Silicon and nitric oxide-mediated mechanisms of cadmium toxicity alleviation in wheat seedlings.

The individual impact of silicon (Si) and nitric oxide (NO, as sodium nitroprusside) on metal toxicity in various plant species has been well documented; however, their combined action in the regulation of metal stress has never been tested yet. Therefore, this study investigates the effects of the combined application of Si and NO in the mitigation of Cd toxicity in wheat seedlings. Seedlings grown on Cd has a significantly declined growth due to an increased accumulation of Cd and oxidative stress markers (due to downregulation of antioxidant defense system particularly ascorbate-glutathione cycle) and a decreased accumulation of NO and Si. Additionally, the altered leaf and root structures resulted into a declined photosynthetic efficiency. However, the addition of Si and NO alone as well as combined significantly alleviated Cd toxicity in wheat seedlings by lowering the accumulation of Cd and oxidative stress markers and improving leaf and root structures, which are collectively responsible for a better photosynthetic rate under Cd toxicity, and hence an improved growth was noticed. Particularly, the application of Si and NO in combination lowered the oxidative stress markers via upregulating the antioxidant defense system (particularly AsA-GSH cycle) suggesting the increased efficacy of Si + NO against the Cd toxicity in wheat seedlings as compared to their alone treatments.

Synergistic action of silicon nanoparticles and indole acetic acid in alleviation of chromium (CrVI) toxicity in Oryza sativa seedlings.

The present study investigates ameliorative effect of silicon nanoparticles (SiNPs) and indole acetic acid (IAA) alone and in combination against hexavalent chromium (CrVI) toxicity in rice seedlings. The results of the study revealed protective effects of SiNPs and IAA against CrVI toxicity. The 100 µM of CrVI imposed toxic effects in rice seedlings at morphological, physiological and biochemical levels which coincided with increased level of intracellular CrVI and declined level of endogenous nitric oxide (NO). The CrVI enhanced levels of superoxide radicals (SOR) (59.51% and 50.1% in shoot and root, respectively) and H2O2 (19.5% and 23.69% in shoot and root, respectively). However, when SiNPs and IAA were applied to plants under CrVI stress, they enhanced tolerance and defence mechanisms as manifested in terms of increased biomass, endogenous NO, photosynthetic pigments, and antioxidants level. It was also noticed that CrVI arrested cell cycle at G2/M phase whereas growth was restored as compared to control when SiNPs and IAA were supplemented. Thus, the hypothesis that combined application of SiNPs and IAA will be effective in alleviating CrVI toxicity is validated from the results of this study. Moreover, in SiNPs and IAA-mediated mitigation of CrVI toxicity, endogenous NO has a positive role. The importance of the study will be that the combination of SiNPs and IAA can be utilized against heavy metal stress and even when supplied alone, they will enhance the crop productivity parameters with and without stress conditions.

Endogenous indole-3-acetic acid and nitric oxide are required for calcium-mediated alleviation of copper oxide nanoparticles toxicity in wheat seedlings.

The action of nanoparticles is increasingly being studied in recent years to minimize their toxic impacts. Besides this, efforts are also being made to minimize their toxicity in crop plants by using various chemicals, i.e. nutrients, donors of signaling molecules, plant hormones, and so on. However, associated alleviatory mechanisms are still not well known. Therefore, in the present study, we have investigated the toxicity of CuONPs and its mitigation by exogenously applied calcium (Ca). The focus was on whether indole-3-acetic acid (IAA) or endogenous nitric oxide (NO) has any role in accomplishing this task. CuONPs declined wheat growth due to increased accumulation of Cu and oxidative stress markers such as superoxide radicals, hydrogen peroxide, and lipid peroxidation (malondialdehyde) and it was also accompanied by a decline in endogenous NO. CuONPs also altered the redox status of ascorbate and glutathione by inhibiting the activity of their regenerating enzymes. This collectively leads to cell death in wheat seedlings. However, exogenous supplementation of Ca mitigated toxic effects of CuONPs by reducing the excess accumulation of Cu, which caused remarkable enhancement in growth, protein contents, photosynthetic pigments, and endogenous NO; altogether protecting wheat roots from cell death. Interestingly, addition of 2,3,5-triiodobenzoic acid (TIBA) further increased CuONPs toxicity even in the presence of Ca, but the addition of IAA rescued this effect of TIBA. These results clearly show that Ca mitigates CuONPs toxicity in wheat seedlings by involving IAA. Further, the results also showed that endogenous NO has a positive and indispensable role in Ca-mediated mitigation of CuONPs toxicity in wheat seedlings.

