Photoinhibition and recovery of photosynthesis in pear leaves.

Photosynthesis and chlorophyll fluorescence parameters are measured on Whangkeumbae and Yali pear leaves and their disks in natural and simulated light. The results showed that net photosynthetic rate(Pn) ,apparent quantum yield(AQY) ,and photochemical efficiency of PSⅡ(Fv/Fm) decreased and minimal initial fluorescence(Fo) was improved after being exposed to midday high irradiance,indicating that photoinhibition of Whangkeumbae pear and Yali pear occurred. However,photoinhibition was only induced by high light and could be recovered after 2-4 hours of low light,it indicated that photoinhibition only induced by high light is reversible. Photochemical efficiency of PSⅡ(Fv/Fm) decreased and minimal initial fluorescence(Fo) was improved after being exposed to DTT,which indicate that Xanthophyll cycle was the major protective mechanism to prevent from the deteriorating effects of strong light in the pear leaves;The capacity of patience and recovery of Yali on strong light stress was stronger than that of Whankgeumbae,indicating that the extent of photoinhibition varied with varieties in pear.