EFFECT OF RED-LIGHT ON ENDOGENOUS INHIBITORS OF GROWTH IN THE HYPOCOTYL OF TALL AND DWARF CULTIVARS OF PHASEOLUS-VULGARIS

In order to clarify the role of endogenous inhibitors of growth in dwarf and tall bean plants, a search for specific inhibitors of growth was undertaken using the neutral fractions of acetone extracts from the hypocotyls of dwarf (cv. Morocco) and tall (cv. Kentucky Wonder) bean seedlings (Phaseolus vulgaris L.). Three inhibitors were isolated from both cultivars and they were named N-1, N-2 and N-3, respectively, on the basis of the order of their elution from a silica-gel column. Variations in the activity of the inhibitors in hypocotyls of both cultivars after the onset of red-light irradiation were determined by use of a bean bioassay, and results were compared with those of red-light-induced inhibition of growth. The difference in the activity of N-1 between the two cultivars was particularly great, and the changes with time in levels of N-1 in hypocotyls of each cultivar matched the time course of the red-light-induced inhibition of growth of hypocotyls of the same cultivar. No such correlation was found with N-2 and N-3. These results suggest that red-light-induced inhibition of growth of bean hypocotyls may be controlled by variations in the levels of N-1. N-2 was spectroscopically identified as a mixture of xanthoxins.