Defoliation, photosynthetic rates, and assimilate transport in grapevine plants

The source-sink relations in grapevine (Vitis vinifera L., var. Rkatsiteli) plants were disturbed by defoliation at different stages of vegetative growth in order to investigate changes in photosynthetic activity and assimilate partitioning. Defoliation was shown to stimulate photosynthesis in the remaining source leaves, enhance the assimilate export, and diminish the midday suppression of photosynthesis. Defoliation created a powerful sink for assimilates, and stimulated their delivery to the affected zone. It is hypothesized that defoliation-induced stress is accompanied by a substantial enhancement of photosynthetic activity and by redistribution of assimilate flows, which enables a sustained supply of assimilates to the sink organs of grapevine plants.