Mechanism of calcium in melatonin enhancement of functional substance-phenolic acid in germinated hulless barley

In vitro safety profile and phyto-ecotoxicity assessment of the eco-friendly calcium oxide nanoparticles

The present study aims to evaluate the toxicity of the green calcium oxide nanoparticles (CaO-NPs) from golden linseed extract (Linum usitatissimum L.) by phytotoxicity in seeds (Daucus carota, Beet shankar, Lactuca sativa and Brassica oleracea), in vitro safety profile and soil toxicity for CaO-NPs solutions from 12.5 to 100 μg mL-1. Ecotoxicity analysis of the soil was conducted using XRD diffractograms, which revealed characteristic peaks of the nanoparticles at 37.35° (12.5, 25, 50, and 100 μg mL-1), as well as a peak at 67.34° (25 and 100 μg mL-1). Additionally, the in vitro safety assessment indicated favorable cell specification and regulation within the first 24 h, demonstrating reductions of 15.9 ± 0.2%, 17.9 ± 0.2%, 17.6 ± 0.2%, and 32.9 ± 0.2% to 12.5, 25, 50, and 100 μg mL-1, respectively. The dsDNA assay revealed initial protection and controlled release within the cells for 48 h. However, after 72 h, there was an increase of 20 ± 0.2%, 16 ± 0.2%, 32 ± 0.2%, and 43 ± 0.2% to 12.5, 25, and 50 μg mL-1. The analysis of ROS generation demonstrated a reduction of 40 ± 0.2%, 33 ± 0.2%, 20 ± 0.2%, and 9 ± 0.2% to 12.5, 25, 50, and 100 μg mL-1, respectively, within 72 h. When compared to the negative control (NC), there was an increase of 50 ± 0.2%, 56 ± 0.2%, 77 ± 0.2%, and 92 ± 0.2% at the same concentrations, suggesting that the nanoparticles generated free radicals, leading to cellular inflammation. This was attributed to the positive surface charge of the nanoparticles, resulting in reduced interaction with the cell membrane and the subsequent release of hydroxyl (•OH), which caused inflammatory processes in the cells. Therefore, CaO-NPs exhibited a low phytotoxicity and high cytocompatibility, while also promoting plant germination and growth.

Integrated transcriptomic and physio-molecular studies unveil the melatonin and PGPR induced protection to photosynthetic attributes in Brassica juncea L. under cadmium toxicity

Cd is highly mobile, non-essential trace element, that has become serious environmental issue due to its elevated concentration in soil. The present study was taken up to work out salutary effect of melatonin (Mlt) and PGPR ((Pseudomonas putida (Pp), Pseudomonas fluorescens (Pf) in 10 days old Cd stressed (0.3 mM) Brassica juncea L. seedlings. The present work investigated growth characteristics, photosynthetic pigments, secondary metabolites in melatonin-PGPR inoculated B. juncea seedlings. It was backed by molecular studies entailing RT-PCR and transcriptomic analyses. Our results revealed, substantial increase in photosynthetic pigments and secondary metabolites, after treatment with melatonin, P.putida, P. fluorescens in Cd stressed B. juncea seedlings, further validated with transcriptome analysis. Comparative transcriptome analyses identified 455, 5953, 3368, 2238 upregulated and 4921, 430, 137, 27 down regulated DEGs, Cn-vs-Cd, Cd-vs-Mlt, Cd-vs-Mlt-Pp-Pf, Cd-vs-Mlt-Pp-Pf-Cd comparative groups respectively. In depth exploration of genome analyses (Gene ontology, Kyoto encyclopaedia of genes), revealed that Cd modifies the expression patterns of most DEGs mainly associated to photosystem and chlorophyll synthesis. Also, gene expression studies for key photosynthetic genes (psb A, psb B, CHS, PAL, and PSY) suggested enhanced expression in melatonin-rhizobacteria treated Cd stressed B. juncea seedlings. Overall, results provide new insights into probable mechanism of Mlt-PGPR induced protection to photosynthesis in Cd stressed B. juncea plants.

