龙须草无融合生殖的胚胎学证据

采用石蜡切片技术对龙须草(Eulaliopsis binata(Rotz)C.E.Hubb)进行了系统的胚胎学研究,证明龙须草为禾本科植物中一种新的无融合生殖材料.龙须草无融合生殖方式为无孢子生殖,在胚珠发育早期,多个珠心细胞特化为无孢子生殖原始细胞,由原始细胞发育为单核胚囊,经两次有丝分裂形成4核胚囊,进一步分化形成两种类型的成熟胚囊:(1)具1个卵细胞,1个助细胞和2个极核,占观察总数的67.6%;(2)具1个卵细胞,2个助细胞和1个极核,占观察总数的32.4%.胚囊发育属大黍型.多个无孢子生殖原始细胞可以同时发育,最后形成2个或多个胚囊,其比例为17.7%.胚珠内没有有性胚囊的发育.胚的发生有两种类型:(1)早发生胚(74%),开花前1～2 d,极核未分裂前卵细胞分裂形成胚;(2)迟发生胚(26%),开花后2～3 d,极核分裂形成多个胚乳游离核后,卵细胞启动分裂形成胚.存在多胚现象,多胚来自不同胚囊内卵细胞的孤雌生殖,多胚发生率为13%.胚乳由极核不经受精自发分裂产生.

Embryological Evidence of Apomixis in Eulaliopsis binata

Embryological investigation was carried out on apomixis in Eulaliopsis binata (Rotz) C. E. Hubb by using paraffin section method. The results indicated that the development pattern of the embryo sac was apospory. In the early stage of the ovule development, a few of the nucellar cells developed into aposporous initial cells, which differentiated later into two forms of mature embryo sac: (1) one form of the mature embryo sac contained one egg cell, one synergid and two polar nuclei; (2) another form possessed one egg cell, two synergids and one polar nucleus. The former occupied about 67.6% and the later only 32.4%. The development pattern of the aposporous embryo sac resembled the Panicum type. Multiple initial cells of apospory might undergo development simultaneously to form two- or multiple-embryo sacs. The ratio of multiple mature embryo sacs in one ovule was 17.7%. No sexual embryo sac was found in the observed ovules. The genesis of the embryo could be classified into two types according to their initial time: (1) the pre-genesis embryo (74%), which originated from unreduced egg cell before the division of the polar nucleus, was observed at one to two days earlier than anthesis. (2) the late-genesis embryo (26%) which was observed at one or two days after anthesis and formation of free endosperm nuclei. The endosperm was derived from the polar nucleus or secondary nucleus without fertilization. The process of the embryonic development followed the sequence of the sexual embryo. The frequency of polyembryony observed was 13%.