Exogenously applied melatonin enhanced the tolerance of Brassica napus against cobalt toxicity by modulating antioxidant defense, osmotic adjustment, and expression of stress response genes

The excessive accumulation of cobalt (Co) in plant tissues severely impairs plant growth that ultimately reduces the yield. However, melatonin (MT) has been known to mediate the abiotic stress tolerance in plants. The present study aimed at investigating the protective mechanisms of exogenously applied MT (0, 50 and 100 μM) under Co (0, 100, 200 and 300 μM) stress by focusing on morpho-physiological, biochemical and cellular characterizations of Brassica napus plants. Cobalt (300 μM) alone treatment drastically inhibited the stomatal conductance, plant height (45%), leaf area (30%), free amino acid (139%), relative electrolyte leakage (109%), and total soluble sugars (71%), compared with the control. However, the exogenous supply of MT notably minimized the oxidative damage, lipid peroxidation and maintained the membrane integrity under Co-toxicity by restricting the overproduction of ROS (H₂O₂ and O₂^•), and MDA in leaves and roots. Melatonin significantly enhanced the activities of ROS-scavenging antioxidant enzymes, secondary metabolism-related phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), stress-responsive genes (heat shock protein as HSP-90, methyl transferase as MT) and regulated the Co-transporters, especially in roots. These findings indicated that an exogenous supply of MT improve the plant morphology, photosynthetic apparatus, osmotic adjustments, and antioxidant defense systems by enhancing the Co-detoxification in B. napus plants.

Comparative metabolomic responses of low- and high-cadmium accumulating genotypes reveal the cadmium adaptive mechanism in Brassica napus

Recently, oilseed rape has gathered interest for its ability to withstand elevated metal contents in plant, a key feature for remediation of contaminated soils. In this study, comparative and functional metabolomic analyses using liquid chromatography/mass spectrometry were undertaken to explore the metabolic basis of this attribute under cadmium (Cd) stress. Results revealed both conserved and differential metabolomic responses between genotype CB671 (tolerant Cd-accumulating) and its sensitive counterpart ZD622. CB671 responded to Cd stress by rearranging carbon flux towards production of compatible solutes, sugar storage forms and ascorbate, as well as jasmonates, ethylene and vitamin B6. Intriguingly, IAA abundance was reduced by 1.91-fold, which was in connection with tryptophan funnelling into serotonin (3.48-fold rise). In ZD622 by contrast, Cd provoked drastic depletion of carbohydrates and vitamins, but subtle hormones alteration. A striking accumulation of unsaturated fatty acids and oxylipins in CB671, paralleled by glycerophospholipids build-up and induction of inositol-derived signalling metabolites (up to 5.41-fold) suggested ability for prompt triggering of detoxifying mechanisms. Concomitantly, phytosteroids, monoterpenes and carotenoids were induced, denoting fine-tuned mechanisms for membrane maintenance, which was not evident in ZD622. Further, ZD622 markedly accumulated phenolics from upstream sub-classes of flavonoids; in CB671 however, a distinct phenolic wiring was activated, prioritizing anthocyanins and lignans instead. Along with cell wall (CW) saccharides, the activation of lignans evoked CW priming in CB671. Current results have demonstrated existence of notable metabolomic-based strategies for Cd tolerance in metal-accumulating oilseed rapes, and provided a holistic view of metabolites potentially contributing to Cd tolerance in this species.

Comparative orchestrating response of four oilseed rape (Brassica napus) cultivars against the selenium stress as revealed by physio-chemical, ultrastructural and molecular profiling

Selenium (Se) is an essential micro-element for human and animals. In higher plants, Se essentiality or phyto-toxicity is less explored. Therefore, we aimed to examine the effects of Se (0, 25, 50, and 100 µM) as sodium selenite on the physio-chemical, cell ultra-structural and genomic alterations in hydroponically grown seedlings of four cultivars of B. napus (cvs. Zheda 619, Zheda 622, ZS 758, and ZY 50). Results showed that excessive (100 µM) Se (IV) exhibited significant reduction in plant growth parameters, declined pigment contents, lower water-soluble protein levels, and overproduction of H₂O₂ and MDA contents. A significant increase in antioxidant enzyme activities and transcript levels of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), except catalase (CAT) were noticed in the leaves and roots. Non-enzymatic antioxidants including glutathione (GSH) and oxidized glutathione (GSSG), except GSSG in roots were enhanced under higher Se (IV) levels. Transmission electron microscopy analysis revealed the ultrastructural damages in leaf mesophyll and root tip cells induced by excessive Se (IV). Less-significant phytotoxic effects were observed in above-mentioned parameters at 50 µM Se (IV). Overall, Se (IV) supplementation at 25 µM displayed marginal beneficial effect by enhancing plant growth, pigment contents, protein levels and restrict H₂O₂ and MDA overproduction. A marginal increase/decrease in ROS-detoxifying enzymes (except CAT activity) and elevated GSH and GSSG levels were noticed. The accumulation of Se (IV) was much higher in roots as compared to leaves. This accumulation was maximum in Zheda 622 and minimum in ZS 758, followed by Zheda 619 and ZY 50. Overall findings showed that Zheda 622 was the most sensitive and ZS 758 as most tolerant to Se (IV) phyto-toxicity. In addition, Se (IV) was found beneficial until 25 µM Se (IV) but phytotoxic at higher Se levels especially at 100 µM Se (IV).