Engineered zinc oxide nanoparticles: an alternative to conventional zinc sulphate in neutral and alkaline soils for sustainable wheat production.

Zinc oxide nanoparticles (ZnONP) were synthesized and characterized using SEM, EDAX, DLS and UV-Vis spectra. Its use as a nanofertilizer as an alternative to conventional zinc sulphate (ZnSO4.7H2O) was evaluated in five Zn-deficient soils with a variable pH range (7.2-8.7). For this, the carbon of the soil microbial biomass (SMBC), the bacterial population, the nutrient dynamics and the biometric parameters of the wheat crop were assessed. The varying dosages (0, 100, 200 and 500 mg/L), sizes (30-100 nm), and the spherical shape of ZnONPs were evaluated in comparison to ZnSO4.7H2O levels. Results showed the maximum SMBC and bacterial population at 100 mg/L of ZnONPs but a sharp decline at higher concentrations. In addition, soil application of ZnONPs at 5 mg/kg produced a higher root elongation (4.3-8.8%), shoot elongation (3.5-4.0%), total chlorophyll (4.9-5.6%), grain yield (1.7-2.3%) and grain Zn-content (1.6-2.1%) in comparison to the conventional ZnSO4.7H2O at 10 mg/L. ZnONPs at 100 mg/L produced a higher soil microbial biomass carbon (3.9-4.6%), bacterial population (7.2-9.0%), germination (22%) and grain Zn-content (17.9-20%) as compared to the conventional ZnSO4.7H2O at 0.5%. The higher grain Zn-contents could be attributed to the small size and high surface area of ZnONPs resulting in easy entry into the plant system either through root or foliar by penetrating the pores present in the cell membranes. Conversely, the conventional ZnSO4.7H2O, due to its larger size and higher solubility as compared to ZnONPs, has low retention in plant systems, high surface run-off and low fertilizer efficiency. Thus, the authors concluded to apply spherically synthesized ZnONPs (average size-36.7 nm) at 5 mg/kg in the soil application and 100 mg/L in the foliar application for maintaining SMBC and bacterial population, improving total chlorophyll, and grain Zn-contents and overall sustaining wheat production in Zn-deficient neutral and alkaline soils. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02861-1.

Drought Tolerant Near Isogenic Lines of Pusa 44 Pyramided With qDTY2.1 and qDTY3.1, Show Accelerated Recovery Response in a High Throughput Phenomics Based Phenotyping.

