Endosperm mitotic activity and endoreduplication in maize affected by defective kernel mutations

Abstract

A group of 35 defective kernel (dek) mutants in maize has been studied with regard to their effect on endosperm development. Information is reported on kernel weight, kernel viability, mutant transmission, DNA content per endosperm nucleus, endosperm cell numbers during development, and DNA endoreduplication patterns. All of the dek mutations reduced mitotic activity and resulted in greatly reduced cell numbers. All except one mutation decreased DNA endoreduplication. The exception indicates that the processes of mitotic activity and endoreduplication can be uncoupled. Notable differences in DNA endoreduplication patterns were observed among the dek strains. Defective kernels with homozygous defective embryos did not germinate in any of these strains, although some morphologically defective kernels did germinate and were shown to have normal embryos of +/+ or +/dek genotype. Dek mutants that had a defective endosperm and an embryo that developed normally were not identified. The mutations investigated are recessive, but F2 segregation for many of the mutants revealed significant deviations from expected 3:1 ratios.Key words: defective kernels, endosperm, endoreduplication.

Endosperm Origin, Development, and Function

“…Maize dek mutants have been described that develop small or reduced amounts of endosperm. Kowles et al (1992) found that endosperm nuclei in severa1 of these mutants have significantly reduced DNA contents compared to their normal counterparts. However, the genetic lesions of these mutants are unknown, and it is difficult to assign cause and effect.…”

A Dominant Negative Mutant of Cyclin-Dependent Kinase A Reduces Endoreduplication but Not Cell Size or Gene Expression in Maize Endosperm

“…Several previous reports provided indirect evidence supporting this relationship (Kowles et al, 1992;Engelen-Eigles et al, 2000;Lemontey et al, 2000), but these studies were largely correlative and endoreduplication could not be separated from pleiotropic effects associated with physiological changes or environmental effects. Surprisingly, we found only a modest (6.5%) reduction in average seed weight for the CDKA-DN mutant compared with the nontransgenic control.…”

“…Based on its temporal relationship with cell expansion and increased metabolic activity, endoreduplication is generally thought to provide a mechanism for increasing cell size and gene transcription (Sugimoto-Shirasu and Roberts, 2003). Notably, the degree to which endoreduplication occurs in seed storage tissues has been correlated with the accumulation of starch and storage proteins as well as yield (Kowles et al, 1992;Cavallini et al, 1995;Lemontey et al, 2000).…”

Endosperm Development in Barley: Microtubule Involvement in the Morphogenetic Pathway.

“…From this perspective, the endosperm emerges as a model system for the study of plant development. It is abundant, fast growing, and consists of only two cell types that can be mechanically separated (Jakobsen et al, 1989), and importantly, genetic mutants affecting the development of the endosperm are known (Sheridan and Neuffer, 1980;Felker et al, 1985;Bosnes et al, 1987Bosnes et al, , 1992Kowles et al, 1992).…”

“…From this perspective, the endosperm emerges as a model system for the study of plant development. It is abundant, fast growing, and consists of only two cell types that can be mechanically separated (Jakobsen et al, 1989), and importantly, genetic mutants affecting the development of the endosperm are known (Sheridan and Neuffer, 1980;Felker et al, 1985;Bosnes et al, 1987Bosnes et al, , 1992Kowles et al, 1992).Three general types of endosperm development are recognized (Brink and Cooper, 1947;Vijayraghavan and Prabhakart, 1984;Friedman, 1994): ab initio cellular, in which all mitoses are followed by wall development; nuclear, in which free nuclear divisions result in a syncytium that later becomes cellularized; and helobial, where the first division divides the central cell into separate micropylar and chalazal chambers that develop independently. Cereal grains undergo the nuclear type of development with cell walls forming in the immediate vicinity of the developing embryo region (micropylar) earlier than those in the large chalazal region (Engell, 1989).…”