photosynthetic supercomplexes was assessed. Besides the well-known role in the stabilization of LHCII complexes, xanthophylls abundance was shown to modulate the PSI relative content: indeed, a positive correlation was assessed between xanthophylls/carotenoids and PSI/PSII ratios, within a wide range of values. These results were obtained by analyzing wild type plants whose xanthophylls/carotenoids content was modulated by the light intensity to which they were acclimated. Moreover, we isolated and studied the nox mutant, completely devoid of xanthophylls and unable to grow on soil since specifically depleted in PSI. Such a characterization lead to the conclusion that xanthophylls have a fundamental role in the biogenesis of PSI, thus making biosynthesis of these molecules crucial for sustaining autotrophic growth. The last part of the thesis aimed at finding new candidate proteins involved in the acclimation response to HL. A number of genes were selected on the strength of their annotation, in which an ubiquitin/proteasome-like domain was identified and the localization was indicated as chloroplastic. Among the tested loci, we selected 3 genes whose corresponding knock-out mutants yielded into impaired PSII photoprotection in high light: AT2G22890, AT4G27030 and AT4G32250. The first two encode for isoforms of fatty acid desaturase 4 (FAD4), thus suggesting a role for lipids biosynthesis in the response to photoxidative stress. The third gene identified encodes for a protein kinase, bound to the chloroplast envelope, whose lack yield into a severe photosensitivity. No homologous proteins are present in the Arabidopsis thaliana genome, while ortholog were found in different plant species, thus indicating that its function has been conserved through evolution. We hypothesized it could be related to some signal transduction pathways, linking chloroplast to nucleus, or might regulate protein import thought the chloroplast envelope, or phosphorylation of stromatic target proteins.