Accumulation of {gamma}-aminobutyric acid due to adding ammonium or glutamine to cultured rice cells

-Aminobutyric acid (GABA) was accumulated in rice cell cultureswhen ammonium was added to the medium. After the addition ofammonium, a temporary increase in the glutamine (Gln) pool wasobserved before the accumulation of GABA. GABA also was markedlyaccumulated when Gln was added to the medium in place of ammonium.When glutamic acid (Glu) was added without ammonium, no accumulationof GABA occurred. When L-methionine-DL-sulfoximine (MSO), an inhibitor of glutaminesynthetase, was added to the nitrate medium, the ammonium poolincreased with no accumulation of Gln and GABA. Even when ammoniumwas supplied to the medium, no GABA accumulated in the presenceof MSO. When azaserine (AZ), which inhibits the transamidationof Gln, was added with Gln, no GABA was accumulated, althoughthe Gln pool in the cell cultures increased significantly. The accumulation of GABA in cultured rice cells produced byammonium as the nitrogen source probably is related directlyto the Gln pool size, which is increased when ammonium is suppliedto the medium. (Received August 6, 1979; )