Salinity reduces 2,4-D efficacy in Echinochloa crusgalli by affecting redox balance, nutrient acquisition, and hormonal regulation

Distinct salinity levels have been reported to enhance plants tolerance to different types of stresses. The aim of this research is to assess the interaction of saline stress and the use of 2,4-D as a means of controlling the growth of Echinochloa crusgalli. The resultant effect of such interaction is vital for a sustainable approach of weed management and food production. The results showed that 2,4-D alone treatment reduces the chlorophyll contents, photosynthetic capacity, enhanced MDA, electrolyte leakage, and ROS production (H₂O₂, O₂^·-) and inhibited the activities of ROS scavenging enzymes. Further analysis of the ultrastructure of chloroplasts indicated that 2,4-D induced severe damage to the ultrastructure of chloroplasts and thylakoids. Severe saline stress (8 dS m^-1) followed by mild saline stress treatments (4 dS m^-1) also reduced the E. crusgalli growth, but had the least impact as compared to the 2,4-D alone treatment. Surprisingly, under combined treatments (salinity + 2,4-D), the phytotoxic effect of 2,4-D was reduced on saline-stressed E. crusgalli plants, especially under mild saline + 2,4-D treatment. This stimulated growth of E. crusgalli is related to the higher activities of enzymatic and non-enzymatic antioxidants and dynamic regulation of IAA, ABA under mild saline + 2,4-D treatment. This shows that 2,4-D efficacy was affected by salinity in a stress intensity-dependent manner, which may result in the need for greater herbicide application rates, additional application times, or more weed control operations required for controlling salt-affected weed.

A High-Density Genetic Map of an Allohexaploid Brassica Doubled Haploid Population Reveals Quantitative Trait Loci for Pollen Viability and Fertility

A doubled haploid (DH) mapping population was obtained from microspore culture of an allohexaploid F₁ from the cross between two recently-synthesized allohexaploid Brassica lines. We used single nucleotide polymorphism (SNP) genetic variation based on restriction-site associated DNA (RAD) sequencing to construct a high density genetic linkage map of the population. RAD libraries were constructed from the genomic DNA of both parents and 146 DH progenies. A total of 2.87 G reads with an average sequencing depth of 2.59 × were obtained in the parents and of 1.41 × in the progeny. A total of 290,422 SNPs were identified from clustering of RAD reads, from which we developed 7,950 high quality SNP markers that segregated normally (1:1) in the population. The linkage map contained all 27 chromosomes from the parental A, B and C genomes with a total genetic distance of 5725.19 cM and an average of 0.75 cM between adjacent markers. Genetic distance on non-integrated linkage groups was 1534.23 cM, or 21% of total genetic distance. Out of 146 DH progenies, 91 had a complete set of 27 chromosomes as expected of a hexaploid species, and 21 out of 27 chromosomes showed high collinearity between the physical and linkage maps. The loss of chromosome(s) or chromosome segment(s) in the DH population was associated with a reduction in pollen viability. Twenty-five additive QTL were associated with pollen viability and fertility-related traits (seed number, seed yield, pod length, plant height, 1000-seed weight). In addition, 44 intra-genomic and 18 inter-genomic epistatic QTL pairs were detected for 4 phenotypic traits. This provides confidence that the DH population may be selected for improved pollen viability and fertility in a future allohexaploid Brassica species.

2,4-D attenuates salinity-induced toxicity by mediating anatomical changes, antioxidant capacity and cation transporters in the roots of rice cultivars

Growth regulator herbicides are widely used in paddy fields to control weeds, however their role in conferring environmental stress tolerance in the crop plants are still elusive. In this study, the effects of recommended dose of 2,4-dichlorophenoxyacetic acid (2,4-D)  on growth, oxidative damage, antioxidant defense, regulation of cation transporter genes and anatomical changes in the roots of rice cultivars XS 134 (salt resistant) and ZJ 88 (salt sensitive) were investigated under different levels of saline stress. Individual treatments of saline stress and 2,4-D application induced oxidative damage as evidenced by decreased root growth, enhanced ROS production, more membrane damage and Na⁺ accumulation in sensitive cultivar compared to the tolerant cultivar. Conversely, combined treatments of 2,4-D and saline stress significantly alleviated the growth inhibition and oxidative stress in roots of rice cultivars by modulating lignin and callose deposition, redox states of AsA, GSH, and related enzyme activities involved in the antioxidant defense system. The expression analysis of nine cation transporter genes showed altered and differential gene expression in salt-stressed roots of sensitive and resistant cultivars. Together, these results suggest that 2,4-D differentially regulates the Na⁺ and K⁺ levels, ROS production, antioxidant defense, anatomical changes and cation transporters/genes in roots of rice cultivars.

