Assessing the regulation of leaf redox status under water stress conditions in Arabidopsis thaliana: Col-0 ecotype (wild-type and vtc-2), expressing mitochondrial and cytosolic roGFP1

Using Arabidopsis plants Col-0 and vtc2 transformed with a redox sensitive green fluorescent protein, (c-roGFP) and (m-roGFP), we investigated the effects of a progressive water stress and re-watering on the redox status of the cytosol and the mitochondria. Our results establish that water stress affects redox status differently in these two compartments, depending on phenotype and leaf age, furthermore we conclude that ascorbate plays a pivotal role in mediating redox status homeostasis and that Col-0 Arabidopsis subjected to water stress increase the synthesis of ascorbate suggesting that ascorbate may play a role in buffering changes in redox status in the mitochondria and the cytosol, with the presumed buffering capacity of ascorbate being more noticeable in young compared with mature leaves. Re-watering of water-stressed plants was paralleled by a return of both the redox status and ascorbate to the levels of well-watered plants. In contrast to the effects of water stress on ascorbate levels, there were no significant changes in the levels of glutathione, thereby suggesting that the regeneration and increase in ascorbate in water-stressed plants may occur by other processes in addition to the regeneration of ascorbate via the glutathione. Under water stress in vtc2 lines it was observed stronger differences in redox status in relation to leaf age, than due to water stress conditions compared with Col-0 plants. In the vtc2 an increase in DHA was observed in water-stressed plants. Furthermore, this work confirms the accuracy and sensitivity of the roGFP1 biosensor as a reporter for variations in water stress-associated changes in redox potentials.     

High Resolution Imaging of Temporal and Spatial Changes of Subcellular Ascorbate,Glutathione and H2O2 Distribution during Botrytis cinerea Infection in Arabidopsis

In order to study the mechanisms behind the infection process of the necrotrophic fungus Botrytis cinerea, the subcellular distribution of hydrogen peroxide (H₂O₂) was monitored over a time frame of 96 h post inoculation (hpi) in Arabidopsis thaliana Col-0 leaves at the inoculation site (IS) and the area around the IS which was defined as area adjacent to the inoculation site (AIS). H₂O₂ accumulation was correlated with changes in the compartment-specific distribution of ascorbate and glutathione and chloroplast fine structure. This study revealed that the severe breakdown of the antioxidative system, indicated by a drop in ascorbate and glutathione contents at the IS at later stages of infection correlated with an accumulation of H₂O₂ in chloroplasts, mitochondria, cell walls, nuclei and the cytosol which resulted in the development of chlorosis and cell death, eventually visible as tissue necrosis. A steady increase of glutathione contents in most cell compartments within infected tissues (up to 600% in chloroplasts at 96 hpi) correlated with an accumulation of H₂O₂ in chloroplasts, mitochondria and cell walls at the AIS indicating that high glutathione levels could not prevent the accumulation of reactive oxygen species (ROS) which resulted in chlorosis. Summing up, this study reveals the intracellular sequence of events during Botrytis cinerea infection and shows that the breakdown of the antioxidative system correlated with the accumulation of H₂O₂ in the host cells. This resulted in the degeneration of the leaf indicated by severe changes in the number and ultrastructure of chloroplasts (e.g. decrease of chloroplast number, decrease of starch and thylakoid contents, increase of plastoglobuli size), chlorosis and necrosis of the leaves.     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

Drought stress induces oxidative stress and the antioxidant defense system in ascorbate-deficient vtc1 mutants of Arabidopsis thaliana

