Auxin-induced Reversal of Geotropic Response in Onion Seedlings

Abstract

IN the course of an investigation concerning the germination of onion seeds and subsequent growth of seedlings in aseptic cultures, a striking and unique response to auxin was observed. In normal germination, as observed in Nature or on the basal medium (comprising Heller's minerals and 5 per cent sucrose solidified with 0.7 per cent agar), there is an intercalary elongation of the cotyledon resulting in the emergence of the root and the shoot apex. Due to a curving of the cotyledon the radicular end is carried downward and thus the seedling is established in the soil or on a synthetic nutrient medium. The free end of the cotyledon remains inserted in the seed coat and, as it elongates farther, the seed coat is lifted from the substratum (Fig. 1A).