Narottam Dey

Antioxidative responses of Salvinia (Salvinia natans Linn.) to aluminium stress and it's modulation by polyamine.

Antioxidative stress response of free-floating aquatic fern (Salvinia natans Linn.) was studied under increasing toxic amount of aluminium (Al) and its modulation by exogenous application of polymaine. Increased levels of superoxide (O2−) and hydrogen peroxide (H2O2) species from affected tissues suggested that plants were undergoing oxidative stress and it was concominant with increased accumulation of Al in a dose dependent manner. Application of polyamine like putrescine (Put) led to a decrease in oxidative stress as revealed by reduced level of O2− and H2O2. Al toxicity resulted into decreased biomass that was ameliorated by the application of Put. The changes observed in lipid peroxidation (MDA) and protein oxidation also indicated that plats are undergoing Al induced oxidative stress. In order to circumvent the oxidative stress resulting from Al toxicity, plants enzymatic and nonenzymatic antioxidant pathways were active. The ratio of both oxidized and reduced cellular glutathione exhibited significant variation in response to Al stress and was improved upon Put treatment. Peroxidase and glutathione were upregulated whereas catalse was downregulated under varying doses of Al. Isozyme profile of above enzymes also showed a trend with increasing amount of Al. The nuclear disintegration study using comet assay was indicative of Al induced oxidative stress. In the present study, we have explored the antioxidative response of aquatic fern Salvinia natans Linn in response to Al toxicity. The application of polyamine Put improved the overall antioxidative response and thus would make it a better candidate to be used as hyper accumulator of Al and other toxic metals.

Responses of the maize plant to chromium stress with reference to antioxidation activity

Two maize varieties, viz. Sartaj and Deccan, have been evaluated according to their responses to chromium (Cr) in terms of specific physiological and biochemical attributes. During the exposure to Cr concentration (0, 50, 100, 200 and 300 µM) of potassium dichromate (K2Cr2O7) for seven days, significant changes of oxidative stress in terms of lipid peroxidation and protein oxidation were recorded along with other antioxidative pathways. It is revealed that irrespective of varieties, Sartaj was more prone to oxidative stress since the amount of superoxide due to Cr exposure was found to be significant, unlike the second variety, Deccan. In addition, for Sartaj the activity of NAD(P)H oxidase recorded a significant linear increase in a dose response manner.The changes of antioxidative enzymes recorded significant variation in both varieties under stress compared to control. However, Deccan maintains a consistent up regulation in SOD and GPX activities. Contrarily, APX activity was less sensitive to both varieties. The activation of antioxidative mechanisms due to the impact of Cr-induced oxidative stress has been described subsequently. The results deriving from this investigation might be effective for the selection of tolerant plant types under chromium contamination.

Promoter methylation regulates the abundance of osa-miR393a in contrasting rice genotypes under salinity stress

MicroRNAs (miRNAs) are important molecules that regulate gene expression under salinity stress. Despite their evolutionary conservation, these regulatory elements have been shown to behave differently in different plant species under a particular environmental stress. In this study, we investigated the behavior of salt responsive osa-miR393a and its target gene (TIR1, LOC_Os05g05800) in salt-tolerant (FL478) and salt-sensitive (IR29) rice genotypes. It was found that the mature and precursor sequences of osa-miR393a as well as its cleavage site in TIR1 were conserved among salt tolerant and sensitive genotypes. Promoters of different salt-responsive miRNAs were also found to be less variable between salt-tolerant and salt-susceptible genotypes. Analysis of gene expression, promoter methylation, and cis-element abundance showed that osa-miR393a behaves differently in FL478 and IR29. Salt stress altered the expression pattern of osa-miR393a-TIR1 module in a time-dependent manner in the roots and shoots of two genotypes. Promoter methylation of this regulatory module was also altered at different time points under salt stress. Expression analysis in two genotypes indicated the overall down-regulation of osa-miR393a and up-regulation of TIR1 in FL478 and their reciprocal regulation in IR29. The expression results were complemented by the differential promoter methylation and cis-element abundance of this regulatory module. Together, the results of transcript abundance and promoter methylation of osa-miR393a-TIR1 module signified the association between these two processes which is reported for the first time in plants to the best of our knowledge.

