Leaf grafting and its prevention by the intact and abraded epidermis

Abstract
Experiments were conducted on leaf laminae to determine the effects of intact, excised, and abraded epidermal layers on the success of graft unions in Catharanthus roseus and Sedum telephoides. Lamina surfaces grafted together within 2 – 4 weeks when the epidermis was removed from both graft partners. In contrast, the presence of epidermis on one or both graft partners prevented grafting. Intact epidermal cells adjacent to wounds did not divide or undergo other visible changes except for plasmolysis and death in a few grafting situations. Epidermal cells are developmentally distinctive from underlying parenchymatous cells in that they fail to respond to stimuli that elicit redifferentiation and dedifferentiation in subepidermal tissues. Abrasion with carborundum effectively stripped the cuticular layer from parts of the leaf surfaces put into contact for grafting and increased the permeability of the surfaces to large, water-soluble, calcofluor-white molecules. Similar to grafting attempts with intact surfaces, abraded surfaces failed to graft, produce callus, or undergo any other of the observable changes that occur in exposed subepidermal cells. These results indicate that the cuticle is not responsible for the failure of intact surfaces to graft. Rather, the epidermal cell appears to be uniquely restricted in its capacity to dedifferentiate and redifferentiate. Grafting failure between freely permeable surfaces (after cuticle abrasion) refutes the notion that the cuticle obstructs passage of diffusible agents necessary to induce epidermal dedifferentiation and grafting.