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-2 . and A-2 Q 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 (1 25 ) were : A-2., 4.3 x 10_ 2; cis-xanthoxin, 1 .2 x 10 -' ; A-2fl, 1 .6 x 10 -' ; trans-xanthoxin, 1 .2 ; R,S-dihydromaleimide, 3 .5 x 102 and pisatin, 4 .0 x 102 nmol plant -' . In 72-h tests, 125 's were : benzyladenine, 1 .5 ; AMO-1618 (ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate), 2 .4 ; R,S-dihydromaleimide, 4 .0 x 102 and CCC (chlorocholine chloride), 1 .1 x 10' nmol plant -' . J3-D-Guucosyl-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-2 . and , in the red light growth inhibition of dwarf peas is discussed .
Abbreviations : AMO-1618 = ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate ; CCC = chlorocholine chloride ; G-DHMD = /3-D-glucosyl-R-dihydromaleimide ; 125 = dose required for a 25% growth inhibition ; R = red light .