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1.
Plant J ; 102(6): 1266-1280, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31975462

RESUMO

Singlet oxygen (1 O2 ) is a by-product of photosynthesis that triggers a signalling pathway leading to stress acclimation or to cell death. By analyzing gene expressions in a 1 O2 -overproducing Arabidopsis mutant (ch1) under different light regimes, we show here that the 1 O2 signalling pathway involves the endoplasmic reticulum (ER)-mediated unfolded protein response (UPR). ch1 plants in low light exhibited a moderate activation of UPR genes, in particular bZIP60, and low concentrations of the UPR-inducer tunicamycin enhanced tolerance to photooxidative stress, together suggesting a role for UPR in plant acclimation to low 1 O2 levels. Exposure of ch1 to high light stress ultimately leading to cell death resulted in a marked upregulation of the two UPR branches (bZIP60/IRE1 and bZIP28/bZIP17). Accordingly, mutational suppression of bZIP60 and bZIP28 increased plant phototolerance, and a strong UPR activation by high tunicamycin concentrations promoted high light-induced cell death. Conversely, light acclimation of ch1 to 1 O2 stress put a limitation in the high light-induced expression of UPR genes, except for the gene encoding the BIP3 chaperone, which was selectively upregulated. BIP3 deletion enhanced Arabidopsis photosensitivity while plants treated with a chemical chaperone exhibited enhanced phototolerance. In conclusion, 1 O2 induces the ER-mediated UPR response that fulfils a dual role in high light stress: a moderate UPR, with selective induction of BIP3, is part of the acclimatory response to 1 O2 , and a strong activation of the whole UPR is associated with cell death.

2.
Commun Biol ; 2: 220, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31240258

RESUMO

Photosynthesis produces organic carbon via a light-driven electron flow from H2O to CO2 that passes through a pool of plastoquinone molecules. These molecules are either present in the photosynthetic thylakoid membranes, participating in photochemistry (photoactive pool), or stored (non-photoactive pool) in thylakoid-attached lipid droplets, the plastoglobules. The photoactive pool acts also as a signal of photosynthetic activity allowing the adaptation to changes in light condition. Here we show that, in Arabidopsis thaliana, proton gradient regulation 6 (PGR6), a predicted atypical kinase located at plastoglobules, is required for plastoquinone homoeostasis, i.e. to maintain the photoactive plastoquinone pool. In a pgr6 mutant, the photoactive pool is depleted and becomes limiting under high light, affecting short-term acclimation and photosynthetic efficiency. In the long term, pgr6 seedlings fail to adapt to high light and develop a conditional variegated leaf phenotype. Therefore, PGR6 activity, by regulating plastoquinone homoeostasis, is required to cope with high light.


Assuntos
Homeostase/fisiologia , Fotossíntese/fisiologia , Plastoquinona/metabolismo , Adaptação Biológica/fisiologia , Arabidopsis , Luz , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Plantas Geneticamente Modificadas , Plântula/crescimento & desenvolvimento , Plântula/metabolismo
3.
Plant Physiol ; 180(3): 1691-1708, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31123095

RESUMO

Singlet oxygen produced from triplet excited chlorophylls in photosynthesis is a signal molecule that can induce programmed cell death (PCD) through the action of the OXIDATIVE STRESS INDUCIBLE 1 (OXI1) kinase. Here, we identify two negative regulators of light-induced PCD that modulate OXI1 expression: DAD1 and DAD2, homologs of the human antiapoptotic protein DEFENDER AGAINST CELL DEATH. Overexpressing OXI1 in Arabidopsis (Arabidopsis thaliana) increased plant sensitivity to high light and induced early senescence of mature leaves. Both phenomena rely on a marked accumulation of jasmonate and salicylate. DAD1 or DAD2 overexpression decreased OXI1 expression, jasmonate levels, and sensitivity to photooxidative stress. Knock-out mutants of DAD1 or DAD2 exhibited the opposite responses. Exogenous applications of jasmonate upregulated salicylate biosynthesis genes and caused leaf damage in wild-type plants but not in the salicylate biosynthesis mutant Salicylic acid induction-deficient2, indicating that salicylate plays a crucial role in PCD downstream of jasmonate. Treating plants with salicylate upregulated the DAD genes and downregulated OXI1 We conclude that OXI1 and DAD are antagonistic regulators of cell death through modulating jasmonate and salicylate levels. High light-induced PCD thus results from a tight control of the relative activities of these regulating proteins, with DAD exerting a negative feedback control on OXI1 expression.

