DIFFERENCES IN CARBOXYLIC-ACID EXUDATION AMONG P-STARVED LEGUMINOUS CROPS IN RELATION TO CARBOXYLIC-ACID CONTENTS IN PLANT-TISSUES AND PHOSPHOLIPID LEVEL IN ROOTS

The amount or composition of carboxylic acids in the root exudates and tissue extracts of leguminous crop plants subjected to P starvation for 3 d in water culture were compared. Also, the changes in the distribution and P content of the P fractions of the roots of the plants subjected to P starvation for 3 d were compared. In the root exudates collected over a 12 h period, malonic, succinic, fumaric, malic, citric, and t-aconitic acids were detected. A large amount of these carboxylic acids, especially citric and malic acids, was exuded from the roots of chickpea as compared with those of soybean, kidney bean, cowpea, and pigeonpea. Groundnut roots exuded an appreciable amount of carboxylic acids, especially fumaric acid. Although the contents of these carboxylic acids in the extracts of leaves and roots of chickpea were the highest as compared with soybean, kidney bean, and cowpea, the differences were much less significant than those in the root exudates. The amount and composition of carboxylic acids exuded from chickpea roots seemed to be correlated with those of the leaves rather than those of the roots. The large amount of carboxylic acids observed in the exudates of chickpea roots could not be directly correlated to the content of phospholipid-P in the roots.