铝离子胁迫下大豆根尖柠檬酸的分泌及SGA1基因的表达

Secretion of Citrate from Root Apices and Expression of SGA1 in Soybean under Al Cl_3 Stress

为揭示铝离子诱导大豆根尖分泌有机酸的特点及介导有机酸分泌的信号途径，采用溶液培养试验方法调查A1C13对大豆品种（广州本地2号）根尖有机酸分泌及SGAl基因表达的影响。结果表明，A1C13胁迫下大豆活体根尖分泌柠檬酸，且分泌量随着铝浓度（25、50μmolL^-1A1C13）和处理时间（2～12h）的增加而增加；大豆根尖以模式11分泌柠檬酸，处理后的前4h，分泌速率很低，其后显著提升；有机酸明显分泌的诱导期长达6h；在50μmolLA1C1，的溶液中添加异三聚体G蛋白抑制剂百日咳毒素（200ngmL^-1），柠檬酸分泌减少38．7％。RT-PCR分析结果显示，A1C13溶液诱导大豆根尖SGAl基因的表达，其表达水平随着铝处理时间（O．5～12．0h）的延长有提升的趋势，而诱导的SGAl基因表达明显早于有机酸开始分泌时间（6h）。这些结果表明，铝离子诱导大豆根尖分泌柠檬酸及SGAl基因的表达，异三聚体G蛋白可能作为铝胁迫信号开关器参与有机酸分泌的调控。

The effects of A1^3＋ on the secretion of organic acids from root apices and the expression of SGAI gene were investigated by hydroponics to elucidate the characteritics of organic acid secretion and A1^3＋ stress signal transduction pathway which mediates the secretion of organic acids in soybean Guangzhou bendi 2. The results showed that soybean root apices （in vivo） secreted citrate under A13＋ stress. The secretion of citrate increased with the increase of A1^3＋ concentrations （25, 50 μmol L-1 A1C13） and the prolongation （2-12 hours） of treatment with A1^3＋. Citrate was secreted from root apices by pattern II in soybean. The secretion rate was very low within initial four hours after Al^3＋ treatment but remarkably elevated thereafter. A gap of time between the secretion and Al^3＋ treatment reached to about six hours. On the other hand, when cholera toxin, an inhibitor of heterotrimeric G-protein, was added to A1^3＋solution, the amount of citrate secreted decreased by 38.7%. RT-PCR analysis results indicated that A1^3＋ induced SGA1 expression. In general, the expression level was elevated with the prolongation of treatment with A1^3＋ （0.5 to 12 hours）. Moreover, A1^3＋ induced expression of SGA1 sooner than the secretion of citrate. These results imply that A1^3＋ induces the secretion of citrate from root apices and SGA1 expression in the soybean, and heterotrimeric G proteins may act as a switch of A1^3＋ stress signal to be involved in the regulation of citrate secretion from root apices under A1^3＋ stress.