Reduced Glutathione Mediates Pheno-Ultrastructure, Kinome and Transportome in Chromium-Induced Brassica napus L

Chromium (Cr) as a toxic metal is widely used for commercial purposes and its residues have become a potential environmental threat to both human and plant health. Oilseed rape (Brassica napus L.) is one of the candidate plants that can absorb the considerable quantity of toxic metals from the soil. Here, we used two cultivars of B. napus cvs. ZS 758 (metal-tolerant) and Zheda 622 (metal-susceptible) to investigate the phenological attributes, cell ultrastructure, protein kinases (PKs) and molecular transporters (MTs) under the combined treatments of Cr stress and reduced glutathione (GSH). Seeds of these cultivars were grown in vitro at different treatments i.e., 0, 400 μM Cr, and 400 μM Cr + 1 mM GSH in control growth chamber for 6 days. Results had confirmed that Cr significantly reduced the plant length, stem and root, and fresh biomass such as leaf, stem and root. Cr noticeably caused the damages in leaf mesophyll cells. Exogenous application of GSH significantly recovered both phenological and cell structural damages in two cultivars under Cr stress. For the PKs, transcriptomic data advocated that Cr stress alone significantly increased the gene expressions of BnaA08g16610D, BnaCnng19320D, and BnaA08g00390D over that seen in controls (Ck). These genes encoded both nucleic acid and transition metal ion binding proteins, and protein kinase activity (PKA) and phosphotransferase activities in both cultivars. Similarly, the presence of Cr revealed elite MT genes [BnaA04g26560D, BnaA02g28130D, and BnaA02g01980D (novel)] that were responsible for water transmembrane transporter activity. However, GSH in combination with Cr stress significantly up-regulated the genes for PKs [such as BnaCnng69940D (novel) and BnaC08g49360D] that were related to PKA, signal transduction, and oxidoreductase activities. For MTs, BnaC01g29930D and BnaA07g14320D were responsible for secondary active transmembrane transporter and protein transporter activities that were expressed more in GSH treatment than either Ck or Cr-treated cells. In general, it can be concluded that cultivar ZS 758 is more tolerant toward Cr-induced stress than Zheda 622.

Differential subcellular distribution and chemical forms of cadmium and copper in Brassica napus

Metal subcellular fractions and chemical profile highly reflect their level of toxicity to plants. Cadmium and Cu, two different but potentially toxic metals, were compared in the present study for their subcellular distribution and chemical forms in two Brassica napus cultivars (Zheda 622 and ZS 758). Five-week-old seedlings were hydroponically exposed to metal stress and analyzed after 15 days of treatment. In both cultivars, Cd was less retained at cell wall, thus major part of Cd accumulated in the soluble fraction. By contrast, handsome amount of Cu was sequestrated in both cell wall and vacuole containing fraction. Across sensitive organelles, Cu preferentially accumulated in chloroplasts, while Cd was equally distributed in chloroplasts and mitochondria; the two metals intruded nucleus at lesser degree. Further, Cd and Cu differentially interacted with various cellular ligands, and the extent of interaction was higher in the tolerant cultivar ZS 758. Copper was remarkably sequestrated by phosphates, and secondarily by peptide-ligands; inversely, the role of phosphates was secondary in Cd complexation, which was mainly achieved by peptide-ligands. Additional amount of Cu was aggregated with oxalates, but oxalate-bound Cd was scarcely detected. Current results have demonstrated varied toxicological and detoxification pathways of Cd and Cu in B. napus, suggesting that the efficiency of different alleviation strategies could vary against Cd and Cu toxicity to plants.

Comparative transcriptome profiling of two Brassica napus cultivars under chromium toxicity and its alleviation by reduced glutathione

BACKGROUND

Chromium (Cr) being multifarious industrial used element, is considered a potential environmental threat. Cr found to be a prospective water and soil pollutant, and thus it is a current area of concern. Oilseed rape (Brassica napus L.) is well known as a major source of edible oil around the globe. Due to its higher growth, larger biomass and capability to uptake toxic materials B. napus is considered a potential candidate plant against unfavorable conditions. To date, no study has been done that described the Cr and GSH mechanism at RNA-Seq level.

RESULTS

Both digital gene expression (DGE) and transcriptome profile analysis (TPA) approaches had opened new insights to uncover the several number of genes related to Cr stress and GSH alleviating mechanism in two leading cultivars (ZS 758 and Zheda 622) of B. napus plants. Data showed that Cr inhibited KEGG pathways i.e. stilbenoid, diarlyheptanoid and gingerol biosynthesis; limonene and pentose degradation and glutathione metabolism in ZS 758; and ribosome and glucosinolate biosynthesis in Zheda-622. On the other hand, vitamin B6, tryptophan, sulfur, nitrogen and fructose and manose metabolisms were induced in ZS 758, and zeatin biosynthesis, linoleic acid metabolism, arginine and proline metabolism, and alanine, asparate and glutamate metabolism pathways in Zheda 622. Cr increased the TFs that were related to hydralase activity, antioxidant activity, catalytic activity phosphatase and pyrophosphatase activity in ZS 758, and vitamin binding and oxidoreductase activity in Zheda 622. Cr also up-regulated the promising proteins related to intracellular membrane bounded organelles, nitrile hyrdatase activity, cytoskeleton protein binding and stress response. It also uncovered, a novel Cr-responsive protein (CL2535.Contig1_All) that was statistically increased as compared to control and GSH treated plants. Exogenously applied GSH successfully not only recovered the changes in metabolic pathways but also induced cysteine and methionine metabolism in ZS 758 and ubiquinone and other terpenoid-quinone biosynthesis pathways in Zheda 622. Furthermore, GSH increased the level of TFs i.e. the gene expression of antioxidant and catalytic activities, iron ion binding and hydrolase activity as compared with Cr. Moreover, results pointed out a novel GSH responsive protein (CL827.Contig3_All) whose expression was found to be significantly increased when compared than Cr stress. Results further delineated that GSH induced TFs such as glutathione disulphide oxidoreducatse and aminoacyl-tRNA ligase activity, and beta glucosidase activity in ZS 758. Similarly in Zheda 622, GSH induced the TFs for instance DNA binding and protein dimerization activity. GSH also highlighted the proteins that were involved in transportation, photosynthesis process, RNA polymerase activity, and against the metal toxicity. These results indicated that cultivar ZS 758 had better metabolism and showed higher tolerance against Cr toxicity.

