Production of low-molecular weight thiols as a response to cadmium uptake by tumbleweed ( Salsola kali)

Abstract

Tumbleweed ( Salsola kali) is a desert plant species that has shown to be a potential Cd hyperaccumulator. In this study, the production of low-molecular weight thiols (LMWT) as a response to cadmium stress was determined in hydroponically grown seedlings exposed to 0, 45, 89, and 178 μM Cd 2+. The treatment of 89 μM Cd 2+ was tested alone and supplemented with an equimolar concentration of ethylenediaminetetraacetic acid (EDTA) to determine the effect of this chelating agent on Cd uptake and thiols production. After 6 days of growth, the Cd concentration in plant tissues was determined by using inductively coupled plasma/optical emission spectroscopy (ICP/OES). Results indicated that Cd uptake by plants was concentration-dependent. Plants treated with 178 μM Cd 2+, had 10 ± 0.62, 9.7 ± 1.4, and 4.3 ± 0.83 mmol Cd kg –1 dry tissue in roots, stems, and leaves, respectively. The production of thiols was dependent on Cd concentration in tissues. According to the stoichiometry performed, plants treated with Cd concentrations up to 178 μM produced 0.131 ± 0.02, and 0.087 ± 0.012 mmol SH per mmol Cd present in roots and stems. In leaves, the production of thiols decreased at the highest Cd concentration tested. Thus, up to 89 μM Cd in the media, 0.528 ± 0.004 mmol SH per mmol Cd in leaf tissues were produced. EDTA equimolar to Cd reduced both Cd uptake and thiols production. Catalase activity (CAT) (EC 1.11.1.6) was significantly depressed at the lowest Cd concentration. None of the conditions tested affected biomass or plant elongation.