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Interação da Seca e do CO2 Elevado nas Relações Hídricas e Atividade Fotossintética - O Cafeeiro como Cultura Modelo
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As alterações climáticas, associadas ao aumento da [CO2] atmosférica (eCO2) e a alterações nos padrões pluviométricos intra e interanuais, tornarão mais frequentes e severos os episódios de défice hídrico sobre as culturas, incluindo a do café uma das mais importantes da região tropical. Pretendeu-se estudar os processos de aclimatação do cafeeiro ao défice hídrico, e compreender o potencial efeito mitigador do eCO2 em plantas: 1) de dois genótipos das principais espécies produtoras, Coffea canephora Pierre ex A. Froehner cv. Conilon Clone 153 (CL153) e C. arabica L. cv. Icatu), 2) desenvolvidas em [CO2] atmosférica ambiente (aCO2, 380 μL L-1) e elevada (eCO2, 700 μL L-1), 3) submetidas a conforto hídrico (WW), e défices hídrico moderado (MWD) e severo (SWD), 4) focando o processo fotossíntético e mecanismos de defesa/aclimatação. Em aCO2, o MWD diminuiu a fotossíntese líquida (Pn), sem efeitos não-estomáticos em ambos os genótipos. SWD afetou significativamente a maquinaria fotossintética de CL153, mas não a de Icatu. Este mostrou tolerância, mantendo o funcionamento potencial (e.g., capacidade fotossintética, Amax; eficiência fotoquímica do fotossistema (PS) II, Fv/Fm; atividade da RuBisCO) e reforçando componentes fotossintéticos (e.g., proteínas ligadas aos PSs; transportadores tilacoidais de eletrões, como PQ-9 e Cit f), e outros ligados a mecanismos de defesa como pigmentos fotoprotetores (zeaxantina, Zea; luteína), enzimas antioxidativas (Cu,Zn-superoxido dismutase, SOD), moléculas de proteção (proteína de choque térmico, HSP70; componentes do transporte cíclico de eletrões, CEF), conjugado com alterações qualitativas e quantitativas dos ácidos gordos (AGs) das membranas cloroplastidiais. Em eCO2 e WW, a Pn aumentou em ambos os genótipos, suportada pela redução da limitação à difusão de CO2 e da fotorespiração, e pelo reforço de componentes foto- e bioquímicos (e.g., PSs, RuBisCO). A interação eCO2 vs. MWD traduziu-se no menor impacto da seca na Pn e reforço de moléculas de proteção (e.g., Zea; ascorbato peroxidase, APX; ascorbato, Asc; HSP70) em ambos os genótipos. Em CL153 sob SWD, o eCO2, promoveu aumentos moderados de carotenoides (significativo para neoxantina), enzimas antioxidativas, Asc, e dos principais AGs (C18:3 e C16:0), reverteu o impacto nos PSs e citocromos, resultando na redução da fotoinibição crónica e do índice de dano membranar. Já em Icatu, a eCO2 reforçou componentes (e.g., citocromos; actividade dos PSs) e moléculas protectoras (SOD; APX; Asc; HSP70), mantendo aumentos já observados em aCO2 (e.g., carotenoides; proteínas ligadas aos fotossistemas, CEF, AGs). Em síntese, o eCO2 melhora a resposta do cafeeiro à seca, o que associado a uma eficiente gestão de rega poderá contribuir a futura sustentabilidade desta cultura.
