Selenium increases antimony uptake in ramie (Boehmeria nivea L.) by enhancing the physiological, antioxidative, and ionomic mechanisms.

Ramie (Boehmeria nivea L.) is a promising phytoremediation candidate due to its high tolerance and enrichment capacity for antimony (Sb). However, challenges arise as Sb accumulated mainly in roots, complicating soil extraction. Under severe Sb contamination, the growth of ramie may be inhibited. Strategies are needed to enhance Sb accumulation in ramie's aboveground parts and improve tolerance to Sb stress. Considering the beneficial effects of selenium (Se) on plant growth and enhancing resistance to abiotic stresses, this study aimed to investigate the potential use of Se in enhancing Sb uptake by ramie. We investigated the effects of Se (0.5, 1, 2, 5, or 10 µM) on ramie growth, Sb uptake and speciation, antioxidant responses, and ionomic profiling in ramie under 10 mg/L of SbIII or antimonate (SbV) stresses. Results revealed that the addition of 0.5 µM Se significantly increased shoot biomass by 75.73% under SbIII stress but showed minimal effects on shoot and root length in both SbIII and SbV treatments. Under SbIII stress, 2 µM Se significantly enhanced Sb concentrations by 48.42% in roots and 62.88% in leaves. In the case of SbV exposure, 10 µM Se increased Sb content in roots by 42.57%, and 1 µM Se led to a 91.74% increase in leaves. The speciation analysis suggested that Se promoted the oxidation of SbIII to less toxic SbV to mitigate Sb toxicity. Additionally, Se addition effectively minimized the excess reactive oxygen species produced by Sb exposure, with the lowest malondialdehyde (MDA) content at 0.5 µM Se under SbIII and 2 µM Se under SbV, by activating antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione peroxidase. Ionomic analysis revealed that Se helped in maintaining the homeostasis of certain nutrient elements, including magnesium, potassium (K), calcium (Ca), iron (Fe), and copper (Cu) in the SbIII-treated roots and K and manganese (Mg) in the SbV-treated roots. The results suggest that low concentrations of Se can be employed to enhance the phytoremediation of Sb-contaminated soils using ramie.

Ionome profiling and arsenic speciation provide evidence of arsenite detoxification in rice by phosphate and arsenite-oxidizing bacteria.

Arsenite (As(III)) as the most toxic and mobile form is the dominant arsenic (As) species in flooded paddy fields, resulting in higher accumulation of As in paddy rice than other terrestrial crops. Mitigation of As toxicity to rice plant is an important way to safeguard food production and safety. In the current study, As(III)-oxidizing bacteria Pseudomonas sp. strain SMS11 was inoculated with rice plants to accelerate conversion of As(III) into lower toxic arsenate (As(V)). Meanwhile, additional phosphate was supplemented to restrict As(V) uptake by the rice plants. Growth of rice plant was significantly inhibited under As(III) stress. The inhibition was alleviated by the introduction of additional P and SMS11. Arsenic speciation showed that additional P restricted As accumulation in the rice roots via competing common uptake pathways, while inoculation with SMS11 limited As translocation from root to shoot. Ionomic profiling revealed specific characteristics of the rice tissue samples from different treatment groups. Compared to the roots, ionomes of the rice shoots were more sensitive to environmental perturbations. Both extraneous P and As(III)-oxidizing bacteria SMS11 could alleviate As(III) stress to the rice plants through promoting growth and regulating ionome homeostasis.

GhMYB4 downregulates lignin biosynthesis and enhances cotton resistance to Verticillium dahliae.

