Varsha Shriram

MicroRNAs As Potential Targets for Abiotic Stress Tolerance in Plants.

The microRNAs (miRNAs) are small (20–24 nt) sized, non-coding, single stranded riboregulator RNAs abundant in higher organisms. Recent findings have established that plants assign miRNAs as critical post-transcriptional regulators of gene expression in sequence-specific manner to respond to numerous abiotic stresses they face during their growth cycle. These small RNAs regulate gene expression via translational inhibition. Usually, stress induced miRNAs downregulate their target mRNAs, whereas, their downregulation leads to accumulation and function of positive regulators. In the past decade, investigations were mainly aimed to identify plant miRNAs, responsive to individual or multiple environmental factors, profiling their expression patterns and recognizing their roles in stress responses and tolerance. Altered expressions of miRNAs implicated in plant growth and development have been reported in several plant species subjected to abiotic stress conditions such as drought, salinity, extreme temperatures, nutrient deprivation, and heavy metals. These findings indicate that miRNAs may hold the key as potential targets for genetic manipulations to engineer abiotic stress tolerance in crop plants. This review is aimed to provide recent updates on plant miRNAs, their biogenesis and functions, target prediction and identification, computational tools and databases available for plant miRNAs, and their roles in abiotic stress-responses and adaptive mechanisms in major crop plants. Besides, the recent case studies for overexpressing the selected miRNAs for miRNA-mediated enhanced abiotic stress tolerance of transgenic plants have been discussed.

A potential plasmid-curing agent, 8-epidiosbulbin E acetate, from Dioscorea bulbifera L. against multidrug-resistant bacteria

Bioassay-guided fractionation of an aqueous methanolic extract of Dioscorea bulbifera L. bulbs was performed using organic solvents. A novel plasmid-curing compound was identified as 8-epidiosbulbin E acetate (EEA) (norditerpene) on the basis of modern spectroscopic analysis and X-ray crystallography. EEA exhibited broad-spectrum plasmid-curing activity against multidrug-resistant (MDR) bacteria, including vancomycin-resistant enterococci. EEA cured antibiotic resistance plasmids (R-plasmids) from clinical isolates of Enterococcus faecalis, Escherichia coli, Shigella sonnei and Pseudomonas aeruginosa with 12-48% curing efficiency. The reference plasmids of Bacillus subtilis (pUB110), E. coli (RP4), P. aeruginosa (RIP64) and Salmonella typhi (R136) were cured with efficiency ranging from 16% to 64%. EEA-mediated R-plasmid curing decreased the minimal inhibitory concentration of antibiotics against MDR bacteria, thus making antibiotic treatment more effective. The antibiotic resistance pattern revealed that the compound was effective in the reversal of bacterial resistance to various antibiotics. In addition, the compound did not show any cytotoxicity against a broad range of human cancer cell lines, namely MCF-7 (breast cancer), SiHa (cervical cancer) and A431 (epidermal carcinoma), and hence has the potential to be used as a lead compound for drug discovery programmes.

Antioxidant enzyme activities and protein profiling under salt stress in indica rice genotypes differing in salt tolerance

The effect of NaCl stress (0–300 mM) was investigated in terms of antioxidant enzymes activity and their isozymatic pattern and SDS-PAGE proteins banding pattern in three rice cultivars (cvs), Panvel-3 (tolerant), Kalarata (moderately tolerant) and Karjat-3 (sensitive). Interestingly, superoxide dismutase activity in roots and glutathione reductase activity in both shoots and roots were decreased significantly under high salinity levels in Karjat-3 and Kalarata, while, a sharp increase was observed in Panvel-3. Catalase and peroxidase activities were increased with salt stress of all cvs, with highest magnitude in Panvel-3. There was an induction of two new POX isoforms in Panvel-3 and Kalarata in stressed plants. Four SOD isoforms were observed in all the genotypes, irrespective of non/saline conditions. Total 33 proteins bands ranging from 17–154.5 kDa were either expressed de novo or up/down-accumulated due to NaCl stress. In Panvel-3, three new bands, one of 32 kDa in shoots while two of 37 and 116.7 kDa appeared in roots under salt stress. A new band of 37 kDa was also observed in roots of Kalarata under salinity stress. Thus, salinity tolerance nature of Panvel-3 may be correlated with higher enzyme activities and expression of some new polypeptides under salt stress.

