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Plant Tissue And Cell Culturesa Very Versatile System

Anistic and metabolic aspects of herbicide resistance were first elucidated with cell cultures (10). Modern plant biotechnology has a wide choice of biochemical solutions for herbicide resistance by inactivation and detoxification reactions. Several major crop plant species (i.e., soybean, cotton, maize, rape) are presently cultivated to a large extent in the form of appropriately manipulated genotypes. This development is on the one hand regarded as a major advantage for agriculture but on the other hand as a subject of extensive and often very critical public debate.

Transformation Products

Detailed information on the chemistry of transformation products of inorganic and organic pollutants and metabolic pathways in susceptible and tolerant trees are scarcely available. In tolerant trees heavy-metal ions may be detoxified via chemical transformation into insoluble forms or chelated with cellular thiols or carboxylic acids and are eventually sequestered into the cell vacuole as described in herbaceous plants 8 . Of the different Phase II reactions that are most commonly involved in pollutant metabolism in trees, conjugation with GSH is one of the most important reactions and often the rate limiting step in the detoxification of an organic compound 23 . GSH transferases (GST, EC. 2.5.1.18) mediate the GSH-conjugation of chloroacetanilide herbicides in poplar trees according to the reaction

Function of SR Genes in Senescence

A second functional class of SR genes appears to encode proteins with a protective or stress response function, and includes a number of genes with homology to previously identified pathogenesis-related (PR) genes. These defense-related genes may serve to protect vulnerable senescing tissues from pathogen attack until the senescence program has been completed and to prevent pathogens from spreading to healthy parts of the plant. A number of these genes may also play a role in detoxification of the by-products of macromolecule and organelle catabolism within the cell and may function in maintaining cell viability until the cell's components have been salvaged. During programmed senescence, mechanisms that protect the cell from free radicals, reduced oxygen species, and other toxic by-products of senescence must be in place in order for the cell to remain viable. Transcripts that encode for catalase, an enzyme that detoxifies H2O2, show differential regulation during senescence in...

Prophylaxis of preeclampsia using antioxidants

Despite increased understanding of the etiology of the syndrome, there is currently no accepted method of prevention of pre-eclampsia. Studies of aspirin and calcium prophylaxis have proved disappointing (Coomarasamy et al., 2003). However, the abundant evidence for oxidative stress in pre-eclampsia provides a potential avenue of hope for the development of new strategies involving antioxidant prophylaxis. The choice of antioxidant is important. Some antiox-idants, particularly vitamin E, not only detoxify free radicals, but also have other properties that may benefit women with pre-eclampsia directly (Azzi et al., 2002 Brigelius et al., 2002). Antioxidants, by altering the cell redox status, are indirectly involved in the regulation of redox-sensitive gene expression. At levels close to those found in plasma, a-tocopherol has been shown to play a role in cell signaling by the inhibition of PKC activation (Azzi et al., 2002). Via this pathway vitamin E exerts anti-proliferative...

Nucleotide metabolism

Glutathione (GSH) is the major intracellular thiol in aerobic cells and is equally important in the red blood cell. It is thought to have a number of critical functions protecting cells against oxidative damage, participation in detoxification of foreign compounds, maintenance of protein sulphydryl groups in a reduced state and, possibly, transport of amino acids. In the red

Hypersensitivity Reaction Carcinggenesis Teratggenesis

FIGURE 16.4 General scheme for the role played by reactive drug metabolites in causing a variety of adverse reactions. The reactive metabolites usually account for only a small fraction of total drug metabolism and are too unstable to be chemically isolated and analyzed. In many cases, covalent binding of these metabolites to tissue macromolecules only occurs after their formation exceeds a critical threshold that overcomes host detoxification and repair mechanisms.