Drought stress has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). To increase our understanding of the effects of drought stress on antioxidant processes, we investigated the response of the ascorbate-deficient Arabidopsis thaliana vtc1 mutant to drought stress. After drought stress, vtc1 mutants exhibited increases in several oxidative parameters, including H₂O₂ content and the production of thiobarbituric acid reactive substances. Decreases in chlorophyll content and chlorophyll fluorescence parameters were also observed. The vtc1 mutants had higher total glutathione than did wild-type (WT) plants after 48 h of drought stress. A reduced ratio of glutathione/total glutathione and an increased ratio of dehydroascorbate/total ascorbate were observed in the vtc1 mutants compared with the WT plants. In addition, the activities of enzymes that are responsible for ROS scavenging, including superoxide dismutase, catalase, and ascorbate peroxidase, were decreased in the vtc1 mutants compared with the WT plants. Similar reductions in activity in the vtc1 mutant were observed for the enzymes that are responsible for the regeneration of ascorbate and glutathione, including monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that low intrinsic ascorbate and impaired ascorbate–glutathione cycling in the vtc1 mutant induced a decrease in the reduced form of ascorbate, which enhanced sensitivity to drought stress.     

N-acetyl-cysteine alleviates Cd toxicity and reduces Cd uptake in the two barley genotypes differing in Cd tolerance

A hydroponic experiment was carried out to study the physiological mechanisms of N-acetyl cysteine (NAC) in mitigating cadmium (Cd) toxicity in two barley (Hordeum vulgare L.) genotypes, Dong 17 (Cd-sensitive) and Weisuobuzhi (Cd-tolerant). Addition of 200 μM NAC to a culture medium containing 5 μM Cd (Cd + NAC) markedly alleviated Cd-induced growth inhibition and toxicity, maintained root cell viability, and dramatically depressed O ₂ ^·? and ·OH, and malondialdehyde accumulation, significantly reduced Cd concentration in leaves and roots, especially in the sensitive genotype Dong 17. External NAC counteracted Cd-induced alterations of certain antioxidant enzymes, e.g., brought root superoxide dismutase and glutathione reductase, leaf/root peroxidase and glutathione peroxidase activities of the both genotypes down towards the control level, but elevated Cd-stress-depressed leaf catalase in Dong 17 and root ascorbate peroxidase activities in both genotypes. NAC counteracted Cd-induced alterations in amino acids and microelement contents. Furthermore, NAC significantly reduced Cd-induced damage to leaf/root ultrastructure, e.g. the shape of chloroplasts in plants treated with Cd + NAC was relatively normal with well-structured thylakoid membranes and parallel pattern of lamellae but less osmiophilic plastoglobuli compared with Cd alone treatment; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes. These results suggested that under Cd stress, NAC may protects barley seedlings against Cd-induced damage by directly and indirectly scavenging reactive oxygen species and by maintaining stability and integrity of the subcellular structure.     

Ectopic Expression of Riboflavin-binding Protein Gene TsRfBP Paradoxically Enhances Both Plant Growth and Drought Tolerance in Transgenic Arabidopsis thaliana

Riboflavin is the precursor of the coenzymes flavin monophosphate (FMN) and flavin adenine dinucleotide (FAD), which serve as indispensable redox cofactors in all plants. Numerous data indicate that riboflavin is involved in pathogen resistance but less data are available on abiotic stress tolerance. In this experiment, the overexpression of the riboflavin-binding protein resulted in an enhancement of vegetative growth and net photosynthetic rate, and an acceleration of floral transition in transgenic Arabidopsis thaliana REAT11 (containing less than half the normal levels of free riboflavin, FMN, and FAD) compared to wild-type Col-0 under nonstressed conditions. The effect of drought stress on the antioxidant response of Col-0 and REAT11 was compared, where 20- and 40-day-old grown plants were subjected to 10 % PEG 6000 treatment for 2 days. Stress conditions caused a significant increase in H₂O₂ accumulation, lipid peroxidation, and membrane permeability in Col-0 over that in REAT11. Greater activity levels of superoxide dismutase, ascorbate peroxidase, and glutathione reductase were observed in the leaves of REAT11 compared to those of Col-0. Significant increases in total ascorbate and glutathione content and higher ratios of ASC/DHA: (ASC and DHA are reduced and oxidized ascorbate, respectively) and GSH/GSSG: (GSH and GSSG are reduced and oxidized glutathione, respectively) were observed in the leaves of REAT11 compared to those in Col-0 under drought conditions. In addition, enhancement of free proline and soluble sugar accumulation was observed in REAT11 compared to Col-0 under stress. Our results suggest that a slight deficiency in free riboflavin can paradoxically induce both a higher vegetative growth rate and an enhanced tolerance to drought in transgenic plants. The “stress escape” hypothesis is proposed here to explain this interesting phenomenon.     

