[Changes of light energy distribution in reaction centers of Citrus unshiu leaf photosystem under different light intensities].

In order to further understand the light energy distribution in photochemical reaction centers of fruit trees, this paper employed modulated fluorescence technique to study the state transition of photosystem in Citrus unshiu leaves under high and low light intensities. The results indicated that under low light intensity of 100 micromol x m(-2) s(-1), the PQ pool was in reduction state due to Q(A) reduction, which made the light energy distribution in photosystem changed from PS II to PS I; while under high light intensity of 1000 micromol x m(-2) s(-1), the PQ pool could not get electron and was in oxidation state, making light energy distribution changed from state 2 to state 1. When the leaves were treated by a phosphatase inhibitor NaF, the state 2 to state 1 transition of photosystem was inhibited under high light intensity, and the excessive light energy distribution from PS I to PS II caused damage to PS II. These findings would be helpful to understand the mechanisms of the photoinhibition of photosynthesis and the photodamage of photosynthetic apparatus of fruit trees.