Salt stress induces Kranz anatomy and expression of C4 photosynthetic enzymes in the amphibious sedge Eleocharis vivipara

Eleocharis vivipara Link is a unique amphibious leafless plant of the Cyperaceae. The terrestrial form develops culms with Kranz anatomy and C₄-like traits, while the submerged form does culms with non-Kranz anatomy and C₃ traits. The submerged form develops new culms with C₄-like mode when exposed to air or exogenous abscisic acid. In this study, we investigated whether salt stress (0.05-0.3 M NaCl) has a similar effect. When the submerged form was grown for one month in solutions of 0.1 M NaCl and more, culm growth was strongly suppressed. However, these plants slowly developed new culms that had Kranz anatomy with chloroplast-abundant Kranz bundle sheath cells. Although the culms of the submerged form had only few stomata, culms grown in the NaCl solution had many stomata. The NaCl-grown culms also accumulated large amounts of C₄ photosynthetic enzymes (phosphoenolpyruvate carboxylase and pyruvate Pi dikinase), and the cellular localization patterns of these enzymes and ribulose 1,5-bisphosphate carboxylase/oxygenase were similar to those in terrestrial culms. Accumulation of C₄ enzymes increased in mature culms of the submerged form (with non-Kranz anatomy) when exposed to 0.2 M NaCl solution for one week. These results suggest that salt stress induces development of Kranz anatomy and expression of C₄ photosynthetic enzymes in the submerged C₃ form of E. vivipara, whereas the anatomical and biochemical traits of C₄ photosynthesis appear to be regulated independently.

Eleocharis dulcis corm: phytochemicals, health benefits, processing and food products

Eleocharis dulcis, an aquatic plant belonging to Cyperaceae family, is indigenous to Asia, and also occurs in tropical Africa and Australia. The edible corm part of E. dulcis is a commonly consumed aquatic vegetable with a planting area of 44.46 × 10³ hm² in China. This work aims to explore the potential of E. dulcis corm for use as a new food source for sufficient nutrients and health benefits by reviewing its nutrients, phytochemicals, functions, processing and food products. Eleocharis dulcis corm contains starches, dietary fibers, non-starch polysaccharides, proteins, amino acids, phenolics, sterols, puchiin, saponins, minerals and vitamins. Among them, phenolics including flavonoids and quinones could be the major bioconstituents that largely contribute to antioxidant, anti-inflammatory, antibacterial, antitumor, hepatoprotective, neuroprotective and hypolipidemic functions. Peel wastes of E. dulcis corm tend to be enriched in phenolics to a much higher extent than the edible pulp. Fresh-cut E. dulcis corm can be consumed as a ready-to-eat food or processed into juice for beverage production, and anti-browning processing is a key to prolonging shelf life. Present food products of E. dulcis corm are centered on various fruit and vegetable beverages, and suffer from single categories and inadequate development. In brief, underutilized E. dulcis corm possesses great potential for use as a new food source for sufficient nutrients and health benefits. © 2021 Society of Chemical Industry.

Arsenic in Sediments, Soil and Plants in a Remediated Area of the Iron Quadrangle, Brazil, and its Accumulation and Biotransformation in Eleocharis geniculata

Since arsenic (As) exposure is largely due to geochemical contamination, this study focused on the remediated area of Santana do Morro, a district of Santa Bárbara, Minas Gerais, Brazil, which was previously contaminated with As due to gold mining. Total As concentrations in sediment, soil and plants were determined, next to As species, anionic arsenic compounds As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), in plants samples. Total As concentrations in soil and sediments were slightly elevated (16-18 µg g-1) and most of the plants contained low levels of As (< 1 µg g-1). The exception was a native plant Eleocharis geniculata (L.) which contained elevated levels of As (4 µg g-1). The exposure of this plant to As under controlled conditions (hydroponics) indicated its possible tolerance to elevated As levels and suggesting its potential use in phytomonitoring of As-contaminated sites. This plant is able to metabolize arsenate to arsenite and contained MMA and DMA, both in its natural habitat and under controlled conditions.