SODIUM CHLORIDEINDUCED CHANGES IN MINERAL NUTRIENTS AND PROLINE ACCUMULATION IN INDICA RICE CULTIVARS DIFFERING IN SALT TOLERANCE

ABSTRACT The effect of increasing sodium chloride (NaCl; 0 to 300 mM) stress was investigated on plant growth, mineral nutrients, and proline accumulation in two indica rice cultivars differing in salt tolerance. The shoots and roots of ‘Karjat-3’ (salt sensitive cv.) showed greater reduction in fresh weight, dry weight, and water content under increasing salinity stress when compared to ‘Panvel-3’ (salt tolerant cv.). The magnitude of chloride (Cl) accumulation with increasing salinity varied between cultivars, with lesser accumulation in ‘Panvel-3’, whereas, calcium (Ca) content was more in ‘Panvel-3’ than ‘Karjat-3’ at all salinity levels. Increase in shoot-sodium (Na) did not show notable variation between cultivars under salinity stress; however, Na accumulation was notably lower in roots of ‘Panvel-3’ than ‘Karjat-3’. Under increasing salinity stress, ‘Panvel-3’ maintained significantly lower sodium/potassium, sodium/calcium and sodium/nitrogen ratios than ‘Karjat-3’, both in shoots and roots, with more differential response in roots. Regardless of treatment, proline concentration was considerably higher in ‘Panvel-3’ than in ‘Karjat-3’. The salt tolerance of cv. ‘Panvel-3’ was positively correlated with better growth, higher proline accumulation and enhanced uptakes of beneficial minerals such as potassium (K) and Ca.

Cytotoxic activity of 9,10-dihydro-2,5-dimethoxyphenanthrene-1,7-diol from Eulophia nuda against human cancer cells.

ETHNOPHARMACOLOGICAL RELEVANCE Eulophia nuda L. (Orchidaceae) is a medicinally important terrestrial orchid used for the treatment of tumours and various health problems by the local healers throughout the Western Ghats region in Maharashtra (India). AIM OF THE STUDY To isolate the active molecule from Eulophia nuda and to study its cytotoxic potential against human cancer cells. MATERIALS AND METHODS The crude methanolic extract of Eulophia nuda tubers was fractionated by stepwise gradient of the solvents-chloroform-methanol to isolate the pure compound. Isolated pure compound was assessed for its cytotoxic potential against human breast cancer cell lines, MCF-7 and MDA-MB-231 using MTT assay. Structure elucidation of the isolated active compound was carried out by extensive spectroscopic analysis including (1)H NMR, (13)C NMR, NOESY, COSY, LC-MS and IR. RESULTS The isolated active molecule was identified as phenanthrene derivative 9,10-dihydro-2,5-dimethoxyphenanthrene-1,7-diol. This compound showed good antiproliferative activity against human breast cancer cell lines MCF-7 (91%) and MDA-MB-231 (85%) at 1000 microg/ml concentration. CONCLUSION 9,10-Dihydro-2,5-dimethoxyphenanthrene-1,7-diol from Eulophia nuda tubers showed good growth suppressive effect against human cancer cell lines MCF-7 and MDA-MB-231 making it a potential biomolecule against human cancer.

Differential response of indica rice genotypes to NaCl stress in relation to physiological and biochemical parameters

Abstract The effect of NaCl stress was studied in indica rice cultivars, Panvel-3 (tolerant), Kalarata (moderately tolerant) and Karjat-3 (sensitive) under various levels (50 – 300 mM) of salinity besides control (0 mM). Salinity stress decreased germination percentage, plant growth, biomass production and chlorophyll pigments, and increased malondialdehyde level (lipid peroxidation) and free proline accumulation. Salinity-induced decrease in germination percentage, biomass production, chlorophyll and total protein contents were significantly higher in Karjat-3 than Panvel-3. The free proline content at all the levels as well as the magnitude of increase in accumulation with increasing salinity was also highest in Panvel-3, as at 300 mM NaCl concentration, it was 8 times more than control, while it was about 5 times more in Karjat-3 and around 4 times in Kalarata. The level of lipid peroxidation was lowest at all levels of salinity in Panvel-3 as compared with Karjat-3, however, Kalarata showed intermediate results. Results showed salinity tolerance of Panvel-3 was manifested by lower decrease in germination, plant growth and chlorophyll pigments and associated with higher proline accumulation and lower lipid peroxidation under high salinity stress.

Engineering Phytohormones for Abiotic Stress Tolerance in Crop Plants

Abiotic stresses including salinity, drought, extreme temperatures, and heavy metals are posing serious threats to agricultural yields as well as the quality of produce. This necessitates the production of cultivars capable to withstand the harsh environmental conditions without substantial yield losses. Owing to the complexity underlying stress tolerance traits, conventional breeding techniques have met with limited success and demand effective supplements to feed the growing food demands worldwide. This necessitates the development and deployment of novel and potent approaches, and engineering of phytohormone metabolism could be a method of choice to produce climate resilient crops with higher yields. Phytohormones are considered critical for regulating and coordinating plant growth and development; however, in recent years, they have received great attention for their multifunctional roles in plant responses to environmental stimuli. Creditable research has shown that phytohormones including the classical ones – auxins, cytokinins, ethylene, gibberellins, and newer members including brassinosteroids, jasmonates, and strigolactones – may prove to be potent targets for their metabolic engineering for producing abiotic stress-tolerant crop plants. This chapter presents short description of the roles of phytohormones in abiotic stress responses and tolerance followed by reviewing attempts made by the plant biotechnologists for engineering of phytohormone metabolism, signal, transport, and perception to develop abiotic stress-tolerant crop plants.

