It is commonly observed that kernels homozygous for a recessive allele of Y1 can be white to pale-yellow in color. This variable expressivity is usually associated with the genetic background of the plant. In some of our stocks we have observed F2 ratios of 12 yellow: 3 pale yellow: 1 white kernels in self pollinations of plants heterozygous for Y1. Vivipary has not been observed in association with the gene(s) responsible for pale yellow color in these crosses. The purpose of this study was to determine whether the pigments responsible for the pale yellow phenotype were carotenoids. Therefore, we extracted total carotenoids from endosperms of yellow, pale yellow and white kernels and separated and quantified them by using high pressure liquid chromatography. The major carotenoids found in all kernels were zeaxanthin/lutein, a xanthophyll monoester,
Table 1. Carotenoid content in the endosperm of pale yellow and white
kernels that are homozygous for a recessive allele of Y1a
|Lutein/zeaxanthin||100||112 ± 5||p<0.05c|
|b-cryptoxanthin||100||100 ± 4||N.S.|
|Lutein/zeaxanthin monoester||100||100 ± 2||N.S.|
|a-carotene||100||132 ± 17||p<0.05|
|b-carotene||100||130 ± 6||p<0.01|
|Total carotenoids||100||109 ± 2||p<0.05|
aData are expressed as the percentage of carotenoids present
in white endosperm.
bEach value represents the mean ± standard error of the mean of endosperm samples from three separate ears measured in triplicate.
cValues were compared by using a paired t test. Samples were not considered to be significantly different (N.S.) if the calculated p value was greater than 0.05.
The allele of the gene responsible for the pale yellow phenotype in the kernels analyzed was contributed from a hybrid of inbred lines M14 and W22. Donald S. Robertson has informed us that in his experience stocks which are homozygous for a recessive allele of Y1 are pale yellow in an M14 background and a "truer white" in W22 background. Therefore, it is likely that the allele of the gene responsible for the pale yellow color is present in the M14 line.
The identity of the gene responsible for pale yellow kernel color in the kernels analyzed in this study is not known. There are several genes such as Y6, Y8, Y11, and Y12 which, when present in a homozygous recessive condition, do not result in vivipary, however, they do influence the intensity of yellow pigmentation in the kernels of plants that have a standard dominant allele of Y1. Plants that are homozygous for the recessive alleles of these genes have decreased yellow pigmentation in their endosperm, presumably due to decreased levels of carotenoids, even when the plants contain a dominant Y1 allele. Other alleles of these genes might be expected to increase the quantity of carotenoids found in the endosperm of maize kernels. Therefore, if these loci, or others with similar effects on carotenoid biosynthesis, segregate independently from the Y1 locus, epistatic ratios such as those described in this study would be expected.
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