Comparative orchestrating response of four oilseed rape (Brassica napus) cultivars against the selenium stress as revealed by physio-chemical, ultrastructural and molecular profiling

Bio-formulated chitosan nanoparticles enhance disease resistance against rice blast by physiomorphic, transcriptional, and microbiome modulation of rice (Oryza sativa L.)

Rice blast disease (RBD) caused by Magnaporthe oryzae, threaten food security by cutting agricultural output. Nano agrochemicals are now perceived as sustainable, cost-effective alternatives to traditional pesticides. This study investigated bioformulation of moringa chitosan nanoparticles (M-CsNPs) and their mechanisms for suppressing RBD while minimizing toxic effects on the microenvironment. M-CsNPs, sized 46 nm with semi-spherical morphology, significantly suppressed pathogen growth, integrity, and colonization at 200 mg L-1in vitro. Greenhouse tests with foliar exposure to the same concentration resulted in a substantial 77.7 % reduction in RBD, enhancing antioxidant enzyme activity and plant health. Furthermore, M-CsNPs improved photosynthesis, gas exchange, and the nutritional profile of diseased rice plants. RNA-seq analysis highlighted upregulated defense-related genes in treated rice plants. Metagenomic study showcased reshaping of the rice microbiome, reducing Magnaporthe abundance by 93.5 %. Both healthy and diseased rice plants showed increased microbial diversity, particularly favoring specific beneficial species Thiobacillus, Nitrospira, Nocardioides, and Sphingomicrobium in the rhizosphere and Azonexus, Agarivorans, and Bradyrhizobium in the phyllosphere. This comprehensive study unravels the diverse mechanisms by which M-CsNPs interact with plants and pathogens, curbing M. oryzae damage, promoting plant growth, and modulating the rice microbiome. It underscores the significant potential for effective plant disease management.

Melatonin alleviated cadmium accumulation and toxicity by modulating phytohormonal balance and antioxidant metabolism in rice

Cadmium (Cd) contamination is an eminent dilemma that jeopardizes global food safety and security, especially through its phytotoxicity in rice; one of the most edible crops. Melatonin (MET) has emerged as a protective phytohormone in stress conditions, but the defensive role and underlying mechanisms of MET against Cd toxicity in rice still remain unclear. To fulfill this knowledge gap, the present study is to uncover the key mechanisms for MET-mediated Cd-stress tolerance in rice. Cd toxicity significantly reduced growth by hindering the process of photosynthesis, cellular redox homeostasis, phytohormonal imbalance, and ultrastructural damages. Contrarily, MET supplementation considerably improved growth attributes, photosynthetic efficiency, and cellular ultrastructure as measured by gas exchange elements, chlorophyll content, reduced Cd accumulation, and ultrastructural analysis via transmission electron microscopy (TEM). MET treatment significantly reduced Cd accumulation (39.25%/31.58%), MDA (25.87%/19.45%), H2O2 (17.93%/9.56%), and O2 (29.11%/27.14%) levels in shoot/root tissues, respectively, when compared with Cd treatment. More importantly, MET manifested association with stress responsive phytohormones (ABA and IAA) and boosted the defense mechanisms of plant by enhancing the activities of ROS-scavenging antioxidant enzymes (SOD; superoxide dismutase, POD; peroxidase, CAT; catalase, APX; ascorbate peroxidase) and as well as regulating the key stress-responsive genes (OsSOD1, OsPOD1, OsCAT2, OsAPX1), thereby reinstate cellular membrane integrity and confer tolerance to ultrastructural damages under Cd-induced phytotoxicity. Overall, our findings emphasized the potential of MET as a long-term and cost-effective approach to Cd remediation in paddy soils, which can pave the way for a healthier and more environmentally conscious agricultural sector.

Efficacy of zinc-based nanoparticles in alleviating the abiotic stress in plants: current knowledge and future perspectives

Due to sessile, plants are unable to avoid unfavorable environmental conditions which leads to inducing serious negative effects on plant growth, crop yield, and food safety. Instead, various approaches were employed to mitigate the phytotoxicity of these emerging contaminants from the soil-plant system. However, recent studies based on the exogenous application of ZnO NPs approve of their important positive potential for alleviating abiotic stress-induced phytotoxicity leads to ensuring global food security. In this review, we have comprehensively discussed the promising role of ZnO NPs as alone or in synergistic interactions with other plant growth regulators (PGRs) in the mitigation of various abiotic stresses, i.e., heavy metals (HMs), drought, salinity, cold and high temperatures from different crops. ZnO NPs have stress-alleviating effects by regulating various functionalities by improving plant growth and development. ZnO NPs are reported to improve plant growth by stimulating diverse alterations at morphological, physiological, biochemical, and ultrastructural levels under abiotic stress factors. We have explained the recent advances and pointed out research gaps in studies conducted in earlier years with future recommendations. Thus, in this review, we have also addressed the opportunities and challenges together with aims to uplift future studies toward effective applications of ZnO NPs in stress management.

