DYNAMICS OF MAIZE ENDOSPERM DEVELOPMENT AND DNA ENDOREDUPLICATION

Endosperm development in Zea mays is characterized by a period of inte nse mitotic activity followed by a period in which mitosis is essentia lly eliminated and the cell cycle becomes one of alternating S and G p hases, leading to endoreduplication of the nuclear DNA. The endosperm represents a significant contribution to the grain yield of maize; thu s, methods that facilitate the study of cellular kinetics may be usefu l in discerning cellular and molecular components of grain yield. Two mathematical models have been developed to describe the kinetics of en dosperm growth. The first describes the kinetics of mitosis during end osperm development; the second describes the kinetics of DNA endoredup lication during endosperm development. The mitotic model is a modifica tion of standard growth curves. The endoreduplication model is compose d of six differential equations that represent the progression of nucl ei from one DNA content to another during the endoreduplication proces s. Total nuclei number per endosperm and the number of 3C, 6C, 12C, 24 C, 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 det ermined by flow cytometry. The results indicate that the change in num ber of nuclei expressed as a function of the number of days after poll ination is the same from one yearly crop to another. These data were u sed in the model to determine the endosperm growth rate, the maximum n uclei number per endosperm, and transition rates from one C value to t he next higher C value. The kinetics of endosperm development are reas onably well represented by the models. Thus, the models provide a mean s to quantify the complex pattern of endosperm development.