Abstract:

Hypertension is a common chronic disease and causes serious damages to human health. The rice variety rich in γ-aminobutyric acid (GABA) has a blood-pressure-lowering effect and is paid more and more attention. W025 is a new rice strain developed from chemical inducement and cross breeding. It has a giant embryo that is controlled by a single recessive gene. The content of GABA and activity of glutamate decarboxylase (GAD) in W025 and its original variety Kinmaze were investigated after the rice grain was soaked in water for 0, 1, 2, 4, 8, 16, 32 h. To measure the expression of GAD homologous genes in steeped rice grain, a Semi-quantitative RT-PCR method was developed using the housekeeping gene Actin as the control. The results indicated that GABA was accumulated mainly in the embryo, and its content in W025 was significantly higher than that in Kinmaze. Meanwhile, the activity of glutamate decarboxylase was found gradually increasing during water soaking, and the enzyme activity in embryo of W025 was markedly higher than that of Kinmaze. The content of GABA in embryo was significantly and positively correlated with the activity of glutamate decarboxylase treated with 2 mmol/L cysteine, which suggested that the accumulation of GABA was due to the enzyme action of glutamate decarboxylase. Gene expression studies indicated OsGAD1 and OsGAD2 had no difference in the transcript level between W025 and Kinmaze. It provided the possibility that there existed other uncharacterized genes of glutamate decarboxylase, which might play a dominant role to GABA accumulation during water soaking.

Key words: Rice, Giant embryo, γ-aminobutyric acid (GABA), Glutamate decarboxylase (GAD)