Endogenous Inhibitors of Growth of Soybean Seedlings Associated with the Inhibition of Growth Induced by Red Light

Summary In order to correlate the role of endogenous inhibitors of growth of soybean plants with the inhibition of such growth by red light (R), a search for specific growth inhibitors was undertaken in the neutral and acidic fractions of acetone extracts from R- and dark-grown hypocotyls of soybean seedlings ( Glycine max L.). Two neutral and two acidic inhibitors were isolated. They were named N-I and N-II (neutral inhibitors) and A-I and A-II (acidic inhibitors), respectively, based on the order of their increasing Rf values during chromatography. Variations in the activity of the inhibitors in the hypocotyls of dark-grown seedlings after the onset of R irradiation were determined in terms of «cress units» which were defined as the activity that causes 50 % inhibition in the cress-root bioassay. The inhibitory activity of N-I and N-II tripled after exposure of plants to R for 24 h, whereas the activity of A-I and A-II remained almost unchanged. These results suggest that R-induced inhibition of growth of soybean hypocotyls may be controlled by variations in the levels of the neutral inhibitors, N-I and/or N-II, in the hypocotyls rather than by the acidic inhibitors.