Durgesh Kumar Tripathi

Tolerance and Reduction of Chromium(VI) by Bacillus sp. MNU16 Isolated from Contaminated Coal Mining Soil

The bacterium MNU16 was isolated from contaminated soils of coal mine and subsequently screened for different plant growth promoting (PGP) activities. The isolate was further identified by 16S rRNA sequencing as Bacillus subtilis MNU16 with IAA concentration (56.95 ± 0.43 6μg/ml), siderophore unit (9.73 ± 2.05%), phosphate solubilization (285.13 ± 1.05 μg/ml) and ACC deaminase activity (116.79 ± 0.019 μmoles α-ketobutyrate/mg/24 h). Further, to evaluate the metal resistance profile of bacterium, the isolate was screened for multi-metal resistance (viz. 900 mg/L for Cr, 600 mg/L for As, 700 mg/L for Ni and 300 mg/L for Hg). Additionally, the resistance pattern of B. subtilis MNU16 against Cr(VI) (from 50 to 300 mg/L) treatments were evaluated. An enriched population was observed at 0–200 mg/L Cr(VI) concentration while slight reductions were observed at 250 and 300 mg/L Cr(VI). Further, the chromium reduction ability at 50 mg/L of Cr(VI) highlighted that the bacterium B. subtilis MNU16 reduced 75% of Cr(VI) to 13.23 mg/L within 72 h. The localization of electron dense precipitates was observed in the TEM images of B. subtilis MNU16 which is might be due to the reduction of Cr(VI) to Cr(III). The data of fluorescence microscopy and flow cytometry with respect to Cr(VI) treatments (50–300 mg/L) showed a similar pattern and clearly revealed the less toxic effect of hexavalent chromium upto 200 mg/L Cr(VI) concentration. However, toxicity effects were more pronounced at 300 mg/L Cr(VI). Therefore, the present study suggests that the plant growth promoting potential and resistance efficacy of B. subtilis MNU16 will go a long way in developing an effective bioremediation approach for Cr(VI) contaminated soils.

Differential Phytotoxic Impact of Plant Mediated Silver Nanoparticles (AgNPs) and Silver Nitrate (AgNO3) on Brassica sp.

Continuous formation and utilization of nanoparticles (NPs) have resulted into significant discharge of nanosized particles into the environment. NPs find applications in numerous products and agriculture sector, and gaining importance in recent years. In the present study, silver nanoparticles (AgNPs) were biosynthesized from silver nitrate (AgNO3) by green synthesis approach using Aloe vera extract. Mustard (Brassica sp.) seedlings were grown hydroponically and toxicity of both AgNP and AgNO3 (as ionic Ag+) was assessed at various concentrations (1 and 3 mM) by analyzing shoot and root length, fresh mass, protein content, photosynthetic pigments and performance, cell viability, oxidative damage, DNA degradation and enzyme activities. The results revealed that both AgNPs and AgNO3 declined growth of Brassica seedlings due to enhanced accumulation of AgNPs and AgNO3 that subsequently caused severe inhibition in photosynthesis. Further, the results showed that both AgNPs and AgNO3 induced oxidative stress as indicated by histochemical staining of superoxide radical and hydrogen peroxide that was manifested in terms of DNA degradation and cell death. Activities of antioxidants, i.e., ascorbate peroxidase (APX) and catalase (CAT) were inhibited by AgNPs and AgNO3. Interestingly, damaging impact of AgNPs was lesser than AgNO3 on Brassica seedlings which was due to lesser accumulation of AgNPs and better activities of APX and CAT, which resulted in lesser oxidative stress, DNA degradation and cell death. The results of the present study showed differential impact of AgNPs and AgNO3 on Brassica seedlings, their mode of action, and reasons for their differential impact. The results of the present study could be implied in toxicological research for designing strategies to reduce adverse impact of AgNPs and AgNO3 on crop plants.

