Studies on the relationship between potassium and cadmium stress of rice seedlings
Date Issued
2010
Date
2010
Author(s)
Liu, Chun-Hsin
Abstract
In this study, rice [ Oryza sativa L. cv. Taichung Native 1（TN1） or cv. Tainung 67（TNG67）] were used as test materials to investigate（a） the interaction between cadmium ( Cd ) and potassium ( K ) deficiency and （b）the effect of Cd on K uptake in rice seedlings.
It was found that K deprivation in nutrient solution significantly decreased K concentration in shoots, leaves, and roots of rice seedlings, and K-deficient rice seedlings appeared stunting with chlorosis in the second leaves comparing to control seedlings. H2O2 content in leaves and roots of rice seedlings increased under K deficiency. Similarly, the activities of superoxide dismutase（SOD）, ascorbate peroxidase（APX）, glutathione reductase（GR）, and catalase（CAT）increased under K deficiency, whereas the contents of ascorbate and glutathione were not affected. Imidazole（IMD）, an inhibitor of NADPH oxidase, reduced the increase in H2O2 content and SOD, APX, GR, and CAT activities under K deficiency. IMD is an inhibitor of NADPH oxidase which catalyzes H2O2 generation, suggesting that NADPH oxidase is a H2O2 generating enzyme in K-deficient leaves. Our results also suggest that the increase in SOD, APX, GR and CAT activities under K deficiency is mediated through H2O2. In addition, abscisic acid（ABA）contents increased in leaves of rice seedlings grown under K deficiency. Treatment with tungstate, an inhibitor of ABA biosynthesis, also reduced K deficiency-induced H2O2 accumulation and increase of SOD, APX, GR, CAT activities. These results indicate that H2O2 accumulation in the second leaves is related to ABA under K deficiency.
For the subsequent Cd treatment, we found that Cd toxicity in K-deficient leaves was less pronounced than that in K-sufficient leaves, indicating that K deficiency protected from the subsequent Cd toxicity in rice seedlings. However, K-deficient rice seedlings didn’t decrease Cd uptake, indicating that the protection of K deficiency from Cd toxicity in rice seedlings is unlikely due to the reduction of Cd uptake, and is more likely due to the increased activities of antioxidative enzymes.
We used two rice cultivars, TN1 and TNG67, cultivars with different sensitivity to Cd stress, to investigate the effect of Cd toxicity on K uptake. TN1 rice cultivar is Cd sensitive, while TNG67 is Cd insensitive. When rice seedlings were treated with CdCl2, it was observed that Cd treatment resulted in a significant decrease in K concentration in TN1, but not in TNG67. In addition, Cd uptake in TN1 was five times higher than that in TNG67. These results suggest that cadmium toxicity of TN1 seedlings might be resulted from the decrease in K uptake. Therefore, we applied additional treatment of K and Cd at the same time to Cd-sensitive cultivar, TN1, and we found that Cd toxicity was decreased by additional K, which further supports the idea that Cd toxicity of TN1 is a result of subsequent reduction in K uptake.
Subjects
K
Cd
rice
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