Relationship of Cytokinin to Lateral Bud Growth at Early Stages after Decapitation

Lateral buds of peas (Pisum sativum L `Alaska') were measured in situ with a dissecting microscope to study early growth after decapitation and to investigate the relationship of cytokinin to this growth. Removal of the apex does not lead to an increase in sensitivity to applied benzyladenine (BA), but high BA concentrations (10 μM) are no longer supraoptimal for growth when compared with growth of intact plants. The change in response to high BA concentrations cannot be mimicked by preincubation in 1 μM BA, but 1 μM can stimulate growth to rates seen in decapitated plants. Bud growth declines sharply 12 h after withdrawal of BA. Removal of roots (which might lower endogenous cytokinin levels) or addition of optimal or supraoptimal amounts of BA does not result in appreciable changes in lag times (6-10 h) or initial growth rates of lateral buds after decapitation. It is concluded that new events, as measured by the response to applied BA, may be initiated by decapitation, that these events cannot be brought about by exogenous applications of BA, and that other factors besides cytokinin are limiting for bud growth in the intact pea plant.