Physiological responses to Cd and Zn in two Cd/Zn hyperaccumulating Thlaspi species (original) (raw)
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PLANTA, 2005
Thlaspi caerulescens (Ganges ecotype) is able to accumulate large concentrations of cadmium (Cd) and zinc (Zn) in the leaves without showing any toxicity, suggesting a strong internal detoxification. The distribution of Cd and Zn in the leaves was investigated in the present study. Although the Cd and Zn concentrations in the epidermal tissues were 2-fold higher than those of mesophyll tissues, 65-70% of total leaf Cd and Zn were distributed in the mesophyll tissues, suggesting that mesophyll is a major storage site of the two metals in the leaves. To examine the subcellular localisation of Cd and Zn in mesophyll tissues, protoplasts and vacuoles were isolated from plants exposed to 50 lM Cd and Zn hydroponically. Pure protoplasts and vacuoles were obtained based on light-microscopic observation and the activities of marker enzymes of cytosol and vacuoles. Of the total Cd and Zn in the mesophyll tissues, 91% and 77%, respectively, were present in the protoplast, and all Cd and 91% Zn in the protoplast were localised in the vacuoles. Furthermore, about 70% and 86% of total Cd and Zn, respectively, in the leaves were extracted in the cell sap, suggesting that most Cd and Zn in the leaves is present in soluble form. These results indicate that internal detoxification of Cd and Zn in Thlaspi caerulescens leaves is achieved by vacuolar compartmentalisation.
New Phytologist, 2007
• In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens.• Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root 109Cd2+ influx were determined.• High-Zn-grown (500 µm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 µm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer 109Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd2+ influx than plants grown on 1 µm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected.• A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens.Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root 109Cd2+ influx were determined.High-Zn-grown (500 µm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 µm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer 109Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd2+ influx than plants grown on 1 µm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected.A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.
Functional Plant Biology, 2006
In order to fully understand the hyperaccumulation process and to increase the potential of plants for phytoextraction purposes, there is a need for more investigation of hyperaccumulating species or populations. Five Swiss populations of Thlaspi caerulescens J. & C. Presl originating from non-metalliferous but naturally Cd-rich soils (1.1–9.2 mg Cd kg–1) were compared with Ganges and Prayon populations and a non-accumulating species, Thlaspi perfoliatum (L.) F.K. Meyer, for their tolerance (shoot and root dry weight and root length) and Cd hyperaccumulation in hydroponics (0, 1, 5, 10, 20 and 50 μm Cd). In the field, the Swiss populations accumulated Zn and clearly hyperaccumulated Cd (up to 505 mg Cd kg–1 dry weight). The general response was significantly different between populations but in general an increasing Cd concentration in solution led to a decrease in dry weight production and an increase in Cd concentration in shoots. The shoot dry weight was a more discriminating par...
Zinc and cadmium uptake by hyperaccumulator Thlaspi caerulescens grown in nutrient solution
Phytoremediation of heavy-metal-contaminated soils can be an inexpensive means to remove hazardous metals from soil. Two metallophytes, Thlaspi caerulescens (J. & C. Presl, a Zn and Cd hyperaccumulator) from Prayon, Belgium, and a Zn-tolerant ecotype of bladder campion [Silene vulgaris (Moench.) Garcke L.] from Palmerton, PA, were compared with tomato [Lycopersicon lycopersicum (L.) Karsten, metal intolerant] in nutrient solution to characterize Zn and Cd uptake and tolerance. Zinc and Cd were added to solutions at a 50:1 molar ratio to simulate concentrations often found on contaminated sites. Seven treatment concentrations were used, ranging (in half-log increments) from 3.16 \aM Zn + 0.063 uM Cd to 10000 uM Zn + 200 uMCd. Thlaspi caerulescens showed much greater tolerance to Zn/Cd treatments than the other species, with toxicity stress only apparent at the 10000 uM Zn/200 uM Cd treatment. In this treatment, shoot concentrations of Zn and Cd were 33600 and 1140 nig kg~', respectively.