Differentiating Thamnocalamus Munro from Fargesia Franchet emend . Yi (Bambusoideae, Poaceae): novel evidence from morphological and neural-network analyses

Fargesia Franchet emend. Yi is closely allied with Thamnocalamus Munro but differs in many major morphological characteristics. Based on traditional morphological characters, it is difficult to differentiate these two genera. The current study measured 19 species in these two genera to determine whether variations in 12 categories of major characters are continuous. In addition, a self-organizing map (SOM) and cluster analysis were used together to reveal whether the known species of Fargesia represent discontinuous sampling of Thamnocalamus. The results show that 46 morphological characteristics exhibited high variation at the generic and species levels. In addition, the cluster analysis showed that 32 morphological characteristics of Thamnocalamus and Fargesia were divided between two species and well separated from the outgroup. Additionally, significant differences (P < 0.01) were observed in the reproductive structures between these two genera. The unrooted dendrogram, which was based on the SOM neural network, shows the same results as the cluster analysis of morphological characteristics. These data indicate that Fargesia is not a result of discontinuous sampling of Thamnocalamus; thus, Fargesia should not be treated as a synonym for Thamnocalamus.

Exploring the Role of Plant-Microbe Interactions in Improving Soil Structure and Function Through Root Exudation: A Key to Sustainable Agriculture

The most astonishing feature of plant roots is their capability of secreting a broad variety of compounds ranging from low molecular to high molecular weights into the rhizosphere. These compounds act as signals for establishing and regulating the interactions among plant roots and microorganisms present in rhizosphere through different mechanisms. The mechanism of establishment of these relationships includes complex signaling cascades and involves different transporter proteins. Exudation is an important process that influences the microbial diversity and relevant biological activities. In addition, these secretions mediate the phenomena of mineral uptake in soil with low nutrient content either through chelation directly or by affecting biological activity of microbes. Further, microbes associated with plants have the potential to upgrade phytoremediation efficiency by facilitating phytoextraction and phytostabilization and through increase in biomass production by plants. Overall these exudation-mediated plant-microbe interactions influence the soil structurally and functionally via orchestrating microbial richness, nutrient acquisition, and phytoremediation. Hence, in light of this, the chapter is intended to provide the perceptivity to comprehend the impact of root exudation-mediated plant-microbe interactions in enriching the structural and functional characteristics of soil.

Current Scenario of Root Exudate–Mediated Plant-Microbe Interaction and Promotion of Plant Growth

Over the last few years, a boom has been witnessed in the area of soil ecology which has produced numerous data on interactions between plant and rhizospheric microbes. The plant-microbe interactions in the rhizospheric niche have proved to be crucial for the advancement of sustainable farming practices which decrease the usage of chemical fertilizers and pesticides. Root exudates are substances released by plant roots that show a significant role in mediating the plant-microbe interactions in soil. These root exudates send chemical signals to microbes which in response are attracted towards the roots and influence growth of plants, soil properties, and microbial community. This chapter is focussed on recent advancements in the utilization of root exudates in plant-microbe interactions to enhance plant growth promotion. The plant-microbe interactions are categorized as beneficial or detrimental depending upon the characteristics of root exudates. This chapter also covers different types of root exudates and their function in modifying the exchanges between rhizospheric microbes and plants for the betterment of soil health and sustainable ecosystems.

Role of PGPR in Sustainable Agriculture: Molecular Approach Toward Disease Suppression and Growth Promotion

Plant concomitant bacteria play a substantial part in plant growth promotion and disease suppression. However, to deliver the best up to their capacity, efficient colonization of the plant roots is of utmost importance. The microbes introduced to the soil, either as a single inoculant or as a consortium, interact with host plant and initiate cascade of reactions which result in plant growth and defense responses. PGPR produce extensive variety of secondary metabolites, allelochemicals, which may work as starting signals or enhancing the necessary reactions. Their action methodology and molecular machineries offer a great cognizance for their application in control of crop diseases. These genes are either upregulated or downregulated, and their expression decides the fate of plant growth and mechanism by which plant resists the disease. Number of genes which will be expressed, encode several metabolites responsible for better growth and synthesis of antimicrobial compounds. Recent developments in expression profiling methods and availability of extensive genome sequence data have permitted important advancements in understanding of responses toward disease resistance in plants. In the later part, we discussed how DNA microarray fits with the current part of PGPR in plant growth promotion and disease resistance. Overall, this chapter will help to better understand the molecular mechanisms behind plant and rhizobacteria interactions.

