Comparison of Growth Responses Induced in Plants by Naphthalene Acetamide and Naphthalene Acetic Acid

Abstract

1. A comparison was made of some of the responses of certain plants when treated with naphthalene acetamide and naphthalene acetic acid. 2. Naphthalene acetamide caused growth curvatures when used in the pea test, and in Avena coleoptiles when applied unilaterally in the form of a 0.02 per cent lanolin mixture. When applied to coleoptiles in relatively low concentrations (250 gamma per liter), using the usual Avena test with agar blocks, the acetamide failed to give growth curvatures. Naphthalene acetic acid caused growth curvatures in both the pea and Avena test at concentrations of 1 mg. per liter and 250 gamma per liter, respectively. 3. Unilateral applications of lanolin containing naphthalene acetamide (2 per cent) on stems of etiolated pea and kidney bean plants resulted in negative curvatures. No apparent curvatures resulted when the stems of four o'clock, soybean, and tomato plants grown in natural light were treated unilaterally with acetamide. Petunia and kidney bean plants treated in this manner showed slight negative curvatures. Applications of a 2 per cent mixture of lanolin and naphthalene acetic acid resulted in first negative then positive bending in all except kidney bean plants grown in light. Negative curvatures were interpreted as resulting from initially low concentrations of the acid. Growth was apparently inhibited, on the side of the stem nearest the application, as the concentration of acid in the tissues became greater. 4. Naphthalene acetamide and naphthalene acetic acid were applied to bean plants in the form of emulsion sprays. Both compounds inhibited development of the terminal buds and expansion of primary leaves when used in strong concentration. The acetamide stimulated root growth over that of untreated plants while the acid was ineffective in this respect. The less concentrated acetamide sprays accelerated top growth to some extent while the acid sprays had no noticeable effect. 5. Terminal applications of 2 per cent lanolin-naphthalene acetamide or naphthalene acetic acid mixture to decapitated beans or lateral applications on the stems resulted in mobilization of solid materials toward the treated region. Mobilization was associated with appreciable secondary thickening in plants treated with naphthalene acetamide, and with marked cellular proliferation when naphthalene acetic acid was applied.