How the Ethylene Biosynthesis Pathway of Semi-Halophytes Is Modified with Prolonged Salinity Stress Occurrence?

The mechanism of ethylene (ET)-regulated salinity stress response remains largely unexplained, especially for semi-halophytes and halophytes. Here, we present the results of the multifaceted analysis of the model semi-halophyte Mesembryanthemum crystallinum L. (common ice plant) ET biosynthesis pathway key components' response to prolonged (14 days) salinity stress. Transcriptomic analysis revealed that the expression of 3280 ice plant genes was altered during 14-day long salinity (0.4 M NaCl) stress. A thorough analysis of differentially expressed genes (DEGs) showed that the expression of genes involved in ET biosynthesis and perception (ET receptors), the abscisic acid (ABA) catabolic process, and photosynthetic apparatus was significantly modified with prolonged stressor presence. To some point this result was supported with the expression analysis of the transcript amount (qPCR) of key ET biosynthesis pathway genes, namely ACS6 (1-aminocyclopropane-1-carboxylate synthase) and ACO1 (1-aminocyclopropane-1-carboxylate oxidase) orthologs. However, the pronounced circadian rhythm observed in the expression of both genes in unaffected (control) plants was distorted and an evident downregulation of both orthologs' was induced with prolonged salinity stress. The UPLC-MS analysis of the ET biosynthesis pathway rate-limiting semi-product, namely of 1-aminocyclopropane-1-carboxylic acid (ACC) content, confirmed the results assessed with molecular tools. The circadian rhythm of the ACC production of NaCl-treated semi-halophytes remained largely unaffected by the prolonged salinity stress episode. We speculate that the obtained results represent an image of the steady state established over the past 14 days, while during the first hours of the salinity stress response, the view could be completely different.

Antidiabetic Effect of Fermented Mesembryanthemum crystallinum L. in db/db Mice Involves Regulation of PI3K-Akt Pathway.

Type 2 diabetes (T2D) is a serious health issue with increasing incidences worldwide. However, current medications have limitations due to side effects such as decreased appetite, stomach pain, diarrhea, and extreme tiredness. Here, we report the effect of fermented ice plant (FMC) in the T2M mouse model of db/db mice. FMC showed a greater inhibition of lipid accumulation compared to unfermented ice plant extract. Two-week oral administration with FMC inhibited body weight gain, lowered fasting blood glucose, and improved glucose tolerance. Serum parameters related to T2D including insulin, glycosylated hemoglobin, adiponectin, and cholesterols were improved as well. Histological analysis confirmed the protective effect of FMC on pancreas and liver destruction. FMC treatment significantly increased the expression and phosphorylation of IRS-1, PI3K, and AKT. Additionally, AMP-activated protein kinase phosphorylation and nuclear factor erythroid 2-related factor 2 were also increased in the liver tissues of db/db mice treated with FMC. Overall, our results indicate the anti-diabetic effect of FMC; therefore, we suggest that FMC may be useful as a therapeutic agent for T2D.

A Culturomics-Based Bacterial Synthetic Community for Improving Resilience towards Arsenic and Heavy Metals in the Nutraceutical Plant Mesembryanthemum crystallinum.

