花椒珠心胚及胚乳的发生和发育

Origin and development of the nucellar embryo and endosperm in apomictic Xanthoxylum bungeanum Maxim.

对花椒珠心胚及胚乳的发生和发育过程进行了详细的细胞学及组织学研究。主要研究结果如下 :珠心胚发生前 ,有性胚囊发育过程中从大孢子发生到胚囊形成的各个阶段均可发生退化 ,退化频率约为 50 % ,未退化的胚囊发育成熟。成熟胚囊仅含卵器和两个极核。卵器最终退化 ,极核不经受精自发形成胚乳。当胚乳游离核达到 1 6或 32个时 ,最早的珠心胚原始细胞由靠近胚囊珠孔端的珠心细胞分化形成。随着子房生长 ,多个原始细胞持续不断地从珠孔端靠近胚囊的 1至几层珠心细胞中分化出来。珠心胚原始细胞发生频率为 2 7%。原始细胞经分裂形成多细胞原胚并进入胚囊腔中。一个胚珠中常有多个原始细胞同时发育 ,因此珠孔端常同时具有多个胚。珠心胚发育经历与合子胚相同的发育阶段。约 1 5%的种子可达到成熟。成熟种子中一般含 1～ 3个胚 ,个别种子中的胚超过 3个。

The origin and development of the nucellar embryo and endosperm in Xanthoxylum bungeanum Maxim,which is unisexual and dioecious and only appears as female plant in Beijing,were studied with cytological and histochemical methods.Before nucellar embryogenesis,50% of degeneration occurred in every stages of megasporogeness and embryo sac development.Mature embryo sac only contained egg apparatus and two closed polar nuclei.The polar nuclei autonomously developed into endosperm without fertilization and the egg apparatus ultimately degenerated.When the free nuclei of the endosperm were 16 or 32,the nucellar embryo initial (s) originated from the nucellar cells near the micropylar end of the embryo sac.More initials specialized from one or more layer of nucellar cells in the micropylar region with the ovary growth.The frequency of initial (s) origination was 27%.The initial divided and developed into multi celled proembryo and the proembryo projected into the cave of embryo sac.More than one embryos always presented side by side in the micropylar region in one seed due to more than one initials synchronic development.The nucellar embryo had a suspensor,its development passed through the similiar stages of the zygotic embryo.About 15% seeds could reach maturity.Normally,one to three mature embryos were contained in one matured seed.More than three embryos occurred in one seed in some cases.