An investigation into spontaneous reversions in a dwarf mutant of Petunia hybrida in connection with the interpretation of the results of transformation experiments

A spontaneous mutant of Petunia is described, which is characterised by the small size of its shoots, leaves and flowers. Apart from showing these size differences, the mutant has more rounded, suborbicular leaves with a wrinkled surface. In his transformation experiments with Petunia Hess obtained plants which according to his description agree in all details with this “dwarf” mutant, including the frequent occurrence of shoots with characters corresponding with those of the original plant form. He assumed that this particular type of plant had arisen as the result of a transplantation of a gene for leaf shape. However, our studies of the dwarf mutant revealed that the phenomena described by Hess can be explained as well by the incidence of somatic mutations and reversions in one of the two tunica layers of the shoot apex, rather than by the transplantation of gene material. The study of revertants of the dwarf mutant yielded data pointing to a predominant influence of the dermal layer on the morphogenesis of the whole plant.