Faisal Islam

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.

Copper-resistant bacteria reduces oxidative stress and uptake of copper in lentil plants: potential for bacterial bioremediation

For effective microbe-assisted bioremediation, metal-resistant plant growth-promoting bacteria (PGPB) must facilitate plant growth by restricting excess metal uptake in plants, leading to prevent its bio-amplification in the ecosystem. The aims of our study were to isolate and characterize copper (Cu)-resistant PGPB from waste water receiving contaminated soil. In addition, we investigated the phytotoxic effect of copper on the lentil plants inoculated with copper-resistant bacteria Providencia vermicola, grown in copper-contaminated soil. Copper-resistant P. vermicola showed multiple plant growth promoting characteristics, when used as a seed inoculant. It protected the lentil plants from copper toxicity with a considerable increase in root and shoot length, plant dry weight and leaf area. A notable increase in different gas exchange characteristics such as A, E, Ci, gs, and A/E, as well as increase in N and P accumulation were also recorded in inoculated plants as compared to un-inoculated copper stressed plants. In addition, leaf chlorophyll content, root nodulation, number of pods, 1,000 seed weight were also higher in inoculated plants as compared with non-inoculated ones. Anti-oxidative defense mechanism improved significantly via elevated expression of reactive oxygen species -scavenging enzymes including ascorbate peroxidase, superoxide dismutase, catalase, and guaiacol peroxidase with alternate decrease in malondialdehyde and H2O2 contents, reduced electrolyte leakage, proline, and total phenolic contents suggesting that inoculation of P. vermicola triggered heavy metals stress-related defense pathways under copper stress. Overall, the results demonstrated that the P. vermicola seed inoculation confer heavy metal stress tolerance in lentil plant which can be used as a potent biotechnological tool to cope with the problems of copper pollution in crop plants for better yield.

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

BackgroundChromium (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.ResultsBoth 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.ConclusionThe 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.

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.

Toxicological effects of bisphenol A on growth and antioxidant defense system in Oryza sativa as revealed by ultrastructure analysis.

The present study was conducted to evaluate the effect of bisphenol A (BPA) on rice seedlings grown in a hydroponic system. The obtained results demonstrated that at lower concentration (up to 10µM) BPA had some stimulatory effects on the growth of rice seedlings but at higher doses it significantly inhibited seedlings growth. The photosynthetic pigments were significantly decreased by high doses of BPA. Exposure to BPA caused increased membrane permeability in root cells and resulted in increased concentration of reactive oxygen species (ROS) and increased lipid peroxidation as revealed by thiobarbituric acid reactive substances (TBARS) assay. In leaves, superoxide dismutase (SOD) activity exhibited an increase at lower concentrations of BPA but was inhibited at the highest dose (200µM) of BPA. At 100µM of BPA, a significant increase in antioxidant activities in leaves was observed but at 200µM this activity was inhibited. In roots, a significant decrease in enzymes activity was recorded at the highest concentration of BPA (200µM); however, ascorbate peroxidase (APX) and catalase (CAT) activities were significantly increased at the concentrations of 10 and 50µM in comparison to the control. Moreover, the present results revealed that BPA severely affected cell organelles in rice seedlings. It can be concluded that the observed adverse effects in rice seedlings by BPA in the present study could be attributed to the oxidative stress caused by BPA.

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.

OsPEX11, a Peroxisomal Biogenesis Factor 11, Contributes to Salt Stress Tolerance in Oryza sativa

