Seed pretreatment with brassinosteroids stimulates sunflower immunity against parasitic weed (Orobanche cumana) infection.

Broomrape (Orobanche cumana) negatively affects sunflower, causing severe yield losses, and thus, there is a need to control O. cumana infestation. Brassinosteroids (BRs) play key roles in plant growth and provide resilience to weed infection. This study aims to evaluate the mechanisms by which BRs ameliorate O. cumana infection in sunflower (Helianthus annuus). Seeds were pretreated with BRs (1, 10, and 100 nM) and O. cumana inoculation for 4 weeks under soil conditions. O. cumana infection significantly reduced plant growth traits, photosynthesis, endogenous BRs and regulated the plant defence (POX, GST), BRs signalling (BAK1, BSK1 to BSK4) and synthesis (BRI1, BR6OX2) genes. O. cumana also elevated the levels of malondialdehyde (MDA), hydroxyl radical (OH-), hydrogen peroxide (H2O2) and superoxide (O2 •-) in leaves/roots by 77/112, 63/103, 56/97 and 54/89%, as well as caused ultrastructural cellular damages in both leaves and roots. In response, plants activated a few enzymes, superoxide dismutase (SOD), peroxidase (POD) and reduced glutathione but were unable to stimulate the activity of ascorbate peroxidase (APX) and catalase (CAT) enzymes. The addition of BRs (especially at 10 nM) notably recovered the ultrastructural cellular damages, lowered the production of oxidative stress, activated the key enzymatic antioxidants and induced the phenolic and lignin contents. The downregulation in the particular genes by BRs is attributed to the increased resilience of sunflower via a susceptible reaction. In a nutshell, BRs notably enhanced the sunflower resistance to O. cumana infection by escalating the plant immunity responses, inducing systemic acquired resistance, reducing oxidative or cellular damages, and modulating the expression of BR synthesis or signalling genes.

Differential responses of Brassica napus cultivars to dual effects of magnesium oxide nanoparticles.

Magnesium oxide nanoparticles (MgO NPs) have great potential to enhance the crop productivity and sustainability of agriculture. Still, a thorough understanding is lacking about its essentiality or toxicity and precise dose for the safe cultivation of oilseed crops. Thus, we assessed the dual effects of MgO NPs (control, 5, 10, 20, 40, 80, and 200 mg/L) on the seed germination, growth performance, photosynthesis, total soluble protein, total carbohydrates, oxidative stress markers (hydrogen peroxide as H2O2 and superoxide anion as O2•‒), lipid peroxidation as MDA, and antioxidant defence machinery (SOD, CAT, APX, and GR activities, and GSH levels) of seven different oilseeds (Brassica napus L.) cultivars (ZY 758, ZD 649, ZD 635, ZD 619, GY 605, ZD 622, and ZD 630). Our findings revealed that low doses of MgO NPs (mainly at 10 mg/L) markedly boosted the seed germination, plant growth (shoot and root lengths) (15‒22%), and biomass (fresh and dry) (11‒19%) by improving the levels of photosynthetic pigments (14‒27%), net photosynthetic rate, stomatal conductance, photosynthetic efficiency (Fv/Fm), total soluble protein and total carbohydrates (16‒36%), antioxidant defence, and reducing the oxidative stress in B. napus tissues. Among all B. napus cultivars, these beneficial effects of MgO NPs were pronounced in ZD 635. ile, elevated levels of MgO NPs (particularly at 200 mg/L) induced oxidative stress, impaired antioxidant scavenging potential, photosynthetic inhibition, protein oxidation, and carbohydrate degradation and lead to inhibit the plant growth attributes. These inhibitory effects were more pronounced in ZD 622. Collectively, low-dose MgO NPs reinforced the Mg contents, protected the plant growth, photosynthesis, total soluble carbohydrates, enzyme activities, and minimized the oxidative stress. While, the excessive MgO NP levels impaired the above-reported traits. Overall, ZD 622 was highly susceptible to MgO NP toxicity and ZD 635 was found most tolerant to MgO NP toxicity.

