Cadmium sorption to plasma membrane isolated from barley roots is impeded by copper association onto membranes.

The present study was designed to examine the effect of copper (Cu) on sorption of cadmium (Cd) to plasma membrane (PM) preparations as one of the models of competition between metals on root PM. Plasma membrane preparations were obtained from roots of barley (Hordeum vulgare L. cv. Minorimugi) and 50 µM CdSO4 with or without 50 µM CuSO4 were added to the PM suspensions. The sorption of Cd to PM vesicles increased with time within 15 min while Cu sorption to the PM occurred instantaneously. The sorption of Cd to PM vesicles was inactivated immediately after the addition of Cu into the reaction mixture. Results indicate that Cu association to PM vesicles occurs quicker than Cd, and, as a result, impedes the access of Cd to PM vesicles. The present study suggests that the competition between Cd and other minerals at root PM of plants can be demonstrated by employing isolated PM preparations. We consider that the difference in the capacity among some minerals for impeding Cd sorption to PM may also be characterized by investigating the interaction between Cd and other minerals on the PM.

Zinc tolerance and uptake by Arabidopsis halleri ssp. gemmifera grown in nutrient solution.

BACKGROUND, AIM, AND SCOPE: Zinc is an essential micronutrient element but its concentrations found in contaminated soils frequently exceed those required by the plant and soil organisms, and thus create danger to animal and human health. Phytoremediation is a technique, often employed in remediation of contaminated soils, which aims to remove heavy metals or other contaminants from soils or waters using plants. Arabidopsis (A.) halleri ssp. gemmifera is a plant recently found to be grown vigorously in heavy metal contaminated areas of Japan and it contained remarkably high amount of heavy metals in its shoots. However, the magnitude of Zn accumulation and tolerance in A. halleri ssp. gemmifera need to be investigated for its use as a phytoremediation plant. MATERIALS AND METHODS: A. halleri ssp. gemmifera was grown for 3 weeks into half-strength nutrient solution with Zn (as ZnSO(4)) levels ranging from 0.2 to 2,000 microM. The harvested plants were separated into shoots and roots, dried in the oven, and ground. The plant tissue was digested with nitric-perchloric acid, and the Zn concentration in the digested solution was measured by atomic absorption spectrophotometer. RESULTS AND DISCUSSION: The results showed no reduction in shoot and root dry weight when plants were grown at 0.2 to 2,000 microM Zn in the solution. The highest Zn concentration measured in the shoots was 26,400 mg kg(-1) at 1,000 microM Zn, while in the roots, it was 71,000 mg kg(-1) at 2,000 microM Zn treatment. Similar to the Zn concentration in plant parts, maximum Zn accumulation of 62 mg plant(-1) in the shoots and 22 mg plant(-1) in the roots was obtained at 1,000 and 2,000 microM Zn in the solution. The percentage of Zn translocation in shoot varied from 69% to 90% of the total Zn, indicating that the shoot was the major sink of Zn accumulation in this plant. CONCLUSIONS: The results of this study indicate that the growth of A. halleri ssp. gemmifera was not affected by the Zn level of up to 2,000 microM in the nutrient solution. The concentration of Zn found in shoot indicated that A. halleri ssp. gemmifera has an extraordinary ability to tolerate and accumulate Zn and hence a good candidate for the phytoremediation of Zn-polluted soil. RECOMMENDATIONS AND OUTLOOK: Based on the results presented in this study and earlier hydroponics, and field study, A. halleri ssp. gemmifera seems to be a potential heavy metals hyperaccumulator, and could be recommended to use for phytoremediation of Cd- and Zn-contaminated soils.

Incorporation of 15 N and 14 C of methionine into the mugineic acid family of phytosiderophores in iron-deficient barley roots.

The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15 N-ammonium sulfate, 14 C-amino acids, and [1-14 C, 15 N]-methionine to iron-deficient barley roots (Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ-amino butyric acid did not act as precursors of MAs. Carbon-14 and 15 N of methionine were incorporated into MAs. This specific incorporation of 14 C and 15 N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs.