Ethylene plays a key role in sex determination of cucumber flowers. Gynoecious cucumber shoots produce more ethylene than monoecious shoots. Because monoecious cucumbers produce both male and female flower buds in the shoot apex and because the relative proportions of male and female flowers vary due to growing conditions, the question arises as to whether the regulation of ethylene biosynthesis in each flower bud determines the sex of the flower. Therefore, the expression of a 1-aminocyclopropane-1-carboxylic acid synthase gene, CS-ACS2, was examined in cucumber flower buds at different stages of development. The results revealed that CS-ACS2 mRNA began to accumulate just beneath the pistil primordia of flower buds at the bisexual stage, but was not detected prior to the formation of the pistil primordia. In buds determined to develop as female flowers, CS-ACS2 mRNA continued to accumulate in the central region of the developing ovary where ovules and placenta form. In gynoecious cucumber plants that produce only female flowers, accumulation of CS-ACS2 mRNA was detected in all flower buds at the bisexual stage and at later developmental stages. In monoecious cucumber, flower buds situated on some nodes accumulated CS-ACS2 mRNA, but others did not. The proportion of male and female flowers in monoecious cucumbers varied depending on the growth conditions, but was correlated with changes in accumulation of CS-ACS2 mRNA in flower buds. These results demonstrate that CS-ACS2-mediated biosynthesis of ethylene in individual flower buds is associated with the differentiation and development of female flowers.

译文

乙烯在黄瓜花的性别决定中起着关键作用。雌雄同株的黄瓜芽比雌雄同株的芽产生更多的乙烯。由于雌雄同株黄瓜在茎尖上同时产生雄花和雌花芽,并且由于生长条件的不同,雄花和雌花的相对比例也不同,因此出现了每个花芽中乙烯生物合成的调节是否决定了花的性别的问题。因此,在不同发育阶段的黄瓜花蕾中检查了1-氨基环丙烷-1-羧酸合酶基因CS-ACS2的表达。结果表明,CS-ACS2 mRNA在两性阶段开始在花蕾的雌蕊原基下方积累,但在雌蕊原基形成之前未检测到。在确定发育为雌花的芽中,CS-ACS2 mRNA继续在胚珠和胎盘形成的发育中的卵巢中央区域积累。在仅产生雌花的雌雄性黄瓜植物中,在两性阶段和后期发育阶段的所有花蕾中都检测到CS-ACS2 mRNA的积累。在雌雄同株黄瓜中,位于某些节点上的花蕾CS-ACS2 mRNA积累,而其他节点则没有。雌雄同株黄瓜中雄花和雌花的比例因生长条件而异,但与花蕾中CS-ACS2 mRNA积累的变化有关。这些结果表明,单个花蕾中乙烯的CS-ACS2-mediated生物合成与雌花的分化和发育有关。

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