Ursolic Acid Limits Salt-Induced Oxidative Damage by Interfering With Nitric Oxide Production and Oxidative Defense Machinery in Rice

Salinity-induced variations in wheat biomass are regulated by the Na+:K+ ratio, root exudates, and keystone species

Salt stress can limit crop productivity, and there are differences in salt tolerance among plant varieties; however, we lack a comprehensive understanding of how keystone species obtained from different plant varieties under salt stress change plant biomass by driving root exudate secretion and regulating the Na+:K+ ratio. We conducted a pot experiment for three wheat varieties (JiMai32 (JM32), XiaoYan60 (XY60), and ShanRong3 (SR3)) under saline/nonsaline soil conditions. Salt stress tended to significantly reduce wheat biomass, and the biomass reduction rates of the different varieties decreased in the order JM32 < XY60 < SR3. The compositions of the bacterial and fungal communities in the root endosphere, rhizosphere and bulk soil were measured, and salt-induced microbial taxa were isolated to identify keystone species from the co-occurrence networks and to study their effects on physiological responses to salinity in wheat varieties. We observed that root exudates participated in the regulation of the Na+:K+ ratio, thereby affecting wheat biomass, and this process was regulated by keystone species. JM32 was enriched in microorganisms that promote plant growth and resistance to salt stress, such as Burkholderiales, Sordariomycetes, Alteromonadaceae, Acremonium, and Dokdonella, and inhibited microorganisms that are sensitive to the environment (salt, nutrients) and plant pathogens, such as Nocardioidaceae, Nitrospira, Cytophagaceae, Syntrophobacteriaceae, and Striaticonidium. XY60 inhibited microorganisms with biological control and disease inhibition potential, such as Agromyces and Kaistobacter. SR3-enriched pathogens, such as Aurantimonadaceae and Pseudogymnoascus, as well as microorganisms with antagonistic pathogen potential and the ability to treat bacterial infections, such as RB41 and Saccharothrix, were inhibited. Our results confirmed the crucial function of salt-induced keystone species in enhancing plant adaptation to salt stress by driving root exudate secretion and regulating the Na+:K+ ratio, with implications for exploring reasonable measures to improve plant salt tolerance.

4-methylumbelliferone (4-MU) enhances drought tolerance of apple by regulating rhizosphere microbial diversity and root architecture

The dwarfing rootstocks-mediated high-density apple orchard is becoming the main practice management. Currently, dwarfing rootstocks are widely used worldwide, but their shallow root system and drought sensitivity necessitate high irrigation requirements. Here, the root transcriptome and metabolome of dwarfing (M9-T337, a drought-sensitive rootstock) and vigorous rootstocks (Malus sieversii, a drought-tolerant species, is commonly used as a rootstock) showed that a coumarin derivative, 4-Methylumbelliferon (4-MU), was found to accumulate significantly in the roots of vigorous rootstock under drought condition. When exogenous 4-MU was applied to the roots of dwarfing rootstock under drought treatment, the plants displayed increased root biomass, higher root-to-shoot ratio, greater photosynthesis, and elevated water use efficiency. In addition, diversity and structure analysis of the rhizosphere soil microbial community demonstrated that 4-MU treatment increased the relative abundance of putatively beneficial bacteria and fungi. Of these, Pseudomonas, Bacillus, Streptomyces, and Chryseolinea bacterial strains and Acremonium, Trichoderma, and Phoma fungal strains known for root growth, or systemic resistance against drought stress, were significantly accumulated in the roots of dwarfing rootstock after 4-MU treatment under drought stress condition. Taken together, we identified a promising compound-4-MU, as a useful tool, to strengthen the drought tolerance of apple dwarfing rootstock.

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.

Antifungal Peptide P852 Controls Fusarium Wilt in Faba Bean (Viciafaba L.) by Promoting Antioxidant Defense and Isoquinoline Alkaloid, Betaine, and Arginine Biosyntheses

Green pesticides are highly desirable, as they are environmentally friendly and efficient. In this study, the antifungal peptide P852 was employed to suppress Fusarium wilt in the Faba bean. The disease index and a range of physiological and metabolomic analyses were performed to explore the interactions between P852 and the fungal disease. The incidence and disease index of Fusarium wilt were substantially decreased in diseased Faba beans that were treated with two different concentrations of P852 in both the climate chamber and field trial. For the first time, P852 exhibited potent antifungal effects on Fusarium in an open field condition. To explore the mechanisms that underlie P852′s antifungal effects, P852 treatment was found to significantly enhance antioxidant enzyme capacities including guaiacol peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and the activities of antifungal enzymes including chitinase and β-1,3-glucanase, as well as plant dry and fresh weights, and chlorophyll content compared to the control group (p ≤ 0.05). Metabolomics analysis of the diseased Faba bean treated with P852 showed changes in the TCA cycle, biological pathways, and many primary and secondary metabolites. The Faba bean treated with a low concentration of P852 (1 μg/mL, IC₅₀) led to upregulated arginine and isoquinoline alkaloid biosynthesis, whereas those treated with a high concentration of P852 (10 μg/mL, MFC) exhibited enhanced betaine and arginine accumulation. Taken together, these findings suggest that P852 induces plant tolerance under Fusarium attack by enhancing the activities of antioxidant and antifungal enzymes, and restoring plant growth and development.

