Insight into mechanisms of multiple stresses tolerance in a halophyte Aster tripolium subjected to salinity and heavy metal stress

Inhibition of microelement accumulation and disorder of saccharide and amino acid metabolism explain rice grain empty under dimethylarsinic acid stress

KEY MESSAGE

Metabolomic and transcriptomic analyses revealed an intensification of energy metabolism in rice grains under DMA stress, possibly causing the consumption of sugars or non-sugars and the development of unfilled grains Excessive dimethylarsinic acid (DMA) causes rice straighthead disease, a physiological disorder typically with erect panicle due to empty grain at maturity. Although the toxicity of DMA and its uptake and transport in rice are well recognized, the underlying mechanism of unfilled grains remains unclear. Therefore, a pot experiment was conducted using a susceptible variety (Ruanhuayou1179, RHY) and a resistant one (Nanjingxiangzhan, NJXZ) via the metabolomic and transcriptomic approaches to explore the mechanisms of empty grains in diseased rice under DMA stress. The results demonstrate an increase in total and methylated As in grains of RHY and NJXZ under DMA addition, with RHY containing higher levels of DMA. DMA addition increased the soluble sugar content in grains of RHY and NJXZ by 17.1% and 14.3% compared to the control, respectively, but significantly reduced the levels of amino acid, soluble protein, and starch. The decrease of grain Zn and B contents was also observed, and inadequate Zn might be a key factor limiting rice grain yield under DMA stress. Notably, DMA addition altered the expression levels of genes involved in the transport of sugar, amino acids, nitrates/peptides, and mineral ions. In sugar and amino acid metabolism, the reduction of metabolites and the upregulated expression of genes reflect positive regulation at the level of energy metabolism, implying that the reduction of grain starch and proteins might be ascribed to generate sufficient energy to resist the stress. This study provides a useful reference for understanding the molecular mechanism of grain emptying under DMA stress.

Sulfur-Oxidizing Bacteria Alleviate Salt and Cadmium Stress in Halophyte Tripolium pannonicum (Jacq.) Dobrocz

The aim of this study was to investigate how introducing halophilic sulfur-oxidizing bacteria (SOB) Halothiobacillus halophilus to the growth substrate affects the physiological and biochemical responses of the halophyte Tripolium pannonicum (also known as sea aster or seashore aster) under salt and cadmium stress conditions. This study assessed the plant's response to these stressors and bacterial inoculation by analyzing various factors including the accumulation of elements such as sodium (Na), chloride (Cl), cadmium (Cd) and sulfur (S); growth parameters; levels of photosynthetic pigments, proline and phenolic compounds; the formation of malondialdehyde (MDA); and the plant's potential to scavenge 2,2-Diphenyl-1-picrylhydrazyl (DPPH). The results revealed that bacterial inoculation was effective in mitigating the deleterious effect of cadmium stress on some growth criteria. For instance, stem length was 2-hold higher, the growth tolerance index was 3-fold higher and there was a 20% increase in the content of photosynthetic pigments compared to non-inoculated plants. Furthermore, the SOB contributed to enhancing cadmium tolerance in Tripolium pannonicum by increasing the availability of sulfur in the plant's leaves, which led to the maintenance of an appropriate, about 2-fold-higher level of phenolic compounds (phenylpropanoids and flavonols), as well as chloride ions. The level of MDA decreased after bacterial application in all experimental variants except when both salt and cadmium stress were present. These findings provide novel insights into how halophytes respond to abiotic stress following inoculation of the growth medium with sulfur-oxidizing bacteria. The data suggest that inoculating the substrate with SOB has a beneficial effect on T. pannonicum's tolerance to cadmium stress.

Can plant hormonomics be built on simple analysis? A review

The field of plant hormonomics focuses on the qualitative and quantitative analysis of the hormone complement in plant samples, akin to other omics sciences. Plant hormones, alongside primary and secondary metabolites, govern vital processes throughout a plant's lifecycle. While active hormones have received significant attention, studying all related compounds provides valuable insights into internal processes. Conventional single-class plant hormone analysis employs thorough sample purification, short analysis and triple quadrupole tandem mass spectrometry. Conversely, comprehensive hormonomics analysis necessitates minimal purification, robust and efficient separation and better-performing mass spectrometry instruments. This review summarizes the current status of plant hormone analysis methods, focusing on sample preparation, advances in chromatographic separation and mass spectrometric detection, including a discussion on internal standard selection and the potential of derivatization. Moreover, current approaches for assessing the spatiotemporal distribution are evaluated. The review touches on the legitimacy of the term plant hormonomics by exploring the current status of methods and outlining possible future trends.