Cadmium induced changes in subcellular glutathione contents within glandular trichomes of Cucurbita pepo L.

Plants cope with cadmium (Cd) stress by complexation with phytochelatins (Pc), metallothioneins and glutathione and sequestration within vacuoles. Especially glutathione was found to play a major role in Cd detoxification as Cd shows a high binding affinity towards thiols and as glutathione is a precursor for Pc synthesis. In the present study, we have used an immunohistochemical approach combined with computer-supported transmission electron microscopy in order to measure changes in the subcellular distribution of glutathione during Cd-stress in mesophyll cells and cells of different glandular trichomes (long and short stalked) of Cucurbita pepo L. subsp. pepo var. styriaca Greb. Even though no ultrastructural alterations were observed in leaf and glandular trichome cells after the treatment of plants with 50 µM cadmium chloride (CdCl₂) for 48 h, all cells showed a large decrease in glutathione contents. The strongest decrease was found in nuclei and the cytosol (up to 76%) in glandular trichomes which are considered as a major side of Cd accumulation in leaves. The ratio of glutathione between the cytosol and nuclei and the other cell compartments was strongly decreased only in glandular trichomes (more than 50%) indicating that glutathione in these two cell compartments is especially important for the detoxification of Cd in glandular trichomes. Additionally, these data indicate that large amounts of Cd are withdrawn from nuclei during Cd exposure. The present study gives a detailed insight into the compartment-specific importance of glutathione during Cd exposure in mesophyll cells and glandular trichomes of C. pepo L. plants.     

γ-Aminobutyric Acid (GABA) Imparts Partial Protection from Heat Stress Injury to Rice Seedlings by Improving Leaf Turgor and Upregulating Osmoprotectants and Antioxidants

Four-day-old rice (Oryza sativa L.) seedlings were subjected to varying temperatures of 30/20, 35/25, and 42/37 °C [light/dark (15/9 h); light intensity: 350 μmol m^?2 s^?1, RH 65–70 %] in glass Petri dishes for 10 days in the absence (control) or the presence of γ-aminobutyric acid (GABA) 1 mM under the controlled conditions of a growth chamber. With rise in temperature, the length of both shoots and roots was inhibited severely and there was a marked decrease in survival, especially at 42/37 °C. Endogenous GABA content increased more than twofold in moderately stressed (MS) 35/25 °C plants, whereas it decreased sevenfold in severely stressed (SS) 42/37 °C plants compared to MS plants, and this decrease was associated with marked reduction in growth and survival. Exogenous application of GABA to the heat-stressed plants significantly improved growth as well as survival. It was linked to reduction in damage to membranes, improvement in cellular reducing ability, chlorophyll content, and photochemical efficiency in shoots. Relative leaf water content and stomatal conductance were also improved with the application of GABA and their improvement was related to increased accumulation of the osmolytes proline and trehalose. In the presence of GABA, the shoots suffered less oxidative damage in terms of malondialdehyde and hydrogen peroxide contents. The activities of enzymatic antioxidants such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase were severely inhibited in plants growing at 42/37 °C compared to those growing at 35/25 °C. The nonenzymatic antioxidants like ascorbate and glutathione followed a similar pattern. GABA-treated SS plants showed enhanced levels of enzymatic and nonenzymatic antioxidants compared to untreated controls. Thus, GABA appears to impart partial protection from heat stress to rice plants by elevating leaf turgor due to increased accumulation of osmolytes and reduction of oxidative damage by stimulation of antioxidants. These findings provided evidence about the involvement of GABA in governing heat sensitivity in rice.     

