[Effects of dark induced senescence on the function of photosystem II in flag leaves of winter wheat released in different years.].

Cultivar renewing is important for the increases of wheat yield. Studying changes of different physiological characteristics in the succession process of wheat varieties has great implications for future breeding. The senescence rate of flag leaf is a key factor affecting winter wheat yield. The variation of photosystem II function during senescence of flag leaves of wheat from different ages is still not clear. 31 wheat varieties planted in Henan Province from different ages since 1941 were examined in this experiment. The variation of photosystem II function was analyzed through measu-ring the relative chlorophyll content, and chlorophyll fluorescence induction dynamics during the senescence of flag leaves which were induced by continued dark. The results showed that the chlorophyll content of flag leaves was gradually increased in the succession of winter wheat. The chlorophyll degradation rate in the leaves of modern varieties was lower than the earlier varieties during the senescnece of flag leaves. Meanwhile, J point of the fluorescence induction kinetics curves in flag leaves of modern varieties increased less than I point. The photosystem II maximum photochemical efficiency and the amount of active reaction centers per unit area gradually increased during succession of wheat varieties, but the reduced extent in leaves of modern varieties was lower than that in the earlier ones. There was no significant correlation between the change of chlorophyll content and F/F in senescent leaves. There was significant positive correlation when the leaves aging degree increased, with the slope of trend line gradually increased. The photosystem II unit area and the amount of active reaction center was positively related with the aging degree, and both the correlation degree and slope of trend line increased with the increases of senescence extent of the leaves. The results suggested that chlorophyll content of flag leaf increased and the degradation rate slowed down gradually during the succession of wheat varieties. The anti-aging ability of photosynthetic electron transfered from Q to Q was improved, which contributed to the slowing down of the decline of F/F and the amount of active reaction center. The increased chlorophyll content and anti-aging ability of photosystem II also contributed to the increases of yield in the succession of winter wheat.