Root Responses and Metal Accumulation in Two Contrasting Ecotypes ofSedum AlfrediiHance Under Lead and Zinc Toxic Stress

Abstract

Sedum alfredii Hance has been reported to be a Zn-hyperaccumulator plant species. In this study, root morphological and physiological response of the hyperaccumulating ecotype of S. alfredii H. (HE) from the mined area and the non-hyperaccumulating ecotype of S. alfredii H. (NHE) from the agricultural area to supplied levels of Zn and Pb were investigated. The results showed that Zn concentrations in the leaves and the stems of the HE were 34 and 41 times higher, whereas lead concentrations were 1.9 and 2.4 times greater, respectively, than those of the NHE when grown at 1224 microM Zn and/or 200 microM Pb. At combined supply of 1224 microM Zn with 200 microM Pb, however, zinc concentrations in the stems and leaves of the, HE decreased, while lead concentrations in the stems increased significantly, as compared with those of single metal treatment. Lead uptake of the HE was enhanced by Zn addition. Root activity of the HE decreased by Pb treatment in the first two days, but recovered afterward and close to the control at day 10 of the treatment. However, root activity of the NHE decreased by each metal treatment, and was not recovered with the advance of treatment time. Root length, root surface area, and root volumes increased obviously due to Zn and/or Pb/Zn combined treatments for the HE, but significantly decreased due to Pb, Zn, or Pb/Zn combined treatment for the NHE. Zinc and Pb concentrations in both ecotypes of S. alfredii H. were positively correlated with root length, root surface area, and root volumes. Root exudates of the HE, especially treated with Zn, increased the extractability of Pb and Zn from the mined soil. At the Zn supply level of 1224microM, the extractability of root exudates on soil Pb was 3-12 times greater for the HE than for the NHE. These results imply that the tolerance and hyperaccumulation of the hyperaccumulating ecotype of S. alfredii H. to Zn and Pb appear to be closely related to its high adaptation of root growth, morphology, and physiology to Pb and Zn toxicity, and through its root excretion of some special substances that can activate Pb and Zn in the mined soil, thus increasing their mobilization and bioavailability.

Phytoremediation potential of Eichhornia crassipes for the treatment of<br>cadmium in relation with biochemical and water parameters

“…The change in pH may be due to release of some root exudates in response to the stress to adapt itself with the existing environment. Wagner (1997) found that at water temperature of 25 o C, both A. pinnata and A. filiculoides showed maximum growth at pH values from 5-7. pH seems to be the most important parameter in the biosorptive process: it affects the solution chemistry of the metals, the activity of functional groups in biomass and competition of metallic ions (Li et al, 2005). Maximum turbidity was observed as 10.60 on the 12 th day at 75 ppm concentration and a minimum turbidity was observed as 0.75 on the 0 day in control set.…”

“…'b' (Table 2). Chlorophyll content in plants correlates directly to the healthiness of plant (Li et al, 2005). Several cases of decreased chlorophyll content owing to metal toxicity have been reported in the plant kingdom growing in wetland ecosystems (Valavanidis et al, 2005).…”

“…On 12 th day however there was increase in moisture content with the increase in the concentrations of cadmium. The decrease in moisture content in the leaves of E. crassipes at higher levels of CdCl₂ might be due to osmotic stress, which could not be maintained by plant while slight increase at higher levels might be the adaptation of plants to osmotic adjustment, which maintains water uptake and turgor with the accumulation of organic solutes (Li et al, 2005).…”

Changes in root morphology and dry matter production in Pfaffia glomerata (Spreng.) Pedersen accessions in response to excessive zinc

“…This result indicates that the production of biomass is partially dependent of the root length, since higher root length promotes higher uptake of water and nutrients. Li et al (2005) reported that length, surface area and volume of roots of the hyperaccumulator ecotype of Sedum alfredii increased with high levels of Zn, whereas in the non-hyperaccumulator these parameters were significantly decreased. It has been reported that under Zn excess, the DNA synthesis and mitotic activity of root tips may be inhibited, which subsequently results in inhibition of root growth (Jain et al, 2010).…”

“…Several environmental factors influence root morphology, such as metal stress (Li et al, 2005) and nutrient availability (Zhang et al, 2003). The inhibition of root elongation is one of the major responses of plants to excess metals and may occur faster than other physiological responses.…”