Characterisation of a glutathione reductase gene and its genetic locus from pea (Pisum sativum L.)

Developmental and seed aging mediated regulation of antioxidative genes and differential expression of proteins during pre- and post-germinative phases in pea

Enzymatic antioxidant system plays an important role in maintaining seed vigor and regulating plant growth and development. It involves a number of enzymes that scavenge excessive reactive oxygen species (ROS) produced during seed aging and also modulate the level of these compounds during plant developmental processes. This study investigated the transcriptional regulation of enzymatic antioxidative capacity in pea during the pre- and post-germinative phases and in response to seed aging by analyzing the spatio-temporal expression of five antioxidative genes: PsAPX, PsSOD, PsGRcyt, PsGRcm and PsCAT. Transcripts of all these genes were found in mature dry seeds, embryo axes and cotyledons of germinating seeds, and cotyledons, roots and shoots of young seedlings. However, PsAPX and PsSOD were predominant and exhibited developmental regulation, suggesting that these genes play important roles in controlling the intracellular homeostasis of ROS for promoting cell elongation, and thereby embryo axis expansion and early seedling growth in pea. Accelerated aging of pea seeds led to reduction in seed viability and seedling growth, and this effect was correlated with substantial decrease in the transcriptional activation of the prominent antioxidative genes. Furthermore, our proteomic analysis indicated the association of seed aging with changes in the abundance of specific proteins, revealing additional mechanisms underlying seed aging in pea.

Plastidial glutathione reductase from Haynaldia villosa is an enhancer of powdery mildew resistance in wheat (Triticum aestivum)

A full-length cDNA (Hv-GR) whose transcript accumulation increased in response to infection by Blumeria graminis DC.f.sp. tritici (Bgt) was isolated from Haynaldia villosa. Southern analysis revealed a single copy of Hv-GR present in H. villosa. This gene encodes a glutathione reductase (GR) with high similarity to chloroplastic GRs from other plant species. Chloroplastic localization of Hv-GR was confirmed by targeting of the green fluorescent protein (GFP)-Hv-GR fusion protein to chloroplasts of epidermal guard cells. Following inoculation with Bgt, transcript accumulation of Hv-GR increased in a resistant line of wheat, but no significant change was observed in a susceptible line. In vivo function of Hv-GR in converting oxidized glutathione (GSSG) to the reduced form (GSH) was verified through heterologous expression of Hv-GR in a yeast GR-deficient mutant. As expected, overexpression of this gene resulted in increased resistance of the mutant to H(2)O(2), indicating a critical role for Hv-GR in protecting cells against oxidative stress. Moreover, overexpression of Hv-GR in a susceptible wheat variety, Triticum aestivum cv. Yangmai 158, enhanced resistance to powdery mildew and induced transcript accumulation of other pathogenesis-related genes, PR-1a and PR-5, through increasing the foliar GSH/GSSG ratio. Therefore, we concluded that a high ratio of GSH to GSSG is required for wheat defense against Bgt, and that chloroplastic GR enzymes might serve as a redox mediator for NPR1 activation.

Cadmium induced oxidative stress influence on glutathione metabolic genes of Camellia sinensis (L.) O. Kuntze

Glutathione, a tripeptide with sulfhydryl (-SH) group is a very crucial compound primarily involved in redox balance maintenance of the cellular environment. In this study, we monitored the influence of Cd exposure on the transcript levels of glutathione metabolic genes in bud tissues, the youngest leaf, of Camellia sinensis L. In addition, some physiochemical parameters were also studied. Cd exposure decreased chlorophyll and protein contents, while increase was observed in lipid peroxidation upon Cd treatments. These changes were found to be concentration and duration dependent, indicating the occurrence of oxidative stress upon Cd exposure. The transcript levels of glutathione biosynthetic genes viz. gamma-glutamylcysteine synthetase (gamma-ECS) and glutathione synthetase (GSHS) increased upon Cd exposure. Furthermore, transcript levels of glutathione reductase (GR), an enzyme involved in reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH), also showed upregulation on Cd exposure. However, the transcript levels of glutathione-S-transferase (GST), an enzyme involved in forming metal-GSH complex and help in sequestration of high levels of metal ions to vacuole, did not show any change on Cd treatment. This study document that Cd exposure induces oxidative stress in Camellia sinensis and the upregulation in transcript levels of glutathione metabolic genes except GST have suggested the role of these enzymes in the protection of plants from high level Cd exposure.

Oxidative stress during selenium deficiency in seedlings of Trigonella foenum-graecum and mitigation by mimosine Part II. Glutathione metabolism

Adaptive alterations in glutathione (GSH) metabolism were studied during oxidative stress induced by selenium (Se) deficiency in germinating seedlings of Trigonella foenum-graecum grown for 72 h and the response to supplementation individually of Se or mimosine was explored. Growth enhancement with improved mitochondrial efficiency was elicited by supplementation of Se at 0.5-0.75 ppm or mimosine at 0.1-0.2 mM. Total thiol and protein levels of mitochondrial and soluble fractions, in general, did not vary significantly with supplementation of either Se or mimosine except that the mitochondrial protein levels in mimosine groups (0.1-0.2 mM) decreased by 20-30%. Mitochondrial glutathione peroxidase (GSH-Px) increased by twofold in activity toward H2O2, cumene hydroperoxide (CHP), and t-butyl hydroperoxide (tBHP) in Se groups, and by 50-60% increase toward H2O2 and CHP but by a twofold enhancement in enzyme activity with tBHP in mimosine groups. Soluble GSH-Px activity increased by 30-40% only in mimosine groups and remained unaltered in Se groups. Glutathione S-transferase activity (GST) in the soluble fraction of both Se and mimosine groups increased dramatically by fivefold to sixfold. Distinct differences were noted in the response of the stressed seedlings toward exposure to Se or mimosine and included a decline in glutathione reductase (GR) activity by 50-60% in both mitochondria and soluble fractions of Se groups and an increase in GR activity of the mitochondria by twofold and of the soluble enzyme activity by 30% in the mimosine groups. Mimosine exposure resulted in a dose-dependent decrease in the gamma-glutamyl transpeptidase levels, but, in contrast, a significant enhancement by 50% was noted in the Se group at 0.75 ppm. The results including the differential response of GR activity to Se or mimosine supplementation are reflective of an effective reductive environment in Se groups and increased turnover of GSH in the presence of mimosine.

Identification of cDNAS encoding plastid-targeted glutathione peroxidase

A cDNA was isolated from pea leaf RNA which encodes a phospholipid hydroperoxide glutathione peroxidase (PHGPX; E.C. 1.1.1.1.9). The N-terminal section of this PHGPX encodes a recognisable chloroplast transit peptide. Efficient import in vitro of the pre-PHGPX protein into the stroma of isolated pea chloroplasts confirmed that the PHGPX is a chloroplast-located enzyme. The pea PHGPX has highly conserved homologues in Arabidopsis, citrus and Nicotiana sylvestris and the authors suggest that these proteins are also localised in the chloroplast and not in the cytosol as previously supposed.