Reactions of Decapitated Bean Plants to Certain of the Substituted Phenoxy Compounds

Abstract

Decapitated 2d internodes of the red kidney bean were treated with 4 of the substituted phenoxy compounds (2-chloro-, 4-chloro-, 2,4-dichloro-, and 2,4,5-trichlorophenoxyacetic acids) at 0.5% and 1% concs. in both Carbowax 1500 and lanolin as carriers. Gross responses were limited largely to the region at, and immediately below, the place of application of the mixtures and to the axillary shoots and their leaves, except when the Carbowax mixtures melted and ran down the axis, often over portions of the 1st internode and sometimes the hypocotyl. Swelling and often root development occurred under these areas. Development of axillary shoots was generally retarded and their leaves were frequently dwarfed, mottled, or otherwise deformed. Neither epinasty nor stem curvature occurred nor were any of the plants killed as a consequence of the treatments in these expts. The earliest responses were most evident when lanolin was the carrier, but at 6 days and subsequently the Carbowax mixtures induced greater responses. Endodermis, cambium, phloem, and ray parenchyma were most responsive. Epidermis, outer cortex, and pericycle were generally unresponsive to all the mixtures. Although some roots may develop internal to the cambium following applications of 4-chloro- and 2,4-dichlorophenoxy-acetic acids, well-formed protruded roots were found only following treatment with 2,4-di- and 2,4,5-trichlorophenoxy acetic acids. Although differences in responses between plants in these expts. and those in which the growth regulators were applied to the bases of the heart-shaped leaves may in part be associated with greater age of the decapitated plants when treated, a factor of much greater possible significance may be the association of transport of the growth-regulating substances with the movement of organic food. In decapitated plants little movement of organic food occurs in the treated internode and little movement of the growth substance. This may account for the limited telemorphic effects in decapitated and treated plants as compared with the conspicuous responses when the same substituted phenoxy compounds were applied to the bases of the heart-shaped leaves.