| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
First published online June 12, 2003; 10.1104/pp.103.021741 Plant Physiology 132:1600-1609 (2003) © 2003 American Society of Plant Biologists The Distribution of Arsenate and Arsenite in Shoots and Roots of Holcus lanatus is Influenced by Arsenic Tolerance and Arsenate and Phosphate SupplyThe University of Western Australia, Soil Science and Plant Nutrition, School of Earth and Geographical Sciences, 35 Stirling Highway, Crawley WA 6009, Australia
The recent discovery that phytochelatins are important for arsenic (As) detoxification in terrestrial plants results in the necessity to understand As speciation and metabolism in plant material. A hydroponic study was therefore conducted to examine the effects of different levels of phosphate and arsenate [As(V)] on As speciation and distribution in tolerant and non-tolerant clones of Holcus lanatus. Speciation of As in tissue (using high-performance liquid chromatography-inductively coupled plasma mass spectrometry) revealed that the predominant species present were the inorganic As species (As(V) and arsenite [As(III)]), although small levels (<1%) of organic As species (dimethylarsinic acid and monomethylarsonic acid) were detected in shoot material. In roots, the proportion of total As present as As(III) generally increased with increasing levels of As(V) in the nutrient solution, whereas in shoots, the proportion of total As present as As(III) generally decreased with increasing levels of As(V). H. lanatus plants growing in the high-phosphorus (P) (100 µM) solution contained a higher proportion of As(V) (with regard to total As) in both roots and shoots than plants supplied with low P (10 µM); in addition, tolerant clones generally contained a higher proportion of As(V) with regard to total As than non-tolerant clones. The study further revealed that As(V) can be reduced to As(III) in both roots and shoots. Although the reduction capacity was limited, the reduction was closely regulated by As influx for all treatments. The results therefore provide a new understanding about As metabolism in H. lanatus.
Arsenic (As) is widely distributed in the environment, originating either from As in the soil parent material or from discharge of As onto land as a result of human activities. Consequently, people and livestock are being exposed to As via contamination of drinking water and consumption of food grown in As-contaminated soil or irrigated with As-contaminated water. Understanding how As is taken up by plants and subsequently transformed in plant tissue is therefore essential for estimating the risks posed to human and wildlife populations by As-contaminated soils (Meharg and Hartley-Whitaker, 2002  ).
In aerobic soils, arsenate [As(V)] is the most thermodynamically stable and
hence dominant species. The uptake of As(V) by plants has been studied
extensively (Hurd-Karrer,
1939
In terrestrial plants, both organic and inorganic As species have been
found (Van den Broeck et al.,
1998
Both inorganic As species, As(V) and As(III), are highly toxic to plants.
As(V) is a phosphate analog, and therefore it can compete with phosphate in
the cytoplasm, replacing phosphate in ATP to form unstable complex ADP-As,
which leads to the disruption of energy flows in cells
(Ullrich-Eberius et al.,
1989
Recent findings that As(III) is complexed with phytochelatins (PCs;
thiol-rich peptides derived from glutathione) in a range of plant tissues
(Sneller et al., 1999
Because As(V) has no affinity for the -SH groups in the PCs, it is believed
that once inside the cytoplasm, As(V) is readily reduced to As(III), making it
the predominant As species in roots and shoots. Pickering et al.
(2000
Screening Experiment The clones from As-contaminated and uncontaminated sites showed a large variation in root growth when exposed to the nutrient solution containing high-As(V) concentration. The root length of tillers originating from plants grown from seed collected at the contaminated site approached a normal distribution with a maximum number of tillers in class 11 (10.1–11 cm root length), whereas distribution of root length of tillers originating from plants grown from seed collected at the uncontaminated site showed a decreasing trend, with a maximum amount of tillers in class 1 (0–1 cm; Fig. 1). Clones tolerant and non-tolerant to As were selected based on the ratio of root growth in the high-As and zero-As solutions after 7 d (Fig. 2). Some plants from the contaminated site had very high ratios due to poor growth in the control solution, whereas they grew well in the high-As solution. Even though these plants may be dependent on As for growth (and thus ultimately very tolerant to As), they were not included in this study.
