Hyperaccumulation of cadmium by hairy roots ofThlaspi caerulescens

Abstract

Hairy roots were used to investigate cadmium uptake by Thlaspi caerulescens, a metal hyperaccumulator plant with potential applications in phytoremediation and phytomining. Experiments were carried out in nutrient media under conditions supporting root growth. Accumulation of Cd in short‐term (9‐h) experiments varied with initial medium pH and increased after treating the roots with H+‐ATPase inhibitor. The highest equilibrium Cd content measured in T. caerulescens roots was 62,800 μg g−1 dry weight, or 6.3% dry weight, at a liquid Cd concentration of 3710 ppm. Cd levels in live T. caerulescens roots were 1.5‐ to 1.7‐fold those in hairy roots of nonhyperaccumulator species exposed to the same Cd concentration, but similar to the Cd content of autoclaved T. caerulescens roots. The ability to grow at Cd concentrations of up to 100 ppm clearly distinguished T. caerulescens hairy roots from the nonhyperaccumulators. The specific growth rate of T. caerulescens roots was essentially unaffected by 20 to 50 ppm Cd in the culture medium; in contrast, N. tabacum roots turned dark brown at 20 ppm and growth was negligible. Up to 10,600 μg g−1 dry weight Cd was accumulated by growing T. caerulescens hairy roots. Measurement of Cd levels in whole roots and in the cell wall fraction revealed significant differences in the responses of T. caerulescens and N. tabacum roots to 20 ppm Cd. Most metal was transported directly into the symplasm of N. tabacum roots within 3 days of exposure; in contrast, T. caerulescens roots stored virtually all of their Cd in the wall fraction for the first 7 to 10 days. This delay in transmembrane uptake may represent an important defensive strategy against Cd poisoning in T. caerulescens, allowing time for activation of intracellular mechanisms for heavy metal detoxification. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 67: 607–615, 2000.

Role of Phytoremediation in Reducing Cadmium Toxicity in Soil and Water

“…The translocation of Cd from solution to upper portions and its concentration of shoots of T. caerulescens was remarkably high [ 84 ]. The hairy root culture of T. caerulescens also showed remediation of Cd from its aqueous solution [ 116 ]. These results confirmed T. caerulescens as a hyperaccumulating plant for the remediation of Cd pollution.…”

“…The mechanism of accumulation and antioxidative metabolism to tolerate Cd by hairy roots of T. caerulescens revealed that Cd metal-induced stress in tissues [ 116 ]. The factors like pH and H + -ATPase inhibitor enzyme affected Cd hyperaccumulation.…”

Target or barrier? The cell wall of early- and later-diverging plants vs cadmium toxicity: differences in the response mechanisms

“…There are many examples of hyperaccumulators and, as the study is continuing, new species are added to this list. The root hairs of T. caerulescens , a metal hyperaccumulator, can accumulate consistent levels of Cd in their cell walls thereby preventing Cd from penetrating in the cytoplasm (Nedelkoska and Doran, 2000). Massive accumulation of Cd in hyperaccumulator plants is also based on complexes with phosphates within the cell wall.…”

Agrobacterium rhizogenes mediated genetic transformation resulting in hairy root formation is enhanced by ultrasonication and acetosyringone treatment

“…A. rhizogenes are also capable of transferring the T-DNA of binary vectors in trans, thereby facilitating the selection of transgenic plants from screened hairy roots (Christey, 2001). Agrobacterium rhizogenes mediated transformation system was found to be very useful in genetic manipulation of plants for the production of phytochemicals (Shanks and Morgan, 1999), large scale secondary metabolite production (Choi et al 2000), monoclonal antibody production (Wongsamuth and Doran, 1997) and phytoremediation (Nedelkoska and Doran, 2000). There are many reports that suggest the successful use of A. rhizogenes harbouring binary vectors with desired gene constructs (Christey, 2001) for plant genetic transformation.…”