A DAILY RHYTHMIC MODEL FOR PH AND VOLUME FROM XYLEM SAP OF TOMATO PLANTS

Ten-day-old tomato plants (Lycopersicon esculentum Mill. cv. Rambo) we re transplanted in a NFT special system. The experiment was repeated t hree consecutive times. Each experiment consists of three replicates. The experiments were carried out first with 30-day-old plants and subs equently with plants which were 45-days-old. The sap flux rates (V) va ry 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 behavio r 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 framewo rk 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 normall y buffered, but may have the possibility to influence processes locali zed within the shoot.