Nutrient Metabolism Pathways Analysis and Key Candidate Genes Identification Corresponding to Cadmium Stress in Buckwheat through Multiomics Analysis

Fagopylum tatarium (L.) Gaertn (buckwheat) can be used both as medicine and food and is also an important food crop in barren areas and has great economic value. Exploring the molecular mechanisms of the response to cadmium (Cd) stress can provide the theoretical reference for improving the buckwheat yield and quality. In this study, perennial tartary buckwheat DK19 was used as the experimental material, its key metabolic pathways in the response to Cd stress were identified and verified through transcriptomic and metabolomic data analysis. In this investigation, 1798 metabolites were identified through non-targeted metabolomic analysis containing 1091 up-regulated and 984down-regulated metabolites after treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differential metabolites was significantly enriched in galactose metabolism, glycerol metabolism, phenylpropane biosynthesis, glutathione metabolism, starch and sucrose metabolism. Linkage analysis detected 11 differentially expressed genes (DEGs) in the galactose metabolism pathway, 8 candidate DEGs in the lipid metabolism pathway, and 20 candidate DEGs in the glutathione metabolism pathway. The results of our study provided useful clues for genetically improving the resistance to cadmium by analyzing the molecular mechanism of cadmium tolerance in buckwheat.

Harnessing the Value of Tripolium pannonicum and Crithmum maritimum Halophyte Biomass through Integrated Green Biorefinery

Bioactive extracts are often the target fractions in bioprospecting, and halophyte plants could provide a potential source of feedstock for high-value applications as a part of integrated biorefineries. Tripolium pannonicum (Jacq.) Dobrocz. (sea aster) and Crithmum maritimum L. (sea fennel) are edible plants suggested for biosaline halophyte-based agriculture. After food production and harvesting of fresh leaves for food, the inedible plant fractions could be utilized to produce extracts rich in bioactive phytochemicals to maximize feedstock application and increase the economic feasibility of biomass processing to bioenergy. This study analyzed fresh juice and extracts from screw-pressed sea aster and sea fennel for their different phenolic compounds and pigment concentrations. Antioxidant and enzyme inhibition activities were also tested in vitro. Extracts from sea aster and sea fennel had phenolic contents up to 45.2 mgGAE/gDM and 64.7 mgGAE/gDM, respectively, and exhibited >70% antioxidant activity in several assays. Ethanol extracts also showed >70% inhibition activity against acetylcholinesterase and >50% inhibition of tyrosinase and α-glucosidase. Therefore, these species can be seen as potential feedstocks for further investigations.

Halophytic Clonal Plant Species: Important Functional Aspects for Existence in Heterogeneous Saline Habitats

Plant modularity-related traits are important ecological determinants of vegetation composition, dynamics, and resilience. While simple changes in plant biomass resulting from salt treatments are usually considered a sufficient indicator for resistance vs. susceptibility to salinity, plants with a clonal growth pattern show complex responses to changes in environmental conditions. Due to physiological integration, clonal plants often have adaptive advantages in highly heterogeneous or disturbed habitats. Although halophytes native to various heterogeneous habitats have been extensively studied, no special attention has been paid to the peculiarities of salt tolerance mechanisms of clonal halophytes. Therefore, the aim of the present review is to identify probable and possible halophytic plant species belonging to different types of clonal growth and to analyze available scientific information on responses to salinity in these species. Examples, including halophytes with different types of clonal growth, will be analyzed, such as based on differences in the degree of physiological integration, ramet persistence, rate of clonal expansion, salinity-induced clonality, etc.

Assessment of Shoot Priming Efficiency to Counteract Complex Metal Stress in Halotolerant Lobularia maritima

The study investigated whether short-term priming supports plant defense against complex metal stress and multiple stress (metals and salinity) in halophyte Lobularia maritima (L.) Desv. Plants were pre-treated with ectoine (Ect), nitric oxide donor-sodium nitroprusside (SNP), or hydrogen sulfide donor-GYY4137 for 7 days, and were transferred onto medium containing a mixture of metal ions: Zn, Pb, and Cd. To test the effect of priming agents in multiple stress conditions, shoots were also subjected to low salinity (20 mM NaCl), applied alone, or combined with metals. Hydropriming was a control priming treatment. Stress impact was evaluated on a basis of growth parameters, whereas defense responses were on a basis of the detoxification activity of glutathione S-transferase (GST), radical scavenging activity, and accumulation of thiols and phenolic compounds. Exposure to metals reduced shoot biomass and height but had no impact on the formation of new shoots. Priming with nitric oxide annihilated the toxic effects of metals. It was related to a sharp increase in GST activity, glutathione accumulation, and boosted radical scavenging activity. In NO-treated shoots level of total phenolic compounds (TPC) and flavonoids remained unaffected, in contrast to other metal-treated shoots. Under combined metal stress and salinity, NO and H₂S were capable of restoring or improving growth parameters, as they stimulated radical scavenging activity. Ect and H₂S did not exert any effect on metal-treated shoots in comparison to hydropriming. The results revealed the stimulatory role of nitric oxide and low doses of NaCl in combating the toxic effects of complex metal stress in L. maritima. Both NO and NaCl interfered with thiol metabolism and antioxidant activity, whereas NaCl also contributed to the accumulation of phenolic compounds.

