2-Chloroethyl Trimethylammonium Chloride and Related Compounds as Plant Growth Substances. V. Growth, Flowering, and Fruiting Responses as Related to Those Induced by Auxin and Gibberellin.

Several compounds closely related to choline and of the structure CHoX-CHo-N+ (CH3)3 * Clare active as plant growth substances when X is a Cl, Br, or = CH2 group (14). Treated plants develop thicker stems, shorter internodes, and intensely dark green leaves (7, 16, 17). The growth changes simulate those caused by exposure of plants to high light intensities, a short photoperiod, and low temperatures. They are opposite to, and more persistent than, those induced by gibberellin. With many plants a stepwise suppression in vegetative extension is possible. Slight, but significant increases in dry matter accumulation occur with tomato plants grown in solution cultures of 10-7 M 2-chloroethyl trimethylammonium chloride (17). Increasing amounts of the chemical cause corresponding reductions in vegetative extension. A consistent acceleration of flowering by tomato plants, however, is obtained over a rather wide range of concentrations which shorten stem length when applied to the root medium. This response is unlike that reported for any other plant growth substance. These unique growth modifying characteristics, the marked specificity of structure for biological activity (14, 15), and the mutually antagonistic effects on vegetative overgrowth from applied gibberellin, suggested the need for further study on several well defined biological systems that respond to gibberellin or auxin. The gibberellins have now been established as naturally occurring plant hormones. Thus, any biochemical explanation of growth and flowering must involve both gibberellin andl auxin. The modifying influences of 2-chloroethyl trimethylammonium chloride and related compounds on some classical auxin and gibberellin responses constitute the subject of this report.