Journal of Plant Nutrition and Soil Science, 2013
Glutathione (GSH) and phenolics play an important role in plant defense against metal-ion toxicity. The antioxidant activity and metal-binding capacity of these compounds can account for the protective effects. In contrast to animal-cell models, however, the possible interplay among these substances in stress defense of plants is poorly investigated. This study compares the influence of cadmium (Cd) on the profiles of both soluble phenolics and GSH in shoots of different Thlaspi and Noccaea species: two ecotypes of the nonhyperaccumulator T. arvense differing in Cd resistance (ecotype Aigues Vives, Cd-sensitive, and ecotype Jena, Cd-resistant) and two Cd-tolerant Cd-Zn hyperaccumulators N. praecox and N. caerulescens (formerly Thlaspi praecox and T. caerulescens). To reveal the possible influence of Cd-induced sulfur (S) shortage on the stress response, plants receiving normal S concentrations (500 lM MgSO 4 ) and plants treated with surplus S (500 lM MgSO 4 + 500 lM K 2 SO 4 ) were analyzed. Our working hypothesis was that species differences in tolerance to high tissue Cd concentrations should be reflected by differences in endogenous levels of GSH and phenolic compounds. The results reveal clear species-dependent differences in both the constitutive patterns and the Cd-and S-induced changes in shoot concentrations of GSH and phenolics. However, no simple relationship between these shoot concentrations and Cd accumulation and tolerance can be established.
Plant Science, 2003
Thlaspi caerulescens is one of the best-known heavy metal hyperaccumulating plant species. It exhibits the ability to extract metals from soils and accumulates them in shoots at extremely high concentrations, particularly zinc (Zn) and cadmium (Cd). Using T. caerulescens (J. and C. Presl, ecotype Prayon) and a closely related non-accumulator species T. arvense , greenhouse experiments were carried out to study shoot growth (dry matter production) and Zn and Cd uptake from a severely Zn-deficient calcareous soil (DTPA-Zn: 0.09 mg kg (1 soil) supplemented with increasing amounts of Zn (0, 0.05, 0.5, 5, 25 and 75 mg kg (1 soil) and Cd (0 and 25 mg kg (1 soil). Shoot dry matter production of T. caerulescens was severely depressed by Zn deficiency, while in T. arvense , Zn deficiency slightly reduced growth. At the lowest Zn supplies (0 and 0.05 mg Zn kg (1 soil), T. caerulescens showed very severe Zn deficiency symptoms, including decreased leaf size and development of chlorosis and whitish-brown necrosis on the younger leaves. These symptoms were slight in T. arvense . At the highest Zn supply, leaves of T. caerulescens did not show any symptoms, but in T. arvense there were some necrotic patches on the margins of older leaves, probably due to Zn toxicity. With increasing Zn supply from 0 to 75 mg kg (1 soil, shoot dry matter production was increased by 4-fold in T. caerulescens and only 1.3-fold in T. arvense . Supply of Cd resulted in marked decrease in shoot growth of T. arvense , particularly under low Zn supply, but had no effect on the growth of T. caerulescens . At the low soil Zn levels ( B/0.5 mg Zn kg (1 ) shoot Zn concentrations were lower in T. caerulescens compared with T. arvense , and were below 10 mg Zn kg (1 dry weight. However, at the high supplies of Zn (/5 mg Zn kg (1 ), shoot Zn concentrations were considerably higher in T. caerulescens than T. arvense . Increase in Zn supply from 0 to 75 mg kg (1 enhanced shoot Zn concentrations by 84-fold in T. caerulescens and only 8-fold in T. arvense . Shoot Zn concentrations of both species were not affected by Cd supply, while increase in Zn supply did not affect Cd concentrations in shoot of T. caerulescens , but markedly reduced them in T. arvense. The results demonstrate that T. caerulescens is extremely sensitive to Zn deficiency in soils, but tolerant to excessive accumulation of Zn and also Cd in shoot, while T. arvense is tolerant to Zn deficiency but not to accumulation of Zn and Cd in shoot. Hyperaccumulation of Zn in T. caerulescens possibly depends on the existence of high concentrations of plant-available Zn in soils, which suggests that root-based mechanisms associated with increasing metal availability in the rhizosphere (e.g., rhizosphere acidification or release of Zn-mobilizing organic compounds from roots) only play a minor role in metal hyperaccumulation by T. caerulescens . The findings also suggest that the processes causing the metal hyperaccumulation trait in T. caerulescens also cause this plant species to be sensitive to Zn deficiency stress. #
Planta, 2002
Thlaspi caerulescens (J. & C. Presl, "Prayon") is a heavy-metal hyperaccumulator that accumulates Zn and Cd to high concentrations (40,000 and 4,000 mg kg DW–1, respectively) without phytotoxicity. The mechanism of Cd tolerance has not been characterized but reportedly involves vacuolar sequestration. The role of phytochelatins (PCs) in metal tolerance in T. caerulescens and the related non-accumulator T. arvense was examined. Although PCs were produced by both species in response to Cd, these peptides do not appear to be involved in metal tolerance in the hyperaccumulator. Leaf and root PC levels for both species showed a similar positive correlation with tissue Cd, but total PC levels in the hyperaccumulator were generally lower, despite correspondingly higher metal concentrations. The lack of a role for PCs in the hyperaccumulator's response to metal stress suggests that other mechanisms are responsible Cd tolerance. The lower level of leaf PCs in T. caerulescens also implies that Cd in the shoot is sequestered in a compartment or form that does not elicit a PC response.
