赤苎无融合生殖细胞胚胎学研究

CYTOEMBRYOLOGICAL STUDIES ON APOMIXIS IN BOEHMERIA SILVESTRII

对赤苎(Boehmeria silvestrii (Pamp.)W.T.Wang)细胞胚胎学研究表明,其生殖模式属无融合生殖的二倍体孢子生殖(diplospory),但其未减数胚囊的发育途径不同于已报道的类型。大孢子母细胞的减数分裂I在到达终变期时停滞,染色体呈单价体状态并维持较长的时间。在尚未到达以核膜、核仁消失,纺锤体出现为特征的中期I前,大孢子母细胞由终变期直接“跳”入间期,从而始终保持了二倍体水平。减数分裂Ⅱ正常进行并产生二倍体二分孢子。珠孔端孢子退化,合点端孢子经3次分裂形成包括1个卵细胞、2个助细胞、2个极核和3个反足细胞的八核胚囊。胚和胚乳分别起源于卵和次生核未受精的自发分裂。胚乳属核型,其发育早于胚。

Cytoembryological studies were carried out to determine the apomictic mechanisms of Boehmeria silvestrii (Pamp.) W.T.Wang. The results showed that the modes of reproduction conforms diplospory. But the development of unreduced embryo sac in B. silvestrii differs from the known types. The first meiotic division in megasporocyte reached diakinesis, but never advanced further. The chromosomes exhibited in the univalent state which maintained at a longer time. Before reaching the metaphase I which was characterized by the disappearance nuclear membrane and the appearance of spindle, the megasporocyte 'jumped' from diakinesis into interkinesis without reduction of chromosome number. The second meiotic division proceeded normally and gave rise to in a dyad of diploid megaspores. The micropylar megaspore degenerated, while the chalazal megaspore underwent three mitoses to form an eight-nucleated mature embryo sac including an egg, two syn-ergids, two polar nuclei and three antipodals. The embryo and the endosperm respectively originated from egg and secondary nucleus autonomously divided without pollination. The endosperm was of the nuclear type and developed earlier than embryo.