CONVERSION MECHANISM OF SOMATIC CELL TO REPRODUCTIVE CELL IN FACULTATIVE APOMICTIC GUINEAGRASS (PANICUM MAXIMUM JACQ.)

本研究结果总结如下：1)为了阐明无孢子初始细胞（AIC）的出现和无融合胚囊形成的机制，对百海草的几个无融合胚和专性胚进行了细胞学和定量研究。大孢子发生后，大孢子通常退化。AIC出现并分裂为4核胚囊。花期前随着子房的生长，AIC的数量增加。花期，珠孔端囊（第一囊）主要形成。花期后，第一胚囊占优势分裂。最后，它占据了胚珠的整个空间。其他胚囊的胚胎与第一个胚囊共存。2)用透射电镜（TEM）分析了豚草减数细胞期和无孢子胚囊形成过程中的珠心超微结构。本研究首次观察到MMC染色期变性。合点核细胞是分生的，直到四分体阶段。之后，它们会变成AIC。它们增大的细胞大小、大的细胞核和许多囊泡的存在可以识别AIC。3)Chen等人（1997）使用一种新的差异筛选策略从豚草中分离出AIC外观阶段特异性基因ASG-2并对其进行了表征。序列分析表明，ASG-2 cDNA全长1199 bp，编码173个氨基酸的蛋白。该氨基酸序列与拟南芥种子特异性干旱诱导基因RD22和蚕豆未知种子蛋白前体USP序列相关。4)原位杂交观察子房大孢子发生（A1）、AIC外观（A2-1）和AIC衍生胚囊形成（A2-2）。A1中未检测到ASG探针。随着子房发育至A2-1， AIC细胞发出强烈信号。在A2-2中，仅在胚囊中检测到信号，特别是在生殖细胞中。豚草的有性幼芽在任何阶段都没有表现出信号。5)建立了豚草小叶组织体胚发生和植株再生的培养条件。胚性愈伤组织和体细胞胚发生是由小叶形成的淡黄色愈伤组织形成的。利用扫描电镜对胚性愈伤组织进行了鉴定。现在，转基因植物的制造正在进行中。少

The results of this study were summarized as the following.1), To clarify the mechanisms of aposporous initial cell (AIC) appearance and apomictic embryo sac formation, several apomictic and obligately sexual varieties of bahiagrass were studied cytological and quantitatively. After megasporogenesis, the megaspore usually degenerated. AIC appeared and was divided into 4-nucleate embryo sac. The numbers of AIC increased as the ovary grew before anthesis. At anthesis, the sac in micropylar end (first sac) was dominantly formed. After anthesis, the first sac divided dominantly. In final, it occupied the whole space of the ovule. And the embryos of the other sacs coexisted with the first sac.2), The nucellar ultrastructure was analyzed during the meiocytic stage and during aposporous embryo sac formation in apomictic guineagrass with TEM.Degeneration of dyed stage of MMC was observed in this study as the first time. The chalazal nucellar cells are meristemic until the tetrad stage. Later, … More they can turn into AIC.Their increased cell size, large nucleus, and the presence of many vesicles can recognize the AIC.3) AIC appearance stage-specific gene, ASG-2, has been isolated and characterized from guineagrass using a novel differential screening strategy according to Chen et al.(1997). Sequence analysis indicated that the ASG-2 cDNA (1199 bp) codes for a protein of 173 amino acids. The amino acid sequence alternatively is related to the sequences of RD22, seed-specific and drought-induced gene of Arabidoposis thaliana, and USP, unknown seed protein precursor of Vicia faba.4) Megasporogenesis (A1), AIC appearance (A2-1) and AIC-derived embryo sac formation (A2-2) of ovary were observed with in situ hybridization. The ASG probes were not detected in A1. As the ovary grew into A2-1, AIC cell gave the strong signals. In the A2-2, the signals were only detected in embryo sacs, especially in the reproductive cells. The sexual young buds of guineagrass showed no signal in any stages tested.5) Culture conditions for somatic embryogenesis and plant regeneration from leaflet tissues of guineagrass are established. Embryogenic calli and somatic embryogenesis were initiated from yellowish calli derived from leaflets. The embryogenic calli were confirmed using SEM.Now, making transgenic plant is in progress. Less