Alleviation of Cadmium and Nickel Toxicity and Phyto-Stimulation of Tomato Plant L. by Endophytic Micrococcus luteus and Enterobacter cloacae

Exploring the synergistic effects of indole acetic acid (IAA) and compost in the phytostabilization of nickel (Ni) in cauliflower rhizosphere

Heavy metals (HMs) contamination, owing to their potential links to various chronic diseases, poses a global threat to agriculture, environment, and human health. Nickel (Ni) is an essential element however, at higher concentration, it is highly phytotoxic, and affects major plant functions. Beneficial roles of plant growth regulators (PGRs) and organic amendments in mitigating the adverse impacts of HM on plant growth has gained the attention of scientific community worldwide. Here, we performed a greenhouse study to investigate the effect of indole-3-acetic acid (IAA @ 10- 5 M) and compost (1% w/w) individually and in combination in sustaining cauliflower growth and yield under Ni stress. In our results, combined application proved significantly better than individual applications in alleviating the adverse effects of Ni on cauliflower as it increased various plant attributes such as plant height (49%), root length (76%), curd height and diameter (68 and 134%), leaf area (75%), transpiration rate (36%), stomatal conductance (104%), water use efficiency (143%), flavonoid and phenolic contents (212 and 133%), soluble sugars and protein contents (202 and 199%), SPAD value (78%), chlorophyll 'a and b' (219 and 208%), carotenoid (335%), and NPK uptake (191, 79 and 92%) as compared to the control. Co-application of IAA and compost reduced Ni-induced electrolyte leakage (64%) and improved the antioxidant activities, including APX (55%), CAT (30%), SOD (43%), POD (55%), while reducing MDA and H2O2 contents (77 and 52%) compared to the control. The combined application also reduced Ni uptake in roots, shoots, and curd by 51, 78 and 72% respectively along with an increased relative production index (78%) as compared to the control. Hence, synergistic application of IAA and compost can mitigate Ni induced adverse impacts on cauliflower growth by immobilizing it in the soil.

Endophytic bacilli from Cyamopsis tetragonoloba (L.) Taub. induces plant growth and drought tolerance

Cyamopsis tetragonoloba (L.) Taub. (guar) is a commercially important crop known for its galactomannan content in seeds. Drought stress is a significant global concern that compromises the productivity of major legumes including guar. The endophytic microbes associated with plants play a significant role in enhancing plant growth and modulating the impact of abiotic stress(s). The present study involved the isolation of 73 endophytic bacteria from the guar seeds of drought-tolerant (RGC-1002 and RGC-1066) and sensitive (Sarada and Varsha) varieties. Based on multiple PGP attributes and drought tolerance, at 50% PEG6000 w/v, 11 efficient isolates were selected and identified through 16S rRNA gene sequencing. Isolates belonging to ten different species of bacilli including Cytobacillus oceanisediminis, Mesobacillus fermenti, Peribacillus simplex from sensitive and Bacillus zanthoxyli, B. safensis, B. velezensis, B. altitudinis, B. licheniformis, B. tequilensis, and B. paralicheniformis isolated from tolerant varieties. A greenhouse experiment with a drought-sensitive guar variety demonstrated that inoculation of selected isolates showed comparatively better plant growth, higher relative water content (RWC), decreased carbon isotope discrimination ratio (Δ13C), increased chlorophyll, carotenoids, anthocyanin, and proline content, decreased malondialdehyde (MDA) and modulated defense enzymes as compared to their uninoculated controls. Tolerant variety isolates B. tequilensis NBRI14G and B. safensis NBRI10R showed the most promising results in improving plant growth and also drought stress tolerance in guar plants. This study represents for the first time that seed endophytic bacterial strains from guar can be utilized to develop the formulation for improving the productivity of guar under drought-stress conditions.

