Effect of the grape chrome-mosaic and grape fanleaf yellow-mosaic virus-infection on the photosynthetical carbon dioxide fixation in vine-leaves

The intensity of photosynthetical C02-fixation in red Veltliner leaves, strongly or slightly infected with GCM, was compared with leaves of healthy individuals. Leaves of white Sultana, slightly infected with GFYM virus were also compared with leaves of healthy plants. The photosynthetic activity was calculated by measuring the CO2-fixation in dark and in light and the data thus obtained were compared with the content of chlorophyll. In GCM infected leaves with slight symptoms the chlorophyll level and the intensity of photosynthetical CO2 -fixation gradually decreased; in leaves with severe symptoms, the specific activity (CO2-fixation/mg chlorophyll) was relatively higher, presumably· due to the increased transparency of the tissues. After GFYM infection the photosynthetical CO2-fixation decreased strinkingly, independently of the strength of leaf symptoms. It is supposed that the destruction of the chlorophyll-protein-complexe caused by the virus infection asserts an inhibiting effect on the photosynthetic activity