Anaerobic Dechlorination

The first reports of PCBs degradation by white rot fungi date back to 1985 46, 47 . The enzymes that are potential candidates for this activity are peroxidases and laccase. These enzymes are involved in lignin degradation and are also active against a wide range of aromatic compounds (PAH, substituted phenols, chlorinated pesticides 48, 49 etc.). The mechanism of degradation by lignin-peroxidase, manganese-peroxidases and laccases is described in degradation of many environmental pollutants. The ligninolytic enzyme system is non-specific, extracellular and free radical based that allows them to degrade structurally diverse range of xenobiotic compounds. Lignin peroxidase and manganese peroxidase carry out direct and indirect oxidation as well as reduction of xenobiotic compounds. Indirect reactions involved redox mediators such as veratrylalcohol and Mn2+. Reduction reactions are carried out by carboxyl, superoxide and semiquinone radicals, etc. Methylation is used as detoxification...

Environmental Pollutants

A variety of bacterial whole-cell sensing systems based on the promoter-reporter gene concept have been developed for the specific or selective detection of single pollutants or classes of pollutants. Many microorganisms have evolved the ability to survive in suboptimal conditions, including contaminated environments. Such ability usually relies on genetically encoded resistance systems. In the presence of toxic compounds such as heavy metals and metalloids, particular bacteria can synthesize specific proteins that confer resistance to those substances. The mechanisms of resistance vary. Some microorganisms develop efflux pumps, loss-of-uptake systems, or chemical detoxification systems 61, 62 . Other bacterial strains living in contaminated sites can degrade organic xenobiotics and utilize them as carbon and energy sources 63 . Many of these resistance pathways are inducible, meaning that protein synthesis occurs only as required by the presence of given compounds, which makes their...

Nitric Oxide And Plasma

However, whether these species represent reporter molecules suitable to monitor the progression of illnesses associated with an increased or decreased NO production, play a protective role in vivo, or rather represent bioinactive detoxification products that is far from being clear.

Pxrsxr Steroid and Xenobiotic Signaling Pathways

Thus, PXR-SXR is a novel steroid and xenobiotic sensor that acts as a broad-specificity receptor involved in the clearance and detoxification of a number of naturally occurring as well as ingested bioactive compounds. The aforementioned studies indicate the existence of another novel steroid hormone signaling pathway, via a unique receptor involved in sterol and hormonal homeostasis as well as drug metabolism and interactions.

Frank Van Breusegem and Dirk Inze

A variety of environmental stresses (such as chilling, ozone, high light, drought, and heat) can severely damage crop plants with consequent high yield losses. A common factor in all these adverse conditions is the occurrence of oxidative stress. Oxidative stress can be defined as the enhanced accumulation of active oxygen species (AOS) within several subcellular compartments of the plant. The AOS can react very rapidly with DNA, lipids, and proteins, with cellular damage as a result. Under normal growth conditions, AOS are efficiently scavenged by both enzymatic and nonen-zymatic detoxification mechanisms. Nevertheless, during prolonged stress conditions, this defense system becomes saturated and cellular damage is inevitable. The key players in the defense system are superoxide dismutases, ascorbate peroxidase, and catalases. These antioxidant enzymes directly eliminate AOS. This chapter gives an overview of transgenic plants with modulated antioxidant enzyme levels (focusing on...

Studies focusing on young people most at risk in developing countries

Interventions for young injecting drug users were identified in Argentina, India and Kenya (24). The Kenyan centre trained 54 volunteers in counselling and HIV prevention, and it provided counselling and detoxification services for 20 young injecting drug users. In Argentina, HIV testing, safer sex workshops and a drug users' network were provided in India a drop-in centre provided counselling and HIV testing as well as support groups for more than

Pharmacogenomic Applications

In addition to the receptor-ligand affinity, another important aspect of drug design is also the behavior (named ADMET for absorption, distribution, metabolism, excretion and toxicity) of drug-candidates in the targeted organisms (hosts and parasites). Empiric rules are now available to predict the behavior of drug candidates. Characterizations of the proteins involved in the various processes (transport, metabolism, detoxification, etc.) may rationalize the former approach. Several specialized databases have been developed for ADMET-associated proteins transporter (http lab.digibench. net transporter ), cytochromes P450 (http medicine.iupui.edu flockhart and http p450.abc.hu ) and ADME-AP (http xin.cz3.nus.edu.sg group admet admet.asp). Obtaining the structure of the corresponding proteins is a major challenge of integrated pharmacogenomics as illustrated by the study of cytochromes P450.

