Department of Plant Biology, University of California, One Shields Avenue, Davis, CA, 95616, USA.
Department of Plant and Soil Sciences, FABI, Innovation Africa, University of Pretoria, Lynwood Road, Hatfield, 0002, South Africa.
New Phytol. 2021 Oct;232(2):868-879. doi: 10.1111/nph.17627. Epub 2021 Aug 5.
Effective insect pollination requires appropriate responses to internal and external environmental cues in both the plant and the pollinator. Helianthus annuus, a highly outcrossing species, is marked for its uniform eastward orientation of mature pseudanthia, or capitula. Here we investigate how this orientation affects floral microclimate and the consequent effects on plant and pollinator interactions and reproductive fitness. We artificially manipulated sunflower capitulum orientation and temperature in both field and controlled conditions and assessed flower physiology, pollinator visits, seed traits and siring success. East-facing capitula were found to have earlier style elongation, pollen presentation and pollinator visits compared with capitula manipulated to face west. East-facing capitula also sired more offspring than west-facing capitula and under some conditions produced heavier and better-filled seeds. Local ambient temperature change on the capitulum was found to be a key factor regulating the timing of style elongation, pollen emergence and pollinator visits. These results indicate that eastward capitulum orientation helps to control daily rhythms in floral temperature, with direct consequences on the timing of style elongation and pollen emergence, pollinator visitation, and plant fitness.
有效的昆虫授粉需要植物和传粉者对内部和外部环境线索做出适当的反应。高度异交的向日葵属植物以成熟假头状花序（或头状花序）向东统一定向为特征。在这里，我们研究了这种定向如何影响花卉微气候，以及对植物和传粉者相互作用和生殖适应性的影响。我们在野外和控制条件下人工操纵向日葵头状花序的定向和温度，并评估花的生理学、传粉者访问、种子特性和父本成功。与人为操纵朝向西方的头状花序相比，朝东的头状花序具有更早的花柱伸长、花粉展示和传粉者访问。在某些条件下，朝东的头状花序比朝西的头状花序产生更多的后代，并且产生的种子更重、更饱满。头状花序上的局部环境温度变化被发现是调节花柱伸长、花粉出现和传粉者访问时间的关键因素。这些结果表明，向东的头状花序定向有助于控制花卉温度的日常节律，对花柱伸长和花粉出现、传粉者访问以及植物适应性的时间直接产生影响。