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.

Exogenously applied melatonin enhanced the tolerance of Brassica napus against cobalt toxicity by modulating antioxidant defense, osmotic adjustment, and expression of stress response genes.

The excessive accumulation of cobalt (Co) in plant tissues severely impairs plant growth that ultimately reduces the yield. However, melatonin (MT) has been known to mediate the abiotic stress tolerance in plants. The present study aimed at investigating the protective mechanisms of exogenously applied MT (0, 50 and 100 µM) under Co (0, 100, 200 and 300 µM) stress by focusing on morpho-physiological, biochemical and cellular characterizations of Brassica napus plants. Cobalt (300 µM) alone treatment drastically inhibited the stomatal conductance, plant height (45%), leaf area (30%), free amino acid (139%), relative electrolyte leakage (109%), and total soluble sugars (71%), compared with the control. However, the exogenous supply of MT notably minimized the oxidative damage, lipid peroxidation and maintained the membrane integrity under Co-toxicity by restricting the overproduction of ROS (H2O2 and O2•), and MDA in leaves and roots. Melatonin significantly enhanced the activities of ROS-scavenging antioxidant enzymes, secondary metabolism-related phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), stress-responsive genes (heat shock protein as HSP-90, methyl transferase as MT) and regulated the Co-transporters, especially in roots. These findings indicated that an exogenous supply of MT improve the plant morphology, photosynthetic apparatus, osmotic adjustments, and antioxidant defense systems by enhancing the Co-detoxification in B. napus plants.

Role of phytomelatonin responsive to metal stresses: An omics perspective and future scenario.

A pervasive melatonin (N-acetyl-5-methoxytryptamine) reveals a crucial role in stress tolerance and plant development. Melatonin (MT) is a unique molecule with multiple phenotypic expressions and numerous actions within the plants. It has been extensively studied in crop plants under different abiotic stresses such as drought, salinity, heat, cold, and heavy metals. Mainly, MT role is appraised as an antioxidant molecule that deals with oxidative stress by scavenging reactive oxygen species (ROS) and modulating stress related genes. It improves the contents of different antioxidant enzyme activities and thus, regulates the redox hemostasis in crop plants. In this comprehensive review, regulatory effects of melatonin in plants as melatonin biosynthesis, signaling pathway, modulation of stress related genes and physiological role of melatonin under different heavy metal stress have been reviewed in detail. Further, this review has discussed how MT regulates different genes/enzymes to mediate defense responses and overviewed the context of transcriptomics and phenomics followed by the metabolomics pathways in crop plants.

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 (Pn) 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.

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.

Dual behavior of selenium: Insights into physio-biochemical, anatomical and molecular analyses of four Brassica napus cultivars.

Selenium (Se) is a prerequisite metalloid for humans and animals. But, its essentialness or phytotoxicity is still obscure. Here, we investigated the dual effects of sodium selenite (0, 25, 50 or 100 µM) on the physio-biochemical, anatomical and molecular alterations in different Brassicca napus L. cultivars (viz. Zheda 619, Zheda 622, ZY 50, and ZS 758). Findings revealed that Se-supplementation markedly boosted the plant growth and biomasses by improving mineral uptake, water-soluble protein, sugar, photosynthetic efficiency regarding the pigments and gas exchange parameters. Higher Se-levels impaired the photosynthetic efficiency, deplete nutrients-uptake, osmotic stress by proline accumulation and higher Se-accumulation in roots led to growth and biomass reduction. Se-supplementation minimized the accumulation of ROS (hydrogen peroxide, superoxide radical), malondialdehyde and methylglyoxal (MG) levels by activating the enzymes engaged in AsA-GSH cycle and ROS-MG detoxification. But, elevated-Se impaired the oxidative metabolism by desynchronizing the antioxidants as revealed by decreasing levels of ascorbic acid, activities and expression levels of catalase, glutathione reductase, and dehydro-ascorbate reductase. Up-regulation of secondary metabolites genes (PAL, PPO) revealed the role of Se in regulating transcriptional networks involved in oxidative stress. The damages in leaf and root ultra-structures disclosed the Se-phytotoxicity. Together, outcomes uncovered the protective mechanism of Se (till 25 µM) by reinforcing the plant morphology, photosynthesis, osmo-protection, redox balance, enzyme activities for ROS-MG detoxification by reducing ROS and MG components. Excessive-Se prompt phytotoxicity by impairing above mentioned parameters, especially at 100 µM Se. Among all B. napus cultivars, Zheda 622 was discovered as highly-susceptible and ZS 758 showed greatest-tolerance against Se stress.