Ascorbate plays a key role in alleviating low temperature-induced oxidative stress in Arabidopsis

Low temperature has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). In order to study the role of ascorbate under chilling stress, the response of an ascorbate-deficient Arabidopsis thaliana mutant vtc2-1 to low temperature (2°C) was investigated. After chilling stress, vtc2-1 mutants exhibited oxidative damage. An increase in the H₂O₂ generation and the production of thiobarbituric acid reactive substances (TBARS), and a decrease in chlorophyll content, the maximal photochemical efficiency of PSII (F_v/F_m) and oxidizable P₇₀₀ were also noted. The ratio of ascorbate/dehydroascorbate and reduced glutathione/oxidzed glutathione in the vtc2-1 mutants were reduced, compared with the wild type (WT) plants. The activities of antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and soluble antioxidants were lower in the vtc2-1 mutants than those in WT plants. These results suggested that the ascorbate-deficient mutant vtc2-1 was more sensitive to chilling treatment than WT plants. The low temperature-induced oxidative stress was the major cause of the decrease of PSII and PSI function in the vtc2-1 mutants. Ascorbate plays a critical role of defense without which the rest of the ROS defense network is unable to react effectively.     

Exogenously applied salicylic acid maintains redox homeostasis in salt-stressed <Emphasis Type="Italic">Arabidopsis gr1</Emphasis> mutants expressing cytosolic roGFP1

Exogenous salicylic acid (SA) can be used for chemical hardening to alleviate oxidative stress in plants exposed to salinity. The treatment of 5-week-old Arabidopsis thaliana plants with increasing doses of SA alters the ascorbate (ASC) and glutathione (GSH) pools, and modulates their redox status and the activity of several antioxidant enzymes, such as ascorbate peroxidase (APX) and glutathione reductase (GR). To investigate the role of GR in the maintenance of cytoplasmic redox homeostasis after hardening by SA, wild type (WT) and gr1 mutant plants, expressing the cytoplasmic redox-sensitive green fluorescent protein (c-roGFP1), were pre-treated with 10^?7 and 10^?5 M SA for 2 weeks and subsequently exposed to 100 mM NaCl. The redox status of the salt-stressed WT plants became more oxidized, which was prevented by pretreatment with 10^?5 M SA. The gr1 mutants showed more positive redox potential than WT plants, which could be reversed by treatment with 10^?5 M SA. In mutants, the increased GSH levels may have compensated for the deleterious effect of GR deficiency and stabilized the redox potential in plants exposed to salinity. The ASC regeneration in WT plants shifted from the GSH-dependent dehydroascorbate reductase (DHAR) reaction to the NAD(P)H-dependent monodehydroascorbate reductase (MDHAR) activity during chemical hardening, which contributed to the preservation of the GSH pool in plants under salt stress. Our results suggest that the maintenance of GSH levels and redox homeostasis by SA-mediated hardening play a major role in priming and defending against salt stress.     

Oxidative damages induced by short-term exposure to cadmium in bean plants: Protective role of salicylic acid

The role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity was investigated in a hydroponic cultivation system. Short-term exposure of bean (Phaseolus vulgaris) plants to 20 μM Cd inhibited biomass production and intensively increased accumulation of Cd in both roots and leaves. At leaf level, Cd significantly decreased mineral ions, chlorophyll and carotenoids concentrations. Concomitantly, Cd enhanced electrolyte leakage, H₂O₂ content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. SA pretreatment decreased the uptake and the transport of Cd, alleviated the Cd-induced inhibition of nutrient absorption and led to a significant increase of chlorophyll and carotenoid content. SA application alleviated the oxidative damages as evidenced by the lowered H₂O₂ and MDA content. SA particularly induced an increase in both CAT and APX activities accompanied by a significant reduction in SOD and POD activities. As important antioxidants, ascorbate and glutathione contents in bean leaves exposed to cadmium were significantly decreased by SA treatment. These results reveal the potentiating effect of salicylic acid in regulating cadmium induced oxidative stress in bean plants.     

