ORGANIC ACID SYNTHESIS IN RESPONSE TO EXCESS CATION ABSORPTION IN VACUOLATE AND NON-VACUOLATE SECTIONS OF CORN AND BARLEY ROOTS

Abstract

14CO2 fixation into organic acids in tips and proximal sections of both corn and barley roots was studied as a function of the nature and concentration of the salt in the external solution. In comparison with the level of 14CO2 fixation by vacuolate proximal sections in KCI, incorporation was markedly enhanced in K2SO4 and diminished in CaCk. By contrast, non-vacuolate root tips were indifferent to the type of external salt with respect to UCO2 incorporation into organic acids. The effect of salt type on organic acid formation from 14CO2 was most pronounced at relatively high concentrations. The conclusion was reached that organic acid synthesis in responseto excess cation uptake is the result of cation movement into the vacuole, and that transport into the vacuole is mediated by the low-affinity component of the dual mechanisms involved in ion absorption.