Diterpenoid Alkaloids as Plant Growth Inhibitors

Abstract

WE report here preliminary studies on the plant growth inhibitory activity of two diterpenoid alkaloids isolated from the common larkspur, Delphinium ajacis. Little is known about the possible metabolic or physiological action on plants of either terpenoids or alkaloids. The diterpenoid alkaloids are an unusual group of “secondary metabolites” produced by plants; they can be derived biogenetically from an isoprenoid pathway which in the early stages is probably similar to that used in gibberellic acid biosynthesis, because the stereochemistry of the A/B ring junction between the two groups of compounds is the same (and antipodal to that of most naturally occurring steroids)1. Delcosine, a diterpenoid alkaloid of the lycoctonine type, and ajaconine, a diterpenoid alkaloid of the atisine type skeleton and an unknown alkaloid with a molecular weight of 467 designated as LBA-III, were isolated from D. ajacis seeds2. Their effect on plant growth was measured by a new method designed for testing water insoluble substances available in limited amounts. The test is based on the ability of auxins to induce cambial growth.