Kanchan Vishwakarma

Abscisic Acid Signaling and Abiotic Stress Tolerance in Plants: A Review on Current Knowledge and Future Prospects

Abiotic stress is one of the severe stresses of environment that lowers the growth and yield of any crop even on irrigated land throughout the world. A major phytohormone abscisic acid (ABA) plays an essential part in acting toward varied range of stresses like heavy metal stress, drought, thermal or heat stress, high level of salinity, low temperature, and radiation stress. Its role is also elaborated in various developmental processes including seed germination, seed dormancy, and closure of stomata. ABA acts by modifying the expression level of gene and subsequent analysis of cis- and trans-acting regulatory elements of responsive promoters. It also interacts with the signaling molecules of processes involved in stress response and development of seeds. On the whole, the stress to a plant can be susceptible or tolerant by taking into account the coordinated activities of various stress-responsive genes. Numbers of transcription factor are involved in regulating the expression of ABA responsive genes by acting together with their respective cis-acting elements. Hence, for improvement in stress-tolerance capacity of plants, it is necessary to understand the mechanism behind it. On this ground, this article enlightens the importance and role of ABA signaling with regard to various stresses as well as regulation of ABA biosynthetic pathway along with the transcription factors for stress tolerance.

Uptake, Accumulation and Toxicity of Silver Nanoparticle in Autotrophic Plants, and Heterotrophic Microbes: A Concentric Review

Nanotechnology is a cutting-edge field of science with the potential to revolutionize today’s technological advances including industrial applications. It is being utilized for the welfare of mankind; but at the same time, the unprecedented use and uncontrolled release of nanomaterials into the environment poses enormous threat to living organisms. Silver nanoparticles (AgNPs) are used in several industries and its continuous release may hamper many physiological and biochemical processes in the living organisms including autotrophs and heterotrophs. The present review gives a concentric know-how of the effects of AgNPs on the lower and higher autotrophic plants as well as on heterotrophic microbes so as to have better understanding of the differences in effects among these two groups. It also focuses on the mechanism of uptake, translocation, accumulation in the plants and microbes, and resulting toxicity as well as tolerance mechanisms by which these microorganisms are able to survive and reduce the effects of AgNPs. This review differentiates the impact of silver nanoparticles at various levels between autotrophs and heterotrophs and signifies the prevailing tolerance mechanisms. With this background, a comprehensive idea can be made with respect to the influence of AgNPs on lower and higher autotrophic plants together with heterotrophic microbes and new insights can be generated for the researchers to understand the toxicity and tolerance mechanisms of AgNPs in plants and microbes.

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.

Contribution of Microbial Inoculants to Soil Carbon Sequestration and Sustainable Agriculture

Soil is the incoherent matter on the earth’s surface having organic and mineral content. It is subjected to environmental changes and hence shows effects of climate change as well as organisms over a period of time. Hence, it is the high time to find ways to increase the crop productivity in soil as green revolution cannot withstand this need. An alternative to this problem is the use of soil microorganism to increase the fertility of soil. Soil enzymes originate from soil microbes and regulate the nutrient cycle. Potential soil isolates can be used to increase nutrients in soil. In addition, these isolates can help in reducing the increase of carbon dioxide by sequestering carbon in soil. It is known that CO2 is one of the major greenhouse gases that contributes to global warming and CO2 fluxes are controlled by soil biota. Thus, soil act as buffer compartment to sequester carbon in relation to climate change. The sequestered soil carbon may further be utilized in agriculture and forestry and as a powerful option for global change mitigation. With this background, the present chapter aims to provide an insight into the contribution of microbial communities to soil carbon sequestration and its benefits to sustainable agriculture.

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.

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.

Plants and Carbon Nanotubes (CNTs) Interface: Present Status and Future Prospects

The unique characteristics of nanomaterials utilizing carbon have drawn great attention and interest since the breakthrough of fullerenes (in 1985), carbon nanotubes (CNTs, in 1991), and graphene (in 2004). This discovery has led to the promotion of developing methods in order to produce it at large industrial scales. Engineered nanomaterials are continuously finding its applications in medical sector, technical devices, environmental purposes, as well as agricultural sector. Despite its wide applications, there is also the unintended release of carbon-based nanostructures into the environment, thereby affecting or posing inimical effect toward the living systems like plants. The researchers are trying to engineer such nanoparticles in a way that it may impose some advanced and beneficial applications in living systems. One of the engineered carbon-based nanomaterials includes carbon nanotubes (CNTs) which can be further classified as single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), water-soluble multiwalled carbon nanotubes, functionalized single-walled carbon nanotubes, double-walled carbon nanotubes etc. This chapter, therefore, focuses on all aforementioned types of carbon nanotubes, techniques utilized in synthesis, and current status of research with respect to the impact of carbon nanotubes on plant growth and development addressing relevant knowledge gap.

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.