The Effect of 2,4-Dichlorophenoxyacetic Acid on the Accumulation of Mineral Elements in Tobacco Plants.

Since the discovery of the herbicidal action of growth regulators such as 2,4-dichlorophenoxyacetic acid (2,4-D), there has been much information obtained concerning the herbicidal mechanism. The action of 2,4-D on organization, physiology and chemical changes of cells and tissues has been studied (6, 7, 8, 9, 10). Several experimenters (2, 5, 6, 9) on different plants have found that 2,4-D induces rapid depletion of carbohydrate reserves. Some information has been presented on accumulation of mineral elements in plant parts as affected by applications of growth regulators at higher concentrations (5). Less information is available concerning the action of growth regulators on mineral uptake of plants and such information is somewhat contradictory (7, 8, 10). Additional investigation is needed on the effect of soil applications of 2,4-D in herbicidal concentrations on the mineral intake of a vigorously growing plant. Wolf et al (10) reported that higher levels of nitrate in the substrate increased the sensitivity of soybeans to toxic concentrations of 2,4-D. Rhodes, Templeman and Thruston (9) found that rape treated with 2-methyl, 4-chlorophenoxyacetic acid (MCPA) failed to accumulate potassium in the tops altho there was accumulation in tops of untreated plants. There were no observable effects on phosphorus intake. Tomato plants treated with MCPA, accumulated potassium in the roots but not in the tops. The total intake by the entire plant was reduced. Similar but less obvious trends in accumulation of phosphorus and total nitrogen were also noted in tomato plant treated with MCPA. No influence on calcium and magnesium content of treated tomato plants was noted. Wolf et al (10) found that soybeans grown on a high nitrate substrate took up less sulfur and phosphorus when the roots were treated with 2,4-D. They also found potassium content lower and calcium content higher in leaves of treated plants, altho when stem and leaves were combined, differences largely disappeared. Loustalot et al (4) have shown an increase of phosphorus content of white bean plants treated with 2,4-D. Rebstock et al (7) noted that total phosphorus in cranberry bean plants treated with 2,4-D was less than in non-treated plants. Young seedlings of tobacco var. Common Havana were selected for uniformity and planted into eightinch pots of sand to which had been added a complete