Responses of duckweed (Lemna minor L.) to aluminum stress: Physiological and proteomics analyses

Differences in gas exchange, chlorophyll fluorescence, and modulated reflection of light at 820 nm between two rhododendron cultivars under aluminum stress conditions

Aluminum (Al) toxicity is an important factor restricting the normal growth of plants in acidic soil. Rhododendron (Ericaceae) can grow relatively well in acidic soil. To uncover the adaptive mechanisms of photosynthesis under Al stress, the influence of Al stress on the photosynthetic activities of Al-sensitive (Baijinpao) and Al-resistant (Kangnaixin) rhododendron cultivars was examined by measuring gas exchange, chlorophyll fluorescence, and the modulated reflection of light at 820 nm. Under Al stress conditions, the net photosynthetic rate and stomatal conductance of the rhododendron leaves decreased, whereas the intercellular CO2 concentration increased. The Al stress treatment damaged the oxygen-evolving complex of the rhododendron seedlings, while also inhibiting electron transport on the photosystem II (PSII) donor side. In addition, the exposure to Al stress restricted the oxidation of plastocyanin (PC) and the photosystem I (PSI) reaction center (P700) and led to the re-reduction of PC+ and P700+. The comparison with Kangnaixin revealed an increase in the PSII connectivity in Baijinpao. Additionally, the donor-side electron transport efficiency was more inhibited and the overall activity of PSII, PSI, and the intersystem electron transport chain decreased more extensively in Baijinpao than in Kangnaixin. On the basis of the study findings, we concluded that Al stress adversely affects photosynthesis in rhododendron seedlings by significantly decreasing the activity of PSII and PSI. Under Al stress, Kangnaixin showed stronger tolerance compared with Baijinpao.

Alginate and chitosan surface coating reduces the phytotoxicity of CeO2 nanoparticles to duckweed (Lemna minor L.)

Little is known about the effect of surface coatings on the fate and toxicity of CeO2 nanoparticles (NPs) to aquatic plants. In this study, we modified nCeO2 with chitosan (Cs) and alginate (Al) to obtain positively charged nCeO2@Cs and negatively charged nCeO2@Al, respectively, and exposed them to a representative aquatic plant, duckweed (Lemna minor L.). Uncoated nCeO2 could significantly inhibit the growth of duckweed, induce oxidative damage and lead to cell death, whereas nCeO2@Cs and nCeO2@Al exhibited lower toxicity to duckweed. ICP-MS analysis revealed that the Ce content in duckweed from the nCeO2 group was 1.74 and 2.85 times higher than that in the nCeO2@Cs and nCeO2@Al groups, respectively. Microscopic observations indicated that the positively charged nCeO2@Cs was more readily adsorbed on the root surface of duckweed than the negatively charged nCeO2@Al. The results of XANES and LCF demonstrated that a certain percentage of Ce(Ⅳ) was reduced to Ce(Ⅲ) after the interaction of the three NPs with duckweed, but the degree of biotransformation differed among the treatments. Specifically, the absolute contents of Ce(III) produced of nCeO2@Cs and nCeO2@Al through biotransformation were reduced by 55.5% and 83.5%, respectively, compared with that of the nCeO2 group, which might be the key factor for the diminished phytotoxicity of the coated nCeO2 to the duckweed. These findings were valuable for understanding the toxicity of metal-based NPs to aquatic plants and for the synthesis of environmentally friendly nanomaterials.

The Physiological Response Mechanism of Peanut Leaves under Al Stress

Aluminum (Al) toxicity in acidic soils can significantly reduce peanut yield. The physiological response of peanut leaves to Al poisoning stress still has not been fully explored. This research examined the influences of Al toxicity on peanut leaves by observing the leaf phenotype, scanning the leaf area and perimeter, and by measuring photosynthetic pigment content, physiological response indices, leaf hormone levels, and mineral element accumulation. Fluorescence quantitative RT-PCR (qPCR) was utilized to determine the relative transcript level of specific genes. The results indicated that Al toxicity hindered peanut leaf development, reducing their biomass, surface area, and perimeter, although the decrease in photosynthetic pigment content was minimal. Al toxicity notably affected the activity of antioxidative enzymes, proline content, and MDA (malondialdehyde) levels in the leaves. Additionally, Al poisoning resulted in the increased accumulation of iron (Fe), potassium (K), and Al in peanut leaves but reduced the levels of calcium (Ca), manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg). There were significant changes in the content of hormones and the expression level of genes connected with hormones in peanut leaves. High Al concentrations may activate cellular defense mechanisms, enhancing antioxidative activity to mitigate excess reactive oxygen species (ROS) and affecting hormone-related gene expression, which may impede leaf biomass and development. This research aimed to elucidate the physiological response mechanisms of peanut leaves to Al poisoning stress, providing insights for breeding new varieties resistant to Al poisoning.

