多胚水稻品系SB-1的细胞胚胎学研究:多胚及其起源

CYTOEMBRYOLOGICAL STUDIES ON POLYEMBRYONIC LINE SB 1 OF ORYZA SATIVA: POLYEMBRYONY AND ITS ORIGIN

对水稻（Ｏｒｙｚａ ｓａｔｉｖａ Ｌ．）多胚品系ＳＢ－１ 中二倍性双胚和三胚的起源所进行的形态解剖观察、杂交后代表现和细胞胚胎学的研究表明，２ｎ－２ｎ 型双胚和２ｎ－２ｎ－２ｎ 型三胚既不是合子胚裂生产生，也不是助细胞受精产生的，而极有可能来源于存在额外卵细胞卵器中卵细胞和类卵细胞分别受精的结果。在成熟胚囊中观察到５．２％ 的二卵卵器和２．２％ 的三卵卵器。二卵卵器中卵细胞和类卵细胞大都并列位于助细胞合点端上方；三卵卵器中，合点端两个卵细胞结构并行排列，其珠孔端侧下方是另一卵细胞结构。各个发育时期的绝大多数多胚颖果中各个胚的排列方式与多卵卵器中卵细胞的排列方式完全一致，而与卵器中助细胞与卵细胞的相对位置迥异。核型分析表明，绝大多数双苗实生苗和三苗实生苗分别为２ｎ－２ｎ 和２ｎ－２ｎ－２ｎ 多胚苗。在正交（ＳＢ－１×马来红，马来红不具多胚特性）Ｆ０ 及Ｆ１ 颖果中都出现了多胚苗，反交（马来红×ＳＢ－１）的Ｆ０ 颖果未出现多胚苗，但其Ｆ１ 颖果观察到多胚苗，表明ＳＢ－１ 的多胚不是合子裂生产生的，而是胚囊的一种特殊性状，这种性状是可以遗传的显性性状。对多胚苗进行的形态解剖学观察表明，各实生苗是完全独立的，相互间无维管束连接。?

Anatomical observations, genetic and cytoembryological studies were conducted to determine the cytological factors in relation to the production of diploid polyembryony within one embryo sac occurring in polyembryonic line SB 1 of O.sativa L.The results showed that the diploid polyembryony in SB 1 was originated not from the fertilization of synergids, but presumably from the megagametophytes with supernumerary egg cells.Potentially polyembryonic megagametophytes at maturity contained either a conventional 3 celled egg apparatus (92 6% of megagametophytes) or the supernumerary eggs forming either a 4 celled (5 2%) or 5 celled (2 2%) egg apparatus.In megagametophyte with one additional supernumerary egg cells were almost situated side by side in adjacent to the synergids and recessed from the micropyle, whereas in megagametophyte with two additional supernumerary eggs, one egg cell occupied the conventional possition and the other two lay above the synergids.The arrangement of embryos in polyembryonic caryopsis at various developmental stages was concordant to that of egg cells in megagametophytes with supernumerary eggs.Karyotype analysis showed that most of the twins and triplets were of 2n-2n and 2n 2n 2n respectively.Polyembryony was observed in F 0 and F 1 caryopsis of cross SB 1×Malaihong (Malaihong is of non polyembryony) and in F 1 caryopsis of its reciprocal but not in F 0 caryopsis.This implies that polyembryony occurring in SB 1 is of a dominant character of embryo sac.Anatomical observations proved that each seedling from twins or triplets was completely independent with no vascular bundle connected with each other.The causes of polyembryony within one embryo sac, the entry of supernumerary sperms and the origin of supernumerary egg cells are discussed.