THE AGE OF PEA TISSUE AND OTHER FACTORS INFLUENCING THE RESPIRATORY RESPONSE TO 2,4‐DICHLOROPHENOXYACETIC ACID AND DINITRO COMPOUNDS

Abstract

IN A PREVIOUS publication the well-known selective action of 2,4-D as a weed-killer was shown to be reflected in its effect on respiration. The oxygen uptake by tissue from peas, for example, was stimulated by lower concentrations and to a greater degree than was that of the cereal grass, oats (Kelly and Avery, 1949). The experiments reported here were designed to give the following information concerning the respiratory response of peas to 2,4-dichlorophenoxyacetic acid (2,4-D) as determined bv the Warburg respirometer: 1) penetration in relation to extent of freshly cut surface of tissue; 2) effect of age of tissue; 3) influence of starvation of tissue. An additional objective was to determine the extent to which pea tissue respiration is affected by certain other physiologically active compounds, namely dinitro compounds. The literature on the effects of 2,4-D and dinitro compounds on plant respiration has been reviewed previously (Kelly and Avery, 1949). Since then, Mitchell, et al. (1949) have reported 2,4-D in concentrations of 20 mg./I. and higher was inhibitory to the respiration of mature tomato stem tissue. Nance (1949) found that 2,4-D at 5 and 10 mg./I. had little influence on the respiration of wheat roots. Nickell (1949) correlating growth and respiration in Rumex virus tumor tissue grown in vitro found that 2,4-D stimulated and inhibited respiration in the same general range of concentrations that it affects pea tissue. Stenlid's experiments (1949b) show that pH may influence the effective concentration range of 2,4-D; at pH 4.5 the concentrations tested inhibited wheat root respiration, while at neutrality they stimulated it. In concentrations from 20-2000 mg./I. 2,4-D had a stimulating effect on the activity of indoleacetic acid oxidase from pea stems (Goldacre, 1949). The inhibitory effect of 2,4-D (2 mg./I. and above) on lupine root respiration was not reversed when respiratory intermediates were added (West and Henderson, 1950). Bonner's report (1949) that 2,4-dinitrophenol stimulated respiration of Avena segments in concentrations of from 1-5 mg./I. and inhibited' it at 10 mg./1. is of interest in view of the fact that a derivative of the compound, 2,4-dinitro-o-cyclohexylphenol, had previously been found to affect respiration in the same range of concentrations (Kelly and Avery, 1949). Stenlid (1949b) found that at acid pH (4.5) less dinitrophenol was required for stimulatory and inhibitory effects on