Thesis

The effects of 2,4-D on a species of the Green Alga Carteria

Ever since the discovery of 2,4-Dichlorophenoxyacetic acid (2,4-D) as an effective herbicide during World War II, extensive research effort has been directed to all aspects of this synthesized subs tame that behaves in some respects similar to plant auxin. First, attention was focused on the selective effect; and it became known that 2,4-D was a very effective killer of the broad-leaved plants while it did not affect the grasses and many other monocots in any way at certain concentrations. It also came to be known that three processes were involved in the herbicidal action of the suxi1u, the material entered the plant; it then was translocated throughout the plant; and toxic actions took place at the level of cellular metabolism (Machlis and Torrey, 1936). Many reports on the effects of 2,4—D on physiological and biochemical processes of plants can be found in the literature. Among them are those that Indicate the inhibitory effect on photosynthesis of plants (Wedding et al., 1954, Erickson et al., 1955), and those that show 2,4-D to be stimulatory to plant respiration (Overbeek et al., 1951; Wedding et al., 1954; Humphreys and Dagger, 1957). Mitochondria from soybeans sprayed with 2,4-D have been observed to swell accompanied by increases in rates of phosphorylation and oxidation (Key et al., 1961), Other reports indicate that 2,4-D stimulates cell proliferation (Steward, 1963), promotes carbohydrate depletion (Rasmuseen, 1947), Inhibits lipase activity (Bagen et al. 1949), Inhibits ascorbic acid oxidase (West and Henderson, 1950), and stimulates phosphatase activity (Overbeek et al., 1951). All these experimental reports represent an effort toward the elucidation of the mechanism with which 2,4-13 operates as a herbicide. How we may ask; How is the concentration of 2,4-D related to its herbicidal action? Is it the undis-sociated molecules, or the charged anions, that penetrate the cell membrane? Adequate answers to these questions will provide clues as to how 2,4-D in particular and auxin in general affect the physiological processes of plants.

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