Modifications in endopeptidase and 20S proteasome expression and activities in cadmium treated tomato (Solanum lycopersicum L.) plants

Evaluation of Cd2+ stress tolerance in transgenic rice overexpressing PgGPx gene that maintains cellular ion and reactive oxygen species homeostasis

Non-essential toxic heavy metal like cadmium (Cd2+) interferes with the plant growth and development in many ways. Cd2+ travels via plant transportation system, specifically through xylem and may integrate into the food chain causing unfavorable condition in human health. Therefore, strategies to develop Cd2+ tolerance and less accumulation in the plant system require urgent attention. Peroxidase gene family is known for metal ions transportation including Cd2+ and thus plays an important role in ion homeostasis. Previously, we have reported the presence of a Cd2+ dependent functional peroxiredoxin from Pennisetum glaucum (PgGPx). The present study elucidates the role of this PgGPx against Cd2+ stress in rice. The transcript levels of PgGPx were found to be highly upregulated in response to exogenous Cd2+. Moreover, recombinant PgGPx protein showed significant glutathione S-transferase activity in vitro. Ectopically expressed PgGPx in transgenic rice plants showed tolerance towards Cd2+ stress as demonstrated by several physiological indices including shoot and root length, biomass, chlorophyll, and hydrogen peroxide content. Moreover, these transgenic plants also showed enhanced capability to cope up with oxidative stress by enhancing the activity of different antioxidant enzymes including Superoxide dismutase, Catalase, Ascorbate peroxidase, Glutathione peroxidase, Glutathione reductase) in response to Cd2+. Hence, maintenance of cellular ion homeostasis and modulation of reactive oxygen species-scavenging pathway are found to be improved by overexpression of PgGPx under Cd2+ stress. These results will pave the way to develop strategies for engineering Cd2+ stress tolerance in economically important crop plants.

Neuroprotective mechanisms of multitarget 7-aminophenanthridin-6(5H)-one derivatives against metal-induced amyloid proteins generation and aggregation

Brain's metals accumulation is associated with toxic proteins, like amyloid-proteins (Aβ), formation, accumulation, and aggregation, leading to neurodegeneration. Metals downregulate the correct folding, disaggregation, or degradation mechanisms of toxic proteins, as heat shock proteins (HSPs) and proteasome. The 7-amino-phenanthridin-6(5H)-one derivatives (APH) showed neuroprotective effects against metal-induced cell death through their antioxidant effect, independently of their chelating activity. However, additional neuroprotective mechanisms seem to be involved. We tested the most promising APH compounds (APH1-5, 10-100 μM) chemical ability to prevent metal-induced Aβ proteins aggregation; the APH1-5 effect on HSP70 and proteasome 20S (P20S) expression, the metals effect on Aβ formation and the involvement of HSP70 and P20S in the process, and the APH1-5 neuroprotective effects against Aβ proteins (1 μM) and metals in SN56 cells. Our results show that APH1-5 compounds chemically avoid metal-induced Aβ proteins aggregation and induce HSP70 and P20S expression. Additionally, iron and cadmium induced Aβ proteins formation through downregulation of HSP70 and P20S. Finally, APH1-5 compounds protected against Aβ proteins-induced neuronal cell death, reversing partially or completely this effect. These data may help to provide a new therapeutic approach against the neurotoxic effect induced by metals and other environmental pollutants, especially when mediated by toxic proteins.

Tomato (Solanum lycopersicum L.) accumulation and allergenicity in response to nickel stress

Vegetables represent a major source of Ni exposure. Environmental contamination and cultural practices can increase Ni amount in tomato posing significant risk for human health. This work assesses the tomato (Solanum lycopersicum L.) response to Ni on the agronomic yield of fruits and the related production of allergens. Two cultivars were grown in pots amended with Ni 0, 30, 60, 120, and 300 mg kg⁻¹, respectively. XRF and ICP-MS analyses highlighted the direct increase of fruit Ni content compared to soil Ni, maintaining a stable biomass. Leaf water content increased at Ni 300 mg kg⁻¹. Total protein content and individual allergenic components were investigated using biochemical (RP-HPLC and N-terminal amino acid sequencing) and immunological (inhibition tests of IgE binding by SPHIAa assay on the FABER testing system) methodologies. Ni affected the fruit tissue concentration of pathogenesis-related proteins and relevant allergens (LTP, profilin, Bet v 1-like protein and TLP). This study elucidates for the first time that tomato reacts to exogenous Ni, uptaking the metal while changing its allergenic profiles, with potential double increasing of exposure risks for consumers. This evidence highlighted the importance of adequate choice of low-Ni tomato cultivars and practices to reduce Ni uptake by potentially contaminated matrices.

