ブドウ‘デラウェア’果実の成熟生理に関する研究

Abstract

The grape berries accumulate sugar very rapidly around 4 weeks before ripening. In order to clarify the mechanism of this sugar accumulation in Delaware grape berries during Stage III, changes in sugar and organic acid content in the growing berries, effects of the number of leaves retained on and time of complete removal of leaves from a bearing shoot on sugar content in the berries, changes in sugar content in the berries detached from the shoot at Stage III, and the conversion of polysaccharides or organic acids into reducing sugars in the berries were investigated.(1) The major sugars in the grape berries were glucose and fructose. These sugars contained totally about 2% in the fresh immature berries, wheras they were about 17% in the mature berries. The ratio of glucose to fructose in the berries changed during the period from bloom to maturity. Glucose in the berries was more predominantly accumulated than fructose during the green color and the early ripening stage of their growth. This relation was reversed at the later ripening stages.(2) As in most fruits, malic acid is present in grape berries. In contrast to them, however, a large amount of tartaric acid contains in the berries, which is the characteristic of this genus. The concentrations of malic acid and tartaric acid in the berries were highest in the beginning of Stage III and the amount of both acids in the berries decreased markedly during the ripening stage, but another peak of tartaric acid concentration was found in the beginning of Stage I.(3) There were no differences in sugar content of the berries on the shoot with 8 leaves or more, as compared to that of the berries on the control shoot, but the berries on the shoot less than 8 leaves had less sugar content. Even the berries on the shoot completely defoliated still accumulated about 6% of reducing sugars.(4) During Stage III, the accumulation of reducing sugars in the berries was found even after complete removal of leaves from the shoot together with girdling at both sides of the node where the cluster was attached.(5) When the enzymes extracted from the berries during Stage III were added into the insoluble substrate prepared from the berries during Stage I, reducing sugar content in the incubation buffer solution increased.(6) When 14C-malic acid was fed into the berries of Stage III through the pedicel for 2 hours in a liquid form, 31% of incorporated 14C was found in the sugar fraction.From these results, it was cleared that the translocation of photosynthates synthesized in the leaves into the berries was most important for the rapid sugar accumulation in grape berries, and also, the translocation of sugars converted from polysaccharides in shoots into the berries and the conversion of polysaccharides and organic acids in the berries themselves into reducing sugars were found to be related to the accumulation as well.