Plant-growth-promoting bacteria (PGPB) help plants thrive in polluted environments and increase crops yield using fewer inputs. Therefore, the design of tailored biofertilizers is of the utmost importance. The purpose of this work was to test two different bacterial synthetic communities (SynComs) from the microbiome of Mesembryanthemum crystallinum, a moderate halophyte with cosmetic, pharmaceutical, and nutraceutical applications. The SynComs were composed of specific metal-resistant plant-growth-promoting rhizobacteria and endophytes. In addition, the possibility of modulating the accumulation of nutraceutical substances by the synergetic effect of metal stress and inoculation with selected bacteria was tested. One of the SynComs was isolated on standard tryptone soy agar (TSA), whereas the other was isolated following a culturomics approach. For that, a culture medium based on M. crystallinum biomass, called Mesem Agar (MA), was elaborated. Bacteria of three compartments (rhizosphere soil, root endophytes, and shoot endophytes) were isolated on standard TSA and MA media, stablishing two independent collections. All bacteria were tested for PGP properties, secreted enzymatic activities, and resistance towards As, Cd, Cu, and Zn. The three best bacteria from each collection were selected in order to produce two different consortiums (denominated TSA- and MA-SynComs, respectively), whose effect on plant growth and physiology, metal accumulation, and metabolomics was evaluated. Both SynComs, particularly MA, improved plant growth and physiological parameters under stress by a mixture of As, Cd, Cu, and Zn. Regarding metal accumulation, the concentrations of all metals/metalloids in plant tissues were below the threshold for plant metal toxicity, indicating that this plant is able to thrive in polluted soils when assisted by metal/metalloid-resistant SynComs and could be safely used for pharmaceutical purposes. Initial metabolomics analyses depict changes in plant metabolome upon exposure to metal stress and inoculation, suggesting the possibility of modulating the concentration of high-value metabolites. In addition, the usefulness of both SynComs was tested in a crop plant, namely Medicago sativa (alfalfa). The results demonstrate the effectiveness of these biofertilizers in alfalfa, improving plant growth, physiology, and metal accumulation.

High-quality ice plant reference genome analysis provides insights into genome evolution and allows exploration of genes involved in the transition from C3 to CAM pathways.

Ice plant (Mesembryanthemum crystallinum), a member of the Aizoaceae family, is a typical halophyte crop and a model plant for studying the mechanism of transition from C3 photosynthesis to crassulacean acid metabolism (CAM). Here, we report a high-quality chromosome-level ice plant genome sequence. This 98.05% genome sequence is anchored to nine chromosomes, with a total length of 377.97 Mb and an N50 scaffold of 40.45 Mb. Almost half of the genome (48.04%) is composed of repetitive sequences, and 24 234 genes have been annotated. Subsequent to the ancient whole-genome triplication (WGT) that occurred in eudicots, there has been no recent whole-genome duplication (WGD) or WGT in ice plants. However, we detected a novel WGT event that occurred in the same order in Simmondsia chinensis, which was previously overlooked. Our findings revealed that ice plants have undergone chromosome rearrangements and gene removal during evolution. Combined with transcriptome and comparative genomic data and expression verification, we identified several key genes involved in the CAM pathway and constructed a comprehensive network. As the first genome of the Aizoaceae family to be released, this report will provide a rich data resource for comparative and functional genomic studies of Aizoaceae, especially for studies on salt tolerance and C3-to-CAM transitions to improve crop yield and resistance.

Functional responses to climate change may increase invasive potential of Carpobrotus edulis.

PREMISE: Biological invasions and climate change are major threats to biodiversity. It is therefore important to anticipate how the climate changes projected for Southern Europe would affect the ecophysiological performance of the invasive South African plant, Carpobrotus edulis (ice plant or sour fig), and its capacity to undergo rapid adaptive evolution. METHODS: We manipulated the climate conditions in a field plot located on the island of Sálvora (northwest of the Iberian Peninsula) to establish a full factorial experiment with C. edulis plants transplanted from four native (southern African) and four invasive (northwestern Iberian Peninsula) populations. Throughout 14 months we measured growth and functional traits of this species under two temperatures (control vs. increased), and two rainfall levels (control vs. reduced). RESULTS: Temperature increased photochemical efficiency and relative growth rate of C. edulis. Rainfall modulated some of the effects of temperature on C and N isotopic composition, and pigment contents. Invasive populations showed lower root mass allocation and higher survival rates, as well as increased water use efficiency, lipid peroxidation, chlorophyll, and xanthophyll cycle pigment contents than native populations. CONCLUSIONS: The increased growth and physiological performances observed under our experimental conditions suggest that the expected climate changes would further promote the invasion of C. edulis. Differences between native and invasive genotypes in survival and functional traits revealed that populations have diverged during the process of invasion, what gives support to the invasiveness hypothesis. Our findings highlight the importance of analyzing intraspecific variability in functional responses to better predict how invasive species will respond to environmental changes.

At the Edges of Photosynthetic Metabolic Plasticity-On the Rapidity and Extent of Changes Accompanying Salinity Stress-Induced CAM Photosynthesis Withdrawal.