How plants respond to heavy metal contamination: a narrative review of proteomic studies and phytoremediation applications

MAIN CONCLUSION

Heavy metal pollution caused by human activities is a serious threat to the environment and human health. Plants have evolved sophisticated defence systems to deal with heavy metal stress, with proteins and enzymes serving as critical intercepting agents for heavy metal toxicity reduction. Proteomics continues to be effective in identifying markers associated with stress response and metabolic processes. This review explores the complex interactions between heavy metal pollution and plant physiology, with an emphasis on proteomic and biotechnological perspectives. Over the last century, accelerated industrialization, agriculture activities, energy production, and urbanization have established a constant need for natural resources, resulting in environmental degradation. The widespread buildup of heavy metals in ecosystems as a result of human activity is especially concerning. Although some heavy metals are required by organisms in trace amounts, high concentrations pose serious risks to the ecosystem and human health. As immobile organisms, plants are directly exposed to heavy metal contamination, prompting the development of robust defence mechanisms. Proteomics has been used to understand how plants react to heavy metal stress. The development of proteomic techniques offers promising opportunities to improve plant tolerance to toxicity from heavy metals. Additionally, there is substantial scope for phytoremediation, a sustainable method that uses plants to extract, sequester, or eliminate contaminants in the context of changes in protein expression and total protein behaviour. Changes in proteins and enzymatic activities have been highlighted to illuminate the complex effects of heavy metal pollution on plant metabolism, and how proteomic research has revealed the plant's ability to mitigate heavy metal toxicity by intercepting vital nutrients, organic substances, and/or microorganisms.

Assessment of ecotoxicological effects of Fojo coal mine waste elutriate in aquatic species (Douro Coalfield, North Portugal)

Introduction: The exploitation of anthracite A in the Pejão mining complex (Douro Coalfield, North Portugal) resulted in the formation of several coal waste piles without proper environmental control. In 2017, a new pedological zonation emerged in the Fojo area, after the ignition and self-burning of some of the coal waste piles, namely: unburned coal waste (UW); burned coal waste, and a cover layer (BW and CL, respectively); uphill soil (US); mixed burned coal waste (MBW); downhill soil (DS). This study aimed to evaluate the toxic effects of 25 soil elutriates from different pedological materials. Methods: Allivibrio fischeri bioluminescence inhibition assay, Lemna minor growth inhibition assay, and Daphnia magna acute assay were used to assess the toxicity effects. Additionally, total chlorophyll and malondialdehyde (MDA) content and catalase (CAT) activity were also evaluated in L. minor. Results and Discussion: The results obtained from each endpoint demonstrated the extremely heterogeneous nature of soil properties, and the species showed different sensibilities to soil elutriates, however, in general, the species showed the same sensitivity trend (A. fischeri > L. minor > D. magna). The potentially toxic elements (PTE) present in the soil elutriates (e.g., Al, Pb, Cd, Ni, Zn) affected significantly the species understudy. All elutriates revealed toxicity for A. fischeri, while US1 and UW5 were the most toxic for L. minor (growth inhibition and significant alterations in CAT activity) and D. magna (100% mortality). This study highlights the importance of studying soil aqueous phase toxicity since the mobilization and percolation of bioavailable PTE can cause environmental impacts on aquatic ecosystems and biota.

Extensive post-transcriptional regulation revealed by integrative transcriptome and proteome analyses in salicylic acid-induced flowering in duckweed (Lemna gibba)

Duckweed is an aquatic model plant with tremendous potential in industrial and agricultural applications. Duckweed rarely flowers which significantly hinders the resource collection and heterosis utilization. Salicylic acid (SA) can significantly induce duckweed to flower; however, the underlying regulatory mechanisms remain largely unknown. In this work, transcriptome and proteome were conducted in parallel to examine the expression change of genes and proteins in Lemna gibba under SA treatment. A high-quality reference transcriptome was generated using Iso-Seq strategy, yielding 42,281 full-length transcripts. A total of 422, 423, and 417 differentially expressed genes (DEGs), as well as 213, 51, and 92 differentially expressed proteins (DEPs), were identified at flower induction, flower initiation, and flowering stages by ssRNA-seq and iTRAQ methods. Most DEGs and DEPs were only regulated at either the transcriptomic or proteomic level. Additionally, DEPs exhibited low expression correlations with the corresponding mRNAs, suggesting that post-transcriptional regulation plays a pivotal role in SA-induced flowering in L. gibba. Specifically, the genes related to photosynthesis, stress, and hormone metabolism were mainly regulated at the mRNA level, those associated with mitochondrial electron transport / ATP synthesis, nucleotide synthesis, and secondary metabolism were regulated at the protein level, while those related to redox metabolism were regulated at the mRNA and/or protein levels. The post-transcriptional regulation of genes relevant to hormone synthesis, transcription factors, and flowering was also extensively analyzed and discussed. This is the first study of integrative transcriptomic and proteomic analyses in duckweed, providing novel insights of post-transcriptional regulation in SA-induced flowering of L. gibba.

