Silicon a key player to mitigate chromium toxicity in plants: Mechanisms and future prospective.

Chromium is a serious heavy metal (HM) and its concentration in plant-soil interface is soaring due to anthropogenic activities, unregulated disposals, and lack of efficient treatments. High concentration of Cr is toxic to ecosystems and human health. Cr stress also diminishes the plant performance by changing the plant's vegetative and reproductive development that ultimately affects sustainable crop production. Silicon (Si) is the second-most prevalent element in the crust of the planet, and has demonstrated a remarkable potential to minimize the HM toxicity. Amending soils with Si mitigates adverse effects of Cr by improving plant physiological, biochemical, and molecular functioning and ensuring better Cr immobilization, compartmentation, and co-precipitation. However, there is no comprehensive review on the role of Si to mitigate Cr toxicity in plants. Thus, in this present review; the discussion has been carried on; 1) the source of Cr, 2) underlying mechanisms of Cr uptake by plants, 3) how Si affects the plant functioning to reduce Cr toxicity, 4) how Si can cause immobilization, compartmentation, and co-precipitation 5) strategies to improve Si accumulation in plants to counter Cr toxicity. We also discussed the knowledge gaps and future research needs. The present review reports up-to-date knowledge about the role of Si to mitigate Cr toxicity and it will help to get better crop productivity in Cr-contaminated soils. The findings of the current review will educate the readers on Si functions in reducing Cr toxicity and will offer new ideas to develop Cr tolerance in plants through the use of Si.

Zinc and nano zinc mediated alleviation of heavy metals and metalloids in plants: an overview.

Heavy metals and metalloids (HMs) contamination in the environment has heightened recently due to increasing global concern for food safety and human livability. Zinc (Zn2+ ) is an important nutrient required for the normal development of plants. It is an essential cofactor for the vital enzymes involved in various biological mechanisms of plants. Interestingly, Zn2+ has an additional role in the detoxification of HMs in plants due to its unique biochemical-mediating role in several soil and plant processes. During any exposure to high levels of HMs, the application of Zn2+ would confer greater plant resilience by decreasing oxidative stress, maintaining uptake of nutrients, photosynthesis productivity and optimising osmolytes concentration. Zn2+ also has an important role in ameliorating HMs toxicity by regulating metal uptake through the expression of certain metal transporter genes, targeted chelation and translocation from roots to shoots. This review examined the vital roles of Zn2+ and nano Zn in plants and described their involvement in alleviating HMs toxicity in plants. Moving forward, a broad understanding of uptake, transport, signalling and tolerance mechanisms of Zn2+ /zinc and its nanoparticles in alleviating HMs toxicity of plants will be the first step towards a wider incorporation of Zn2+ into agricultural practices.

Drought and heat stress mediated activation of lipid signaling in plants: a critical review.

Lipids are a principal component of plasma membrane, acting as a protective barrier between the cell and its surroundings. Abiotic stresses such as drought and temperature induce various lipid-dependent signaling responses, and the membrane lipids respond differently to environmental challenges. Recent studies have revealed that lipids serve as signal mediators forreducing stress responses in plant cells and activating defense systems. Signaling lipids, such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, and N-acylethanolamines, are generated in response to stress. Membrane lipids are essential for maintaining the lamellar stack of chloroplasts and stabilizing chloroplast membranes under stress. However, the effects of lipid signaling targets in plants are not fully understood. This review focuses on the synthesis of various signaling lipids and their roles in abiotic stress tolerance responses, providing an essential perspective for further investigation into the interactions between plant lipids and abiotic stress.

Nitrogen enhances the effect of pre-drought priming against post-anthesis drought stress by regulating starch and protein formation in wheat.