Water Content of Plant Tissues: So Simple That Almost Forgotten?

The aim of the present review was to reconsider basic information about various functional aspects related to plant water content and provide evidence that the usefulness of measuring absolute water content in plant sciences is undervalued. First, general questions about water status in plants as well as methods for determining water content and their associated problems were discussed. After a brief overview of the structural organization of water in plant tissues, attention was paid to the water content of different parts of plants. Looking at the influence of environmental factors on plant water status, the differences caused by air humidity, mineral supply, biotic effects, salinity, and specific life forms (clonal and succulent plants) were analyzed. Finally, it was concluded that the expression of absolute water content on a dry biomass basis makes easily noticeable functional sense, but the physiological meaning and ecological significance of the drastic differences in plant water content need to be further elucidated.

Halophytes for the sustainable remediation of heavy metal-contaminated sites: Recent developments and future perspectives

Increasing land degradation by high level of metal wastes is of prime concern for the global research communities. In this respect, halophytes having specific features like salt glands, exclusion of excess ions, heavy metals (HMs) compartmentalization, large pool of antioxidants, and associations with metal-tolerant microbes are of great promise in the sustainable clean-up of contaminated sites. However, sustainable clean-up of HMs by a particular halophyte plant species is governed considerably by physico-chemical characteristics of soil and associated microbial communities. The present review has shed light on the superiority of halophytes over non-halophytes, mechanisms of metal-remediation, recent developments and future perspectives pertaining to the utilization of halophytes in management of HM-contaminated sites with the aid of bibliometric analysis. The results revealed that the research field is receiving considerable attention in the last 5-10 years by publishing ∼50-90% documents with an annual growth rate of 15.41% and citations per document of 29.72. Asian (viz., China, India, and Pakistan) and European (viz., Spain, Portugal, Belgium, Argentina) countries have been emerged as the major regions conducting and publishing extensive research on this topic. The investigations conducted both under in vitro and field conditions have reflected the inherent potential of halophyte as sustainable research tool for successfully restoring the HM-contaminated sites. The findings revealed that the microbial association with halophytes under different challenging conditions is a win-win approach for metal remediation. Therefore, exploration of new halophyte species and associated microorganisms (endophytic and rhizospheric) from different geographical locations, and identification of genes conferring tolerance and phytoremediation of metal contaminants would further advance the intervention of halophytes for sustainable ecological restoration.

Cultivation and characterisation of Salicornia europaea, Tripolium pannonicum and Crithmum maritimum biomass for green biorefinery applications

Salt-tolerant halophytes have shown potential for biorefinery and agricultural use in salt-affected soils, increasing the value of marginal lands. They could provide a bio-based source for compounds obtained from the petrochemical industry or an alternative for biomass currently imported overseas. Salicornia europaea, Tripolium pannonicum and Crithmum maritimum were cultivated in hydroponic systems under various salinity conditions, harvested green but not food-grade, and fractionated to green juice and fibre residue. Obtained fractions were characterised for contents of carbohydrates, Klason lignin, crude protein, organic acids, lipids, and minerals to evaluate the biomass' suitability for biorefinery. Significant differences were observed in the biomass yield and the composition of the biomass fractions from different cultivation salinities. High concentrations of crude protein were found. Thus, these species could have the potential for green protein production. Fractions rich in carbohydrates could be used for lignocellulose processing and processes utilising micro-organisms.

Cd Phytoextraction Potential in Halophyte Salicornia fruticosa: Salinity Impact

The phytoextraction potential of halophytes has been broadly recognized. Nevertheless, the impact of salt on the accumulation proprieties of cadmium (Cd) in different halophytic species, likely linked to their salt tolerance, remains unclear. A hydroponic culture was used to investigate the impact of salinity on Cd tolerance as well as accumulation in the distinct halophyte Salicornia fruticosa (S. fruticosa). The plant was subjected to 0, 25, and 50 μg L⁻¹ Cd (0-Cd, L-Cd, and H-Cd, respectively), with or without 50, 100, and 200 mM NaCl in the nutrient solution. Data demonstrated that Cd individually induced depletion in biomass accumulation. NaCl amplified the Cd tolerance induced by enhanced biomass gaining and root length, which was associated with adequate transpiration, leaf succulence, elevated levels of ascorbic acid (ASA), reduced glutathione (GSH), phytochelatins (PCs), and proline as well as antioxidant enzymatic capacity via upregulation of peroxidases (PO), glutathione peroxidase, ascorbate peroxidase, and superoxide dismutase. All Cd treatments decreased the uptake of calcium (Ca) as well as potassium (K) and transport to the shoots; however, sodium (Na) accumulation in the shoots was not influenced by Cd. Consequently, S. fruticosa retained its halophytic properties. Based on the low transfer efficiency and high enrichment coefficient at 0–50 mM NaCl, an examination of Cd accumulation characteristics revealed that phytostabilization was the selected phytoremediation strategy. At 100–200 mM NaCl, the high aboveground Cd-translocation and high absorption efficiency encourage phytoremediation via phytoextraction. The results revealed that S. fruticosa might be also potentially utilized to renovate saline soils tainted with heavy metals (HMs) because of its maximized capacity for Cd tolerance magnified by NaCl. Cd accumulation in S. fruticosa is mainly depending on the NaCl concentration. Future studies may be established for other heavy metal pollutants screening, to detect which could be extracted and/or stabilized by the S. fruticosa plant; moreover, other substrates presenting high electrical conductivity should be identified for reclamation.

Abscisic acid-catabolizing bacteria: A useful tool for enhancing phytoremediation

Bacteria-facilitated phytoextraction has been gaining recognition for the phytoremediation of heavy metal (HM)-contaminated soils. Nevertheless, it remains unclear whether catabolizing abscisic acid (ABA) in hyperaccumulating plants via rhizobacteria could facilitate HM phytoextraction. In this study, inoculation with the ABA-catabolizing bacterium, Rhodococcus qingshengii, increased HM (Cd, Zn, Pb, and Cu) concentrations in the shoots of hyperaccumulators Vetiveria zizanioides, Brassica juncea, Lolium perenne L., Solanum nigrum L., and Sedum alfredii Hance grown in mildly and severely contaminated soils by 28.8%-331.3%, 8.5%-393.4%, 21.2%-222.5%, 14.7%-115.5%, and 28.3%-174.2%, respectively, compared with non-inoculated plants. The fresh biomass of these hyperaccumulators was elevated by 16.5%-94.4%, compared to that of the bacteria-free control. Phytoremediation potential indices, including bioconcentration and translocation factors, also revealed that the bacteria markedly boosted the phytoextraction efficacy from soil. Furthermore, principal component analysis (PCA) suggested that the effects of bacteria on the concentrations of Cd and Zn in hyperaccumulators were significantly correlated with ABA metabolism, but not with Pb and Cu. Combined with the synergistic effects on plant biomass, the bacteria also improved the phytoextraction of Pb and Cu in hyperaccumulators. Overall, the application of microorganism-assisted remediation based on ABA-catabolizing bacteria might be an alternative strategy for enhancing phytoremediation efficiency in HM-contaminated soils.

Treatment wetlands and phyto-technologies for remediation of winery effluent: Challenges and opportunities

The composition and concentration of contaminants present in winery wastewater fluctuate through space and time, presenting a challenge for traditional remediation methods. Bio-hydrogeochemical engineered systems, such as treatment wetlands, have been demonstrated to effectively reduce contaminant loads prior to disposal or reuse of the effluent. This review identifies and details the status quo and challenges associated with (i) the characteristics of winery wastewater, and the (ii) functional components, (iii) operational parameters, and (iv) performance of treatment wetlands for remediation of winery effluent. Potential solutions to challenges associated with these aspects are presented, based on the latest literature. A particular emphasis has been placed on the phytoremediation of winery wastewater, and the rationale for selection of plant species for niche bioremediatory roles. This is attributed to previously reported low-to-negative removal percentages of persistent contaminants, such as salts and heavy metals that may be present in winery wastewater. A case for the inclusion of selected terrestrial halophytes in treatment wetlands and in areas irrigated using winery effluent is discussed. These are plant species that have an elevated ability to accumulate, cross-tolerate and potentially remove a range of persistent contaminants from winery effluent via various phytotechnologies (e.g., phytodesalination).

ROS-Scavengers, Osmoprotectants and Violaxanthin De-Epoxidation in Salt-Stressed Arabidopsis thaliana with Different Tocopherol Composition

To determine the role of α- and γ-tocopherol (TC), this study compared the response to salt stress (200 mM NaCl) in wild type (WT) Arabidopsis thaliana (L.) Heynh. And its two mutants: (1) totally TC-deficient vte1; (2) vte4 accumulating γ-TC instead of α-TC; and (3) tmt transgenic line overaccumulating α-TC. Raman spectra revealed that salt-exposed α-TC accumulating plants were more flexible in regulating chlorophyll, carotenoid and polysaccharide levels than TC deficient mutants, while the plants overaccumulating γ-TC had the lowest levels of these biocompounds. Tocopherol composition and NaCl concentration affected xanthophyll cycle by changing the rate of violaxanthin de-epoxidation and zeaxanthin formation. NaCl treated plants with altered TC composition accumulated less oligosaccharides than WT plants. α-TC deficient plants increased their oligosaccharide levels and reduced maltose amount, while excessive accumulation of α-TC corresponded with enhanced amounts of maltose. Salt-stressed TC-deficient mutants and tmt transgenic line exhibited greater proline levels than WT plants, lower chlorogenic acid levels, and lower activity of catalase and peroxidases. α-TC accumulating plants produced more methylated proline- and glycine- betaines, and showed greater activity of superoxide dismutase than γ-TC deficient plants. Under salt stress, α-TC demonstrated a stronger regulatory effect on carbon- and nitrogen-related metabolites reorganization and modulation of antioxidant patterns than γ-TC. This suggested different links of α- and γ-TCs with various metabolic pathways via various functions and metabolic loops.

