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1.
Martin Bačkor Barbara Pawlik-Skowrońska Jana Bud’ová Tadeusz Skowroński 《Plant Growth Regulation》2007,52(1):17-27
Cysteine, glutathione (GSH) and phytochelatins were determined in the cells of both wild and copper tolerant strains of the
lichen alga Trebouxia erici following short-term (24 h) exposure to copper and cadmium and long-term (4 weeks) exposure to copper. Both metals caused
concentration dependent synthesis of phytochelatins (PC2–PC5), but cadmium was a more potent activator of phytochelatin synthesis, even inducing synthesis of PC5. The copper-tolerant strain did not reveal a higher degree of phytochelatin synthesis than the wild strain, and at 5 μM Cu
production of phytochelatins was in fact significantly lower. Lower levels of phytochelatin correlated with significantly
decreased intracellular copper content in the copper-tolerant strain. Both strains maintained high GSH levels even at a high
copper concentration of 5 μM, and only the highest copper concentration (10 μM) was toxic for both strains, causing a decrease
of GSH and PC content in algal cells. Cadmium had less effect on GSH in the cells of both tested strains. In the long term
experiments, only relatively small amounts of PC2 were detected in both strains, but the copper-tolerant strain retained significantly higher levels of reduced glutathione,
probably due to the lesser degree of oxidative stress caused by Cu. The significant increase of cysteine synthesis in the
copper-tolerant strain found in the present study may be related to copper tolerance in T. erici, while decreased intracellular Cu uptake, detoxification by PCs and increased free proline levels for protection of chloroplast
membranes may also be implicated. 相似文献
2.
Ralf Kneer Toni M. Kutchan Andreas Hochberger Meinhart H. Zenk 《Archives of microbiology》1992,157(4):305-310
In fungi, cellular resistance to heavy metal cytotoxicity is mediated either by binding of metal ions to proteins of the metallothionein type or by chelation to phytochelatin-peptides of the general formula (-Glu-Cys)n-Gly. Hitherto, only one fungus, Candida glabrata has been shown to contain both metal inactivating systems. Here we show by unambiguous FAB-MS analysis that both a metallothionein-free mutant of Saccharomyces cerevisiae as well as a wildtype strain synthesize phytochelatin (PC2) upon exposure to 250 M Cd2+ ions. The presence of Zn and/or Cu ions in the nutrient broth also induces PC2 synthesis in this organism. By 109Cd exchange and subsequent monobromobimane fluorescence HPLC, it could be shown that the presence of Cd2+ in the growth medium also induces phytochelatin synthesis in Neurospora crassa, which contains metallothioneins. 相似文献
3.
Growth of three strains of Tetracladium marchalianum was inhibited by Cd-, and, to a lesser extent, by Cu-and Zn-chloride. In the presence of 50 μM Cd(II), all strains increased
total thiol and glutathione production to 6, 11, and 21 μmoles · mg−1 dry mass, respectively. Cd(II) also induced the synthesis of one to several compounds reacting with 5,5′-dithio-bis-(2-nitrobenzoic
acid). In order to identify buffer-soluble thiolic compounds other than cysteine, γ-EC and γ-ECG (glutathione) were analyzed
and confirmed by mass spectrometry. No water soluble sulfides were detectable in any of the culture filtrates, but Cd(II)
exposure at a concentration of 50 μM raised sulfide levels in the mycelia of two of the strains between 3 and 7-fold, Cu(II)
and Zn(II) had no effect. Energy Dispersive X-ray-analysis (EDX) and Electron Spectrometry-Images (ES-I) of one strain revealed
increased levels of Cu and Zn in the cytoplasm and even higher levels in vacuolar precipitates. Zn and Cu are accumulated
in the vacuoles as polyphosphates, identified by Electron Energy Loss-Spectrometry (EELS). Cd was found only in the vacuoles. 相似文献
4.