Involvement of antioxidant defense system in chill hardening-induced chilling tolerance in Jatropha curcas seedlings

Jatropha curcas L. is a sustainable energy plant with great potential for biodiesel production, and low temperature is an important limiting factor for its distribution and production. In this present work, chill hardening-induced chilling tolerance and involvement of antioxidant defense system were investigated in J. curcas seedlings. The results showed that chill hardening at 10 or 12 °C for 1 and 2 days greatly lowered death rate and alleviated electrolyte leakage as well as accumulation of the lipid peroxidation product malondialdehyde (MDA) of J. curcas seedlings under severe chilling stress at 1 °C for 1–7 days, indicating that the chill hardening significantly improved chilling tolerance of J. curcas seedlings. Measurement of activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and glutathione reductase (GR), and the levels of the antioxidants ascorbic acid (AsA) and glutathione (GSH) showed the chill hardening at 12 °C for 2 days could obviously increase the activities of these antioxidant enzymes and AsA and GSH contents in the hardened seedlings. When the hardened and non-hardening (control) seedlings were subjected to severe chilling stress at 1 °C for 1–7 days, the chill-hardened seedlings generally maintained significantly higher activities of the antioxidant enzymes SOD, APX, CAT, POD, and GR, and content of the antioxidants AsA and GSH as well as ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)], when compared with the control without chill hardening. All above-mentioned results indicated that the chill hardening could enhance the chilling tolerance, and the antioxidant defense system plays an important role in the chill hardening-induced chilling tolerance in J. curcas seedlings.     

5-Aminolevulinic acid ameliorates salinity-induced metabolic, water-related and biochemical changes in Brassica napus L.

A number of studies have established that plant growth and development in oilseed rape (Brassica napus L.) are hampered by salinity stress. Nowadays, researchers have focused on the use of plant growth regulators to increase plant tolerance against salinity. An experiment was performed to evaluate the effects of 5-aminolevulinic acid (ALA, 30 mg l^?1) on Brassica napus L. (cv. ??ZS 758??) plants under NaCl (100, 200 mM) salinity. Data presented here were recorded on two different leaf positions (first and third) to have a better understanding of the ameliorative role of ALA on NaCl-stressed oilseed rape plants. Results have shown that increasing salinity imposed negative impact on relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), whereas enhanced the level of relative conductivity, malondialdehyde (MDA) content, osmolytes (soluble sugar, soluble protein, free amino acid and proline) concentration, reactive oxygen species (ROS), and enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in two different leaf position samples. Foliar application of ALA improved relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), and also triggered the further accumulation of osmolytes (soluble sugar, soluble protein, free amino acid and proline) as well as enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in both leaf samples, whereas decreased the membrane permeability, MDA content and ROS production. Our results also indicate that osmolytes are preferentially accumulated in younger tissues.     

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20 μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20 μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.     

