WATER-DEFICIT IN DEVELOPING ENDOSPERM OF MAIZE - CELL-DIVISION AND NUCLEAR-DNA ENDOREDUPLICATION

Water deficit severely decreases maize (Zea mays L.) kernel growth; th e effect is most pronounced in apical regions of ears, The capacity fo r accumulation of storage material in endosperms is thought to be part ially determined by the extent of cell division and endoreduplication (post-mitotic nuclear DNA synthesis). To gain a better understanding o f the regulatory mechanisms involved, we have examined the effect of w ater deficit on cellular development during the post-fertilization per iod, Greenhouse-grown maize was subjected to water-limited treatments during rapid cell division [from 1 to 10 days after pollination (DAP)] or rapid endoreduplication (9 to 15 DAP). The number of nuclei and th e nuclear DNA content were determined with flow cytometry, Water defic it from 1 to 10 DAP substantially decreased the rate of endosperm cell division in apical-region kernels, but had little effect on middle-re gion endosperms, Rewatering did not allow cell division to recover in apical-region endosperms, Water deficit from 9 to 15 DAP also decrease d cell division in apical-region endosperms, Endoreduplication was not affected by the late treatment in either region of the ear, but was i nhibited by the early treatment in the apical region, In particular, t he proportion of nuclei entering higher DNA-content size classes was r educed. We conclude that cell division is highly responsive to water d eficit, whereas endoreduplication is less so, We also conclude that th e reduced proportion of nuclei entering higher DNA-content size classe s during endoreduplication is indicative of multiple control points in the mitotic and endoreduplication cycles.