Climate change, associated with the atmospheric [CO2] increase (eCO2) and changes in intra- and inter-annual rainfall patterns, will boost the frequency and severity of water deficit episodes to crops, including coffee, one of the most important one in the tropical region. The aim was to study the acclimation processes of coffee to water deficit, and the unveil the potential mitigating effect of eCO2 on plants: 1) of two genotypes from the main producing species, Coffea canephora Pierre ex A. Froehner cv. Conilon Clone 153 (CL153) and C. arabica L. cv. Icatu), 2) grown under ambient (aCO2, 380 μL L-1) and elevated (eCO2, 700 μL L-1) ai [CO2], 3) subjected to well-water (WW), moderate (MWD) and severe (SWD) water deficits conditions, 4) focusing on the photosynthetic processes and the defence/acclimation mechanisms. Under aCO2, MWD reduced net photosynthesis (Pn), without non-stomatal effects in both genotypes. SWD significantly affected the photosynthetic machinery of CL153, but not of Icatu. The latter showed tolerance, keeping the potential functioning (e.g., photosynthetic capacity, Amax; photosystem (PS) II photochemical efficiency, Fv/Fm; RuBisCO activity), and reinforcing photosynthetic components (e.g., PS associated proteins; thylakoid electron carriers, such as PQ-9 and Cit f), and others linked to defence mechanisms, such as photoprotective pigments (zeaxanthin, Zea; lutein), antioxidative enzymes (Cu,Zn-superoxide dismutase, SOD), protective molecules (heat shock protein, HSP70; components of cyclic electron transport; CEF), coupled with qualitative and quantitative changes in fatty acids (FAs) of chloroplast membranes. Under eCO2 and WW, Pn raised in both genotypes, supported by reduced CO2 diffusion limitation and photorespiration, and by enhanced photo- and biochemical components (e.g., PSs, RuBisCO). The eCO2 and MWD interaction was shown by the lower drought impact on Pn and enhancement of protective molecules (e.g., Zea; ascorbate peroxidase, APX; ascorbate, Asc; HSP70) in both genotypes. In CL153 exposed to SWD, eCO2 promoted moderate increases in carotenoids (significant for neoxanthin), antioxidative enzymes, Asc and the major FAs (C18:3 and C16:0), reverted the impact on PSs and cytochromes, ultimately reducing chronic photoinhibition and the membrane injury index. In Icatu, eCO2 reinforced components (e.g., cytochromes; PSs activity) and protective molecules (SOD; APX; Asc; HSP70), while kept increases already found under aCO2 (e.g., carotenoids; proteins associated to PSs, CEF; AGs). In summary, eCO2 improves the coffee plant response to drought, which associated with efficient irrigation management may contribute to the future sustainability of this crop.
Climate change, associated with the atmospheric [CO2] increase (eCO2) and changes in intra- and inter-annual rainfall patterns, will boost the frequency and severity of water deficit episodes to crops, including coffee, one of the most important one in the tropical region. The aim was to study the acclimation processes of coffee to water deficit, and the unveil the potential mitigating effect of eCO2 on plants: 1) of two genotypes from the main producing species, Coffea canephora Pierre ex A. Froehner cv. Conilon Clone 153 (CL153) and C. arabica L. cv. Icatu), 2) grown under ambient (aCO2, 380 μL L-1) and elevated (eCO2, 700 μL L-1) ai [CO2], 3) subjected to well-water (WW), moderate (MWD) and severe (SWD) water deficits conditions, 4) focusing on the photosynthetic processes and the defence/acclimation mechanisms. Under aCO2, MWD reduced net photosynthesis (Pn), without non-stomatal effects in both genotypes. SWD significantly affected the photosynthetic machinery of CL153, but not of Icatu. The latter showed tolerance, keeping the potential functioning (e.g., photosynthetic capacity, Amax; photosystem (PS) II photochemical efficiency, Fv/Fm; RuBisCO activity), and reinforcing photosynthetic components (e.g., PS associated proteins; thylakoid electron carriers, such as PQ-9 and Cit f), and others linked to defence mechanisms, such as photoprotective pigments (zeaxanthin, Zea; lutein), antioxidative enzymes (Cu,Zn-superoxide dismutase, SOD), protective molecules (heat shock protein, HSP70; components of cyclic electron transport; CEF), coupled with qualitative and quantitative changes in fatty acids (FAs) of chloroplast membranes. Under eCO2 and WW, Pn raised in both genotypes, supported by reduced CO2 diffusion limitation and photorespiration, and by enhanced photo- and biochemical components (e.g., PSs, RuBisCO). The eCO2 and MWD interaction was shown by the lower drought impact on Pn and enhancement of protective molecules (e.g., Zea; ascorbate peroxidase, APX; ascorbate, Asc; HSP70) in both genotypes. In CL153 exposed to SWD, eCO2 promoted moderate increases in carotenoids (significant for neoxanthin), antioxidative enzymes, Asc and the major FAs (C18:3 and C16:0), reverted the impact on PSs and cytochromes, ultimately reducing chronic photoinhibition and the membrane injury index. In Icatu, eCO2 reinforced components (e.g., cytochromes; PSs activity) and protective molecules (SOD; APX; Asc; HSP70), while kept increases already found under aCO2 (e.g., carotenoids; proteins associated to PSs, CEF; AGs). In summary, eCO2 improves the coffee plant response to drought, which associated with efficient irrigation management may contribute to the future sustainability of this crop.
Descrição
Palavras-chave
aclimatação alterações climáticas cafeeiro CO2 elevado fotossíntese seca