Abstract

Ten-day-old tomato plants (Lycopersicon esculentum Mill. cv. Rambo) were transplanted in a NFT special system. The experiment was repeated three consecutive times. Each experiment consists of three replicates. The experiments were carried out first with 30-day-old plants and subsequently with plants which were 45-days-old. The sap flux rates (V) vary considerably during the day at both harvest dates and there was has highly significant correlation (p>0.999) with the chronophysiological rhythm (Halberg, 1969) which has the highest rates in the day and the lowest rates at night. The pH rhythm, which shows an opposite behavior of the sap flux rate, is related to organic anion equivalents (C-A). A markedly difference in the behavior of C-A values occurred at both harvest dates. The model presented in this paper may provide a framework for the explanation of short and long term V and pH fluctuation of xylem sap. The changes in the pH of the xylem sap are probably normally buffered, but may have the possibility to influence processes localized within the shoot.