Effect of 2,4-Dichlorophenoxyacetic Acid on the Readily Available Carbohydrate Constitutents in Annual Morning-Glory

Abstract

1. Plants of annual morning-glory, Ipomoea lacunosa L., grown in a green-house under conditions favoring vigorous vegetative growth and seed production, were sprayed with an aqueous mixture containing 1000 p.p.m. of 2,4-dichlorophenoxyacetic acid and 0.6% Carbowax 1500. Other plants of morning-glory grown under conditions of photoperiod and soil fertility less favorable for vegetative growth were treated in a similar way. 2. No apparent growth occurred, either in those treated plants that were in a vigorous vegetative condition or in those that were relatively dormant at the time of treatment. Following treatment, the total dry weight of untreated plants increased while that of the sprayed ones decreased. Neither those that were vegetative nor the dormant ones showed external evidence of gall formation or root initiation as the result of treatment. In the sprayed plants, necrosis was first evident in the flower buds, and none of these developed mature seeds. Both the vegetative and the nonvegetative plants died within 3 weeks following treatment. 3. Readily available carbohydrates (sugars, starch, and dextrin) were essentially depleted within a period of 3 weeks in plants that were growing vigorously, and also in plants that were relatively dormant when treated. Carbohydrate reserves (starch and dextrin) were rapidly depleted in the flower buds, and also in the roots, of the sprayed plants, a response of significance in connection with the use of 2,4-dichlorophenoxyacetic acid in the control of weeds. 4. Sugars in treated plants at first increased above the amount in the untreated ones, then decreased, and they were nearly depleted during the second and third week after treatment.