The Accumulation Of Gamma-Aminobutyric Acid In Rice Grain During Water Soaking And Its Molecular Mechanisms

The pollution of environment, unreasonable diet structure, fast life style, and the old trend of society are together result in the increase of the many illness in our country, such as so called "three high" ailments including glycemia, hypertension and high blood lipid, diabetes, renal failure, cancer, obesity, osteoporosis and imbalance growth and development. Especially hypertension is a common chronic disease and causes serious damages to human health, which has became the main cause led to the death and deformity of people. Medicine therapies are effective and widely used in controlling and curing hypertension worldwide. However, these medical treatments hold many associated problems, such as high costs and side effects, Which often brings the large mental and economic pressure to the patients. It a alternative method to research and development the active substance that can adjust human function and satisfy the need of different and special consumers, these substances comprise functional proteins, i.e. low glutelin protein, 14-16KD allergy -resistant protein, soybean globulin, active amylase such as resistant starch, functional rice oil that including unsaturated lipid acid, functional vitamin such as beta- carotene, micronutrient e.g. iron, zinc and selenium, flavone compound, functional peptides, and amino acid such as lysine and tryptophan. It is a economic and effective strategy, since these products can achieve the result of "food and drug serve the same effect". At the same time, the discover and utilization of functional component in crop are promising to play a important role in enhancing the human enginery and metabolism balance. Furthermore, the health-promoting crop can increase the market value, and enlarge the utilized range. Even it can be used as a new kind of health care product and important raw materials in food process industry. Rice is one of the most important crop, and about half of the population in the world is depend on this crop as primary food. It has reported that GABA has a function to reduce blood pressure in experimental animals and human without obvious negative effect. Therefore it may be expected as the attractivecandidate of function food for hypertension patient.Glutamate decarboxylase (GAD, EC 4.1.1.15), which catalyzes the irreversible decarboxylation of glutamate in the presence of the cofactor pyridoxal 5'-phosphate (PLP), is believed to be the key enzyme in GABA synthesis. W025 is a new rice strain derived from chemical inducement and cross breeding method. It is characteristic for its giant embryo. Moreover, the content of gamma-aminobutyric acid and activity of glutamate decarboxylase in rice W025 and its original variety Kinmaze during water soaking were investigated. Semi-quantitative RT-PCR was carried out to detect the gene expression of glutamate decarboxylase. The results indicated that the contents of the gamma-aminobutyric acid in W025 were significantly higher than that of Kinmaze, and the embryo of W025 showed maximal accumulation. 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 studies further demonstrated that the content of gamma-aminobutyric acid in embryo was significantly positive correlated with the activity of glutamate decarboxylase treated with 2mmol/L cysteine, which suggested that the accumulation of GABA was due to the enzyme action of glutamate decarboxylase. Gene expression studies indicated OsGADl and 0sGAD2 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.A novel full-length cDNA, designated OsGAD3, has been isolated by the combination of bioinformatics and PCR based approaches. A homology tree of GADs from various plant species revealed OsGAD3 had a closer evolutionary relationship with dicocotyledonous plant...