Physiological and proteomic analysis of rice (Oryza sativa L.) in flag leaf during flowering stage and milk stage under drought stress

Hybrid rice has the inferiority of early senescence during reproductive stage. Early senescence of leaves induced by drought causes a constraint on crop productivity. Hence, to better understand traits of drought responsive mechanism in hybrid rice flag leaves during sensitive reproductive stage, we performed physiological measurements and conducted 2-D electrophoresis to investigate proteomic profile of rice flag leaves at flowering and milk stage. 43 proteins showed significant changes in silver stained gels were identified by MS/MS at flowering stage and 54 proteins at milk stage. For flowering stage, inactive CO2 assimilation and ATP synthesis as well abnormal floral development could be postulated from decreased proteins. Additionally, higher levels of defense-related proteins and antioxidases in drought-stressed leaves suggested active ROS scavenging system. For milk stage, both photosynthesis and CO2 assimilation were impaired. Disrupted oxidative defense and proteolysis system indicated redox imbalance. Upregulation of NADP-MDH facilitated for CO2 assimilation and antioxidant system. In conclusion, drought stress during reproductive stage impacted a lot on biological processes in rice leaves at protein level, especially energy metabolism and redox balance.