Early responses of maize seedlings to Cu stress include sharp decreases in gibberellins and jasmonates in the root apex

Copper (Cu) interferes with numerous biological functions in plants, including plant growth, which is partly governed by plant hormones. In the present study, Cu stress effect on the roots of pre-emerging maize seedlings in terms of growth, nutrient composition, protein modifications, and root hormone homeostasis was investigated, focusing on possible metabolic differences between the root apex and the rest of the root tissues. Significant decreases in root length and root biomass after 72 h of Cu exposure (50 and 100 μM CuCl₂), accompanied by reductions in Ca, Mg, and P root contents, were found. Cu also generated cell redox imbalance in both root tissues and revealed by altered enzymatic and non-enzymatic antioxidant defenses. Oxidative stress was evidenced by an increased protein carbonylation level in both tissues. Copper also induced protein ubiquitylation and SUMOylation and affected 20S proteasome peptidase activities in both tissues. Drastic reductions in ABA, IAA, JA (both free and conjugated), GA3, and GA4 levels in the root apex were detected under Cu stress. Our results show that Cu exposure generated oxidative damage and altered root hormonal homeostasis, mainly at the root apex, leading to a strong root growth inhibition. Severe protein post-translational modifications upon Cu exposure occurred in both tissues, suggesting that even when hormonal adjustments to cope with Cu stress occurred mainly at the root apex, the entire root is compromised in the protein turnover that seems to be necessary to trigger and/or to sustain defense mechanisms against Cu toxicity.

Hormone profile changes occur in roots and leaves of Micro-Tom tomato plants when exposing the aerial part to low doses of UV-B radiation

During the last decades, many studies investigated the effects of UV-B on the above-ground organs of plants, directly reached by the radiation but, to the best of our knowledges, the influence of mild UV-B doses on root hormones was not explored. Consequently, this research aimed at understanding whether low, not-stressful doses of UV-B radiation applied above-ground influenced the hormone concentrations in leaves and roots of Micro-Tom tomato (Solanum lycopersicum L.) plants during 11 days of treatment and after 3 days of recovery. In particular, ethylene, abscisic acid, jasmonic acid, salicylic acid and indoleacetic acid were investigated. The unchanged levels of chlorophyll a and b, lutein, total xanthophylls and carotenoids, as well as the similar H₂O₂ concentration between control and treated groups suggest that the UV-B dose applied was well tolerated by the plants. Leaf ethylene emission decreased after 8 and 11 days of irradiation, while no effect was found in roots. Conversely, indoleacetic acid underwent a significant reduction in both organs, though in the roots the decrease occurred only at the end of the recovery period. Salicylic acid increased transiently in both leaves and roots on day 8. Changes in leaf and root hormone levels induced by UV-B radiation were not accompanied by marked alterations of plant architecture. The results show that irradiation of above-ground organs with low UV-B doses can affect the hormone concentrations also in roots, with likely implications in stress and acclimation responses mediated by these signal molecules.

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

Cadmium (Cd), which is a toxic non-essential heavy metal capable of entering plants and thus the food chain, constitutes a major environmental and health concern worldwide. An understanding of the tools used by plants to overcome Cd stress could lead to the production of food crops with lower Cd uptake capacity and of plants with greater Cd uptake potential for phytoremediation purposes in order to restore soil efficiency in self-sustaining ecosystems. The signalling molecule nitric oxide (NO), whose function remains unclear, has recently been involved in responses to Cd stress. Using different mutants, such as nia1nia2, nox1, argh1-1 and Atnoa1, which were altered in NO metabolism, we analysed various parameters related to reactive oxygen and nitrogen species (ROS/RNS) metabolism and seedling fitness following germination and growth under Cd treatment conditions for seven days. Seedling roots were the most affected, with an increase in ROS and RNS observed in wild type (WT) seedling roots, leading to increased oxidative damage and fitness loss. Mutants that showed lower NO levels in seedling roots under Cd stress were more resistant than WT seedlings due to the maintenance of antioxidant systems which protect against oxidative damage.

Cadmium induces reactive oxygen species-dependent pexophagy in Arabidopsis leaves

Cadmium treatment induces transient peroxisome proliferation in Arabidopsis leaves. To determine whether this process is regulated by pexophagy and to identify the mechanisms involved, we analysed time course-dependent changes in ATG8, an autophagy marker, and the accumulation of peroxisomal marker PEX14a. After 3 hr of Cd exposure, the transcript levels of ATG8h, ATG8c, a, and i were slightly up-regulated and then returned to normal. ATG8 protein levels also increased after 3 hr of Cd treatment, although an opposite pattern was observed in PEX14. Arabidopsis lines expressing GFP-ATG8a and CFP-SKL enabled us to demonstrate the presence of pexophagic processes in leaves. The Cd-dependent induction of pexophagy was demonstrated by the accumulation of peroxisomes in autophagy gene (ATG)-related Arabidopsis knockout mutants atg5 and atg7. We show that ATG8a colocalizes with catalase and NBR1 in the electron-dense peroxisomal core, thus suggesting that NBR1 may be an autophagic receptor for peroxisomes, with catalase being possibly involved in targeting pexophagy. Protein carbonylation and peroxisomal redox state suggest that protein oxidation may trigger pexophagy. Cathepsine B, legumain, and caspase 6 may also be involved in the regulation of pexophagy. Our results suggest that pexophagy could be an important step in rapid cell responses to cadmium.

