巨胚水稻W025糙米浸水后γ-氨基丁酸含量变化的研究

Accumulation of the γ-aminobutyric Acid in Brown Rice—A New Rice Strain W025 with Giant-embryo during Water Soaking

富含γ-氨基丁酸(GABA)的降血压功能水稻正受到越来越多的关注。W025是通过化学诱变和杂交选育而成的水稻新品系,具有巨胚特征,遗传分析表明巨胚基因受单隐性基因控制。进一步研究W025和其原始品种金南风浸水后γ-氨基丁酸(GABA)含量及其合成关键酶———谷氨酸脱羧酶活性的动态,并用半定量RT-PCR检测了2个谷氨酸脱羧酶转录本在浸水过程的表达变化。结果表明,(1)GABA主要集中在胚部,浸水后W025的GABA积累量显著高于金南风。(2)随着浸水时间延长,谷氨酸脱羧酶(GAD)的活性呈逐渐增加趋势,W025胚部的酶活性显著高于金南风。GAD活性的变化与GABA的积累呈显著正相关,表明浸水后种胚GABA的积累与谷氨酸脱羧酶的催化反应有关。(3)2个谷氨酸脱羧酶基因OsGAD1与OsGAD2在W025和金南风之间没有转录水平的差异。提示可能存在其他的谷氨酸脱羧酶基因对浸水后GABA的积累起关键作用。

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 and 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.