DNA Synthesis in Rice Endosperm

水稻胚乳细胞核的DNA含量不是保持在预期的3C水平，而是增加到更高的值。被问到的问题如下。在该组织发育的整个过程中，胚乳细胞核中DNA的合成和积累方式是什么？如果胚乳细胞核表现出DNA含量的模式增加，这是指细胞融合、多倍体、多线、内复制或选择性基因扩增？在胚乳的个体发育过程中，是否有某些基因表达不足的证据？用放射自显影(包括DNA纤维放射自显影术)和Feulgen显微分光光度法研究DNA合成和积累的变化规律。胚乳DNA与叶或胚DNA以及与克隆基因的再结合动力学将被用来确定高DNA含量是由于内复制还是基因扩增。分析胚乳DNA与rRNA杂交的动力学，以确定在胚乳发育过程中rRNA基因是否处于低复制状态。

The DNA content of rice endosperm nuclei, instead of remaining at the expected 3C level, increases to higher values. The questions that are being asked are the following. What is the pattern of DNA synthesis and accumulation in endosperm nuclei during the entire course of development of this tissue? If the endosperm nuclei exhibits a modal increase in DNA content, is this referable to cell fusion, polyploidy, polyteny, endoreduplication or selective gene amplification? Is there evidence for the under.representation of certain genes during the ontogeny of the endosperm? Autoradiographic (including DNA fiber autoradiography) and Feulgen microspectrophotometic methods will be used to study the changing pattern of DNA synthesis and accumulation. The reassociation kinetics of endosperm DNA with leaf or embryo DNA and with cloned genes will be employed to establish whether the high DNA content is due to endoreduplication or gene amplification. The kinetics of hybridization between endosperm DNA and rRNA will be analyzed to determine whether the rRNA genes are under.replicated during endosperm development.