Relation of 2,4-D-Induced Growth Aberrations to Changes in Nucleic Acid Metabolism in Soybean Seedlings

Abstract

The relationship of 2,4-D-[2-4-dichlorophenoxyacetate]-induced growth aberrations in etiolated soybean seedlings to alterations in nucleic acid and protein metabolism was studied. Cell division and cell elongation were inhibited in the apical region of the hypocotyl and in the epicotyl; cell elongation was inhibited, and radial enlargement was markedly enhanced in the region 0.5-2 cm below the cotyledons; and slight radial expansion was noted in the fully elongated cells of the hypocotyl. Cell divisions, leading to lateral root formation, were initiated in the basal hypocotyl within 12 hr. and in the "swollen" zone (B) by 36 hr. Treatment with 2,4-D blocked nucleic acid and protein synthesis in the apical zone (A) of the hypocotyl, with resumption of synthesis occurring somewhat before the recovery of growth. RNA synthesis in response to 2,4-D preceded somewhat the DNA and protein synthesis in other zones of the hypocotyl. The large synthesis of RNA resulted in an increase in the RNA/DNA ratio and a decrease in the protein/RNA ratio. There was a preferential synthesis of r-RNA in response to 2,4-D. The newly synthesized RNA had a normal base composition and size distribution on sucrose-gradient centrifugation. The results are consistent with the view that the herbicidal action of 2,4-D is associated with the renewal of RNA and protein synthesis leading to massive tissue proliferation, disorganized growth, and finally death of the plant.