Hairy Roots In Phytoremediation And Phytomining Studies

Hairy roots have been applied to investigate heavy metal uptake and detoxification by rare plant species capable of growing in high-metal environments and accumulating elevated levels of specific metal ions. These species, known as hyperaccumulators, store heavy metals in their tissues at concentrations at least 100 times greater than those found in non-hyper-accumulator plants (75). About 400 hyperaccumulators have been identified, including 300 that hyperaccumulate nickel, 26 cobalt, 24 copper, 19 selenium, 16 zinc, 11 manganese, 1 thallium, and 1 cadmium (75). At the present time, the mechanisms of metal uptake by hyperaccumulating plants and the basis of their metal specificity are poorly understood. Hairy roots of several hyperaccumulators have been applied in metal uptake studies in liquid culture systems (67,76,77) these include Alyssum bertolonii and Thlaspi caerulescens, which were tested for hyperaccumulation of nickel and cadmium, respectively. As shown in Fig. 1, hairy...

GSR glutathione conjugate of the pollutant

GSTs represent a family of enzymes with usually broad and overlapping substrate specificities, which facilitate the above reactions of hydrophobic, electrophilic substrates. Our knowledge on plant GSTs in trees has expanded greatly in recent years. Evidence is accumulating on the regulation of gene expression, molecular characteristics, and specific catalytic action of the multiple forms of these enzymes. The majority of the information on plant GSTs concerns enzymes which are involved in the detoxification of a number of herbicides 23, 24 , but evidence is gathering that plant GSTs have a much wider role, and may be involved in general plant stress phenomena 25 . Although the Phase II conjugation system is regarded as a detoxification process of xenobiotics, GSH conjugates are not devoid of biological activity. Therefore, processes reducing the concentration of GSH conjugates in the cytosol are important detoxification steps 23 . Because of their active metal-uptake systems plants...

Methods applications and concepts of metabolite profiling Secondary metabolism

In addition to the large diversity in basic chemical structures, many natural products are further conjugated with a variety of sugars and or organic acids. The conjugation process is believed to be an import part of the cellular detoxification and storage mechanisms. However, they can also dramatically impact the biological activity of these compounds. Additional derivatives of natural products are achieved

Nitric Oxide Synthesis In Plants

NITRIC OXIDE STORAGE, DELIVERY AND DETOXIFICATION IN PLANTS 31 . Moreover, hexacoordinate hemoglobin AHbl from A. thaliana metabolizes both NO and GSNO. The nitrate forming reactions involve an Fe3+ intermediate, which is efficiently reduced by NADPH. It was proposed that this hemoglobin takes part in NO detoxification, principally during stresses that produce over-accumulation of NO such as hypoxia 31 . However, the rate of S-nitrosohemoglobin decomposition is low at physiological conditions, suggesting that hemoglobin S-nitrosylation could be a means for NO storage. There is no evidence of hemoglobin transport in the plant vascular system and it is highly improbable that hemoglobin function as NO carrier between plant tissues and organs, as it was suggested for mammals 32 . Therefore, the attention is focused to low-molecular-weight NO-containing compounds that could be responsible for NO trafficking in plants.