Involvement of ROS and calcium ions in developing heat resistance and inducing antioxidant system of wheat seedlings under melatonin's effects

The stress-protective effect of melatonin (N-acetyl-5-methoxytryptamine) on plant cells is mediated by key signaling mediators, in particular calcium ions and reactive oxygen species (ROS). However, the links between changes in calcium and redox homeostasis and the formation of adaptive responses of cultivated cereals (including wheat) to the action of high temperatures have not yet been studied. In the present study, we investigated the possible involvement of ROS and calcium ions as signaling mediators in developing heat resistance in wheat (Triticum aestivum L.) seedlings and activating their antioxidant system. Treatment of 3-day-old etiolated seedlings with melatonin solutions at concentrations 0.01-10 µM increased their survival after exposure to 45 °C for 10 min. The most significant stress-protective effect was exerted by melatonin treatment at 1 µM concentration. Under the influence of melatonin, a transient enhancement of superoxide anion radical (O2•-) generation and an increase in hydrogen peroxide content were observed in roots, with a maximum at 1 h. Four hours after treatment with melatonin, the activity of catalase and guaiacol peroxidase increased in roots, while the activity of superoxide dismutase did not change significantly. After exposure to 45 °C, the activity of catalase and guaiacol peroxidase was higher in the roots of melatonin-treated wheat seedlings, and the indices of ROS generation, content of the lipid peroxidation product malonic dialdehyde, and cell membrane damage were lower than in control seedlings. Melatonin-induced changes in root ROS generation and antioxidant enzyme activities were eliminated by pretreatment with the hydrogen peroxide scavenger dimethylthiourea (DMTU), NADPH oxidase inhibitor imidazole, and calcium antagonists (the extracellular calcium chelator EGTA and phospholipase C inhibitor neomycin). Treatment with DMTU, imidazole, EGTA, and neomycin also abolished the melatonin-induced increase in survival of wheat seedlings after heat stress. The role of calcium ions and ROS, generated with the participation of NADPH oxidase, as signaling mediators in the melatonin-induced antioxidant system and heat stress resistance of wheat seedlings have been demonstrated.

Salicylic acid promotes phenolic acid biosynthesis for the production of phenol acid-rich barley sprouts

BACKGROUND

Phenolic acid exhibits a variety of well-known physiological functions. In this study, optimal germination conditions to ensure total phenolic acid enrichment in barley sprouts induced by salicylic acid treatment and its effects on sprout physiology and activity, as well as the gene expression of key enzymes for phenolic acid biosynthesis, were investigated.

RESULTS

When sprouts were treated with 1 mmol L-1 salicylic acid during germination and germinated at 25 °C for 4 days, the phenolic acid content was 1.82 times that of the control, reaching 1221.54 μg g-1 fresh weight. Salicylic acid significantly increased the activity of phenylalanine aminolase and cinnamic acid-4-hydroxylase and the gene expression of phenylalanine aminolase, cinnamic acid-3-hydroxylase, cinnamic acid-4-hydroxylase, 4-coumaric acid-coenzyme A, caffeic acid O-methyltransferase, and ferulate-5-hydroxylase in barley sprouts. However, salicylic acid treatment significantly increased malondialdehyde and H2O2 content, H2O2 and O2 - fluorescence intensity, as well as significantly decreasing sprout length and fresh weight. Salicylic acid treatment markedly increased the activity of peroxidase and catalase and the gene expression of peroxidase, catalase, and ascorbate peroxidase in barley sprouts.

CONCLUSION

Salicylic acid treatment during barley germination significantly promoted the enrichment of total phenolic acid by increasing the activities and gene expression levels of enzymes involved in the phenolic acid biosynthesis pathway. Salicylic acid induced the accumulation of reactive oxygen species, inhibited sprout growth, and activated the antioxidant system. This study provides a basis for the future development of functional foods using phenol acid-rich plants as raw materials. © 2024 Society of Chemical Industry.

