Physiological Response of Field Grown Grapevine (Vitis vinifera L. cv. Marzemino) to Grapevine Leafroll-Associated Virus (GLRaV-1)

Abstract

The physiological response of field grown grapevine (Vitis vinifera L. cv. Marzemino) plants to grapevine
leafroll-associated virus (GLRaV-1) was studied. Changes in photosynthetic pigments and in photosynthetic activity
were investigated. GLRaV-1 considerably decreased the leaf net photosynthetic rate (Pn), stomatal conductance (gs)
and the transpiration rate (E) in grapevine leaves, and also strongly reduced pigments, soluble proteins, ribulose-1,5-
bisphosphate carboxylase (RuBPC) and nitrate reductase activity. In isolated thylakoids, the virus strongly inhibited
whole-chain and photosystem (PS) II activity, while PSI activity was only marginally inhibited. The artificial exogenous
electron donors diphenyl carbazide, manganese chloride (MnCl2) and hydroxylamine (NH2OH) did not restore
lost PSII activity to virus-infected leaves. Chlorophyll fluorescence suggested that the inhibition of primary light
reactions was a major effect of virus infection. Immunological studies showed that D1 protein levels of the PSII
reaction centre were significantly lower in virus-infected leaves. It is concluded that the decreases in photosynthetic
pigments and photosynthetic activities caused by the virus strongly impair photosynthesis in Marzemino grapevine
plants.