Promotion of Growth and Hydrogen Ion Efflux by Auxin in Roots of Maize Pretreated with Ethylene Biosynthesis Inhibitors

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Abstract
Low concentrations of auxin (e.g. 10−10m) do not promote the growth of intact seedling roots of maize (Zea mays L. Bear Hybrid WF 9 × 38). Higher concentrations are inhibitory. When the roots are pretreated with the ethylene biosynthesis inhibitors, cobalt and aminoethoxyvinylglycine, auxin (10−10 to 10−8m) strongly promotes their growth. The promotion of growth by auxin in pretreated roots is preceded by enhanced hydrogen ion secretion from the roots. The data indicate that hormone-enhanced hydrogen ion secretion may play a role in the rapid promotion of root growth by auxin. The ability of auxin to promote the growth of intact roots is discussed in relation to the Cholodny/Went hypothesis of hormonal control of root geotropism.