Methyl Jasmonate and Zinc Sulfate Induce Secondary Metabolism and Phenolic Acid Biosynthesis in Barley Seedlings

This study aimed to reveal the impact of MeJA and ZnSO4 treatments on the physiological metabolism of barley seedlings and the content of phenolic acid. The results showed that MeJA (100 μM) and ZnSO4 (4 mM) treatments effectively increased the phenolic acid content by increasing the activities of phenylalanine ammonia-lyase and cinnamate-4-hydroxylase (PAL) and cinnamic acid 4-hydroxylase (C4H) and by up-regulating the expression of genes involved in phenolic acid synthesis. As a result of the MeJA or ZnSO4 treatment, the phenolic acid content increased by 35.3% and 30.9% at four days and by 33.8% and 34.5% at six days, respectively, compared to the control. Furthermore, MeJA and ZnSO4 treatments significantly increased the malondialdehyde content, causing cell membrane damage and decreasing the fresh weight and seedling length. Barley seedlings responded to MeJA- and ZnSO4-induced stress by increasing the activities of antioxidant enzymes and controlling their gene expression levels. Meanwhile, MeJA and ZnSO4 treatments significantly upregulated calcium-adenosine triphosphate, calmodulin-dependent protein kinase-related kinase, and calmodulin-dependent protein genes in barley seedlings. This suggested that Ca2+ may be the signaling molecule that promotes phenolic acid synthesis under MeJA and ZnSO4 treatment. This study deepens the understanding of the phenolic acid enrichment process in barley seedlings under MeJA and ZnSO4 treatments.

Melatonin-Mediated Molecular Responses in Plants: Enhancing Stress Tolerance and Mitigating Environmental Challenges in Cereal Crop Production

Cereal crops are crucial for global food security; however, they are susceptible to various environmental stresses that significantly hamper their productivity. In response, melatonin has emerged as a promising regulator, offering potential benefits for stress tolerance and crop growth. This review explores the effects of melatonin on maize, sorghum, millet, rice, barley, and wheat, aiming to enhance their resilience to stress. The application of melatonin has shown promising outcomes, improving water use efficiency and reducing transpiration rates in millet under drought stress conditions. Furthermore, it enhances the salinity and heavy metal tolerance of millet by regulating the activity of stress-responsive genes. Similarly, melatonin application in sorghum enhances its resistance to high temperatures, low humidity, and nutrient deficiency, potentially involving the modulation of antioxidant defense and aspects related to photosynthetic genes. Melatonin also exerts protective effects against drought, salinity, heavy metal, extreme temperatures, and waterlogging stresses in maize, wheat, rice, and barley crops by decreasing reactive oxygen species (ROS) production through regulating the antioxidant defense system. The molecular reactions of melatonin upregulated photosynthesis, antioxidant defense mechanisms, the metabolic pathway, and genes and downregulated stress susceptibility genes. In conclusion, melatonin serves as a versatile tool in cereal crops, bolstering stress resistance and promoting sustainable development. Further investigations are warranted to elucidate the underlying molecular mechanisms and refine application techniques to fully harness the potential role of melatonin in cereal crop production systems.

