No abstract

Heavy metal pollution has potential hazards to plant, animal, and human health, and phytoremediation is recognized as a safe and efficient technique for the revegetation of heavy-metal-polluted soil. Macleaya cordata was found in heavily tailing areas with fast growth rates, large biomass, and huge taproots. In our study, the seedlings of M. cordata were exposed to cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) in a Hoagland solution. After 20 days, the tolerance index as well as the content and distribution of Cd, Pb, Cu, and Zn in roots, stems, and leaves were determined. The results showed M. cordata had higher tolerance to Pb and Zn than to Cd and Cu under hydroponic culture conditions. Pb and Cu mainly accumulated in the roots, and the translocation efficiency to the shoots was very low, while about three-quarters of Zn concentrations in the plants were accumulated in the shoots; even the Cd content per shoot of M. cordata exceeded some Cd hyperaccumulators. In the present study, the metal ions in the roots or leaves of M. cordata were firstly determined in situ using dithizone staining, and the degree of root-tip staining was consistent with the amountof the total metal content in the roots. The addition of Zn or Cu in the Pb treatment solution increased the Pb content in the stems and leaves of M. cordata, while the addition of Zn or Cu in the Cd treatment solution had the opposite effect. Pb or Cd in the compound treatment decreased the Zn content in all parts of M. cordata. Our results suggest that Pb can be transported above ground via some special pathways in M. cordata. The different absorption and transport mechanisms of M. cordata in relation to Cd, Zn, Cu, and Pb can be important for the plant to be applied for the remediation of compound-polluted soil or water.

Cadmium (Cd) and excess copper (Cu) are toxic to plants, causing a wide range of deleterious effects including the formation of reactive oxygen species. Metallothioneins (MTs) may protect plant cells from heavy metal toxicity by chelating heavy metals via cysteine thiol groups. They may also function as antioxidants. The study investigated the relationship of H 2 O 2 production and ricMT expression in rice radicles and rice suspension cells under Cu or Cd stress. The results showed that H 2 O 2 production in the rice radicles increased before Cu-induced ricMT expression, and after Cd-induced ricMT expression. Rice suspension cells of sense-and antisense-ricMT transgenic lines were obtained by an Agrobacterium-mediated transformation. Overexpression of ricMT significantly decreased the death rate of rice cells, which was accompanied by blocked H 2 O 2 accumulation in rice suspension cells subject to Cu and Cd stress. Our findings confirm that H 2 O 2 is involved in the MT-mediated tolerance of Cu and Cd toxicity in rice.

Heavy metal pollution possesses potential hazards to plant, animal and human health, which has become the focus of recent attention. Hence, phytoremediation has been regarded as one of the most important remediation technologies for heavy-metal-contaminated soils. In this research, a dominant mine tailing plant, Macleaya cordata, was used as the experimental material to compare the metal transport and oxidative stress response in its roots under lead (Pb) and zinc (Zn) treatments. The result showed that Pb was mainly accumulated in the roots of M. cordata under the Pb treatment; less than 1% Pb was transported to the parts above. An analysis of the Zn content demonstrated a 39% accumulation in the shoots. The production of reactive oxygen species was detected using the in situ histological staining of roots, which showed that hydrogen peroxide in the root tips was observed to increase with the increase in both Pb and Zn concentrations. No significant superoxide anion changes were noted in the root tips under the Pb treatment. An analysis of the root enzyme activity showed that increase in NADPH oxidase activity can be responsible for the production of superoxide anions, subsequent the inhibition of root growth and decrease in antioxidant enzyme activities in the roots of M. cordata exposed to excess Zn. In total, this research provides evidence that the root of M. cordata has a high antioxidant capacity for Pb stress, so it can accumulate more Pb without oxidative damage. On the other hand, the Zn accumulated in the roots of M. cordata causes oxidative damage to the root tips, which can stimulate more Zn transport to the shoots to reduce the damage to the roots. This result will provide a basis for the application of M. cordata in the phytoremediation of soil polluted by Pb-Zn compounds.