Prevalence of antibodies against visceralizing Leishmania spp. in brown rats from Grenada, West Indies

Background and Aim

Leishmania spp. are known to cause disease in man and animals. Rats are considered important reservoir hosts and transmission takes place through the bite of female sand fly, Phlebotomus spp. To the best of our knowledge, there is no published information on Leishmania infection in rats in Grenada. This study was conducted to estimate the antibodies for visceralizing Leishmania spp. (VL) in rats (Rattus norvegicus) from Grenada.

Materials and Methods

A total of 146 brown rats (R. norvegicus) were trapped live from two parishes (St. George and St. David) in Grenada. Following anesthesia, blood was collected from the heart through thoracic puncture. The serum was collected after the centrifugation of blood. Serum was tested for antibodies to VL. with a commercially available immunochromatographic dipstick test which is licensed for use in animals and humans.

Results

The seroprevalence of antibodies against Leishmania spp. was found in 34 of 146 rats (23.3%; CI 95% from 16.70 to 30.99). No significant differences were found between sexes and young or adults. The prevalence between parishes (St. George and St. David) was also not significant.

Conclusion

The results show that rats (R. norvegicus) in Grenada are exposed to Leishmania spp. The rats could play an important role in the transmission of leishmaniasis to humans and other animals in Grenada.

Sulfur Protects Pakchoi (Brassica chinensis L.) Seedlings against Cadmium Stress by Regulating Ascorbate-Glutathione Metabolism

Cadmium (Cd) pollution in food chains pose a potential health risk for humans. Sulfur (S) is a significant macronutrient that plays a significant role in the regulation of plant responses to diverse biotic and abiotic stresses. However, no information is currently available about the impact of S application on ascorbate-glutathione metabolism (ASA-GSH cycle) of Pakchoi plants under Cd stress. The two previously identified genotypes, namely, Aikangqing (a Cd-tolerant cultivar) and Qibaoqing (a Cd-sensitive cultivar), were utilized to investigate the role of S to mitigate Cd toxicity in Pakchoi plants under different Cd regimes. Results showed that Cd stress inhibited plant growth and induced oxidative stress. Exogenous application of S significantly increased the tolerance of Pakchoi seedlings suffering from Cd stress. This effect was demonstrated by increased growth parameters; stimulated activities of the antioxidant enzymes and upregulated genes involved in the ASA-GSH cycle and S assimilation; and by the enhanced ASA, GSH, phytochelatins, and nonprotein thiol production. This study shows that applying S nutrition can mitigate Cd toxicity in Pakchoi plants which has the potential in assisting the development of breeding strategies aimed at limiting Cd phytoaccumulation and decreasing Cd hazards in the food chain.

Over-expression of tobacco UBC1 encoding a ubiquitin-conjugating enzyme increases cadmium tolerance by activating the 20S/26S proteasome and by decreasing Cd accumulation and oxidative stress in tobacco (Nicotiana tabacum)

Ubiquitin (Ub)-conjugating enzyme (UBC, E2) receives Ub from Ub-activating enzyme (E1) and transfers it to target proteins, thereby playing a key role in Ub/26S proteasome-dependent proteolysis. UBC has been reported to be involved in tolerating abiotic stress in plants, including drought, salt, osmotic and water stresses. To isolate the genes involved in Cd tolerance, we transformed WT (wild-type) yeast Y800 with a tobacco cDNA expression library and isolated a tobacco cDNA, NtUBC1 (Ub-conjugating enzyme), that enhances cadmium tolerance. When NtUBC1 was over-expressed in tobacco, cadmium tolerance was enhanced, but the Cd level was decreased. Interestingly, 20S proteasome activity was increased and ubiquitinated protein levels were diminished in response to cadmium in NtUBC1 tobacco. By contrast, proteasome activity was decreased and ubiquitinated protein levels were slightly enhanced by Cd treatment in control tobacco, which is sensitive to Cd. Moreover, the oxidative stress level was induced to a lesser extent by Cd in NtUBC1 tobacco compared with control plants, which is ascribed to the higher activity of antioxidant enzymes in NtUBC1 tobacco. In addition, NtUBC1 tobacco displayed a reduced accumulation of Cd compared with the control, likely due to the higher expression of CAX3 (Ca2+/H+ exchanger) and the lower expression of IRT1 (iron-responsive transporter 1) and HMA-A and -B (heavy metal ATPase). In contrast, atubc1 and atubc1atubc2 Arabidopsis exhibited lower Cd tolerance and proteasome activity than WT. In conclusion, NtUBC1 expression promotes cadmium tolerance likely by removing cadmium-damaged proteins via Ub/26S proteasome-dependent proteolysis or the Ub-independent 20S proteasome and by diminishing oxidative stress through the activation of antioxidant enzymes and decreasing Cd accumulation due to higher CAX3 and lower IRT1 and HMA-A/B expression in response to 50 µM Cd challenge for 3 weeks.

