Effect of 2,4-Dichlorophenoxyacetic acid Application on Activity and Composition of Mitochondria from Soybeans

Abstract

Mitochondria isolated from hypocotyl tissue of soybean seedlings which had been sprayed 24 hours previously with 5 x 10-4 M 2,4-D possessed higher oxidative and phosphorylative activities than mitochondria from Comparable untreated seedlings. This enhanced activity was associated only with mitochondria from the basal tissue which was growing, although abnormally; mitochondria from the inhibited apical hook of the hypocotyl possessed lower activity. Studies of tissue respiration and the phosphate accumulation indicated that the mitochondrial changes obtained in situ. Electron micrographs showed the mitochondria from the swollen tissue of 2,4-D-treated plants to be larger and swollen in appearance. During 2,4-D-induced growth the mitochondria increased in acid-soluble nucleotides, phos-pholipides, and possibly ribonucleic acid per unit mitochondrial N. The increased phosphorylation could be almost completely uncoupled by ribonuclease, and exogenous adenosine monophosphate was not required for maximum substrate oxidation. Normal growth of soybean tissue also involved an increase in mitochondrial activity.