Production, characterization and in vitro biological activities of crude pigment from endophytic Micrococcus luteus associated with Avicennia marina

Due to their non-toxic and non-carcinogenic nature, biopigments have a phenomenal benefit over synthetic pigments, making them a desirable source for human utilization and a potential alternative to traditional synthetic pigments that are hazardous to the environment and public health. Endosymbiotic interactions between mangrove plants and bacteria could provide an alternate source for the synthesis of unique compounds with potent biomedical applications. Pigmented endophytic bacteria were screened from the explants of Avicennia marina, a mangrove plant, and identified as Micrococcus luteus by molecular characterization. The intracellular pigment was successfully extracted using the sonication-assisted solvent extraction method, and screening factors impacting the pigmentation bioprocess were determined using a one-factor-at-a-time approach. The endophyte produced yellow pigment in the liquid medium, with the maximum growth and pigment production recorded in nutrient broth at 37 ℃ and pH 7 after 96 h of incubation, while the maximum accumulation of pigment was observed in the media supplemented with glucose and tryptone as carbon and nitrogen sources, respectively. The extracted crude pigment was further characterized by ultraviolet, followed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. The obtained crude pigment has been evaluated for its antioxidant and anticancer activity by various assays, such as DPPH radical scavenging activity, FRAP assay, superoxide anion and nitric oxide radical scavenging, metal chelating activity, phosphomolybdenum assay, and MTT assay, respectively, at varying concentrations. The results of our study revealed that the yellow pigment produced by the endophyte showed significant dose-dependent antioxidant and anticancer activity.

Synergistic mitigation of nickel toxicity in pepper (Capsicum annuum) by nitric oxide and thiourea via regulation of nitrogen metabolism and subcellular nickel distribution

Nickel (Ni) contamination hinders plant growth and yield. Nitric oxide (NO) and thiourea (Thi) aid plant recovery from heavy metal damage, but their combined effects on pepper (Capsicum annuum ) plant tolerance to Ni stress need more study. Sodium nitroprusside (0.1mM, SNP) and 400mgL-1 Thi, alone and combined, were studied for their impact on pepper growth under Ni toxicity. Ni stress reduces chlorophyll, PSII efficiency and leaf water and sugar content. However, SNP and Thi alleviate these effects by increasing leaf water, proline and sugar content. It also increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase. Nickel stress lowered nitrogen assimilation enzymes (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase) and protein content, but increased nitrate, ammonium and amino acid content. SNP and Thi enhanced nitrogen assimilation, increased protein content and improved pepper plant growth and physiological functions during Ni stress. The combined treatment reduced Ni accumulation, increased Ni in leaf cell walls and potentially in root vacuoles, and decreased Ni concentration in cell organelles. It effectively mitigated Ni toxicity to vital organelles, surpassing the effects of SNP or Thi use alone. This study provides valuable insights for addressing heavy metal contamination in agricultural soils and offers potential strategies for sustainable and eco-friendly farming practices.

Molecular Basis of Crops and Fruit Plants in Response to Stress

This editorial summarizes the main scientific contributions from 11 papers comprising the Special Issue (SI) "Molecular Basis of Crops and Fruit Plants in Response to Stress". Here, we collected papers from different research groups encompassing molecular studies from monocots (ginger, rice, maize) and eudicots (common hazel, cowpea, pepper, soybean, tomato) species submitted to abiotic stresses as heat, cold, salt, drought, and heavy metals or biotic stresses induced by different viruses, such as BPEV, PepGMV, PMMoV, and TEV. These studies explored different aspects of molecular mechanisms involved in plant stress tolerance, establishing comparative analyses among genotypes/cultivars to identify potential molecular markers of stresses that are now available for future application in biotechnological studies. This SI presents a collection of advanced concepts and emerging strategies for readers and researchers aiming to accelerate plant breeding.

Insight into the genome of an arsenic loving and plant growth-promoting strain of Micrococcus luteus isolated from arsenic contaminated groundwater

Contamination of arsenic in drinking water and foods is a threat for human beings. To achieve the goal for the reduction of arsenic availability, besides conventional technologies, arsenic bioremediation by using some potent bacteria is one of the hot topics for researchers. In this context, bacterium, AKS4c was isolated from arsenic contaminated water of Purbasthali, West Bengal, India, and through draft genome sequence; it was identified as a strain of Micrococcus luteus that comprised of 2.4 Mb genome with 73.1% GC content and 2256 protein coding genes. As the accessory genome, about 22 genomic islands (GIs) associated with many metal-resistant genes were identified. This strain was capable to tolerate more than 46,800 mg/L arsenate and 390 mg/L arsenite salts as well as found to be tolerable to multi-metals such as Fe, Pb, Mo, Mn, and Zn up to a certain limit of concentrations. Strain AKS4c was able to oxidize arsenite to less toxic arsenate, and its arsenic adsorption property was qualitatively confirmed through X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR) analysis. Quantitative estimation of plant growth-promoting attributes like Indole acetic acid (IAA), Gibberellic acid (GA), and proline production and enhancement of rice seedling growth in laboratory condition leads to its future applicability in arsenic bioremediation as a plant growth-promoting rhizobacteria (PGPR).