RETRACTED: Signalling cross-talk between nitric oxide and active oxygen in Trifolium repens L. plants responses to cadmium stress

The significant influence of •NO on the stress response is well established; however, the precise metabolic pathways of •NO and RNS under metal stresses remain unclear. Here, the key components of ROS and RNS metabolism under Cd stress were investigated with multi-level approaches using high-quality forage white clover (Trifolium repens L.) plants. For the studied plants, Cd disturbed the redox homeostasis, affected the absorption of minerals, and exacerbated the degree of lipid peroxidation, thus triggering oxidative stress. However, •NO was also involved in regulating mineral absorption, ROS-scavenger levels and mRNA expression in Cd-treated white clover plants. In addition, GSNOR activity was up-regulated by Cd with the simultaneous depletion of •NO generation and GSNO but was counteracted by the •NO donor sodium nitroprusside. Response to Cd-stressed SNOs was involved in generating ONOO- and NO2-Tyr in accordance with the regulation of •NO-mediated post-translational modifications in the ASC-GSH cycle, selected amino acids and NADPH-generating dehydrogenases, thereby provoking nitrosative stress. Taken together, our data provide comprehensive metabolite evidence that clearly confirms the relationships between ROS and RNS in Cd-stressed plants, supporting their regulatory roles in response to nitro-oxidative stress and providing an in-depth understanding of the interaction between two families subjected to metal stresses.

Emerging Significance of Rhizospheric Probiotics and Its Impact on Plant Health: Current Perspective Towards Sustainable Agriculture

Plants act as a shelter for vast numbers of microorganisms known as plant microbiome which is the key to plant health. Microbial population residing in plants interacts with plants through a series of complex mechanism. The plant microbe interactions can be beneficial, neutral or detrimental depending upon the nature of microbiome in the plant. Plant roots and rhizosphere are the most populated regions of plant where microbial activity is highest due to the secretion of bioactive compounds from roots. The beneficial soil microorganisms are also known as plant probiotics and have the potential to improve plant health and fitness both in natural and adverse environmental conditions. The microorganism which acts as potential probiotics utilized for the manufacturing of biofertilizers because they serve in promoting plant growth and it is now possible to formulate any type of probiotics, because of their common physiological characters. In the present chapter, the main focus is given to the rhizospheric microbiome which functions as plant probiotics and the importance of rhizospheric probiotics in plant growth promotion during stressed conditions. The chapter also includes the details for the delivery of successful biofertilizers by combining various probiotics and guidelines for their registration for providing a safe and efficient biofertilizer in the market.

New adventitious root formation and primary root biomass accumulation are regulated by nitric oxide and reactive oxygen species in rice seedlings under arsenate stress

Nitric oxide (NO) and reactive oxygen species (ROS) are important signaling molecules regulating development of plants. However under metal stress, in developmental processes of plants their implications are not largely known. Therefore, in the present study, role of NO and ROS crosstalk in the regulation of formation of new adventitious roots (NARs) and primary root biomass accumulation (PRBA) has been investigated in rice seedlings under arsenate (AsV) stress. Addition of sodium nitroprusside (SNP, a donor of NO) induced formation of NARs, increased PRBA, and maintained the redox status of ascorbate and cell cycle dynamics. However, addition of NG-nitro-l-arginine methyl ester (L-NAME, an inhibitor of nitric oxide synthase) and 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, a NO scavenger) either in presence of SNP or in its absence blocked formation of NARs and reduced PRBA. Further, to decipher crosstalk of NO and ROS, we used diphenylene iodonium (DPI, an inhibitor of NADPH oxidase), and even in presence of SNP it blocked formation of NARs which indicate that ROS are also essential for formation of NARs. Further a connection of NO-ROS signaling with the redox status of ascorbate and the cell cycle dynamics, governing formation of NARs and PRBA in rice seedlings under AsV stress is discussed.

Microbial Interactions in Litchi Rhizosphere

The litchi is one of the chief fruits of the Asian continent. It is grown almost half of the year and is enjoyed by people for its sweet juice as well as its soft pulp. Also, it is very rich in vitamin C and important minerals and antioxidants. Modern farming does not use chemical fertilizers; thus, bio-fertilizers are used, exploiting the relationship of microbial interactions to plant growth. Mycorrhizal fungi associations are found in the litchi rhizosphere, and these fungi acquire their nutrition from the associated host plants and consequently enhance access to phosphorus and nitrogen. The association between fungi and trees such as the litchi is recognized as vesicular arbuscular mycorrhizae (VAM). In soil habitat, arbuscular mycorrhizal fungi (AMF) are present in symbiosis with litchi roots and cause increase in root length by secreting plant hormones. Availability of appropriate temperature and nutrients will strongly influence the association of arbuscular mycorrhizal fungi with plant growth. Thus, the present chapter focuses on understanding how microbial flora interaction with the litchi rhizosphere helps to enhance the potential productivity of the litchi.