Protective Role of Mentha arvensis Aqueous Extract against Manganese Induced Toxicity by Reducing Mn Translocation and Promoting Antioxidative Defense in growing Indica Rice Seedlings

Magnesium and manganese induced changes on chemical, nutritional, antioxidant and antimicrobial properties of the pansy and Viola edible flowers

Pansy and viola edible flowers were grown hydroponically with different levels of Mg and Mn. The nutritional composition was determined using standard methods. Free sugars, fatty acids, organic acids, tocopherols, and phenolic compounds were analyzed using various HPLC and GC devises. The extract's antimicrobial, antioxidant, cytotoxicity, and anti-inflammatory activity were assessed. The results indicated that Mg enrichment negatively affected plant growth and mineral accumulation but improved photosynthetic performance. The edible flowers contained significant amounts of protein, low levels of fat, and varying sugar contents, such as glucose and fructose. Various fatty acids and phenolic compounds were identified, with different concentrations depending on the treatment. The flowers exhibited antioxidant potential, antimicrobial activity, cytotoxic effects, and anti-inflammatory properties. The correlations between the investigated parameters not only expand knowledge on Mg and Mn interaction but also catalyze significant advancements in sustainable agriculture and food health, fostering a healthier and more conscious future.

Silencing of PpNRAMP5 improves manganese toxicity tolerance in peach (Prunus persica) seedlings

The natural resistance-associated macrophage protein (NRAMP) gene family assists in the transport of metal ions in plants. However, the role and underlying physiological mechanism of NRAMP genes under heavy metal toxicity in perennial trees remain to be elucidated. In Prunus persica, five NRAMP family genes were identified and named according to their predicted phylogenetic relationships. The expression profiling analysis indicated that PpNRAMPs were significantly induced by excess manganese (Mn), iron, zinc, and cadmium treatments, suggesting their potential role in heavy metal uptake and transportation. Notably, the expression of PpNRAMP5 was tremendously increased under Mn toxicity stress. Heterologous expression of PpNRAMP5 in yeast cells also confirmed Mn transport. Suppression of PpNRAMP5 through virus-induced gene silencing enhanced Mn tolerance, which was compromised when PpNRAMP5 was overexpressed in peach. The silencing of PpNRAMP5 mitigated Mn toxicity by dramatically reducing Mn contents in roots, and effectively reduced the chlorophyll degradation and improved the photosynthetic apparatus under Mn toxicity stress. Therefore, PpNRAMP5-silenced plants were less damaged by oxidative stress, as signified by lowered H₂O₂ contents and O₂^•- staining intensity, also altered the reactive oxygen species (ROS) homeostasis by activating enzymatic antioxidants. Consistently, these physiological changes showed an opposite trend in the PpNRAMP5-overexpressed peach plants. Altogether, our findings suggest that downregulation of PpNRAMP5 markedly reduces the uptake and transportation of Mn, thus activating enzymatic antioxidants to strengthen ROS scavenging capacity and photosynthesis activity, thereby mitigating Mn toxicity in peach plants.

Effects of exogenous taurine on growth, photosynthesis, oxidative stress, antioxidant enzymes and nutrient accumulation by Trifolium alexandrinum plants under manganese stress

Plants essentially require manganese (Mn) for their normal metabolic functioning. However, excess Mn in the cellular environment is detrimental to plant growth, development, and physio-biochemical functions. Taurine (TAU) is an amino acid with potent antioxidant and anti-inflammatory properties in animals and humans. However, no previous study has investigated the potential of TAU in plant metal stress tolerance. The current study provides some novel insights into the effect of TAU in modulating the defense system of Trifolium alexandrinum plants under Mn toxicity. Manganese toxicity resulted in higher oxidative stress and membrane damage through increased superoxide radical, hydrogen peroxide, malondialdehyde, and methylglyoxal generation alongside enhanced lipoxygenase (LOX) activity. Mn toxicity also resulted in limited uptake of potassium (K⁺), phosphorus (P), calcium (Ca²⁺), and increased the accumulation of Mn in both leaf and roots. However, TAU circumvented the Mn-induced oxidative stress by upregulating the activities of antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase, glutathione-S-transferase, and superoxide dismutase) and levels of ascorbic acid, proline, anthocyanins, phenolics, flavonoids and glutathione (GSH). Taurine conspicuously improved the growth, photosynthetic pigments, hydrogen sulphide (H₂S), and nitric oxide (NO) levels of Mn stressed plants. Taurine also improved the uptake of K⁺, Ca²⁺, P and reduced the Mn content in stressed plants. Overall, exogenous taurine might be a suitable strategy to combat Mn stress in T. alexandrinum plants but applications at field levels for various crops and metal toxicities and economic suitability need to be addressed before final recommendations.