Drought stress is one of the most serious environmental stress factor constraining crop production across the globe. Among cereals, wheat grains are very sensitive to drought as a small degree of stress can affect the enzymatic system. This study aimed to investigate whether nitrogen and pre-anthesis drought priming could enhance the action of major regulatory enzymes involved in starch accumulation and protein synthesis in bread wheat (Triticum aestivum L.). For this purpose, cultivars YM-158 (medium gluten) and YM-22 (low gluten) were grown in rain-controlled conditions under two nitrogen levels, that is, N180 (N1) and N300 (N2). Drought priming was applied at the jointing stage and drought stress was applied 7 days after anthesis. Drought stress reduced starch content but enhanced protein content in grains. N2 and primed plants kept higher contents of nonstructural carbohydrates, fructans, and sucrose; with higher activity of sucrose-phosphate synthase in flag leaves. Furthermore, N2 and priming treatments showed higher sink ability to develop grains by showing higher sucrose-to-starch conversion activities of adenosine diphosphate-glucose pyrophosphorylase, uridine diphosphate glucose pyrophosphorylase, sucrose-synthase, soluble-starch synthase, starch branching enzyme, and granule-bound starch synthase as compared to N1 and non-primed treatments. The application of N2 and primed treatment showed a greater ability to maintain grain filling in both cultivars as compared to N1 and non-primed crops. Our study suggested that high nitrogen has the potential to enhance the effect of pre-drought priming to change source-sink relationships and grain yield of wheat under drought stress during the filling process.

Isolation and characterization of peroxidase P7-like gene and Rab-GDI like gene from potential medicinal plants: A step toward understanding cell defense signaling.

Defensin genes form part of a plant's defense system and are activated when exposed to biotic or abiotic stress. They play a vital role in controlling many signaling pathways involved in various plant defense mechanisms. This research aimed to isolate and characterize novel defensin genes from selected medicinally important plants to explore their signaling mechanisms and defense associated roles for breeding. The DNA of Albizia lebbeck and Moringa oleifera was subjected to PCR amplification using gene-specific primers of defensin genes. Two novel defensin genes were isolated in each species, with sequence lengths of 300 bp in A. lebbeck and 150 bp in M. oleifera. In-silico analysis undertaken to retrieve and align their orthologous sequences revealed 100% similarity of the A. lebbeck gene with the Musa acuminate peroxidase P7-like gene and 85% similarity of the M. oleifera gene with the Manihot esculenta GDP dissociation inhibitor gene. The reliability, stability and physiochemical properties of homology models of these sequences was confirmed through online computational studies. This preliminary study confirmed the presence of novel genes with peroxidase P7 and Rab GDP dissociation inhibitor gene-like activity in A. lebbeck and M. oleifera, respectively, and their potential defense role in plants. Thus, the defensin genes of both species could be used in the synthesis of transgenic self-defensive plants with increased disease resistance and as potential candidates for improved crop production and thraputic formulation in the future.

Chemical priming enhances plant tolerance to salt stress.

Salt stress severely limits the productivity of crop plants worldwide and its detrimental effects are aggravated by climate change. Due to a significant world population growth, agriculture has expanded to marginal and salinized regions, which usually render low crop yield. In this context, finding methods and strategies to improve plant tolerance against salt stress is of utmost importance to fulfill food security challenges under the scenario of the ever-increasing human population. Plant priming, at different stages of plant development, such as seed or seedling, has gained significant attention for its marked implication in crop salt-stress management. It is a promising field relying on the applications of specific chemical agents which could effectively improve plant salt-stress tolerance. Currently, a variety of chemicals, both inorganic and organic, which can efficiently promote plant growth and crop yield are available in the market. This review summarizes our current knowledge of the promising roles of diverse molecules/compounds, such as hydrogen sulfide (H2S), molecular hydrogen, nitric oxide (NO), hydrogen peroxide (H2O2), melatonin, chitosan, silicon, ascorbic acid (AsA), tocopherols, and trehalose (Tre) as potential primers that enhance the salinity tolerance of crop plants.

Salicylic Acid Priming Regulates Stomatal Conductance, Trichome Density and Improves Cadmium Stress Tolerance in Mentha arvensis L.

