Abstract
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.
Highlights
Salinity and drought are important stress factors that limit plant growth and development
Obtained values were analysed statistically using least significant difference (LSD, p=0.01). Both stress factors (NaCl and PEG) caused significant decrease in growth parameters (Fig. 1) plant growth was more reduced by salinity than PEG
Fresh weights of cucumber roots grown under PEG and NaCl were respectively 32 and 54% lower than in control plants
Summary
Salinity and drought are important stress factors that limit plant growth and development. Osmotic stress reduces water availability and causes nutritional imbalance in plants (ion excess or deficit) (Grattan and Grieve 1999). To maintain turgor and prevent water losses, plant cells must readjust their osmotic potential. This can be achieved by uptake of inorganic ions from external solution or synthesis and accumulation of organic compounds (compatible solutes). It is well known that in salinized media the uptake of mineral nutrients is inhibited This negative effect includes the uptake of nitrogen which is quantitatively the most important for plant. It was reported that salinity induces phosphorus deficiency in some plants and this effect may reduce the cellular tolerance for ion accumulation under salt stress (Gibson 1988; Kaya et al 2001). Some investigators maintain that adequate phosphorus nutrition may minimize salt toxicity and ameliorate negative effects of water stress (Kaya et al 2001; Shubhra et al 2004)
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