Stress Responses of Zea mays to Cadmium and Mercury 总被引:2,自引:1,他引:1
Rubén Rellán-Álvarez Cristina Ortega-Villasante Ana Álvarez-Fernández Francisca F. del Campo Luis E. Hernández 《Plant and Soil》2006,279(1-2):41-50
A hydroponic experiment was carried out to characterize the oxidative stress responses of maize seedlings (Zea mays L. cv. Dekalb DK604) to cadmium (Cd) and mercury (Hg). Plants were grown hydroponically for 7 days in a nutrient solution
supplemented with several concentrations of Cd and Hg: 0.0 (control), 6 or 30 μM. Growth was inhibited by both metals. The
effect was more severe in plants exposed to Hg. Oxidative stress was caused by the exposure to the metals, as quantified by
malondialdehyde and carbonyl accumulation, by-products of lipid peroxidation and protein oxidation, respectively. The activity
of ascorbate peroxidase (APX) and superoxide dismutase (SOD), enzymes involved in the scavenging of reactive oxygen species,
were measured upon metal treatment. We found an activation of a cytosolic APX isoform, as identified by using a specific polyclonal
antiserum. However, there were negligible changes in SOD activity. Analysis of thiol-peptides revealed that at 6 μM Cd a remarkable
increase in root reduced glutathione (GSH) content occurred, and little effect on the relative content of oxidised glutathione
(GSSG) was observed. However, at 30 μM Cd and in plants exposed to 6 and 30 μM of Hg, GSH root content either remained stable
or decreased significantly, while the proportion of GSSG increased. Moreover, only Cd was able to induce accumulation of phytochelatins
at both assayed concentrations. Apparently, Hg was more toxic than Cd, as inferred from the magnitude of the changes found
in the physiological parameters tested. 相似文献
5.
Chris Fabien Moussavou Moudouma Vincent Gloaguen Catherine Riou Lionel Forestier Ga?lle Saladin 《Acta Physiologiae Plantarum》2012,34(3):1083-1091
In Arabidopsis thaliana, two genes encoding phytochelatin synthase (PCS; EC 2.3.2.15), AtPCS1 and AtPCS2, have been identified. Until now, only AtPCS1 was shown to play a role in response to Cd. To gain insight into the putative role of AtPCS2, three Cd concentrations (50, 100 and 200 μM) and long-term exposure (7 days) were tested on 1-week-old A. thaliana ecotype Wassilewskija (Ws) seedlings. Since 100 μM Cd did not alter seedling metabolism, as shown by unchanged total soluble
protein and free proline contents, we investigated plantlet response to this concentration in addition to Cd accumulation.
Seedlings accumulated Cd in roots and shoots. As phytochelatins and glutathione (GSH) contents increased in treated seedlings,
we suggested that Cd might be translocated via the phytochelatin pathway. Specific enzymatic activities of γ-glutamylcysteine
synthetase (GCS; EC 6.3.2.2), glutathione synthetase (GS; EC 6.3.2.3) and PCS were twice much more stimulated in shoots and
roots after Cd exposure except GS that remained constant in shoots. As expression of genes encoding GCS and GS was unchanged
in response to Cd, we suggested a regulation at translational or post-translational level. Surprisingly, AtPCS1 and AtPCS2 were differentially up-regulated after Cd treatment: AtPCS1 in shoots and AtPCS2 in whole plantlets. This last result suggests that PCS2 could be involved in plant response to high concentration of Cd in
Ws ecotype and supports a putative role of PCS2, not redundant with PCS1, in a long-term response to Cd. 相似文献
6.
Phytochelatins (PCs) are heavy metal binding peptides that play an important role in sequestration and detoxification of heavy
metals in plants. In this study, our goal was to develop transgenic plants with increased tolerance for and accumulation of
heavy metals from soil by expressing an Arabidopsis
thaliana
AtPCS1 gene, encoding phytochelatin synthase (PCS), in Indian mustard (Brassica juncea L.). A 35S promoter fused to a FLAG–tagged AtPCS1 cDNA was expressed in Indian mustard, and transgenic lines, designated pc lines, were evaluated for tolerance to and accumulation
of Cd and Zn. Transgenic plants with moderate AtPCS1 expression levels showed significantly higher tolerance to Cd and Zn
stress, but accumulated significantly less Cd and Zn than wild type plants in both shoot and root tissues. However, transgenic
plants with highest expression of the transgene did not exhibit enhanced Cd and Zn tolerance. Shoots of Cd-treated pc plants
had significantly higher levels of phytochelatins and thiols than wild-type plants. Significantly lower concentrations of
gluthatione in Cd-treated shoot and root tissues of transgenic plants were observed. Moderate expression levels of phytochelatin
synthase improved the ability of Indian mustard to tolerate certain levels of heavy metals, but at the same time did not increase
the accumulation potential for Cd and Zn. 相似文献
7.
