Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision

Abstract

The correlation between osmotic potential and epicotyl growth in intact and decotyiized mung bean seedlings (Vigna radiata (L.) Wilczek) grown under osmotic stress was studied. The following results were obtained: 1) Epicotyl elongation in intact seedlings grown in vermiculite containing 0.2 M mannitol was not substantially affected, but was strongly inhibited in decotylized ones. 2) Osmotic potential in the epicotyl was. decreased by osmotic stress due to 0.2 M mannitol, and was increased by cotyledon excision. 3) Epicotyl elongation was well correlated with net osmotic concentration, which is. the difference in osmotic concentration between the vacuolar sap of epicotyl cells and the 0.2 M mannitol added to the vermiculite. The net osmotic concentration was also correlated with cell elongation, but not with cell division in the epicotyl. 4) The concentrations of soluble sugars, free amino acids and potassium ions in the epicotyl increased in response to osmotic stress. Cotyledon excision decreased the concentrations of soluble sugars and free amino acids, while it had no effect on potassium ion concentration.Based on these results, a role of osmoregulation in regulating epicotyl growth of mung bean is discussed in relation to osmotic stress and cotyledon excision.