Auxin-like activity of 1,2-benzisothiazole derivatives

The 1,2-benzisothiazol-3-yl-acetic and -3-yl-butyric acids and their ethyl esters, amides and nitriles are generally active in the split pea stem test, induce an increase in both length and fresh weight of pea internodes, inhibit the development of pea roots, and, with some exceptions (1,2-benzisothiazol-3-yl-butyric amide and nitrile), induce the production of ethylene by pea segments. Moreover they stimulate cell multiplication and raise the degree of hydration of Helianthus tuberosus explants grown in vitro. These activities are often similar or sometimes higher than those of IAA. By contrast, the 1,2-benzisothiazole derivatives having a side chain with an odd number of carbon atoms (-3-yl-carboxylic and propionic acids, amides, ethyl esters and nitriles) are inactive or show a far lower activity.