The concentration of starch, soluble carbohydrates, free abscisic acid (ABA) and activities of α-amylases and invertases (the acid and the alkaline form) were investigated in buds and internodes of Vitis vinifera L. cv. Merlot during annual cycle. The levels of starch increased in the two organs from middle august to middle of November and the decreased until middle February. These variations seem to be controlled by α-amylase which activity was low during periods of starch accumulation and high when starch contents decreased. As the bud burst draws near (since the middle of February), starch accumulated in internodes and buds. However at the same time of the activity of α-amylase which activity also increased. Starch contents could be controlled by ABA which is known to reduce α-amylase activity. Indeed in internodes ABA content was high when α-amylase activity was low. This was also the case in the buds but after break dormancy phase. This difference of comportment of α-amylase towards ABA in the buds during the annual cycle could be in relation with the change of the physiological state of buds induced by the winter chilling.
The invertases activities in buds and internodes changed inversely to the sucrose and raffinose contents during all the annual cycle suggesting that the levels of these sugars were controlled by invertases, highly by the acid form and slightly by the alkaline form. Nevertheless, in the buds, when alkaline activity of invertase was high, sucrose content was maximal. These invertases seem also implicated, with α-amylase, in the development of starch content particularly when starch was accumulated by glucose providing. In the case of buds, invertases activities appeared to change in the same sense of ABA content but not during all the cycle. This suggested that this growth regulator may not be crucial for the control of invertases activities.
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