Seed priming with nano-silica effectively ameliorates chromium toxicity in Brassica napus

Plant yield is severely hampered by chromium (Cr) toxicity, affirming the urgent need to develop strategies to suppress its phyto-accumulation. Silicon dioxide nanoparticles (SiO2 NPs) have emerged as a provider of sustainable crop production and resistance to abiotic stress. But, the mechanisms by which seed-primed SiO2 NPs palliate Cr-accumulation and its toxic impacts in Brassica napus L. tissues remains poorly understood. To address this gap, present study examined the protective efficacy of seed priming with SiO2 NPs (400 mg/L) in relieving the Cr (200 µM) phytotoxicity mainly in B. napus seedlings. Results delineated that SiO2 NPs significantly declined the accumulation of Cr (38.7/35.9%), MDA (25.9/29.1%), H2O2 (27.04/36.9%) and O2• (30.02/34.7%) contents in leaves/roots, enhanced the nutrients acquisition, leading to improved photosynthetic performance and better plant growth. SiO2 NPs boosted the plant immunity by upregulating the transcripts of antioxidant (SOD, CAT, APX, GR) or defense-related genes (PAL, CAD, PPO, PAO and MT-1), GSH (assists Cr-vacuolar sequestration), and modifying the subcellular distribution (enhances Cr-proportion in cell wall), thereby confer tolerance to ultrastructural damages under Cr stress. Our first evidence to establish the Cr-detoxification by seed-primed SiO2 NPs in B. napus, indicated the potential of SiO2 NPs as stress-reducing agent for crops grown in Cr-contaminated areas.

Seed priming with nitric oxide and/or spermine mitigate the chromium toxicity in rice (Oryza sativa) seedlings by improving the carbon-assimilation and minimising the oxidative damages

Chromium (Cr) is a serious environmental contaminant that drastically limited the crop yields. Nitric oxide (NO) and spermine (Spm) portrayal significance in improving the plant tolerance against abiotic stresses. Therefore, we investigate the protective efficacy of seed priming with NO (100μM) and/or Spm (0.01mM) in minimising the Cr-induced toxic effects in rice (Oryza sativa L.) plants. Our outcomes revealed that Cr alone treatments (100μM) notably reduced the seed germination rate, plant growth, photosynthetic apparatus, nutrients uptake and antioxidant defence system, but extra generation of reactive oxygen species (ROS). Interestingly, the combine applications of NO and Spm significantly reversed the Cr-induced toxic effects by reducing the Cr-accumulation, maintaining the nutrient balance, improving the germination indices, levels of photosynthetic pigments (chl a by 24.6%, chl b by 36.3%, chl (a+b ) by 57.2% and carotenoids by 79.4%), PSII, photosynthesis gas exchange parameters and total soluble sugar (74.9%) by improving antioxidative enzyme activities. As a result, NO+Spm lowered the accumulation of oxidative markers (H2 O2 by 93.9/70.4%, O2 ˙- by 86.3/69.9% and MDA by 97.2/73.7% in leaves/roots), electrolyte leakage (71.4% in leaves) and improved the plant growth traits. Based on these findings, it can be concluded that NO triggers Spm to minimise the Cr-accumulation and its adverse effects on rice plants. Additionally, combined treatments (NO+Spm) were more effective in minimising the Cr-induced toxic effects in comparison to NO and Spm alone treatments. Thus, co-exposure of NO and Spm may be utilised to boost rice tolerance under Cr stress conditions.