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

Selenium (Se) is an essential micro-element for human and animals. In higher plants, Se essentiality or phyto-toxicity is less explored. Therefore, we aimed to examine the effects of Se (0, 25, 50, and 100 µM) as sodium selenite on the physio-chemical, cell ultra-structural and genomic alterations in hydroponically grown seedlings of four cultivars of B. napus (cvs. Zheda 619, Zheda 622, ZS 758, and ZY 50). Results showed that excessive (100 µM) Se (IV) exhibited significant reduction in plant growth parameters, declined pigment contents, lower water-soluble protein levels, and overproduction of H2O2 and MDA contents. A significant increase in antioxidant enzyme activities and transcript levels of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), except catalase (CAT) were noticed in the leaves and roots. Non-enzymatic antioxidants including glutathione (GSH) and oxidized glutathione (GSSG), except GSSG in roots were enhanced under higher Se (IV) levels. Transmission electron microscopy analysis revealed the ultrastructural damages in leaf mesophyll and root tip cells induced by excessive Se (IV). Less-significant phytotoxic effects were observed in above-mentioned parameters at 50 µM Se (IV). Overall, Se (IV) supplementation at 25 µM displayed marginal beneficial effect by enhancing plant growth, pigment contents, protein levels and restrict H2O2 and MDA overproduction. A marginal increase/decrease in ROS-detoxifying enzymes (except CAT activity) and elevated GSH and GSSG levels were noticed. The accumulation of Se (IV) was much higher in roots as compared to leaves. This accumulation was maximum in Zheda 622 and minimum in ZS 758, followed by Zheda 619 and ZY 50. Overall findings showed that Zheda 622 was the most sensitive and ZS 758 as most tolerant to Se (IV) phyto-toxicity. In addition, Se (IV) was found beneficial until 25 µM Se (IV) but phytotoxic at higher Se levels especially at 100 µM Se (IV).

Beryllium Stress-Induced Modifications in Antioxidant Machinery and Plant Ultrastructure in the Seedlings of Black and Yellow Seeded Oilseed Rape.

Beryllium (Be) could be a threatening heavy metal pollutant in the agroecosystem that may severely affect the performance of crops. The present study was conducted to evaluate the toxic effects of Be (0, 100, 200, and 400 µM) on physiological, ultrastructure, and biochemical attributes in hydroponically grown six-day-old seedlings of two cultivars of Brassica napus L., one tolerant (ZS 758, black seeded) and one sensitive (Zheda 622, yellow seeded). Higher Be concentrations reduced the plant growth, biomass production, chlorophyll contents, and the total soluble protein contents. A significant accumulation of ROS (H2O2, OH-) and MDA contents was observed in a dose-dependent manner. Antioxidant enzymatic activities including SOD, POD, GR, APX, and GSH (except CAT) were enhanced with the increase in Be concentrations in both cultivars. Relative transcript gene expression of above-mentioned antioxidant enzymes further confirmed the alterations induced by Be as depicted from higher involvement in the least susceptible cultivar ZS 758 as compared to Zheda 622. The electron microscopic study showed that higher level of Be (400 µM) greatly damaged the leaf mesophyll and root tip cells. More damage was observed in cultivar Zheda 622 as compared to ZS 758. The damage in leaf mesophyll cells was highlighted as the disruption in cell wall, immature nucleus, damaged mitochondria, and chloroplast structures. In root tip cells, disruption in Golgi bodies and damage in cell wall were clearly noticed. As a whole, the present study confirmed that more inhibitory effects were recorded in yellow seeded Zheda 622 as compared to black seeded ZS 758 cultivar, which is regarded as more sensitive cultivar.

