Mutational and tissue culture analysis of regulatory mechanism in rice embryogenesis

到目前为止，我们已经确定了150个影响水稻胚胎发生的单隐性突变。表型表征使他们被分为7组。1. 早期球形阶段的致死率为2。3.基区缺失；4.器官缺失；改良胚大小，5。5 .器官位置异常；7.器官形态异常；可变异常表型，尽管单章动。这种分类表明，至少有五个调控过程在胚胎发生过程中起作用：模式形成，2。3.器官分化的测定；3 .胚胎大小的调控；4 .器官位置的调节；器官的形态发生。在每个过程中，检测到两种类型的基因；一个在整个胚胎中起作用，另一个在特定器官中局部起作用。本研究还揭示了两种控制胚胎大小的方法。当胚乳特异性基因突变导致胚乳减少时，鳞茎在不影响茎和根大小的情况下变为巨大。另一方面，迄今为止确定的胚胎特异性基因调节着每个器官的大小。我们已经分离出一个克隆，在胚胎诱导培养基上培养7天的愈伤组织中特异性表达。该无性系在合子胚中表达，但在芽、根或花中不表达。另一克隆在胚胎诱导培养基和不定芽诱导培养基中普遍表达，而在愈伤组织诱导培养基中不表达。这两个克隆将在胚胎发生和器官分化中发挥重要作用。

To date, we have identified 150 single, recessive mutations affecting embryogenesis in rice. Phenotypic characterization enabled them to be categorized into seven groups. 1. lethality at the early globular stage, 2. deletion of basal region, 3. deletion of ogans, 4. modified embryo size, 5. abnormal organ position, 6. abnormal mprphology of organs, and 7. variable abnormal phenotypes in spite of single nutation. This categorization indicates at least five regulatory processes are operating during embryogenesis : 1. pattern formation, 2. determination of organ differentiation, 3. regulation of embryo size, 4. regulation of organ position, and 5. morphogenesis of organs. In each process, two types of genes are detected ; one functioning in the whole embryo and the other functioning locally, in a specific organ. The present study also revealed that embryo size was controlled in two ways. When endosperm is reduced by the mutation of endosperm-specific gene, scutellum becomes giant without affecting shoot and root sizes. On the other hand, embryo-specific genes thus far identified regulate every organ size.We have isolated a clone which was expressed specifically in the callus cultured for seven days on a embryo-inducing medium. This clone is expressed in zygotic embryo but not in shoots, roots or flowers. another clone is expressed commonly in embryo-inducing medium and adventitious bud-inducing medium, but not callus-inducing medium. These two clones would play important roles in embryogenesis and organ differentiation.