PDF(Pubmed)
Abstract：
n the Neotropics, the focus of apomictic studies predominantly centres on trees within the Brazilian savanna, characterized, mostly as sporophytic and facultative, associated with polyploidy and polyembryony. To enhance our understanding of the mechanisms governing apomixis and sexual reproduction in tropical herbaceous plants, we clarify the relationship between apomixis, chromosome counts, and polyembryony in the epiphytic orchid Zygopetalum mackayi, which forms a polyploid complex within rocky outcrops in both the Brazilian savanna and the Atlantic forest. To define embryo origins and describe megasporogenesis and megagametogenesis, we performed manual self-pollinations in first-day flowers of cultivated plants, considering all three cytotypes (2x, 3x, 4x) of this species. Flowers and fruits at different stages were collected to describe the development and morphology of ovules and seeds considering sexual and apomictic processes. As self-pollination treatments resulted in high fruit abortion in diploids, we also examined pollen tube development in aborted flowers and fruits to search for putative anomalies. Megasporogenesis and megagametogenesis occur regularly in all cytotypes. Apomixis is facultative and sporophytic, and associated with polyploid cytotypes, while diploid individuals exclusively engage in sexual reproduction. Polyembryony is caused mainly by the production of adventitious embryos from nucellar cells of triploids and tetraploids, but also by the development of multiple archesporia in all cytotypes. Like other apomictic angiosperms within the Brazilian savanna, our findings demonstrate that apomixis in Z. mackayi relies on pollinators for seed production. We also consider the ecological implications of these apomictic patterns in Z. mackayi within the context of habitat loss and its dependence on pollinators.
摘要：
在新热带，无融合生殖研究的重点主要集中在巴西稀树草原内的树木上，characterized,主要是孢子体和兼性，与多倍体和多胚性有关。为了增强我们对热带草本植物无融合生殖和有性生殖机制的理解，我们澄清了无融合生殖之间的关系，染色体计数,和附生兰花的多胚性，在巴西稀树草原和大西洋森林的岩石露头中形成多倍体复合体。为了定义胚胎起源并描述大孢子发生和大胚发生，我们在栽培植物的第一天花上进行了手工自花授粉，考虑到所有三种细胞类型(2x，3x,4x）的这个物种。收集了不同阶段的花朵和果实，以描述考虑有性和无融合生殖过程的胚珠和种子的发育和形态。由于自花授粉处理导致二倍体的高果实流产，我们还检查了流产花和果实中的花粉管发育，以寻找推定的异常。在所有细胞类型中都有规律地发生大孢子发生和巨细胞发生。无融合生殖是兼性的和孢子体的，与多倍体细胞类型有关，而二倍体个体只从事有性生殖。多胚性主要是由三倍体和四倍体的核细胞产生不定胚引起的，而且在所有细胞类型中都有多个古生孢子的发展。像巴西稀树草原内的其他无融合生殖被子植物一样，我们的发现表明，Z.mackayi的无融合生殖依赖于传粉媒介进行种子生产。在栖息地丧失及其对传粉媒介的依赖性的背景下，我们还考虑了Z.mackayi中这些无融合生殖模式的生态意义。
