Renewal of vascular connections between grapevine buds and canes during bud break

Abstract

Abstract With the seasonal change from winter to spring, grapevine compound buds break dormancy and start a new annual developmental cycle. The rebuilding of vascular connections between buds and canes is vital to ensure normal development of the bud. We monitored the dynamic development of grapevine buds under natural field conditions, observed vascular connections using light microscopy, and investigated the uptake and transport of water in buds and canes from dormancy to bud break. During dormancy, the bud was isolated from the cane and no xylem was observed in the bud or the junction region between the bud and the cane. However, at the stage of bud swelling (stage II), xylem was observed at the cane to bud junction. The rate of water uptake through the xylem at the junction increased as bud development progressed. These results suggest that buds were hydraulically isolated from the cane during dormancy and the formation of xylem between bud and cane started with swelling of the bud. The velocity of water transport into the bud also increased with bud development. We discuss several factors that affect the formation and differentiation of xylem, including temperature, hormones and water. It is likely that the rebuilding of vascular connections between buds and canes is related to multiple factors rather than any one individual factor.