Osmoregulation in the Avena coleoptile in relation to auxin and growth

A study has been made of the effects of auxin and growth on the ability of Avena coleoptile sections to osmoregulate, i.e. to take up solutes so as to maintain their osmotic concentration, turgor pressure, and growth rate. The high auxin-induced growth rate of Avena coleoptiles is maintained when cells are provided sucrose, glucose, NaCl, or KCl as a source of absorbable solutes, but not when 2-deoxy-d-glucose or 3-O-methyl-d-glucose is used. In the absence of auxin, cells take up solutes from a 2% sucrose solution and the osmotic concentration increases. The rate of solute uptake is even greater in the presence of auxin or fusicoccin, but the osmotic concentration rises only slightly because of the water taken up during growth. Solute uptake is not stimulated by auxin when growth is inhibited osmotically or by calcium ions. Solute uptake appears to have two components: a basal rate, independent of auxin or growth, and an additional uptake which is proportional to growth. Osmoregulation of sections may be limited by the rate of entry of solutes into the tissue rather than by their rate of uptake into the cells.