4.
Commun Biol ; 2: 159, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31069268

RESUMO

In the last common enzymatic step of tetrapyrrole biosynthesis, prior to the branching point leading to the biosynthesis of heme and chlorophyll, protoporphyrinogen IX (Protogen) is oxidised to protoporphyrin IX (Proto) by protoporphyrinogen IX oxidase (PPX). The absence of thylakoid-localised plastid terminal oxidase 2 (PTOX2) and cytochrome b 6 f complex in the ptox2 petB mutant, results in almost complete reduction of the plastoquinone pool (PQ pool) in light. Here we show that the lack of oxidised PQ impairs PPX function, leading to accumulation and subsequently uncontrolled oxidation of Protogen to non-metabolised Proto. Addition of 3(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) prevents the over-reduction of the PQ pool in ptox2 petB and decreases Proto accumulation. This observation strongly indicates the need of oxidised PQ as the electron acceptor for the PPX reaction in Chlamydomonas reinhardtii. The PPX-PQ pool interaction is proposed to function as a feedback loop between photosynthetic electron transport and chlorophyll biosynthesis.


Assuntos
Proteínas de Algas/genética , Chlamydomonas reinhardtii/enzimologia , Clorofila/biossíntese , Regulação da Expressão Gênica de Plantas , Plastoquinona/metabolismo , Protoporfirinogênio Oxidase/genética , Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/efeitos dos fármacos , Chlamydomonas reinhardtii/genética , Complexo Citocromos b6f/genética , Complexo Citocromos b6f/metabolismo , Diurona/farmacologia , Transporte de Elétrons , Retroalimentação Fisiológica , Herbicidas/farmacologia , Oxirredução , Fotossíntese/efeitos dos fármacos , Fotossíntese/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plastídeos/efeitos dos fármacos , Plastídeos/enzimologia , Plastídeos/genética , Protoporfirinogênio Oxidase/metabolismo , Protoporfirinas/metabolismo
5.
Plant Cell ; 30(10): 2495-2511, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30262551

RESUMO

When exposed to unfavorable environmental conditions, plants can absorb light energy in excess of their photosynthetic capacities, with the surplus energy leading to the production of reactive oxygen species and photooxidative stress. Subsequent lipid peroxidation generates toxic reactive carbonyl species whose accumulation culminates in cell death. ß-Cyclocitral, an oxidized by-product of ß-carotene generated in the chloroplasts, mediates a protective retrograde response that lowers the levels of toxic peroxides and carbonyls, limiting damage to intracellular components. In this study, we elucidate the molecular mechanism induced by ß-cyclocitral in Arabidopsis thaliana and show that the xenobiotic detoxification response is involved in the tolerance to excess light energy. The involvement of the xenobiotic response suggests a possible origin for this pathway. Furthermore, we establish the hierarchical structure of this pathway that is mediated by the ß-cyclocitral-inducible GRAS protein SCARECROW LIKE14 (SCL14) and involves ANAC102 as a pivotal component upstream of other ANAC transcription factors and of many enzymes of the xenobiotic detoxification response. Finally, the SCL14-dependent protective mechanism is also involved in the low sensitivity of young leaf tissues to high-light stress.


Assuntos
Aldeídos/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Diterpenos/metabolismo , Estresse Fisiológico/fisiologia , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Inativação Metabólica , Luz , Mutação , Folhas de Planta/fisiologia , Plantas Geneticamente Modificadas , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Xenobióticos/farmacologia
6.
Plant J ; 2018 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-29901834