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants

Soil salinization, which is aggravated by climate change and inappropriate anthropogenic activities, has emerged as a serious environmental problem, threatening sustainable agriculture and future food security. Although there has been considerable progress in developing crop varieties by introducing salt tolerance-associated traits, most crop cultivars grown in saline soils still exhibit a decline in yield, necessitating the search for alternatives. Halophytes, with their intrinsic salt tolerance characteristics, are known to have great potential in rehabilitating salt-contaminated soils to support plant growth in saline soils by employing various strategies, including phytoremediation. In addition, the recent identification and characterization of salt tolerance-related genes encoding signaling components from halophytes, which are naturally grown under high salinity, have paved the way for the development of transgenic crops with improved salt tolerance. In this review, we aim to provide a comprehensive update on salinity-induced negative effects on soils and plants, including alterations of physicochemical properties in soils, and changes in physiological and biochemical processes and ion disparities in plants. We also review the physiological and biochemical adaptation strategies that help halophytes grow and survive in salinity-affected areas. Furthermore, we illustrate the halophyte-mediated phytoremediation process in salinity-affected areas, as well as their potential impacts on soil properties. Importantly, based on the recent findings on salt tolerance mechanisms in halophytes, we also comprehensively discuss the potential of improving salt tolerance in crop plants by introducing candidate genes related to antiporters, ion transporters, antioxidants, and defense proteins from halophytes for conserving sustainable agriculture in salinity-prone areas.

Genome-wide identification and function analysis of HMAD gene family in cotton (Gossypium spp.)

BACKGROUND

The abiotic stress such as soil salinization and heavy metal toxicity has posed a major threat to sustainable crop production worldwide. Previous studies revealed that halophytes were supposed to tolerate other stress including heavy metal toxicity. Though HMAD (heavy-metal-associated domain) was reported to play various important functions in Arabidopsis, little is known in Gossypium.

RESULTS

A total of 169 G. hirsutum genes were identified belonging to the HMAD gene family with the number of amino acids ranged from 56 to 1011. Additionally, 84, 76 and 159 HMAD genes were identified in each G. arboreum, G. raimondii and G. barbadense, respectively. The phylogenetic tree analysis showed that the HMAD gene family were divided into five classes, and 87 orthologs of HMAD genes were identified in four Gossypium species, such as genes Gh_D08G1950 and Gh_A08G2387 of G. hirsutum are orthologs of the Gorai.004G210800.1 and Cotton_A_25987 gene in G. raimondii and G. arboreum, respectively. In addition, 15 genes were lost during evolution. Furthermore, conserved sequence analysis found the conserved catalytic center containing an anion binding (CXXC) box. The HMAD gene family showed a differential expression levels among different tissues and developmental stages in G. hirsutum with the different cis-elements for abiotic stress.

CONCLUSIONS

Current study provided important information about HMAD family genes under salt-stress in Gossypium genome, which would be useful to understand its putative functions in different species of cotton.

Atmospheric pressure plasma treatment induces abscisic acid production, reduces stomatal aperture and improves seedling growth in Arabidopsis thaliana

Cold atmospheric pressure plasmas (CAPPs) have been widely used for pre-sowing treatment in agriculture to accelerate seed germination; however, information on their application to pre-transplant seedlings is scarce. The roles of the phytohormone abscisic acid (ABA) on guard cell aperture that control air exchange with the environment were investigated after CAPPs treatment. In this study, Arabidopsis thaliana seedling growth was evaluated under CAPPs treatment at different doses. Besides, the optimal growth stimulation dose was selected to further evaluate changes in ABA, ROS, Ca²⁺ and stomatal aperture during growth .The expression of most ABA signalling genes were aslo examined to investigate the mechanism. CAPPs treatment for 1 min significantly promoted Arabidopsis seedling growth; the ABA concentration in seedlings increased and peaked 48 h after treatment but was lower than in the control after 96 h. Transcript levels of most ABA signalling genes were markedly enhanced at 48 h, although their transcripts were significantly downregulated after 96 h. CAPPs treatment also reduced stomatal aperture after 24 h and accelerated ROS accumulation in guard cells. The Ca²⁺ concentration in the treatment group was markedly higher than in the control at 24 and 96 h. The results suggest that CAPPs treatment accelerates ABA accumulation in Arabidopsis at early growth stages and ABA regulates ROS and Ca²⁺ concentrations to affect stomatal aperture, and both ABA and stoma size are affected in CAPPs stimulation of Arabidopsis seedling growth.