The common ice plant (Mesembryanthemum crystallinum L.) is a facultative crassulacean acid metabolism (CAM) plant, and its ability to recover from stress-induced CAM has been confirmed. We analysed the photosynthetic metabolism of this plant during the 72-h response period following salinity stress removal from three perspectives. In plants under salinity stress (CAM) we found a decline of the quantum efficiencies of PSII (Y(II)) and PSI (Y(I)) by 17% and 15%, respectively, and an increase in nonphotochemical quenching (NPQ) by almost 25% in comparison to untreated control. However, 48 h after salinity stress removal, the PSII and PSI efficiencies, specifically Y(II) and Y(I), elevated nonphotochemical quenching (NPQ) and donor side limitation of PSI (YND), were restored to the level observed in control (C3 plants). Swelling of the thylakoid membranes, as well as changes in starch grain quantity and size, have been found to be components of the salinity stress response in CAM plants. Salinity stress induced an over 3-fold increase in average starch area and over 50% decline of average seed number in comparison to untreated control. However, in plants withdrawn from salinity stress, during the first 24 h of recovery, we observed chloroplast ultrastructures closely resembling those found in intact (control) ice plants. Rapid changes in photosystem functionality and chloroplast ultrastructure were accompanied by the induction of the expression (within 24 h) of structural genes related to the PSI and PSII reaction centres, including PSAA, PSAB, PSBA (D1), PSBD (D2) and cp43. Our findings describe one of the most flexible photosynthetic metabolic pathways among facultative CAM plants and reveal the extent of the plasticity of the photosynthetic metabolism and related structures in the common ice plant.

Molecular changes in Mesembryanthemum crystallinum guard cells underlying the C3 to CAM transition.

ABSTARCT: KEY MESSAGE: The timing and transcriptomic changes during the C3 to CAM transition of common ice plant support the notion that guard cells themselves can shift from C3 to CAM. Crassulacean acid metabolism (CAM) is a specialized type of photosynthesis: stomata close during the day, enhancing water conservation, and open at night, allowing CO2 uptake. Mesembryanthemum crystallinum (common ice plant) is a facultative CAM species that can shift from C3 photosynthesis to CAM under salt or drought stresses. However, the molecular mechanisms underlying the stress induced transition from C3 to CAM remain unknown. Here we determined the transition time from C3 to CAM in M. crystallinum under salt stress. In parallel, single-cell-type transcriptomic profiling by 3'-mRNA sequencing was conducted in isolated stomatal guard cells to determine the molecular changes in this key cell type during the transition. In total, 495 transcripts showed differential expression between control and salt-treated samples during the transition, including 285 known guard cell genes, seven CAM-related genes, 18 transcription factors, and 185 other genes previously not found to be expressed in guard cells. PEPC1 and PPCK1, which encode key enzymes of CAM photosynthesis, were up-regulated in guard cells after seven days of salt treatment, indicating that guard cells themselves can shift from C3 to CAM. This study provides important information towards introducing CAM stomatal behavior into C3 crops to enhance water use efficiency.

Development and evaluation of novel salt-tolerant Eucalyptus trees by molecular breeding using an RNA-Binding-Protein gene derived from common ice plant (Mesembryanthemum crystallinum L.).

The breeding of plantation forestry trees for the possible afforestation of marginal land would be one approach to addressing global warming issues. Here, we developed novel transgenic Eucalyptus trees (Eucalyptus camaldulensis Dehnh.) harbouring an RNA-Binding-Protein (McRBP) gene derived from a halophyte plant, common ice plant (Mesembryanthemum crystallinum L.). We conducted screened-house trials of the transgenic Eucalyptus using two different stringency salinity stress conditions to evaluate the plants' acute and chronic salt stress tolerances. Treatment with 400 mM NaCl, as the high-stringency salinity stress, resulted in soil electrical conductivity (EC) levels >20 mS/cm within 4 weeks. With the 400 mM NaCl treatment, >70% of the transgenic plants were intact, whereas >40% of the non-transgenic plants were withered. Treatment with 70 mM NaCl, as the moderate-stringency salinity stress, resulted in soil EC levels of approx. 9 mS/cm after 2 months, and these salinity levels were maintained for the next 4 months. All plants regardless of transgenic or non-transgenic status survived the 70 mM NaCl treatment, but after 6-month treatment the transgenic plants showed significantly higher growth and quantum yield of photosynthesis levels compared to the non-transgenic plants. In addition, the salt accumulation in the leaves of the transgenic plants was 30% lower than that of non-transgenic plants after 15-week moderate salt stress treatment. There results suggest that McRBP expression in the transgenic Eucalyptus enhances their salt tolerance both acutely and chronically.

