Fusicoccin structure‐activity relationships: Stimulation of growth by cell enlargement and promotion of seed germination

The activity of a number of fusicoccin derivatives and analogues has been assayed on growth by cell enlargement and on proton extrusion in pea (Pisum sativum L, cv. Alaska) internode segments, on growth by cell enlargement in isolated squash (Cucurbita maxima Dechesne in Lam. variety Mantovana) cotyledons, and on germination of light‐requiring lettuce (Lactuca sativa L. cv. Grand Rapids) and of abscisic acid‐inhibited radish (Raphanus sativus L. variety Tondo Rosso Quarantino) seeds. A similar pattern of activity in the different tests was found for most fusicoccin derivatives and analogues. As with fusicoccin, the activity of its derivatives and analogues on growth of pea internodes is paralleled by the activity on the capability of the tissue to acidify the incubation medium. The obtained data are in full agreement with the view that the activity of fusicoccin on different physiological processes depends on its primary activation of a single system, involved in proton extrusion.