Histological changes associated with the graft union development in tomato

Abstract

Background. Despite the importance of grafting in agriculture, particularly in horticultural crops such as tomato (Solanum lycopersicum L.), the structural changes that occur during the establishment of a graft are little understood. Using histochemical techniques, the present work examines the progression of the structure of the graft junction in tomato plants over time.Results. At 10 days after grafting, the cell walls of the scion and rootstock in the area of the graft junction were thicker than usual, and undifferentiated cells appeared associated with the pre-existing vascular tissue. New vascular tissue appeared as branches arising from the pre-existing vasculature, as vascular pockets dispersed within the callus, and as the result of the transdifferentiation of parenchyma cells. Areas showing vascular connections between the scion and rootstock were also seen. Adventitious roots appeared on the scion, arising from the pre-existing vasculature. At 20 days, a great deal of vascular tissue was visible, along with large areas showing vascular connection. At 210 days, vestiges of the changes undergone were still visible. However, no adventitious roots persisted. Conclusions. The area of the graft junction undergoes modifications essential for adequate physiological functioning of grafted plant. The cell walls of the adhesion line change during the process. Pre-existing vasculature plays an important role in the appearance of callus tissue, new vascular cells, and adventitious roots. A long time later the tissues maintain vestiges of graft union development.