四倍体双穗雀稗兼性无孢子生殖的研究

Facultative Apospory in Tetraploid Paspalum distichum L.

研究了四倍体双穗雀稗(PaspalumdistichumL.)无孢子生殖胚囊、胚胎发育以及假受精特点。当其大孢子母细胞发育至四分体阶段时,大多数情况下会发生四分体退化,同时有多个特化珠心细胞发育为1-3个无孢子生殖胚囊的现象。成熟无孢子生殖胚囊一般3核,包括1个卵细胞和2个极核。卵细胞在抽穗前就能自发分裂形成原胚团,而极核则在抽穗和传粉后参与假受精形成胚乳。当胚珠内存在多个无孢子生殖胚囊时,只是靠近珠孔端的1个无孢子生殖胚囊内的极核与精核结合,而其它的并不参与。种子成熟后出现很低频率的二胚苗。此外,还能观察到少量的有性生殖胚囊的发育以及有性生殖胚囊和无孢子生殖胚囊在同一胚珠中的发育现象,因此判断该类群为兼性无孢子生殖体。

Development of aposporous embryo sac, embryo and pseudogamy were studied in tetraploid Paspalum distichum. In most cases, shortly after the megasporocyte developed into a tetrad, it began to deteriorate, meanwhile several nucellar cells became active and enlarged. Normally, 1-3 nucellar cells developed into mature aposporous embryo sacs characterized by 1 egg cell and 2 polar nuclei. The egg cell could spontaneously develop into proembryo prior to anthesis, whereas polar nuclei were involved in pseudogamy to develop endosperm after heading and pollination. When several aposporous sacs occurred in an ovule, only the sac near the micropyle developed endosperm while the other sacs did not. The frequency of twin-embryo seedlings geminated from mature seeds was low. Few sexual 8-nucleus embryo sacs as well as both sexual and aposporous sacs in the same ovule were found. It is suggested that the tetraploid P. distichum is considered to be a facultative apomict reproduced by apospory.