Abstract

The study of reproductive mechanisms is of particular interest for a real understanding of seed plant evolution. Spermatophytes comprise angiosperms and four orders of gymnosperms (Cycadales, Ginkgoales, Coniferales, and Gnetales) whose main characteristic is the reproduction via seeds. Ginkgo and cycads form a sister clade to the other gymnosperms and occupy a key phylogenetic position in-between the extinct Paleozoic seed ferns and the other extant gymnosperms. This review focuses on the similarities and differences between the reproductive mechanisms of Ginkgo and Cycas, from the morphogenesis of the male and female organs to the pollination and fertilization events. Together with the morphological and cytological description, the latest available molecular data on the reproductive organ development of the two plant genera are discussed. This will, hopefully, pave the path for new studies aiming at filling the gaps in our understanding of the hormonal and genetic regulation of their reproductive mechanisms. The whole reproductive process is presented in detail, providing a comprehensive and organic picture together with complete illustrations and photographic material. Each phase of the reproductive process is dissected, pointing out the main similarities and differences found among the two genera. The comparison comprises the male and female reproductive organs development, with a focus on pollen ontogeny, shape, ultrastructure, and germination as well as ovule development and patterning, female gametophyte formation, and ovule integument differentiation. Particular attention is given to the pollination and fertilization events focusing on the role of reproductive fluids as well as zoogamy.

摘要

繁殖机制的研究对于真正了解种子植物的进化特别有意义。种子植物包括被子植物和裸子植物四个目（苏铁目、银杏目、松柏目和买麻藤目），其主要特征是通过种子繁殖。银杏和苏铁植物与其他裸子植物形成姐妹分支，并在已灭绝的古生代种子蕨类植物和其他现存裸子植物之间占据重要的系统发育地位。本文重点讨论银杏和苏铁生殖机制的异同，从雄性和雌性器官的形态发生到授粉和受精事件。结合形态学和细胞学描述，讨论了两个植物属生殖器官发育的最新分子数据。希望这将为新研究铺平道路，旨在填补我们对其生殖机制的激素和遗传调控的理解空白。整个生殖过程被详细呈现，提供了全面、有机的画面，并配有完整的插图和摄影材料。详细剖析了繁殖过程的每个阶段，指出了两个属之间的主要相似点和不同点。比较包括男性和女性生殖器官的发育，重点是花粉个体发育，形状、超微结构和发芽以及胚珠发育和图案、雌配子体形成和胚珠珠被分化。特别关注授粉和受精事件，重点关注生殖液和动物受精的作用。