RESUMO

Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen (1 O2 ) formed during high light stress in higher plants. Although quenching of 1 O2 by prenylquinols has been previously studied, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is limited in vivo. In the present study, the role of plastoquinol-9 (PQH2 -9) in chemical quenching of 1 O2 was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene (SPS1oex) involved in PQH2 -9 and plastochromanol-8 biosynthesis. In this work, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques in vivo. Chemical quenching of 1 O2 was associated with consumption of PQH2 -9 and formation of its various oxidized forms. Oxidation of PQH2 -9 by 1 O2 leads to plastoquinone-9 (PQ-9), which is subsequently oxidized to hydroxyplastoquinone-9 [PQ(OH)-9]. We provide here evidence that oxidation of PQ(OH)-9 by 1 O2 results in the formation of trihydroxyplastoquinone-9 [PQ(OH)3 -9]. It is concluded here that PQH2 -9 serves as an efficient 1 O2 chemical quencher in Arabidopsis, and PQ(OH)3 -9 can be considered as a natural product of 1 O2 reaction with PQ(OH)-9. The understanding of the mechanisms underlying 1 O2 chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.

7.
Plant Cell Environ ; 41(10): 2299-2312, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29749622

RESUMO

The capacity of a Quercus pubescens forest to resist recurrent drought was assessed on an in situ experimental platform through the measurement of a large set of traits (ecophysiological and metabolic) studied under natural drought (ND) and amplified drought (AD) induced by partial rain exclusion. This study was performed during the third and fourth years of AD, which correspond to conditions of moderate AD in 2014 and harsher AD in 2015, respectively. Although water potential (Ψ) and net photosynthesis (Pn) were noticeably reduced under AD in 2015 compared to ND, trees showed similar growth and no oxidative stress. The absence of oxidative damage could be due to a strong accumulation of α-tocopherol, suggesting that this compound is a major component of the Q. pubescens antioxidant system. Other antioxidants were rather stable under AD in 2014, but slight changes started to be observed in 2015 (carotenoids and isoprene) due to harsher conditions. Our results indicate that Q. pubescens could be able to cope with AD, for at least 4 years, likely due to its antioxidant system. However, growth decrease was observed during the fifth year (2016) of AD, suggesting that this resistance could be threatened over longer periods of recurrent drought.


Assuntos
Quercus/metabolismo , Mudança Climática , Desidratação , Secas , Região do Mediterrâneo , Estresse Oxidativo , Fotossíntese , Quercus/fisiologia , Fatores de Tempo
8.
Plant Cell Environ ; 41(10): 2277-2287, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29601642

RESUMO

The Arabidopsis vte1 mutant is devoid of tocopherol and plastochromanol (PC-8). When exposed to excess light energy, vte1 produced more singlet oxygen (1 O2 ) and suffered from extensive oxidative damage compared with the wild type. Here, we show that overexpressing the solanesyl diphosphate synthase 1 (SPS1) gene in vte1 induced a marked accumulation of total plastoquinone (PQ-9) and rendered the vte1 SPS1oex plants tolerant to photooxidative stress, indicating that PQ-9 can replace tocopherol and PC-8 in photoprotection. High total PQ-9 levels were associated with a noticeable decrease in 1 O2 production and higher levels of Hydroxyplastoquinone (PQ-C), a 1 O2 -specific PQ-9 oxidation product. The extra PQ-9 molecules in the vte1 SPS1oex plants were stored in the plastoglobules and the chloroplast envelopes, rather than in the thylakoid membranes, whereas PQ-C was found almost exclusively in the thylakoid membranes. Upon exposure of wild-type plants to high light, the thylakoid PQ-9 pool decreased, whereas the extrathylakoid pool remained unchanged. In vte1 and vte1 SPS1oex plants, the PQ-9 losses in high light were strongly amplified, affecting also the extrathylakoid pool, and PQ-C was found in high amounts in the thylakoids. We conclude that the thylakoid PQ-9 pool acts as a 1 O2 scavenger and is replenished from the extrathylakoid stock.