Reproductive stage drought stress (RSDS) is a major challenge in rice production worldwide. Cultivar development with drought tolerance has been slow due to the lack of precise high throughput phenotyping tools to quantify drought stress-induced effects. Most of the available techniques are based on destructive sampling and do not assess the progress of the plant's response to drought. In this study, we have used state-of-the-art image-based phenotyping in a phenomics platform that offers a controlled environment, non-invasive phenotyping, high accuracy, speed, and continuity. In rice, several quantitative trait loci (QTLs) which govern grain yield under drought determine RSDS tolerance. Among these, qDTY2.1 and qDTY3.1 were used for marker-assisted breeding. A set of 35 near-isogenic lines (NILs), introgressed with these QTLs in the popular variety, Pusa 44 were used to assess the efficiency of image-based phenotyping for RSDS tolerance. NILs offered the most reliable contrast since they differed from Pusa 44 only for the QTLs. Four traits, namely, the projected shoot area (PSA), water use (WU), transpiration rate (TR), and red-green-blue (RGB) and near-infrared (NIR) values were used. Differential temporal responses could be seen under drought, but not under unstressed conditions. NILs showed significant level of RSDS tolerance as compared to Pusa 44. Among the traits, PSA showed strong association with yield (80%) as well as with two drought tolerances indices, stress susceptibility index (SSI) and tolerance index (TOL), establishing its ability in identifying the best drought tolerant NILs. The results revealed that the introgression of QTLs helped minimize the mean WU per unit of biomass per day, suggesting the potential role of these QTLs in improving WU-efficiency (WUE). We identified 11 NILs based on phenomics traits as well as performance under imposed drought in the field. The study emphasizes the use of phenomics traits as selection criteria for RSDS tolerance at an early stage, and is the first report of using phenomics parameters in RSDS selection in rice.

Silicon tackles butachlor toxicity in rice seedlings by regulating anatomical characteristics, ascorbate-glutathione cycle, proline metabolism and levels of nutrients.

Reckless use of herbicides like butachlor (Buta) in the fields represents a serious threat to crop plants, and hence to their productivity. Silicon (Si) is well known for its implication in the alleviation of the effects of abiotic stresses; however, its role in mitigating Buta toxicity is not yet known. Therefore, this study was carried out to explore the role of Si (10 µM) in regulating Buta (4 µM) toxicity in rice seedlings. Buta reduced growth and photosynthesis, altered nitric oxide (NO) level and leaf and root anatomy, inhibited enzyme activities of the ascorbate-glutathione cycle (while transcripts of associated enzymes, increased except OsMDHAR), as well as its metabolites (ascorbate and glutathione) and uptake of nutrients (Mg, P, K, S, Ca, Fe, etc. except Na), while addition of Si reversed Buta-induced alterations. Buta stimulated the expression of Si channel and efflux transporter genes- Lsi1 and Lsi2 while the addition of Si further greatly induced their expression under Buta toxicity. Buta increased free proline accumulation by inducing the activity of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and decreasing proline dehydrogenase (PDH) activity, while Si reversed these effects caused by Buta. Our results suggest that Si-governed mitigation of Buta toxicity is linked with favorable modifications in energy flux parameters of photosynthesis and leaf and root anatomy, up-regulation of Si channel and transporter genes, ascorbate-glutathione cycle and nutrient uptake, and lowering in oxidative stress. We additionally demonstrate that NO might have a crucial role in these responses.

NO and ROS implications in the organization of root system architecture.

Over the past decades the role of nitric oxide (NO) and reactive oxygen species (ROS) in signaling and cellular responses to stress has witnessed an exponential trend line. Despite advances in the subject, our knowledge of the role of NO and ROS as regulators of stress and plant growth and their implication in signaling pathways is still partial. The crosstalk between NO and ROS during root formation offers new domains to be explored, as it regulates several plant functions. Previous findings indicate that plants utilize these signaling molecules for regulating physiological responses and development. Depending upon cellular concentration, NO either can stimulate or impede root system architecture (RSA) by modulating enzymes through post-translational modifications. Similarly, the ROS signaling molecule network, in association with other hormonal signaling pathways, control the RSA. The spatial regulation of ROS controls cell growth and ROS determine primary root and act in concert with NO to promote lateral root primordia. NO and ROS are two central messenger molecules which act differentially to upregulate or downregulate the expression of genes pertaining to auxin synthesis and to the configuration of root architecture. The investigation concerning the contribution of donors and inhibitors of NO and ROS can further aid in deciphering their role in root development. With this background, this review provides comprehensive details about the effect and function of NO and ROS in the development of RSA.

Avenues of the membrane transport system in adaptation of plants to abiotic stresses.

