Effects of 2,4-D and Other Growth Substances on Photosynthesis and Respiration in Anacharis

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Abstract
Photosynthesis and respiration, in terms of O2 exchange, were measured for Anacharis canadensis before and after treatment with 2,4-D, gamma-(indole-3)-n-butyric, indole-3-acetic, and beta-naphthoxyacetic acids at concns. of 30 and 100 ppm. Each substance caused a decrease in the rate of photosynthesis with the reduction being more at the higher concns. This effect persisted over a period of 48 hrs. and could not be explained on the basis of changes in respiration. Both indole-acetic and naphthoxyacetic acid, at 30 and 100 ppm., resulted in a temporary acceleration of respiration which was later depressec except at the lower concn. of the latter. Following treatment with either indolebutyric acid or 2,4-D there was first a decrease in the rate of respiration followed by partial or complete recovery by the end of 48 hrs.