Simultaneous chloroplast, mitochondria isolation and mitochondrial protein preparation for two-dimensional electrophoresis analysis of Ice plant leaves under well watered and water-deficit stressed treatments.

This paper presents a simultaneous isolation of pure, intact chloroplasts and mitochondria from mature leaves of Ice plant (Mesembryanthemum crystallinum) and mitochondrial protein preparation for two-dimensional electrophoresis (2DE) analysis under well watered and water -deficit stressed treatments. The washed chloroplasts and mitochondria were purified with Percoll gradients prepared using a Master flex R pump. The chloroplast and mitochondrial proteins were extracted in lysis buffer containing a protease inhibitor mix supplemented with 1 µM Leupeptin and 1 µM E64, followed by precipitation with ice-cold acetone. The protein contents were determined by an EZQ protein quantitation kit. The results show that chloroplast and mitochondria isolated from Ice plant leaves via this protocol have pure and intact. The shape of chloroplast and mitochondria observed by microscopy were clear and sharp. This procedure was employed for assessing the significant differences in mitochondrial protein expression patterns from the well watered and water-deficit stressed treatment leaves collected at dawn (6 a.m.) and dusk (6 p.m.). The results showed 71 and 20 differentially abundant spots between control and CAM for 6 a.m. and 6 p.m., respectively. In addition, 32 protein spots were differentially abundant for 6 a.m. control compared with 6 p.m. control, and 45 protein spots were differentially abundant for 6 a.m. CAM compared with 6 p.m. CAM. Spots that displayed differential abundance for control compared with CAM likely included proteins involved in mitochondrial processes necessary for CAM function. Through further analysis, these proteins will be identified and characterized in the near future using mass-spectrometry-based techniques.

Ecophysiological differentiation between two invasive species of Carpobrotus competing under different nutrient conditions.

PREMISE: Hybridization between the South African invasive species Carpobrotus edulis and C. acinaciformis in Europe has led to the formation of highly aggressive morphotypes referred to in the scientific literature as the new large "hybrid swarm" C. aff. acinaciformis. In the present study, we aimed to determine whether the taxonomic differentiation between taxa coincides with ecophysiological differentiation. With this aim, we tested for differences between both morphotypes in functional traits related to competitive ability and resource-use efficiency. Assuming that the complex hybrid C. aff. acinaciformis is more vigorous, depends more strongly on vegetative reproduction, and invests less in sexual reproduction than C. edulis, we predicted that the hybrid would show higher competitive ability and better physiological performance compared with the species. METHODS: We used a comparative ecophysiological approach to assess the extent to which two Carpobrotus morphotypes coexisting in northwestern Spain differ in physiological, reproductive, and growth traits when competing under different soil nutrients in controlled greenhouse conditions. RESULTS: C. aff. acinaciformis had a greater relative growth rate and water-use and photochemical efficiencies compared to C. edulis. However, C. edulis appeared to be more responsive to incremental change in soil nutrients than C. aff. acinaciformis. They also differed in the amount of resources invested in reproduction. CONCLUSIONS: The study findings demonstrate that the taxonomic differentiation between taxa corresponds to ecophysiological differentiation, warranting a detailed examination of all existing trades-offs to predict the long-term outcomes of the interaction between these taxa.

Functional analysis of McSnRK1 (SNF1-related protein kinase 1) in regulating Na/K homeostasis in transgenic cultured cells and roots of halophyte Mesembryanthemum crystallinum.

