Studies on Graft Unions IV. Assimilate Transport and Sieve Element Restitution in Homo- and Heterografts

Abstract

Summary Using 14 C-labelling techniques the rates of assimilate transport between scion and stock of the compatible intrafamiliar graft Lycopersicon esculentum on Solanum tuberosum and the less compatible interfamiliar graft Vicia faba on Helianthus annuus were compared. The homografts Lycopersicon/Lycopersicon, Helianthus/Helianthus and Vicia/Vicia served as controls. Corresponding with the transport experiments the phloem contacts in graft unions at different stages of development were examined. Assimilate transport across the graft interface started in the compatible heteroplastic and homoplastic combinations 5–7 days after grafting. In the less compatible Vicia/Helianthus grafts label from the scion could not be detected in the stock until 10 days after grafting. The maximum rate of assimilate transport from one partner to the other was significantly lower in Vicia/Helianthus grafts than in the other systems. The first, sieve tubes traversing the graft interface could be found in Lycopersicon/Solanum simultaneously with the appearance of assimilates in the stock. With further differentiation the increasing numbers of sieve tubes in the graft unions correlated with an increasing rate of transported assimilates, indicating that the route of translocation was via the phloem.