Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA.
Am J Bot. 2009 Jan;96(1):144-65. doi: 10.3732/ajb.0800070. Epub 2008 Dec 19.
A remarkable number of the defining features of flowering plants are expressed during the life history stage between pollination and fertilization. Hand pollinations of Amborella trichopoda (Amborellaceae) in New Caledonia show that when the stigma is first receptive, the female gametophyte is near maturity. Pollen germinates within 2 h, and pollen tubes with callose walls and plugs grow entirely within secretions from stigma to stylar canal and ovarian cavity. Pollen tubes enter the micropyle within 14 h, and double fertilization occurs within 24 h. Hundreds of pollen tubes grow to the base of the stigma, but few enter the open stylar canal. New data from Amborella, combined with a review of fertilization biology of other early-divergent angiosperms, show that an evolutionary transition from slow reproduction to rapid reproduction occurred early in angiosperm history. I identify increased pollen tube growth rates within novel secretory carpel tissues as the primary mechanism for such a shift. The opportunity for prezygotic selection through interactions with the stigma is also an important innovation. Pollen tube wall construction and substantial modifications of the ovule and its associated structures greatly facilitated a new kind of reproductive biology.
在授粉和受精之间的生活史阶段，有许多开花植物的特征表现得非常明显。在新喀里多尼亚对 Amborella trichopoda（Amborellaceae）进行的人工授粉表明，柱头刚开始接受花粉时，雌性配子体接近成熟。花粉在 2 小时内发芽，带有胼胝质壁和塞子的花粉管完全在柱头到花柱管和卵巢腔的分泌物中生长。花粉管在 14 小时内进入珠孔，双受精在 24 小时内发生。数以百计的花粉管生长到柱头的基部，但很少有进入开放的花柱管。来自 Amborella 的新数据，结合对其他早期分化的被子植物受精生物学的回顾，表明从缓慢繁殖到快速繁殖的进化转变在被子植物历史的早期就发生了。我确定在新的分泌心皮组织中花粉管生长速度的增加是这种转变的主要机制。通过与柱头的相互作用进行预配子选择的机会也是一个重要的创新。花粉管壁的结构和胚珠及其相关结构的大量修饰极大地促进了一种新的生殖生物学。