KEY MESSAGE: Transgenic callus and roots of ice plant with altered SnRK1 function were established using Agrobacterium-mediated transformation. The role of McSnRK1 in controlling Na+ influx and Na/K ratio was demonstrated. SnRK1 kinases (SNF1-related protein kinase1) control metabolic adaptation during energy deprivation and regulate protective mechanisms against environmental stress. Yeast SNF1 activates a P-type ATPase, the Na+ exclusion pump, under glucose starvation. The involvement of plant SnRK1 in salt stress response is largely unknown. We previously identified a salt-induced McSnRK1 in the halophyte ice plant (Mesembryanthemum crystallinum). In the current study, the function of McSnRK1 in salt tolerance was analyzed in transgenic cultured cells and roots of ice plant. Ice plant callus constitutively expressed a high level of McSnRK1 and introducing the full-length McSnRK1 did not alter the Na/K ratio at 24 h after 200 mM NaCl treatment. However, interfering with McSnRK1 activity by introducing a truncate McSnRK1 to produce a dominant-negative form of McSnRK1 increased cellular Na+ accumulation and Na/K ratio. As a result, the growth of cultured cells diminished under salt treatment. Hydroponically grown ice plants with roots expressing full-length McSnRK1 had better growth and lowered Na/K ratio compared to the wild-type or vector-only plants. Roots expressing a truncate McSnRK1 had reduced growth and high Na/K ratio under 400 mM NaCl treatment. The changes in Na/K ratio in transgenic cells and whole plants demonstrated the function of SnRK1 in controlling Na+ flux and maintaining Na/K homeostasis under salinity. The Agrobacterium-mediated transformation system could be a versatile tool for functional analysis of genes involved in salt tolerance in the ice plant.

Ice plant (Mesembryanthemum crystallinum) improves hyperglycaemia and memory impairments in a Wistar rat model of streptozotocin-induced diabetes.

BACKGROUND: Ice plant (Mesembryanthemum crystallinum) has been used as an anti-diabetic agent in Japan because it contains d-pinitol. The efficacy of ice plant in the regulation of blood glucose is unclear at present. Recently, memory impairment and development of Alzheimer's disease found in diabetic patients are thought to be caused by high blood glucose. The mechanism by which ice plant protects against the impairment of memory and learning abilities caused by high blood glucose remains unclear. The aim of this study was to evaluate the protection of ice plant water extracts (IPE) and D-pinitol against memory impairments in a Wistar rat model of streptozotocin (STZ)-induced diabetes. We hypothesised that IPE and D-pinitol could suppress blood glucose and elevate insulin sensitivity in these rats. RESULTS: For memory evaluation, IPE and D-pinitol also improved the passive avoidance task and the working memory task. In addition, inhibition of acetylcholinesterase activity in hippocampus and cortex was found in this rat model administered IPE or D-pinitol. IPE and D-pinitol also markedly elevated superoxide dismutase activity against oxidative stress and reduced malondialdehyde production in hippocampus and cortex of the rats. CONCLUSION: These findings indicated that IPE and D-pinitol possess beneficial effects for neural protection and memory ability in a rat model of diabetes.

Nutrients and phytochemical density in Mesembryanthemum crystallinum L. cultivated in growing media supplemented with dosages of nitrogen fertilizer.

Mesembryanthemum crystallinum L. is an annual halophyte that originated from southern Africa. However, little has been reported about factors that modulate the quantity of secondary metabolites in the plant. In this study, the twin effect of different nitrogen concentrations (0.36, 0.6, 0.8 g/L) and growing media (LECA clay, peat, vermiculite and silica sand) on plant growth, chlorophyll contents, minerals, proximate and antioxidant metabolites in hydroponically cultivated M. crystallinum was investigated. This is important to determine the dosage of N fertilizer that will optimize the bio-productivity and biosynthesis of secondary metabolites and antioxidants in M. crystallinum grown in a hydroponic system. The untreated plant (0 g/L N) was taken as the control. At the end of the experiment, optimum yields in leaf number (9.2), fresh weight (50.40 g), Ca, N, and Protein (34.04 %) were recorded in M. crystallinum grown with peat enhanced with different dosages of N-fertilizer. Likewise, chlorophyll level, dry weight, ABTS/TEAC, FRAP, ADF and NDF contents were optimized in LECA clay treated with N-fertilizer. Silica sand with 0.36 g/L dosage of nitrogen fertilizer optimized P, Mn and Zn levels, so also the moisture (9.83 % at 0.8 g/L N), fat (2.38 %, 0 g/L N) and carbohydrates (44.98 and 44.95 %). The highest ash content, Mg and Fe were recorded in the untreated vermiculite as well as polyphenols and K, at 0.6 g/L; Cu and root length (14.60 cm), at 0.8 g/L. In conclusion, different dosages of nitrogen fertilizer and growing media could enhance the growth potential, chlorophyll, phytochemicals, and nutritional properties of M. crystallinum.