Exogenous salicylic acid protects phospholipids against cadmium stress in flax (Linum usitatissimum L.)

Salicylic acid (SA) promotes plant defense responses against toxic metal stresses. The present study addressed the hypothesis that 8-h SA pretreatment, would alter membrane lipids in a way that would protect against Cd toxicity. Flax seeds were pre-soaked for 8h in SA (0, 250 and 1000µM) and then subjected, at seedling stage, to cadmium (Cd) stress. At 100µM CdCl2, significant decreases in the percentages of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (MGDG) and changes in their relative fatty acid composition were observed in Cd-treated roots in comparison with controls. However, in roots of 8-h SA pretreated plantlets, results showed that the amounts of PC and PE were significantly higher as compared to non-pretreated plantlets. Additionally, in both lipid classes, the proportion of linolenic acid (18:3) increased upon the pretreatment with SA. This resulted in a significant increase in the fatty acid unsaturation ratio of the root PC and PE classes. As the exogenous application of SA was found to be protective of flax lipid metabolism, the possible mechanisms of protection against Cd stress in flax roots were discussed.

Positive effects of salicylic acid pretreatment on the composition of flax plastidial membrane lipids under cadmium stress

Interest in use of flax (Linum usitatissimum L.) as cadmium (Cd)-accumulating plant for phytoextraction of contaminated soils opened up a new and promising avenue toward improving tolerance of its varieties and cultivars to Cd stress. The aim of this study is to get insights into the mechanisms of Cd detoxification in cell membranes, by exploring the effects of salicylic acid (SA)-induced priming on fatty acids and lipid composition of flax plantlets, grown for 10 days with 50 and 100 μM Cd. At leaf level, levels of monogalactosyldiacylglycerol (MGDG), phosphatidylcholine (PC), phosphatidylglycerol (PG), and neutral lipids (NL) have shifted significantly in flax plantlets exposed to toxic CdCl2 concentrations, as compared to that of the control. At 100 μM Cd, the linoleic acid (C18:2) decreases mainly in digalactosyldiacylglycerol (DGDG) and all phospholipid species, while linolenic acid (C18:3) declines mostly in MGDG and NL. Conversely, at the highest concentration of the metal, SA significantly enhances the levels of MGDG, PG and phosphatidic acid (PA), and polyunsaturated fatty acids mainly C18:2 and C18:3. Furthermore, SA pretreatment seems to reduce the Cd-induced alterations in both plastidial and extraplastidial lipid classes, but preferentially preserves the plastidial lipids by acquiring higher levels of polyunsaturated fatty acids. These results suggest that flax plantlets pretreated with SA exhibits more stability of their membranes under Cd-stress conditions.

Olive mill waste biochar: a promising soil amendment for metal immobilization in contaminated soils

The potential use of biochar from olive mill waste for in situ remediation of metal contaminated soils was evaluated. Biochar was mixed with metal contaminated soil originating from the vicinity of an old zinc smelter. Soil-biochar mixtures were equilibrated for 30 and 90 days. At these time points, Ca(NO3)2 exchangeable metals were determined, and effects of the biochar amendment on soil toxicity were investigated using plants, bacteria, and earthworms. Bean (Phaseolus vulgaris) growth, metal content, antioxidative enzymes activities, and soluble protein contents were determined. Furthermore, effects on soil microbial communities (activity, diversity, richness) were examined using Biolog ECOplates. After 120 days of soil-biochar equilibration, effects on weight and reproduction of Eisenia foetida were evaluated. With increasing biochar application rate and equilibration period, Ca(NO3)2 exchangeable metals decreased, and growth of bean plants improved; leaf metal contents reduced, the activities of antioxidative stress enzymes decreased, and soluble protein contents increased. Soil microbial activity, richness, and diversity were augmented. Earthworm mortality lowered, and their growth and reproduction showed increasing trends.