Alternative Approaches To Find Prostate Cancer Susceptibility Genes

Another important approach to find prostate cancer susceptibility genes has been to perform association studies in populations of men with and without prostate cancer, typically without regard to family history. These case control studies have been greatly aided by the increased understanding of the variability of the human genome sequence among different individuals and the concept that common diseases may be caused by common genetic variants in the population (65). Thus, by simply examining the frequency of polymorphic alleles, typically single-nucleotide polymorphisms, among cases and controls, associations between genes and disease risk can be rapidly assessed. A large number of genes involved in critical processes that occur in prostate cells, such as androgen action and metabolism, growth factor signaling, carcinogen detoxification, and DNA repair and inflammation, are being systematically evaluated in this fashion. Additionally, genome-wide association studies of prostate...

Tissue Lesions Liver Necrosis

Widely used analgesic which causes liver necrosis and sometimes renal failure after overdoses in many species. The half-life is increased after overdoses due to impaired conjugation of the drug. Toxicity is due to metabolic activation and is increased in patients or animals exposed to microsomal enzyme inducers. The reactive metabolite (NAPQI) reacts with glutathione, but depletes it after an excessive dose and then binds to liver protein. Metabolic activation is catalysed by cytochrome P-450, and the particular isoform (2E1, 1A2 or 3A4) depends on the dose. Antidote is N-acetylcysteine which promotes the synthesis of new glutathione and may also be involved in the detoxication. Bromobenzene. A hepatotoxic industrial solvent which causes centrilobular liver necrosis. It is metabolized in the liver to a reactive epoxide (3,4) which is detoxified by conjugation with glutathione, leading to excretion of a mercapturic acid. Depletion of glutathione with an excess dose leads...

Estrogen Effect on Initiation Growth and Progression of Prostate Cancer

In prostate, estrogen induced cancerous transformation may be partially due to their genotoxic metabolites, including 2-hydroxy-estrogens, 4-hydroxy-estrogens, quinone, and semiquinone intermediates. These metabolites may directly induce genomic damage or function via formation of reactive oxygen species (ROS).80'81 In addition, the enzymes responsible for the formation or inactivation of these estrogen metabolites may also play critical roles in the estrogen mediated transformation in prostate. These enzymes include (1) cytochrome p4501A1, which can convert estrogen into 2-hydroxy-estrogens, (2) cytochrome p4501B1, which can concert estrogens to 4-hydroxy-estrogens, (3) cathecol-O-methyl-transferase, which can inactivate 2- and 4-hydroxy-estrogens, and (4) glutathione-S-transferases that detoxify ROS.81-83 Although these may be important factors for estrogen mediated effects in prostate, few of them have been investigated for their contribution in prostate cancer.

Significance of Chlorophyll Breakdown

They represent efficient quenchers of triplet state activated Chl as well as of singlet oxygen which occur when the harvesting of quanta is not balanced by deactivation of Chl through photosynthetic electron transport. Hence, free Chl produced upon dismantling of complexes must immediately be inactivated in order to prevent photodynamic damage in the senescing cells. This vitally important process must be attributed primarily to macrocycle cleavage catalyzed by the PaO RCCR system. In land plants, the abolition of photodynamism is particularly important as catabolites are stored intracellularly until the very end of the senescence period. It is justified, therefore, to apostrophize Chl breakdown as a kind of detoxification process. Nevertheless, alternative mechanisms of Chl breakdown almost certainly play a role at stages of development other than senescence. Thus, turnover of Chl in developing and mature leaves (Stobart and Hendry, 1984) is not associated with the...

Functional ironcontaining proteins

Substrates and the simultaneous production of adenosine triphosphate. Haem is an essential component of microsomal and mitochondrial cytochrome P450, which is concerned with hydroxylation reactions (including drug detoxification by the liver), and of cyclo-oxygenase, involved in prostaglandin synthesis. Other haem proteins include the enzymes catalase and lactoperoxidase, which are concerned with peroxide breakdown, and tryptophan pyrrolase, involved in the oxidation of tryptophan to formylkynurenine. There is a smaller group of iron sulphur proteins (e.g. xanthine oxidase, reduced nicotinamide adenine dinucleotide dehydrogenase and aconitase). Iron is also necessary for the function of ribonucleotide reduc-tase, a key enzyme in DNA synthesis.