CONCLUSION

The responses of ZS 758 and Zheda 622 differed considerably at both physiological and transcriptional level. Moreover, RNA-Seq method explored the hazardous behavior of Cr as well as GSH up-regulating mechanism by activating plant metabolism, stress responsive genes, TFs and protein encyclopedia.

Salicylic acid mediates antioxidant defense system and ABA pathway related gene expression in Oryza sativa against quinclorac toxicity

The auxin herbicide quinclorac is widely used for controlling weeds in transplanted and direct-seeded rice fields. However, its phytotoxic responses on rice are still unknown. Therefore, in the present investigation we studied the effects of different concentrations (0, 0.1 and 0.5g/L) of quinclorac herbicide on the physiological and biochemical changes of two rice cultivars (XS 134 and ZJ 88) and further analyzed the ameliorating role of salicylic acid (SA) on quinclorac toxicity in rice plants. The results revealed that exogenous application of SA significantly increased plant biomass and total chlorophyll contents in herbicide stressed plants. The lipid peroxidation and ROS (H2O2, O2(-.), (-)OH) production were significantly increased in roots and leaves of both rice cultivars under quinclorac stress, demonstrating an oxidative burst in rice plants. Whereas, application of SA significantly lowered ROS contents under quinclorac stress. Further, exogenous SA treatment significantly modulated antioxidant enzymes and enhanced GSH concentration in stress plants. Anatomical observations of leaf and root revealed that herbicide affected internal structures, while SA played a vital role in protection from toxic effects. Expression analysis of stress hormone ABA genes (OsABA8oxs, OsNCEDs) revealed that quinclorac application enhanced stress condition in cultivar ZJ 88, while SA treatment downregulated ABA genes more in cultivar XS 134, which correlated with the enhanced tolerance to quinclorac induced oxidative stress in this cultivar. The present study delineated that SA played a critical role under quinclorac stress in both rice cultivars by regulating antioxidant defense system, reducing ROS formation and preventing the degradation of internal cell organelles.

Role of exogenous salicylic acid in regulating physio-morphic and molecular changes under chromium toxicity in black- and yellow- seeded Brassica napus L

Salicylic acid (SA) mediates tolerance mechanisms in plants against a wide spectrum of biotic and abiotic stresses. Therefore, the present study was carried out to determine how SA regulates the plant protection mechanisms in two cultivars of oilseed rape (Brassica napus L.) under chromium (Cr) stress. Exogenously applied SA enhanced plant growth, increased dry biomasses, and strengthened the reactive oxygen scavenging system by improving cell organelles that were severely damaged via Cr toxicity. The contents of Cr were significantly enhanced in both root and leaf of cultivar Zheda 622 (yellow color) compared with cultivar ZS 758 (black color). Exogenous application of SA significantly reduced the Cr contents in both plant organs as well as enhanced the SA contents under Cr stress. A dose-dependent increase was observed in reactive oxygen species (ROS) generation under Cr stress. To ease the inimical effects of ROS, plants' defense systems were induced under Cr stress, and SA further enhanced protection. Further, TEM micrographs results showed that Cr stress alone significantly ruptured the plant cell organelles of both cultivars by increasing the size of starch grain and the number of plastoglobuli, damaging the chloroplast and mitochondrion structures. However, exogenously applied SA significantly recovered these damages in the plant cells of both cultivars. It was also observed that cultivar ZS 758 was proved to be more tolerant under Cr toxicity. Gene expression analysis revealed that combined treatments of Cr and SA increased antioxidant-related gene expression in both cultivars. Findings of the present study demonstrate that SA induces the enzymatic antioxidant activities and related gene expression, secondary metabolism, and improves the cell structural changes and the transcript level of specific stress-associated proteins in root and leaf of two oilseed rape cultivars under Cr toxicity.

Combined herbicide and saline stress differentially modulates hormonal regulation and antioxidant defense system in Oryza sativa cultivars

Plants are simultaneously exposed to a combination of biotic and abiotic stresses in field conditions. Crops respond to the combined stress in a unique way which cannot be understood by extrapolating the results of individual stress. In the present study, effects of individual and combined stress of herbicide (2,4-dichlorophenoxyacetic acid) and salinity (NaCl) on two Oryza sativa cultivars (ZJ 88 and XS 134) were investigated. Both herbicide and saline stress affected the plant growth differentially and produced oxidative stress in rice cultivars. Interestingly, the combination of herbicide and salinity showed a significant protection to both rice cultivars by reducing ROS (H2O2, O2(-)) and lipid peroxidation through modulation of enzymatic (SOD, POD, CAT and APX) and non-enzymatic (TSP, sugars, phenolic and proline) antioxidants. In addition, active regulation of transcript levels of genes encoding Na(+) and K(+) (OsHKT1;5, OsLti6a,b, OsHKT2;1, OsSOS1, OsCNGC1, OsNHX1 and OsAKT1) transporter proteins reduced sodium and enhanced potassium accumulation under combined stress, resulted a better growth and ionic homeostasis in both rice cultivars. The production of ABA and IAA was significantly higher in cultivar XS 134 compared to cultivar ZJ 88 under control conditions. However, combined herbicide and saline stress enhanced the accumulation of phytohormones (IAA and ABA) and transcription of ethylene in cultivar ZJ 88, which might be one of the factors responsible for poor salt tolerance in sensitive cultivar. These findings indicated that herbicide application under saline stress confers tolerance to salinity in rice cultivars, likely by reducing oxidative damage, modulating mineral absorption, upgradation of antioxidant defense and by dynamic regulation of key genes involved in Na(+) and K(+) homeostasis in plants.

