Effect of Uv Radiation on Endogenous Inhibitors of Growth in the Hypocotyl of Phaseolus vulgaris

Abstract

In order to correlate the role of endogenous inhibitors of growth of bean plants with the inhibition of such growth by UV radiation, a search for specific growth inhibitors was undertaken using the neutral and acidic fractions of acetone extracts from the hypocotyls of UV-irradiated bean seedlings (Phaseolus vulgaris L. cv. Morocco). Tho neutral and two acidic inhibitors were isolated and they were named N-1 and N-2 (neutral inhibitors) and A-1 and A-2 (acidic inhibitors), 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 two cultivars (cvv. Morocco and Kentucky 101) after the onset of UV radiation were determined by use of a bean bioassay, and results were compared with those of UV-induced inhibition of growth. The growth of hypocotyls of the two cultivars decreased rapidly. However, the more noticeable change was a marked decrease in the growth of the hypocotyls of cv. Morocco. On the other side, 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 UV-induced inhibition of growth of hypocotyls of the same cultivar. No such correlation was found with N-2, A-1 and A-2. These results suggest that the activity of N-1 may serve to distinguish the growth habit of the two cultivars to UV radiation.