The dry weight and P concentration of roots and shoots are presented in Table I, whereas the analysis of variance of these data is presented in Table II. Root dry weight was not influenced significantly by any of the interactions (Table II). Increasing levels of As(V) in the nutrient solution resulted in a decrease in the root dry weight (Table I). Tolerant clones produced more roots than the non-tolerant clones, and the plants supplied with 100 µM phosphate produced significantly (P < 0.001) more roots than the plants growing in the 10 µM phosphate solution. The dry weight of shoots was significantly influenced by the As x P interaction; the shoot biomass decreased with increasing levels of As(V) in the nutrient solution only when the plants were supplied with low phosphate (10 µM). The dry weight of the shoots was further influenced by the As x clone interaction. Therefore, the shoot biomass of the non-tolerant clones decreased significantly with increasing levels of As(V) in the nutrient solution, whereas for the tolerant clones, the shoot biomass decreased only when the plants were growing in the high-As(V) solution (107 µM). The non-tolerant clones that were growing in the solution with low phosphate (10 µM) and high As(V) (107 µM) died within 4 d of As(V) application.
Phosphorus concentrations in roots and shoots were significantly influenced by the As x P interaction (Table II). Therefore, in plants treated with 100 µM phosphate, the P concentration in roots and shoots decreased with increasing levels of As(V), whereas for plants supplied with 10 µM phosphate, the P concentration increased with higher levels of As(V) in the nutrient solution (Table I). The non-tolerant clones contained significantly (P < 0.001) more P in roots and shoots than the tolerant clones.
As concentration in roots was not influenced by any of the interactions (Table III). The tolerant clones contained significantly (P < 0.001) less As in roots than the non-tolerant clones (Fig. 3). The As concentration in the roots increased significantly with increasing levels of As(V) in the nutrient solution, whereas increasing phosphate concentration from 10 to 100 µM decreased the As concentration in the roots by up to 90% in both tolerant and non-tolerant clones and across all levels of As(V) applied.
For the total As concentration in shoots, the clone x P interaction was significant, indicating that the As concentration in shoots was lower in tolerant than in non-tolerant clones at low P (10 µM), but not at high P (100 µM; Fig. 4; Table III). The As x P interaction was also significant, indicating that the As concentration in the shoots increased more with increasing levels of As(V) in the solution at high P (100 µM) than at low P (10 µM). The significance of the As x clone interaction indicated that the non-tolerant clones contained more As than tolerant clones only at 1.33 and 107 µM solution concentration of As(V).
The distribution of As within the plants showed that a greater percentage of As was transported to shoots in tolerant than in non-tolerant clones (20% versus 9%, respectively, averaged across all levels of As(V); see Fig. 5). Increasing the phosphate concentration from 10 to 100 µM enhanced transport of As from roots to shoots, especially in tolerant clones grown at 8 and 107 µM As(V) in the nutrient solution (significant clone x P and As x P interactions).
