Glycine betaine application in grain filling wheat plants alleviates heat and high light-induced photoinhibition by enhancing the psbA transcription and stomatal conductance

Wheat (Triticum aestivum) plants often suffer from heat stress combined with high irradiance during the grain filling stage. Glycine betaine (GB) is a compatible solute that accumulates rapidly to enhance stress tolerance in wheat under abiotic stress. In this study, the effect of foliar application of GB on photosystem II (PSII) photochemistry in wheat leaves under the heat and high light stresses were investigated. The results showed that GB-supplemented wheat plants maintained higher chlorophyll content, photochemical activity of PSII and net photosynthetic rate (P (n)) than stressed only plants. Moreover, GB-treated plants could retard the decrease of psbA gene transcription and accelerate the endogenous accumulation of GB in leaves. The results suggested that the increasing stress tolerance by GB accumulation was associated with an improvement in D1 protein synthesis, which accelerated the repair of PSII following stress-enhanced photoinhibition. Moreover, the accumulation of abscisic acid under the heat and high light stresses was retarded by foliar application of GB, and the decrease of stomatal conductance was inhibited as well. The results suggested that GB accumulation in vivo was involved in the regulation of stomatal conductance. Further work is required to elucidate the mechanism of GB-induced stomatal movement and PSII photoprotection.