Effects of Sequential Exposure to Auxin and Cytokinin on Xylogenesis in Cultured Explants of Jerusalem Artichoke (Helianthus tuberosus L.)

During the course of a 4-d culture period, explants of Jerusalem artichoke tuber were exposed to auxin (0.2 mg 1−1 2, 4-dichlorophenoxyacetic acid), and cytokinin (5.0 mg 1−1 benzyl-amino purine), under a range of sequential regimes, to study the influence of each hormone on tracheary element formation. The results indicate that auxin was necessary early in the culture period and was primarily involved in cell proliferation. Cytokinin stimulated xylogenesis when present late in the culture period, concomitant with the phase of cytodifferentiation, but not when restricted to the early period. The implications for a sustained period of commitment to differentiation are discussed.