As species were extracted quantitatively from the freeze-dried plant material (average recovery 110% ± 15%). The recovery was determined as the sum of the extracted As species (measured by HPLC-ICP-MS) relative to the total As concentrations in plant material (measured in plant digests by hydride generation-ICP-MS). The recovery was slightly better (109% ± 9%) when it was expressed as the total As concentration in the plant extract (independent measurement by flow injection ICP-MS) relative to the total As concentration in plant material (measured in plant digests by hydride generation-ICP-MS). Most of the As species detected in roots and shoots were the inorganic As species As(V) and As(III). Only small amounts of organic As species (MMA and DMA) were detected in shoot material (<1%). The total As(V) concentration in H. lanatus plants increased with increasing As(V) supply (Fig. 4; Table III). The roots of non-tolerant clones generally contained more As(V) than the roots of tolerant clones, especially at 8 and 107 µM As(V) (As x clone interaction was significant). Plants growing in high-P solution (100 µM) contained less As(V) in roots compared with plants supplied with low P (10 µM). However, the significance of the clone x P interaction indicated that the difference was greater for non-tolerant clones compared with tolerant ones. For the As(V) concentration in the shoots, all of the main and the interaction effects were significant, mainly because of the high value of As(V) concentration in dead shoot material of non-tolerant clones treated with 107 µM As(V) and low P (10 µM). The total As(III) concentration in roots generally increased with increasing levels of As(V) in the nutrient solution, but not for plants grown in the low-P (10 µM) and the high-As(V) (107 µM) nutrient solution (significant As x P interaction; Fig. 5; Table III). The application of P decreased the concentration of As(III) in the roots, but only at 1.33 and 8 µM As(V) in the nutrient solution (significant As x P interaction). The non-tolerant clones contained more As(III) than the tolerant clones, except at low P in one case (significant clone x P interaction). In the shoots, the total concentration of As(III) increased with increasing levels of As(V) in the nutrient solution (Fig. 5; Table III). The As x P interaction was significant, therefore the application of P generally decreased the concentration of As(III) in shoots, but not at 107 µM As(V) in the nutrient solution. In roots, the proportion of total As present as As(III) generally increased with increasing levels of As(V) in the nutrient solution but not for plants grown in the low-P (10 µM) solution (significant As x P interaction; Tables IV and V). In the shoots, the proportion of total As present as As(III) generally decreased with increasing levels of As(V) in the nutrient solution. However, the increase between 1.33 and 8 µM As(V) was not significant for plants grown in high-P (100 µM) nutrient solution (significant As x P interaction). Both roots and shoots of tolerant clones generally contained a smaller proportion of total As present as As(III) compared with non-tolerant clones. However, the significance of the As x clone and the clone x P interactions indicated that the difference was not significant for clones grown in the low-P solution (10 µM) or clones grown in the high-As solution (107 µM). The application of phosphate significantly (P < 0.001) decreased the proportion of total As present as As(III) in roots and increased it in shoots.
For all treatments, the proportion of total As present as As(III) in roots increased with increasing concentrations of As in the roots, until the roots contained mostly As(III) (90%) at total As concentration in tissue greater than 250 mg kg–1 (Fig. 6). In contrast to the roots, the proportion of total As present as As(III) in shoots decreased with increasing concentrations of As in shoots regardless of P supply or As tolerance until the shoots contained about 35% of total As present as As(III) at total As concentrations greater than 75 mg As kg–1 in shoots (Fig. 6).
In roots, the concentration of As(III) was linearly related to the concentration of total As in roots, regardless of As tolerance of clones, P nutrition, and As(V) supply (Fig. 7). In contrast, the concentration of As(V) in roots plotted against the root concentration of total As approached an exponential curve. At low concentrations of total As in roots, the concentration of As(V) increased slightly with increasing total concentration in roots; however, at total As concentrations of more than 1,200 mg kg–1, the concentration of As(V) increased sharply with increasing concentrations of total As in roots, with a slope similar to the As(III) concentration increase (Fig. 7). In contrast to roots, the As(V) concentration in shoots increased linearly with elevated total concentrations of As in shoots. The relationship between shoot concentration of As(III) and total concentration of As, however, was logarithmic, with the As(III) concentration in shoots leveling off at total As concentrations greater than 120 mg kg–1. Dead shoot and root material contained mostly As(V) (>90% of total As).
The root dry weight remained constant with increasing proportions of total As present as As(III) until roots contained around 80% of total As as As(III) (Fig. 8). After that, the dry weight of the roots decreased with increasing proportions of total As present as As(III). There was, however, no clear trend apparent between shoot dry weight and proportion of As(III) in shoots (Fig. 8).
H. lanatus plants that originated from the As-contaminated site exhibited a higher degree of tolerance than plants growing on an uncontaminated site, a result similar to that reported by Meharg and Macnair (1992 ; Figs.