Organic Acids Accumulation and Antioxidant Enzyme Activities in Thlaspi caerulescens under Zn and Cd Stress 总被引:2,自引:0,他引:2
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 Plombières, 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 μM Zn and CAT activity only at 500 μM 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 Plombières, 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. 相似文献
8.
The lelvels of seven heavy metals and their toxicity towardGanoderma lucidum under various cultivation conditions were assessed. The contents of Mn, Cu, Zn, Cd, Hg, Pb and U in the fruitbodies of cultivatedG. lucidum, and sawdust substrates were determined to be at trace levels for U, 0.01–0.1 μg/g for Cd and Hg, and 1–5 μg/g for Pb, 10–120
μg/g for Mn, Cu and Zn. The effects of heavy metals, on the growth of mycelia ofG. lucidium in pure cultures were examined over a wide range of concentrations (10–3,000 μg/ml), and their toxicities were found to decrease
in the order: Hg>Cd>Cu>U>Pb>Mn=Zn. The translocation and accumulation of Zn from contaminated substrates (at 10 μg/g) in fruitbodies
were investigated by using65Zn tracer, andG. lucidum was found to take up Zn with an efficiency of >60%, leading to accumulation of >100 μ/g, in fruitbodies and >80 μ/g Zn in
basidiospores. 相似文献
9.
The effects of heavy metals on the growth, mineral composition (P, K, Fe and Mn) and metal accumulation of five populations of Cistus ladanifer subsp. ladanifer from NE Portugal were investigated in hydroponic experiments. Plants were exposed to increasing concentrations (0–2000 M) of one of eight heavy metals: Cd, Co, Cr, Cu, Mn, Ni, Pb or Zn. Populations of C. ladanifer, whose origin was ultramafic soils (S and UB) or soils developed on basic rocks (B), showed a higher tolerance to the metals Cd, Co, Cr, and Mn, and a considerable degree of tolerance to Ni. In contrast, populations originating on acid-rock soils (M and SC) showed higher tolerance to the metals Cu and Zn. Populations showed different patterns of metal accumulation and distribution in the plant parts, suggesting different mechanisms of metal tolerance are used. The more Cd-, Co- and Mn-tolerant populations (S, UB, B and SC (Cd)) showed accumulation of these three metals in the shoots (shoot:root metal concentration ratios (S:R) > 1). Shoot concentrations of up to 309 g Cd g–1, 2667 g Co g–1 and 6214 g Mn g–1 were found in these populations. The populations, UB and M, showed considerable tolerance to Ni and Zn, respectively. These populations accumulated up to 4164 g Ni g–1 and 7695 g Zn g–1 in their shoot tissues, and these metals were efficiently transported from the roots to aerial parts (S:R > 3 (Ni), S:R > 1 (Zn)). In contrast, the S and SC populations maintained higher growth rates in the presence of Ni and Zn, respectively, but showed exclusion mechanisms of metal tolerance: reduced Ni and Zn transport to shoots (S:R < 1). Cistus ladanifer was not able to efficiently transport Cr, Cu or Pb from its roots to its aerial parts (S:R ranged from 0–0.4). The more Cu-tolerant populations, M and SC, showed a greater restriction of Cu transport to the shoots than the ultramafic- or basic-rock populations. Significant changes in the plant mineral composition were found, however, concentrations were generally above mineral deficiency levels. Based on these preliminary results the possible usefulness of this plant for phytoremediation technologies is discussed. However, further investigations are necessary to evaluate its growth and metal accumulation under soil and field conditions. 相似文献
10.