High salinity helps the halophyte <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis> in defense against Cd toxicity by maintaining redox balance and photosynthesis

Main conclusion

NaCl alleviates Cd toxicity in Sesvium portulacastrum by maintaining plant water status and redox balance, protecting chloroplasts structure and inducing some potential Cd ²⁺ chelators as GSH and proline. It has been demonstrated that NaCl alleviates Cd-induced growth inhibition in the halophyte Sesuvium portulacastrum. However, the processes that mediate this effect are still unclear. In this work we combined physiological, biochemical and ultrastructural studies to highlight the effects of salt on the redox balance and photosynthesis in Cd-stressed plants. Seedlings were exposed to different Cd concentrations (0, 25 and 50 µM Cd) combined with low (0.09 mM) (LS), or high (200 mM) NaCl (HS) in hydroponic culture. Plant–water relations, photosynthesis rate, leaf gas exchange, chlorophyll fluorescence, chloroplast ultrastructure, and proline and glutathione concentrations were analyzed after 1 month of treatment. In addition, the endogenous levels of stress-related hormones were determined in plants subjected to 25 µM Cd combined with both NaCl concentrations. In plants with low salt supply (LS), Cd reduced growth, induced plant dehydration, disrupted chloroplast structure and functioning, decreased net CO₂ assimilation rate (A) and transpiration rate (E), inhibited the maximum potential quantum efficiency (Fv/Fm) and the quantum yield efficiency (Φ _PSII) of PSII, and enhanced the non-photochemical quenching (NPQ). The addition of 200 mM NaCl (HS) to the Cd-containing medium culture significantly mitigated Cd phytotoxicity. Hence, even at similar internal Cd concentrations, HS-Cd plants were less affected by Cd than LS-Cd ones. Hence, 200 mM NaCl significantly alleviates Cd-induced toxicity symptoms, growth inhibition, and photosynthesis disturbances. The cell ultrastructure was better preserved in HS-Cd plants but affected in LS-Cd plants. The HS-Cd plants showed also higher concentrations of reduced glutathione (GSH), proline and jasmonic acid (JA) than the LS-Cd plants. However, under LS-Cd conditions, plants maintained higher concentration of salicylic acid (SA) and abscisic acid (ABA) than the HS-Cd ones. We conclude that in S. portulacastrum alleviation of Cd toxicity by NaCl is related to the modification of GSH and proline contents as well as stress hormone levels thus protecting redox balance and photosynthesis.

     

Ontogenic variation in response of Brassica campestris L. to cadmium toxicity

Abstract

Rapeseed (Brassica campestris L.) cv Pusa Gold plants, exposed to different cadmium (Cd) levels (0, 25, 50 and 100 mg kg^?1 soil) in greenhouse, pot culture experiment, were analyzed with reference to distribution of metal, accumulation of biomass and the degree of growth stage Cd-sensitivity. A significant maximum decrease in plant biomass was observed at Cd-exposed flowering stage followed by pre-flowering and post-flowering stages. Activities of enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) differentially increased; while, the concentrations of non-enzymatic antioxidants such as ascorbic acid (AsA) and glutathione (GSH) drastically decreased in plants exposed to Cd at various growth stages. However, the concentrations of GSH and AsA decreased maximally in plant groups exposed to Cd at their flowering stage. The maximum Cd-accumulation occurred in roots followed by leaves and stem. Various Cd levels inhibited also the contents of plant nutrients such as nitrogen (N), phosphorous (P), potassium (K) and sulfur (S) in leaves. The present endeavor hence concludes the existence of close relationships among growth parameters, Cd-sensitivity of phenological stages of the crop and the components of antioxidant system in rapeseed plants exposed at various growth stages.     

Differential responses to cadmium induced oxidative stress in marine macroalga Ulva lactuca (Ulvales, Chlorophyta)

