Interaction between PGPR and PGR for water conservation and plant growth attributes under drought condition

Drought is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Drought stress accompanied by reduction in precipitation pose major challenges to future food safety. Strategies should be develop to enhance drought tolerance in crops like chickpea and wheat, in order to enhance their growth and yield. Drought tolerance strategies are costly and time consuming however, recent studies specify that plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can help plants to withstand under harsh environmental condition and enable plants to cope with drought stress. PGPR can act as biofertilizer and bioenhancer for different legumes and non-legumes. The use of PGPR and symbiotic microorganisms, may be valuable in developing strategies to assist water conservation in plants. The use of PGPR has been confirmed to be an ecologically sound way of enhancing crop yields by facilitating plant growth through direct or indirect mechanism. The mechanisms of PGPR for water conservation include secretion of exopolysaccharides, biofilm formation, alternation in phytohormone content, improvement in sugar concentration, enhancing availability of micro- and macronutrients and changes in plant functional traits. Similarly, plant growth regulators (PGRs) are specially noticed in actively growing tissues under stress conditions and have been associated in the control of cell division, embryogenesis, root formation, fruit development and ripening, and reactions to biotic and abiotic stresses and upholding water conservation status in plants. Previous studies also suggest that plant metabolites interact with plant physiology under stress condition and impart drought tolerance. Metabolites like, sugars, amino acids, organic acid and polyols play a key role in drought tolerance of crop plants grown under stress condition. It is concluded from the present study that PGRs in combination with PGPR consortium can be an effective formulation to promote plant growth and maintenance of plant turgidity under drought stress. This review is a compilation of the effect of drought stress on crop plants and described interactions between PGPR/PGRs and plant development, knowledge of water conservation and stress release strategies of PGPR and PGRs and the role of plant metabolites in drought tolerance of crop plants. This review also bridges the gaps that summarizes the mechanism of action of PGPR for drought tolerance of crop plants and sustainability of agriculture and applicability of these beneficial rhizobacteria in different agro-ecosystems under drought stress.     

Chemical Composition and Biological Studies of the Essential Oil from Aerial Parts of Beta vulgaris subsp. maritima (L.) Arcang. Growing in Tunisia

The chemical composition, antioxidant, cytotoxic, anticholinesterase and anti‐tyrosinase activities of the hydrodistilled essential oil of the aerial parts of Beta vulgaris subsp. maritime (L.) Arcang . from Tunisia have been evaluated. The chemical composition of the oil (yield 0.037% [w/w]), determined by GC‐FID and GC/MS is reported for the first time. Twenty five components, accounting for 98.1% of the total oil have been identified. The oil was characterized by a high proportion of oxygenated sesquiterpenes (39.2%), followed by sesquiterpene hydrocarbons (30.3%) and one apocarotenoids (26.3%). The main compounds were γ‐irone (26.3%), α‐cadinol (12.1%), T‐cadinol (10.6%), bicyclogermacrene (10.4%) and δ‐cadinene (6.0%). The isolated oil was tested for its antioxidant activity using the DPPH^·, ABTS^+·, catalase, and paraoxonase assays and also for its cytotoxic, anticholinesterase, and anti‐tyrosinase activities. The essential oil exhibited high antioxidant activity (IC₅₀ = 0.055 ± 0.006 mg/ml) and important result oncatalase (524.447 ± 2.58 Units/mg protein). Furthermore, it exerted a significant cytotoxic effect against A549 cell line, with IC₅₀ = 42.44 ± 1.40 μg/ml. The results indicate that the essential oil of B. vulgaris subsp. maritima (L.) Arcang . aerial parts may be used in future as an alternative to synthetic antioxidant agents, with potential application in the food and pharmaceutical industries.     

Effects of cadmium stress upon activities of antioxidative enzymes, photosynthetic rate, and production of phytochelatins in leaves and chloroplasts of wheat cultivars differing in yield potential

We tested the mode of action of Cd on photosynthesis and activities of ATP-sulfurylase (ATP-S), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), and on contents of phytochelatins (PCs) and glutathione (GSH) in two cultivars of wheat (Triticum aestivum L.) PBW-343 and WH-542 differing in yield potential. Cd treatment increased Cd content and photosynthetic activity in PBW-343 more than in WH-542. The activities of APX, GR, ATP-S, and synthesis of PCs and GSH were also increased by Cd, but the CAT and SOD activities were inhibited in both the cultivars. The efficient functioning of antioxidative enzymes, production of PCs and GSH, helped in counteracting the effects of Cd namely in PBW-343, protected photosynthetic ability, and increased the tolerance to Cd.     

