The contamination of soils and water with metals has created a major environmental problem, leading to considerable losses in plant productivity and hazardous health effects. Exposure to toxic metals can intensify the production of reactive oxygen species (ROS), which are continuously produced in both unstressed and stressed plants cells. Some of the ROS species are highly toxic and must be detoxified by cellular stress responses, if the plant is to survive and grow. The aim of this review is to assess the mode of action and role of antioxidants in protecting plants from stress caused by the presence of heavy metals in the environment.

Making the life of heavy metal-stressed plants a little easier

Effect of heavy metal stress on antioxidative enzymes and lipid peroxidation in leaves and roots of two mangrove plant seedlings (Kandelia candel and Bruguiera gymnorrhiza)

Nitric oxide (NO) as a key signaling molecule has been involved in mediation of various biotic and abiotic stress-induced physiological responses in plants. In the present study, we investigated the effect of NO on Cassia tora L. plants exposed to aluminum (Al). Plants pre-treated for 12 h with 0.4 mM sodium nitroprusside (SNP), an NO donor, and subsequently exposed to 10 microM Al treatment for 24 h exhibited significantly greater root elongation as compared with the plants without SNP treatment. The NO-promoted root elongation was correlated with a decrease in Al accumulation in root apexes. Furthermore, oxidative stress associated with Al treatment increased lipid peroxidation and reactive oxygen species, and the activation of lipoxygenase and antioxidant enzymes was reduced by NO. Such effects were confirmed by the histochemical staining for the detection of peroxidation of lipids and loss of membrane integrity in roots. The ameliorating effect of NO was specific, because the NO scavenger cPTIO [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] completely reversed the effect of NO on root growth in the presence of Al. These results indicate that NO plays an important role in protecting the plant against Al-induced oxidative stress.

Nitric oxide reduces aluminum toxicity by preventing oxidative stress in the roots of Cassia tora L.

Metabolic adaptations to mercury-induced oxidative stress in roots of Medicago sativa L.

Nanoparticles applied to plant science: a review.

The effects of the heavy metal Cadmium (Cd) on the growth and the activities of the antioxidant enzymes, catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) have been investigated in Crotalaria juncea seedlings. Concentrations above 0.2 mM CdCl2 were shown to inhibit strongly the growth of roots and shoots. Cd was shown to accumulate to very high concentrations in the roots, whilst in the leaves, the maximum concentration obtained following treatment with 2 mM CdCl2, was only 6% of that determined in the roots. Although CAT activity did not exhibit any major variation in the roots following CdCl2 treatment, 2 mM CdCl2 induced a 6-fold increase in activity in the leaves when compared to the untreated control. Non-denaturing PAGE gels stained for SOD activity revealed four isoenzymes, two Mn-SOD and two Cu/Zn-SOD. The results observed for SOD were different of those observed for CAT activity, since in both, leaves and roots, no significant changes in the total activity or of the four isoenzymes were observed following the treatment with CdCl2. GR activity exhibited a similar pattern of that of CAT activity. The concentration of 2 mM CdCl2 induced a small increase in activity in the roots after 48 h of exposure, whereas in leaves a 7-fold increase in GR activity was detected after 48 hr exposure to 2 mM CdCl2. The results suggest that in C. juncea the reactive oxygen species (ROS) induced by Cd, are metabolised by CAT in the peroxisomes. In the case of GR activity, the increase observed in the leaves suggest that GR is also playing a role in the detoxification of Cd-induced ROS possibly via the glutathione-ascorbate cycle.

Activity of antioxidant enzymes in response to cadmium in Crotalaria juncea

The response of a group of rice (Oryza sativa L) genotypes to cadmium (Cd) exposure was tested using root growth as a parameter over the duration of the treatment Three distinct response patterns were identified: a significant initial (001 mM) dosage effect, which was maintained with the increase of CdCl2 concentration to 1 mM; a significant initial effect, which was intensified with the increase of CdCl2 concentration, resistant to the CdCl2 concentration tested shown by a group of varieties Significant interactions between dosage and varieties were observed Enzymatic assays for catalase and glutathione reductase were also carried out in plants exposed to CdCl2 Similar response patterns for both enzymes were observed The activities of catalase and glutathione reductase in leaves and roots were increased, and in the case of glutathione reductase in roots, such an increase was highly significant, suggesting that the synthesis of reduced glutathione may be stimulated for subsequent synthesis

Guilherme Jose Gonçalves Pereira

Papers

Activity of antioxidant enzymes in response to cadmium in Crotalaria juncea

Response of rice inbred lines to cadmium exposure

Analise de enzimas antioxidantes em resposta a estresse por Cd e estudo de filogenia em plantulas de Crotalaria