IN-SITU [C-14] GLUTAMATE METABOLISM BY DEVELOPING SOYBEAN COTYLEDONS .1. METABOLIC ROUTES

Glutamate metabolism was investigated in developing cotyledons of soyb ean (Glycine max (L.) Merrill). Intact excised cotyledons were injecte d with carrier-free C-14-glutamate and incubated, in the dark, in seal ed vials containing a CO2 trap. Detection of C-14-radioactivity as rel eased CO2, and ethanol-soluble and -insoluble fractions during 40-minu te and 6-hour time courses, indicates that exogenously supplied glutam ate was metabolized via CO2, 2-oxoglutarate, 4-aminobutyrate and Krebs -cycle intermediates. C-14-Labeled 4-aminobutyrate was recovered from the metabolism of [U-C-14]glutamate, but not [1-C-14]glutamate, demons trating its production by decarboxylation of the carbon one of glutama te. The rapid metabolism of [C-14]4-aminobutyrate and the recovery of C-14-radioactivity in protein-aspartate suggest that glutamate decarbo xylation is not a response to stress, but could contribute Krebs-cycle -derived amino acids for protein synthesis in co-operation with glutam ate deamination and transamination. Recovery of C-14 as protein-argini ne and -glutamate suggests that glutamate was also incorporated into a rginine and protein, possibly without degradation. Multiple cellular a mino acid pools were suggested from the rate of glutamate incorporatio n and the significant, but incomplete utilization of the soluble fract ion.