Graduate School of Human Development and Environment, Kobe University, Kobe, Japan.
Faculty of Human Development, Kobe University, Kobe, Japan.
Plant Biol (Stuttg). 2022 Aug;24(5):798-805. doi: 10.1111/plb.13414. Epub 2022 Mar 15.
In zoophilous plants, floral orientation evolved under both biotic and abiotic pressure to enhance pollination success. However, the adaptive significance of horizontal orientation in radially symmetrical (actinomorphic) flowers remains largely unknown, although that of bilaterally symmetrical flowers has been well studied. We experimentally altered floral angle in a population of insect-pollinated Platycodon grandiflorus flowers to examine the effects of floral orientation on pollinator behaviour, pollination success and pollen rain damage avoidance. To further investigate the potential pollen damage by rain, we obtained past precipitation records for the study area during the flowering season, and experimentally tested P. grandiflorus pollen damage by water. Horizontally oriented flowers received more pollinator visits and had pollen grains on the stigma in male and/or female phases than downward- and/or upward-oriented flowers and avoided pollen damage by rainfall better than upward-oriented flowers. A pollen germination experiment showed that approximately 30% of pollen grains burst in distilled water, indicating that pollen damage by rainfall may be significant in P. grandiflorus. Our field experiments revealed that upward-oriented flowers cannot avoid pollen damage by rainfall during the flowering period, and that both upward- and downward-oriented flowers experience pollinator limitation in female success. Therefore, horizontal flower orientation appears to be adaptive in this insect-pollinated actinomorphic species that blooms during the rainy season.
在虫媒植物中，花的朝向是在生物和非生物压力下进化的，以提高授粉成功率。然而，径向对称（辐射对称）花中水平朝向的适应意义在很大程度上仍然未知，尽管对双边对称花的适应意义已有很好的研究。我们通过实验改变了一种昆虫授粉的桔梗花的花角度，以研究花朝向对传粉者行为、授粉成功率和避免花粉雨伤害的影响。为了进一步研究由雨引起的潜在花粉伤害，我们获取了研究区域在开花季节的过去降水记录，并通过实验测试了水对桔梗花粉的伤害。水平朝向的花朵比向下和/或向上朝向的花朵接受了更多的传粉者访问，并且在雄性和/或雌性阶段在柱头处有花粉粒，比向上朝向的花朵更好地避免了由降雨引起的花粉伤害。花粉萌发实验表明，大约 30%的花粉粒在蒸馏水中破裂，表明在桔梗中由降雨引起的花粉伤害可能很重要。我们的野外实验表明，向上朝向的花朵在开花期不能避免由降雨引起的花粉伤害，而向上和向下朝向的花朵在雌性成功方面都经历了传粉者限制。因此，水平花朝向在这个在雨季开花的昆虫授粉的辐射对称物种中似乎是适应性的。
