Coordinate changes in photosynthesis, sugar accumulation and antioxidative enzymes improve the performance of Jatropha curcas plants under drought stress

The aim of this study was to assess the relationships between photosynthesis, sugars and photo-oxidative protection mechanisms in Jatropha curcas under drought stress. Leaf CO2 assimilation rate (PN) and instantaneous carboxylation efficiency decreased progressively as the water deficit increased. The sucrose and reducing sugar concentrations were negatively and highly correlated with photosynthesis indicating a modulation by negative feedback mechanism. The alternative electron sinks (ETRs'/PN), relative excess of light energy (EXC) and non-photochemical quenching were strongly increased by drought, indicating effective mechanisms of energy excess dissipation. The photochemistry data indicate partial preservation of photosystem II integrity and function even under severe drought. EXC was positively correlated with superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities evidencing an effective role of these enzymes in the oxidative protection against excess of reactive oxygen species in chloroplasts. Leaf H2O2 content and lipid peroxidation were inversely and highly correlated with catalase (CAT) activity indicating that drought-induced inhibition of this enzyme might have allowed oxidative damage. Our data suggest that drought triggers a coordinate down-regulation in photosynthesis through sucrose and reducing sugar accumulation and an energy excess dissipation at PSII level by non-photochemical mechanisms associate with enhancement in photorespiration, restricting photo-damages. In parallel, drought up-regulates SOD and APX activities avoiding accumulation of reactive oxygen species, while CAT activity is not able to avoid H2O2 accumulation in drought-stressed J. curcas leaves.

► Drought triggers a down-regulation in photosynthesis by sucrose and reducing sugar.
► Drought induces energy dissipation at PSII level and increase in photorespiration.
► Drought up-regulates SOD and APX activities avoiding accumulation of ROS.
► CAT activity is not able to avoid H2O2 accumulation in drought-stressed Jatropha curcas.