Melatonin as a key regulator in seed germination under abiotic stress

Seed germination (SG) is the first stage in a plant's life and has an immense importance in sustaining crop production. Abiotic stresses reduce SG by increasing the deterioration of seed quality, and reducing germination potential, and seed vigor. Thus, to achieve a sustainable level of crop yield, it is important to improve SG under abiotic stress conditions. Melatonin (MEL) is an important biomolecule that interplays in developmental processes and regulates many adaptive responses in plants, especially under abiotic stresses. Thus, this review specifically summarizes and discusses the mechanistic basis of MEL-mediated SG under abiotic stresses. MEL regulates SG by regulating some stress-specific responses and some common responses. For instance, MEL induced stress specific responses include the regulation of ionic homeostasis, and hydrolysis of storage proteins under salinity stress, regulation of C-repeat binding factors signaling under cold stress, starch metabolism under high temperature and heavy metal stress, and activation of aquaporins and accumulation of osmolytes under drought stress. On other hand, MEL mediated regulation of gibberellins biosynthesis and abscisic acid catabolism, redox homeostasis, and Ca2+ signaling are amongst the common responses. Nonetheless factors such as endogenous MEL contents, plant species, and growth conditions also influence above-mentioned responses. In conclusion, MEL regulates SG under abiotic stress conditions by interacting with different physiological mechanisms.

Phytomelatonin: A key regulator of redox and phytohormones signaling against biotic/abiotic stresses

Plants being sessile in nature, are exposed to unwarranted threats as a result of constantly changing environmental conditions. These adverse factors can have negative impacts on their growth, development, and yield. Hormones are key signaling molecules enabling cells to respond rapidly to different external and internal stimuli. In plants, melatonin (MT) plays a critical role in the integration of various environmental signals and activation of stress-response networks to develop defense mechanisms and plant resilience. Additionally, melatonin can tackle the stress-induced alteration of cellular redox equilibrium by regulating the expression of redox hemostasis-related genes and proteins. The purpose of this article is to compile and summarize the scientific research pertaining to MT's effects on plants' resilience to biotic and abiotic stresses. Here, we have summarized that MT exerts a synergistic effect with other phytohormones, for instance, ethylene, jasmonic acid, and salicylic acid, and activates plant defense-related genes against phytopathogens. Furthermore, MT interacts with secondary messengers like Ca²⁺, nitric oxide, and reactive oxygen species to regulate the redox network. This interaction triggers different transcription factors to alleviate stress-related responses in plants. Hence, the critical synergic role of MT with diverse plant hormones and secondary messengers demonstrates phytomelatonin's importance in influencing multiple mechanisms to contribute to plant resilience against harsh environmental factors.

Synergistic effects of calcium and melatonin on physiological and phytochemical attributes of Dracocephalum kotschyi genotypes under salinity stress

Since regulatory roles of calcium (Ca) and melatonin (MT) in physiological responses of plants to salinity stress are lacking, various Dracocephalum kotschyi genotypes (Bojnord, Urmia, Fereydunshahr, and Semirom) were pretreated with exogenous Ca (5 mM), MT (100 μM), and Ca + MT in the presence of salt (75 mM NaCl). In addition measuring the concentration of phenolic compounds by high performance liquid chromatography (HPLC), histochemical evaluations of essential oils and phenolic compounds in glandular trichomes of leaf samples were performed by light microscope. Salt stress reduced shoot fresh (SFW) and dry weight (SDW), leaf area (LA), relative water content (RWC), and maximum efficiency of photosystem II (F_v /F_m ), but enhanced total phenolic content (TPC) and total flavonoids content (TFC), phenolic compounds concentrations, DPPH radical scavenging capacity, electrolyte leakage (EL), proline and hydrogen peroxide (H₂ O₂ ) concentrations, and Na⁺ /K⁺ and essential oils and TPC of the glandular trichomes of leaves in all D. kotschyi genotypes. Foliar spraying of Ca, MT, and particularly Ca + MT on D. kotschyi seedlings improved SFW, SDW, RWC, TPC, TFC, proline and phenolic compounds concentrations, F_v /F_m , and DPPH radical scavenging capacity, but reduced H₂ O₂ , EL, and Na⁺ /K⁺ in the leaves and essential oils and TPC in the glandular trichomes of all genotypes under both non-stress and salt stress conditions. These findings indicate that the crosstalk between MT and Ca synergistically improves salt tolerance, TPC and TFC, phenolic compounds concentration, and essential oils accumulation in glandular trichomes of different D. kotschyi genotypes.