A Dual Role of Vanadium in Environmental Systems-Beneficial and Detrimental Effects on Terrestrial Plants and Humans

The importance of vanadium (V) in the functioning of land systems is extremely diverse, as this element may exert both positive and harmful effects on terrestrial organisms. It recently become considered an element of beneficial character with a range of applications for human welfare. The health-ameliorative properties of this transition element depend on its degree of oxidation and on optimal concentration in the target cells. It was found that a similar relationship applies to vascular plants. However, excessive amounts of vanadium in the environment contaminate the soil and negatively affect the majority of living organisms. A significantly elevated level of V results in the destabilization of plant physiological balance, slowing down the growth of biomass which significantly reduces yield. In turn, low doses of the appropriate vanadium ions can stimulate plant growth and development, exert cytoprotective effects, and effectively enhance the synthesis of some biologically active compounds. We present the scientific achievements of research teams dealing with such topics. The issues discussed concern the role of vanadium in the environment, particular organisms, and highlight its dualistic influence on plants. Achievements in the field of V bioremediation, with the use of appropriately selected microorganisms and plant species, are emphasized.

Anatomical and ultrastructural alterations in Ceratopteris pteridoides under cadmium stress: A mechanism of cadmium tolerance

The present research is an appraisal of anatomical and ultrastructural alterations in aquatic fern, Ceratopteris pteridoides under cadmium (Cd) exposure. Plants were cultured hydroponically for 12 consecutive days in different Cd treatments: 10 µM L-1 (CDT1), 20 µM L-1 (CDT2), 40 µM L-1 (CDT3) and 60 µM L-1 (CDT4). Anatomical and ultrastructural changes of different vegetative tissues of C. pteridoides were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cd stress significantly (P < 0.05) decreased water content percentage (WC%), relative growth rate (RGR) and root activity in C. pteridoides, especially at highest Cd concentration (treatment CDT4). Significant (P < 0.05) drop of stress tolerance indices (STI) was noticed in C. pteridoides under treatment CDT4. Anatomical study of the Cd-treated C. pteridoides showed stomatal closure of leaves, reduction of diameter in xylem tracheids of stem and root, and decrease of intercellular spaces. Furthermore, ultrastructural alterations of leaf, stem, and root cells were evident with a damaged membrane system of chloroplast and mitochondria, disorganization of chloroplastic components, accumulation of large starch grains and plastoglobules, and formation of multivesicular bodies. The deposition of electron-dense material in the cell wall of root cells can be regarded as an important tolerance mechanism of C. pteridoides under Cd stress. Fourier transform infrared (FTIR) spectroscopy analysis of Cd-treated C. pteridoides biomass illustrated Cd-binding interaction with O-H, N-H, C-H, C≡C, C˭O, P˭O, -C-OH and CS functional groups of different metabolites.

Priming Strategies for Benefiting Plant Performance under Toxic Trace Metal Exposure

Combating environmental stress related to the presence of toxic elements is one of the most important challenges in plant production. The majority of plant species suffer from developmental abnormalities caused by an exposure to toxic concentrations of metals and metalloids, mainly Al, As, Cd, Cu, Hg, Ni, Pb, and Zn. However, defense mechanisms are activated with diverse intensity and efficiency. Enhancement of defense potential can be achieved though exogenously applied treatments, resulting in a higher capability of surviving and developing under stress and become, at least temporarily, tolerant to stress factors. In this review, I present several already recognized as well as novel methods of the priming process called priming, resulting in the so-called “primed state” of the plant organism. Primed plants have a higher capability of surviving and developing under stress, and become, at least temporarily, tolerant to stress factors. In this review, several already recognized as well as novel methods of priming plants towards tolerance to metallic stress are discussed, with attention paid to similarities in priming mechanisms activated by the most versatile priming agents. This knowledge could contribute to the development of priming mixtures to counteract negative effects of multi-metallic and multi-abiotic stresses. Presentation of mechanisms is complemented with information on the genes regulated by priming towards metallic stress tolerance. Novel compounds and techniques that can be exploited in priming experiments are also summarized.

