Schweizer L, Yerk-Davis G L, Phillips R L, Srienc F, Jones R J
Institute for Advanced Studies in Biological Process Technology, University of Minnesota, St. Paul 55108, USA.
Proc Natl Acad Sci U S A. 1995 Jul 18;92(15):7070-4. doi: 10.1073/pnas.92.15.7070.
Endosperm development in Zea mays is characterized by a period of intense mitotic activity followed by a period in which mitosis is essentially eliminated and the cell cycle becomes one of alternating S and G phases, leading to endoreduplication of the nuclear DNA. The endosperm represents a significant contribution to the grain yield of maize; thus, methods that facilitate the study of cellular kinetics may be useful in discerning cellular and molecular components of grain yield. Two mathematical models have been developed to describe the kinetics of endosperm growth. The first describes the kinetics of mitosis during endosperm development; the second describes the kinetics of DNA endoreduplication during endosperm development. The mitotic model is a modification of standard growth curves. The endoreduplication model is composed of six differential equations that represent the progression of nuclei from one DNA content to another during the endoreduplication process. Total nuclei number per endosperm and the number of 3C, 6C, 12C, 24C, 48C, and 96C nuclei per endosperm (C is the haploid DNA content per nucleus) for inbred W64A from 8 to 18 days after pollination were determined by flow cytometry. The results indicate that the change in number of nuclei expressed as a function of the number of days after pollination is the same from one yearly crop to another. These data were used in the model to determine the endosperm growth rate, the maximum nuclei number per endosperm, and transition rates from one C value to the next higher C value. The kinetics of endosperm development are reasonably well represented by the models. Thus, the models provide a means to quantify the complex pattern of endosperm development.
玉米胚乳发育的特点是有一段强烈的有丝分裂活动期，随后是一个有丝分裂基本消除且细胞周期变为S期和G期交替的时期，导致核DNA的核内复制。胚乳对玉米籽粒产量有重要贡献；因此，有助于研究细胞动力学的方法可能有助于识别籽粒产量的细胞和分子成分。已经开发了两个数学模型来描述胚乳生长的动力学。第一个描述胚乳发育过程中有丝分裂的动力学；第二个描述胚乳发育过程中DNA核内复制的动力学。有丝分裂模型是对标准生长曲线的修改。核内复制模型由六个微分方程组成，这些方程表示在核内复制过程中细胞核从一种DNA含量转变为另一种DNA含量的进程。通过流式细胞术测定了授粉后8至18天自交系W64A每个胚乳的总细胞核数以及每个胚乳中3C、6C、12C、24C、48C和96C细胞核的数量（C是每个细胞核的单倍体DNA含量）。结果表明，以授粉后天数为函数表示的细胞核数量变化在不同年份的作物中是相同的。这些数据被用于模型中以确定胚乳生长速率、每个胚乳的最大细胞核数以及从一个C值到下一个更高C值的转变速率。胚乳发育的动力学可以通过这些模型得到合理的良好体现。因此，这些模型提供了一种量化胚乳发育复杂模式的方法。