Effect of mixing oak leaf biomass with soil on cadmium toxicity and translocation in tomato genotypes

The environmental non-element cadmium (Cd) is toxic to all forms of life, and it also has a negative impact on plant development and growth. In order to ascertain the effects of cadmium on tomato growth and the function of oak leaf biomass in the reduction of toxicity and translocation of cadmium in different parts of tomato genotypes, two tolerant and two sensitive tomato genotypes were exposed to cadmium stress through the availability or unavailability of oak leaf biomass. The experiment involved two factors. The first factor was the various treatment levels, including soil without Cd treatment and sodium hydroxide (NaOH) oak leaf biomass pretreatment (COC-control), soil with Cd treatment and without NaOH oak leaf biomass pretreatment (CdC), and soil with Cd treatment and NaOH oak leaf biomass pretreatment (CdOBC). The second element consists of four tomato genotypes. Comparing to control conditions, all tomato genotypes spotted significant reductions in all morphological traits under Cd stress in the presence or absence of NaOH oak leaf pretreatment. Related to CdC conditions, root length, shoot length, root fresh weight per plant, shoot fresh weight per plant, root dry weight per plant, shoot dry weight per plant, and total fruit weight per plant were significantly improved by 4.25%, 9.75%, 23.24%, 10.10%, 28.10%, 9.08%, and 4.61%, respectively, under the availability of pretreatment of oak leaf biomass. The tolerant genotypes (Karazi and Sirin) exhibited the greatest increase in all traits evaluated, with the exception of root length, under the CdOBC condition compared to the CdC statement. Significant increases in leaf biochemical parameters were seen with the availability or absence of NaOH pretreatment of oak leaf biomass in the soil. The maximum values of proline content, soluble sugar content, antioxidant activity, and guaiacol peroxidase were stated in the presence of oak biomass under Cd conditions (CdOBC), with mean values of 1772.46 μg g -1, 687.18 μg g -1, 1025.74 μg g -1-, and 0.43 units min -1 g -1, respectively. The in vitro-tolerant genotypes exhibited the maximum values of all biochemical parameters. The concentration of cadmium in the studied tomato genotypes revealed that cadmium accumulated more in the roots than other parts. According to these outcomes, NaOH pretreatment of oak leaf biomass can be employed to diminish the hazard of cadmium absorption by edible parts.

Selenium hyperaccumulator plant Cardamine enshiensis: from discovery to application

Selenium (Se) is an essential trace element for animals and humans. Se biofortification and Se functional agriculture are emerging strategies to satisfy the needs of people who are deficient in Se. With 200 km2 of Se-excess area, Enshi is known as the "world capital of Se." Cardamine enshiensis (C. enshiensis) is a Se hyperaccumulation plant discovered in the Se mine drainage area of Enshi. It is edible and has been approved by National Health Commission of the People's Republic of China as a new source of food, and the annual output value of the Se-rich industry in Enshi City exceeds 60 billion RMB. This review will mainly focus on the discovery and mechanism underlying Se tolerance and Se hyperaccumulation in C. enshiensis and highlight its potential utilization in Se biofortification agriculture, graziery, and human health.

