Abstract
In this study, investigated were the effects of NaCl (60 mmol/dm<sup>-3</sup>) and NaCl supplemented with different salts (5 mmol/dm<sup>-3</sup> CaCl<sub>2</sub>, CaSO<sub>4</sub>, CaCO<sub>3</sub>, KCl), on growth of two maize varieties (Cyrkon and Limko). After 7 days of cultivation in nutrient solution the growth response to salinity of both maize varieties was similar. NaCl led to a dramatic decrease in growth of plants (approx. 50% reduction in fresh and dry weight of root, and 70% reduction in fresh weight of shoot). Addition of extra Ca<sup>2+</sup> or K<sup>+</sup> to nutrient solution containing NaCl did not definitely improve the growth parameters of maize. However, among the tested salts, CaCl<sub>2</sub> had a beneficial visual effect on maize seedlings. In other cases the plants showed noticeable symptoms of salt damage. In long term exposure to salinity (two weeks) growth of Cyrkon was more inhibited than Limko. Comparison of growth responses in short-term exposure to salinity (7 days) with long-term (14 days) showed that in Cyrkon variety the negative effects of NaCl were intensified and addition of CaCl<sub>2</sub> to salinized solution had not positive effects on growth. On the contrary, in Limko variety, there was a significant improvement in growth (especially in root dry weight). This fact indicates that during longer exposure to salinity Limko was able to adapt to those conditions. Salinity caused a significant decrease in leaf nitrate reductase activity (60% and 30% reduction respectively in Limko and Cyrkon). Addition of CaCl<sub>2</sub> to salinized nutrient solution resulted in greater enzyme inhibition in Cyrkon (50% decline in relation to plants grown under sole NaCl), and 30% increase in Limko. Inhibition of nitrate reductase activity did not cause a decrease in concentration of soluble protein in maize leaves.
Highlights
Excessive soil salinity is one of the important factors that limit plant growth and productivity
In our previous study (Saca3a et al 2002), we have shown that both growth of maize seedlings and nitrate reductase are sensitive to mild salinity
We examined the combined action of NaCl and CaCl2 on nitrate reductase activity and soluble protein content in maize leaves
Summary
Excessive soil salinity is one of the important factors that limit plant growth and productivity. Under saline condition plants are subjected to both osmotic stress (reduction in water availability) and excessive amount of salt (Na+ and Cl- toxicity) (Greenway and Munns 1980; Munns 1993, 2002). When exposed to salinity for a short time, growth of plant is limited predominantly by the osmotic effect of salts in soil solution. To overcome osmotic stress same plants use Na+ and/or Cl- for osmotic adjustment (Greenway and Munns 1980; Leidi and Saiz 1997). Such ions are energetically efficient osmolytes, but they can have serious effects on plant metabolism. Some scientists have suggested that application of extra K+ can reduce deleterious effects of salinity (Helal and Mengel 1979) and plant tolerance towards salt stress correlates with K+ content in plant tissues (Zhu et al 1998)
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