Assuntos
Depuradores de Radicais Livres/metabolismo , Plastoquinona/metabolismo , Oxigênio Singlete/metabolismo , Tilacoides/metabolismo , Alquil e Aril Transferases/metabolismo , Proteínas de Arabidopsis/metabolismo , Clorofila/metabolismo , Cloroplastos/metabolismo , Cromatografia Líquida de Alta Pressão , Espectroscopia de Ressonância de Spin Eletrônica , Luz , Peroxidação de Lipídeos , Estresse Oxidativo/efeitos da radiação
9.
Plant Cell Environ ; 40(2): 216-226, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27813110

RESUMO

Singlet oxygen (1 O2 ) signalling in plants is essential to trigger both acclimatory mechanisms and programmed cell death under high light stress. However, because of its chemical features, 1 O2 requires mediators, and the players involved in this pathway are largely unknown. The ß-carotene oxidation product, ß-cyclocitral, is one such mediator. Produced in the chloroplast, ß-cyclocitral induces changes in nuclear gene expression leading to photoacclimation. Recently, the METHYLENE BLUE SENSITIVITY protein MBS has been identified as a key player in 1 O2 signalling leading to tolerance to high light. Here, we provide evidence that MBS1 is essential for acclimation to 1 O2 and cross-talks with ß-cyclocitral to mediate transfer of the 1 O2 signal to the nucleus, leading to photoacclimation. The presented results position MBS1 downstream of ß-cyclocitral in 1 O2 signalling and suggest an additional role for MBS1 in the regulation of plant growth and development under chronic 1 O2 production.


Assuntos
Aclimatação , Aldeídos/farmacologia , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Diterpenos/farmacologia , Oxigênio Singlete/farmacologia , Aclimatação/efeitos da radiação , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Proteínas de Fluorescência Verde/metabolismo , Luz , Mutação/genética , Fenótipo , Fotossíntese/efeitos da radiação , Folhas de Planta/fisiologia , Folhas de Planta/efeitos da radiação , Estresse Fisiológico/efeitos da radiação
10.
Sci Rep ; 5: 10919, 2015 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-26039552

RESUMO

Plastoquinone-9 is known as a photosynthetic electron carrier to which has also been attributed a role in the regulation of gene expression and enzyme activities via its redox state. Here, we show that it acts also as an antioxidant in plant leaves, playing a central photoprotective role. When Arabidopsis plants were suddenly exposed to excess light energy, a rapid consumption of plastoquinone-9 occurred, followed by a progressive increase in concentration during the acclimation phase. By overexpressing the plastoquinone-9 biosynthesis gene SPS1 (solanesyl diphosphate synthase 1) in Arabidopsis, we succeeded in generating plants that specifically accumulate plastoquinone-9 and its derivative plastochromanol-8. The SPS1-overexpressing lines were much more resistant to photooxidative stress than the wild type, showing marked decreases in leaf bleaching, lipid peroxidation and PSII photoinhibition under excess light. Comparison of the SPS1 overexpressors with other prenyl quinone mutants indicated that the enhanced phototolerance of the former plants is directly related to their increased capacities for plastoquinone-9 biosynthesis.


Assuntos
Adaptação Biológica , Luz , Estresse Oxidativo , Fotossíntese , Fenômenos Fisiológicos Vegetais , Plastoquinona/metabolismo , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Vias Biossintéticas , Regulação da Expressão Gênica de Plantas , Mutação , Fenótipo , Folhas de Planta/metabolismo
12.
Plant Cell Environ ; 37(2): 368-81, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-23837879

RESUMO

Lipocalins are a group of multifunctional proteins, recognized as carriers of small lipophilic molecules, which have been characterized in bacteria and animals. Two true lipocalins have been recently identified in plants, the temperature-induced lipocalin (TIL) and the chloroplastic lipocalin (CHL), the expression of which is induced by various abiotic stresses. Each lipocalin appeared to be specialized in the responses to specific stress conditions in Arabidopsis thaliana, with AtTIL and AtCHL playing a protective role against heat and high light, respectively. The double mutant AtCHL KO × AtTIL KO deficient in both lipocalins was more sensitive to temperature, drought and light stresses than the single mutants, exhibiting intense lipid peroxidation. AtCHL deficiency dramatically enhanced the photosensitivity of mutants (vte1, npq1) affected in lipid protection mechanisms (tocopherols, zeaxanthin), confirming the role of lipocalins in the prevention of lipid peroxidation. Seeds of the AtCHL KO × AtTIL KO double mutant were very sensitive to natural and artificial ageing, and again this phenomenon was associated with the oxidation of polyunsaturated lipids. The presented results show that the Arabidopsis lipocalins AtTIL and AtCHL have overlapping functions in lipid protection which are essential for stress resistance and survival.


Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/fisiologia , Lipocalinas/fisiologia , Estresse Fisiológico , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Secas , Temperatura Alta , Luz , Peroxidação de Lipídeos , Lipocalinas/genética , Estresse Oxidativo , Sementes/genética , Sementes/fisiologia , Sementes/efeitos da radiação
13.
Plant Signal Behav ; 8(12): e26655, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24103864

RESUMO

Under stress conditions that bring about excessive absorption of light energy in the chloroplasts, the formation of singlet oxygen ( (1)O2) can be strongly enhanced, triggering programmed cell death. However, the (1)O2 signaling pathway can also lead to acclimation to photooxidative stress, when (1)O2 is produced in relatively low amounts. This acclimatory response is associated with a strong downregulation of the jasmonate biosynthesis pathway and the maintenance of low jasmonate levels, even under high light stress conditions that normally induce jasmonate synthesis. These findings suggest a central role for this phytohormone in the orientation of the (1)O2 signaling pathway toward cell death or acclimation. This conclusion is confirmed here in an Arabidopsis double mutant obtained by crossing the (1)O2-overproducing mutant ch1 and the jasmonate-deficient mutant dde2. This double mutant was found to be constitutively resistant to (1)O2 stress and to display a strongly stimulated growth rate compared with the single ch1 mutant. However, the involvement of other phytohormones, such as ethylene, cannot be excluded.


Assuntos
Aclimatação/efeitos dos fármacos , Arabidopsis/citologia , Arabidopsis/fisiologia , Ciclopentanos/metabolismo , Oxilipinas/metabolismo , Oxigênio Singlete/farmacologia , Aclimatação/efeitos da radiação , Arabidopsis/efeitos dos fármacos , Arabidopsis/efeitos da radiação , Morte Celular/efeitos dos fármacos , Morte Celular/efeitos da radiação , Luz , Mutação/genética , Estresse Oxidativo/efeitos dos fármacos , Estresse Oxidativo/efeitos da radiação , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/efeitos da radiação
14.
Front Plant Sci ; 4: 390, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24137166

RESUMO

Plants display a remarkable diversity of thioredoxins (Trxs), reductases controlling the thiol redox status of proteins. The physiological function of many of them remains elusive, particularly for plastidial Trxs f and m, which are presumed based on biochemical data to regulate photosynthetic reactions and carbon metabolism. Recent reports revealed that Trxs f and m participate in vivo in the control of starch metabolism and cyclic photosynthetic electron transfer around photosystem I, respectively. To further delineate their in planta function, we compared the photosynthetic characteristics, the level and/or activity of various Trx targets and the responses to oxidative stress in transplastomic tobacco plants overexpressing either Trx f or Trx m. We found that plants overexpressing Trx m specifically exhibit altered growth, reduced chlorophyll content, impaired photosynthetic linear electron transfer and decreased pools of glutathione and ascorbate. In both transplastomic lines, activities of two enzymes involved in carbon metabolism, NADP-malate dehydrogenase and NADP-glyceraldehyde-3-phosphate dehydrogenase are markedly and similarly altered. In contrast, plants overexpressing Trx m specifically display increased capacity for methionine sulfoxide reductases, enzymes repairing damaged proteins by regenerating methionine from oxidized methionine. Finally, we also observed that transplastomic plants exhibit distinct responses when exposed to oxidative stress conditions generated by methyl viologen or exposure to high light combined with low temperature, the plants overexpressing Trx m being notably more tolerant than Wt and those overexpressing Trx f. Altogether, these data indicate that Trxs f and m fulfill distinct physiological functions. They prompt us to propose that the m type is involved in key processes linking photosynthetic activity, redox homeostasis and antioxidant mechanisms in the chloroplast.