Synergistic Effects of Kaolin and Silicon Nanoparticles for Ameliorating Deficit Irrigation Stress in Maize Plants by Upregulating Antioxidant Defense Systems

Water deficit is a significant environmental stress that has a negative impact on plant growth and yield. In this research, the positive significance of kaolin and SiO₂ nanoparticles in moderating the detrimental effects of water deficit on maize plant growth and yield is investigated. The foliar application of kaolin (3 and 6%) and SiO₂ NPs (1.5 and 3 mM) solutions increased the growth and yield variables of maize plants grown under normal conditions (100% available water) and drought stress conditions (80 and 60% available water (AW)). In addition, plants treated with SiO₂ NPs (3 mM) demonstrated increased levels of important osmolytes, such as proline and phenol, and maintained more of their photosynthetic pigments (net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO₂ concentration (Ci), and transpiration rate (E)) than with other applied treatments under either stress or non-stress conditions. Furthermore, the exogenous foliar application of kaolin and SiO₂ NPs also reduced the amounts of hydroxyl radicals (OH), superoxide anions (O₂), hydrogen peroxide (H₂O₂), and lipid peroxidation in maize plants experiencing a water deficit. In contrast, the treatments led to an increase in the activity of antioxidant enzymes such as peroxidase (POX), ascorbate peroxidase (APX), glutathione peroxidase (GR), catalase (CAT), and superoxide dismutase (SOD). Overall, our findings indicate the beneficial impact of the application of kaolin and silicon NPs, particularly the impact of SiO₂ NPs (3 mM) on managing the negative, harmful impacts of soil water deficit stress in maize plants.

Interactive Effect of Arbuscular Mycorrhizal Fungi (AMF) and Olive Solid Waste on Wheat under Arsenite Toxicity

Heavy metal such as arsenite (As^III) is a threat worldwide. Thus, to mitigate As^III toxicity on plants, we investigated the interactive effect of olive solid waste (OSW) and arbuscular mycorrhizal fungi (AMF) on wheat plants under As^III stress. To this end, wheat seeds were grown in soils treated with OSW (4% w/w), AMF-inoculation, and/or As^III treated soil (100 mg/kg soil). AMF colonization is reduced by As^III but to a lesser extent under As^III + OSW. AMF and OSW interactive effects also improved soil fertility and increased wheat plants' growth, particularly under As^III stress. The interactions between OSW and AMF treatments reduced As^III-induced H₂O₂ accumulation. Less H₂O₂ production consequently reduced As^III-related oxidative damages i.e., lipid peroxidation (malondialdehyde, MDA) (58%), compared to As stress. This can be explained by the increase in wheat's antioxidant defense system. OSW and AMF increased total antioxidant content, phenol, flavonoids, and α-tocopherol by approximately 34%, 63%, 118%, 232%, and 93%, respectively, compared to As stress. The combined effect also significantly induced anthocyanins accumulation. The combination of OSW+AMF improved antioxidants enzymes activity, where superoxide dismutase (SOD, catalase (CAT), peroxidase (POX), glutathione reductase (GR), and glutathione peroxidase (GPX) were increased by 98%, 121%, 105%, 129%, and 110.29%, respectively, compared to As^III stress. This can be explained by induced anthocyanin percussors phenylalanine, cinamic acid and naringenin, and biosynthesic enzymes (phenylalanine aminolayse (PAL) and chalcone synthase (CHS)). Overall, this study suggested the effectiveness of OSW and AMF as a promising approach to mitigate As^III toxicity on wheat growth, physiology, and biochemistry.

Threonine Facilitates Cd Excretion by Increasing the Abundance of Gut Escherichia coli in Cd-Exposed Mice

Cadmium (Cd) can easily enter the body through the food chain and threaten health since Cd pollution is prevalent in the environment. Gut microbiota is necessary for the reduction of metal ions. To reduce Cd-induced harmful impacts and Cd accumulation in the body, we investigated the effect of amino acids on gut microbiota and Cd excretion in (fecal Cd) Cd-exposed mice. The screening of 20 amino acids showed that threonine (Thr) effectively increased fecal Cd, and reduced Cd-induced intestinal structural damage. The abundance of Escherichia-Shigella genus and KF843036_g significantly increased after the oral administration of Thr. As the type species of the Escherichia-Shigella genus, Escherichia coli exhibited high similarity to KF843036_g species and significantly decreased Cd-induced gut damage. Cd contents in the liver, kidney, and gut of Cd-exposed mice were also significantly (p < 0.05) decreased after E. coli treatment, while the contents in the feces were increased. The results demonstrated the potential roles that gut E. coli might play in Thr-mediated Cd excretion in Cd-exposed mice. The findings may provide important data for better understanding the molecular biological mechanism of Thr in reducing Cd accumulation in the body.