Xanthophyll cycle and photosynthetic electron transport enhanced by galactolipid modification alleviate drought-induced leaf senescence

Abstract

Previous studies have demonstrated galactolipid modification was involved in drought-induced leaf senescence. Under drought stress, overactivation of the photosynthetic electron transfer chain leads to excessive light energy absorption, resulting in photooxidative damage to crops. The xanthophyll cycle, a key photoprotective mechanism, mitigates light-induced damage by dissipating excess energy as heat. However, the role of the xanthophyll cycle pigments and photosynthetic electron transport in the process of galactolipid modification alleviates drought-induced leaf senescence has not yet been clarified clearly. In this study, a comparative experiment was conducted to investigate changes in the xanthophyll cycle and photosynthetic electron transport during drought and re-watering in two maize varieties: a drought-tolerant variety (Liangyu66) and a senescent variety (Liangyu99). Drought stress induced more severely wilted and leaf senescence in Liangyu99, with lower shoot biomass, photosynthetic rate, chlorophyll a/b, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) content, corresponding gene expression level and DGDG/MGDG ratio compared to Liangyu66. Furthermore, PSII electron transport rate (ETRⅡ), the PSI electron transport rate (ETRⅠ), and cyclic electron flow (CEF) in Liangyu66 were 14 %, 47 %, and 83 % higher, respectively, than in Liangyu99 under drought stress. Notably, the de-epoxidation state of the xanthophyll cycle (A + Z)/(A + Z + V) was significantly higher in Liangyu66 than in Liangyu99. Non-photochemical quenching (NPQ) increased in both varieties under drought stress, Liangyu66 displayed a higher NPQ than Liangyu99. These findings suggest that galactolipid modification alleviates drought-induced leaf senescence by enhancing the xanthophyll cycle and optimizing photosynthetic electron transport.