Response to Vertical Load in the Seedlings of Several Epigeal Leguminous Crops.

Abstract

Etiolated seedlings (1 cm height) of several epigeal leguminous crops, grown in the soil with 13% moisture at 25°C, were used to investigate the response against the imitated pressure of covered soil after sowing. Changes in hypocotyl length. stem thickness and ethylene production were measured 48 hs after placing various weights on the tip of the seedlings. Accompaning with the increase of weights, decrease in hypocotyl length and increase of ethylene production as well as hypocotyl thickness were observed. The minimal sensitive weight (M. S. W.), in which the elongation of hypocotyl was inhibited significantly (at 5% level), was 5 g in moth bean and black gram, 7.5 g in soybean cv. Asoaogari, 10 g in mung bean and cowpea, 20 g in soybean cv. Akisengoku, 30 g in kidney bean and hyacinth bean and 160 g in peanut. The ethylene production was found to increase significantly (i) at smaller weights than the M. S. W. in the seedlings of moth bean, kidney bean and peanut, (ii) at about the same M. S. W. in the seedlings of mung bean and soybean cv. Akisengoku, and (iii) at larger weights than the M. S. W. in the seedlings of other species. Hypocotyl thickness increased significantly at the same or larger weights than those of inhibited elongation and enhanced ethylene evolution of the seedlings. The M. S. W. was found to correlate positively with seed weight (r=0.851**), stem thickness (r=0.978***) and maximal elongation force (r=0.922***). The M. S. W. per unit stem thickness was smaller in the seedlings of black gram and cowpea, larger in the seedlings of peanut and kidney bean compared with those of the other species. The weights that inhibited hypocotyl elongation mostly were smaller than maximal elongation force and correlated significantly with the M. S. W. in all species except cowpea.