Abiotic stress imposed by many factors such as: extreme water regimes, adverse temperatures, salinity, and heavy metal contamination result in severe crop yield losses worldwide. Plants must be able to quickly respond to these stresses in order to adapt to their growing conditions and minimize metabolic losses. In this context, transporter proteins play a vital role in regulating stress response mechanisms by facilitating movement of a variety of molecules and ions across the plasma membrane in order to maintain fundamental cellular processes such as ion homeostasis, osmotic adjustment, signal transduction, and detoxification. Aquaporins play a crucial role in alleviating abiotic stress by transporting water and other small molecules to maintain cellular homeostasis. Similarly, other transporter families such as CDF, ZIP, ABC, NHX, HKT, SWEETs, TMTs, and ion channels also contribute to abiotic stress tolerance. Hormones and other signaling molecules are necessary to coordinate responses across different tissues and to precisely regulate molecular trafficking. The present review highlights the current understanding of how membrane transporters orchestrate stress responses in plants. It also provides insights about the importance of these sensing and adaptive mechanisms for ensuring improved sustainable crop production during unfavorable conditions. Finally, this review discusses future prospects for the use of computational tools in constructing signaling networks to improve our understanding of the behavior of transporters under abiotic stress.

Regulation of cadmium toxicity in roots of tomato by indole acetic acid with special emphasis on reactive oxygen species production and their scavenging.

Toxic impact of cadmium (Cd) on plants is well known which affects their productivity. To mitigate toxic impact of metals such as Cd, exogenous application of phytohormones like indole acetic acid (IAA) has been well recognized in the recent past. But, mechanisms related to the IAA-mediated mitigation of metal toxicity remain elusive. Therefore, in this study, effect of IAA on growth and photosynthetic attributes, nitric oxide, cell viability, reactive oxygen species (ROS) and ascorbate-glutathione cycle (AsA-GSH cycle) was investigated in tomato roots exposed to Cd stress. Cd declined growth and photosynthetic attributes which were accompanied by the excess accumulation of Cd and decreased level of nitric oxide (NO). Among photosynthetic attributes, quantum yield parameters were more sensitive to Cd and these results were in parallel of photosynthetic pigments. However, exogenously applied IAA together with Cd significantly improved level of NO, growth and photosynthetic attributes together with reduced accumulation of Cd. Cd enhanced level of superoxide radical and hydrogen peroxide leading to severe damage to lipids and membranes as indicated by increased level of lipid peroxidation and electrolyte leakage which collectively reduced cell viability of roots. Moreover, components of the AsA-GSH cycle i.e. enzymes (ascorbate peroxidase, monodehydroascorbate reducatse, dehydroascorbate reducatse and glutathione reductase) and metabolites (ascorbate and glutathione) were declined by the Cd. However, addition of IAA with Cd had up-regulated components of the AsA-GSH cycle. Interestingly, application of 2,4,6-triiodobenzoic acid (TIBA, a polar auxin transport inhibitor) diminished growth attributes and its combination with Cd worsened its toxicity and these events were in parallel with decline in NO content and enhancement in Cd accumulation. The results also showed that IAA was also able in mitigating Cd toxicity in tomato roots even in the presence of TIBA. Overall results show the essentiality of IAA in mitigating Cd stress in tomato roots through NO that up-regulates components of the AsA-GSH cycle for balancing ROS and their associated damages and hence much improved growth and photosynthetic attributes were noticed.

Unravelling the potential of microbes isolated from rhizospheric soil of chickpea (Cicer arietinum) as plant growth promoter.