1 and
2). Although tolerant clones
contain generally less As than non-tolerant ones when exposed to the same
concentration of As (Fig. 3),
tolerant clones can still have high concentrations in roots and shoots after a
period of exposure (Hartley-Whitaker et al., 2001). Therefore, the reduced
influx of As(V) alone is not enough to explain As(V) tolerance in H.
lanatus. The recent finding that tolerant clones, exposed to As(V),
contain significantly higher concentrations of As-PC complexes compared with
non-tolerant clones, suggested an important role of As-PC complexes in
detoxifying high internal As concentrations
(Sneller et al., 1999;
Pickering et al., 2000;
Schmöger et al., 2000;
Hartley-Whitaker et al., 2001b,
2002). The current
understanding of As(V) metabolism in higher plants indicated that, after being
taken up by the plasma membrane phosphate transport system, As(V) is reduced
to As(III) in the cytoplasm (possibly by glutathione;
Delnomdedieu et al., 1994) and
then complexed by PCs. Because the As(III)-PC complexes are unstable at pH
>7.2, it is likely that the As(III)-PC complexes are stored in the vacuole
(pH 4.5–5.9) rather then in the cytoplasm (pH 7.2–7.4).
In most studies on As-PCs in terrestrial plants, it was assumed that
As(III) was the dominant As species tested in both roots and shoots,
regardless of the plant species or the As(V) and phosphate concentrations in
the growth medium. Pickering et al.
(2000
When As species are extracted from plant material, however, the PC-As(III)
complexes may dissociate into PC and free As(III), with the latter getting
oxidized to As(V) if the pH of the extraction media is >7.2
(Meharg and Hartley-Whitaker,
2002
Although the proportion of As(III) varied significantly depending on P
nutrition, As(V) supply, and As tolerance of clones, the proportion of As(III)
in roots plotted against the concentration of total As in the roots approached
a hyperbole (Fig. 6). In vitro
studies have shown that both As(V) and As(III) decrease plant cell growth and
ultimately lead to plant death; however, As(V) is more toxic than As(III)
(Schmöger et al., 2000
Hartley-Whitaker et al.
(2001b
In the present study, the As(III) concentration in the roots correlated
linearly (slope 0.87, R2 = 1.00) with the concentration of
total As in the roots regardless of As tolerance of clones (and for various
proportions of As(III) in roots). The slope of the PC production versus total
As concentration in roots (slope = 2.4; data from Hartley-Whitaker et al.
[2001b
No xylem sap was collected in this study due to inherent difficulties in
collecting xylem sap in grasses. In contrast, Pickering et al.
(2000 In contrast with roots, the proportion of total As as As(III) in shoots plotted against the concentration of total As in shoots approached a logarithmic curve (Fig. 6). Therefore, it seems that at low-As concentrations in the roots, most of As(V) is reduced to As(III) in the roots, and only a small amount of As(V) is translocated from roots to shoots. At these low concentrations of As(V) in shoots, the shoots are also able to reduce As(V) to As(III) (Fig. 7). However, with increasing concentrations of As in the roots, the maximum capacity to reduce As(V) to As(III) will be reached in roots (Fig. 7), after which more As(V) will be translocated from roots to shoots, eventually overwhelming the shoot capacity to reduce As(V) to As(III). A limited capacity of both roots and shoots to reduce As(V) to As(III) might be due to a requirement for reductants.
Shoots and roots of H. lanatus contain mainly inorganic As species As(V) and As(III), and the speciation of As was closely regulated by As(V) influx in both tolerant and non-tolerant clones. The reduction of As(V) to As(III) is the first step in the detoxification of As(V), followed by the formation of As(III)-PC complexes, illustrating the importance of As speciation in understanding As metabolism in H. lanatus.
