Saito Sayoko, Fujii Nobuharu, Miyazawa Yutaka, Yamasaki Seiji, Matsuura Seiji, Mizusawa Hidemasa, Fujita Yukio, Takahashi Hideyuki
Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
J Exp Bot. 2007;58(11):2897-907. doi: 10.1093/jxb/erm141. Epub 2007 Jul 13.
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.
乙烯在黄瓜花的性别决定中起关键作用。雌性黄瓜嫩梢产生的乙烯比雌雄同株的嫩梢多。由于雌雄同株的黄瓜在茎尖产生雄花芽和雌花芽，并且由于生长条件的不同，雄花和雌花的相对比例也会发生变化，因此就产生了一个问题，即每个花芽中乙烯生物合成的调节是否决定了花的性别。因此，研究了1-氨基环丙烷-1-羧酸合酶基因CS-ACS2在黄瓜花芽不同发育阶段的表达情况。结果表明，CS-ACS2 mRNA在两性期花芽的雌蕊原基下方开始积累，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在发育中的子房中央区域继续积累，子房和胎盘在该区域形成。在只产生雌花的雌性黄瓜植株中，在两性期和后期发育阶段的所有花芽中都检测到了CS-ACS2 mRNA的积累。在雌雄同株的黄瓜中，位于某些节上的花芽积累了CS-ACS2 mRNA，而其他节上的花芽则没有。雌雄同株黄瓜中雄花和雌花的比例因生长条件而异，但与花芽中CS-ACS2 mRNA积累的变化相关。这些结果表明，CS-ACS2介导的单个花芽中乙烯的生物合成与雌花的分化和发育有关。
