Role of antioxidant defense system and biochemical adaptation on stress tolerance of high mountain and steppe plants

Eleven species were collected from Northwest Anatolian Mountains (1500-2000 m) and 18 species were collected from the Central Anatolian steppes (850-1000 m) in June 1998 and 1999. In all the species investigated, the water and dry matter percentages and solute contents were measured. The chlorophyll, beta-carotene, ascorbate and alpha-tocopherol contents and catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) enzyme activities of the plants were also determined. The steppe plants had lower water content compared with alpine plants. The chlorophyll contents of the plants investigated did not change with altitude. However, the carotenoid/chlorophyll ratio of alpine plants was found to be significantly higher. The antioxidant/chlorophyll ratio of the trees and shrubs was higher than that of herbaceous plants. Carotenoid concentrations and SOD activity were higher in alpine plants than in steppe plants. Proline and soluble protein concentrations were significantly higher in alpine plants than in steppe plants. There was a significant difference between the plants as regards to antioxidant capacity at the family level. Though there was a high antioxidant capacity in alpine Poaceae, Lamiaceae species from steppe had very low concentrations of antioxidants. In conclusion, it was shown that although antioxidant protection was important in alpine plants, there were significant differences among the plant species. In addition to antioxidant protection, the higher Soluble protein and proline contents have a very important role in the stress resistance of the alpine plants. (C) 2004 Elsevier SAS. All rights reserved.