Profiling of selected indigenous rice (Oryza sativa L.) landraces of Rarh Bengal in relation to osmotic stress tolerance.

A total of ten rare indigenous rice landraces of West Bengal were screened for germination potential and seedling growth under varying concentrations of sodium chloride (NaCl) and polyethylene glycol (PEG) solutions as osmotic stress inducing agents. Among the studied rice landraces Kelas and Bhut Moori showed highest degree of tolerance to induced osmotic stresses. Proline content of the studied lines was also determined. Genetic relationship among the studied rice landraces was assessed with 22 previously reported osmotic stress tolerance linked Simple Sequence Repeat (SSR) markers. The identified allelic variants in form of amplified products size (molecular weight) for each SSR marker were documented to find out allele mining set for the linked markers of the studied genotypes in relation to osmotic stress tolerance. A Microsatellite Panel was constructed for the different allelic forms (size of amplified products) of each used marker. Among 22 SSR markers, ten showed unique alleles in form of single specific amplified product for the studied four genotypes which can be used for varietal identification. Genetic relationship among the studied rice lines was determined and a dendrogram was constructed to reveal their genetic inter-relationship. Polymorphism Information Content (PIC) for each used marker was also calculated for the studied rice lines.

Effects of putrescine on oxidative stress induced by hydrogen peroxide in Salvinia natans L.

Salvinia natans L. response to hydrogen peroxide (H2O2) induced oxidative stress through physiological activities was evaluated. The plants were incubated with varying concentrations (0, 50, 100 µM) of H2O2 and 100 µM of H2O2 supplemented with 1 mM putrescine (Put) in hydroponic culture. This is observed with the decline in proline content and its biosynthetic enzymes viz. γ-glutamyl kinase and γ-glutamyl phosphate reductase activity. Protein carbamylated derivative by protein oxidation was another trait for oxidative damages by H2O2. The antioxidative enzymes like guaiacol peroxidase (GPX), glutathione reductase (GR), and catalase (CAT) recorded to express through in-gel staining with the H2O2 exposure. On nuclear level, plants were sensitive to H2O2 where the DNA disintegration was studied with comet assay and maximum comet tail observed at 100 µM H2O2 treatment. Application of Put reduced the generation of protein oxidation and comet tail length as well as moderated the enzyme activity as revealed through in-gel staining.

Assessment of genetic diversity in salt-tolerant rice and its wild relatives for ten SSR loci and one allele mining primer of salT gene located on 1st chromosome

A heterogeneous collection of rice genotypes which included seven salt-tolerant rice lines, one salt-sensitive improved line, one wild rice (Oryza rufipogon) and one salt-tolerant wild rice relative (Porteresia coarctata) was screened with ten salt-tolerance-linked simple sequence repeat markers, of which nine were from the Saltol QTL mapped on rice 1st chromosome and the rest one from 8th chromosome, having high phenotypic variance for salt tolerance. Variation in molecular weight (in the form of base pairs) of the different amplified products using RM primers was used to find out the genetic relationship among the studied rice genotypes. Genomic DNA of the studied genotypes was also amplified with a reported allele mining primer for a salt-inducible gene (salT). The amplified products were sequenced and aligned to find out the closeness among the rice lines for the studied gene. Dendrogram derived from marker profiles showed partial similarity with salT gene-derived tree. Commonly, all the salt-tolerant lines were grouped into a single cluster, including IR36 (a salt-sensitive line) to which O. rufipogon (the wild rice) and P. coarctata (the wild rice relative) joined separately. The taxonomic identity and evolutionary relationship among the three groups (rice, wild rice and wild rice relative) were bioinformatically analysed using the nucleotide sequence of the studied salT gene.

Bio indices for 2,4-D sensitivity between two plant species: Azolla pinnata R.Br. and Vernonia cinerea L. with their cellular responses.

