Photoinhibition of photosynthesis in mature and young leaves of grapevine ( Vitis vinifera L.)

Abstract

Photoinhibition of photosynthesis was studied in young (fully expanded) and mature sun leaves of grapevine ( Vitis vinifera L.), under controlled conditions (irradiation of detached leaves to about 1900 μE m −2 s −1). The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. Compared with the mature leaves, the young leaves, containing about half the amount of Chl a+b per unit area, exhibited a higher proportion of total carotenoids as xanthophyll cycle pigments and had an increased ratio of total carotenoids to Chl a+b. The potential efficiency of PS II, Fv/Fm, markedly declined in high light irradiated young leaves without significant increase of Fo level. In contrast, Fv/Fm ratio declined with significant increase of Fo level in mature leaves. When various photosynthetic activities were followed on isolated thylakoids, the rate of whole chain and PS II activity were markedly decreased in high light irradiated young leaves than mature leaves. A smaller inhibition of PS I activity was also observed in both leaves. In the subsequent dark incubation, fast recovery was observed in both leaves and reached maximum PSII efficiencies similar to those observed in non-photoinhibited leaves. The artificial exogenous electron donors DPC, NH 2OH and Mn 2+ failed to restore the high light induced loss of PS II activity in mature leaves, while DPC and NH 2OH significantly restored in young leaves. It is concluded that high light inactivates on the donor side of PS II and acceptor side of PS II in young and mature leaves, respectively. Quantification of the PS II reaction center protein D1 and 33 kDa protein of water splitting complex following high light exposure of leaves showed pronounced differences between young and mature leaves. The marked loss of PS II activity in high light irradiated leaves was due to the marked loss of D1 protein of the PS II reaction center and 33 kDa protein of the water splitting complex in mature and young leaves, respectively.