Department of Biology, Creighton University, Omaha, Nebraska, 68178, USA.
Am J Bot. 2020 Apr;107(4):689-699. doi: 10.1002/ajb2.1447. Epub 2020 Mar 13.
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.
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.
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.
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.
水授粉（亲水）是一种罕见但重要的授粉机制，它使被子植物能够在海洋和水生栖息地中殖民。亲水植物面临着独特的繁殖挑战，许多亲水植物已经进化出了特征性的花粉特征和授粉策略，这些特征和策略可能会对花粉性能产生下游影响。然而，关于亲水植物授粉和受精（配子体阶段）之间的生殖发育过程知之甚少。本研究的目的是描述水授粉植物鲁宾逊海蓬子的生殖生态学和授粉后发育。
从野外采集自然授粉的鲁宾逊海蓬子花序。在温室中进行了使用假定异交和自交花粉的实验授粉，并在授粉后适当的时间间隔采集花序。描述了花粉接收、花粉萌发、花粉管生长和心皮形态。
鲁宾逊海蓬子表现出不完全的雌雄同熟，允许延迟自交。花粉在授粉后 15 分钟内萌发。最短可能的花粉管路径的平均值为 425μm，花粉管在授粉后 45 分钟到达胚珠。平均调整后的花粉管生长速率为 551μm/h。
鲁宾逊海蓬子的花粉适应于快速花粉萌发，这在水生环境中可能是有利的。有效的花粉负荷较小，表明花粉竞争强度较低。选择具有较长柱头接受期、快速花粉萌发和心皮形态等特征的性状，可能在塑造鲁宾逊海蓬子授粉后生殖发育方面比花粉管生长速率的进化起到更大的作用。