Nanoparticle Effects on Ice Plant Mineral Accumulation under Different Lighting Conditions and Assessment of Hazard Quotients for Human Health.

Nanotechnologies can improve plant growth, protect it from pathogens, and enrich it with bioactive and mineral substances. In order to fill the lack of knowledge about the combined environmental effects of lighting and nanoparticles (NPs) on plants, this study is designed to investigate how different HPS and LED lighting combined with CuO and ZnO NPs influence the elemental composition of ice plants (Mesembryanthemum crystallinum L.). Plants were grown in hydroponic systems with LED and HPS lighting at 250 ± 5 µmol m-2 s-1 intensity, sprayed with aqueous suspensions of CuO (40 nm, 30 ppm) and ZnO (35-45 nm, 800 ppm) NPs; their elemental composition was measured using an ICP-OES spectrometer and hazard quotients were calculated. LED lighting combined with the application of ZnO NPs significantly affected Zn accumulation in plant leaves. Cu accumulation was higher when plants were treated with CuO NPs and HPS illumination combined. The calculated hazard quotients showed that the limits are not exceeded when applying our selected concentrations and growth conditions on ice plants. In conclusion, ice plants had a more significant positive effect on the accumulation of macro- and microelements under LED lighting than HPS. NPs had the strongest effect on the increase in their respective microelements.

Optimization of Nutrient-Rich Ice Plant (Mesembryanthemum crystallinum L.) Paste Fresh Noodle Pasta Using Response Surface Methodology.

The ice plant is a species that is grown mainly in the dry regions of the American West and contains various minerals and ingredients beneficial for human health, such as inositol and beta-carotene. With the growing trend towards healthy foods, pasta consumption has also increased. Pasta is a convenient and low-glycemic-index food that is composed mainly of carbohydrates, proteins, lipids, dietary fiber, and trace amounts of minerals. The optimal mixing ratio was evaluated to produce pasta of the highest quality in terms of blood sugar elevation and antioxidant efficacy. The components and minerals of the ice plant, including D-pinitol and inositol, were analyzed, and 20 essential amino acids were identified. In this study, we also investigated the quality and characteristics of ice plant paste and eggs, as well as the quality, antioxidant activity, and formulation of raw materials mixed with ice plant at different ratios. Optimal conditions were found to be 46.73 g of ice plant paste in 100 g of durum wheat flour, 20.23 g of egg, and 2 g of salt, providing a way to develop fresh pasta that enhances the health benefits of ice plant paste without excessive moisture and other ingredients.

The first released available genome of the common ice plant ( Mesembryanthemum crystallinum L.) extended the research region on salt tolerance, C 3-CAM photosynthetic conversion, and halophilism.

