Physiological effects of cadmium and UV-B radiation in phytochelatin-deficient Arabidopsis thaliana, cad1-3

Abstract

Plants are most often exposed to multiple environmental stress, rather than single stress phenomena. Therefore, the aim of this study was to investigate plant response to two potential stress factors. We also wished to determine whether one of the stress factors would be dominant, and to assess the outcome in terms of the importance for plant survival. Arabidopsis thaliana L. plants were subjected to both enhanced levels of cadmium (Cd) and ultraviolet-B (UV-B, 280–315 nm) radiation. Wild type plants and a phytochelatin (PC)-deficient mutant, cad1-3, were used. To assess the contribution of Cd and/or UV-B to plant stress, chlorophyll fluorescence, oxygen (O 2 ) evolution, pigment content and Cd and nutrient content were measured. Cadmium inhibited O₂ evolution at irradiances above growth light in both wild type and cad1-3. In the latter, photochemical yield (Φ_p ) was lowered by Cd, and was accompanied by a decreased and light-independent non-photochemical quenching (NPQ), whereas UV-B radiation did not influence these parameters when applied alone. In combination with Cd, UV-B radiation resulted in no detectable change as compared with results with only Cd exposure. The effect of Cd on the content of essential nutrients was analysed by inductively coupled plasma emission (ICP), which showed that Cd and zinc (Zn) were significantly lower in both the root and shoot of cad1-3, compared with the wild type. In roots, the content of potassium (K), magnesium (Mg) and sulfur (S) was significantly lower in cad1-3 than in wild type, whereas Cd or Cd + UV resulted in higher calcium (Ca) amounts in cad1-3. Compared with Cd alone, the Cd + UV treatment reduced the content of Ca in wild type roots. Supplemental UV-B radiation decreased the content of Mg and S; otherwise Cd was the stronger stress factor, generally overriding the sometimes stimulatory effect of the UV-B radiation.