Peroxisomes are single membrane-bound organelles, whose basic enzymatic constituents are catalase and H2O2-producing flavin oxidases. Previous reports showed that peroxisome is involved in numerous processes including primary and secondary metabolism, plant development and abiotic stress responses. However, knowledge on the function of different peroxisome genes from rice and its regulatory roles in salt and other abiotic stresses is limited. Here, a novel prey protein, OsPEX11 (Os03g0302000), was screened and identified by yeast two-hybrid and GST pull-down assays. Phenotypic analysis of OsPEX11 overexpression seedlings demonstrated that they had better tolerance to salt stress than wild type (WT) and OsPEX11-RNAi seedlings. Compared with WT and OsPEX11-RNAi seedlings, overexpression of OsPEX11 had lower level of lipid peroxidation, Na+/K+ ratio, higher activities of antioxidant enzymes (SOD, POD, and CAT) and proline accumulation. Furthermore, qPCR data suggested that OsPEX11 acted as a positive regulator of salt tolerance by reinforcing the expression of several well-known rice transporters (OsHKT2;1, OsHKT1;5, OsLti6a, OsLti6b, OsSOS1, OsNHX1, and OsAKT1) involved in Na+/K+ homeostasis in transgenic plants under salinity. Ultrastructural observations of OsPEX11-RNAi seedlings showed that they were less sensitive to salt stress than WT and overexpression lines. These results provide experimental evidence that OsPEX11 is an important gene implicated in Na+ and K+ regulation, and plays a critical role in salt stress tolerance by modulating the expression of cation transporters and antioxidant defense. Thus, OsPEX11 could be considered in transgenic breeding for improvement of salt stress tolerance in rice crop.

Synergism of herbicide toxicity by 5-aminolevulinic acid is related to physiological and ultra-structural disorders in crickweed (Malachium aquaticum L.)

Selection of effective herbicides to control weeds has been one of the major objectives of scientists. This study determines the differential tolerance or susceptibility of crickweed (Malachium aquaticum L.) to various concentration combinations of 5-aminolevulinic acid (ALA) (1, 10 and 100mg/L) and propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate (ZJ0273) (100, 200, and 500mg/L). ALA was applied as pre- and post-treatment alone or in combination with ZJ0273. Results showed that ZJ0273 stress alone imposed negative effects on M. aquaticum seedlings growth, net photosynthetic rates and SPAD values, and the rate of decline was consistently increased with the increase in ZJ0273 concentration. The ZJ0273 treatment showed a gradual decrease in the activities of antioxidant enzymes peroxidase (POD), superoxide dismutase (SOD), and ascorbate peroxidase (APX), and increase in the accumulation of malondialdehyde (MDA). Changes in chloroplast swelling, increased number of plastoglobuli, disruption of thylakoid, disintegrated mitochondria and turbid nucleoplasm were noticed. Moreover, SDS-PAGE analysis of total proteins revealed that herbicide stress in the leaves was associated with the decrease or disappearance of some protein bands. Further, two-dimensional gel electrophoresis (2-DE) results showed that proteins in different spots were classified into three types for M. aquaticum. These results indicate that the combined treatment of ALA and ZJ0273 synergizes the herbicide toxicity which is different from its independent effects on M. aquaticum and thus, could improve weed control efficacy.

Biochemical responses and ultrastructural changes in ethylene insensitive mutants of Arabidopsis thialiana subjected to bisphenol A exposure

Bisphenol A (BPA), an important raw material in plastic industry, has become a serious environmental contaminant due to its wide spread use in different products and increasing release into the environment. BPA is known to cause adverse effects in living organisms including plants. Several studies reported that BPA affects growth and development in plants, mainly through oxidative stress. Plants are known to generally cope with stress mainly through hormonal regulation and adaptation, but little is known about the role of plant hormones in plants under BPA stress. The present study was conducted to investigate the role of ethylene in BPA induced oxidative stress in plants using Arabidopsis thaliana as a test plant. The response of ethylene insensitive mutants of Arabidopsis (ein2-1 and etr1-3) to BPA exposure was studied in comparison to the wild type Arabidopsis (WT). In all three genotypes, exposure to BPA adversely affected cellular structures, stomata and light-harvesting pigments. An increase in reactive oxygen species (ROS) lipid peroxidation and other oxidative stress markers indicated that BPA induced toxicity through oxidative stress. However, the overall results revealed that WT Arabidopsis had more pronounced BPA induced damages while ein2-1 and etr1-3 mutants withstood the BPA induced stress more efficiently. The activity of antioxidant enzymes and expression of antioxidants related genes revealed that the antioxidant defense system in both mutants was more efficiently activated than in WT against BPA induced oxidative stress, which further evidenced the involvement of ethylene in regulating BPA induced oxidative stress. It is concluded that ethylene perception and signaling may be involved in BPA induced oxidative stress responses in plants.