Accumulation of 4-Aminobutyrate in Trifolium subterraneum Root Nodules: Effect of Rhizobium trifolii Strain on Aminotransferase Activity

Abstract

This paper reports a study of the metabolism of 4-aminobutyrate in root nodules of T. subterraneum, as it affects the differential accumulation of this amino acid in nodules formed by two strains of R. trifolii-NA30 (accumulating) and TA1 (non-accumulating).

Examination of glutamate decarboxylase activity in extracts of TA1 and NA30 nodules indicated that both systems could form 4-aminobutyrate with equal facility. On the other hand, similar preparations of TA1 nodules could transaminate 4-aminobutyrate to succinic semialdehyde up to seven times more rapidly than preparations from NA30 nodules.

Endogenous inhibitors were found in extracts of both TA1 and NA30 nodules but they did not appear to be the reason for the large difference in aminotransferase activity which remained after most of the inhibitors had been removed by dialysis. The difference in aminotransferase activity may be due to a difference in amounts of enzymes in TA1 and NA30 nodules but further work on the reactions of purified enzymes will be required to substantiate the suggestion.