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The aim of the study was to investigate the effect of hydrogen cyanamide (HC) on dormancy release and carbohydrates metabolism in the bud and underlying internode tissues of Superior Seedless grapevines. Starch, sucrose, glucose and fructose concentrations were determined and total amylolitic, α-amylase, alkaline invertase and acid invertase activities were also characterized. HC treatment caused an abrupt increase in starch hydrolysis and a transient accumulation of soluble sugars in the bud and the internode tissues during the first five days following treatment. This coincided with a transient induction of amylolitic activity represented mainly by α-amylase (EC 3.2.1.1) implying a possible HC stimulating effect on this enzyme. These changes, which occurred shortly after HC application, seemed to be associated with a process leading to endodormancy release. In fact, as budbreak started, we observed a rapid decline in sucrose, glucose and fructose concentrations in both tissues, while, acid invertase (EC 3.2.1.26) activity remained high in treated buds but not in the internodes. Such a situation can enhance the role of the buds as strong utilizing sinks which attract sucrose from underlying tissues leading to the reactivation of cell metabolism with sucrose possibly playing the role a signal. Our data suggest that the difference in the timing of soluble sugars accumulation/consumption processes between HC-treated and control cuttings may account for the differences in the timing of growth resumption and budbreak rates. |
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