Cell suspension cultures of red spruce (Picea rubens Sarg.) were selected to study the effects of cadmium (Cd) and zinc (Zn) on phytochelatins (PCs) and related metabolites after
24 h exposure. The PC2 and its precursor, γ-glutamylcysteine (γ-EC) increased two to fourfold with Cd concentrations ranging from 12.5 to 200 μM
as compared to the control. However, Zn-treated cells showed a less than twofold increase in γ-EC and PC2 levels as compared to the control even at the highest concentration of 800 μM. In addition, unidentified higher chain PCs
were also found in both the Cd and Zn treated cells and they increased significantly with increasing concentrations of Cd
and Zn. The cellular ratio of PC2 : Cd or Zn content clearly indicated that Cd (with ratios ranging from 0.131 to 0.546) is a more effective inducer of PC2 synthesis/accumulation than Zn (with ratios ranging from 0.032 to 0.102) in red spruce cells. A marginal decrease in glutathione
(GSH) was observed in both Cd and Zn treated cells. However, the GSH precursor, cysteine, declined twofold with all Cd concentrations
while the decrease with Zn was 1.5–2-fold only at the higher treatment concentrations of Zn as compared to control. In addition,
changes in other free amino acids, polyamines, and inorganic ions were also studied. These results suggest that PCs and their
biosynthetic intermediates play a significant role in red spruce cells protecting against Cd and Zn toxicity. 相似文献
11.
AlthoughArabidopsis thaliana is known as a model plant, in molecular studies, as well as heavy metal tolerance of higher plants, there have been no detailed studies of its cadmium accumulation, tolerance and cellular distribution in a wild type of this species. In hydroponic experiments the wild type of A. thaliana (L.) Heynh cv. Columbia plants grew at cadmium concentrations varying from 5 to 100 M with phytotoxicity symptoms depending on the concentration and time of application. The concentration of cadmium in roots and shoots increased from 0.28 and 0.08 mg g–1 d.wt at 5 M Cd treatment after 7 days to 0.82 and 0.85 mg g–1 d.wt at 100 M Cd treatment after 14 days, respectively. Most of the cadmium (69–88% of its total pool) was found in shoot. Cd application induced the biosynthesis of phytochelatins (PCs) in root and shoot tissues. Studies with buthionine sulfoximine [BSO, specific inhibitor of glutathione (GSH) synthesis] supported the presence of Cd–phytochelatin complexes and their role in Cd detoxification and tolerance in wild type of A. thaliana. Cellular distribution of cadmium was examined using energy-dispersive X-ray micro-analysis. Particularly interesting was the observation of cadmium localized in the root pericycle. 相似文献
12.
Copper-induced changes in the growth, oxidative metabolism, and saponin production in suspension culture roots of Panax ginseng in bioreactors 总被引:3,自引:0,他引:3
Roots of Panax ginseng exposed to various concentrations of Cu (0.0, 5, 10.0, 25.0, and 50.0 μM) accumulated high amounts of Cu in a concentration-dependent and duration-dependent manner. Roots treated with 50 μM Cu resulted in 52% and 89% growth inhibition after 20 and 40 days, respectively. Saponin synthesis was stimulated at a Cu concentration between 5 and 25 μM but decreased at 50 μM Cu. Malondialdehyde content (MDA), lipoxygenase activity (LOX), superoxide ion (O2
•−) accumulation, and H2O2 content at 5 and 10 μM Cu-treated roots were not increased but strongly increased at 50 μM Cu resulting in the oxidation of ascorbate (ASC) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively indicating a clear oxidative stress. Seven well-resolved bands of superoxide dismutase (SOD) were detected in the gel and an increase in SOD activity seemed to be mainly due to the induction of Fe-SOD 3. Five to 10 μM Cu slightly induced activity of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR), guaiacol peroxidase (G-POD) but inhibited monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) enzyme activities. No changes in catalase (CAT) activity and in activity gel were found up to 25 μM Cu, but both G-POD and CAT activities were inhibited at 50 μM Cu. Glutathione metabolism enzymes such as γ-glutamylcysteine synthetase (γ-GCS), glutathione-S-transferase (GST), and glutathione peroxidase activities (GPx) were activated at 5 and 10 μM Cu but were strongly inhibited at 50 μM Cu due to the Cu accumulation in root tissues. The strong depletion of GSH at 50 μM Cu was associated to the strong induction of γ-glutamyltranspeptidase (γ-GGT) activity. These results indicate that plant could grow under Cu stress (5–25 μM) by modulating the antioxidant defense mechanism for combating Cu induced oxidative stress. 相似文献
13.
