AUXIN PRODUCTION IN SEEDLINGS OF DWARF MAIZE

Abstract

Dwarf races of corn are mainly characterized by the length of stem which is, at vegetative maturity, less than 50 per cent, of the length of the normal sibs. It is known that the growth in length of stems, and more especially the elongation of the cells, is regulated by auxin (11). In an earlier paper on dwarfism (8) I stated that nana corn, one of the genetic types of dwarfs, shows its dwarfism even in the seedling stage by its reduced growth of the mesocotyl. It was shown that this reduced growth was attributable to inhibited elongation rather than to a reduced number of cells. Recently Abbe (1) showed that in mature plants of nana and dwarf-1 the number of internodes is the same as in their normal sibs. It is the shorter length of the cells in the ground parenchyma, as well as in the vascular tissue, which accounts for the short stems of the dwarfs. It was demonstrated (8) that 5 days after they were sown in sand in a physiological darkroom, nana plants produce less auxin than do normal ones. It was also shown that the sensitivity to auxin (measured as auxin curvatures) is less in the nana coleoptiles than in the normal ones. Both differences were attributed to the greater destruction of auxin in the nana plants, which was found to be especially high in the mesocotyls. The destruction was thought to be caused by the action of peroxidases, which were found to be much more active in the apical part of the mesocotyl of nana plants than of normal corn. In 1936 a few studies on other plants appeared in which an attempt was made to link dwarfism with auxin. Hinderer (?) showed that hybrids of Epilobium have an auxin production which is smaller the more dwarfed the hybrid is. De Haan and Gorter (4) studied a tall and a shorter variety of Pisum and concluded that the destruction of auxin is the determining factor for the growth of the pea stem, thereby reaching the same conclusion as I had reached for the nana dwarf in corn. (8). The purpose of the present investigation was to study the auxin production in several of the known genetic dwarf races of corn. In order to have comparable controls, seeds were used which segregated either 50 or 25 per cent, dwarfs. The dwarfs of the types here described were easily distinguished from normal control plants 4 days after they had been sown in the darkroom. The seeds were sown and the plants were grown in pure sand (without nutrient solution). The experiments were carried out in the same darkroom where the plants were grown. The temperature was 24? C. and