Effects of 2,4-Dichlorophenoxyacetic Acid Upon the Nitrogen Metabolism and Water Relations of Soybean Plants Grown at Different Nitrogen Levels

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Abstract
High- and low-N soybean plants grown in water culture were exposed for 23 hrs. to 4 ppm. 2, 4-D dissolved in minus-N nutrient soln. and then grown 6 days further in nutrient soln. lacking 2,4-D. Twisting of stem tips and epinasty of petioles, later followed by yellowing of leaves and swelling of stems and petiole bases, and ultimately by wilting and drying of leaves after exposure to 2,4-D, were seen sooner in high-N than in low-N plants. Plants exposed to 2,4-D did not increase in size or dry wt. At first, % dry wt. was lower in treated plants than in controls, especially in leaves, but later % dry wt. was higher in the treated plants when wilting occurred. Roots of treated plants apparently did not absorb NO3. The concn. of protein-N decreased in the leaves and increased in the stems and roots of treated plants. All organs of treated plants showed increases in concn. of soluble organic-N fractions, including alpha-amino-N and amide-N, and especially in residual (undetermined forms of) soluble organic-N.

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