Sodium Chloride (NaCl)-Induced Physiological Alteration and Oxidative Stress Generation in Pisum sativum (L.): A Toxicity Assessment

Salinity stress has a deleterious impact on plant development, morphology, physiology, and biochemical characteristics. Considering the NaCl-induced phytotoxicity, current investigation was done to better understand the salt-tolerant mechanisms using Pisum sativum L. (pea) as a model crop. Generally, NaCl resulted in a progressive decrease in germinative attributes and physiological and biochemical parameters of P. sativum (L.). The 400 mM NaCl level had a higher detrimental effect and reduced the germination rate, plumule, radicle length, and seedling vigor index (SVI) by 78, 89, 84, and 77%, respectively, under in vitro. Furthermore, after 400 mM NaCl exposure, physiological and enzymatic profiles like root dry biomass (71%) chl-a (66%), chl-b (54%), total chlorophyll (45%), and nitrate reductase activity (NRA) (59%) of peas were decreased. In addition, a NaCl dose-related increase in soluble protein (SP) and sugar (SS), Na⁺ and K⁺ ions, and stressor metabolites was recorded. For instance, at 400 mM NaCl, SP, SS, Na⁺ ion, K⁺ ion, root proline, and malondialdehyde (MDA) contents were significantly and maximally elevated by 65, 33, 84, 79, 85, and 89%, respectively, compared to the control (0 mM NaCl). Data analysis indicated that greater doses of pesticides dramatically increased reactive oxygen species (ROS) levels and induced membrane damage through production of thiobarbituric acid reactive substances (TBARS), as well as increased cell injury. To deal with NaCl-induced oxidative stress, plants subjected to higher salinity stress showed a considerable build-up in antioxidant levels. As an example, ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were maximally and significantly (p ≤ 0.05) increased by 68, 80, 74, and 58%, respectively, after 400 mM NaCl exposure. The propidium iodide (PI)-stained and NaCl-treated plant roots corroborated the damaging effect of salinity-induced stress on the cell membrane, which was observed under a confocal laser microscope (CLSM). The cells exposed to 400 mM NaCl had maximum fluorescence intensity, indicating that higher level of salts can cause pronounced cell damage and reactive oxygen species (ROS) generation. The increases in superoxide ion (O₂ ^-) and hydrogen peroxide (H₂O₂) content in NaCl-treated plant tissues indicated the elevation of ROS with increasing salt levels. This finding revealed that salt stress can cause toxicity in plants by causing alteration in metabolic activity, oxidative injury, and damage to cell membrane integrity.

The Interplay between Hydrogen Sulfide and Phytohormone Signaling Pathways under Challenging Environments

Hydrogen sulfide (H₂S) serves as an important gaseous signaling molecule that is involved in intra- and intercellular signal transduction in plant–environment interactions. In plants, H₂S is formed in sulfate/cysteine reduction pathways. The activation of endogenous H₂S and its exogenous application has been found to be highly effective in ameliorating a wide variety of stress conditions in plants. The H₂S interferes with the cellular redox regulatory network and prevents the degradation of proteins from oxidative stress via post-translational modifications (PTMs). H₂S-mediated persulfidation allows the rapid response of proteins in signaling networks to environmental stimuli. In addition, regulatory crosstalk of H₂S with other gaseous signals and plant growth regulators enable the activation of multiple signaling cascades that drive cellular adaptation. In this review, we summarize and discuss the current understanding of the molecular mechanisms of H₂S-induced cellular adjustments and the interactions between H₂S and various signaling pathways in plants, emphasizing the recent progress in our understanding of the effects of H₂S on the PTMs of proteins. We also discuss future directions that would advance our understanding of H₂S interactions to ultimately mitigate the impacts of environmental stresses in the plants.