In the present experiment a pteridophytic species Azolla and an angiospermic species Vernonia were evaluated on the basis of cellular reactivity for herbicidal action through ongoing concentrations. Initially, both the species recorded a significant activity of IAA-oxidase as mark of IAA metabolism with herbicidal sensitivity. Still, Vernonia species were more affected on 2,4-D mediated auxin catabolism. The loss of auxin concentrations on the tissues by 2,4-D reaction was also reflected on growth parameters including relative growth rate and chlorophyll biosynthesis. In a dose dependent manner Vernonia plants were more affected with loss of chlorophyll content and decline in relative growth rate. On the other hand, both those parameters were adjusted significantly with 2,4-D accumulation in Azolla. The stability of cellular metabolism was documented by significant down regulation of protein and lipid peroxidation with concomitant moderation to superoxide and hydrogen peroxide accumulation. The later two were more vulnerable to damage in the Vernonia plant with profuse accumulation of protein and lipid peroxidation products. Similarly, tissue specific reaction to superoxide and hydrogen peroxide accumulation were distinctly demarcated in two species significantly. As a whole, the cellular responses and metabolite distribution to 2,4-D sensitization are the features to describe bio-indices for aquatic fern species Azolla with comparison to angiospermic species Vernonia.

Interaction of polyamine on oxidative stress induced by exogenously applied hydrogen peroxide in Salvinia natans Linn

A hydroponics experiment was carried out to study the role of hydrogen peroxide (H 2 O 2 ) through changes of oxidative stress and antioxidation activity in Salvinia natans Linn. H 2 O 2 is an active oxygen species, widely generated in many biological systems, and mediates various physiological and biochemical processes in plants. In this study, we demonstrated that exogenous H 2 O 2 causes the degradation of pigments and induces the oxidative stress and the antioxidation activity. These effects enhanced with increments of applied H 2 O 2 concentration. Application of polyamine reduced the generation and the accumulation of H 2 O 2 and modulated the enzyme activities.

Effects of Exogenous Spermidine on Cell Wall Composition and Carbohydrate Metabolism of Marsilea Plants under Cadmium Stress

Effects of Exogenous Spermidine on Cell Wall Composition and Carbohydrate Metabolism of Marsilea Plants under Cadmium Stress In an experiment to detect the cellular changes of carbohydrate content and its related enzymatic activities, a study was undertaken with Marsilea minuta L., an aquatic fern species in simulated condition of cadmium (Cd) toxicity. From the varying doses of Cd (0, 50, 100 and 200 μM) and supplemented with spermidine (2 mM), it revealed that plants were suffered from accumulation of total carbohydrate in a dose-dependent manner under Cd stress. Maximum depletion of carbohydrate content was 58% with respect to control which was retrieved by 1.42 fold with spermidine application. In a similar manner, plants were also affected with starch, total reducing sugar content by 42% and 63.04% respectively over the control. The fall in both starch and total reducing sugar were retrieved by plants by 1.32 fold and 1.52 fold, respectively.

Micromorphic and Molecular Studies of Floral Organs of a Multiple Seeded Rice (Oryza sativa L.)

Jugal is a natural mutant which produces more than one seed in most of its grain. In rice, development of floral organs is directly linked with seed production; thus, to elucidate the underneath mechanism of multiple seeded trait of Jugal, floral organ development was investigated. Microscopic study showed that most of the Jugal flowers bear more than one carpel; the presence of multiple carpels in Jugal flowers was confirmed by scanning electron microscopy (SEM) study. To understand the mechanism of multiple carpels in Jugal flowers, floral meristems of Jugal and IR36 were investigated, and Jugal floral meristem was found enlarged in comparison to IR36. Fourteen floral organ developmental genes of Jugal were sequenced partially, of which seven were sequenced successfully. Six among the successfully sequenced genes found to have variations and of them three genes showed changes in their corresponding amino acid sequences. Three out the seven genes possess unique variations. Expression study showed Jugal flowering genes expressing differently when compared to normal rice IR36.