Phylogenetic diversity and mutational analysis of New Delhi Metallo-β-lactamase (NDM) producing E. coli strains from pediatric patients in Pakistan

The evolution of NDM genes (bla_NDM) in E. coli is accounted for expansive multidrug resistance (MDR), causing severe infections and morbidities in the pediatric population. This study aimed to analyze the phylogeny and mutations in NDM variants of E. coli recovered from the pediatric population. Carbapenem-resistant clinical strains of E. coli were identified using microbiological phenotypic techniques. PCR technique used to amplify the bla_NDM genes, identified on agarose gel, and analyzed by DNA sequencing. The amino acid substitutions were examined for mutations after aligning with wild types. Mutational and phylogenetic analysis was performed using Lasergene, NCBI blastn, Clustal Omega, and MEGA software, whereas PHYRE2 software was used for the protein structure predictions. PCR amplification of the bla_NDM genes detected 113 clinical strains of E. coli with the contribution of bla_NDM-1 (46%), bla_NDM-4 (3.5%), and bla_NDM-5 (50%) variants. DNA sequencing of bla_NDM variants showed homology to the previously described bla_NDM-1, bla_NDM-4, and bla_NDM-5 genes available at GenBank and NCBI database. In addition, the mutational analysis revealed in frame substitutions of Pro60Ala and Pro59Ala in bla_NDM-4 and bla_NDM-5, respectively. The bla_NDM-1 was ortholog with related sequences of E. coli available at GenBank. The phylogenetic analysis indicated that the NDM gene variants resemble other microbes reported globally with some new mutational sites.     

Potential of Bacillus species against Meloidogyne javanica parasitizing eggplant (Solanum melongena L.) and induced biochemical changes

Aims

The biocontrol potential of three Bacillus species, namely Bacillus subtilis (BS), Bacillus firmus (BF), and Bacillus coagulans (BC) was tested against the root-knot nematode Meloidogyne javanica (Treub) Chitwood in eggplants (Solanum melongena L.). Plant growth and biochemical effects were also measured in these interactions.

Methods

Bacillus species were inoculated in soil around the seedlings of eggplants (Solanum melongena L.) with and without nematodes in a greenhouse experiment. Plant growth, biochemical changes, and nematode parasitism were observed at 15 and 45 days after inoculation (DAI).

Results

BC significantly enhanced plant growth, chlorophyll “b” and total chlorophyll contents, and polyphenol oxidase (PPO) activity in the leaves of eggplants, while BS showed greatest reduction in root-knot nematode parasitism. Non-infected and untreated control (C?) plants showed lesser chlorophyll “b,” carotenoids, soluble protein contents, and guaiacol peroxidase but higher catalase and PPO activities compared to infected and untreated controls (C+) at 15 and 45 DAI. Superoxide dismutase activity declined in most of the treated plants at 45 DAI following rise at 15 DAI. Ascorbate peroxidase activity increased at 45 DAI compared to 15 DAI in C? and C+ plants. PAL activity was greatly enhanced at 45 DAI in all treatments and controls over that at 15 DAI.

Conclusions

BC is a potentially plant growth-promoting bacteria although it was less effective against nematode infection compared to BS. Enzymes activities varied with infection and DAI. BC at 15 DAI in general increased the activity of most of the stress enzymes and thereby overcoming the effect of nematode parasitism.     

Methyl jasmonate counteracts boron toxicity by preventing oxidative stress and regulating antioxidant enzyme activities and artemisinin biosynthesis in <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