Melatonin-mediated resistance to copper oxide nanoparticles-induced toxicity by regulating the photosynthetic apparatus, cellular damages and antioxidant defense system in maize seedlings

The pollution of nanoparticles (NPs) has linked with severe negative effects on crop productivity. Thus, effective strategies are needed to mitigate the phytotoxicity of NPs. The aim of present study was to evaluate the efficacy of exogenously applied melatonin (MT) in mitigating the toxic effects of copper oxide nanoparticles (CuO NPs) from maize seedlings. Therefore, we comprehensively investigated the inhibitory effects of MT against CuO NPs-induced toxicity on morpho-physiological, biochemical and ultrastructural levels in maize. Our results show that CuO NPs (300 mg L^-1) exposure displayed significantly reduction in all plant growth traits and induced toxicity in maize. Furthermore, 50 μM MT provided maximum plant tolerance against CuO NPs-induced phytotoxicity. It was noticed that MT improved plant growth, biomass, photochemical efficiency (Fv/Fm), chlorophyll contents (Chl a and Chl b), SPAD values and gas exchange attributes (stomatal conductance, net photosynthetic rate, intercellular CO₂ concentration and transpiration rate) under CuO NPs stress. In addition, MT enhanced the antioxidant defense system and conferred protection to ultrastructural (mainly chloroplast, thylakoids membrane and plastoglobuli) damages and stomatal closure in maize plants subjected to CuO NPs stress. Together, it can be stated that the exogenous supply of MT improves the resilience of maize plants against the CuO NPs-induced phytotoxicity. Our current findings can be useful for the enhancement of plant growth and yield attributes in CuO NPs-contaminated soils. The reported information can provide insight into the MT pathways that can be used to improve crop stress tolerance in a challenging environment.

Nano-selenium enhances the antioxidant capacity, organic acids and cucurbitacin B in melon (Cucumis melo L.) plants

Pesticides are widely used in melon production causing safety issues around the consumption of melon and increasing pathogen and insect tolerance to pesticides. This study investigated whether a nano-selenium (Nano-Se) spray treatment can improve resistance to biological stress in melon plants, reducing the need for pesticides, and how this mechanism is activated. To achieve this, we examine the ultrastructure and physio-biochemical responses of two melon cultivars after foliar spraying with Nano-Se. Nano-Se treatment reduced plastoglobulins in leaf mesophyll cells, thylakoid films were left intact, and compound starch granules increased. Nano-Se treatment also increased root mitochondria and left nucleoli intact. Nano-Se treatment enhanced ascorbate peroxidase, peroxidase, phenylalanine ammonia lyase, β-1,3-glucanase, chitinase activities and their mRNA levels in treated melon plants compared to control plants (without Nano-Se treatments). Exogenous application of Nano-Se improved fructose, glucose, galactitol, stachyose, lactic acid, tartaric acid, fumaric acid, malic acid and succinic acid in treated plants compared to control plants. In addition, Nano-Se treatment enhanced cucurbitacin B and up-regulated eight cucurbitacin B synthesis-related genes. We conclude that Nano-Se treatment of melon plants triggered antioxidant capacity, photosynthesis, organic acids, and up-regulated cucurbitacin B synthesis-related genes, which plays a comprehensive role in stress resistance in melon plants.

Ethylene participates in zinc oxide nanoparticles induced biochemical, molecular and ultrastructural changes in rice seedlings

Nowadays, the applications of engineered nanoparticles (ENPs) have been significantly increased, thereby negatively affecting crop production and ultimately contaminating the food chain worldwide. Zinc oxide nanoparticles (ZnO NPs) induced oxidative stress has been clarified in previous studies. But until now, it has not been investigated that how ethylene mediates or participates in ZnO NPs-induced toxicity and related cellular ultrastructural changes in rice seedlings. Here, we reported that 500 mg/L of ZnO NPs reduced the fresh weight (54.75% and 55.64%) and dry weight (40.33% and 47.83%) in shoot and root respectively as compared to control. Furthermore, ZnO NPs (500 mg/L) reduced chlorophyll content (72% Chla, 70% Chlb), induced the stomatal closure and ultrastructural damages by causing oxidative stress in rice seedlings. These cellular damages were significantly increased by exogenous applications of ethylene biosynthesis precursor (ACC) in the presence of ZnO NPs. In contrary, ZnO NPs induced damages on the above-mentioned attributes were reversed through the exogenous supply of ethylene signaling and biosynthesis antagonists such as silver (Ag) and cobalt (Co) respectively. Interestingly, ZnO NPs accelerate ethylene biosynthesis by up-regulating the transcriptome of ethylene biosynthesis responsive genes. The antioxidant enzymes activities and related gene expressions were further increased in ethylene signaling and biosynthesis associated antagonists (Ag and Co) treated seedlings as compared to sole ZnO NPs treatments. In contrary, the above-reported attributes were further decreased by ACC together with ZnO NPs. In a nutshell, ethylene effectively contributes in ZnO NPs induced toxicity and causing ultrastructural and stomatal damage in rice seedlings. Such findings could have potential implications in producing genetic engineered crops, which will be able to tolerate nanoparticles toxicity in the environment.

