THE RELATION BETWEEN THE FOUR-CARBON ACIDS AND THE GROWTH OF OAT SEEDLINGS

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Abstract
The effects of adding auxin and fumarate (which increase the activity of this system) and iodoacetate (which poisons this system) to the growing plants were detd. Growth of the coleoptile is stimulated by the auxin in the seedling itself. When plants (of the var. Fulghum) were grown in various concs. of iodoacetate, coleoptile growth was inhibited, the highest concs. (0.00005-0.0001 M) resulting in a final size of but 50% normal. The addition of auxin, and to a greater extent, of fumarate, negated the iodoacetate poisoning. In contrast to the coleoptile, the growth of oat roots is known to be inhibited by the presence of applied auxin (10 mg. per liter). In the presence of iodoacetate this inhibition was partially removed, and conversely the inhibition was greatly magnified in the presence of fumarate. Root number, which like the coleoptile length gives a positive response to this conc. of auxin, behaved like the coleoptile toward iodoacetate and fumarate. It has been suggested by Thimann that all organs show a similar response to auxin, the direction of the effect being a function of auxin concn. Thus, low concs. stimulate, higher concs. give an optimum plateau, and even greater concs. inhibit. The different effect of the same auxin conc. on different organs is accounted for by the displacement of each of these curves along the auxin conc. axis, and also by the intrinsic auxin present in the particular species or var. Testing the effect of various concs. of iodoacetate on these phenomena confirmed and extended this interpretation. When iodoacetate and auxin conc. are plotted in opposite directions on the same abscissa, and the effect on the ordinate, it is possible to produce the hypothetical curves relating effect to active auxin conc.

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