Subcellular distribution, modulation of antioxidant and stress-related genes response to arsenic in Brassica napus L

Arsenic (As) is an environmental toxin pollutant that affects the numerous physiological processes of plants. In present study, two Brassica napus L. cultivars were subjected to various concentrations (0, 50, 100, and 200 µM) of As for 14 days, plants were examined for As subcellular distribution, photosynthesis parameters, oxidative stress, and ultrastructural changes under As-stress. Differential fraction analysis showed that significant amount of As was accumulated in the cell wall as compared to other organelles. Decline in photosynthetic efficiency under As stress was observed in term of reduced pigment contents and gas exchange parameters. Differential responses of antioxidants at both enzymatic and gene levels to higher As stress were more pronounced in cultivar ZS 758 as compared to Zheda 622. The qRT-PCR analysis showed that heat shock protein 90 (Hsp90) and metallothionein were over-expressed in As stressed B. napus plants. Disorganization of cell structure and the damages in different organelles were some of the obvious variations in cultivar Zheda 622 as compared to ZS 758.

Methyl Jasmonate Regulates Antioxidant Defense and Suppresses Arsenic Uptake in Brassica napus L

Methyl jasmonate (MJ) is an important plant growth regulator, involved in plant defense against abiotic stresses, however, its possible function in response to metal stress is poorly understood. In the present study, the effect of MJ on physiological and biochemical changes of the plants exposed to arsenic (As) stress were investigated in two Brassica napus L. cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type). The As treatment at 200 μM was more phytotoxic, however, its combined application with MJ resulted in significant increase in leaf chlorophyll fluorescence, biomass production and reduced malondialdehyde content compared with As stressed plants. The application of MJ minimized the oxidative stress, as revealed via a lower level of reactive oxygen species (ROS) synthesis (H2O2 and OH(-)) in leaves and the maintenance of high redox states of glutathione and ascorbate. Enhanced enzymatic activities and gene expression of important antioxidants (SOD, APX, CAT, POD), secondary metabolites (PAL, PPO, CAD) and induction of lypoxygenase gene suggest that MJ plays an effective role in the regulation of multiple transcriptional pathways which were involved in oxidative stress responses. The content of As was higher in yellow seeded plants (cv. Zheda 622) as compared to black seeded plants (ZS 758). The application of MJ significantly reduced the As content in leaves and roots of both cultivars. Findings of the present study reveal that MJ improves ROS scavenging through enhanced antioxidant defense system, secondary metabolite and reduced As contents in both the cultivars.

Physiological and molecular analyses of black and yellow seeded Brassica napus regulated by 5-aminolivulinic acid under chromium stress

Brassica napus L. is a promising oilseed crop among the oil producing species. So, it is prime concern to screen the metal tolerant genotypes in order to increase the oilseed rape production through the utilization of pollutant soil regimes. Nowadays, use of plant growth regulators against abiotic stress is one of the major objectives of researchers. In this study, an attempt was carried out to analyze the pivotal role of exogenously applied 5-amenolevulinic acid (ALA) on alleviating chromium (Cr)-toxicity in black and yellow seeded B. napus. Plants of two cultivars (ZS 758 - a black seed type, and Zheda 622 - a yellow seed type) were treated with 400 μM Cr with or without 15 and 30 mg/L ALA. Results showed that exogenously applied ALA improved the plant growth and increased ALA contents; however, it decreased the Cr concentration in B. napus leaves under Cr-toxicity. Moreover, exogenous ALA reduced oxidative stress by up-regulating antioxidant enzyme activities and their related gene expression. Further, results suggested that stress responsive protein's transcript level such as HSP90-1 and MT-1 were increased under Cr stress alone in both cultivars. Exogenously applied ALA further enhanced the expression rate in both genotypes and obviously results were found in favor of cultivar ZS 758. The ultrastructural changes were observed more obvious in yellow seeded than black seeded cultivar; however, exogenously applied ALA helped the plants to recover their cell turgidity under Cr stress. The present study describes a detailed molecular mechanism how ALA regulates the plant growth by improving antioxidant machinery and related transcript levels, cellular modification as well as stress related genes expression under Cr-toxicity.

Oxidative injury and antioxidant enzymes regulation in arsenic-exposed seedlings of four Brassica napus L. cultivars

Environmental contamination due to arsenic (As) has become a major risk throughout the world; this affects plant growth and productivity. Its accumulation in food chain may pose a severe threat to organisms. The present study was carried out to observe the toxic effects of As (0, 50, 100, and 200 μM) on physiological and biochemical changes in four Brassica napus cultivars (ZS 758, Zheda 619, ZY 50, and Zheda 622). Results showed that As toxicity provoked a significant inhibition in growth parameters of B. napus cultivars and this reduction was more obvious in cultivar Zheda 622. The highest concentration of MDA, H2O2, and O2 (-) contents in both leaf and root tissues were observed at 200 μM As level, and a gradual decrease was observed at lower concentrations. Increasing As concentration gradually decreased chlorophyll and carotenoids contents. Activity of antioxidant enzymes such as SOD, CAT, APX, GR, and GSH was positively correlated with As treatments in all cultivars. The microscopic study of leaves and roots at 200 μM As level showed the disorganization in cell organelles. Disturbance in the morphology of chloroplast, broken cell wall, increase in size, and number of starch grains and immature nucleus were found in leaf ultrastructures under higher concentration of As. Moreover, damaged nucleus, diffused cell wall, enlarged vacuoles, and a number of mitochondria were observed in root tip cells at 200 μM As level. These results suggest that B. napus cultivars have efficient mechanism to tolerate As toxicity, as evidenced by an increased level of antioxidant enzymes.