Physiological and Proteomic Changes in Camellia semiserrata in Response to Aluminum Stress

Camellia semiserrata is an important woody edible oil tree species in southern China that is characterized by large fruits and seed kernels with high oil contents. Increasing soil acidification due to increased use of fossil fuels, misuse of acidic fertilizers, and irrational farming practices has led to leaching of aluminum (Al) in the form of free Al3+, Al(OH)2+, and Al(OH)2+, which inhibits the growth and development of C. semiserrata in South China. To investigate the mechanism underlying C. semiserrata responses to Al stress, we determined the changes in photosynthetic parameters, antioxidant enzyme activities, and osmoregulatory substance contents of C. semiserrata leaves under different concentrations of Al stress treatments (0, 1, 2, 3, and 4 mmol/L Alcl3) using a combination of physiological and proteomics approaches. In addition, we identified the differentially expressed proteins (DEPs) under 0 (CK or GNR0), 2 mmol/L (GNR2), and 4 mmol/L (GNR4) Al stress using a 4D-label-free technique. With increasing stress concentration, the photosynthetic indexes of C. semiserrata leaves, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), soluble protein (SP), and soluble sugar (SS) showed an overall trend of increasing and then decreasing, and proline (Pro) and malondialdehyde (MDA) contents tended to continuously increase overall. Compared with the control group, we identified 124 and 192 DEPs in GNR2 and GNR4, respectively, which were mainly involved in metabolic processes such as photosynthesis, flavonoid metabolism, oxidative stress response, energy and carbohydrate metabolism, and signal transduction. At 2 mmol/L Al stress, carbon metabolism, amino sugar and nucleotide sugar metabolism, and flavonoid metabolism-related proteins were significantly changed, and when the stress was increased to 4 mmol/L Al, the cells accumulated reactive oxygen species (ROS) at a rate exceeding the antioxidant system scavenging capacity. To deal with this change, C. semiserrata leaves enhanced their glutathione metabolism, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, and other metabolic processes to counteract peroxidative damage to the cytoplasmic membrane caused by stress. In addition, we found that C. semiserrata resisted aluminum toxicity mainly by synthesizing anthocyanidins under 2 mmol/L stress, whereas proanthocyanidins were alleviated by the generation of proanthocyanidins under 4 mmol/L stress, which may be a special mechanism by which C. semiserrata responds to different concentrations of aluminum stress.

Coordinated Regulation of Central Carbon Metabolism in Pyroligneous Acid-Treated Tomato Plants under Aluminum Stress

Aluminum (Al) toxicity is a major threat to global crop production in acidic soils, which can be mitigated by natural substances such as pyroligneous acid (PA). However, the effect of PA in regulating plant central carbon metabolism (CCM) under Al stress is unknown. In this study, we investigated the effects of varying PA concentrations (0, 0.25 and 1% PA/ddH₂O (v/v)) on intermediate metabolites involved in CCM in tomato (Solanum lycopersicum L., 'Scotia') seedlings under varying Al concentrations (0, 1 and 4 mM AlCl₃). A total of 48 differentially expressed metabolites of CCM were identified in the leaves of both control and PA-treated plants under Al stress. Calvin-Benson cycle (CBC) and pentose phosphate pathway (PPP) metabolites were considerably reduced under 4 mM Al stress, irrespective of the PA treatment. Conversely, the PA treatment markedly increased glycolysis and tricarboxylic acid cycle (TCA) metabolites compared to the control. Although glycolysis metabolites in the 0.25% PA-treated plants under Al stress were comparable to the control, the 1% PA-treated plants exhibited the highest accumulation of glycolysis metabolites. Furthermore, all PA treatments increased TCA metabolites under Al stress. Electron transport chain (ETC) metabolites were higher in PA-treated plants alone and under 1 mM, Al but were reduced under a higher Al treatment of 4 mM. Pearson correlation analysis revealed that CBC metabolites had a significantly strong positive (r = 0.99; p < 0.001) association with PPP metabolites. Additionally, glycolysis metabolites showed a significantly moderate positive association (r = 0.76; p < 0.05) with TCA metabolites, while ETC metabolites exhibited no association with any of the determined pathways. The coordinated association between CCM pathway metabolites suggests that PA can stimulate changes in plant metabolism to modulate energy production and biosynthesis of organic acids under Al stress conditions.