To understand how plants from the Fabaceae family maintain zinc (Zn) homeostasis, we have characterized the kinetics of three
Zn transporting proteins from the ZIP family of divalent metal transporters in the model legume Medicago truncatula. Of six ZIP’s studied, MtZIP1, MtZIP5 and MtZIP6 were the only members from this family determined to transport Zn and were
further characterized. MtZIP1 has a low affinity for Zn with a Km of 1 μM as compared to MtZIP5 and MtZIP6 that have a higher affinity for Zn with Km of 0.4 μM and 0.3 μM, respectively. Zn transport by MtZIP1 was more sensitive to inhibition by copper (Cu) concentrations
than MtZIP5 and MtZIP6, because 3 μM Cu inhibited Zn transport by 80% in MtZIP1 while 5 μM Cu was required to achieve the
same inhibition of Zn transport in MtZIP5 and MtZIP6. Cadmium (Cd) had a greater effect on the ability of MtZIP1 to transport
Zn than MtZIP5 and MtZIP6, because at a concentration of 3 μM Cd, the Zn transport by MtZIP1 was inhibited 55% and the transport
of Zn by MtZIP5 and MtZIP6 was inhibited by 20–30%. However, only MtZIP6 transported Cd at higher rates than those observed
in the control plasmid pFL61, demonstrating a low affinity for Cd based on a Km of 57 μM. These results suggest that Medicago truncatula has both high and low affinity Zn transporters to maintain Zn homeostasis and that these transporters may function in different
compartments within the plant. 相似文献
14.
Cadmium (Cd) homeostasis and detoxification in sunflower (Helianthus annuus L.) cells differing in Cd sensitivity/tolerance were studied by analyzing the glutathione-mediated antioxidant mechanism
vis-à-vis phytochelatin biosynthesis in vitro. Calluses exposed to Cd-shock/-acclimatization (150μM) were assayed for oxidative stress, reduced glutathione (GSH), glutathione
disulfide (GSSG), phytochelatins (PCs) and reactive oxygen species (ROS). Although Cd did not induce any oxidative stress
in Cd-tolerant callus (TCd), it generated oxidative stress in Cd-shock callus (SCd) both in terms of lipid peroxidation and
protein oxidation. GSH/GSSG ratio remained similar to control values in the cadmium-acclimatized calluses. However, after
acute treatment, there was a decline in both GSH and GSSG levels in SCd with concomitant reduction in the GSH/GSSG ratio.
Analysis of PCs was performed using HPLC and mass spectrometry methods. PC concentration in TCd were approximately twice those
that in SCd, showing in both cases a 1:2:1 relative proportion for PC n = 2 (PC2): PC n = 3 (PC3): PC n = 4 (PC4). Calluses growing in the presence of Cd developed an increased resistance to paraquat oxidative stress generation.
These results indicated that PCs synthesis was an important mechanism for Cd detoxification in sunflower calluses, but the
capacity to grow in the presence of Cd is related to the tissues ability to maintain high intracellular levels of GSH. 相似文献
15.
Rios-Barrera D Vega-Segura A Thibert V Rodríguez-Zavala JS Torres-Marquez ME 《Archives of microbiology》2009,191(1):47-54
Living organisms are subject to stress, and among these stressors, heavy metals exposure triggers accumulation of sulfur metabolites.
