Abstract
The effects of viral diseases on the photosynthetic activity of grapevine ( Vitis rupestris var. Rupes- tris du Lot) leaves were investigated. The third and sixth leaves used for measurements were obtained from in vitro grown healthy plants and cultured plants affected by grapevine fanleaf and rupestris stem pitting viruses. The induction curves of prompt and delayed chlorophyll fluorescence, as well as the temperature characteristics of steady-state prompt and delayed emission, were investigated. Age-dependent changes were found, which were related, on the one hand, to the acceleration of electron transport and the enhancement of thylakoid ener- gization and, on the other hand, to a smaller extent of transmembrane Δμ H + in the younger sixth leaf as com- pared to that in the third leaf. The infected plants characteristically showed faster electron transport, an elevated energetic efficiency of photosynthesis, and the suppression of CO 2 fixation owing to a presumable activation of the adenylate metabolism. An analysis of the thermograms of prompt and delayed fluorescence revealed the shifts in the position of the M 1 peak and a half-inhibition temperature T 50 towards a higher temperature in infected plants, which indicates a certain increase in the thermal tolerance of thylakoid membranes. The data suggest that the viral metabolism affects the functional activity and stability of thylakoid membranes.
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