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The effect of 2, 4-D on certain enzymes in the bean plant Cowie, Lillian Matheson

Abstract

A study was undertaken of effects of 2,4-D on enzyme action in plants (in vivo) and on enzyme kinetics (in vitoo). Bean plants were treated by spraying with a water solution of NH₄2,4-D. Harvests were made at intervals and enzyme activity was estimated using standard procedures. Extracts were prepared for estimation by grinding the plant material in water using a Waring Blendor. The enzymes amylase, peroxidase, catalase, phosphatase and phosphorylase were studied. Amylase activity in stem and leaf increased at first then decreased. Peroxidase in stem, decreased, then increased very greatly. In leaf, peroxidase increased steadily, Phosphorylase increased in stem and leaf for most of the period of six day over which determinations were made. Phosphatase increased in leaf, showed little change in stem. Catalase in leaf decreased. In vitro studies indicate slight activation of catalase at low concentrations and up to 100ppm. Stem phosphatase shows inhibition at concentrations of 500 and 1000 ppm. Effect on leaf phosphatase is variable. Stem phosphorylase is activated at concentrations of 1 to 1000 ppm. Modifications of metabolism resulting from enzyme changes are discussed. A theory of action of 2,4-D is put forth, which suggests that the chemical acts by inhibition or by activation of enzyme systems and that the plant responds by accelerated or depressed production of the enzyme in question, in accord with Hinshelwood’s theory of drug adaptation by bacteria.

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