Effect of grapevine latent buds (<em>Vitis vinifera</em> L., cv. Merlot) chilling on their starch content: biochimical and cytological approachs

Biochimical analysis and photonic microscopy observations of starch were investigated in latent buds of Vitis vinifera L. (cv. Merlot) collected during their dormancy phase and during their cold storage at 2°C. Biochimical analysis showed that starch levels of grapevine latent buds was high (70 mg/g DW). Microscopical observations confirmed this result and showed a gradient of starch content in different regions of bud in which the foliars primordiums and scales were the starch richer. Buds conservation at 2°C reduced their starch content but this decrease begun only after 9 days of chilling corresponding to the time necessary for budbreak and for the beginning of increase the bud burst ability. The hydrolysis of starch seems begun at the first in apex and then propaged to the other regions of bud. In the scales, the most exposed region to cold, storage at 2°C during 56 days induced an increase of cellular tannins content and cell walls polysaccharides. These results were discuted in relation to the increase of bud burst ability and to their cold acclimatation