Flavonoids play important roles in regulating plant growth and development. In this study, three kaempferol 3-O-glycosides were identified and mainly accumulated in flowers but not in leaves or fruits of Malus. In Malus, flower petal color is normally white, but some genotypes have red flowers containing anthocyanin. Anthocyanin biosynthesis appears to be in competition with kaempferol 3-O-glycosides production and controlled by the biosynthetic genes. The white flower Malus genotypes had better-developed seeds than the red flower genotypes. In flowers, the overexpression of MYB10 in Malus domestica enhanced the accumulation of anthocyanin, but decreased that of kaempferol 3-O-glycosides. After pollination the transgenic plants showed slower pollen tube growth and fewer developed seeds. Exogenous application of different flavonoid compounds suggested that kaempferol 3-O-glycosides, especially kaempferol 3-O-rhamnoside, regulated pollen tube growth and seed set rather than cyanidin or quercetin 3-O-glycosides. It was found that kaempferol 3-O-rhamnoside might regulate pollen tube growth through effects on auxin, the Rho of plants (ROP) GTPases, calcium and the phosphoinositides signaling pathway. With the inhibition of auxin transport, the transcription levels of Heat Shock Proteins (HSPs) and ROP GTPases were downregulated while the levels were not changed or even enhanced when blocking calcium signaling, suggesting that HSPs and ROP GTPases were downstream of auxin signaling, but upstream of calcium signaling. In summary, kaempferol glycoside concentrations in pistils correlated with auxin transport, the transcription of HSPs and ROP GTPases, and calcium signaling in pollen tubes, culminating in changes to pollen tube growth and seed set.

中文翻译：

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花青素与山柰酚苷生物合成的竞争影响苹果花粉管的生长和结实

黄酮类化合物在调节植物生长发育中发挥重要作用。在这项研究中，三种山柰酚 3-○-糖苷类已被鉴定并主要在花中积累，但在叶或果实中不积累海棠. 在海棠，花瓣颜色通常为白色，但有些基因型的花朵呈红色，含有花青素。花青素生物合成似乎与山柰酚 3- 竞争○-糖苷的产生和由生物合成基因控制。那朵白花海棠基因型比红花基因型具有更好的种子发育。在花丛中，过度表达MYB10在海棠增强花青素的积累，但减少山柰酚 3-的积累○-糖苷。授粉后转基因植物表现出较慢的花粉管生长和较少发育的种子。不同黄酮类化合物的外源应用表明山柰酚 3-○-苷类，尤其是山奈酚 3-○-鼠李糖苷，调节花粉管生长和结实，而不是花青素或槲皮素 3-○-糖苷。发现山柰酚 3-○-鼠李糖苷可能通过对生长素、植物 Rho (ROP) GTP酶、钙和磷酸肌醇信号通路的影响来调节花粉管的生长。随着生长素转运的抑制，热休克蛋白（HSPs）和ROP GTP酶的转录水平下调，而在阻断钙信号时水平没有改变甚至增强，表明HSP和ROP GTP酶位于生长素信号的下游，但在上游钙信号。总之，雌蕊中的山柰酚糖苷浓度与生长素转运、HSP 和 ROP GTPase 的转录以及花粉管中的钙信号传导相关，最终导致花粉管生长和种子结实的变化。