Effects of exogenous cytokinins on root formation in pea cuttings

Benzylaminopurine (BAP) or zeatin continuously supplied through the rooting solution to cuttings of pea ( Pisum sativum L. cv. Weibull's Marma), inhibited root formation down to a concentration of 3.10 −9 M . The inhibitory effect of BAP in the concentration range 10 −8 –10 −7 M was readily reversible if the cuttings were transferred to solutions without cytokinin after treatment for 1–4 days. A slight increase in the number of roots formed was obtained after treatment with low cytokinin concentrations for 1–2 days. Evidence from microscopic studies of primordia formation indicates that BAP inhibits differentiation of primordia at an early stage in their development. Growth of already formed primordia, or root elongation, was considerably less sensitive to the inhibitory effect of BAP. The results indirectly support the hypothesis that endogenous cytokinins prevent root formation in stems of intact plants and may be of importance for the regulation of rooting in cuttings.