Tolerance Test
Seed of Holcus lanatus was collected from an uncontaminated site
(University of Exeter, Devon, UK) and an As-Cu contaminated site (Gawton
United mine, Devon, UK; grid ref. SX452688). Plants of each population were
grown from seed in potting mix and maintained in a greenhouse, with tillers
screened for As(V) tolerance using a test described by Wilkins
(1957
Around 20 un-rooted tillers per clone (12 tolerant and 12 non-tolerant clones used) were placed in a solution containing 0.25 mM CaCl2 and 5 µM H3BO3. After 3 d, 12 rooted tillers (one from each tolerant or non-tolerant clone) were transferred to each plastic pot (5.5 L) containing the full-strength nutrient solution (0.2 mM KNO3, 0.2 mM NH4NO3, 0.5 mM CaCl2, 0.25 mM MgSO4, 20 µM FeNa-EDTA, 1 µM MnCl2, 0.1 µM CuCl2, 0.5 µM ZnCl2, 5 µM H3BO3, 0.05 µM Na2MoO4·2H2O, and 1 mM MES). The P treatment was either 10 or 100 µM KH2PO4. The pH of the nutrient solution was 6.0 (adjusted with 1 M HCl or 1 M KOH). The As treatments (1.33, 8, or 107 µM As as Na2HAsO4) were applied on d 6, after the tillers had 3 d to adjust to the full-strength nutrient solution. The solution was aerated continuously and was changed every 3 d.
The experiment was set up in a completely randomized design with factorial
arrangements of treatments. There were two clones (tolerant or non-tolerant),
two P levels (10 or 100 µM), and three As(V) levels (1.33, 8, or
107 µM). Each treatment was replicated two times. Plants were
grown in a controlled temperature room (25°C/20°C). After 30 d, root
and shoot material was harvested. Whereas the shoot material was snap frozen
in liquid nitrogen, the roots were first rinsed in ice-cold phosphate buffer
(1 mM Na2HPO4 + 10 mM MES + 0.5
mM Ca(NO3)2) to desorb As(V) from the root
free space (Asher and Reay,
1979
Freeze-dried root and shoot material (0.500 g) was digested in concentrated
HNO3 (10 mL) at 130°C until the volume of acid was reduced to
around 1 mL. The mixture was then made up to 10 mL with milliQ-water (18
m
Phosphorus was determined spectrophotometrically by reaction with malachite
green and measurement of A630
(Motomizu et al., 1983
Extraction of As species was done according to the method described by
Quaghebeur et al. (2003
A dual head HPLC pump (600E, Waters, Milford, MA) was used to deliver the
mobile phase for the chromatographic work. Samples were injected using a model
7725i injector (Rheodyne, Rohnert Park, CA) equipped with a fixed 20-µL
sample loop. Separations were performed on a PRP-X100 anion-exchange column
(250-x 4.1-mm i.d., 10 µm) from Hamilton (Reno, NV). The column
temperature was 40°C, and the mobile phase consisted of 20 mM
NH4H2PO4 (pH 5.6 adjusted with aqueous
NH3). The mobile phase flow rate was 1.5 mL
min–1. The outlet of the HPLC column was connected
via an 800-mm, 0.0625-inch PEEK capillary tube (0.13-mm i.d.) to the cyclonic
spray chamber of a PerkinElmer SCEEX ELAN 6000 ICP-MS. The ion intensities at
m/z 75 and 77 were monitored. The lens voltage and nebulizer
gas flow were optimized daily for maximum counts (m/z 75)
using a solution of the mobile phase containing 20 µg As
L–1. As compounds were quantified by external
calibration with standard solutions of As(III), As(V), DMA, and MMA. For
further details on the method, see Quaghebeur et al.
(2003
Data were analyzed using ANOVA (Genstat 5th Edition, 2000, Lawes Agricultural Trust, Rothamsted Experimental Station, Harpenden, UK).
