New Phenolic Plant Growth-regulating Compounds

Abstract

IT has been reported that 2,6-dichlorophenol and the corresponding dibromo- and diiodo- compounds show appreciable activity in promoting cell elongation when examined in the pea segment and pea curvature tests, and that they induce severe epinastic responses when applied through the soil to tomato plants¹. Further work has now revealed other 2,6-substituted phenols which are active in these tests. Thus, in the pea tests, 2-chloro-, 2-bromo- and 2-iodo-6-nitrophenols possess activities approaching that of 2,4-dichlorophenoxyacetic acid (2,4-D); the corresponding 6-cyanophenols are also active (Table 1). 2-Methyl-6-nitrophenol is inactive in the pea tests over the concentration range investigated, but replacing the methyl by trifluoromethyl, a strongly electron-attracting group, confers appreciable activity (Table 1). 2,6-Dinitrophenol is very phytotoxic and was reported inactive in our earlier tests¹. At very small concentrations, however, it does show activity in the two pea tests, although it is completely inactive in the wheat cylinder test. (For details of all bioassay methods used see Fawcett et al.².)