Radiation-Induced Genetic Markers in the Study of Leaf Growth in Zea

Abstract

Stein, Otto L. (Montana State U., Missoula.), and Dale Steffensen. Radiation-induced genetic markers in the study of leaf growth in Zea. Amer. Jour. Bot. 46(7): 485–489. Illus. 1959.—Corn embryos heterozygous for the plant color mutant yellow-green were treated with moderate doses of radiation. The sectors resulting from the loss of the dominant gene Yg2 furnish a graphic illustration of the growth of an organ in space and time. Wet embryos were irradiated and leaves 3 through 6 were analyzed. The total number of sectors per leaf increases in relation to the amount of leaf tissue present at time of irradiation and their distribution varies, indicating a change in mitotic activity during early ontogeny of the leaf. As represented by leaf 6 in the mature embryo, cell division is rather uniform throughout the young primordium. Soon thereafter (leaf 5) cell divisions in the apical region increase, though cell lineages remain short. In the basal region of the leaf, the proportion of cell division decreases but those cells which do divide continue their activity over a longer period than the apical cells. Longer files of mutant cells are formed in such a way. The mid regions of the leaf maintain their status quo in terms of distribution of sectors. The results indicate that differentiation of the intercalary meristem as a thin band occurs early in the development of the leaf primordium. The use of genetic techniques in conjunction with radiation, in this case as a “timed” release of genetic markers, may be a useful tool in the precise analysis of the dynamic aspects of organogenesis and histogenesis.