15.
Plant Physiol ; 163(1): 263-75, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23878079

RESUMO

The fungal elicitor cryptogein triggers a light-dependent hypersensitive response in tobacco (Nicotiana tabacum). To assess the effect of light on this nonhost resistance in more detail, we studied various aspects of the response under dark and light conditions using the tobacco-cryptogein experimental system. Here, we show that light drastically alters the plant's transcriptional response to cryptogein, notably by dampening the induction of genes involved in multiple processes, such as ethylene biosynthesis, secondary metabolism, and glutathione turnover. Furthermore, chlorophyll fluorescence measurements demonstrated that quantum yield and functioning of the light-harvesting antennae decreased simultaneously, indicating that photoinhibition underlies the observed decreased photosynthesis and that photooxidative damage might be involved in the establishment of the altered response. Analysis of the isomer distribution of hydroxy fatty acids illustrated that, in the light, lipid peroxidation was predominantly due to the production of singlet oxygen. Differences in (reduced) glutathione concentrations and the rapid development of symptoms in the light when cryptogein was coinfiltrated with glutathione biosynthesis inhibitors suggest that glutathione might become a limiting factor during the cryptogein-induced hypersensitive response in the dark and that this response might be modified by an increased antioxidant availability in the light.


Assuntos
Proteínas Fúngicas/farmacologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Tabaco/efeitos dos fármacos , Vias Biossintéticas , Resistência à Doença , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Glutationa Transferase/metabolismo , Glutationa Transferase/fisiologia , Glicosiltransferases/metabolismo , Glicosiltransferases/fisiologia , Oxilipinas/metabolismo , Doenças das Plantas/genética , Tabaco/microbiologia , Tabaco/efeitos da radiação
16.
Plant Cell ; 25(4): 1445-62, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23590883

RESUMO

Singlet oxygen (¹O2) is a reactive oxygen species that can function as a stress signal in plant leaves leading to programmed cell death. In microalgae, ¹O2-induced transcriptomic changes result in acclimation to ¹O2. Here, using a chlorophyll b-less Arabidopsis thaliana mutant (chlorina1 [ch1]), we show that this phenomenon can also occur in vascular plants. The ch1 mutant is highly photosensitive due to a selective increase in the release of ¹O2 by photosystem II. Under photooxidative stress conditions, the gene expression profile of ch1 mutant leaves very much resembled the gene responses to ¹O2 reported in the Arabidopsis mutant flu. Preexposure of ch1 plants to moderately elevated light intensities eliminated photooxidative damage without suppressing ¹O2 formation, indicating acclimation to ¹O2. Substantial differences in gene expression were observed between acclimation and high-light stress: A number of transcription factors were selectively induced by acclimation, and contrasting effects were observed for the jasmonate pathway. Jasmonate biosynthesis was strongly induced in ch1 mutant plants under high-light stress and was noticeably repressed under acclimation conditions, suggesting the involvement of this hormone in ¹O2-induced cell death. This was confirmed by the decreased tolerance to photooxidative damage of jasmonate-treated ch1 plants and by the increased tolerance of the jasmonate-deficient mutant delayed-dehiscence2.


Assuntos
Aclimatação/efeitos da radiação , Arabidopsis/genética , Luz , Mutação , Oxigenases/genética , Oxigênio Singlete/metabolismo , Aclimatação/genética , Acetatos/farmacologia , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Vias Biossintéticas/efeitos dos fármacos , Vias Biossintéticas/genética , Vias Biossintéticas/efeitos da radiação , Clorofila/metabolismo , Ciclopentanos/metabolismo , Ciclopentanos/farmacologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Peroxidação de Lipídeos/efeitos da radiação , Análise de Sequência com Séries de Oligonucleotídeos , Oxirredução/efeitos da radiação , Oxigenases/metabolismo , Oxilipinas/metabolismo , Oxilipinas/farmacologia , Complexo de Proteína do Fotossistema II/genética , Complexo de Proteína do Fotossistema II/metabolismo , Reguladores de Crescimento de Planta/farmacologia , Folhas de Planta/genética , Folhas de Planta/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transcriptoma/efeitos dos fármacos , Transcriptoma/genética , Transcriptoma/efeitos da radiação
17.
J Plant Physiol ; 170(7): 633-45, 2013 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-23541087