We thank Prof. Andrew Meharg (University of Aberdeen, Aberdeen, UK) for supplying seed of H. lanatus and Dr. Longbin Huang (Murdoch University, Perth, Australia) for the use of the microwave extraction system. Received February 5, 2003; returned for revision February 24, 2003; accepted March 2, 2003.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.021741. * Corresponding author; email zrengel{at}agric.uwa.edu.au; fax 61–8–9380–1050.
Asher CJ, Reay PF (1979) Arsenic uptake by barley seedlings. Aust J Plant Physiol 6: 459–466 Byrne AR, Slejkovec Z, Stijve T, Fay L, Goessler W, Gailer J, Irgolic KJ (1995) Arsenobetaine and other arsenic species in mushrooms. Appl Organomet Chem 9: 305–313[CrossRef]
De Knecht JA, Koevoets PLM, Verkeij JAC, Ernst WHO
(1992) Evidence against a role for phytochelatins in naturally
selected increased cadmium tolerance in Silene vulgaris (Moench)
Garcke. Plant Physiol 98:
853–858 Delnomdedieu M, Basti MM, Otvos JD, Thomas DJ (1994) Reduction and binding of arsenate and dimethylarsinate by glutathione: a magnetic resonance study. Chem Biol Interact 90: 139–155[CrossRef][Web of Science][Medline] Francesconi K, Visoottiviseth P, Sridokchan W, Goessler W (2002) Arsenic species in an arsenic hyperaccumulating fern, Pityrogramma calomelanos: a potential phytoremediator of arsenic-contaminated soils. Sci Total Environ 284: 27–35[CrossRef][Medline] Halliwell B, Gutteridge MC (1984) Oxygen toxicity, oxygen radicals, transition metals and disease. Biochem J 219: 1–14[Web of Science][Medline] Hartley-Whitaker J, Ainsworth G, Meharg AA (2001a) Copper and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity. Plant Cell Environ 24: 713–722[CrossRef]
Hartley-Whitaker J, Ainsworth G, Vooijs R, Ten bookum W, Schat
H, Meharg AA (2001b) Phytochelatins are involved in
differential arsenate tolerance in Holcus lanatus. Plant
Physiol 126:
299–306 Hartley-Whitaker J, Woods C, Meharg AA (2002) Is differential phytochelatin production related to decreased arsenate influx in arsenate tolerant Holcus lanatus? New Phytol 155: 219–225[CrossRef]
Hurd-Karrer AM (1939) Antagonism of certain
elements essential to plants towards chemically related toxic elements.
Plant Physiol 14:
9–29 Jocelyn PC (1972) Biochemistry of the SH Group: The Occurrence, Chemical Properties, Metabolism and Biological Function of Thiols and Disulphides. Academic Press, London
Khattak RA, Page AL, Parker DR, Bakhtar D
(1991) Accumulation and interactions of arsenic, selenium,
molybdenum and phosphorus in alfalfa. J Environ Qual
20:
165–168 Koch I, Feldmann J, Wang L, Andrews P, Reimer KJ, Cullen WR (1999) Arsenic in the Meager Creek hot springs environment, British Columbia, Canada. Sci Total Environ 236: 101–107[Medline] Koch I, Wang L, Ollson C, Cullen WR, Reimer KJ (2000) The predominance of inorganic arsenic species in plants from Yellowknife, Northwest Territories, Canada. Environ Sci Technol 34: 22–26 Linge KL, Oldham E (2001) Interference from arsenate when determining phosphate by the malachite green spectrophotometric method. Anal Chim Acta 450: 247–252[CrossRef] Lombi E, Zhao F-J, Fufrmann M, Ma LQ, McGrath SP (2002) Arsenic distribution and speciation in the fronds of the hyperaccumulator Pteris vittata. New Phytol 156: 195–203[CrossRef] Mattusch J, Wennrich R, Schmidt AC, Reisser W (2000) Determination of arsenic species in water, soil and plants. Fresenius' J Anal Chem 366: 200–203[CrossRef][Medline] Meharg