The application of phytohormones through seed priming could enhance quality of important medicinal and aromatic plants (MAPs) under heavy metal stress. We evaluated the potential of salicylic acid (SA) priming for overcoming the adverse effects of cadmium stress in Mentha arvensis L. plants. Suckers of plants were primed with SA before transplanting them into soil. At 30 days after transplanting, two doses (50 and 100 µm) of CdCl2 were applied to the soil. Both Cd treatments altered plant growth, photosynthetic pigments, leaf gas exchange attributes, and mineral nutrient contents. The 50 and 100 µm Cd treatments increased endogenous Cd content by 97.95 and 98.03%, electrolyte leakage (EL) by 34.21 and 44.38%, hydrogen peroxide (H2O2) by 34.71 and 55.80%, malondialdehyde (MDA) by 53.08 and 63.15%, and superoxide content (O2 -•) by 24.07 and 38.43%, respectively. Cd triggered the up-regulation of antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; and glutathione reductase GR) and increased osmolyte biosynthesis and, interestingly, secondary metabolite (SM) accumulation. The presence of SA and Cd had an additive effect on these parameters. Nevertheless, plants primed with SA regulated stomatal conductance under Cd stress. SA priming to menthol mint plants under Cd stress overcome the effects of Cd stress while increasing SMs.

CRISPR-Based Genome Editing Tools: Insights into Technological Breakthroughs and Future Challenges.

Genome-editing (GE) is having a tremendous influence around the globe in the life science community. Among its versatile uses, the desired modifications of genes, and more importantly the transgene (DNA)-free approach to develop genetically modified organism (GMO), are of special interest. The recent and rapid developments in genome-editing technology have given rise to hopes to achieve global food security in a sustainable manner. We here discuss recent developments in CRISPR-based genome-editing tools for crop improvement concerning adaptation, opportunities, and challenges. Some of the notable advances highlighted here include the development of transgene (DNA)-free genome plants, the availability of compatible nucleases, and the development of safe and effective CRISPR delivery vehicles for plant genome editing, multi-gene targeting and complex genome editing, base editing and prime editing to achieve more complex genetic engineering. Additionally, new avenues that facilitate fine-tuning plant gene regulation have also been addressed. In spite of the tremendous potential of CRISPR and other gene editing tools, major challenges remain. Some of the challenges are related to the practical advances required for the efficient delivery of CRISPR reagents and for precision genome editing, while others come from government policies and public acceptance. This review will therefore be helpful to gain insights into technological advances, its applications, and future challenges for crop improvement.

Efficacy of multi-walled carbon nanotubes in regulating growth performance, total glutathione and redox state of Calendula officinalis L. cultivated on Pb and Cd polluted soil.

Multi-walled carbon nanotubes (MWCNTs) have recently attracted huge attention to their impacts on the environment and plants. Therefore, this experiment was conducted to investigate the responses of lead (Pb) and cadmium (Cd) exposed pot marigold plants to various levels of MWCNT. Calendula officinalis (L.) seedlings were cultivated in Pb and Cd-polluted soils with exposure to 0, 50, 100, 250, 500 and 1000 mg L-1 of MWCNT. The results demonstrated that foliar-applied MWCNT up to 250 mg L-1 not only alleviated Pb and Cd-induced toxicity by reducing oxidative damage and boosting both enzymatic and non-enzymatic antioxidant defense system but also promoted the phytoremediation property of pot marigold plants by enhancing the accumulation of both Pb and Cd from the soil. Interestingly, oxidative damage exacerbation and both Pb and Cd accumulation reduction were noticed in pot marigold seedlings exposed to 500 and 1000 mg L-1 MWCNTs. The findings of this study clearly showed that the use of appropriate concentrations of MWCNTs in increasing the phytoremediation properties of pot marigold was justified, while the use of high concentrations is toxic to the plant and intensifies the toxic effects of heavy metals (HMs) on plant physiology. This study provides a novel method to facilitate the phytoremediation of HMs polluted soils using MWCNT as well as explores the potential risks of these nanoparticles to the plants.

