Guy E. Farish

Date of Award

5-1-1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Embryogenesis in maize (Zea mays L.) is a genetically regulated process that gives rise to a large embryo with shoot and root apical meristems, a large scutellum, and five or six leaf primordia. An embryo-lethal defective kernel mutation dek23, located on chromosome arm 2L, affects the formation of the shoot apical meristem, coleoptilar ring, and leaf primordia in mutant embryos. Comparison of mutant and normal embryo development at the structural and biochemical levels should give insight into the role of the dek23 normal gene product in normal development. Fresh dissection, light microscopy, and transmission electron microscopy of normal and mutant embryos at different developmental stages reveal a divergence between mutant and normal embryo morphology at nine days after pollination (dap). Mutant embryos are developmentally delayed and the cells of the shoot apical meristem region contain enlarged vacuoles and abnormal nuclei and subsequently become necrotic. Two-dimensional polyacrylamide gel protein profiles of normal embryos from the transition stage (nine dap) through stage 5/6 (40 dap) were obtained and used as standards for comparison to mutant embryo protein profiles at five different developmental stages. Normal embryo protein profiles exhibited a set of 16 landmark spots found at all stages. Two early embryonic proteins were found in embryos up to stage 1. Three stage specific proteins were observed at the coleoptilar stage, as well as a set of spots that increased in intensity until stage 3 and then decreased. Accumulation of globulin storage proteins was clearly evident. Mutant embryo profiles were generally similar to normal profiles of an earlier chronological age. Two landmark spots found in normal profiles were absent or diminished in mutant profiles. One early embryonic protein identified in normal profiles was also absent from mutant profiles, and may provide a marker for identifying mutant embryos before morphological differences are evident. Mutant embryos failed to accumulate any globulins. The dek23 locus was mapped 22 centimorgans distal to w3. Reduced sexual transmission of the mutant allele through the pollen and unequal distribution of mutant kernels on a self pollinated ear indicate that the dek23 gene is active in the male gametophyte.

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