Effect of 2,4-Dichlorophenoxyacetic Acid on Photosynthesis and Respiration

Abstract

The inhibition of photosynthesis in leaves of Washington Navel orange and in Chlorella pyrenoidosa by 2,4-D is shown to be related to the concn. of undissociated 2,4-D molecules in the soln. used for treatment, regardless of whether the difference in undissociated acid concn. was obtained by varying the pH of buffer solutions containing a constant amount of 2,4-D or by varying the concn. of 2,4-D added to buffers of the same pH. Two phases of inhibition are shown, one proportional to the log of the undissociated acid concn., the other directly proportional to the concn. of undissociated molecules. The effect of 2,4-D on the respiration of these tissues was slight, but tended to show stimulation in intermediate ranges of undissociated acid concn. and inhibition from higher concentrations.