Exogenous spermidine enhances salt-stressed rice photosynthetic performance by stabilizing structure and function of chloroplast and thylakoid membranes

Spermidine (Spd) is a ubiquitous low-molecular-mass aliphatic amine that acts in abiotic stress tolerance in plants. We investigated how the treatment with exogenous Spd contributed to the protection against salt stress in rice chloroplasts. Analysis of the chlorophyll (Chl) fluorescence showed that there were many negative effects of salinity on different sites of the photosynthetic machinery; however, these were alleviated by adding Spd. Spd prevented the damage of structure and function of chloroplasts under salt stress; thylakoid membrane protein components and photosynthetic pigments were not severely affected by salinity in Spd-treated plants. Spd enhanced the activities of antioxidant enzymes and decreased contents of reactive oxygen species and malondialdehyde accumulation, suggesting that Spd may participate in the redox homeostasis in chloroplasts under salt stress. These results highlighted the positive effects of Spd on rice chloroplasts under salt stress through maintaining chloroplast structure stability.