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

主要研究结果如下：1）、为了阐明无孢子生殖起始细胞（AIC）的出现和无融合生殖胚囊形成的机制，对几个无融合生殖和专性生殖的百喜草品种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，分裂为4核胚囊。开花前随着子房的发育，AIC的数量逐渐增加。开花时，珠孔端的囊（第一囊）占优势。开花后，第一个胚囊以分裂为主。最终占据胚珠的整个空间。用透射电镜观察了无融合生殖天竺葵减数分裂期和无孢子胚囊形成期珠心的超微结构，首次观察到染色期MMC的退化。合点端的珠心细胞在四分体时期之前都是分生组织。后来， ...更多信息 AIC的细胞体积增大、细胞核大、存在许多囊泡，这些都可以识别AIC。3）AIC出现阶段特异性基因ASG-2已经从天竺葵中分离出来，并根据Chen等人的新的差异筛选策略进行了表征。（1997年）。序列分析表明，ASG-2cDNA全长1199 bp，编码173个氨基酸。4）利用原位杂交技术，观察了拟南芥种子特异干旱诱导基因RD 2 - 2和蚕豆种子蛋白前体USP的发生过程，以及大孢子发生（A1）、AIC出现（A2-1）和AIC胚囊形成（A2-2）。在A1中未检测到ASG探针。随着卵巢发育到A2-1，AIC细胞发出较强的信号。在A2-2中，仅在胚囊中检测到信号，尤其是在生殖细胞中。5）建立了天竺葵叶片组织体细胞胚胎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均由小叶黄色愈伤组织诱导。胚性愈伤组织经扫描电镜证实。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