Phytoremediation in flooded environments: Dynamics of barium absorption and translocation by Eleocharis acutangula

Macrophytes are widely used in water treatment and have potential for remediation of flooded soils. Many techniques have been proposed to increase the phytoextraction of metals by macrophytes, however, the knowledge of periods of maximum absorption and translocation is essential and is a gap in the management of phytoremediation. To evaluate the absorption and translocation of Ba over time by Eleocharis acutangula, a greenhouse experiment was conducted and the dry matter production of plants, Ba content in the roots and aerial parts, mass of Ba accumulated in plants, translocation factors and removal coefficients of Ba, and Ba content in two layers of the soil (0.0-0.1 m and 0.1-0.2 m) were determined. The highest translocation rates were observed after 105 days of cultivation, when the plants reached a state of hyperaccumulation. The maximum accumulation of barium occurred in the aerial parts of the plants at 105 days and in the roots at both 120 and 180 days. The barium content was reduced up to 120 days, as a result of an increase in available barium content in the soil layer of 0.0-0.1 m up to 105 days and in the layer 0.10-0.20 m up to 120 days, favoring the intense accumulation of Ba during this period. After 120 days of cultivation, the accumulation in the roots maintained a high coefficient of removal of Ba from the soil to the plant. After 180 days the available barium in the soil was depleted due to this high rate of removal by the roots.

Pathway Analysis and Metabolites Identification by Metabolomics of Etiolation Substrate from Fresh-Cut Chinese Water Chestnut (Eleocharis tuberosa)

Fresh-cut Chinese water chestnuts (CWC) turn yellow after being peeled, reducing their shelf life and commercial value. Metabolomics, the systematic study of the full complement of small molecular metabolites, was useful for clarifying the mechanism of fresh-cut CWC etiolation and developing methods to inhibit yellowing. In this study, metabolic alterations associated with etiolation at different growth stages (0 day, 2 days, 3 days, 4 days, 5 days) from fresh-cut CWC were investigated using LC–MS and analyzed by pattern recognition methods (principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA), and orthogonal projection to latent structures-discriminant analysis (OPLS-DA)). The metabolic pathways of the etiolation molecules were elucidated. The main metabolic pathway appears to be the conversion of phenylalanine to p-coumaroyl-CoA, followed by conversion to naringenin chalcone, to naringenin, and naringenin then following different pathways. Firstly, it can transform into apigenin and its derivatives; secondly, it can produce eriodictyol and its derivatives; and thirdly it can produce dihydrokaempferol, quercetin, and myricetin. The eriodictyol can be further transformed to luteolin, cyanidin, dihydroquercetin, dihydrotricetin, and others. This is the first reported use of metabolomics to study the metabolic pathways of the etiolation of fresh-cut CWC.

Natural attenuation of weathered oil using aquatic plants in a farm in Southeast Mexico

An experiment was conducted in field for three years to assess the sustainability of aquatic plants Leersia hexandra, Cyperus articulatus, and Eleocharis palustris for use in the removal of total hydrocarbons of weathered oil in four areas contaminated with 60916-119373 mg/kg of hydrocarbons. The variables evaluated were coverage of plant, dry matter, density of plant growth-promoting rhizobacteria, and the removal of total weathered oil. The variables showed statistical differences (p = 0.05) due to the effects of time and the amount of oil in the soil. The three aquatic plants survived on the farm during the 36-month evaluation. The grass L. hexandra yielded the greatest coverage of plant but was inhibited by the toxicity of the oil, which, in contrast, stimulated the coverage of C. articulatus. The rhizosphere of L. hexandra in control soil was more densely colonized by N-fixing bacteria, while the density of phosphate and potassium solubilizing rhizobacteria was stimulated by exposure to oil. C. articulatus coverage showed positive relationship with the removal of weathered oil; positive effect between rhizosphere and L. hexandra grass coverage was also identified. These results contributed to the removal of weathered oil in Gleysols flooded and affected by chronic discharges of crude oil.

