γ-Amino butyric acid (GABA) and proline play a crucial role in protecting plants during various environmental stresses. Their synthesis is from the common precursor glutamic acid, which is catalyzed by glutamate decarboxylase and △1-pyrroline-5-carboxylate synthetase respectively. However, the dominant pathway under water stress has not yet been established. To explore this, excised tobacco leaves were used to simulate a water-stress condition. The results showed GABA content was much higher than that of proline in leaves under water-deficit and non-water-deficit conditions. Specifically, the amount of GABA significantly increased compared to proline under continuous water loss for 16 h, indicating that GABA biosynthesis is the dominant pathway from glutamic acid metabolism under these conditions. Quantitative reverse transcription polymerase chain reaction and protein Western gel-blot analysis further confirmed this. To explore the function of GABA accumulation, a system producing superoxide anion (O 2 - ), peroxide hydrogen (H 2 O 2 ), and singlet oxygen ( 1 O 2 ) was employed to investigate the scavenging role on free-radical production. The results demonstrated that the scavenging ability of GABA for O 2 - , H 2 O 2 , and 1 O 2 was significantly higher than that of proline. This indicated that GABA acts as an effective osmolyte to reduce the production of reactive oxygen species under water stress.
为了探讨γ-氨基丁酸(GABA)对拟南芥植物开花的影响机制,以3种不同浓度(1、5,10 mmol/L)的GABA采用隔天喷施的方法,处理7天龄的拟南芥幼苗至4周龄,以双蒸水作为对照,观察拟南芥的开花时间的变化。结果表明,在长日照(16 h光照/8 h黑暗)和短日照(8 h光照/16 h黑暗)条件下,GABA能不同程度地促进拟南芥早开花2～5天。运用荧光定量PCR技术,对开花途径的开花抑制因子基因Flowering Locusc C(FLC)、自主开花途径基因FCA(FLOWERING TIME CONTROL PROTEIN FCA)和花序分生组织特征基因LEAFY(LFY)的表达进行研究。与对照相比,GABA处理下调FLC的表达2～5倍,而促进FCA(1.5～6倍)和花序分生基因LFY(3～11倍)的表达。初步的实验结果表明,GABA对拟南芥开花的促进作用有可能通过上调FCA的表达,抑制FLC从而促进LFY的表达而最终促进植物提早开花。