Regulation of Cadmium-Induced Proteomic and Metabolic Changes by 5-Aminolevulinic Acid in Leaves of Brassica napus L

It is evident from previous reports that 5-aminolevulinic acid (ALA), like other known plant growth regulators, is effective in countering the injurious effects of heavy metal-stress in oilseed rape (Brassica napus L.). The present study was carried out to explore the capability of ALA to improve cadmium (Cd²⁺) tolerance in B. napus through physiological, molecular, and proteomic analytical approaches. Results showed that application of ALA helped the plants to adjust Cd²⁺-induced metabolic and photosynthetic fluorescence changes in the leaves of B. napus under Cd²⁺ stress. The data revealed that ALA treatment enhanced the gene expressions of antioxidant enzyme activities substantially and could increase the expression to a certain degree under Cd²⁺ stress conditions. In the present study, 34 protein spots were identified that differentially regulated due to Cd²⁺ and/or ALA treatments. Among them, 18 proteins were significantly regulated by ALA, including the proteins associated with stress related, carbohydrate metabolism, catalysis, dehydration of damaged protein, CO2 assimilation/photosynthesis and protein synthesis/regulation. From these 18 ALA-regulated proteins, 12 proteins were significantly down-regulated and 6 proteins were up-regulated. Interestingly, it was observed that ALA-induced the up-regulation of dihydrolipoyl dehydrogenase, light harvesting complex photo-system II subunit 6 and 30S ribosomal proteins in the presence of Cd²⁺ stress. In addition, it was also observed that ALA-induced the down-regulation in thioredoxin-like protein, 2, 3-bisphosphoglycerate, proteasome and thiamine thiazole synthase proteins under Cd²⁺ stress. Taken together, the present study sheds light on molecular mechanisms involved in ALA-induced Cd²⁺ tolerance in B. napus leaves and suggests a more active involvement of ALA in plant physiological processes than previously proposed.

Chromium-induced physio-chemical and ultrastructural changes in four cultivars of Brassica napus L

In nature, plants are continuously exposed to several biotic and abiotic stresses. Among these stresses, chromium (Cr) stress is one of the most adverse factors that affects the plant growth, and productivity, and imposes a severe threat for sustainable crop production. In the present study, toxic effects of Cr were studied in hydroponically grown seedlings of four different cultivars of Brassica napus L. viz. ZS 758, Zheda 619, ZY 50 and Zheda 622. The study revealed that elevated Cr concentrations reduced the plant growth rate and biomass as compared to respective controls in all the cultivars and this decline was more obvious in Zheda 622. It was observed that reduction of photosynthetic attributes was more pronounced in Zheda 622 as compared to other cultivars; while, cultivar ZS 758 performed better under Cr-toxicity. Results showed that Cr contents in different parts of seedlings were higher in Zheda 622 as compared to other cultivars and Cr contents were higher in roots than shoots in all the cultivars. Accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) were induced under different Cr concentrations. Results showed that some of anti-oxidant enzyme activities in leaves and roots were increased under the Cr-toxicity. The electron microscopic study showed that ultrastructural damages in leaf mesophyll and root tip cells were more prominent in Zheda 622 as compared to other cultivars under 400 μM Cr stress. Under 400 μM Cr concentration, changes like broken cell wall, immature nucleus, a number of mitochondria, ruptured thylakoid membranes and large size of vacuole and starch grains were observed in leaf ultrastructures. The damages in root cells were observed in the form of disruption of golgibodies and diffused cell wall under the higher concentration of Cr (400 μM). On the basis of these observations, it was concluded that Zheda 622 was found to be more sensitive as followed by ZY 50, Zheda 619 and ZS 758 under Cr-toxicity.

Hydrogen sulfide alleviates the aluminum-induced changes in Brassica napus as revealed by physiochemical and ultrastructural study of plant

In the present study, ameliorating role of hydrogen sulfide (H2S) in oilseed rape (Brassica napus L.) was studied with or without application of H2S donor sodium hydrosulfide (NaHS) (0.3 mM) in hydroponic conditions under three levels (0, 0.1 and 0.3 mM) of aluminum (Al). Results showed that addition of H2S significantly improved the plant growth, photosynthetic gas exchange, and nutrients concentration in the leaves and roots of B. napus plants under Al stress. Exogenously applied H2S significantly lowered the Al concentration in different plant parts, and reduced the production of malondialdehyde and reactive oxygen species by improving antioxidant enzyme activities in the leaves and roots under Al stress. Moreover, the present study indicated that exogenously applied H2S improved the cell structure and displayed clean mesophyll and root tip cells. The chloroplast with well-developed thylakoid membranes could be observed in the micrographs. Under the combined application of H2S and Al, a number of modifications could be observed in root tip cell, such as mitochondria, endoplasmic reticulum, and golgi bodies. Thus, it can be concluded that exogenous application of H2S under Al stress improved the plant growth, photosynthetic parameters, elements concentration, and biochemical and ultrastructural changes in leaves and roots of B. napus.