RESUMO

Barley displays a great genetic diversity, constituting a valuable source to delineate the responses of contrasted genotypes to environmental constraints. Here, we investigated the level of oxidative stress and the participation of antioxidant systems in two barley genotypes: Express, a variety known to be sensitive to drought, and Saïda, an Algerian landrace selected for its tolerance to water deficit. Soil-grown 15-day-old plants were subjected to water deficit for 8 days and then rewatered. We observed that upon water stress Express exhibits compared to Saïda accelerated wilting and a higher level of oxidative stress evaluated by HPLC measurements of lipid peroxidation and by imaging techniques. In parallel, Express plants also display lower levels of catalase and superoxide dismutase activity. No great difference was observed regarding peroxiredoxins and methionine sulfoxide reductases, enzymes detoxifying peroxides and repairing oxidized proteins, respectively. In contrast, upon water stress and recovery, much higher contents and oxidation ratios of glutathione and ascorbate were measured in Express compared to Saïda. Express also shows during water deficit greater increases in the pools of lipophilic antioxidants like xantophyll carotenoids and α-tocopherol. Altogether, these data show that the differential behavior of the two genotypes involves distinct responses regarding antioxidant mechanisms. Indeed, the drought sensitivity of Express compared with Saïda is associated with oxidative damage and a lower enzymatic ROS-scavenging capacity, but in parallel with a much stronger enhancement of most mechanisms involving low-molecular weight antioxidant compounds.


Assuntos
Antioxidantes/metabolismo , Depuradores de Radicais Livres/metabolismo , Hordeum/fisiologia , Estresse Fisiológico/fisiologia , Água/fisiologia , Ácido Ascórbico/metabolismo , Carotenoides/metabolismo , Catalase/metabolismo , Clorofila/metabolismo , Desidratação , Secas , Genótipo , Glutationa/metabolismo , Hordeum/química , Hordeum/enzimologia , Peróxido de Hidrogênio/metabolismo , Peroxidação de Lipídeos , Estresse Oxidativo , Fenótipo , Folhas de Planta/química , Folhas de Planta/enzimologia , Folhas de Planta/fisiologia , Especificidade da Espécie , Superóxido Dismutase/metabolismo , Tocoferóis/metabolismo
18.
Proc Natl Acad Sci U S A ; 108(34): 14354-9, 2011 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-21844348

RESUMO

Lipid droplets are ubiquitous cellular structures in eukaryotes and are required for lipid metabolism. Little is currently known about plant lipid droplets other than oil bodies. Here, we define dual roles for chloroplast lipid droplets (plastoglobules) in energy and prenylquinone metabolism. The prenylquinones--plastoquinone, plastochromanol-8, phylloquinone (vitamin K(1)), and tocopherol (vitamin E)--are partly stored in plastoglobules. This work shows that NAD(P)H dehydrogenase C1 (NDC1) (At5g08740), a type II NAD(P)H quinone oxidoreductase, associates with plastoglobules. NDC1 reduces a plastoquinone analog in vitro and affects the overall redox state of the total plastoquinone pool in vivo by reducing the plastoquinone reservoir of plastoglobules. Finally, NDC1 is required for normal plastochromanol-8 accumulation and is essential for vitamin K(1) production.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Cloroplastos/enzimologia , Cromanos/metabolismo , Lipídeos/química , NADH NADPH Oxirredutases/metabolismo , Plastoquinona/metabolismo , Quinona Redutases/metabolismo , Quinonas/metabolismo , Tocoferóis/metabolismo , Vitamina E/análogos & derivados , Vitamina K 1/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Cloroplastos/genética , Regulação da Expressão Gênica de Plantas , Medições Luminescentes , Mutação/genética , NADH NADPH Oxirredutases/genética , Fotossíntese , Transporte Proteico , Vitamina E/metabolismo
19.
Plant J ; 67(6): 1103-15, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21595761

