Genetic interaction between the tissues of carnation petals as periclinal chimeras

Abstract

The Jacqueline and Jacky varietics of carnation with orange red-striped or orange flowers are natural mutants of the red-flowered variety William Sim. Gamma irradiation of their cuttings with 5000 R leads to the formation of a considerable proportion of stems with red flowers and with yellow ones, attesting to their structure as periclinal chimeras. In order to investigate this structure, Jacqueline has been treated with colchicine, and cytochimeras produced whose flowers have remained orange. By irradiating cuttings 4-2-2, homogeneous tetraploid stems with yellow flowers and diploid branches with red flowers have been obtained. Conversely, after irradiation of cuttings 2-4-4, all the diploid branches have yellow flowers and the tetraploid ones, red flowers. Thus the varieties of orange flowers are chimeras whose T1 alone has mutated for the yellow flower characteristic; however their petal epidermal cells, the only pigmented cells, are orange in colour. It is suggested that the mesophyll of the petal carrying the red flower genotype, while not pigmented itself, has an influence on the synthesis of pigments in the epidermal cells. This interaction between the genotypes of a chimera is not universal and seems to depend on the mode of action of the genes involved in biochemical syntheses. Thus the variety White Sim, whose T1 alone carries the white flower mutation, has no pink flowers in spite of T2 and the corpus having retained the red flower genotype. Carnation petals are simple organs which lend themselves well to biochemical analyses; no doubt they might be used profitably for the study of enzymatic processes linked with the different modes of gene action.