Phytoplasma [Stolbur-subgroup (Bois Noir-BN)] infection inhibits photosynthetic pigments, ribulose-1,5-bisphosphate carboxylase and photosynthetic activities in field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves

In this work we have studied the influence of phytoplasma-induced grapevine yellows (yellowing) on some features of the thylakoids from field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose-1,5-bisphosphate carboxylase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll and carotenoids, on a unit fresh weight basis, showed a progressive decrease in phytoplasma infected leaves. Similar results were also observed for total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused marked inhibition of whole chain and photosystem (PS) II activity. Smaller inhibition of PSI activity was observed even in severely infected leaves. The artificial exogenous electron donors, DPC and NH2OH significantly restored the PSII activity in both mild and severely infected leaves. The same results were obtained when F-v/F-m was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in infected leaves was evidently due to the loss of 33, 28-25, 23, 17 and 10 kDa polypeptides. This conclusion was confirmed by immunological studies showing that the content of the 33 kDa protein of the water-splitting complex was diminished significantly in infected leaves. Phytoplasma infection induced a fast degradation of LHCP II which became visible as yellowish colour in leaves. (C) 2003 Elsevier Science Ltd. All rights reserved.