外源ABA对木薯叶片内源激素及淀粉合成相关基因的影响

在盆栽条件下,用外源脱落酸(Abscisic acid,ABA)处理块根形成期的木薯品种,测定处理及对照在不同时刻叶片中ABA等激素变化、ABA合成与失活以及淀粉合成途径关键基因的表达变化。结果表明:1)正常条件下木薯叶片内源ABA水平及ABA合成途径基因均存在明显的夜间低而白天较高的昼夜节律,ABA信号转导相关基因也表现出下午的高峰表达,它们与淀粉合成途径基因的夜间表达一般具有相反的趋势。2)ABA处理后,木薯叶片内源ABA含量迅速下降,与观察到的ABA合成途径基因表达下降与后期ABA失活基因激活表达相一致,同时发现细胞分裂素中的玉米素核苷(Zeatin riboside,ZR)和生长素(Indole acetic acid,IAA)水平发生改变,预示木薯具有迅速恢复ABA平衡态的机制,并且与其他类激素存在协同作用。3)与此同时,外源ABA处理明显抑制淀粉合成上游基因表达,特别是夜晚高峰期的表达,而对下游基因的抑制相对较小。说明这些基因及相关酶类不同程度受到ABA的调控;ABA明显倾向于调控淀粉合成上游相关基因;外源ABA处理改变了叶片临时淀粉合成速率。

Change of endogenous hormones and expression levels of genes for ABA synthesis,signaling and starch synthesis in leaves of cassava under exogenous ABA treatment

In the study,exogenous abscisic acid(ABA) agent was used for treatment of young plants of SC124 and Arg7 at 60 growth days under pot cultivated condition.Then the contents of the endogenous hormones included ABA and change of expression level of genes for ABA biosynthesis,deactivation and signaling,starch synthesis were detected indifferent time points compared to non-treatment.It was shown that:1)In the normal condition(non-treatment),the endogenous ABA level in leaves of cassava was higher in day and lower at night,this result coincided with expression level of genes for ABA biosynthesis in the day and night.The expression of genes for ABA signal transduction as MePYL and MeABF also was higher in PM than in the night,this had reversed trend with higher expression of genes for starch synthesis in leaves.2) Under treatment condition,the endogenous ABA content fast decreased.Similarly,expression of all genes for ABA synthesis were depressed,too,except that the MeUGT gene for ABA deactivation was activated.Meantime,we found zeatin riboside (ZR),indole acetic acid(IAA) contents were changed that maybe had interaction with ABA.It seemed that there was a kind of balance mechanism to keep ABA in a modest level for its biological functions in cassava.However,it was clear that ABA treatment significantly affected expression of genes for starch synthesis in leaves of cassava,especially the genes in upstream of the pathway such as MeCWI,MeAGPase and MePGI particularly in the night,the higher expression period.3) At last,the starch accumulated genes were all inhibited by the exogenous ABA.With these results,we could draw a conclusion that under there was a threshold value,the of cassava''s endogenous ABA hormone,activated the starch synthesis.When the endogenous ABA content in leaves of the cassava exceeded the threshold value,it''s starch accumulation might be inhibited.