ENDOREDUPLICATION OF NUCLEAR-DNA IN THE DEVELOPING MAIZE ENDOSPERM

Multiparametric flow cytometry was used to analyze the development of the endosperm in Zea mays L. during the period from 8 to 20 days after pollination (dap). Nuclear size, DNA content per nucleus, and frequencies of nuclei with varying properties were measured in preparations that included all of the endosperm nuclei of single kernels of the inbred strain Al88. Characteristics of nuclear populations from different kernels on the same ear showed minimal variation. The dynamic changes of non‐mitotic cells involved in endosperm development consisted of alternating periods of DNA replication with non‐replication. Seven rounds of DNA replication had occurred in some nuclei in the later developmental stages with the rate averaging approximately one round per 24‐hour period. Analysis of the DNA levels in the nuclei showed an exact doubling pattern indicating an endoreduplication process, that is, replication of the entire genome during each round. The loosely organized polytenization of the chromatin occurred to varying extents among the nuclei within an endosperm. A weak positive correlation existed between DNA content and size of nuclei suggesting that DNA increases and nuclear growth may not be highly coordinated in this tissue. Increased proportions of the larger nuclei occurred in the later stages of endosperm development. Considering the entire endosperm, the average DNA content per nucleus at the 15‐dap peak level was approximately 12.8 C constituting a 2.7‐fold overall increase from 8 dap. Copyright © 1990 Wiley‐Liss, Inc.