Boron is an essential plant micronutrient, but it is phytotoxic if present in excessive amounts in soil for certain plants such as Artemisia annua L. that contains artemisinin (an important antimalarial drug) in its areal parts. Artemisinin is a sesquiterpene lactone with an endoperoxide bridge. It is quite expensive compound because the only commercial source available is A. annua and the compound present in the plant is in very low concentration. Since A. annua is a major source of the antimalarial drug and B stress is a deadly threat to its cultivation, the present research was conducted to determine whether the exogenous application of methyl jasmonate (MeJA) could combat the ill effects of excessive B present in the soil. According to the results obtained, the B toxicity induced oxidative stress and reduced the stem height as well as fresh and dry masses of the plant remarkably. The excessive amounts of soil B also lowered the net photosynthetic rate, stomatal conductance, internal CO₂ concentration and total chlorophyll content in the leaves. In contrast, the foliar application of MeJA enhanced the growth and photosynthetic efficiency both in the stressed and non-stressed plants. The excessive B levels also increased the activities of antioxidant enzymes, such as catalase, peroxidase and superoxide dismutase. Endogenous H₂O₂ and O₂⁻ levels were also high in the stressed plants. However, the MeJA application to the stressed plants reduced the amount of lipid peroxidation and stimulated the synthesis of antioxidant enzymes, enhancing the content and yield of artemisinin as well. Thus, it was concluded that MeJA might be utilized in mitigating the B toxicity and improving the content and yield of artemisinin in A. annua plant.     

Salicylic acid mitigates salinity stress by improving antioxidant defence system and enhances vincristine and vinblastine alkaloids production in periwinkle [<Emphasis Type="Italic">Catharanthus roseus</Emphasis> (L.) G. Don]

A pot experiment was conducted to find out whether the foliar spray of salicylic acid (SA) could successfully ameliorate the adverse effects of salinity stress on periwinkle. Thirty-day-old plants were supplied with Control; 0 mM NaCl + 10⁻⁵ M SA (T₁); 50 mM NaCl + 0 SA (T₂); 100 mM NaCl + 0 SA (T₃); 150 mM NaCl + 0 SA (T₄); 50 mM NaCl + 10⁻⁵ M SA (T₅); 100 mM NaCl + 10⁻⁵ M SA (T₆); 150 mM NaCl + 10⁻⁵ M SA (T₇). The plants were sampled 90 days after sowing to assess the effect of SA on stressed and unstressed plants. Salt stress significantly reduced the growth attributes including plant height, leaf-area index, shoot and root fresh weights, shoot and root dry weights. Increasing NaCl concentrations led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. Ascorbic acid, total alkaloids and antioxidants enzymes superoxide dismutase, catalase and peroxidase also declined in NaCl-treated plants. The plants, undergoing NaCl stress, exhibited a significant increase in electrolyte leakage and proline content. Foliar application of SA (10⁻⁵ M) reduced the damaging effect of salinity on plant growth and accelerated the restoration of growth processes. It not only improved the growth parameters but also reversed the effects of salinity. Total alkaloid content was improved by SA application both in unstressed and stressed plants. The highest level of total alkaloid content recorded in leaves of SA-treated stressed plants was 11.1%. Foliar spray of SA overcame the adverse effect of salinity by improving the content of vincristine (14.0%) and vinblastine (14.6%) in plants treated with 100 M NaCl.     

Genetic analysis of the pnp-deaD genetic region reveals membrane lipoprotein NlpI as an independent participant in cold acclimatization of Salmonella enterica serovar Typhimurium

Plasmid pAMI7 of the methylotrophic bacterium Paracoccus aminophilus JCM 7686 (Alphaproteobacteria) encodes a functional type II restriction-modification (R-M) system designated PamI. Homologous systems were identified in the genomes of distinct taxonomic groups of Bacteria and Archaea, which provides evidence that horizontal gene transfer has contributed to the wide dissemination of R-M modules - even between domains. Analysis of the cleavage specificity of the R.PamI endonuclease revealed that this protein is an isoschizomer of restriction enzyme NcoI. Interestingly, bioinformatic analyses suggest that R.PamI and NcoI are accompanied by methyltransferases of different methylation specificities (C5-methylcytosine and N4-methylcytosine methyltransferases, respectively), which possibly exemplifies recombinational shuffling of genes coding for individual components of R-M systems. The PamI system can stabilize plasmid pAMI7 in a bacterial population, most probably at the postsegregational level. Therefore, it functions in an analogous manner to plasmid-encoded toxin-antitoxin (TA) systems. Since the TA system of pAMI7 is nonfunctional, it is highly probable that this lack is compensated by the stabilizing activity of PamI. This indicates the crucial role of the analyzed R-M system in the stable maintenance of pAMI7, which is, to our knowledge, the first report of 'symbiosis' between a R-M system and a plasmid in the Alphaproteobacteria.