AA, Hartley-Whitaker J (2002) Arsenic uptake and metabolism in arsenic resistant and non-resistant plant species. New Phytol 154: 29–43[CrossRef] Meharg AA, Macnair MR (1990) An altered phosphate uptake system in arsenate-tolerant Holcus lanatus L. New Phytol 116: 29–35[CrossRef] Meharg AA, Macnair MR (1991) The mechanisms of arsenate tolerance in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L. New Phytol 119: 291–297[CrossRef] Meharg AA, Macnair MR (1992) Polymorphism and physiology of arsenate tolerance in Holcus lanatus L. from an uncontaminated site. Plant Soil 146: 219–225 Motomizu S, Wakimoto T, Tôei K (1983) Spectrophotometric determination of phosphate in river waters with molybdate and malachite green. Analyst 108: 361–367 Philips DJH (1990) Arsenic in aquatic organisms: a review emphasizing chemical speciation. Aquat Toxicol 16: 151–186[CrossRef]
Pickering IJ, Prince RC, George MJ, Smith RD, George GN, Salt
DE (2000) Reduction and coordination of arsenic in Indian
mustard. Plant Physiol 122:
1171–1177 Quaghebeur M, Rengel Z, Smirk M (2003) Arsenic speciation in terrestrial plant material using microwave-assisted extraction, ion chromatography and inductively coupled plasma mass spectrometry. J Anal At Spectrom 18: 128–134[CrossRef]
Schat H, Kalff A (1992) Are phytochelatins
involved in differential metal tolerance or do they merely reflect
metal-imposed strain? Plant Physiol
99:
1475–1480
Schmöger MEV, Oven M, Grill E (2000)
Detoxification of arsenic by phytochelatins in plants. Plant
Physiol 122:
793–801 Sneller FEC, Van Heerwaarden LM, Kraaijeveld-Smit FJL, Ten Bookum WM, Koevoets PLM, Schat H, Verkleij JAC (1999) Toxicity of arsenate in Silene vulgaris, accumulation and degradation of arsenate-induced phytochelatins. New Phytol 144: 223–232[CrossRef]
Ullrich-Eberius CI, Sanz A, Novacky J (1989)
Evaluation of arsenate- and vanadate-associated changes of electrical membrane
potential and phosphate transport in Lemna gibba G1. J Exp
Bot 40:
119–128 Van den Broeck K, Vandecasteele C, Geuns JMC (1998) Speciation by liquid chromatography-inductively coupled plasma-mass spectrometry of arsenic in mung bean seedlings used as a bio-indicator for arsenic contamination. Anal Chim Acta 361: 101–111[CrossRef] Vela NP, Heitkemper DT, Stewart KR (2001) Arsenic extraction and speciation in carrots using accelerated solvent extraction, liquid chromatography and plasma mass spectrometry. Analyst 126: 1011–1017[Medline] Webb SM, Gaillard J-F, Ma LQ, Tu C (2003) XAS speciation of arsenic in a hyper-accumulating fern. Environ Sci Technol 37: 754–760[Medline] Wilkins DA (1957) A technique for the measurement of lead tolerance in plants. Nature 180: 37–38[Medline] This article has been cited by other articles:
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ASPB Publications | PLANT PHYSIOLOGY® | THE PLANT CELL | |
|---|---|---|---|
TOP
ABSTRACT
RESULTS
0.05. d.f., degrees of
freedom.
cm–1 resistivity). Total As concentration
was measured by mixing 1 mL of digest with 9 mL of a reducing solution
containing 1.5% (w/v) potassium iodide, 1.5% (w/v) ascorbic acid, and 10%
(v/v) hydrochloric acid. This mixture was heated in a water bath at 50°C
for 1 h. Total As was determined by a hydride generation technique using a
B050–5540 continuous flow vapor system (PerkinElmer Life Sciences,
Boston) interfaced with a PerkinElmer SCEEX ELAN 6000 series ICP-MS (SCIEX,
Toronto; for further details, see
Quaghebeur et al., 2003
