Abstract
The Magnoliaceae shows strong phylogenetic niche conservatism, in which temporal petal closure has been extensively reported. However, it is yet elusive whether temporal petal closure is an idle floral character inherited from their ancestors or an adaptive trait to their habitats. Here, we monitored the process of temporal floral closure and re-opening in a thermogenic plant, Magnolia denudata (Magnoliaceae). Furthermore, we artificially interrupted temporal petal closure and investigated its effects on development of female and male gametophytes. Intriguingly, we found considerable anatomical changes in the anthers shortly after temporal closure of petals: disintegration of tapeta, crack of anther walls, and release of matured pollens. In comparison with normal flowers, artificially interrupted flowers (no petal closure) showed delayed anther development and slower pollen germination on stigmas, while little difference in embryo morphology was observed during the early stage of embryo development. Moreover, seed set and quality were significantly decreased when petal closure was prevented. In addition, we found pollination accelerated floral closure in M. denudata. Taken together, temporal floral closure benefits reproduction of M. denudata in early spring by promoting anther development and pollen function, which suggests that it is an adaptive floral trait to its specific habitat.
Highlights
The flowering stage is of crucial importance to plants since it marks the onset of double fertilization and subsequent seed set, which leads to regeneration of the population
In former studies, we found that thermogenic flowers of M. denudata were hermaphroditic and protogynous, usually with temporal petal closure occurring during the anthesis (Wang et al, 2013)
We investigated the process of floral opening and closure during the anthesis of M. denudata, with emphasis on the effects of temporal floral closure on stamen development, pollen function, embryo development, as well as seed production
Summary
The flowering stage is of crucial importance to plants since it marks the onset of double fertilization and subsequent seed set, which leads to regeneration of the population. In order to adapt to diverse environments, flowers have evolved wonderful variation in morphology, such as color, shape, and size, which is beneficial for pollinator visiting and protection of internal structures (Clark and Husband, 2007). Except for morphological variations, there are non-morphological changes in flowers, namely floral movement. As one of the most extensively observed non-morphological changes of flowers, the opening and closure of petals is an important trait of the productive syndrome (van Doorn and Kamdee, 2014). Some flowers maintain open until petal withering, such as rose, while others
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