In the present study, the Cicer arietinum (chickpea) rhizosphere bacterial strains Azotobacter chroococcum (AU-1), Bacillus subtilis (AU-2), Pseudomonas aeruginosa (AU-3) and Bacillus pumilis (AU-4) were isolated and characterized for plant growth-promoting traits with an aim of developing bio-fertilizing agent to improve growth and yield of chickpea plants under normal conditions. The ACC degrading potential of strains AU-1, AU-2, AU-3, and AU-4 was in the range of 600-1700 nmol α-ketobutyrate per mg of cellular protein per hour, respectively. These four rhizobacteria exhibited Indole acetic acid production approximately between 20 and 35.34 µg/ml. The phosphate solubilization potential was in the range of 78-87.64 mg Soluble P/L with maximum solubilization displayed by strains P. aeruginosa and B. pumilis. All the growth-promoting isolates displayed Fe-chelating siderophore and ammonia production while no isolate was able to produce hydrocyanic acid. Besides evaluating the presence of multifaceted in vitro plant growth-promoting traits, these four rhizobacterial isolates were halotolerant as well as water stress (drought) tolerant of up to - 1.2 Mpa of PEG 6000. The optimum pH and temperature for their growth were found to be pH 7 and 30 °C temperature. Under normal conditions, inoculation with formulated bacterial consortia significantly improved the (P ≤ 0.05) germination index, plant height, leaf area index, stem diameter, and chlorophyll content by ~ 50%, 100%, 63%, 185%, and 63%, respectively, as compared to uninoculated chickpea plants. The consortia of halotolerant and drought tolerant bacterial strains were shown to exert a positive impact on the growth of chickpea plants under normal conditions.

Liquid assisted pulsed laser ablation synthesized copper oxide nanoparticles (CuO-NPs) and their differential impact on rice seedlings.

Hydroponic experiments were conducted to investigate impact of laser ablated copper oxide nanoparticles (CuO-NPs) on rice seedlings. The present work demonstrates that exposure of lower concentrations (5, 10, 20, and 50 µM) of CuO-NPs enhance growth (in terms of fresh and dry weight and length), of rice seedlings. However, at higher concentrations (100, 200, and 500 µM) of CuO-NPs, growth (in terms of length, fresh weight and dry weight) decreased significantly (P < 0.05). Further, photosynthetic pigments (total chlorophyll and carotenoids) and protein contents were also found to be in accordance with the results of growth. This had occurred due to enhanced level of CuO-NPs accumulation at higher doses which also enhanced the level of oxidative stress markers such as hydrogen peroxide (H2O2) and malondialdehyde (MDA). Chlorophyll a fluorescence parameters (Fv/Fm and qP and except NPQ) and amount of some minerals (Ca, Mg, Na, and K) increased at lower concentrations of CuO-NPs. In contrast, the levels of Fv/Fm and qP were significantly (P < 0.05) reduced at higher concentration of CuO-NPs, which might be due to enhanced accumulation of Cu and oxidative stresses markers. Our results showed that lower dosages of pulsed laser ablated CuO-NPs (5, 10, 20, and 50 µM) might be beneficial for growth and development of rice seedlings.

Nanomaterials and microbes' interactions: a contemporary overview.

Use of nanomaterials in the field of science and technology includes different fields in food industry, medicine, agriculture and cosmetics. Nanoparticle-based sensors have wide range of applications in food industry for identification and detection of chemical contaminants, pathogenic bacteria, toxins and fungal toxins from food materials with high specificity and sensitivity. Nanoparticle-microbe interactions play a significant role in disease treatment in the form of antimicrobial agents. The inhibitory mechanism of nanoparticles against different bacteria and fungi includes release of metal ions that interacts with cellular components through various pathways including reactive oxygen species (ROS) generation, pore formation in cell membranes, cell wall damage, DNA damage, and cell cycle arrest and ultimately inhibits the growth of cells. Nanoparticle-based therapies are growing to study the therapeutic treatments of plant diseases and to prevent the growth of phytopathogens leading to the growing utilization of engineered nanomaterials. Hence, with this background, the present review focuses thoroughly on detailed actions and responses of nanomaterials against different bacteria and fungi as well as food sensing and storage.