ANALYSIS OF DEFECTIVE LEAF SECTORS AND ABORTED KERNELS IN NCS2 MUTANTMAIZE PLANTS

The NCS2 mutation of maize is a rearrangement in the mitochondrial DNA resulting in a partial deletion of the nad4 gene, which encodes a sub unit of Complex I of the electron transfer chain. The phenotype of the heteroplasmic NCS2 plants, which contain mixtures of mutant and norma l mtDNA, includes pale-green leaf striping and sectors of kernel abort ion on the ears. PCR amplification with specific primers was used to i nvestigate the relative amounts of mutant and normal nad4 genes in the defective tissues. The earliest aborting kernels and some of the pale -green leaf sectors were found to be homoplasmic for the NCS2 mitochon drial mutation. However, trace amounts of the normal nad4 gene were fo und in some of the aborting kernels. This suggests that a ''threshold' ' level of normal mitochondria is required to rescue the kernels from abortion. Microscopic analysis showed that the embryos develop to a re latively late stage prior to aborting. Analysis of the genotypes and o f the phenotypic effects of the NCS mutants can be used to assess tile importance of different mitochondrial functions during plant developm ent.