Effects of salicylic acid on protein kinase activity and chloroplast D1 protein degradation in wheat leaves subjected to heat and high light stress

In the north of China, wheat plants are often stressed by heat and high light during grain-filling stage, which leads to injury in photosynthetic apparatus and decline in photosynthetic rate. In order to develop a method to protect photosynthetic apparatus in wheat leaves subjected to heat and high light stress, the effects of SA (salicylic acid) and FSBA (5′-p-fluorosulfonylbenzoyl adenosine) on PK (protein kinase) activity, D1 protein degradation and the performance of PSII were investigated in present work. Our results showed that PK activity enhanced under heat and high light stress and declined when stress was removed. FSBA pretreatment resulted in marked decreases in PK activity and D1 protein level, suggesting a correlationship between degradation of D1 protein and phosphorylation. After 2 h of stress, D1 protein level in water-pretreated leaves decreased to 79% of control and then recovered to 81% after 3 h of recovery. This clearly indicated that the damage of D1 protein induced by heat and high light stress was reversible. Compared to the control, SA pretreatment could not only increase PK activity, retard the degradation of D1 protein during heat and high light stress, but also accelerate the recovery of D1 protein level when the stress was removed. Correspondingly, Fv/Fm (maximum photochemical efficiency of PSII), ΦPSII (actual photochemical efficiency of PSII), ETR (electron transfer rate) and Pn (net photosynthetic rate) in SA-treated leaves were higher than that in leaves of control under both stress and non-stress conditions. Taken together, our results revealed that SA pretreatment could significantly alleviate damages of heat and high light stress on D1 protein and PSII of wheat leaves, and accelerate restoration of photosynthetic function.