RESUMO

Plants, like almost all living organisms, spontaneously emit photons of visible light. We used a highly sensitive, low-noise cooled charge coupled device camera to image spontaneous photon emission (autoluminescence) of plants. Oxidative stress and wounding induced a long-lasting enhancement of plant autoluminescence, the origin of which is investigated here. This long-lived phenomenon can be distinguished from the short-lived chlorophyll luminescence resulting from charge recombinations within the photosystems by pre-adapting the plant to darkness for about 2 h. Lipids in solvent were found to emit a persistent luminescence after oxidation in vitro, which exhibited the same time and temperature dependence as plant autoluminescence. Other biological molecules, such as DNA or proteins, either did not produce measurable light upon oxidation or they did produce a chemiluminescence that decayed rapidly, which excludes their significant contribution to the in vivo light emission signal. Selective manipulation of the lipid oxidation levels in Arabidopsis mutants affected in lipid hydroperoxide metabolism revealed a causal link between leaf autoluminescence and lipid oxidation. Addition of chlorophyll to oxidized lipids enhanced light emission. Both oxidized lipids and plants predominantly emit light at wavelengths higher than 600 nm; the emission spectrum of plant autoluminescence was shifted towards even higher wavelengths, a phenomenon ascribable to chlorophyll molecules acting as luminescence enhancers in vivo. Taken together, the presented results show that spontaneous photon emission imaged in plants mainly emanates from oxidized lipids. Imaging of this signal thus provides a simple and sensitive non-invasive method to selectively visualize and map patterns of lipid oxidation in plants.


Assuntos
Metabolismo dos Lipídeos/fisiologia , Peróxidos Lipídicos/análise , Medições Luminescentes/métodos , Arabidopsis/genética , Arabidopsis/metabolismo , Clorofila/metabolismo , Técnicas In Vitro , Medições Luminescentes/instrumentação , Mutação , Oxirredução , Estresse Oxidativo , Fótons
20.
BMC Plant Biol ; 9: 130, 2009 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-19903353

RESUMO

BACKGROUND: Vitamin B6 is a collective term for a group of six interconvertible compounds: pyridoxine, pyridoxal, pyridoxamine and their phosphorylated derivatives. Vitamin B6 plays essential roles as a cofactor in a range of biochemical reactions. In addition, vitamin B6 is able to quench reactive oxygen species in vitro, and exogenously applied vitamin B6 protects plant cells against cell death induced by singlet oxygen (1O2). These results raise the important question as to whether plants employ vitamin B6 as an antioxidant to protect themselves against reactive oxygen species. RESULTS: The pdx1.3 mutation affects the vitamin B6 biosynthesis enzyme, pyridoxal synthase (PDX1), and leads to a reduction of the vitamin B6 concentration in Arabidopsis thaliana leaves. Although leaves of the pdx1.3 Arabidopsis mutant contained less chlorophyll than wild-type leaves, we found that vitamin B6 deficiency did not significantly impact photosynthetic performance or shoot and root growth. Chlorophyll loss was associated with an increase in the chlorophyll a/b ratio and a selective decrease in the abundance of several PSII antenna proteins (Lhcb1/2, Lhcb6). These changes were strongly dependent on light intensity, with high light amplifying the difference between pdx1.3 and the wild type. When leaf discs were exposed to exogenous 1O2, lipid peroxidation in pdx1.3 was increased relative to the wild type; this effect was not observed with superoxide or hydrogen peroxide. When leaf discs or whole plants were exposed to excess light energy, 1O2-mediated lipid peroxidation was enhanced in leaves of the pdx1.3 mutant relative to the wild type. High light also caused an increased level of 1O2 in vitamin B6-deficient leaves. Combining the pdx1.3 mutation with mutations affecting the level of 'classical' quenchers of 1O2 (zeaxanthin, tocopherols) resulted in a highly photosensitive phenotype. CONCLUSION: This study demonstrates that vitamin B6 has a function in the in vivo antioxidant defense of plants. Thus, the antioxidant activity of vitamin B6 inferred from in vitro studies is confirmed in planta. Together with the finding that chloroplasts contain vitamin B6 compounds, the data show that vitamin B6 functions as a photoprotector that limits 1O2 accumulation in high light and prevents 1O2-mediated oxidative damage.


Assuntos
Antioxidantes/metabolismo , Arabidopsis/efeitos da radiação , Luz , Estresse Oxidativo , Vitamina B 6/biossíntese , Arabidopsis/enzimologia , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Carbono-Nitrogênio Liases , Clorofila/metabolismo , Regulação da Expressão Gênica de Plantas , Peroxidação de Lipídeos , Mutação , Transferases de Grupos Nitrogenados/genética , Fotossíntese , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Espécies Reativas de Oxigênio/farmacologia
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