Influence of Marker Genes on the Expression of Somatic Mutations in Barley

Mutagenic agents have been evaluated in terms of their effects on germ cells. The study of induced somatic mutations is a faster, more economical, and less laborious method than the traditional ones. The induction of somatic sectors by x-rays, ethyl methanesulfonate, and sodium azide was studied in cultivated barley. Four stocks were used: a normal one, a balanced lethal genotype carrying two chlorophyll-deficiency genes of different expression (albina and golden), and two (semidominant) chlorophyll mutants of the same dominant gene, which in the progeny of selling segregate 1 normal green: 2 light green: 1 yellow seedlings. Treatments were applied to seeds, and the fourth, fifth, and sixth leaves of the main shoot were examined in the M1 generation for the presence of sectors showing conspicuous changes in chlorophyll content. Highly significant frequencies of dark green sectors were induced by all three mutagens in the (semidominant) heterozygous plants, whereas evidence of somatic crossing over or mitotic nondisjunction was very rare in this material and in the balanced lethal genotype. In all cases, the frequencies of induced sectors without chlorophyll were much higher in the heterozygotes than in the normal homozygotes, with each mutagen showing typical dose-response curves. A notable interaction between mutagen and genotype was found. The variation in the relative frequencies of sector types in the various genotypes points to the differential influence of the marker genes.