Amino acids in the bleeding sap of the grapevine. II

Hourly fluctuations in the amino acid composition during a 24 hours cycle

Abstract

The hourly diurnal and nightly changes in the free amino acids composition of the bleeding sap of Vitis vinifera L. cv. Vigne de Michel, were studied during one day of their bleeding period. The total soluble nitrogen content showed three maxima during the light period, viz., at 11 a.m., 5 p.m. and 7 p.m. During the night hours the nitrogen content remained rather low. Besides glutamine, glutamic and aspartic acid, which were the prominent compounds, 15 more amino acids were encountered. Two of them, lysine and arginine, appeared only during the night. Presence and absence of the different nitrogen compounds were observed throughout the samples examined. 67% of total-N appeared during the light hours, and this was mainly glutamine-N. Changes of volume in the hourly exuded sap also were recordered. The amount was higher at dawn and lower at noon and late afternoon. 40% of the total daily bleeded sap was exuded at night hours.

The possible causes uf the observed fluctuations were discussed.