Influence of the Y11 and Y12 genes on carotenoid biosynthesis
--Diane Janick-Buckner and Brent Buckner

The yellow color of maize endosperm is due to the synthesis and accumulation of carotenoids. Several genes have been identified that are involved in the carotenoid biosynthetic pathway. Plants that are homozygous for the recessive allele of either y11 or y12 exhibit lemon yellow kernels as opposed to normal yellow kernels (MNL 61:96, 1987). The influence of the Y11 and Y12 genes on the carotenoid biosynthetic pathway in endosperm was investigated in this study.

Carotenoids from the endosperm of sibling lemon yellow and yellow kernels were extracted and analyzed from four separate ears in triplicate. Kernels were obtained from ears produced by self pollinating plants that were heterozygous for the recessive allele of either y11 or y12. The carotenoids in the extract were then separated and quantified by using high performance liquid chromatography (HPLC) while monitoring at 450 nm. The distribution of carotenoids was similar in all endosperm extracts analyzed. The major carotenoids present in both yellow and lemon yellow endosperm were lutein/zeaxanthin, a xanthophyll monoester, alpha-carotene, ß-carotene, alpha-cryptoxanthin and ß-cryptoxanthin. However, the quantity of some carotenoids was significantly reduced in lemon yellow endosperm in both homozygous recessive y11 and y12 endosperm. Xanthophylls were affected to a greater extent than were carotenes.

When carotenoid extract from homozygous recessive y12 endosperm was analyzed on an HPLC equipped with a photodiode array detector, it was evident that a large quantity of zeta-carotene was present. Only a very small quantity of this carotenoid was present in carotenoid extract prepared from sibling yellow endosperm. Thus, it appears that homozygous recessive y12 endosperm has a reduced ability to convert zeta-carotene to neurosporene, and consequently accumulates zeta-carotene. We have also observed that under field conditions the leaves of homozygous recessive y12 plants display a diurnal pattern, suggesting that this allele could be temperature sensitive and also influence carotenoid biosynthesis in the leaf. In addition, homozygous recessive y12 kernels exhibit a low frequency of vivipary, suggesting that this gene influences kernel abscisic acid levels. 

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