Hydrogen sulfide alleviates cadmium-induced morpho-physiological and ultrastructural changes in Brassica napus

In the present study, role of hydrogen sulfide (H2S) in alleviating cadmium (Cd) induced stress in oilseed rape (Brassica napus L.) was studied under greenhouse conditions. Plants were grown hydroponically under three levels (0, 100, and 500µM) of Cd and three levels (0, 100 and 200µM) of H2S donor, sodium hydrosulfide (NaHS). Results showed that application of H2S significantly improved the plant growth, root morphology, chlorophyll contents, elements uptake and photosynthetic activity in B. napus plants under Cd stress. Moreover, addition of H2S reduced the Cd concentration in the leaves and roots of B. napus plants under Cd-toxicity. Exogenously applied H2S decreased the production of malondialdehyde and reactive oxygen species in the leaves and roots by improving the enzymatic antioxidant activities under Cd stress conditions. The microscopic examination indicated that application of exogenous H2S improved the cell structures and enabled a clean mesophyll cell having a well developed chloroplast with thylakoid membranes, and a number of mitochondria could be observed in the micrographs. A number of modifications could be found in root tip cell i.e. mature mitochondria, long endoplasmic reticulum and golgibodies under combined application of H2S and Cd. On the basis of these findings, it can be concluded that application of exogenous H2S has a protective role on plant growth, photosynthetic parameters, elements uptake, antioxidants enzyme activities and ultrastructural changes in B. napus under high Cd stress conditions.

Hydrogen sulfide alleviates lead-induced photosynthetic and ultrastructural changes in oilseed rape

The role of hydrogen sulfide (H2S) in alleviating lead (Pb) induced stress in oilseed rape (Brassica napus L.) was studied under laboratory conditions. Plants were grown hydroponically in greenhouse conditions under three levels (0, 100, and 400 µM) of Pb and three levels (0, 100 and 200 µM) of H2S donor, sodium hydrosulfide (NaHS). Application of H2S significantly improved the plant growth, root morphology, chlorophyll contents and photosynthetic activity in leaves of B. napus under Pb stress. Moreover, exogenously applied H2S significantly lowered the Pb concentration in shoots and roots of plants under Pb stress. The microscopic examination indicated that application of exogenous H2S enabled a clean mesophyll cell having a well developed chloroplast with thylakoid membranes and starch grains. A number of modifications could be observed in root tip cell i.e. mature mitochondria, long endoplasmic reticulum and golgibodies under combined application of H2S and Pb. On the basis of these findings, it can be concluded that application of exogenous H2S has a protective role on plant growth, net photosynthesis rate and ultrastructural changes in B. napus plants under high Pb exposures.

5-Aminolevolinic acid mitigates the cadmium-induced changes in Brassica napus as revealed by the biochemical and ultra-structural evaluation of roots

In the present study, the ameliorating effects of 5-aminolevulinic acid (ALA) under cadmium (Cd) stress conditions were studied with special emphasis on root morphology and ultra-structure in oilseed rape. For this purpose, plants were treated hydroponically at three different Cd levels (0, 100, 500μM) and foliar spray of ALA with three concentrations (0, 12.5, 25mg/l) simultaneously. The results showed that foliar application of ALA improved the plant growth, root morphology and reduced the reactive oxygen species and malondialdehyde contents in roots under Cd stress conditions. The higher concentration of Cd (500μM) decreased the activities of antioxidants enzymes like catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and glutathione reductase (GR) and also reduced the oxidized glutathione and total glutathione contents in roots. Application of ALA at 25mg/l dosage significantly enhanced the antioxidant activities e.g. APX, SOD, POD, and GSH contents under Cd stress. The microscopic micrographs showed that application of exogenous ALA improved the cell structure under Cd toxicity. A whole cell with developed nucleus, nuclear membrane, smooth cell wall, continuous endoplasmic reticulum, and well shaped mitochondria was observed under the combine application of ALA and Cd. These results suggest that, application of ALA helped the plants to improve root growth, root antioxidant enzymes, and ultra-structural changes in root tip cells under fifteen days Cd-induced stress.

Contamination of surface soils, river water and sediments by trace metals from copper processing industry in the Churnet River Valley, Staffordshire, UK

The impacts of a functional and a demolished copper processing works on the aquatic and terrestrial environment in the vicinity of the works was investigated by determining the levels of selected trace metals in river water, river sediments, channel margin sediments and overbank soils. Samples were taken at five sites within an area of the Churnet Valley in Staffordshire, where the River Churnet flows through the two works. Analysis of river water samples by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) has shown that only copper is present above background levels considered to typify uncontaminated rivers. Analysis of river sediments, channel margin sediments and overbank soils by nitric-perchloric acid digestion and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) analysis has indicated contamination by arsenic, cadmium and copper in the vicinity of both works. Arsenic and copper are deposited primarily within the aquatic environment, although some contamination of the terrestrial environment by copper is also observed. Cadmium is deposited primarily within the terrestrial environment. The deposition of arsenic and copper in river and channel margin sediments respectively is also related to current and historical contamination.