Cascade utilization of water chestnut: recovery of phenolics, phosphorus, and sugars

Overgrowth of aquatic plants, such as water chestnut, has been reported as a regional problem in various areas. We proposed cascade utilization of water chestnut through the recovery of phenolics, phosphorus, and sugars. Phenolics were extracted using 50 g (wet weight) of biomass with 300 mL of acetone, methanol, or hot water, and the yields of total phenolics were 80.2, 56.2, and 49.7 mg g(-1) dry weight of native biomass, respectively. The rate of eluted phosphorus in the phenolic extraction step was 8.6, 14.8, and 45.3 % of that in the native biomass, respectively, indicating that the use of polar organic solvents suppressed phosphorus elution at the phenolic extraction step. Extraction of phosphorus following the phenolic extraction was combined with alkaline pretreatment (1 % NaOH solution) of biomass for saccharification; 64.1 and 51.0 % of phosphorus in the native biomass were extracted using acetone and methanol for the phenolic extraction, respectively. Saccharification following the alkaline pretreatment showed that the glucose recovery rates were significantly increased (p<0.05) with the phenolic extraction step compared to alkaline pretreatment alone. This finding indicates that extraction of phenolics not only provides another useful material but also facilitates enzymatic saccharification.

Performance of Eleocharis macrostachya and its importance for arsenic retention in constructed wetlands

INTRODUCTION

Arsenic (As) can be removed from water via rhizofiltration using phytostabilizing plants. The aim of this study was to investigate the performance of Eleocharis macrostachya in constructed wetland prototypes, as well as the plant's arsenic mass retention and the distribution of As along the wetland flow gradient and the soil in the wetland mesocosmos.

MATERIALS AND METHODS

Experiments were carried out in laboratory-scale wetland prototypes, two planted with E. macrostachya and one without plants. Samples of water were taken at the inlet and outlet of the wetlands during the 33-week test period. At the end of the experiment, plants and soil (silty-sand) from each prototype were divided in three equal segments (entrance, middle and exit) and analyzed for their arsenic content. Results revealed that the planted wetlands have a higher As-mass retention capacity (87-90% of the total As inflow) than prototypes without plants (27%).

RESULTS

As mass balance in the planted wetlands revealed that 78% of the total inflowing As was retained in the soil bed. Nearly 2% was absorbed in the plant roots, 11% was flushed as outflow, and the fate of the remaining 9% is unknown. In the prototype without plants, the soil retained 16% of As mass, 72% of the arsenic was accounted for in the outflow, and 12% was considered unknown. Although E. macrostachya retained only 2% of the total arsenic mass in their roots, its presence was a determining factor for arsenic retention in the wetland soil medium.

CONCLUSION

Hence, planted wetlands might be a suitable option for treating As-contaminated water.

Trace element uptake by Eleocharis equisetina (spike rush) in an abandoned acid mine tailings pond, northeastern Australia: implications for land and water reclamation in tropical regions

This study was conducted to determine the uptake of trace elements by the emergent wetland plant species Eleocharis equisetina at the historic Jumna tin processing plant, tropical Australia. The perennial emergent sedge was found growing in acid waters (pH 2.45) and metal-rich tailings (SnAsCuPbZn). E. equisetina displayed a pronounced acid tolerance and tendency to exclude environmentally significant elements (Al, As, Cd, Ce, Co, Cu, Fe, La, Ni, Pb, Se, Th, U, Y, Zn) from its above-substrate biomass. This study demonstrates that geobotanical and biogeochemical examinations of wetland plants at abandoned mined lands of tropical areas can reveal pioneering, metal-excluding macrophytes. Such aquatic macrophytes are of potential use in the remediation of acid mine waters and sulfidic tailings and the reclamation of disturbed acid sulfate soils in subtropical and tropical regions.