Tritrophic Trinity

For example, in the event a microorganism encounters a novel molecule, it might perish if the molecule is toxic, as are many SPMe, or a mutant enzyme might emerge from the population, enabling the molecule's detoxification or metabolism. The mutant enzyme would develop in the leaves as it is the location of enzymes which are responsible for interacting with the environment (e.g. detoxification, communication, assimilation). Moreover, as the novel chemical is metabolised it may continue down the tree into central metabolic pathways, or it may persist without any further metabolism 14, 22 . Persistent metabolites would be further evidence of enzymatic activity in the leaves, as catabolism of molecules with relatively novel structures or substituents (1) might produce equally novel metabolites requiring additional modification to indigenous enzymes for further metabolism (2) require low substrate specific enzymes for primary and secondary catabolism, which is...

Rhizosphere Ecology

With supplementation of autoclaved roots. Conversely, gnotobiotic hydroponic and sand-grown roots did not increase the rate of 2,4-D degradation, which suggested that the stimulatory component was both a function of the plant and cultivation medium. The authors also found evidence that unfractionated legume rhizodeposits enhanced 2,4-D mineralization. The implication was that flavonoids, as major signalling components of the rhizobia-legume symbiosis 1 , might select for microorganisms capable of detoxifying and utilising the flavanoid signals or their metabolites 66 . For example, cinnamic acid is one of the possible metabolites of flavanoid degradation and has been shown to induce TfdA, the gene responsible for the first step of 2,4-D catabolism 66 . 2,4-D is structurally analogous to p-coumaryl alcohol, a lignin monomer, which has been proposed to be a natural inducer of PCB degradation (Figures 3 and 4) 26 . 13 Wackett, LP (2003) Evolution of new enzymes and pathways Soil microbes...

A General Overview

Biological membranes fulfil vital functions as interfaces to the outside world, as interfaces between cells, and as boundaries of intracellular compartments. Membrane proteins share a common property part of their structure is embedded in a lipid bilayer. Therefore, being located at an interface, it is almost inevitable that they mediate communication between both sides of the membrane receptors, pores and channels are all signal transducers. Membrane proteins are abundant they are estimated to constitute a third of the complement of proteomes. An analysis of the genomes of eubacterial, Archaean and eukaryotic organisms predicted that 20-30 of the open reading frames encode integral membrane proteins (Wallin and von Heijne 1998). The number of lipid-interacting proteins should be increased if we consider the proteins presenting two conformational states, one of them stable in solution and the other one attached to a membrane or a lipid interface. This is the case for the great family...

Other Applications

Some drugs need to be metabolized for detoxification. Some drugs are only metabolized by enzymes that are encoded by a single pleiothropic gene. They involve the risk of drug accumulation to toxic concentrations in individuals carrying specific polymorphisms of that gene (17). With mechanistic toxicology, one can try to identify the crucial enzyme that is involved in the mechanism of detoxification. Subsequent genetic analysis can then lead to an a priori prediction to determine whether a xenobiotic should be avoided in populations with particular genetic susceptibilities.

Antioxidant Systems

One antioxidant mechanism is to scavenge free radicals with various enzymes and proteins, of which one major player is superoxide dismutase (SOD), which is present in all the aerobic organisms (60). SOD is uniquely dedicated to scavenge superoxide radicals by converting them to H2O2 (61-63), which can be further detoxified into water and oxygen by catalase in the cell (47). Oxidants can also be removed by various other kinds of proteins such as glutathione-S-transferase (64) for detoxification of xenobiotics, endogenous toxins, and hydroperoxides, and ferritin for sequestration of oxidation catalyst iron (62-64).

