Effects of grapevine fanleaf and stem pitting viruses on the photosynthetic activity of grapevine plants grown in vitro

The effects of viral diseases on the photosynthetic activity of grapevine ( Vitis rupestris var. Rupestris du Lot) leaves were investigated. The third and sixth leaves used for measurements were obtained from in vitro grown he althy plants and plants affected by grapevine fanleaf and rupestris stem pi tting viruses. The induction curves of prompt and delayed chlorophyll fluor escence, as well as the temperature characteristics of steady-state, prompt , and delayed emissions, were investigated. Age-dependent changes were foun d, which were related, on the one hand, to the acceleration of electron tra nsport and the enhancement of thylakoid energization and, on the other hand , to a smaller extent of transmembrane Delta muH(+) in the younger sixth le af compared to that in the third leaf. The infected plants characteristical ly showed faster electron transport, an elevated energetic efficiency of ph otosynthesis, and the suppression Of CO2 fixation owing to a presumable act ivation of the adenylate metabolism. An analysis of the thermograms of prom pt 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 toleran ce of thylakoid membranes. The data suggest that the viral metabolism affec ts the functional activity and stability of thylakoid membranes.