Plant Growth Regulation, 2006
Growth, organic acid and phytochelatin accumulation, as well as the activity of several antioxidative enzymes, i.e. superoxide dismutase (SOD), ascorbate peroxidase (APX) guaiacol peroxidase (POX) and catalase (CAT) were investigated under Zn and Cd stress in hydroponically growing plants of Thlaspi caerulescens population from Plombie`res, Belgium. Tissue Zn and Cd concentration increased (the highest concentration of both was in roots) as the concentration of these metals increased in the nutrient solution. Increasing Zn concentration enhanced plant growth, while with Cd it declined compared to the control. Both metals stimulated malate accumulation in shoots, Zn also caused citrate to increase. Zn did not induce phytochelatin (PC) accumulation. In plants exposed to Cd, PC concentration increased with increasing Cd concentration, but decreased with time of exposure. Under Zn stress SOD activity increased, but APX activity was higher at 500 and 1000 lM Zn and CAT activity only at 500 lM Zn in comparison with the control. CAT activity decreased in Cd-and Zn-stressed plants. The results suggest that relative to other populations, a T. caerulescens population from Plombie`res, when grown in hydroponics, was characterized by low Zn and Cd uptake and their translocation to shoots and tolerance to both metals. The accumulation of malate and citrate, but not PC accumulation was responsible for Zn tolerance. Cd tolerance seems to be due to neither PC production nor accumulation of organic acids.
Zinc and cadmium uptake by hyperaccumulator Thlaspi caerulescens and metal …
Environmental Science & …, 1995
Phytoremediation of heavy-metal-contaminated soils can be an inexpensive means to remove hazardous metals from soil. Two metallophytes, Thlaspi caerulescens (J. & C. Presl, a Zn and Cd hyperaccumulator) from Prayon, Belgium, and a Zn-tolerant ecotype of bladder campion [Silene vulgaris (Moench.) Garcke L.] from Palmerton, PA, were compared with tomato [Lycopersicon lycopersicum (L.) Karsten, metal intolerant] in nutrient solution to characterize Zn and Cd uptake and tolerance. Zinc and Cd were added to solutions at a 50:1 molar ratio to simulate concentrations often found on contaminated sites. Seven treatment concentrations were used, ranging (in half-log increments) from 3.16 \aM Zn + 0.063 uM Cd to 10000 uM Zn + 200 uMCd. Thlaspi caerulescens showed much greater tolerance to Zn/Cd treatments than the other species, with toxicity stress only apparent at the 10000 uM Zn/200 uM Cd treatment. In this treatment, shoot concentrations of Zn and Cd were 33600 and 1140 nig kg~', respectively.
Plant and Soil, 2006
The influence of Cd on growth, Cd accumulation and glucosinolate (GS) contents was investigated in Thlaspi praecox in comparison to Thlaspi arvense. Accumulation of up to 2,700 μg Cd g-1 dry weight in shoots of T. praecox, growing in nutrient solution with 50 μM Cd without growth inhibition, confirmed this species as a Cd-hyperaccumulator. Cadmium increased the level of total GS in T. praecox without a statistically significant influence on total sulphur. This increase in GS was due to the enhancement of benzyl-GS, mainly sinalbin. In the Cd sensitive T. arvense Cd caused a shift from alkenyl-GS, mainly sinigrin, to indolyl-GS. The Cd-induced increase of total GS in T. praecox indicates that in this species Cd hyperaccumulation is not linked to trade-off of organic defences. The distinctive influence of Cd on GS profiles in Cd-sensitive T. arvense and Cd-tolerant T. praecox favouring indolyl-GS and benzyl-GS, respectively, is discussed in relation to jasmonate and salicylate as possible key molecules in Cd-stress transduction in these contrasting Thlaspi species.