Plants exposed to osmotic stress exhibit changes in their physiology and metabolism. In general, osmotic stress reduces water availability and causes nutritional imbalance in plants. In the present study, we compared the response of cucumber (<em>Cucumis sativus</em> L. var. Władko F-1) to ionic (100 mmol•dm-3 NaCl) and osmotic stress (10% PEG 6000). Both stress factors reduced significantly fresh and dry weight of 7-day-old cucumber seedlings. Under PEG treatment reduction of cucumber dry mass was lesser than in fresh mass, whereas under salt stress decrease in dry weight of cucumber shoots was more pronounced than in fresh mass. Salt stress caused severe decrease in nitrate concentration and activity of nitrate reductase (NR). In cotyledons nitrate content declined to 17% of the control and similar reduction in NR activity was observed. In the roots, observed changes were not so drastic but there was also strong interaction between reduction in nitrate content and NR activity. Under 10% PEG both nitrate concentration and NR activity in cucumber roots were significantly higher in comparison to control plants. In cotyledons NR activity was significantly lower than in control plants, while decrease in nitrate content was not statistically significant. Phosphate concentration did not change significantly in cucumber cotyledons but increased in roots treated both NaCl (32% increase) and PEG (53% increase). Similar tendencies were observed in acid phosphatase activity. Obtained results indicated that osmotic and salt stresses evoke differential responses, particularly in growth reduction and nitrogen metabolism in cucumber seedlings.
Effects of Exogenous Melatonin on the Physiological Characteristics of Kiwifruit Hayward under Salt Stress
