PREMISE Water-pollination (hydrophily) is a rare but important pollination mechanism that has allowed angiosperms to colonize marine and aquatic habitats. Hydrophilous plants face unique reproductive challenges, and many have evolved characteristic pollen traits and pollination strategies that may have downstream consequences for pollen performance. However, little is known about reproductive development in the life history stage between pollination and fertilization (the progamic phase) in hydrophilous plants. The purpose of this study was to characterize reproductive ecology and postpollination development in water-pollinated Ruppia maritima L. METHODS Naturally pollinated inflorescences of R. maritima were collected from the field. Experimental pollinations using both putatively outcross and self pollen were conducted in the greenhouse and inflorescences were collected at appropriate intervals after pollination. Pollen reception, pollen germination, pollen tube growth, and carpel morphology were characterized. RESULTS Ruppia maritima exhibits incomplete protogyny, allowing for delayed selfing. Pollen germinated within 15 min after pollination. The average shortest possible pollen tube pathway was 425 μm and pollen tubes first reached the ovule at 45 min after pollination. The mean adjusted pollen tube growth rate was 551 μm/h. CONCLUSIONS Ruppia pollen is adapted for rapid pollen germination, which is likely advantageous in an aquatic habitat. Small effective pollen loads suggest that pollen competition intensity is low. Selection for traits such as a long period of stigma receptivity, fast pollen germination, and carpel morphology likely played a larger role in shaping postpollination reproductive development in Ruppia than evolution in pollen tube growth rates.

中文翻译：

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亲水性单子叶植物Ruppia maritima的生殖生态和授粉后发育

前提 水花授粉（亲水性）是一种罕见但重要的授粉机制，它允许被子植物在海洋和水生栖息地定居。亲水植物面临着独特的生殖挑战，许多植物已经进化出特有的花粉性状和授粉策略，可能会对花粉性能产生下游影响。然而，对亲水植物在授粉和受精之间的生活史阶段（繁殖期）的生殖发育知之甚少。本研究的目的是表征水授粉刺槐的生殖生态学和授粉后发育。方法 从田间收集自然授粉的刺槐花序。在温室中使用推定的异交花粉和自花粉进行实验授粉，授粉后以适当的时间间隔收集花序。表征了花粉接收、花粉萌发、花粉管生长和心皮形态。结果 Ruppia maritima 表现出不完整的原型，允许延迟自交。花粉在授粉后15分钟内萌发。平均最短可能的花粉管通路为 425 μm，花粉管在授粉后 45 分钟首先到达胚珠。平均调整后的花粉管生长速率为 551 μm/h。结论 Ruppia 花粉适合快速花粉萌发，这在水生栖息地可能是有利的。小的有效花粉负荷表明花粉竞争强度低。