KEY MESSAGE: GhMYB4 acts as a negative regulator in lignin biosynthesis, which results in alteration of cell wall integrity and activation of cotton defense response. Verticillium wilt of cotton (Gossypium hirsutum) caused by the soil-borne fungus Verticillium dahliae (V. dahliae) represents one of the most important constraints of cotton production worldwide. Mining of the genes involved in disease resistance and illuminating the molecular mechanisms that underlie this resistance is of great importance in cotton breeding programs. Defense-induced lignification in plants is necessary for innate immunity, and there are reports of a correlation between increased lignification and disease resistance. In this study, we present an example in cotton whereby plants with reduced lignin content also exhibit enhanced disease resistance. We identified a negative regulator of lignin synthesis, in cotton encoded in GhMYB4. Overexpression of GhMYB4 in cotton and Arabidopsis enhanced resistance to V. dahliae  with reduced lignin deposition. Moreover, GhMYB4 could bind the promoters of several genes involved in lignin synthesis, such as GhC4H-1, GhC4H-2, Gh4CL-4, and GhCAD-3, and impair their expression. The reduction of lignin content in GhMYB4-overexpressing cotton led to alterations of cell wall integrity (CWI) and released more oligogalacturonides (OGs) which may act as damage-associated molecular patterns (DAMPs) to stimulate plant defense responses. In support of this hypothesis, exogenous application with polygalacturonic acid (PGA) in cotton activated biosynthesis of jasmonic acid (JA) and JA-mediated defense against V. dahliae, similar to that described for cotton plants overexpressing GhMYB4. This study provides a new candidate gene for cotton disease-resistant breeding and an increased understanding of the relationship between lignin synthesis, OG release, and plant immunity.

Ionomic responses of rice plants to the stresses of different arsenic species in hydroponics.

Different ionomic profiles of plants are associated with different external stresses to which they are exposed. Investigation of ionomic variation is necessary for understanding the migration and detoxification of toxic elements in plants. In the current study, rice plants were treated with arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid in hydroponics. The ionomic responses of the rice plants to different arsenic (As) species stresses were measured and analyzed. The multielement approach is more sensitive at detecting significant variations from external environmental stresses than the consideration of several individual elements. The pairs of significant correlations between elements varied based on the rice tissues and As species used in treatment, resulting in specific correlation networks. However, some pairs of correlations existed regardless of As species treatment used in this study. Positive correlations between P and Fe were observed in rice roots treated with any of the As species, implying that P and Fe share similar biological processes. The heatmap from hierarchical cluster analysis (HCA) agreed with the principal component analysis (PCA) results in ionomic differentiation between roots and shoots. Furthermore, ionomic differences between rice plants treated with different As species were identified through PCA. This study revealed that the ionomic profiles in rice plants are sufficient to detect responses to environmental perturbations. Association studies between ionomics and genomics are necessary to further understand the potential mechanisms that promote uptake or exclusion of elements in plants.

Immobilizing unicellular microalga on pellet-forming filamentous fungus: Can this provide new insights into the remediation of arsenic from contaminated water?

Response surface methodology was employed to investigate the effects of nitrogen (X1), phosphorus (X2), and glucose (X3) on arsenic removal by fungal-algal pellets. X1, X3, and X1X3 had significant effects. Arsenic accumulation and transformation were compared among Chlorella vulgaris, Aspergillus oryzae, and fungal-algal pellets under different arsenate and phosphorus concentrations. Fungal-algal pellets had the highest removal rate and was best able to accumulate arsenate in all treatments. The reduction of arsenate to arsenite was found in all tested organisms, while arsenic methylation was only identified in C. vulgaris. The biomass of fungal-algal pellets was not inhibited by arsenate. SEM micrographs showed that arsenic led to a change in mycelial structure from compact to loose pellets. FT-IR spectra showed that four functional groups might be involved in arsenate adsorption. Arsenic tolerance and accumulation in fungal-algal pellets opens the way to its potential application in the remediation of arsenic from contaminated water.

Biosorption of U(VI) by modified Hottentot Fern: Kinetics and equilibrium studies.

Batch experiments were conducted to investigate the biosorption of U(VI) onto Hottentot Fern (Cyclosorus interruptus). The selective adsorption, the adsorption of different sections of Cyclosorus interruptus (CI), and the adsorption of polluted CI compared with that of unpolluted one were studied in detail. The raw CI and the CI modified by CaCl2, MgCl2, MgCl2/H2O2 were investigated for adsorption of U(VI) from aqueous solution. The results indicate that raw CI showed good adsorption selectivity for U(VI), compared with the adsorption of Cu(II), Co(II) and Ni(II). The stem of CI possesses a prominent adsorption capacity compared to the leaf and root of CI, and the unpolluted CI showed its superiority in adsorption capacity than the polluted CI. Adsorption rate was very fast during the first 30 min in the whole adsorption process. The pseudo-second-order kinetics model was proposed for the adsorption of U(VI) and the equilibrium data fitted well to Langmuir adsorption isotherms. The maximum adsorption capacity of R-CI, Ca-CI, Mg-CI and Mg/H2O2-CI is 41.67, 52.63, 62.50 and 71.43 mg g-1 at 20 °C, respectively.