Genetic variation at the vp7 locus

Identification/isolation of certain maize mutants often depends upon or is made easier by observing one or more specific developmental stages. Prevalent among such mutants are those which delay but do not ultimately inhibit pigment development. Over the years, I have had occasion to "tide over" my hogs from one dry maize crop to the next by shucking and feeding immature ears. Thus I have had economic reason to observe a considerable number of immature endosperms of field maize wherein the major pigment is carotene. Several seed mutants with delayed carotene development have come to my attention. This report concerns a class which accumulates the pink carotene precursor, lycopene.

During the summer of 1979, out of about 30,000 dough stage ears from the high-lysine hybrid, "Pioneer 3369L," I found five with scattered pink endosperms. Two of these had mild vivipary (slight plumule elongation) associated with the pink endosperms, while three did not. As all five ears dried, the pink endosperms faded to an indistinguishable yellow. Embryos retained the pink color, though it was difficult to detect without sectioning them. Among about 250,000 additional ears from the same hybrid examined at maturity the same year, I found one with scattered pink endosperms and highly viviparous embryos (extensive plumule and radical elongation).

During the spring of 1980, all kernels from one non-viviparous ear, one mildly viviparous ear, and the highly viviparous ear were planted in separate isolation plots. Pink embryos from the non-viviparous ear produced albino seedlings which died at the three leaf stage. None of the mildly or highly viviparous seeds germinated. About half the open pollinated ears from each plot had scattered pink kernels in the late dough stage. Several plants in each plot were selfed, and approximately half of these produced a 3:1 yellow to pink endosperm ratio in the late dough stage. Bulk pollinations proved all three of my isolates to be alleles of one another and of vp7 supplied by Dr. R. J. Lambert. Mutant hybrid kernels expressed the degree of vivipary of the least viviparous parent. In other words, my non-viviparous allele suppressed vivipary when combined with either of my other two alleles or with Dr. Lambert's (mildly viviparous) allele. Likewise, my mildly viviparous allele attenuated vivipary when combined with my highly viviparous allele. The pink pigment of all three alleles was identified as lycopene by TLC.

Once genetic backgrounds have been stabilized, I intend to quantify the relative amounts of lycopene and other carotenoids and of abscisic acid produced by each allele. My family enjoyed "strawberries and cream" roasting ears left over from samplings for chromatography, and I have begun to move the non-viviparous allele into su and sh2 backgrounds. Homozygous vp7 seedlings produced from seed using the non-viviparous allele should prove to be of value in carotenoid pathway analysis.

Absalom F. Williams


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