Mode of Action of 1-Naphthylphthalamic Acid in Conspicuous Local Stem Swelling of Succulent Plant, Bryophyllum calycinum: Relevance to the Aspects of Its Histological Observation and Comprehensive Analyses of Plant Hormones

The mode of action of 1-naphthylphthalamic acid (NPA) to induce conspicuous local stem swelling in the area of its application to the growing internode in intact Bryophyllum calycinum was studied based on the aspects of histological observation and comprehensive analyses of plant hormones. Histological analyses revealed that NPA induced an increase in cell size and numerous cell divisions in the cortex and pith, respectively, compared to untreated stem. In the area of NPA application, vascular tissues had significantly wider cambial zones consisting of 5–6 cell layers, whereas phloem and xylem seemed not to be affected. This indicates that stem swelling in the area of NPA application is caused by stimulation of cell division and cell enlargement mainly in the cambial zone, cortex, and pith. Comprehensive analyses of plant hormones revealed that NPA substantially increased endogenous levels of indole-3-acetic acid (IAA) in the swelling area. NPA also increased endogenous levels of cytokinins, jasmonic acid, and its precursor, 12-oxo-phytodienoic acid, but did not increase abscisic acid and gibberellin levels. It was shown, using radiolabeled ¹⁴C-IAA, that NPA applied to the middle of internode segments had little effect on polar auxin transport, while 2,3,5-triiodobenzoic acid substantially inhibited it. These results strongly suggest that NPA induces changes in endogenous levels of plant hormones, such as IAA, cytokinins, and jasmonic acid, and their hormonal crosstalk results in a conspicuous local stem swelling. The possible different mode of action of NPA from other polar auxin transport inhibitors in succulent plants is extensively discussed.

Evaluating multiple stressor research in coastal wetlands: A systematic review

Multiple stressors are ubiquitous in coastal ecosystems as a result of increased human activity and development along coastlines. Accurately assessing multiple stressor effects is essential for predicting stressor impacts and informing management to efficiently and effectively mitigate potentially complex ecological responses. Extracting relevant information on multiple stressor studies conducted specifically within coastal wetlands is not possible from existing reviews, posing challenges in highlighting knowledge gaps and guiding future research. Here, we systematically review manipulative studies that assess multiple anthropogenic stressors within saltmarsh, mangrove, and seagrass ecosystems. In the past decade, there has been a rapid increase in publications, with seagrasses receiving the most attention (76 out of a total of 143 studies). Across all studies, nutrient loading and temperature were tested most often (N = 64 and N = 48, respectively), while the most common stressor combination was temperature with salinity (N = 12). Stressor application and study design varied across ecosystems. Studies are mostly conducted in highly controlled environments, without considering how natural variations in the physicochemical environment of coastal ecosystems may influence stressor intensity and timing under these conditions. This may result in vastly different ecological responses across levels of biological organisation. Shifting focus from univariate analytical approaches to multivariate, particularly path analysis, will help elucidate complex ecological relationships and highlight direct and indirect effects of multiple stressors in coastal ecosystems. There is a solid foundation of multiple stressor research in coastal wetlands. However, we recommend future research enhance ecological realism in experimental design by studying the effects of stressor combinations whilst accounting for spatiotemporal variability that reflects natural conditions of coastal ecosystems.

Tocopherols mutual balance is a key player for maintaining Arabidopsis thaliana growth under salt stress

Enhanced channeling carbon through pathways: shikimate/chorismate, benzenoid-phenylopropanoid or 2-C-methyl-D-erythritol 4-phosphate (MEP) provides a multitude of secondary metabolites and cell wall components and allows plants response to environmental stresses. Through the biosynthetic pathways, different secondary metabolites, like tocopherols (TCs), are bind to mutual dependencies and metabolic loops, that are not yet fully understood. We compared, in parallel, the influence of α- and γ-TCs on metabolites involved in osmoprotective/antioxidative response, and physico-chemical modification of plasma membrane and cell wall. We studied Arabidopsis thaliana Columbia ecotype (WT), mutant vte1 deficient in α- and γ-TCs, mutant vte4 over-accumulating γ-TC instead of α-TC, and transgenic line tmt over-accumulating α-TC; exposed to NaCl. The results indicate that salt stress activates β-carboxylation processes in WT plants and in plants with altered TCs accumulation. In α-TC-deficient plants, NaCl causes ACC decrease, but does not change SA, whose concentration remains higher than in α-TC accumulating plants. α/γ-TCs contents influence carbohydrates, poliamines, phenolic (caffeic, ferrulic, cinnamic) acids accumulation patterns. Salinity results in increased detection of the LM5 galactan and LM19 homogalacturonan epitopes in α-TC accumulating plants, and the LM6 arabinan and MAC207 AGP epitopes in α-TC deficient mutants. Parallel, plants with altered TCs composition show decreased both the cell turgor and elastic modulus determined at the individual cell level. α-TC deficient plants reveal lower values of cell turgor and elastic modulus, but higher cell hydraulic conductivity than α-TC accumulating plants. Under salt stress, α-TC shows stronger regulatory effect than γ-TC through the impact on chloroplastic biosynthetic pathways and ROS/osmotic-modulating compounds.

