Osmotic Stress-Induced Growth Suppression of Dark-Grown Wheat (Triticum aestivum L.) Coleoptiles

Abstract

Application of 60 mM polyethylene glycol (PEG) to dark-grown wheat (Triticum aestivum L.) roots substantially reduced growth of coleoptiles. However, when PEG was removed, the growth rate of these coleoptiles greatly increased. Cell walls of stressed coleoptiles remained loosened as compared with those of unstressed ones. The osmotic potential of the stressed coleoptiles decreased to that of the 60 mM PEG solution. On the other hand, the extent of decrease in the osmotic potential of stressed roots was smaller than that of stressed coleoptiles. The osmotic potential difference (An) between the cell sap and the incubation medium of stressed roots was substantially higher than that of unstressed ones. The amount of ink moved from roots, where it was applied, to the apical region of coleoptiles was significantly reduced under osmotic stress conditions. When water was exogenously applied to abraded coleoptiles, the growth of these stressed coleoptiles was greatly promoted. These results suggest that inhibition of coleoptile growth under osmotic stress conditions is not directly related to a decrease in cell wall extensibility or to loss of the capacity to maintain osmotic potential gradients, but is caused by the reduction of the water supply from the roots to the coleoptiles.