黄瓜子叶源生长素对下胚轴不定根发生的调控作用

Regulatory Roles of Cotyledon-generated Auxin in Adventitious Root Formation on the Hypocotyls of Cucumber Seedlings

为了明确黄瓜(Cucumis sativus L.)子叶和顶芽在幼苗下胚轴不定根发生中的作用,采用琼脂培养基扦插的方法,研究了子叶和顶芽的去留对下胚轴基部内源IAA和GA3积累水平及不定根发生的影响。结果表明,子叶对下胚轴不定根的发生非常关键。保留双子叶的幼苗下胚轴基部IAA含量呈先升高后降低的趋势,GA3呈先降低后升高的趋势,不定根正常发生;去除单片子叶,下胚轴基部IAA和GA3积累显著减少,不定根发生相关基因及IAA、GA3响应基因(Cs ARL1、Cs GH3.5、Cs GASA4等)表达水平降低,不定根发生区缩小、数量减少;去除双子叶,下胚轴基部IAA和GA3无法积累,不定根不发生。顶芽去留对下胚轴不定根发生没有显著影响。外源施用IAA可以部分缓解因去除单片子叶对不定根发生的抑制作用,喷施IAA极性运输抑制剂,下胚轴不定根发生受到抑制;与IAA不同,外源施用GA3抑制下胚轴不定根发生,喷施GA合成抑制剂促进不定根发生,GA对IAA响应基因具有负调控作用,表明子叶合成的IAA是诱导下胚轴不定根发生的关键。去除双子叶时,无论单独或交互施用IAA与GA3,均不能诱导下胚轴形成不定根,表明IAA并非不定根发生的唯一诱因。进一步分析发现去除子叶后下胚轴基部可溶性蛋白质和可溶性糖含量显著降低,可能是影响不定根发生的其他因素。子叶作为黄瓜幼苗生长素、蛋白质和糖的主要合成和输出源,对黄瓜幼苗下胚轴不定根发生起关键作用。

In this study,the roles of cotyledons and apical bud in adventitious root formation on hypocotyls of cucumber seedlings were analyzed. The results suggested that cotyledon is required for adventitious root formation. In the seedlings with two cotyledons,the adventitious root could form normally. During adventitious root formation,the content of endogenous IAA increased firstly and then decreased,while the content of GA3 showed an opposite changing pattern. Removing one of the cotyledons resulted in significantly lower levels of IAA and GA3,reduced expression of IAA- and GA-responsive genes（eg. CsARL1,CsGH3.5,CsGASA4,etc.）,and therefore led to shorter root zone and less root numbers on cucumber hypocotyls. Complete removal of two cotyledons diminished the accumulation of endogenous IAA and GA3 in hypocotyls and reasonably diminished adventitious root formation entirely. Removal of apical bud had no significant effect on adventitious root formation. The inhibitory effects on adventitious root formation caused by removal of one cotyledon could be partially reversed by application of exogenous IAA. On the other hand,foliar spraying with IAA-transport inhibitor caused an inhibitory effect on adventitious root formation. Different from IAA,application GA3 to the hypocotyls inhibited the adventitious root formation,while foliar spraying of GA biosynthesis inhibitor increased root formation. GA exerted an inhibition on the IAA-responsive genes during adventitious root formation. These results suggested that the cotyledon-generated IAA was essential for adventitious root formation in cucumber hypocotyls. Furthermore, application of IAA and GA3 individually or simultaneously could not induce adventitious root formation in the hypocotyls without cotyledons attached,suggesting that IAA was not the only necessary factor. Removal of cotyledons led to a substantial decrease in the contents of soluble proteins and soluble sugars in the basal hypocotyls,and this might be another reason for the diminished adventitious root formation. Taken together,these results suggested that cotyledons,as the major resource of auxin,proteins and sugars,were necessary for adventitious root formation in cucumber hypocotyls.