Overexpression of glutathione reductase in Brassica juncea: Effects on cadmium accumulation and tolerance

Abstract

showed no chlorosis, and their chlorophyll fluorescence To determine the importance of glutathione reductase (GR, EC 1.6.4.2) for heavy metal accumulation and tolerance, a parameters F v /F m and photochemical quenching were higher. bacterial GR was expressed in Indian mustard (Brassica Cadmium tolerance at the whole-plant level (plant growth) juncea L.), targeted to the cytosol or the plastids. GR activ-was not affected. The lower cadmium stress experienced by the cpGR chloroplasts may be the result of reduced cad-ity in the cytosolic transgenics (cytGR) was about two times higher compared to wild-type plants; in the plastidic trans-mium uptake and/or translocation: cadmium levels in shoots genics (cpGR) the activity was up to 50 times higher. When of cpGR plants were half as high as those in wild-type treated with 100 mM CdSO 4 , cytGR plants did not differ shoots. These differences in cadmium tolerance and accumulation may result from increased root glutathione levels, from wild type in cadmium tolerance or accumulation. CpGR plants, however, showed enhanced cadmium tolerance which were up to two times higher in cpGR plants than in the wild type. at the chloroplast level: in contrast to wild-type plants they make chloroplasts a major source of active oxygen intermediates in photosynthetic tissues of plants (Allen 1995, Prasad, 1995. Heavy metals like Cd are effective inhibitors of photosynthesis (Prasad, 1995). Cadmium exposure was shown to result in a reduction in chlorophyll content (Ouzounidou et al. 1997), inhibition of photosystem II (Atal et al. 1993), and a negative effect on chlorophyll fluorescence (Horvath et al. 1996). The hypothesis tested in this study is that overexpression of GR will reduce the damage that Cd has on plant function, based on the assumptions that Cd causes oxidative stress and GR activity alleviates oxidative stress. To test this hypothesis the E. coli gor gene encoding GR was introduced in Indian mustard, targeted either to the cytosol or to the plastids. The transgenic plants were characterized with respect to GR activity profiles and GSH levels, and the Cd tolerance of the transgenic GR plants was compared with that of wild-type plants, in particular with respect to chloroplast function.

Molecular Responses to Cadmium in Roots of Pisum Sativum L.

“…Likewise, increased γ -glutamylcysteine synthetase activity (encoded by gsh1) occurs in roots and shoots of maize seedlings exposed to Cd (Rüegsegger and Brunold, 1992), and increased glutathione synthetase activity (encoded by gsh2) has been reported in roots of another pea genotype (Rüegsegger et al, 1990). Induction of glutathione reductase (encoded by gr) has been suggested to provide defence against oxidative damage imposed by HM (Dixit et al, 2001), higher tolerance to Cd stress in chloroplasts, and decreased Cd accumulation in shoots (Pilon-Smits et al, 2000). In legumes, synthesis of hGSH has also been implicated in plant responses to HM through the activity of a homoglutathione synthetase encoded by hgsh2, reported as being preferentially expressed in roots and nodules of M. truncatula (Klapheck, 1988;Frendo et al, 1999Frendo et al, , 2001).…”

Cadmium has contrasting effects on polyethylene glycol – Sensitive and resistant cell lines in the Mediterranean halophyte species Atriplex halimus L.

“…This key enzyme dedicated to re-reduction of glutathione disulfide (GSSG) at the expense of NADPH, contains highly conserved disulfide bridges that may undergo cleavage by heavy metals resulting in inhibition of its activity (Schützendübel et al, 2001). Although Pilon-Smits et al (2000) reported that the chloroplastic GR assumes crucial functions in Cd-tolerance in Brassica juncea, this isoform is probably not involved in our nonphotosynthetic tissues and further work should therefore focus on the cytosolic isoform. It has also been demonstrated that Cd may reduce GR activity despite the fact that it up-regulated the corresponding gene expression (Rodríguez-Serrano et al, 2006) and both transcriptional and post-translational impacts of Cd on this enzyme should therefore be considered.…”

“…It has been established that dehydration tolerance requires a coordinated series of events that are associated with preventing oxidative damage and maintaining the native structure of macromolecules and membranes (Hoekstra et al, 2001). Although Cd is not a transition metal able to catalyse the Fenton reaction, numerous authors demonstrated that it may be directly or indirectly responsible for several cellular disorders linked to oxidative stress (Pilon-Smits et al, 2000;Schützendübel et al, 2001;Garnier et al, 2006;Rodríguez-Serrano et al, 2006). It is therefore worth noting that the lipid peroxidation index, estimated on the basis of MDA concentration (Fig.…”

Photosystem II photochemistry, photoinhibition, and the xanthophyll cycle in heat-stressed rice leaves

“…It has been shown that enhanced chloroplastic GR activity in transgenic plants results in increased protection against oxidative stress (Broadbent et al, 1995;Foyer et al, 1995;Pilon-Smit et al, 2000). In addition, transgenic plants over-expressing superoxide dismutase (SOD) and APX were found to be more tolerant than wild-type plants to a combination of temperature and high light (Allen, 1995;Yabuta et al, 2002).…”