Nitrogen use efficiency (NUE): elucidated mechanisms, mapped genes and gene networks in maize (Zea mays L.).

Nitrogen, the vital primary plant growth nutrient at deficit soil conditions, drastically affects the growth and yield of a crop. Over the years, excess use of inorganic nitrogenous fertilizers resulted in pollution, eutrophication and thereby demanding the reduction in the use of chemical fertilizers. Being a C4 plant with fibrous root system and high NUE, maize can be deployed to be the best candidate for better N uptake and utilization in nitrogen deficient soils. The maize germplasm sources has enormous genetic variation for better nitrogen uptake contributing traits. Adoption of single cross maize hybrids as well as inherent property of high NUE has helped maize cultivars to achieve the highest growth rate among the cereals during last decade. Further, considering the high cost of nitrogenous fertilizers, adverse effects on soil health and environmental impact, maize improvement demands better utilization of existing genetic variation for NUE via introgression of novel allelic combinations in existing cultivars. Marker assisted breeding efforts need to be supplemented with introgression of genes/QTLs related to NUE in ruling varieties and thereby enhancing the overall productivity of maize in a sustainable manner. To achieve this, we need mapped genes and network of interacting genes and proteins to be elucidated. Identified genes may be used in screening ideal maize genotypes in terms of better physiological functionality exhibiting high NUE. Future genome editing may help in developing lines with increased productivity under low N conditions in an environment of optimum agronomic practices. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01113-z.

Mitigation of Copper Stress in Maize by Inoculation with Paenibacillus polymyxa and Bacillus circulans.

Copper (Cu) is a micronutrient that assumes a principal role in plant growth and development. However, its excess concentration in soil is imperiling crop productivity. Inoculation with different bacterial strains in cereals could modify growth traits, photosynthetic effectiveness, and generation of strong antioxidant defense systems to make them more tolerant of Cu stress. Therefore, a pot study was designed to test plant growth-promoting rhizobacteria (PGPR) including Paenibacillus polymyxa and Bacillus circulans to Cu exposed maize (Zea mays L.) plants. Increasing Cu (100 to 500 µM of CuSO4) concentration decreased growth traits, photosynthetic pigments, soluble sugars, phosphorous (P) and potassium (K) contents, and the activity of catalase (CAT) but increased proline and malondialdehyde (MDA) content, the activity of peroxidase (POD) and Cu ions at root and shoot level. Moreover, the bacterial treatment also modulated the antioxidant capability in stress-free plants. Nevertheless, inoculation with P. polymyxa and B. circulans alleviated Cu-induced growth, photosynthetic pigments and mineral nutrient (P and K) on one hand and regulating the pools of osmolytes and antioxidant enzymes, whilst simultaneously reducing MDA and Cu root and shoot contents. These improved activities of antioxidant enzymes and the regulation of osmolytes content elicited by the blend of bacterial inoculation would have retained the ability of maize plants to confer resilience to Cu stress. This study further affirms that the application of two specific bacterial strains to maize plants proved very effective to ameliorate the Cu toxicity.

Plant growth regulators improve growth, photosynthesis, mineral nutrient and antioxidant system under cadmium stress in menthol mint (Mentha arvensis L.).

Menthol mint (Mentha arvensis L.) cultivation is significantly affected by the heavy metals like cadmium (Cd) which also imposes severe health hazards. Two menthol mint cultivars namely Kosi and Kushal were evaluated under Cd stress conditions. Impact of plant growth regulators (PGRs) like salicylic acid (SA), gibberellic acid (GA3) and triacontanol (Tria) on Cd stress tolerance was assessed. Reduced growth, photosynthetic parameters, mineral nutrient concentration, and increased oxidative stress biomarkers like electrolyte leakage, malondialdehyde, and hydrogen peroxide contents were observed under Cd stress. Differential upregulation of proline content and antioxidant activities under Cd stress was observed in both the cultivars. Interestingly, low electrolyte leakage, lipid peroxidation, hydrogen peroxide and Cd concentration in leaves were observed in Kushal compared to Kosi. Among all the PGRs tested, SA proved to be the best in improving Cd-stress tolerance in both the cultivars but Kushal responded better than Kosi.