Background: The common ice plant ( Mesembryanthemum crystallinum L.) is an annual herb belonging to the genus Mesembryanthemum of the family Aizoaceae, native to Southern Africa. Methods: We performed shotgun genome paired-end sequencing using the Illumina platform to determine the genome sequence of the ice plants. We assembled the whole genome sequences using the genome assembler "ALGA" and "Redundans", then released them as available genomic information. Finally, we mainly estimated the potential genomic function by the homology search method. Results: A draft genome was generated with a total length of 286 Mb corresponding to 79.2% of the estimated genome size (361 Mb), consisting of 49,782 contigs. It encompassed 93.49% of the genes of terrestrial higher plants, 99.5% of the ice plant transcriptome, and 100% of known DNA sequences. In addition, 110.9 Mb (38.8%) of repetitive sequences and untranslated regions, 971 tRNA, and 100 miRNA loci were identified, and their effects on stress tolerance and photosynthesis were investigated. Molecular phylogenetic analysis based on ribosomal DNA among 26 kinds of plant species revealed genetic similarity between the ice plant and poplar, which have salt tolerance. Overall, 35,702 protein-coding regions were identified in the genome, of which 56.05% to 82.59% were annotated and submitted to domain searches and gene ontology (GO) analyses, which found that eighteen GO terms stood out among five plant species. These terms were related to biological defense, growth, reproduction, transcription, post-transcription, and intermembrane transportation, regarded as one of the fundamental results of using the utilized ice plant genome. Conclusions: The information that we characterized is useful for elucidation of the mechanism of growth promotion under salinity and reversible conversion of the photosynthetic type from C3 to Crassulacean Acid Metabolism (CAM).

Cadmium-Tolerant Rhizospheric Bacteria of the C3/CAM Intermediate Semi-Halophytic Common Ice Plant (Mesembryanthemum crystallinum L.) Grown in Contaminated Soils.

The common ice plant, Mesembryanthemum crystallinum L., has recently been found as a good candidate for phytoremediation of heavy-metal polluted soils. This semi-halophyte is a C3/CAM (Crassulacean acid metabolism) intermediate plant capable of tolerating extreme levels of cadmium in the soil. The aim of the work was to obtain and characterize novel, Cd-tolerant microbial strains that populate the root zone of M. crystallinum performing different types of photosynthetic metabolism and growing in Cd-contaminated substrates. The plants exhibiting either C3 or CAM photosynthesis were treated for 8 days with different CdCl2 doses to obtain final Cd concentrations ranging from 0.82 to 818 mg⋅kg-1 of soil d.w. The CAM phase was induced by highly saline conditions. After treatment, eighteen bacterial and three yeast strains were isolated from the rhizosphere and, after preliminary Cd-resistance in vitro test, five bacterial strains were selected and identified with a molecular proteomics technique. Two strains of the species Providencia rettgeri (W6 and W7) were obtained from the C3 phase and three (one Paenibacillus glucanolyticus S7 and two Rhodococcus erythropolis strains: S4 and S10) from the CAM performing plants. The isolates were further tested for Cd-resistance (treatment with either 1 mM or 10 mM CdCl2) and salinity tolerance (0.5 M NaCl) in model liquid cultures (incubation for 14 days). Providencia rettgeri W7 culture remained fully viable at 1 mM Cd, whereas Rh. erythropolis S4 and S10 together with P. glucanolyticus S7 were found to be resistant to 10 mM Cd in the presence of 0.5 M NaCl. It is suggested that the high tolerance of the common ice plant toward cadmium may result from the synergic action of the plant together with the Cd/salt-resistant strains occurring within rhizospheral microbiota. Moreover, the isolated bacteria appear as promising robust microorganisms for biotechnological applications in bio- and phytoremediation projects.

Antioxidant, Antihypertensive, Hypoglycaemic and Nootropic Activity of a Polyphenolic Extract from the Halophyte Ice Plant (Mesembryanthemum crystallinum).

This study aims to determine the potential antioxidant, antihypertensive, hypoglycaemic and nootropic activity of a purified polyphenolic extract from the halophyte ice plant (Mesembryanthemum crystallinum). The ice plant extract showed good antioxidant activity measured by DPPH, ORAC, TEAC, FRAP and ferrous ion chelating activity. Moreover, the extract showed potent ACE, DPP-IV and PEP-inhibitory activity (90.5%, 98.6% and 73.1%, respectively, at a final concentration of 1 mg/mL). The extract was fractionated and the fraction with the highest content of total phenolic compounds showed the highest bioactivity, suggesting that polyphenols could be mainly responsible for the abovementioned activities. The tentative polyphenol identification by HPLC-ESI-QTOF-MS in this fraction revealed that flavones (>65%) are the major group, with apigenin (38%) predominating, followed by diosmin (17.7%) and luteolin (11.9%). They could presumably be the main elements responsible for the enzymatic inhibition activity. Additionally, 4-hydroxybenzoic acid, p-coumaric acid and a hydroxycinnamic acid derivative (2-O-(p-cumaroyl)-l-malic acid) were found in the extract. To our knowledge, this is the first time that some of these activities have been reported for halophyte extracts.

