Photosynthesis of the grapevine (Vitis vinifera) inflorescence.

To further characterize carbohydrate physiology in grapevine flowers, we examined inflorescence autotrophy in the 'Gewurztraminer' and 'Pinot noir' cultivars, which differ in sensitivity to flower abscission. In both cultivars, positive net photosynthesis occurred in inflorescences. The rate of photosynthesis gradually decreased throughout flower development and there was no net carbon assimilation at fruit set. The rate of photosynthesis was positively correlated with chlorophyll concentration but not to stomatal conductance. Throughout flower development, the internal CO2 concentration increased in inflorescence tissues, suggesting that assimilates are also formed through refixation of respiratory CO2 by the phosphoenolpyruvate carboxylase (PEPC) pathway. Significant differences between the two cultivars were recorded during meiosis, when photosynthesis was higher in 'Gewurztraminer'. We conclude that the inflorescence of grapevine contributes to its own carbon nutrition by photosynthesizing throughout flower development. Moreover, the differential patterns of photosynthesis in the inflorescences of 'Gewurztraminer' and 'Pinot noir' might account for their differing fertilization rates and sensitivity to flower abscission.