Effect of cadmium on growth and antioxidant enzymes in two barley cultivars
Tiryakioğlu, Melis (2002) Effect of cadmium on growth and antioxidant enzymes in two barley cultivars. [Thesis]
Cadmium (Cd) pollution is a growing environmental problem affecting human health and crop production. One strategy to minimize adverse affects of Cd toxicity on crop production is to develop plant genotypes having higher genetical ability to tolerate Cd toxicity. In the present MSc study, using two barley (Hordeum vulgare) cultivars (Tokak and Hamidiye) nutrient solution experiments were conducted to study genotypic variation in tolerance to Cd toxicity based on i) development of leaf symptoms and lipid peroxidation, ii) decreases in dry matter production, iii) Cd uptake and accumulation and changes in antioxidative defence system in leaves (i.e., superoxide dismutase, ascorbate peroxidase, glutathione reductase, catalase, ascorbic acid and non-protein SH-compounds). Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentration of Cd (e.g., 0, 15, 30, 60 and 120 ìM Cd) for different periods. The results obtained showed that among the barley cultivars Hamidiye is particularly sensitive to Cd as judged from the severity and development time of Cd toxicity symptoms on leaves. Within 48 h Hamidiye developed very rapidly and severely leaf symptoms of Cd toxicity while in Tokak the leaf symptoms of Cd toxicity appeared only slightly. Hamidiye also tended to show stronger decreases in growth caused by Cd supply for 48 h. Cadmium supply enhanced the level of lipid peroxidation in Hamidiye, but remained without effect in Tokak. The differences in sensitivity to Cd between Tokak and Hamidiye were not related to Cd concentrations in roots or shoots. Both barley cultivars were more or less similar in both concentration and accumulation (amount of Cd per plant) of Cd. The activities of enzymes involved in detoxification of hydrogen peroxide in chloroplasts and the activity of superoxide dismutase, scavenger of superoxide radical, were markedly enhanced in Hamidiye by increasing Cd supply. However, in the case of Tokak there was either only a slight increase or no change in the levels of the enzymes. Interestingly, in both barley cultivars the activity of catalase was not influenced by Cd supply, indicating a particular affect of Cd on defence enzymes located in chloroplasts. The results indicate existence of a large genotypic variation between barley cultivars for Cd tolerance. The differential Cd tolerance found in the barley cultivars was not related to uptake or accumulation of Cd in plants, indicating importance of internal mechanisms in expression of differential Cd tolerance in barley. Particular increases in antioxidative mechanisms in Cd-sensitive barley cultivar Hamidiye as a response to increasing Cd supply suggest that high Cd sensitivity of Hamidiye is related to enhanced production and oxidative attack of reactive oxygen species (ROS).
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