Among these metabolites, glutathione and phytochelatins are found in several organisms, such as Euglena gracilis. Pre-exposing E. gracilis to low concentrations of Hg2+ generates a population with resistance to even 0.2 mM Cd2+, and this resistance relies partly on phytochelatins. p38 MAPK is stimulated by stress and is involved in apoptotic as well
as survival mechanisms. In this study, we explored its participation in heavy metal-induced stress and its possible role in
sulfur metabolite accumulation. We found that about 51% of the E. gracilis pretreated with Hg2+ becomes resistant to Cd2+ and proliferates despite the presence of this metal. The accumulation of the sulfur metabolites γ-glu-cys, glutathione and
phytochelatin 2 displayed cyclic patterns that were disturbed by a challenge with Cd2+. We observed a p38 MAPK-like activity that was stimulated by acute or chronic heavy metal exposure, and its inhibition by
SB203580 slightly diminished the accumulation of sulfur compounds. p38 MAPK inhibition also affected basal levels of glutathione
in either pretreated or control cells. Thus, it appears that p38 MAPK mediates redox stress component of the signal pathway
induced by heavy metals. 相似文献
16.
To elucidate the role of low molecular weight chelators in long-distance root-to-shoot transport of heavy metals in Indian
mustard, an “off-line” size exclusion high-performance liquid chromatography–graphite furnace atomic absorption spectrometry
was developed to investigate heavy metals associated with low molecular weight chelators in xylem saps of Indian mustard (Brassica juncea). The size exclusion chromatogram presented only the peaks with molecular weight for all xylem saps and directly indicated
the long-distance transport of phytochelatins (PCs) of Indian mustard under Cd stress. In the absence of Cd stress, only organic
acids and inorganic anions participated in the long-distance transport of Cd, but organic acids, inorganic anions, glutathione
(GSH), and cysteine might relate to the long-distance transport of Cu or Zn. In the presence of Cd stress, PCs were induced,
and Cd ions in xylem saps were associated with the induced PCs. As the Cd levels in nutrient solution increased, more Cd in
xylem saps adopted the form of PC–Cd. Although PCs might participate in the long-distance transport of Cd under Cd stress,
the majority of Cd was still transported by organic acids and inorganic anions in xylem vessels. Moreover, results indicated
the existence of complexation competition for GSH and cysteine between Cd and Cu (or Zn) and complexation competition for
Cd between PCs and GSH (or cysteine) in xylem vessels. Our work might be very useful for understanding the mechanism of long-distance
transport of heavy metals in hyperaccumulator. 相似文献
17.
Pinus sylvestris seedlings infected with either the ectomycorrhizal (ECM) fungus Paxillus involutus or Suillus variegatus were exposed to a range of Cd or Zn concentrations. This was done to investigate the relationship between the sensitivity
of ECM fungi and their host plants over a wide range of concentrations. P. involutus ameliorated the toxicity of Cd and Zn to P. sylvestris with respect to root length, despite significant inhibition of ECM infection levels by Cd (Cd EC50 [effective concentration which inhibits ECM infection by 50%] values were: P. involutus 3.7 μg g-1 Cd; S. variegatus 2.3 μg g-1 Cd). ECM infection by P. involutus also decreased Cd and Zn transport to the plant shoots at potentially toxic concentrations and also influenced the proportion
of Zn transported to the roots and shoots, with a higher proportion retained in the roots of the seedlings. ECM infection
did increase host biomass production, but this was not affected by the presence of Cd or Zn. Root and shoot biomass production
by P. sylvestris, in both the presence and absence of ECM fungi, was unaffected by Cd and Zn at all concentrations tested.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Conjugation of xenobiotic compounds and endogenous metabolites to glutathione is an ubiquitous process in eukaryotes. In animals, the first and rate-limiting step of glutathione-S-conjugate metabolism is characterized by the removal of the aminoterminal glutamic acid residue of glutathione. In plants, however, glutathione-S-conjugates are generally metabolized by removal of the carboxylterminal glycine residue of the tripeptide glutathione to give rise to the S-glutamylcysteinyl-derivative. Purification of the glutathione-conjugate catabolizing activity from cell suspension cultures of the plant Silene cucubalus indicated that phytochelatin synthase catalyzes the first step of the pathway. Heterologously expressed phytochelatin synthase from Arabidopsis efficiently converted S-bima ne-glutathione to S-bimane-glutamylcysteine, the formation of which was unequivocally identified by mass spectrometry. No further products, such as S-derivatives of phytochelatins, were observed. Several different glutathione-S-conjugates served as substrates for the enzyme and were processed to the corresponding glutamylcysteinyl-adducts. Affinity-purified phytochelatin synthase preparations required divalent heavy metal ions such as Cd(2+), Zn(2+) or Cu(2+) for detectable turnover of glutathione-S-conjugates. Characterization of the enzymatic properties of phytochelatin synthase argues for both cellular functions of the gamma-glutamylcysteinyl-dipeptidyltransferase: (1) formation of heavy-metal binding peptides and (2) degradation of glutathione-S-conjugates. Mechanistically, the former role is the result of gamma-glutamylcysteinyl transpeptidation onto glutathione or derivatives thereof, while the catabolic function reflects transpeptidation of S-glutamylcysteinyl-adducts onto the acceptor molecule water. Thus, phytochelatin synthase seems to fulfil a second crucial role in glutathione metabolism. 相似文献
19.
