BIOAVAILABILITY OF CADMIUM 
    Cation Exchange Capacity (CEC)
    pH
    Soil Amendments
    Competitive Cations
    Fertilizer
    Mycorrhizae
    Chelation
       Phytochelatins (PCs)
       Phytochelatin Effectiveness
       Role of Sulfur in PCs
       Oxidative Stress
       Translocation
       Metallothioneins
       Organic Acids
       EDTA / EGTA

CADMIUM TOLERANCE AND
ACCUMULATION IN PLANTS
    Cell Wall Binding
    Reduced Transport
    Compartmentalization
    Chelation
    Phytoextraction factors
       Table 1.  Plant Accumulation
       Hyperaccumulators

CONCLUSIONS

LINKS

BIBLIOGRAPHY
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Hyperaccumulators

     Some plants have demonstrated a remarkable ability to accumulate  several hundred times more metal in shoot tissue than most plants. Hyperaccumulation involves translocating metals from soil to shoot tissue in excess of 100 mg Kg-1 Cd, 1000 mg Kg-1 Ni or 10,000 mg Kg-1 Zn (Baker and Brooks, 1989). Unfortunately, hyperaccumulation is often linked with slow growth rate and low biomass production, such that net removal of metal contaminants via phytoextraction may not exceed that of normal accumulators that produce large biomass. 
 
     The hyperaccumulation feature of some plants is curious. Why would a plant have a mechanism to uptake extremely high levels of metals for which there is no biological function? Suggested explanations of hyperaccumulation include protection from predators and pathogens, an effective method of tolerating high soil-metal concentrations and a by-product of an aqcuisition mechanism designed to scavenge limited nutrients (Kramer, 2000). 
 
     One of the most promising Cd hyperaccumulators is Thlaspi caerulescens, a small forbe found in several parts of Europe. Many have been found growing on heavily contaminated soils near smelters. Different strains have been found and studied which apparently have different hyperaccumulating "specialties". Different species of Thlaspi have been found to hyperaccumulate Zn, Ni, Pb and Cd (Baker and Brooks, 1989). Baker (1994) found Cd accumulation in a population of T. caerulescens from Whitesike, Britain of 164mg Kg-1. Brown, et al. (1995) reported Cd accumulation in leaves of 29 mg Kg-1 from a population at Prayon, Belgium. Lombi, et al. (1999) examined a population of T. carulescens from the Cevennes region in southern France and found Cd accumulation in shoots at a level much higher than the Prayon or Whitesike populations at 500 mg Kg-1 (50% extraction of available Cd in soil). It should be noted that all of these experiments were carried out under different conditions, and are not directly comparable. Nevertheless, Lombi, et al. (1999) did directly compare the three populations and found the French population to be a superior hyperccumulator of Cd. 
 
     A drawback to the use of T. caerulescens is that it has a rosette growth form and produces very little biomass. The importance of its discovery lies more in understanding the hyperaccumulation mechanism with an eye towards genetically manipulating other plants to do the same. 
 

Previous                    Next