Comparative transcriptome mining for terpenoid biosynthetic pathway genes in wild and cultivated species of Plantago

Plantagos are important economical and medicinal plants that possess several bioactive secondary metabolites, such as phenolics, iridoids, triterpenes, and alkaloids. Triterpenoids are the ubiquitous and dynamic secondary metabolites that are deployed by plants for chemical interactions and protection under biotic/abiotic stress. Plantago ovata, a cultivated species, is the source of psyllium, while Plantago major, a wild species, has significant therapeutic potential. Wild species are considered more tolerant to stressful conditions in comparison to their cultivated allies. In view of this, the present study aimed to decipher the terpenoid biosynthetic pathway operative in P. ovata and P. major using a comparative transcriptomics approach. Majority of terpenoid biosynthetic genes were observed as upregulated in P. major including rate limiting genes of MVA (HMGR) and MEP (DXR) pathways and genes (α-AS, BAS, SM, and CYP716) involved in ursolic acid biosynthesis, an important triterpenoid prevalent in Plantago species. The HPLC output further confirmed the higher concentration of ursolic acid in P. major as compared to P. ovata leaf samples, respectively. In addition to terpenoid biosynthesis, KEGG annotation revealed the involvement of differentially expressed unigenes in several metabolic pathways, aminoacyl-tRNA biosynthesis, biosynthesis of antibiotics, and biosynthesis of secondary metabolites. MYB was found as the most abundant transcription factor family in Plantago transcriptome. We have been able to generate valuable information which can help in improving terpenoid production in Plantago. Additionally, the present study has laid a strong foundation for deciphering other important metabolic pathways in Plantago.

Ursolic Acid Protects Sodium Dodecyl Sulfate-Induced Drosophila Ulcerative Colitis Model by Inhibiting the JNK Signaling

Ursolic acid (UA) is a bioactive molecule widely distributed in various fruits and vegetables, which was reported to play a therapeutic role in ulcerative colitis (UC) induced by toxic chemicals. However, the underlying mechanism has not been well clarified in vivo. Here, using a Drosophila UC model induced by sodium dodecyl sulfate (SDS), we investigated the defensive effect of UA on intestinal damage. The results showed that UA could significantly protect Drosophila from the damage caused by SDS exposure. Further, UA alleviated the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) induced by SDS and upregulated the activities of total superoxide dismutase (T-SOD) and catalase (CAT). Moreover, the proliferation and differentiation of intestine stem cells (ISCs) as well as the excessive activation of the c-Jun N-terminal kinase (JNK)-dependent JAK/STAT signaling pathway induced by SDS were restored by UA. In conclusion, UA prevents intestine injury from toxic compounds by reducing the JNK/JAK/STAT signaling pathway. UA may provide a theoretical basis for functional food or natural medicine development.

Mitigation effects of exogenous melatonin-selenium nanoparticles on arsenic-induced stress in Brassica napus

Melatonin (MT) and selenium (Se) application known to decrease heavy metal uptake and toxicity in plants. By mixing the Se in MT medium a new complex MT-Se nanoparticles (MT-Se NPs) was synthesized and we investigated the role of MT-Se NPs on B. napus growth and tolerance against As stress. The MT-Se particles significantly enhanced the plant growth and other associated physiological attributes under As stress. The As treatment at 80 μM was more phytotoxic, however MT-Se NPs application resulted in a substantial increase in leaf chlorophyll fluorescence, biomass accumulation, and decreased ROS relative to As stressed plants. The use of MT-Se NPs to As stressed plants reduced photosynthetic inhibition and oxidative stress and attenuated the increase in MDA and H₂O₂ contents. The application of MT-Se NPs also boosted the antioxidant enzymes activities such as SOD, POD and CAT as well as the APX, GR and GSH activates under As stress. The results also showed MT-Se NPs treatments alleviated the growth inhibition induced by As and reduced the accumulation of As in leaves and roots of B. napus seedlings. Moreover, treatment with MT-Se NPs improved the plant growth more successfully than treatment of MT and Se alone. This study explored the mechanism of melatonin and selenium efficiency in the composition can be jointly encouraged to exert synergistic effects and boost plant enzymatic activities.

The molecular events underpinning cultivar differences in melatonin counteracting salt damage in Phaseolus vulgaris

Melatonin (N -acetyl-5-methoxytryptamine) plays important roles in multiple stress responses, especially under salt stress. However, cultivar differences in melatonin mediated salt stress tolerance are unclear. Phaseolus vulgaris L. (common bean) cultivars Jiyin 1 (JY, salt-tolerant) and Xuliyabai (XL, salt-sensitive) were used in this study. Exogenous melatonin significantly improved root growth under salt stress in JY, but had little effect on XL. Physiology analysis showed significant differences in activities of antioxidant enzymes (superoxide, SOD; and catalase, CAT) and malondialdehyde content between JY and XL. Meanwhile, the change of ABA content in JY and XL root was opposite in salt plus melatonin treatment. Comparative root transcriptomes of JY and XL revealed 3505 and 668 differentially expressed genes (DEGs) regulated by salt stress and melatonin. The most enriched melatonin-responsive genes under salt stress are mainly involved in regulation of transcription, oxidation-reduction process, transcription factor activity, oxidoreductase activity. In addition, melatonin induced more obvious changes of DEGs in JY than that in XL under salt condition. Melatonin also significantly induced 41 DEGs only in JY, including signal transduction genes, transcription factors, ubiquitin protein ligases, ion homeostasis and osmotic adjustment genes etc. This study uncovered the molecular mechanism of cultivar difference of melatonin response under salt stress in common bean.