School of Ecology and Environmental Science, Yunnan University, Kunming, Yunnan, China.
Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology and Institute of Biodiversity, Yunnan University, Kunming, 650504, Yunnan, China.
Planta. 2023 Jun 21;258(2):23. doi: 10.1007/s00425-023-04178-0.
The pistillate flowers of Lithocarpus dealbatus show two pollen tube (PT) arresting sites (the style-joining and micropyle) within the pistil during the postpollination-prezygotic stage. The PT, arrested at the pre-ovule stage, enhanced PT competition allowing the most compatible PTs to enter the ovary to ensure the highest fertilization success. During the shift from animal pollination to wind pollination, plants require a series of changes in reproductive traits. The mode of pollination is striking labile in Fagaceae. Lithocarpus is insect pollinated and is closely related to wind-pollinated Quercus. Little is known about the sexual reproduction of Lithocarpus. This study aimed to reveal the sexual reproduction of Lithocarpus dealbatus and to explore the evolutionary pattern of the key sexual reproduction traits to better understand their possible role in labile pollination. We found that after pollination, L. dealbatus PTs grew slowly in the style reaching style-joining in mid-January of the second year; then PT growth was arrested at style-joining for four months. Only two to three PTs resumed growth in mid-May to reach the micropyle, where PT growth ceased for one month before one PT resumed growth and passed through the micropyle to the embryo sac. Fagaceae showed a generalized mating system. Vast pollen production, small-sized pollen grains, long stigmatic receptive time, and reduced perianth were compatible with beetle pollination syndrome, representing the plesiomorphic status in Fagaceae. A large stigmatic surface and dry pollen grains linked to wind pollination might be independently derived several times in fagaceous lineages. Beetle pollination syndrome can cope with the uncertainty of pollinators to ensure conspecific pollen capture, which represents pre-adaptation status and has a selective advantage when conditions change, favouring wind pollination. The arrest of the PT at style-joining is a unique mechanism in later derived fagaceous lineages to enhance PT competition and promote outcrossing.
花皮柯的雌花在授粉后-合子前阶段于雌蕊内具有两个花粉管（PT）截获位点（花柱联合处和珠孔）。在胚珠前阶段被截获的 PT 增强了 PT 竞争，使最相容的 PT 进入子房，以确保最高的受精成功率。在从动物传粉向风传粉转变的过程中，植物需要一系列生殖特征的变化。壳斗科植物的传粉方式非常不稳定。花皮柯是昆虫传粉的，与风媒传粉的栎属密切相关。关于花皮柯的有性繁殖知之甚少。本研究旨在揭示花皮柯的有性繁殖，并探讨关键有性繁殖特征的进化模式，以更好地理解它们在不稳定传粉中的可能作用。我们发现，授粉后，L. dealbatus 的 PT 在花柱中缓慢生长，于第二年 1 月中旬到达花柱联合处；然后，PT 生长在花柱联合处被截获四个月。只有两到三个 PT 在 5 月中旬恢复生长，到达珠孔，在一个 PT 恢复生长并穿过珠孔进入胚囊之前，PT 生长在珠孔处停止一个月。壳斗科植物表现出一种普遍的交配系统。大量的花粉产生、小粒花粉、长的柱头可接受时间和减少的花被与甲虫传粉综合征相匹配，代表了壳斗科植物的原始状态。大的柱头表面和干燥的花粉粒与风传粉有关，可能在壳斗科植物的谱系中独立衍生了几次。甲虫传粉综合征可以应对传粉者的不确定性，以确保同种花粉的捕获，这代表了预适应状态，当条件发生变化时具有选择优势，有利于风传粉。PT 在花柱联合处的截获是后期衍生的壳斗科植物谱系中增强 PT 竞争和促进异交的独特机制。
