BORON UPTAKE BY PEACH LEAF SLICES

The objective of this study was to determine if plasmalemma transport is a limiting step for boron (B) uptake by peach leaf. Only about 0.3% of the B applied could be absorbed by peach (Prunus persica L. Batsch) leaves when enriched B-10-boric acid was used as a tracer. Boron uptake increased proportionally to the external B concentration in the range of 1 mM to 20 mM. The highest B content was found in the 20 mM treatment. Boron uptake was rapid for the initial 6 to 8 hours, but it then slowed down steadily until the end of the experiment. A linear correlation between the external B concentration and leaf B content was obtained (y = -8.98 + 46.1x, R2 = 0.999). pH had a profound effect on B uptake by peach leaf slices with pH 7 and 8 had the highest B absorption. Boron uptake was strongly dependent on temperature over the 2-degrees-C to 40-degrees-C range. Peach leaf slices had the highest B absorption at 40-degrees-C. B uptake decreased sharply when the temperature dropped to 2-degrees-C. Adenosine Triphosphate (ATP) increased B uptake significantly in the range from 1 to 2 mM. ATP concentrations higher or lower than this range did not affect B uptake. Diethylstilbestrol (DES) and 2,6 - Diiodo - 4- nitrophenol (DNP) both inhibited B uptake with DNP the more effective inhibitor than DES. It is suggested that plasmalemma transport is not the rate limiting step in B absorption by peach leaves. Boron uptake by peach leaf slices involves both an active and a passive process with the active uptake as a major component.