EFFECTS OF LOW PH AND A1 ON ABSORPTION AND TRANSLOCATION OF SOME ESSENTIAL NUTRIENTS IN EXCISED BARLEY ROOTS

Effects of low pH (3.8) and Al (200 mu mol L(-1) soluble Al, pH 3.8) on the absorption and translocation of P, K(Rb-86), Ca, Mn, and Zn in roots excised from 5-d old barley seedlings were examined using a multi-compartment transport box and radioisotopes. Effects of pH and Al on the nutrient absorption were first examined, with emphasis placed on the accumulation, cortical efflux, redistribution and xylem exudation fractions. Radioactive tracers were applied in two different root zones, the apex (0 to 10 mm from tip) and the translocation peak zones (root zones between 13 to 50 mm from the tip, where absorbed nutrients zones are translocated more efficiently as compared to the apex) of the respective nutrients in barley roots. When a radioactive target ion was applied to a root apex, the rate of accumulation was apparently highest among all the absorbed fractions, and this phenomenon is common to all the present treatments (-Al at pH 5.5, -Al at pH 3.8, and +Al at pH 3.8) except for the case of Ca. The absorption and translocation of the nutrients in the root apex and the translocation peak zones were inhibited by a low pH, and the inhibition was severe for Zn and slight for P and K(Rb-86). The presence of Al in the ambient solution clearly inhibited the absorption and translocation of Ca and Mn in both loading zones. In contrast, Al in the low pH ambient solution enhanced P absorption, by increasing both rates of the accumulation and the translocation in the apex and the translocation peak zones. Similarly, Al stimulated the absorption and translocation of K(Rb-86) in both loading zones. Despite the differences in the magnitude of inhibition or stimulation in the accumulation, cortical efflux, redistribution and xylem exudation fractions in both loading zones, the effect of a low pH or a low level of Al on nutrient absorption appeared to be uniform throughout a certain area of young barley roots.