This study describes various biochemical processes involved in the mitigation of cadmium toxicity in green alga Ulva lactuca. The plants when exposed to 0.4 mM CdCl₂ for 4 days showed twofold increase in lipoperoxides and H₂O₂ content that collectively decreased the growth and photosynthetic pigments by almost 30% over the control. The activities of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione peroxidase (GPX) enhanced by twofold to threefold and that of catalase (CAT) diminished. Further, the isoforms of these enzymes, namely, Mn-SOD (~85 kDa), GR (~180 kDa) and GPX (~50 kDa) responded specifically to Cd²⁺ exposure. Moreover, the contents of reduced glutathione (3.01 fold) and ascorbate (1.85 fold) also increased substantially. Lipoxygenase (LOX) activity increased by two fold coupled with the induction of two new isoforms upon Cd²⁺ exposure. Among the polyunsaturated fatty acids, although n ? 3 PUFAs and n ? 6 PUFAs (18:3n ? 6 and C18:2n ? 6) showed relatively higher contents than control, the latter ones showed threefold increase indicating their prominence in controlling the cadmium stress. Both free and bound soluble putrescine increased noticeably without any change in spermidine. In contrast, spermine content reduced to half over control. Among the macronutrients analysed in exposed thalli, the decreased K content was accompanied by higher Na and Mn with no appreciable change in Ca, Mg, Fe and Zn. Induction of antioxidant enzymes and LOX isoforms together with storage of putrescine and n ? 6 PUFAs in cadmium exposed thallus in the present study reveal their potential role in Cd²⁺ induced oxidative stress in U. lactuca.     

α-Tocopherol Application Modulates the Response of Wheat (Triticum aestivum L.) Seedlings to Elevated Temperatures by Mitigation of Stress Injury and Enhancement of Antioxidants

Wheat seedlings (4 days old) were subjected to varying temperatures of 25, 30, and 35 °C for 7 days in a growth chamber under hydroponic conditions in the absence or presence of α-tocopherol (5 μM). The growth of shoots and roots was inhibited severely at 35 °C. The endogenous α-tocopherol increased in the shoots at 30 °C over the controls but decreased significantly at 35 °C over the previous temperature. The exogenous application of α-tocopherol elevated the endogenous levels in the heat-stressed plants, which were consequently able to maintain significantly greater growth associated with reduction in damage to membranes, cellular oxidizing ability, chlorophyll content, and photochemical efficiency in shoots. The relative leaf water content and stomatal conductance were not affected significantly with the application of tocopherol. The oxidative stress induced by high temperature (35 °C) in terms of malondialdehyde and hydrogen peroxide contents was significantly lower in the presence of α-tocopherol. The enzymatic antioxidants such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase showed considerable reduction in their activities at 35 °C compared to those at 30 °C, with greater effects on APX and GR. The nonenzymatic antioxidants like ascorbate, glutathione, and proline increased at 30 °C but decreased appreciably at 35 °C, suggesting impairment in their synthesis at stressful temperatures. α-Tocopherol-treated plants, especially those growing at 35 °C, had improved levels of enzymatic and nonenzymatic antioxidants. These observations provided evidence about the involvement of α-tocopherol in governing heat sensitivity in wheat and suggested manipulation of its endogenous levels to induce heat tolerance in this crop.     

Physiology and selected genes expression under cadmium stress in Arundo donax L

The effects of cadmium stress (0, 25, 50, 75, and 100 mg/L) on morpho-physiological features and selected genes (carotenoid hydroxilase, amidase, GR, bHLH, NRAMP and YSL) expression were demonstrated in Arundo donax L. The plants were assessed for Cd uptake and its effects on chlorophyll and antioxidants after 30 days of exposure. The expression of genes conferring metal tolerance was evaluated after 10 days of Cd exposure. The results showed a maximum Cd uptake in roots (872 mg/kg) followed by stem (734 mg/kg) and leaves (298 mg/kg) at highest supplied Cd concentration. The Cd uptake reduced dry weight, Chla, Chlb, and total Chl contents of giant reed. The SOD, CAT, POD activities and MDA content increased at the maximum Cd concentration over control. The highest genes expression for carotenoid hydroxylase, glutathione reductase and amidase was observed in plants exposed to 100 mg/L. However, differential bHLH gene expression and slightly increased gene expression of NRAMP was noted for different Cd treatments. Amidase expressed under Cd stress which is pioneer report in A. donax. These results provided insights into the mechanisms of A. donax tolerance and survival under Cd Stress.