Photoprotective function of energy dissipation by thermal processes and photorespiratory mechanisms in Jatropha curcas plants during different intensities of drought and after recovery

Abstract

The role of photorespiration in plants under drought is not well understood. It can act both as an alternative electron sink and a source of reactive oxygen species (ROS). In this study, we evaluated in which stage of water deficit the energy dissipation by thermal processes and photorespiration act as photoprotective mechanisms, alleviating the photodamage in photosystem II (PSII) of Jatropha curcas plants. The experiment lasted 20 days; every 5 days (0, 5, 10, 15, and 20 days), measurements of gas exchange, chlorophyll fluorescence, and biochemical analysis were performed. On the 10th day of treatment, re-hydration in a separate group of drought-stressed plants was applied. The electron flow used for ribulose bisphosphate (RuBP) carboxylation (JC) progressively decreased with time of exposure to increasing drought. On the other hand, the electron flow used for RuBP oxygenation (JO) decreased during 5–10 days of exposure to water deficit and was significantly enhanced from 10 to 20 days. The JC/JO ratio was lower in plants exposed to drought compared to non-stressed plants. In addition, the photorespiration and the PR/PN and JT/PN ratios also were stimulated by drought. The non-photochemical quenching coefficient (NPQ) and relative energy excess level at PSII (EXC) in drought-stressed plants significantly increased between 5 and 10 days of treatment compared to control plants. Leaf H2O2 content was enhanced in plants exposed to water deficit reaching their concentrations more elevated in the period of 15–20 days when compared to control. In addition, the drought stress stimulated ascorbate peroxidase activity. On the other hand, the glycolate oxidase (GO) activity intensely increased, while catalase activity progressively decreased with increasing water deficit. In general, our results reveal that both excessive energy dissipation as heat and photorespiration play important roles in protecting the photosynthetic apparatus from photoinhibition.