Epigenetic and Phenotypic Responses to Experimental Climate Change of Native and Invasive Carpobrotus edulis.

Despite the recent discoveries on how DNA methylation could help plants to adapt to changing environments, the relationship between epigenetics and climate change or invasion in new areas is still poorly known. Here, we investigated, through a field experiment, how the new expected climate scenarios for Southern Europe, i.e., increased temperature and decreased rainfall, might affect global DNA methylation in relation to phenotypic variation in individuals of clonal plant, Carpobrotus edulis, from its native (Southern African) and invaded (northwestern Iberian Peninsula) area. Our results showed that changes in temperature and rainfall induced phenotypic but not global DNA methylation differences among plants, and the climatic effects were similar for plants coming from the native or invaded areas. The individuals from the Iberian Peninsula showed higher levels of global methylation than their native counterparts from South Africa. We also observed differences between natives and invasive phenotypes in traits related to the pattern of biomass partitioning and to the strategies for water uptake and use and found an epigenetic contribution to phenotypic changes in some leaf traits, especially on the nitrogen isotopic composition. We conclude that the increased temperature and decreased rainfall projected for Southern Europe during the course of the twenty-first century may foster phenotypic changes in C. edulis, possibly endowing this species with a higher ability to successful cope the rapid environmental shifts. The epigenetic and phenotypic divergence that we observed between native and invasive plants suggests an intraspecific functional variation during the process of invasion. This result could indicate that phenotypic plasticity and global DNA methylation are related to the colonization of new habitats. Our findings reinforce the importance of epigenetic plasticity on rapid adaptation of invasive clonal plants.

Sensory Evaluation of Common Ice Plant (Mesembryanthemum crystallinum L.) in Response to Sodium Chloride Concentration in Hydroponic Nutrient Solution.

Common ice plant (Mesembryanthemum crystallinum L.) is a novel edible plant with a succulent and savory flavor. The plants display prominent epidermal bladder cells (EBCs) on the surface of the leaves that store water and sodium chloride (NaCl). The plants have high nutritional value and are adapted to saline soils. Previous research has determined the impact of NaCl on the growth and mineral content of ice plant, but as NaCl has an impact on a food's sensory properties, an interesting question is whether saline growth media can affect the plant's taste and texture, and if this alters consumers' sensory response to ice plant. The objective of this study was to evaluate the sensory aspects of ice plant, as well as consumer liking in response to increasing NaCl concentration in hydroponic nutrient solution. Four-week-old seedlings of ice plant were transplanted into deep water culture (DWC) hydroponic systems and treated with five NaCl concentrations (0 M [control], 0.05 M, 0.10 M, 0.20 M, and 0.40 M NaCl). Eight-week-old plants (after four weeks of NaCl treatment) were harvested, and the middle leaves of each plant were sampled for consumer testing. A total of 115 participants evaluated various flavor, texture, and appearance aspects of ice plant and provided their liking ratings. The consumers were able to discriminate differences in salt intensity from the plants based on NaCl treatment in the hydroponic nutrient solution. Low NaCl concentrations (0.05-0.10 M) did not have obvious adverse effect on consumer liking, which aligns with the result of previous research that 0.05-0.10 M NaCl could largely stimulate the growth of ice plant. NaCl concentrations higher than 0.20 M are not recommended from both a production and consumer perspective. With increased NaCl level in plant samples, the consumers detected more saltiness, sourness, and fishiness, less green flavor, and similar levels of bitterness and sweetness. NaCl treatment had no effects on leaf appearance and texture, and the consumers' overall liking was mainly determined by flavor. Overall, ice plant presents some unique attributes (salty and juicy) compared to other edible salad greens; however, consumer awareness of ice plant is very low, and purchase intent is relatively low as well. Consumers picture ice plant being used mainly in salads and in restaurants.