Relation between Carotenoid Content and Number of Genes per Cell in Diploid and Tetraploid Corn^

The evaluation of induced chromosome doubling as a method of plant breeding requires more information on the specific effects of chromosome doubling than is available at the present time. It is important that this information be procured from comparisons of related diploid and tetraploid strains of known origin and similar genetic constitution, Such strains have not been generally available because of the infrequency with which chromosome doubling occurs spontaneously and because of the lack of methods for the experimental production of autotetraploids generally applicable to crop plants. But with the development of the heat-treatment technique for the experimental doubling of chromosome numbers (10) ^ comparable diploid and tetraploid strains of corn (Zea mays L.) and other plants have been made available for study. The effect of chromosome doubling on the carotenoid pigments in corn is of special interest because of the vitamin A potency of two of these pigments. The investigation reported in this paper was undertaken to determine the relation between carotenoid content, cell volume, and gene number in comparable strains of diploid and tetraploid corn and to determine the carotenoid content of examples of commercial varieties, inbred strains, and hybrids of ordinary diploid com. A preliminary report of these studies has already been published (12). The carotenoids of the com kernel are located in the endosperm tissue, which is relatively homogeneous in cellular organization and is thus favorable material for a study of cell-volume relations. In corn of the ordinary diploid sort the chromosomes and genes are present in triplicate, while in the derived tetraploid there are six sets of chromosomes and genes. Since the character in question is definitely localized in the endosperm tissue, a favorable opportunity is presented for a study of the effect of gene number on the degree of development of the yellow pigment. Yellow corn meal contains the carotenoid pigments beta-carotene and cryptoxanthin, precursors of vitamin A, and zeaxanthin, which