OsACA6, a P-type 2B Ca(2+) ATPase functions in cadmium stress tolerance in tobacco by reducing the oxidative stress load

MAIN CONCLUSION

The present study demonstrates the first direct evidence of the novel role of OsACA6 in providing Cd (2+) stress tolerance in transgenic tobacco by maintaining cellular ion homeostasis and modulating ROS-scavenging pathway. Cadmium, a non-essential toxic heavy metal, interferes with the plant growth and development. It reaches the leaves through xylem and may become part of the food chain, thus causing detrimental effects to human health. Therefore, there is an urgent need to develop strategies for engineering plants for Cd(2+) tolerance and less accumulation. The members of P-type ATPases family transport metal ions including Cd(2+), and thus play important role an ion homeostasis. The present study elucidates the role of P-type 2B Ca(2+) ATPase (OsACA6) in Cd(2+) stress tolerance. The transcript levels of OsACA6 were up-regulated upon Cd(2+), Zn(2+) and Mn(2+) exposure. Transgenic tobacco expressing OsACA6 showed tolerance towards Cd(2+) stress as demonstrated by several physiological indices including root length, biomass, chlorophyll, malondialdehyde and hydrogen peroxide content. The roots of the transgenic lines accumulated more Cd(2+) as compared to shoot. Further, confocal laser scanning microscopy showed that Cd(2+) exposure altered Ca(2+) uptake in OsACA6 transgenic plants. OsACA6 expression in tobacco also protected the transgenic plants from oxidative stress by enhancing the activity of enzymatic (SOD, CAT, APX, GR) and non-enzymatic (GSH and AsA) antioxidant machinery. Transgenic lines also tolerated Zn(2+) and Mn(2+) stress; however, tolerance for these ions was not as significant as observed for Cd(2+) exposure. Thus, overexpression of OsACA6 confers Cd(2+) stress tolerance in transgenic lines by maintaining cellular ion homeostasis and modulating reactive oxygen species (ROS)-scavenging pathway. The results of the present study will help to develop strategies for engineering Cd(2+) stress tolerance in economically important crop plants.

Resistance through inhibition: ectopic expression of serine protease inhibitor offers stress tolerance via delayed senescence in yeast cell

Protease inhibitors have been known to confer multiple stress tolerance in transgenic plants. We have assessed growth of yeast (Pichia pastoris GS115) strains expressing inhibitory repeat domains (PpIRD(+)) of previously characterized Capsicum annuum protease inhibitors under high salt, heavy metal and oxidative stress. PpIRD(+) strains exhibited multiple stress tolerance and showed differential molecular responses at transcriptional and translational level on exposure to stress inducing agents like heavy metal, high salt and H2O2. PpIRD(+) strains display significant reduction in metacaspase (Yca1) activity, the key enzyme in apoptosis, indicates the possibility of cross reactivity of IRDs (serine protease inhibitor) with cysteine proteases. PpIRD(+) and Saccharomyces cerevisiae knockout with Yca1 (ΔYca1) strain showed similar growth characteristics under stress, which indicated the delayed senescence due to cellular metacaspase inhibition. Molecular docking study showed a close proximity of IRDs reactive site and the active site of metacaspase in the complex that signified their strong interactions. Maintenance of GAPDH activity, primary target of metacaspase, in PpIRD(+) strain evidenced the inhibition of metacaspase activity and survival of these cells under stress. This report demonstrates a potential molecular mechanism of protease inhibitor-based multiple stress tolerance in yeast strains.

Responses of proteolytic enzymes in embryonic axes of germinating bean seeds under copper stress

The changes in protease activities in embryonic axes during the first days of bean (Phaseolus vulgaris L.) seed germination were investigated in response to copper stress. Synthetic substrates and specific protease inhibitors have been used to define qualitatively and quantitatively different catalytic classes, particularly endoproteases (EP), carboxypeptidases (CP) and aminopeptidases (AP), then identify which ones were affected in the presence of copper. In fact, a failure in storage proteins mobilization and a disorder of nitrogen supply at enzymatic level occurred in Cu. In fact, Cu inhibited azocaseinolytic activity (ACA) and cysteine-, aspartic-, serine-, and metallo-endopeptidases activities (Cys-EP, Asp-EP, Ser-Ep, and Met-EP, respectively). Besides, Cu affected leucine- and proline-aminopeptidases (LAP and PAP, respectively) and glycine-carboxypeptidases (Gly-CP). The proteolytic responses might also be associated with the decrease in defense capacity in the Cu-treated embryos.

Protective role of selenium on pepper exposed to cadmium stress during reproductive stage

