Studies of vegetative compatibility-incompatibility in higher plants

Summary

In order to determine whether graft incompatibility betweenSedum telephoides andSolanum pennellii required a prior wounding of tissues, we monitored the cellular events that occurred during grafting of intact (i.e., non-wounded) surfaces ofSedum andSolanum callus tissuein vitro. The only cytological events that occurred in response to autografting ofSedum callusin vitro were (1) dilation of the endoplasmic reticulum in cells adjacent to the graft interface, and (2) the formation of a conspicuously thickened cell wall between the grafted cells. The only cytological event that occurred in callus cells ofSolanum that were heterografted to callus cells ofSedum was a slightly reduced staining intensity of the cytoplasm.Sedum cells of the heterograft, on the other hand, underwent a progressive cellular necrosis when grafted toSolanum in vitro. These results indicate that (1) a prior wounding of tissues is not necessary to elicit the incompatibility response betweenSedum andSolanum, although the wounding induced from an initial graft incision acts to exaggerate and accelerate incompatibility, and (2) graft incompatibility betweenSedum andSolanum occursin vitro between callus cells as it doesin vivo between stems. Thus, the incompatibility factor is probably a normal component of the ground tissue and not the exclusive product of more highly differentiated tissues. Finally, the mechanism of autografting of non-wounded callus cells is compared to the known mechanism of postgenital tissue fusions.