Preliminary evidence for the metabolism of benzo(a) pyrene by Plantago lanceolata

Polycyclic aromatic hydrocarbons (PAHs) have long been recognised as potential carcinogens in animals in which biotransformation into reactive metabolites can lead to DNA damage. In animals PAHs metabolism mainly occurs in hepatic microsomes and is associated with the cytochrome p-450 mediated mixed functional oxidase (MFO) system. PAH metabolism in plants has been shown to occur via a similar enzyme system, but has received relatively little attention. This study is looking at how the plant species Plantago lanceolata metabolizes benzo(a)pyrene (B(a)P), which is one of the PAHs whose metabolism has been studied extensively in animals. The aim of the work is to establish firstly that the B(a)P is taken up and secondly that it is biotransformed by the plant to products possibly similar to those found in animals. This work is achieved by using C-14-B(a)P along with whole body autoradiography, scintillation analysis and chromatography techniques to locate the B(a)P and its metabolites.

The relationship between epilithic periphyton (biofilm) bound metals and metals bound to sediments in freshwater systems

Surficial sediments and epilithic periphyton (biofilm) were sampled from six sites on the River Churnet and five sites on the River Manifold in Staffordshire and analysed for cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). The sites demonstrated a wide range of sediment trace metal concentrations determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic absorbtion spectroscopy (AAS). Biofilm was removed from the substrate using physical abrasion and 0.005 M ethylenediaminoethanetetra-acetic acid (EDTA) extractant. The European Standards, Measurements and Testing Programmes (BCR) operationally defined geochemical speciation scheme was used to determine the exchangeable, acid soluble fraction of the sediments. Significant positive correlations were determined between the EDTA extractable biofilm and the exchangeable sediment fraction for Cd, Cu and Zn but not for Pb. Natural epilithic periphyton may be a potential metal biomonitor particularly of Cu, Cd and Zn in aquatic systems and provide supporting information in relation to potential sediment toxicity.

Ecosystem consequences of plant life form changes at three sites in the semiarid United States

Many semiarid rangelands have recently experienced changes in dominant plant life form. Both woody plant expansion into grasslands and the invasion of annual grasses into shrublands have potential influence on regional carbon cycling. Soil carbon content, chemistry, and distribution may change following shifts in dominant plant life form because plant life forms differ in litter chemistry and patterns of detrital input. This study assesses the amount, quality, and distribution of soil C below woody vegetation and grasses at three rangelands in Texas, New Mexico, and Utah. At each of these sites there has been a well-documented shift in dominant plant life form. In Texas and New Mexico, woody plants have increased in grasslands, while grasses have invaded into former shrublands in Utah. We measured total soil carbon, particulate organic matter (POM) C, and the carbon isotopic composition of soil carbon beneath woody plants and grasses at each of these three sites. At the La Copita Research Area in south-central Texas there was significantly more soil C found beneath Prosopis glandulosa, the dominant woody plant, than was found beneath grasses. Mean soil C content to 1 m was 7.2 kg C m^-2 beneath P. glandulosa and 6.0 kg C m^-2 beneath grasses. There was also significantly more POM C beneath P. glandulosa than beneath grasses. Stable carbon isotopic composition indicated that the expansion of P. glandulosa in savannas in Texas first influences carbon cycling in surface soils, then deep soil C, and finally throughout the soil profile. At the Sevilleta National Wildlife Refuge in central New Mexico, we found that there was significantly more soil C in the upper 10 cm of the soil profile beneath Larrea tridentata than was found beneath Bouteloua spp. Stable carbon isotopic composition indicated that the expansion of L. tridentata influenced C cycling throughout the soil profile. At Curlew Valley in northern Utah, we found no significant differences in total profile soil C beneath different plant life forms. However, there was significantly more soil C found at the soil surface beneath woody plants than was observed beneath annual grasses. There was significantly less POM C beneath annual grasses than was found beneath woody plants or perennial grasses. Based on stable carbon isotopic analyses, we concluded that the invasion of grasses into shrublands influenced only the upper 30 cm of the soil profile. We determined that following changes in plant life form dominance, the most consistent change in soil C was an alteration in content and distribution of POM C, a slowly cycling pool of soil C. While we failed to find a consistent change in total profile soil C with plant life form across our sites, the change in soil C chemistry may have important implications for long-term soil C storage in semiarid systems where there have been shifts in plant life form.

Aminopyrine breath test predicts surgical risk for patients with liver disease

To determine whether the [14C] aminopyrine breath test (ABT) predicts surgical risk in patients with liver disease, it was obtained prior to various surgeries in 38 patients with known or suspected liver disease. A modified Child's classification was also determined. Six of the seven operative deaths (three Child's A, two B, two C) had ABTs less than 2.3%, while 30 of 31 survivors (24 Child's A, seven B) had ABTs greater than 2.3% (p less than 0.000018). Seven of the 16 patients with normal ABTs had biopsy-proven cirrhosis and had postoperative courses indistinguishable from the remainder of the group. We conclude that surgery in patients with ABTs less than 2.3% is associated with extremely high mortality. In addition, cirrhotics with normal ABTs tolerate elective surgery well.

Hepatic veno-occlusive disease caused by 6-thioguanine

Clinically reversible veno-occlusive disease of the liver developed in a 23-year-old man with acute lymphocytic leukemia after 10 months of maintenance therapy with 6-thioguanine. Serial liver biopsies showed the development and resolution of intense sinusoidal engorgement. Although this disease was clinically reversible, some subintimal fibrosis about the terminal hepatic veins persisted. This case presented a unique opportunity to observe the histologic features of clinically reversible hepatic veno-occlusive disease over time, and may be the first case of veno-occlusive related solely to 6-thioguanine.