Control of assimilatory sulphate reduction

Control of S flux from sulphate to cysteine appears to be controlled in several ways (Figure 4). The first concerns the transcriptional control over the sulphate transporting membrane proteins. As discussed before,, expression of these proteins is linked to low concentrations of cysteine, glutathione and sulphate though there are reasons for suspecting that glutathione serves as the long distance signal and that cysteine acts as the principal direct sensor for initiating transcription....

Perturbation Of The Intracellular Concentration Of Glutathione

A number of environmental and physiological factors cause changes in the endogenous glutathione concentration, some positive, some negative. Factors that serve to decrease the concentration of glutathione include increased demand to support growth, production of phytochelatins in response to heavy metals, detoxification of xenobiotics, sequestration of S in secondary metabolites, glutathione export (a process involving long distance transport to sites of high demand for organic S such as...

Role of GST activity in infected plants

A major obstacle in understanding the role of GSTs in infected plants is the fact that the endogenous, physiological substrates of GST isoenzymes are in most cases not known. Among the possible substrates are fatty acid hydroperoxides, which are major products of oxidative membrane damage and can be also produced by lipoxygenase action. Bartling et al. (1993) isolated a cDNA clone for a novel GST from Arabidopsis. The encoded protein catalysed the decomposition of several fatty acid...

The Role Of Gsh In The Antioxidative Defence System Of Plant Cells

Gsh Ascorbate Cycle

Since a certain amount of ROS is produced under normal metabolic conditions (Foyer and Noctor 2000), plants have developed effective defence systems to survive. These systems include a number of different functions, such as protection against excess energy absorption, alternative regeneration of the electron acceptor (NADP), the scavenging of ROS, the repair of oxi-datively damaged structures, and regulation processes. Glutathione may participate in different parts of the defence systems (1)...

Detoxification Of Electrophilic Xenobiotics

Various electrophilic xenobiotics, i.e. compounds with centres of low electron density that can accept an electron pair to form a covalent bond, exhibit the tendency to react spontaneously with nucleophilic sites (i.e. centres of electron richness, non-bonded pairs of electrons or bonds) of bio-molecules. Thus, electrophilic xenobiotics may be highly dangerous to the cell, because they are able to bind to proteins and genetic material, i.e. DNA and RNA and thereby disturb metabolic networks....

Glutathione Peroxidase Glutathione Stransferase Glutathione Reductase

The selenoprotein glutathione peroxidase (GPX) detoxifies H202 in animal tissues but an equivalent reaction is not found in plants. Plant GPXs are not constitutive but are induced in response to stress. They do not contain selenium and do not catalyse the GSH-dependent reduction of H202 (Eshdat et al. 1997). In plants ascorbate peroxidase (APX) and catalase (CAT) detoxify H202 while GPXs have more sophisticated roles, including the removal of lipid and alkyl peroxides (Kranner and Grill 1996,...

Glutathione An Ancient Metabolite With Modern Tasks

Glutathione and its homologues comprise a group of tripeptides that are synthesised from the constituent amino acids rather than by direct translation of mRNA. The group of tripeptides is characterised by an N-terminal y-glutamyl moiety, a central cysteine residue, and a variable C-terminal amino acid. Numerous functions have been attributed to glutathione and its homologues that are all connected with its cysteine residue. These functions include storage and transport of reduced sulphur...

Glutathione Stransferases in fungal infections

Among the enzymes related to GSH metabolism, the role of glutathione S-transferase (GST, E.C. 2.5.1.18) isoenzymes has been the most extensively studied in infected plants. This isoenzyme family has been known since 1970 to have a significant and well-defined role in plant detoxification reactions (Marrs 1996, Edwards et al. 2000). The GST enzymes are homo- or heterodimeric combinations of different subunits. GSTs catalyse the binding of various xenobiotics (including numerous pesticides) and...

Thioldisulphide interchange reactions

The thiol-disulphide interchange reaction is important in maintaining the thiol status of cells (Figure 1, reaction 10) RS + R'SSR' > RSSR + R'S The activation parameters for the thiolate-disulphide exchange reactions resemble those for other nucleophilic displacement reactions of thiols, suggesting that the exchange is a nucleophilic displacement on sulphur. The thiol status of a biological system may be described as the distribution of thiols, exogenous or endogenous, among different...

Induction of yGlu Cys peptides by metals

Various metals cause the appearance of yGluCys peptides in plants Table 2 . For four studies single concentrations of metals ranging from 10 to o.M were used, in others comparisons between metals were based on a series of concentrations e.g. tomato cells, Rubia tinctorum roots, a marine diatom . Environmentally realistic metal concentrations in the realm,of 1 pM to 100 nM were used by Ahner and Morel 1995 in their study with the marine diatom Thalassiosira weissflogii. The metals in Table 2 are...

Dedicated to our friend colleague and teacher Prof Dr Hermann Esterbauer who died too early

Hermann Esterbauer, Institute of Biochemistry, University of Graz, Austria 1936 - 1997 We would like to thank Edith Hertl and Maria Grill for formatting and editing of the manuscripts and Daniel J.A. De Kok for preparing the index, John W. Anderson Australia Malcolm J. Hawkesford U.K. George Hendry U.K. Jonathan Howarth U.K. Graham Noctor U.K. Marinus L. Otte Ireland Nancy Grulke U.S.A. Nick Smirnoff U.K. for critical reading of the manuscripts.