Hyperaccumulation of cadmium by hairy roots of Thlaspi 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 microg 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 microg 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.

Distribution and concentration of cadmium in root tissue of Populus alba determined by scanning electron microscopy and energy-dispersive x-ray microanalysis

“…In turn, this behaviour might highlight differences in the translocation capacity between clones; clone 14P11 being more efficient than clone 6K3 in the translocation process of metal and nu trients from roots to the stem. A delay in Cd transport through membranes inside cells might represent, according to Nedelkoska & Doran (2000), an important defence mechan ism against metal poisoning, enabling simul taneous activation of intracellular detoxifica tion mechanisms of Cd. Cryo-SEM images of frozen-hydrated transversally freeze-fractured young poplar roots did not show, in both clones, any dam age to the whole root structure, such as shrinkage or collapse (Fig.…”

Induction of in vitro roots cultures of Thypha latifolia and Scirpus americanus and study of their capacity to remove heavy metals

“…This response could be a critical defensive strategy of the plant, providing time for the development of intracellular mechanism of metal complexation with specific proteins or sequestration onto the vacuole. In the particular case of Thlaspi caerulescens the analysis of root cell wall fractions revealed that the hairy roots partitioned virtually all the Cd uptake by the biomass in the cell wall fraction for 7 to 10 days before allowing passage into the symplast (Nedelkoska and Doran, 2000). The mechanism of Cd hyperaccumualtion in this species seems to be related to an efficient antioxidative defense, particularly an enhanced catalase activity (Boominathan and Doran, 2003).…”

“…Previous papers have demonstrated the effectiveness of in vitro roots cultures to remove metals (Nedelkoska and Doran, 2000). Yet, the metal concentrations in biomass grown in liquid culture are usually greater than those in soil-grown plants due to the greater bioavailability of metal ions in solution.…”

“…Experiments using separately cultured organs also allow the metal accumulation properties of each organ to be identified. Some examples include the removal of Sr 2+ by shoots of Solanum laciniatum (Kartosentono et al 2001), and hyper-accumulation of Cd by hairy roots of Thlaspi caerulescens (Nedelkoska and Doran, 2000). Another advantages of in vitro cultures is the facility to obtain variants with different tolerance to several biotic stresses (Ben-Hayyim, 1987;Santos-Díaz and Ochoa-Alejo, 1994).…”

Transgenic Plants for Enhanced Phytoremediation – Physiological Studies

“…Experiments had shown that Agrobacterium rhizogenes could enhance the root biomass in some hyperaccumulator plants (Eapen, unpublished work). The hairy roots induced in some of the hyperaccumulators were shown to have high efficiency for rhizofiltration of radionuclide (Eapen et al, 2003) and heavy metals (Nedelkoska and Doran, 2000;Eapen et al, unpublished work). Nowadays there are many different examples o f g e n e s t h a t h a v e b e e n u s e d f o r t h e development of transgenic plants for metal tolerance and/or phytoremediation, as shown on Table 2.…”