Brassica Species in Phytoextractions: Real Potentials and Challenges

The genus Brassica is recognized for including species with phytoaccumulation potential and a large amount of research has been carried out in this area under a variety of conditions, from laboratory experiments to field trials, with spiked or naturally contaminated soils, using one- or multi-element contaminated soil, generating various and sometimes contradictory results with limited practical applications. To date, the actual field potential of Brassica species and the feasibility of a complete phytoextraction process have not been fully evaluated. Therefore, the aim of this study was to summarize the results of the experiments that have been performed with a view to analyzing real potentials and limitations. The reduced biomass and low metal mobility in the soil have been addressed by the development of chemically or biologically assisted phytoremediation technologies, the use of soil amendments, and the application of crop management strategies. Certain issues, such as the fate of harvested biomass or the performance of species in multi-metal-contaminated soils, remain to be solved by future research. Potential improvements to current experimental settings include testing species grown to full maturity, using a greater amount of soil in experiments, conducting more trials under real field conditions, developing improved crop management systems, and optimizing solutions for harvested biomass disposal.

Salicylic acid underpins silicon in ameliorating chromium toxicity in rice by modulating antioxidant defense, ion homeostasis and cellular ultrastructure

Chromium (Cr) phytotoxicity affirmed the need of mitigation strategies to remediate polluted soils and restricts its accumulation in the food chains. Salicylic acid (SA) and silicon (Si) play pivotal roles in stimulating the plant performance and stress resilience. So far, their interactive effects against Cr-phytotoxicities are less known. Thus, we evaluated the beneficial roles of alone or/and combine applications of SA and Si in mitigating the toxic effects of Cr in the leaves and roots of rice (Oryza sativa) seedlings. Results indicated that SA (10 μM) and/or Si (5 μM) markedly retrieved the Cr (100 μM) induced toxicities by minimizing the Cr-accretion in both leaves and roots, enhancing the performance of light harvesting pigments (total chlorophylls and carotenoids), water retention and accumulation of osmolytes (water-soluble protein and total soluble sugars) and ultimately improved the growth and biomass. Additionally, SA and/or Si maintained the ionic balance by enhancing the nutrients transport, upregulated the ascorbate-glutathione (AsA-GSH) cycle enzymes, minimized the extra accumulation of reactive oxygen species (ROS) (H₂O₂ and O₂^•‒), malondialdehyde (MDA), recovered the membrane stability and damages in cellular ultrastructure in Cr-stressed rice plants. Overall findings suggested that SA underpins Si in mitigating the Cr-induced phytotoxicities on the above-reported parameters and combined applications of SA and Si were more effective than alone treatments. The uptake or cellular accumulation of Cr, osmoprotectants level and antioxidant defense system against oxidative stress can be considered as key toxicity biomarkers for the safe cultivation of rice in Cr-contaminated soils.

Selenium as a potential fungicide could protect oilseed rape leaves from Sclerotinia sclerotiorum infection

Sclerotinia sclerotiorum (S. sclerotiorum) is a soil-borne pathogen causing serious damage to the yield of oilseed rape. Selenium (Se) acted as a beneficial element for plants, and also proved to inhibit the growth of plant pathogens. However, whether Se could reduce S. sclerotiorum infection in oilseed rape, the related mechanism is still unclear. In this study, proper Se levels (0.1 mg/kg and 0.5 mg/kg) applied in soil decreased the lesion diameter and incidence of S. sclerotiorum in rape leaves. Se enfeebled the decrease of net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), and maintained leaf cell structure. Se enhanced the antioxidant system of leaves, as evidenced by the maintenance of mitochondrial function, reduction of reactive oxygen species (ROS) accumulation and malondialdehyde (MDA) content, and the improvement of antioxidant enzyme activities including catalase (CAT), polyphenol oxidase (PPO) and peroxidase (POD). The upregulated defense gene expressions (CHI, ESD1, NPR1 and PDF1.2) of leaves were also observed under Se treatments. Furthermore, metabolome analysis revealed that Se promoted the metabolism of energy and amino acids in leaves infected with S. sclerotiorum. These findings inferred that Se could act as a potential eco-fungicide to protect oilseed rape leaves from S. sclerotiorum attack. The result arising from this study not only introduces an ecological method to control S. sclerotiorum, but also provides a deep insight into microelement for plant protection.