Phytoremediation

Plants can remediate environments contaminated with organic compounds directly via root uptake, detoxification by phytotransformation and conjugation with glutathione or sugars, and subsequent storage of nonphytotoxic metabolites in plant tissues and or indirectly by the release of exudates or enzymes which can enhance degradation by rhizosphere microorganisms 30, 31 .

Heavy Metals

Most of the references on potential mechanisms of plants-mycorrhizae-xenobiotics interaction are again related to heavy metals. It is generally acknowledged that mycorrhizal amelioration of metal toxicity is achieved via several physiological processes rather than through a single mechanism and that participation of single mechanisms in metal detoxification is metal- and species-specific 4, 95, 96 . completely opposite results in some cases and significantly enhanced translocation of HMs from roots to shoots of mycorrhizal plants was observed 68, 103 . Retention of HMs in fungal structures inside colonised roots was supported also by several microanalytical studies. Accumulation of metals within intracellular AM hyphae, mainly in phosphate-rich materials in the vacuoles, was reported in the mycorrhizal roots of the fern Pteridium aquilinum from a contaminated soil 104 . A massive accumulation of heavy metals in inner cortical cells of AM colonised maize roots where arbuscules and...

Antioxidants

We now know that the body has a comprehensive anti-oxidant defense network in which each component part has a role to play.11'12 What are the components of this antioxidant defense network One group of enzymes function to destroy or detoxify common oxidants. For example, hydrogen peroxide is one oxidant commonly formed as a byproduct as the tissues in the body perform their daily tasks. There are several enzymes capable of detoxifying hydrogen peroxide. The enzyme, catalase, reacts two hydrogen peroxide molecules together to form oxygen and water. A second family of enzymes, called glutathione peroxidases, reduces hydrogen peroxide to water. Most of the known glutathione peroxidases require selenium. A second group of components are vitamins that act as antioxidants. Vitamin C and vitamin E are prominent members of this group. Vitamin C is soluble in water and acts as an antioxidant in the water phase of the cell. Vitamin E is soluble in body fat and other lipids, but not in water....

Endothelial Cells

Additional studies in human umbilical vein endothelial cells exposed to higher levels of shear stress (25 dynes cm2 for 6 or 24 h) also appear to provide evidence to support the concept that physiological levels of shear stress are protective to en-dothelium 25 . A total of 52 genes were differentially regulated genes (32 up-, 20 down-regulated out of 4,000 genes) in response to shear stress results which were further confirmed by Northern blot analysis. For example, expression of members of the cytochrome P450 (CYP) family of genes (including 1A1 and 1B1) whose gene products are associated with cellular detoxification mechanisms, were dramatically increased. Consistent with this concept, the connective tissue growth factor (CTGF) gene whose product has been postulated to play a role in the develop

Chelation

DNAs (cDNAs) in S. cerevisiae (14,28). The analysis of a Schizosaccha-romyces pombe PCS knockout strain and of S. cerevisiae cells expressing PCS genes from different sources showed that the formation of PCs confers Cd tolerance and to a limited degree Cu, arsenate, and Hg tolerance. Based on these yeast studies, there is no indication for a role in, for instance, Zn, Co, or Ni detoxification. In the meantime, PC-mediated As tolerance was confirmed for plants (29,30). contributes to copper detoxification (35). A disruption of cupl causes Cu hypersensitivity the overexpression of cupl enhances Cu tolerance. CUP1 as well as the mammalian MTs can also bind Cd. MT-Cd complexes are formed in S. pombe cells expressing the S. cerevisiae MT gene (36). For a number of mammalian cell lines it was shown that MT deficiency results in Cd hypersensitivity and that MT overexpression leads to an elevation of Cd tolerance (37). Still, in the light of numerous genetic experiments demonstrating the...

