Activities of growth inhibitors isolated from light-grown dwarf pea shoots

Abstract

The growth inhibitory activities of 6 endogenous growth inhibitors isolated from light-grown dwarf peas (Pisum sativum cv. Progress No. 9) were examined in the epicotyl of dark-grown seedlings of the same cultivar in the dark in order to examine the possible contribution of these compounds to the growth inhibition brought about by red light. The activities of these natural inhibitors, including two A-2α and A-2β of as yet undetermined structure, were compared with those of synthetic growth retardants and benzyladenine. Samples were applied directly into the epicotyls via a glass capillary tube. In 24-h tests doses for a 25% inhibition (I25) were: A-2α, 4.3 × 10-2: cis-xanthoxin, 1.2 × 10-1 ; A-2β, 1.6 × 10-1; trans-xanthoxin, 1.2; R,S-dihydromaleimide, 3.5 × 102 and pisatin, 4.0 × 102 nmol plant-1 . In 72-h tests, I25's were: benzyladenine, 1.5; AMO-1618 (ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate), 2.4; R,S-dihydromaleimide, 4.0 × 102 and CCC (chlorocholine chloride), 1.1 × 103 nmol plant-1. β-D-Glucosyl-R-dihydromaleimide had no activity at all. Benzyladenine caused the thickening as well as elongation inhibition of the epicotyls of intact plants. The possible involvement of A-2α and β in the red light growth inhibition of dwarf peas is discussed.