Identification of C4 photosynthesis metabolism and regulatory-associated genes in Eleocharis vivipara by SSH

This is the first effort to investigate the candidate genes involved in kranz developmental regulation and C(4) metabolic fluxes in Eleocharis vivipara, which is a leafless freshwater amphibious plant and possesses a distinct culms anatomy structure and photosynthetic pattern in contrasting environments. A terrestrial specific SSH library was constructed to investigate the genes involved in kranz anatomy developmental regulation and C(4) metabolic fluxes. A total of 73 ESTs and 56 unigenes in 384 clones were identified by array hybridization and sequencing. In total, 50 unigenes had homologous genes in the databases of rice and Arabidopsis. The real-time quantitative PCR results showed that most of the genes were accumulated in terrestrial culms and ABA-induced culms. The C(4) marker genes were stably accumulated during the culms development process in terrestrial culms. With respect to C(3) culms, C(4) photosynthesis metabolism consumed much more transporters and translocators related to ion metabolism, organic acids and carbohydrate metabolism, phosphate metabolism, amino acids metabolism, and lipids metabolism. Additionally, ten regulatory genes including five transcription factors, four receptor-like proteins, and one BURP protein were identified. These regulatory genes, which co-accumulated with the culms developmental stages, may play important roles in culms structure developmental regulation, bundle sheath chloroplast maturation, and environmental response. These results shed new light on the C(4) metabolic fluxes, environmental response, and anatomy structure developmental regulation in E. vivipara.

Do tropical wetland plants possess convective gas flow mechanisms?

• Internal pressurization and convective gas flow, which can aerate wetland plants more efficiently than diffusion, are common in temperate species. Here, we present the first survey of convective flow in a range of tropical plants. • The occurrence of pressurization and convective flow was determined in 20 common wetland plants from the Mekong Delta in Vietnam. The diel variation in pressurization in culms and the convective flow and gas composition from stubbles were examined for Eleocharis dulcis, Phragmites vallatoria and Hymenachne acutigluma, and related to light, humidity and air temperature. • Nine of the 20 species studied were able to build up a static pressure of > 50 Pa, and eight species had convective flow rates higher than 1 ml min(-1). There was a clear diel variation, with higher pressures and flows during the day than during the night, when pressures and flows were close to zero. • It is concluded that convective flow through shoots and rhizomes is a common mechanism for below-ground aeration of tropical wetland plants and that plants with convective flow might have a competitive advantage for growth in deep water.

Accumulation of Indium and other heavy metals by Eleocharis acicularis: an option for phytoremediation and phytomining

Eleocharis acicularis was exposed to different concentrations of In, Ag, Pb, Cu, Cd, and Zn in the laboratory to assess its capability in accumulating these metals. After 15 days, 477 mg/kg dry wt. of In was accumulated by the roots; concentrations of Ag, Pb, Cu, Cd, and Zn in the shoots were 326, 1120, 575, 195, and 213 mg/kg dry wt., respectively. The results indicate that E. acicularis has the ability to accumulate these metals from water, making it a good candidate species for phytoremediation and phytomining.

Cd (II) removal from aqueous solution by Eleocharis acicularis biomass, equilibrium and kinetic studies

Batch experiments were carried out to determine the capacity of Eleocharis acicularis biomass to adsorb Cd(2+) ions from contaminated solutions with respect to pH, initial Cd(2+) concentration, contact time, solution ionic strength and biomass dose. The experimental data were modeled by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Freundlich and D-R models resulted in the best fit of the adsorption data. The maximum adsorption capacity for Cd(2+) was 0.299 mmol g(-1) (33.71 mg g(-1)) with efficiency higher than 80% (pH 6.0 and 5 g L(-1) biomass dose). The mean adsorption free energy value derived from the D-R model (8.058 kJ mol(-1)) indicated that adsorption was governed by an ionic exchange process. The pseudo-first order, pseudo-second order, Elovich kinetic models and the intra-particle diffusion models were used to describe the kinetic data and to evaluate rate constants. The best correlation was provided by the second-order kinetic model, implying that chemical sorption was the rate-limiting step, although intra-particle diffusion could not be ignored. The practical implication of this study is the development of an effective and economic technology for Cd(2+) removal from contaminated waters. The macrophyte biomass used in this study did not undergo any chemical or physical pre-treatment, which added to macrophyte abundance and its low cost makes it a good option for Cd(2+) removal from waste water.

