Direct differentiation of tracheary elements in cultured explants of gamma-irradiated tubers of Helianthus tuberosus.

Exposure of Jerusalem artichoke (Helianthus tuberosus) tubers to 20 krad doses of γ-irradiation inhibits mitosis and DNA synthesis in cultures subsequently inititated from such material. When cultures were initiated from immature, developing tubers, tracheary elements differentiated from parenchyma cells in response to auxin in the culture medium. The capacity for direct differentiation in irradiated tissues declined with tuber maturity, and in fully mature tubers xylem differentiation only occurred in non-irradiated controls, following a period of cell division. An hypothesis concerning changes in developmental plasticity of cells in relation to the cell cycle is discussed.