The aim of the present study was to examine the effects of exogenous selenium (Se) supplementation on the tolerance of pepper (Capsicum annuum L.) cv. Suryamukhi Cluster plants to cadmium (Cd) phytotoxicity at the reproductive stage. The pepper plants were supplied with Cd (0, 0.25 or 0.50 mM) and Se (0, 3 or 7 μM), individually or simultaneously, three times during the experiment. The obtained results show that Cd had deleterious effect on pepper plants at the reproductive stage. However, Se supplementation improved the flower number, fruit number and fruit diameter in plants exposed to 0.50 mM Cd. Moreover, both Se concentrations used in 0.25 mM Cd-treated plants and 3 μM Se in 0.50 mM Cd-treated plants enhanced fruit yield per plant as compared to Cd-alone treatment. The chlorophyll concentrations significantly increased in the fruits of Cd-exposed plants after Se addition. However, Se supplementation reduced total carotenoids and total soluble solid (TSS) concentrations in the pepper fruits exposed to Cd. Selenium also generally enhanced the total antioxidant activity of pepper fruits subjected to Cd. Both Se concentrations used increased mean productivity (MP), stress tolerance index (STI) and yield stability index (YSI) in plants grown in the medium containing 0.25 mM Cd. At low concentration (3 μM), Se significantly increased geometric mean productivity (GMP), STI and YSI of plant exposed to 0.50 mM Cd. The highest Cd concentration in the fruits was achieved at 0.50 mM Cd and Se application significantly reduced Cd accumulation in the Cd-exposed plants. Our results indicate that application of Se can alleviate Cd toxicity in pepper plants at the reproductive stage by restricting Cd accumulation in fruits, enhancing their antioxidant activity and thus improving the reproductive and stress tolerance parameters.

Cadmium induces two waves of reactive oxygen species in Glycine max (L.) roots

Cadmium (Cd) is a non-essential heavy metal that may be toxic or even lethal to plants as it can be easily taken up by the roots and loaded into the xylem to the leaves. Using soybean roots (Glycine max L.) DM 4800, we have analysed various parameters related to reactive oxygen metabolism and nitric oxide (NO) during a 6 day Cd exposure. A rise in H(2)O(2) and NO, and to a lesser extent O(2)(·-) content was observed after 6 h exposure with a concomitant increase in lipid peroxidation and carbonyl group content. Both oxidative markers were significantly reduced after 24 h. A second, higher wave of O(2)(·-) production was also observed after 72 h of exposure followed by a reduction until the end of the treatment. NOX and glicolate oxidase activity might be involved in the initial Cd-induced reactive oxygen species (ROS) production and it appears that other sources may also participate. The analysis of antioxidative enzymes showed an increase in glutathione-S-transferase activity and in transcript levels and activity of enzymes involved in the ascorbate-glutathione cycle and the NADPH-generating enzymes. These results suggest that soybean is able to respond rapidly to oxidative stress imposed by Cd by improving the availability of NADPH necessary for the ascorbate-glutathione cycle.

Effect of aluminum on protein oxidation, non-protein thiols and protease activity in seedlings of rice cultivars differing in aluminum tolerance

The effect of toxic concentrations of aluminum (Al) was investigated on contents of protein-thiols, non-protein and total thiols, protein carbonylation and protease activity in the seedlings of Al-sensitive (Al-S) Indica rice cv. HUR-105 and Al-tolerant (Al-T) cv. Vandana grown in sand cultures. Al treatment of 178 μM and 421 μM for 3-12 days caused a significant decline in the level of protein thiols, rise in non-protein thiols (NPTs) as well as protein carbonyl content and an insignificant alteration in the level of total thiols in cv. HUR-105 seedlings. However, in the seedlings of Al-T cv. Vandana, no significant alteration could be observed on any of these parameters with Al treatment. Al treatment inhibited protease activity in roots, whereas the opposite trend was seen in shoots. New isozymes of protease appeared in shoots of cv. Vandana with increased level of Al treatment. Our results show a link between protein thiols and NPTs and suggest the role of NPTs in the repair and protection of protein thiols. Inhibitory effect of Al on protease activity in roots could be a major reason for Al rhizotoxic effects. Al tolerance in rice appears to be associated with lesser content of protein thiols in roots, smaller amount of carbonylated proteins in roots as well as shoots and higher protease activity in shoots.

Role of the ubiquitin-proteasome pathway and some peptidases during seed germination and copper stress in bean cotyledons

The role of the ubiquitin (Ub)-proteasome pathway and some endo- and aminopeptidases (EPs and APs, respectively) was studied in cotyledons of germinating bean seeds (Phaseolus vulgaris L.). The Ub system appeared to be important both in the early (3 days) and late (9 days) phases of germination. In the presence of copper, an increase in protein carbonylation and a decrease in reduced -SH pool occurred, indicating protein damage. This was associated with an enhancement in accumulation of malondialdehyde, a major product of lipid peroxidation, and an increase in content of hydrogen peroxide (H2O2), showing oxidative stress generation. Moreover, copper induced inactivation of the Ub-proteasome (EC 3.4.25) pathway and inhibition of leucine and proline aminopeptidase activities (EC 3.4.11.1 and EC 3.4.11.5, respectively), thus limiting their role in modulating essential metabolic processes, such as the removal of regulatory and oxidatively-damaged proteins. By contrast, total trypsin and chymotrypsin-like activities (EC 3.4.21.4 and EC 3.4.21.1, respectively) increased after copper exposure, in parallel with a decrease in their inhibitor capacities (i.e. trypsin inhibitor and chymotrypsin inhibitor activity), suggesting that these endoproteases are part of the protective mechanisms against copper stress.