Phytoremediation of metal-contaminated rare-earth mining sites using Paspalumconjugatum

Over-exploitation of rare-earth elements causes cadmium (Cd)- and lead (Pb)-contamination of rare-earth mine tailings. Here, Paspalum conjugatum was used as a hyperaccumulating perennial herb to evaluate its phytoextraction potential for removing metals in a hydroponic experiment. Further, an in-situ experiment was conducted for two years (2016-2018) to investigate the potential of P. conjugatum for reducing soil metal concentrations and to assess microbiome recovery on abandoned rare-earth mining land. Pinus massoniana was used for control treatments. We found that P. conjugatum produced metal transfer coefficients of 0.85 and 0.89 for Cd and Pb, respectively. The concentrations of Cd and Pb accumulated in P. conjugatum were 98.33 mg kg^-1 and 137 mg kg^-1, respectively. Using P. conjugatum, soil Pb and Cd concentrations were significantly decreased, and Cd concentrations approached acceptable levels (0.209 mg kg^-1). The bacterial diversity in P. conjugatum-restored soil was higher than that in soil of P. massoniana. The bacterial genera Chloroflexi, Acidobacteria, and Actinobacteria were predominant in the restored soils. P. conjugatum was tolerant to drought and exhibited enhanced enzymatic activity. These results suggest that P. conjugatum can be used for efficient phytoremediation of Pb- and Cd-contaminated soils.

Distinct co-tolerance responses to combined salinity and cadmium exposure in metallicolous and non-metallicolous ecotypes of Silene vulgaris

This study compared co-tolerance to salinity and cadmium and investigated its mechanisms in a facultative metallophyte Silene vulgaris originating from distinct habitats. Shoots of calamine (Cal) and non-metallicolous (N-Cal) ecotypes grown in vitro were exposed to 10 and 100 mM NaCl, 5 μM CdCl₂ and their combinations. Stress effects were evaluated based on growth, oxidative stress parameters, and DNA content and damage. Tolerance mechanisms were assessed by analyzing non-enzymatic antioxidants, osmolytes and ion accumulation. Irrespective of the ecotype, Cd stimulated shoot proliferation (micropropagation coefficients MC = 15.2 and 12.1 for Cal and N-Cal, respectively, growth tolerance index GTI = 148.1 and 156.7%). In Cal ecotype this was attributed to an increase in glutathione content and reorganization of cell membrane structures under Cd exposure, whereas in N-Cal to enhanced synthesis of other non-enzymatic antioxidants, mainly carotenoids and ascorbate. Low salinity stimulated growth of Cal ecotype due to optimizing Cl^- content. High salinity inhibited growth, especially in Cal ecotype, where it enhanced DNA damage and disturbed ionic homeostasis. Species-specific reaction to combined salinity and Cd involved a mutual inhibition of Na⁺, Cl^- and Cd²⁺ uptake. N-Cal ecotype responded to combined stresses by enhancing its antioxidant defense, presumably induced by Cd, whereas the metallicolous ecotype triggered osmotic adjustment. The study revealed that in S. vulgaris Cd application ameliorated metabolic responses to simultaneous salinity exposure. It also shed a light on distinct strategies of coping with combined abiotic stresses in two ecotypes of the species showing high plasticity in environmental conditions.

Formation of the Secondary Abscission Zone Induced by the Interaction of Methyl Jasmonate and Auxin in Bryophyllum calycinum: Relevance to Auxin Status and Histology

The interaction of methyl jasmonate (JA-Me) and indole-3-acetic acid (IAA) to induce the formation of the secondary abscission zone in the middle of internode segments of Bryophyllum calycinum was investigated in relation to auxin status and histology. When IAA at 0.1% (w/w, in lanolin) was applied to the segments, the formation of the secondary abscission zone at a few mm above the treatment in the apical direction was observed. On the contrary, IAA at 0.5% (w/w, in lanolin) did not induce the formation of the secondary abscission zone. JA-Me at 0.5% (w/w, in lanolin) applied to the middle of internode segments kept in the normal (natural) or inverted positions also induced the formation of the secondary abscission zone below and above parts of the treatment. IAA at 0.5% applied to the cut surface of the upper part of the segments completely prevented the formation of the secondary abscission zone induced by JA-Me. Simultaneous application of IAA 0.5% with JA-Me 0.5% in the middle part of the internode segments induced the formation of the secondary abscission zone at 10 mm to 12 mm above the treatment. Histological analyses indicated that the formation of the secondary abscission zone was characterized by the presence of newly synthesized cell plates that resulted from periclinal cell division within one layer of mother cells in stems. The effects of IAA (0.1%) and JA-Me (0.5%) on the formation of the secondary abscission zone were histologically similar. Comprehensive analyses of plant hormones revealed that the balance of the endogenous levels of IAA in both sides adjacent to the abscission zone was significantly disturbed when the secondary abscission formation was induced by the application of IAA. These results strongly suggest that an auxin gradient is important in the formation of the secondary abscission zone in the internode segments of B. calycinum, and IAA gradient results from polar IAA transport from the application site. IAA is important in the regulation of formation of the secondary abscission zone induced by JA-Me. Further possible mechanisms of the formation of the secondary abscission zone in the internode segments of B. calycinum are also discussed in the interaction of JA-Me and IAA.