Cdna Libraries

Studies on P450 metabolism of herbicides have reported the use of two yeast-expressed plant enzymes, CYP73A1 31 and CYP81B1 32 , in which ring-methyl hydroxylation of chlortoluron was observed. In both cases, however, the reaction was extremely slow if compared to a previous investigation, where a very fast N-demethylation catalysis was observed with CYP76B1 33 . It was found that CYP76B1 catalyzes the mono- and di-N-demethylation of both chlortoluron and isoproturon in higher plants, and plays a significant role in the detoxification of most phenylureas, including the methoxylated forms 33 . Other studies showed that 2,4-D treated S401 tobacco cells could metabolize chlorotoluron using four different P450 enzymes identified as CYP71A11, CYP81B2, CYP81C1 and CYP81C2 34 . Because only CYP71A11 and CYP81B2 were highly induced, both cDNA clones were expressed in yeast S. cerevisiae, which exhibited enhanced chlorotoluron metabolism 34 .

Example 111

11.3.1.4 Route of Exposure The biokinetic behavior of a contaminant also helps to explain the strong dependence of toxicity on the route of exposure. The route through which a contaminant is administered may significantly affect the concentration at the target organ and thus the degree of toxic response. Substances that undergo detoxification or metabolic activation may have significantly different toxicities when exposure is through inhalation rather than through ingestion. This is because most chemical contaminants pass through the liver when taken orally. Since the liver is a site of a great deal of metabolic activity, there is a high chance of either activation or detoxification prior to entering systemic circulation. Extensive metabolism of an administered compound in the liver is referred to as the first-pass effect and can result in significant differences between ingestion toxic-ity and toxicity due to other intake pathways. Inhalation of contaminants, on the other hand,...

Major Organ Systems

The pancreas secrete enzymatic fluids that aid in digestion. Nutrients absorbed from the small intestine are carried by blood to the liver. In the liver, the nutrients are metabolized and released into the circulatory system for delivery to the different parts of the body. The liver serves a variety of functions, the most important of which revolve around its role in digestion and the metabolism of nutrients absorbed from the small intestine. The metabolic action of the liver is a major mechanism for detoxifying substances absorbed along with the nutrients. The liver also plays an important role in the circulatory system through the synthesis of blood proteins, the destruction of old red blood cells, and the storage of iron and vitamins. Because of the liver's many functions, contaminants can act in a variety of ways to cause liver injury. The principal types of liver damage are necrosis (tissue destruction), cirrhosis (hardening of tissue), and the accumulation of abnormal amounts of...

Sequestration

In S. cerevisiae, the transporter YCF1 is required for Cd tolerance of yeast cells (69). YCF1-deficient cells are Cd hypersensitive. From transport studies with vacuolar membrane vesicles purified from wild-type and ycf S. cerevisiae cells it is known that YCF1 mediates the Mg-ATP dcpcndenl transport of bis(giutathionato)cadmium into vacuoles (70). YCF1 apparently also represents one of two pathways in S. cerevisiae for arsenite detoxification (71). A ycfl-knockout strain is As(III) hypersensitive and deficient in MgATP- and glutathione-dependent vacuolar uptake of As(III). incorporated into proteins, may lead to dysfunction (113). Two principal pathways for detoxification can be found in plants, chemical reduction and incorporation into organic compounds. The uptake of Se occurs mainly as selenate via high-affinity sulfate transporters. Because the reduction appeared to be the main factor limiting accumulation, the Arabidopsis ATP sulfurylase (APS), hypothesized to be the enzyme...

Potassium

Ligand joining ions of iron, zinc and copper to metalloproteins and enzymes. The reactive sites of some enzymes are -SH groups. Sulphur is therefore an essential element and deficiency results in a lack of protein synthesis. Sulphur-deficient plants are rigid, brittle and thin-stemmed. Important sulphur compounds are glutathione, which acts in detoxification of oxygen radicals, and the proteins thioredoxin and ferrodoxin that are involved in redox chemistry.