Selenium mitigates the chromium toxicity in Brassicca napus L. by ameliorating nutrients uptake, amino acids metabolism and antioxidant defense system

The phytotoxicity of chromium (Cr) makes it obligatory for the researchers to develop strategies that seek to hinder its accumulation in food chains. While, protective role of selenium (Se) has not been discussed in detail under adverse conditions in oilseed rape. Here, our aim was to investigate the potential use of Se (0, 5 and 10 μM) in alleviating the Cr toxicity (0, 100 and 200 μM) in Brassica napus L. Results delineated that Se-supplementation notably recovered the Cr-phytotoxicity by reducing the Cr accumulation in plant tissues and boosted the inhibition in plant growth and biomass. Under Cr stress, the exogenously applied Se significantly recovered the impairment in photosynthesis related parameters (chlorophyll a, chlorophyll b, carotenoids, net photosynthetic rate, stomatal conductance, and photochemical efficiency of photosystem II), and counteracted the reduction in nutrients uptake and improved the essential amino acids (EAAs) levels. In addition, Se activated the antioxidants enzymes included in AsA-GSH cycle (SOD, CAT, APX, GR, DHAR, MDHAR, GSH, and AsA) and glyoxalase (Gly) system (Gly I and Gly II) and minimized the excessive generation of reactive oxygen species (ROS) and methylglyoxal (MG) contents in response to Cr stress. In a nutshell, Se (more effective at 5 μM) alleviated the Cr and MG induced phytotoxicity and oxidative damages by minimizing their (Cr and MG) accumulation and enhanced the plant growth, nutrients element level, nutrition quality by improving EAAs, antioxidant and Gly system. By considering the above-mentioned biomarkers, the addition of exogenous Se in Cr polluted soils might be effective approach to decrease the Cr uptake and its linked phytotoxicity in B. napus.

Protective mechanisms of melatonin against selenium toxicity in Brassica napus: insights into physiological traits, thiol biosynthesis and antioxidant machinery

BACKGROUND

The ubiquitous signaling molecule melatonin (N-acetyl-5-methoxytryptamine) (MT) plays vital roles in plant development and stress tolerance. Selenium (Se) may be phytotoxic at high concentrations. Interactions between MT and Se (IV) stress in higher plants are poorly understood. The aim of this study was to evaluate the defensive roles of exogenous MT (0 μM, 50 μM, and 100 μM) against Se (IV) (0 μM, 50 μM, 100 μM, and 200 μM) stress based on the physiological and biochemical properties, thiol biosynthesis, and antioxidant system of Brassica napus plants subjected to these treatments.

RESULTS

Se (IV) stress inhibited B. napus growth and biomass accumulation, reduced pigment content, and lowered net photosynthetic rate (P_n) and PSII photochemical efficiency (Fv/Fm) in a dose-dependent manner. All of the aforementioned responses were effectively alleviated by exogenous MT treatment. Exogenous MT mitigated oxidative damage and lipid peroxidation and protected the plasma membranes from Se toxicity by reducing Se-induced reactive oxygen species (ROS) accumulation. MT also alleviated osmotic stress by restoring foliar water and sugar levels. Relative to standalone Se treatment, the combination of MT and Se upregulated the ROS-detoxifying enzymes SOD, APX, GR, and CAT, increased proline, free amino acids, and the thiol components GSH, GSSG, GSH/GSSG, NPTs, PCs, and cys and upregulated the metabolic enzymes γ-ECS, GST, and PCS. Therefore, MT application attenuates Se-induce oxidative damage in plants. MT promotes the accumulation of chelating agents in the roots, detoxifies Se there, and impedes its further translocation to the leaves.

CONCLUSIONS

Exogenous MT improves the physiological traits, antioxidant system, and thiol ligand biosynthesis in B. napus subjected to Se stress primarily by enhancing Se detoxification and sequestration especially at the root level. Our results reveal better understanding of Se-phytotoxicity and Se-stress alleviation by the adequate supply of MT. The mechanisms of MT-induced plant tolerance to Se stress have potential implications in developing novel strategies for safe crop production in Se-rich soils.