Early transcriptional responses to mercury: a role for ethylene in mercury-induced stress

Understanding the cellular mechanisms of plant tolerance to mercury (Hg) is important for developing phytoremediation strategies of Hg-contaminated soils. The early responses of alfalfa (Medicago sativa) seedlings to Hg were studied using transcriptomics analysis. A Medicago truncatula microarray was hybridized with high-quality root RNA from M. sativa treated with 3 μM Hg for 3, 6 and 24 h. The transcriptional pattern data were complementary to the measurements of root growth inhibition, lipid peroxidation, hydrogen peroxide (H2 O2 ) accumulation and NADPH-oxidase activity as stress indexes. Of 559 differentially expressed genes (DEGs), 91% were up-regulated. The majority of DEGs were shared between the 3 and 6 h (60%) time points, including the 'stress', 'secondary metabolism' and 'hormone metabolism' functional categories. Genes from ethylene metabolism and signalling were highly represented, suggesting that this phytohormone may be relevant for metal perception and homeostasis. Ethylene-insensitive alfalfa seedlings preincubated with the ethylene signalling inhibitor 1-methylcyclopronene and Arabidopsis thaliana ein2-5 mutants confirmed that ethylene participates in the early perception of Hg stress. It modulates root growth inhibition, NADPH-oxidase activity and Hg-induced apoplastic H2 O2 accumulation. Therefore, ethylene signalling attenuation could be useful in future phytotechnological applications to ameliorate stress symptoms in Hg-polluted plants.

Proteolytic activities in Phaseolus vulgaris cotyledons under copper stress

The changes in the protease activities of bean cotyledons were investigated in response to copper stress. Assays using synthetic substrates and specific protease inhibitors followed by activity measurements and electrophoresis analysis allowed to study the classes of enzymes involved in the storage protein mobilization during the germination of bean (Phaseolus vulgaris L) seeds, and then identify which ones were affected in the presence of 200 μM CuCl2 in the imbibition medium. Copper treatment affected embryo growth and total protease activity. The results of SDS-gelatin-PAGE show that Cu excess led to a decrease in protease activity of 45 to 66 kDa. Moreover, cysteine-, aspartic- and metallo-protease activities were markedly lowered under copper stress, while serine-protease one was enhanced as well as its activity dependent abundance in comparison with control. However, the relative distribution of major cysteine protease in H2O-germinated seeds was significantly diminished after Cu exposure. Thus, copper excess can disturb the nitrogen freeing from reserve tissues at enzymatic level; differential responses of protease classes are discussed, notably, cysteine protease in the way of storage protein mobilization and serine protease in protective mechanism one.

Up-regulation of leucine aminopeptidase-A in cadmium-treated tomato roots

The effects of cadmium (Cd) on aminopeptidase (AP) activities and Leucine-AP (LAP) expression were investigated in the roots of tomato (Solanum lycopersicum L., var Ibiza) plants. Three-week-old plants were grown for 10 days in the presence of 0.3-300 μM Cd and compared to control plants grown in the absence of Cd. AP activities were measured using six different p-nitroanilide (p-NA) substrates. Leu, Met, Arg, Pro and Lys hydrolyzing activities increased in roots of Cd-treated plants, while Phe-pNA cleavage was not enhanced after Cd treatments. The use of peptidase inhibitors showed that most of the Leu-pNA hydrolyzing activity was related to one or several metallo-APs. Changes in Lap transcripts, protein and activities were measured in the roots of 0 and 30-μM Cd-treated plants. LapA transcript levels increased in Cd-treated roots, whereas LapN RNAs levels were not modified. To assess amount of Leu-pNA hydrolyzing activity associated with the hexameric LAPs, LAP activity was measured following immunoprecipitation with a LAP polyclonal antiserum. LAP activity increased in Cd-treated roots. There was a corresponding increase in LAP-A protein levels detected in 2D-immunoblots. The role of LAP-A in the proteolytic response to Cd stress is discussed.

Investigating the plant response to cadmium exposure by proteomic and metabolomic approaches

Monitoring molecular dynamics of an organism upon stress is probably the best approach to decipher physiological mechanisms involved in the stress response. Quantitative analysis of proteins and metabolites is able to provide accurate information about molecular changes allowing the establishment of a range of more or less specific mechanisms, leading to the identification of major players in the considered pathways. Such tools have been successfully used to analyze the plant response to cadmium (Cd), a major pollutant capable of causing severe health issues as it accumulates in the food chain. We present a summary of proteomics and metabolomics works that contributed to a better understanding of the molecular aspects involved in the plant response to Cd. This work allowed us to provide a finer picture of general signaling, regulatory and metabolic pathways that appeared to be affected upon Cd stress. In particular, we conclude on the advantage of employing different approaches of global proteome- and metabolome-wide techniques, combined with more targeted analysis to answer molecular questions and unravel biological networks. Finally, we propose possible directions and methodologies for future prospectives in this field, as many aspects of the plant-Cd interaction remain to be discovered.