Identification of major phenolic compounds of Chinese water chestnut and their antioxidant activity

Chinese water chestnut (CWC) is one of the most popular foods among Asian people due to its special taste and medical function. Experiments were conducted to test the antioxidant activity and then determine the major phenolic compound components present in CWC. CWC phenolic extract strongly inhibited linoleic acid oxidation and exhibited a dose-dependent free-radical scavenging activity against alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radicals, superoxide anions and hydroxyl radicals, which was superior to ascorbic acid and butylated hydroxytoluene (BHT), two commercial used antioxidants. Furthermore, the CWC extract was found to have a relatively higher reducing power, compared with BHT. The major phenolic compounds present in CWC tissues were extracted, purified and identified by high-performance liquid chromatograph (HPLC) as (-)-gallocatechin gallate, (-)-epicatechin gallate and (+)-catechin gallate. This study suggests that CWC tissues exhibit great potential for antioxidant activity and may be useful for their nutritional and medicinal functions.

[Accelerated senescence of fresh-cut Chinese water chestnut tissues in relation to hydrogen peroxide accumulation]

Accelerated senescence of fresh-cut Chinese water chestnut (CWC) tissues in relation to active oxygen species (AOS) metabolism was investigated. Fresh-cut CWC (2 mm thick) and intact CWC were stored at 4 degrees C in trays wrapped with plastic films. Changes in superoxide anion production rate, activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were monitored, while contents of hydrogen peroxide, ascorbic acid, MDA as well as electrolyte leakage were measured. Fresh-cutting of CWC induced activities of SOD, CAT and APX to a certain extent (Fig. 2B and Fig. 3), but simultaneously stimulated superoxide anion production markedly (Fig. 2A), enhanced hydrogen peroxide accumulation and accelerated loss in ascorbic acid (Figs. 4 and 5), which resulted in increased lipid peroxidation indicated by malondialdehyde (MDA) content and electrolyte leakage (Fig. 1). Statistics analysis indicated that there was a significantly positive correlation among hydrogen peroxide accumulation, MDA content and electrolyte leakage (Table 1). Histochemical detection with 3, 3'-diaminobenzidine further demonstrated that hydrogen peroxide accumulation increased in fresh-cut CWC during storage (Fig. 5). AOS production rate and activities of SOD, CAT and APX changed little while no obvious hydrogen peroxide accumulation was observed, in intact CWC during storage.

The uptake of uranium by Eleocharis dulcis (Chinese water chestnut) in the Ranger Uranium Mine constructed wetland filter

Eleocharis dulcis has proliferated in a constructed wetland used to treat uranium mine runoff water, where it rapidly accumulates significant quantities of uranium (U) in its roots and relatively little in its stems. We investigated the mechanism of U uptake and accumulation by E. dulcis using field-sampling techniques and microcosm test work. Results from the microcosm trials and outcomes from statistical tests of field sampled macrophyte, water and sediment indicate that the primary source of U for E. dulcis is the water column. Basipetal translocation of U to the plant's roots was indicated by significant correlations between the U content of stems, taproots and rhizomes and XPS detection of U inside root segments. U sequestering from sediment interstitial water by Fe hydroxides on root surfaces was also evident. No basipetal translocation was evident following the 28-day duration of the microcosm experiments, indicating that it is a longer-term process.