Serratia marcescens BM1 Enhances Cadmium Stress Tolerance and Phytoremediation Potential of Soybean Through Modulation of Osmolytes, Leaf Gas Exchange, Antioxidant Machinery, and Stress-Responsive Genes Expression.

The heavy metal contamination in plant-soil environment has increased manifold recently. In order to reduce the harmful effects of metal stress in plants, the application of beneficial soil microbes is gaining much attention. In the present research, the role of Serratia marcescens BM1 in enhancing cadmium (Cd) stress tolerance and phytoremediation potential of soybean plants, was investigated. Exposure of soybean plants to two Cd doses (150 and 300 µM) significantly reduced plant growth, biomass, gas exchange attributes, nutrients uptake, antioxidant capacity, and the contents of chlorophyll, total phenolics, flavonoids, soluble sugars, and proteins. Additionally, Cd induced the stress levels of Cd, proline, glycine betaine, hydrogen peroxide, malondialdehyde, antioxidant enzymes (i.e., catalase, CAT; ascorbate peroxidase, APX; superoxide dismutase, SOD; peroxidise, POD), and the expression of stress-related genes (i.e., APX, CAT, Fe-SOD, POD, CHI, CHS, PHD2, VSO, NR, and P5CS) in soybean leaves. On the other hand, inoculation of Cd-stressed soybean plants with Serratia marcescens BM1 significantly enhanced the plant growth, biomass, gas exchange attributes, nutrients uptake, antioxidant capacity, and the contents of chlorophyll, total phenolics, flavonoids, soluble sugars, and proteins. Moreover, Serratia marcescens BM1 inoculation reduced the levels of cadmium and oxidative stress markers, but significantly induced the activities of antioxidant enzymes and the levels of osmolytes and stress-related genes expression in Cd-stressed plants. The application of 300 µM CdCl2 and Serratia marcescens triggered the highest expression levels of stress-related genes. Overall, this study suggests that inoculation of soybean plants with Serratia marcescens BM1 promotes phytoremediation potential and Cd stress tolerance by modulating the photosynthetic attributes, osmolytes biosynthesis, antioxidants machinery, and the expression of stress-related genes.

Harnessing Genome Editing Techniques to Engineer Disease Resistance in Plants.

Modern genome editing (GE) techniques, which include clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system, transcription activator-like effector nucleases (TALENs), zinc-finger nucleases (ZFNs) and LAGLIDADG homing endonucleases (meganucleases), have so far been used for engineering disease resistance in crops. The use of GE technologies has grown very rapidly in recent years with numerous examples of targeted mutagenesis in crop plants, including gene knockouts, knockdowns, modifications, and the repression and activation of target genes. CRISPR/Cas9 supersedes all other GE techniques including TALENs and ZFNs for editing genes owing to its unprecedented efficiency, relative simplicity and low risk of off-target effects. Broad-spectrum disease resistance has been engineered in crops by GE of either specific host-susceptibility genes (S gene approach), or cleaving DNA of phytopathogens (bacteria, virus or fungi) to inhibit their proliferation. This review focuses on different GE techniques that can potentially be used to boost molecular immunity and resistance against different phytopathogens in crops, ultimately leading to the development of promising disease-resistant crop varieties.

Salicylic acid enhances nickel stress tolerance by up-regulating antioxidant defense and glyoxalase systems in mustard plants.