Phosphorus confers tolerance against manganese toxicity in Prunus persica by reducing oxidative stress and improving chloroplast ultrastructure

In this study, we evaluated the mitigative role of phosphorus (P) in terms of manganese (Mn) toxicity in peach (Prunus persica L.) plants. Ten-day-old seedlings were treated with excess Mn (1 mM MnSO₄) alone and in combination with different P levels (100, 150, 200 and 250 μM KH₂PO₄) in half-strength Hoagland medium. The results demonstrated that Mn toxicity plants accumulated a significant amount of Mn in their tissues, and the concentration was higher in roots than in leaves. The accumulated Mn led to a considerable reduction in plant biomass, water status, chlorophyll content, photosynthetic rate, and disrupted the chloroplast ultrastructure by increasing oxidative stress (H₂O₂ and O₂^•-). However, P supplementation dramatically improved plant biomass, leaf relative water and chlorophyll contents, upregulating the ascorbate-glutathione pool and increasing the activities of antioxidant enzymes (superoxide dismutase; peroxidase dismutase; ascorbate peroxidase; monodehydroascorbate reductase; dehydroascorbate reductase), thus reducing oxidative damage as evidenced by lowering H₂O₂ and O₂^•- staining intensity. Moreover, P application markedly restored stomatal aperture and improved chloroplast ultrastructure, as indicated by the improved performance of photosynthetic machinery. Altogether, our findings suggest that P (250 μM) has a great potential to induce tolerance against Mn toxicity by limiting Mn accumulation in tissues, upregulating antioxidant defense mechanisms, alleviating oxidative damage, improving chloroplast ultrastructure and photosynthetic performance in peach plants.

Manganese-induced oxidative stress, ultrastructural changes, and proteomics studies in rice plants

Manganese (Mn) is an essential element for plant growth but it becomes phytotoxic at higher concentrations. The effect of Mn-excess in hydroponics medium was examined on growth, oxidative stress, and ultrastructural changes in chloroplasts and mitochondria as well proteomic alterations in rice (Oryza sativa L.) seedlings. Seedlings grown with 1 mM and 2 mM Mn in nutrient medium for 8 days showed decline in length and fresh biomass, and decline in net photosynthetic rate, transpiration rate, and stomatal conductance. Shoots of the seedlings had higher Mn content than roots. Mn-treated seedlings showed increased production of O₂^·-, H₂O₂, and ^.OH, increased lipid peroxidation, increased carbonylation of proteins, and increased proteolytic activity compared to untreated seedlings. Mn-treated seedlings showed disorganization and swelling of chloroplasts with appearance of plastoglobuli in TEM images and deformity in shape of mitochondria. Using confocal microscopy depolarization of mitochondrial membrane was observed marked by green fluorescence of JC-1 dye monomers in Mn-treated roots. Proteomics studies from leaves of Mn-treated seedlings involving 2DE and PDQuest analysis showed differential expression of 23 proteins, among which MALDI-TOF/TOF mass spectrometry analysis revealed Mn-led downregulation of photosynthesis-related proteins, namely oxygen-evolving complex protein associated with PSII, PAP-3, enzyme involved in protein folding peptidyl-prolyl cis-trans isomerase (PPIase) and carbohydrate metabolizing enzymes hydrolase, fructose-bisphosphate aldolase, transketolase, and isocitrate dehydrogenase, whereas ATP-dependent Clp protease, peroxidase, and nucleic acid-binding proteins were downregulated due to Mn treatment. Results indicate that Mn-excess inhibits growth of rice plants with induction of oxidative stress, causing structural alterations in chloroplasts, mitochondria, inhibiting photosynthesis, and downregulating many photosynthesis and carbohydrate metabolism-related proteins.

Green synthesis of sulfur nanoparticles using Ocimum basilicum leaves and its prospective effect on manganese-stressed Helianthus annuus (L.) seedlings

A novel green approach was utilized to fabricate sulfur nanoparticles (SNPs) with the aid of Ocimum basilicum leaves extract. The effective formation of the synthesized SNPs was examined and approved using UV-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The average particle size was 23 nm with spherical shape and crystalline in nature. In the pot experiment, the synthesized SNPs were applied with different concentrations (12.5, 25, 50, 100 and 200 μM) as pre-soaking to Helianthus annuus seeds and irrigated with 100 mM MnSO₄. As a result of manganese (Mn) exposure, the harvested 14-day sunflower seedlings showed a significant decline in the growth parameters (shoot length, leaf area and the relative water content of both shoot and root), photosynthetic pigments, mineral content (N, P, K, Ca, and Mg), and protein content compared to the control. The root length, electrolyte leakage, Na and Mn levels, metabolites content (amino acids, protein, glycine betaine, proline, and cysteine) were greatly raised as affected by Mn stress. Mn toxicity reduction using SNPs was demonstrated, as the medium doses enhanced seedlings growth, photosynthetic pigments, and mineral nutrients. Application of SNPs decreased Mn uptake and enhanced S metabolism through increasing cysteine level. Likewise, SNPs elevated seedlings water content and eliminated physiological drought via increasing osmolytes such as amino acids and proline. It can be concluded that green-synthesized SNPs had the potential to limit the deleterious effects of Mn stress.