Glycinebetaine-Mediated Abiotic Oxidative-Stress Tolerance in Plants: Physiological and Biochemical Mechanisms

Plants face many stressful conditions during their lifetimes and because of their sessile nature they have to adapt to these conditions in order to survive. One unfortunate and unavoidable consequence of all major biotic and abiotic stresses is the overproduction of reactive oxygen species (ROS). ROS are highly reactive and toxic chemical entities and can cause serious damage to cellular proteins, lipids, carbohydrates and DNA, leading to irreparable metabolic dysfunction and cell death. Plant cells and their organelles, particularly the chloroplasts, mitochondria and peroxisomes have antioxidant defence systems, composed of enzymatic and non-enzymatic components, to counter the deleterious effects of ROS and/or to perform signalling functions. It is an established fact that the timely induction of antioxidant defences is a key to protection of plant cells from oxidative damage due to stress. Enzymatic antioxidants include superoxide dismutase, catalase, peroxidases and glutathione reductase, while the major non-enzymatic antioxidants are compatible osmolytes (glycinebetaine, GB; and proline), ascorbic acid, reduced glutathione, α-tocopherol, amino acids and polyphenols. Stimulated biosynthesis and accumulation of low molecular weight compatible osmolytes is one of the most effective mechanisms evolved by plants to maintain their cellular integrity and ensure survival when exposed to multiple abiotic stresses. Glycinebetaine, an N-trimethyl derivative of glycine and a quaternary ammonium compound, is one of the most studied and efficient compatible solutes. Due to its unique structural features, it interacts both with the hydrophobic and hydrophilic domains of macromolecules, including enzymes and proteins. GB has been reported to protect plants from the antagonistic effects of a range of abiotic stresses, by maintaining the water balance between plant cells and environment, osmotic adjustment, protecting the thylakoid membrane system, protein stabilization, photosystem and photosynthetic electron transport chain protection and by modulating ROS detoxification. In recent years, GB has attained unprecedented attention due to its multifunctional roles in plants under stressful conditions. In this chapter, we summarize our understanding of ROS formation under abiotic stress and GB biosynthesis and accumulation, as an adaptive mechanism, with particular emphasis on the new insights into the biochemical and molecular mechanisms involved in GB-mediated abiotic oxidative stress tolerance in plants.

RNAi Technology: The Role in Development of Abiotic Stress-Tolerant Crops

Abstract Over the past two decades, genetic engineering and related techniques have demonstrated striking progress in manipulation of the genes for induction of the desired characteristics into transgenic organisms. The regulatory mechanism of RNA interference (RNAi) has been studied in many higher organisms. The accuracy and precision of this phenomenon assures a great success rate in plant improvement. The RNAi provides us with an explicit methodology for down-regulation of genes of interest without hampering the expression of any other gene in the plant. The examination of different RNAi pathways, along with their components, including microRNAs and small interfering RNAs, have provided us with more than one way to achieve gene manipulation for mediated crop improvement. The phenomenon of RNAi has been studied in different abiotic environments; such as salinity, drought, extreme temperatures, heavy metals, and nutrition deprivation and radiation in various crops. RNAi-mediated crop manipulations have been reported that incorporate the utilization of vital stress-responsive elements with their subsequent mRNA and/or protein targets. Hence, collectively, RNAi technology has proven to be a promising tool for abiotic stress improvement in crops. This chapter focuses on the potential and successful application of RNAi technology for crop improvement in response to various abiotic stress factors.

Effects of Toxic Gases, Ozone, Carbon Dioxide, and Wastes on Plant Secondary Metabolism

Various kinds of human activities along with environmental interactions or changes are occasioning the addition and accumulation of hazardous entities in the environment. The subsequent result of this is negative effects of these factors on living systems including plants. Factors such as heavy metals, toxic gases, ozone, and carbon dioxide have a major impact on plant growth and secondary metabolism of the plants. Secondary metabolites are the key players in plant adaptation to these environmental stresses and play a role in mitigating the negative effects of these stresses. Both primary and secondary metabolisms are altered under these stress environments, however, plants have evolved to endure these conditions through inducing several regulating mechanisms such as evapotranspiration of available water, controlled openings and closings of stomata as per the availability of water, over accumulation of various osmoprotectants and osmoregulators, induction of antioxidant machinery and fine tuning of transcriptional and post-transcriptional regulations of gene expressions. In most of the plants, the ultimate result of these defensive adaptations is regulated production of the secondary metabolites. In this chapter, we have discussed the effects of toxic gases, ozone, carbon dioxide as well as other wastes including the nanoparticles-wastes on plant secondary metabolites.