Reduced Glutathione Mediates Pheno-Ultrastructure, Kinome and Transportome in Chromium-Induced Brassica napus L.

Chromium (Cr) as a toxic metal is widely used for commercial purposes and its residues have become a potential environmental threat to both human and plant health. Oilseed rape (Brassica napus L.) is one of the candidate plants that can absorb the considerable quantity of toxic metals from the soil. Here, we used two cultivars of B. napus cvs. ZS 758 (metal-tolerant) and Zheda 622 (metal-susceptible) to investigate the phenological attributes, cell ultrastructure, protein kinases (PKs) and molecular transporters (MTs) under the combined treatments of Cr stress and reduced glutathione (GSH). Seeds of these cultivars were grown in vitro at different treatments i.e., 0, 400 µM Cr, and 400 µM Cr + 1 mM GSH in control growth chamber for 6 days. Results had confirmed that Cr significantly reduced the plant length, stem and root, and fresh biomass such as leaf, stem and root. Cr noticeably caused the damages in leaf mesophyll cells. Exogenous application of GSH significantly recovered both phenological and cell structural damages in two cultivars under Cr stress. For the PKs, transcriptomic data advocated that Cr stress alone significantly increased the gene expressions of BnaA08g16610D, BnaCnng19320D, and BnaA08g00390D over that seen in controls (Ck). These genes encoded both nucleic acid and transition metal ion binding proteins, and protein kinase activity (PKA) and phosphotransferase activities in both cultivars. Similarly, the presence of Cr revealed elite MT genes [BnaA04g26560D, BnaA02g28130D, and BnaA02g01980D (novel)] that were responsible for water transmembrane transporter activity. However, GSH in combination with Cr stress significantly up-regulated the genes for PKs [such as BnaCnng69940D (novel) and BnaC08g49360D] that were related to PKA, signal transduction, and oxidoreductase activities. For MTs, BnaC01g29930D and BnaA07g14320D were responsible for secondary active transmembrane transporter and protein transporter activities that were expressed more in GSH treatment than either Ck or Cr-treated cells. In general, it can be concluded that cultivar ZS 758 is more tolerant toward Cr-induced stress than Zheda 622.

Silicon (Si) alleviates cotton (Gossypium hirsutum L.) from zinc (Zn) toxicity stress by limiting Zn uptake and oxidative damage.

Silicon (Si) is as an important fertilizer element, which has been found effective in enhancing plant tolerance to variety of biotic and a-biotic stresses. This study investigates the Si potential to alleviate zinc (Zn) toxicity stress in cotton (Gossypium hirsutum L.). Cotton plants were grown in hydroponics and exposed to different Zn concentration, 0, 25, and 50 µM, alone and/or in combination with 1 mM Si. Incremental Zn concentration in growth media instigated the cellular oxidative damage that was evident from elevated levels of hydrogen peroxide (H2O2), electrolyte leakage, and malondialdehyde (MDA) and consequently inhibited cotton growth, biomass, chlorophyll pigments, and photosynthetic process. Application of Si significantly suppressed Zn accumulation in various plant parts, i.e., roots, stems, and leaves and thus promoted biomass, photosynthetic, growth parameters, and antioxidant enzymes activity of Zn-stressed as well unstressed plants. In addition, Si reduced the MDA and H2O2 production and electrolyte leakage suggesting its role in protecting cotton plants from Zn toxicity-induced oxidative damage. Thus, the study indicated that exogenous Si application could improve growth and development of cotton crop experiencing Zn toxicity stress by limiting Zn bioavailability and oxidative damage.