Effects of long-term cadmium exposure on growth and metabolomic profile of tomato plants

The response of tomato plants to long-term cadmium exposure was evaluated after a 90-days long culture in hydroponic conditions (0, 20, and 100 μM CdCl(2)). Cadmium preferentially accumulated in roots, and to a lower extent in upper parts of plants. Absolute quantification of 28 metabolites was obtained through (1)H NMR, HPLC-PDA, and colorimetric methods. The principal component analysis showed a clear separation between control and Cd treated samples. Proline and total ascorbate amounts were reduced in Cd-treated leaves, whereas α-tocopherol, asparagine, and tyrosine accumulation increased, principally in 100 μM Cd treated leaves. Carotenoid and chlorophyll contents decreased only in 100 μM Cd-mature-leaves, which correlate with a reduced expression of genes essential for isoprenoid and carotenoid accumulations. Our results show that tomato plants acclimatize during long-term exposure to 20 μM Cd. On the contrary, 100μM Cd treatment results in drastic physiological and metabolic perturbations leading to plant growth limitation and fruit set abortion.

Housekeeping gene selection in poplar plants under Cd-stress: comparative study for real-time PCR normalisation

Real-time RT-PCR is currently the most sensitive, specific and precise approach to analyse gene expression changes in plant stress studies. The determination of biologically meaningful transcript quantities requires accurate normalisation of the raw data. During relative quantification the reliability of the results depends on the stable expression of the endogenous control genes across the experimental samples. Four widely used internal control genes (cyclophilin, elongation factor 1α, polyubiquitin, tubulin β-chain) and two potential candidates (serine/threonine-protein phosphatase 2A and ubiquitin-conjugating enzyme) genes were assessed under Cd-stress and at different developmental stages in leaves of Populus jacquemontiana D. var. glauca H. Complementary DNA (RiboGreen) based quantification method revealed variations in the expression level of reference genes. The variability was more pronounced under severe stress conditions. Less variation was observed in the case of ef-1α, pp2a and ubc10. Transcript level changes of a target gene, psa-h, was also evaluated by two independent normalisation strategies, by the RiboGreen method or by using multiple references. The impact of variability of reference gene on the target gene evaluation was demonstrated. It was proved that in the absence of suitable housekeeping genes, for example under severe stress, RiboGreen method is convenient tool for transcript normalisation.

Evidence for the Existence in Arabidopsis thaliana of the Proteasome Proteolytic Pathway: ACTIVATION IN RESPONSE TO CADMIUM

Heavy metals are known to generate reactive oxygen species that lead to the oxidation and fragmentation of proteins, which become toxic when accumulated in the cell. In this study, we investigated the role of the proteasome during cadmium stress in the leaves of Arabidopsis thaliana plants. Using biochemical and proteomics approaches, we present the first evidence of an active proteasome pathway in plants. We identified and characterized the peptidases acting sequentially downstream from the proteasome in animal cells as follows: tripeptidyl-peptidase II, thimet oligopeptidase, and leucine aminopeptidase. We investigated the proteasome proteolytic pathway response in the leaves of 6-week-old A. thaliana plants grown hydroponically for 24, 48, and 144 h in the presence or absence of 50 mum cadmium. The gene expression and proteolytic activity of the proteasome and the different proteases of the pathway were found to be up-regulated in response to cadmium. In an in vitro assay, oxidized bovine serum albumin and lysozyme were more readily degraded in the presence of 20 S proteasome and tripeptidyl-peptidase II than their nonoxidized form, suggesting that oxidized proteins are preferentially degraded by the Arabidopsis 20 S proteasome pathway. These results show that, in response to cadmium, the 20 S proteasome proteolytic pathway is up-regulated at both RNA and activity levels in Arabidopsis leaves and may play a role in degrading oxidized proteins generated by the stress.

Transcriptome analysis of cadmium response in Ganoderma lucidum

Ganoderma species are white-rot fungi widespread throughout the world. In this study, a wild isolate of Ganoderma lucidum was first collected and its tolerance was tested in a medium containing 3.0 mM CdCl(2). The cDNA-amplified fragment length polymorphism method was conducted to analyze the transcription profiling of this Ganoderma species in response to Cd treatment. In total, 12 925 transcript-derived fragments (TDFs) were amplified using 256 primer combinations. Forty-nine differentially expressed TDFs were confirmed by DNA dot-blot analysis. Northern blot analysis was used to verify the transcription levels of 34 Cd-inducible TDFs. Sequence analysis indicated that genes involved in reactive oxygen species generation, synthesis of sulfur-containing metabolites, translation machinery, DNA repair, transporting system, proteolysis pathway, mitochondria function, and cell wall biosynthesis were upregulated by Cd treatment. Our results provide a genome-wide transcriptome profiling of Cd response in Ganoderma species.