Effects of zinc (12–180 μM) alone and in mixtures with 12 μM Cd on metal accumulation, dry masses of roots and shoots, root
respiration rate, variable to maximum fluorescence ratio (FV/FM), and content of photosynthetic pigments were studied in hydroponically cultivated chamomile (Matricaria recutita) plants. The content of Zn in roots and shoots increased with the increasing external Zn concentration and its accumulation
in the roots was higher than that in the shoots. While at lower Zn concentrations (12 and 60 μM) the presence of 12 μM Cd
decreased Zn accumulation in the roots, treatment with 120 and 180 μM Zn together with 12 μM Cd caused enhancement of Zn content
in the root. Presence of Zn (12–120 μM) decreased Cd accumulation in roots. On the other hand, Cd content in the shoots of
plants treated with Zn + Cd exceeded that in the plants treated only with 12 μM Cd. Only higher Zn concentrations (120 and
180 μM) and Zn + Cd mixtures negatively influenced dry mass, chlorophyll (Chl) and carotenoid content, FV/FM and root respiration rate. Chl b was reduced to a higher extent than Chl a. 相似文献
20.
Radomír Čabala L’udmila Slováková Manal El Zohri Hartmut Frank 《Acta Physiologiae Plantarum》2011,33(4):1239-1248
Translocation of cadmium (Cd) in the tissues of Vicia faba, the water content in biomass, the biomass production, and the glutathione and phytochelatin tissue concentrations were studied
and correlated with the plant sensitivity and/or tolerance to Cd. The total concentrations of Cd were determined by inductively
coupled plasma/mass spectrometry (ICP-MS), the concentrations of glutathione (GSH) and phytochelatins 2 and 3 (PC2 and PC3)
were determined by on-line high performance liquid chromatography/electrospray-ionization tandem mass spectrometry (HPLC–ESI–MS–MS)
in the roots and leaves of the sensitive and the tolerant cultivars of V. faba grown in Cd containing nutrient solutions (NS, 0–100 μmol l−1 Cd2+). Both the cultivars of V. faba accumulate a major portion of Cd in the roots and only a minor part of ca. 4% in the leaves. The differences between the
cultivars concerning Cd accumulation in leaves were apparent from higher Cd concentrations in NS and the Cd amount in the
sensitive cultivar was approximately twice as high. In the roots, the differences between the cultivars in the Cd accumulation
were only statistically significant with the highest Cd concentrations in NS, with the tolerant cultivar accumulating about
16% more of Cd compared to the sensitive one. The biomass production of the sensitive cultivar decreased approximately twice
as fast with increasing Cd concentration in NS. The biomass water content decreased with increasing Cd concentration in NS
in both the cultivars. In general, the GSH concentration did not linearly correlate with Cd accumulation, except for the roots
of the sensitive cultivar where it was independent, and was higher in the sensitive cultivar than in the tolerant one in both
the leaves and roots. The GSH concentration in leaves was approximately one order of magnitude higher than that in the roots
for both the cultivars. The relationships between the PC and Cd concentrations in tissues were found nonlinear. At lower Cd
accumulation levels, the PC concentrations followed an increase in the Cd accumulation in both the roots and leaves, whereas
at higher Cd accumulations the relations differed between roots and leaves. In the roots, the PC concentrations decreased
with increasing Cd accumulation, whereas the PC concentration in the leaves followed the decrease in the Cd accumulation. 相似文献