Cellular particularities of medium size shot grape berries of Vitis vinifera L. var. Merlot

Abstract

The subject of this study is the development of medium size shot berries of Vitis vinifera. At the time of vintage, their size reaches 4-7 mm. Their cell structure development is compared stage by stage with that of normal berries. On the same cluster of grape, others are very smaller (2-3 mm in diameter at stage maturity). This smaller shot berries are already be studied and aren't the subject of this paper.

The medium size shot berries have a growth delay and their histological and cellular structures are also late with regard to normal development. What is more, veraison is delayed in some berries whereas other berries stay green with their structure frozen in the growth stage.

Only coloured shot berries have caught up with the development of normal berries when they arrive at the overripeness stage of the cluster of grapes : they are small (6-7mm) but have the structure of nonnal mature berries with a typical pulp and a reduced hypodennis : the cells have lost their vacuolar tannins and more their cell walls become thinner.

However, shot benies recommence starch accumulation during berry maturation : this is an unexpected and unusual evolution, or, some recent papers associate the presence of polyamines and/or abscissic acid in berries to the regulation of α-amylase activity. If polyamines inhibit the α-amylase activity, the honnone unbalance « polyamines/ abscissic acid » can have an effect on the induction of this enzyme activity and therefore explain the abnormal presence of starch in shot berries on and after their veraison.