RELATIONSHIP BETWEEN MAGNESIUM AND THE PHYSIOLOGICAL EFFECTS OF 2,4-DICHLOROPHENOXYACETIC ACID ON AZOTOBACTER VINELANDII AND RHIZOBIUM MELILOTI

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Abstract
Using conventional Warburg apparatus, the relationship between magnesium concentration of the external environment and the inhibition of the respiration of A. vinelandii and R. meliloti by 2,4-D was tested. In the absence of added Mg it was found that the respiration of cell suspensions proceeded at the usual rate for the respective organisms. In the presence of 1.85 x 10-2 [image] 2,4-D, with no added Mg, respiration was almost completely inhibited. The prior addition of 3.2 x 10-3 [image] MgSO4 to the assay system prevented this inhibition and with this concentration of Mg 3.7 x 10-2 [image] 2,4-D was required to inhibit the respiration. The addition of MgSO4, after the 2,4-D had been allowed to act on the cells, did not reverse the inhibition by 2,4-D. The superimposition of 50 [mu]moles of phosphate with the addition of the 2,4-D enhanced the toxicity of the agent either with or without added Mg; however, the prior addition of Mg afforded protection from the increased toxicity of phosphate and 2,4-D observed in the absence of Mg. An in vitro test, in the absence of cells, demonstrated an interaction between Mg, phosphate, and 2,4-D, by the formation of a precipitate.