Response of grapevines to subzero temperatures: Effect of controlled cooling on sugar reserves of the leaf bud complex preceding and during budding

Sugar concentrations were analyzed in grapevine (Vitis vinifera) buds at three different phenological stages (stage 1, dormant bud; stage 2, woolly bud; stage 5, green tip) and were submitted, under controlled conditions, to negative temperatures corresponding to the intracellular liquid crystallization points. In absence of any treatment, starch concentration diminished according to the phenological evolution, indicating its utilization during bud breaking. Starch and raffinose accumulated when controlled cooling was applied, except for stage 1 buds collected on March 6, 1993. Similarly, saccharose concentrations were reduced in bud complexes after temperature reductions. Fructose and glucose concentrations seemed to be less sensitive to thermal variations. The accumulation of starch observed at the end of a cold treatment could be partly explained by the inhibition of amylase activity under cold conditions.