The present study identified inverse relationships between nickel (Ni) levels and growth, photosynthesis and physio-biochemical attributes, but increasing levels of Ni stress enhanced methylglyoxal, electrolyte leakage, hydrogen peroxide, and lipid peroxidation content. Exogenous application of salicylic acid (SA) (10-5 M) ameliorated the ill-effects of Ni by restoring growth, photosynthesis and physio-biochemical attributes and increasing the activities of enzymes associated with antioxidant systems, especially the ascorbate-glutathione (AsA-GSH) cycle and glyoxalase system. In addition, SA application to Ni-stressed plants had an additive effect on the activities of the ascorbate and glutathione pools, and the AsA-GSH cycle enzymes (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase), superoxide dismutase, catalase, glutathione S-transferase, and osmolyte biosynthesis). This trend also follows in glyoxalase system viz. glyoxalase I and glyoxalase II enzymes. Nevertheless, exogenous SA supplementation restored mineral nutrient contents. Principal component analysis showed that growth, photosynthesis, and mineral nutrient parameters were positively correlated with each other and negatively correlated with antioxidant enzymes and oxidative stress biomarkers. Hence, SA is an alternative compound with potential application in the phytoremediation of Ni.

Evaluation of potassium solubilizing rhizobacteria (KSR): enhancing K-bioavailability and optimizing K-fertilization of maize plants under Indo-Gangetic Plains of India.

Imbalanced potassium (K) fertilization in agricultural fields has led to considerable negative impacts and remains to be the foremost challenge for maize production in India-Gangetic region. Plant growth-promoting rhizobacteria, particularly potassium solubilizing rhizobacteria (KSR), could serve as inoculants and a promising strategy for enhancement of plant absorption of K hence reducing dependency on chemical fertilizers. Maize seeds were microbiolized for 30 min with KSR suspensions. In the present study, the use of chemical fertilizers along with Agrobacterium tumefaciens strain OPVS10 showed pronounced beneficial effect on growth and yield attributes in maize. There was a significant difference among different parameters studied when varying doses of K and KSR strains were applied. Results showed that the combined application of KSR strain OPVS10 with 100% RDK (recommended dose of K) was most effective in modulating growth, physio-biochemical, and yield attributes in maize thus could be regarded as a promising alternative to mineral K-fertilization. Principal component analysis (PCA) revealed that 100-grain weight and grain yield were the most important properties to improve the sustainable growth of maize. Therefore, these KSR strains have different mechanisms for modulating various activities in maize plants. Results suggested that the synergistic application of KSR strain OPVS10 with 100% RDK can be used for optimized breeding, screening, and nutrient assimilation in maize crop. Hence, this eco-friendly approach may be one of the efficient methods for reducing dependency on chemicals, which pose adverse effects on human health directly and indirectly.

Transcriptional regulation of osmotic stress tolerance in wheat (Triticum aestivum L.).

KEY MESSAGE: The current review provides an updated, new insights into the regulation of transcription mediated underlying mechanisms of wheat plants to osmotic stress perturbations. Osmotic stress tolerance mechanisms being complex are governed by multiple factors at physiological, biochemical and at the molecular level, hence approaches like "OMICS" that can underpin mechanisms behind osmotic tolerance in wheat is of paramount importance. The transcription factors (TFs) are a class of molecular proteins, which are involved in regulation, modulation and orchestrating the responses of plants to a variety of environmental stresses. Recent reports have provided novel insights on the role of TFs in osmotic stress tolerance via direct molecular links. However, our knowledge on the regulatory role TFs during osmotic stress tolerance in wheat remains limited. The present review in its first part sheds light on the importance of studying the role of osmotic stress tolerance in wheat plants and second aims to decipher molecular mechanisms of TFs belonging to several classes, including DREB, NAC, MYB, WRKY and bHLH, which have been reported to engage in osmotic stress mediated gene expression in wheat and third part covers the systems biology approaches to understand the transcriptional regulation of osmotic stress and the role of long non-coding RNAs in response to osmotic stress with special emphasis on wheat. The current concept may lead to an understanding in molecular regulation and signalling interaction of TFs under osmotic stress to clarify challenges and problems for devising potential strategies to improve complex regulatory events involved in plant tolerance to osmotic stress adaptive pathways in wheat.