A novel cultivation platform of duckweed (Lemna minor) via application of beeswax superhydrophobic coatings

Conventional establishment of laboratory cultures of duckweed Lemna minor are prepared in beakers, Erlenmeyer flasks or Schott bottles. These conventional cultivation methods limit the available surface area for growth which then causes layering of fronds that reduces the efficiency of plants in sunlight capturing. Here, acrylic sheets were spray-coated with a superhydrophobic (SHP) beeswax suspension and these coated acrylic sheets were used as a novel cultivation platform for L. minor. L. minor was grown for 7 days in conventional glass jar which acted as the control and were compared to SHP coated acrylic (SHPA) and SHP coated acrylic with aluminium mesh centrally placed (SHPAM) at similar duration and cultivation conditions. Addition of mesh was to entrap the plantlets and fixed the plantlets' position on the growing platform. The effects of cultivation platforms on growth rate and biochemical compositions of L. minor were monitored. The highest biomass growth was obtained from SHPA cultivation where the relative growth rate (RGR) was 0.0909 ± 0.014 day^-1 and the RGR was 2.17 times higher than the control. Moreover, L. minor harvested from SHPA displayed the highest values in total protein content, total carbohydrates content and crude lipid percentage. The values were 156.04 ± 12.13 mg/g, 94.75 ± 9.02 mg/g and 7.09 ± 1.14% respectively. However, the control showed the highest total chlorophyll content which was 0.7733 ± 0.042 mg/g FW. Although SHPA obtained a slightly lower chlorophyll content than the control, this growing platform is still promising as it displayed the highest growth rate as well as other biochemical composition. Hence, this study proved that the proposed method that applied superhydrophobic properties in cultivation of L. minor provided a larger surface area for L. minor to grow, which then resulted in a greater biomass production while simultaneously maintaining the quality of the biochemical compositions of duckweeds.

Phytoremediation of fluoroalkylethers (ether-PFASs): A review on bioaccumulation and ecotoxilogical effects

Fluoroalkylethers (ether-PFASs), as alternatives to phased-out per- and perfluoroalkyl substances (PFASs), have attracted mounting attention due to their ubiquitous detection in aquatic environment and their similarity to legacy PFASs in terms of persistence and toxicity. In this review, the sources and distribution of ether-PFASs in soil ecosystem as well as their toxic impacts on soil microbial community are summarized. The plant uptake and bioaccumulation potential of ether-PFASs are presented, and a wide range of the influencing factors for their uptake and translocation is discussed. In response to ether-PFASs, the corresponding phytotoxic effects, such as seed germination, plant growth, photosynthesis, oxidative damage, antioxidant enzymes activities, and genotoxicity, are systematically elucidated. Finally, the current knowledge gaps and future research prospective are highlighted. The findings of this review will advance our understanding for the environmental behavior and implications ether-PFASs in soil-plant systems and help explore the strategies for ether-PFASs remediation to minimize their adverse toxicity.

Response to microplastic exposure: An exploration into the sea urchin immune cell proteome

It is now known that the Mediterranean Sea currently is one of the major hotspot for microplastics (MPs; < 5 mm) pollution and that the risks will be even more pronounced in the coming years. Thus, the in-depth study of the mechanisms underlying the MPs toxicity in key Mediterranean organisms, subjected to high anthropic pressures, has become a categorical imperative to pursue. Here, we explore for the first time the sea urchins immune cells profile combined to their proteome upon in vivo exposure (72 h) to different concentrations of polystyrene-microbeads (micro-PS) starting from relevant environmental concentrations (10, 50, 10³, 10⁴ MP/L). Every 24 h, immunological parameters were monitored. After 72 h, the abundance of MPs was examined in various organs and coelomocytes were collected for proteomic analysis based on a shotgun label free proteomic approach. While sea urchins treated with the lowest concentration tested (10 and 50 micro-PS/L) did not show the presence of micro-PS in any tissue, in the specimens exposed to the highest concentration (10³ and 10⁴ micro-PS) there was an internalisation of 9.75 ± 2.75 and 113.75 ± 34.5 MP/g, respectively. Proteomic analyses revealed that MPs exposure altered coelomocytes protein profile not only compared to the control group but also among the different micro-PS concentrations and these variations are micro-PS concentration dependent. The proteins exclusively expressed in the coelomocytes of specimens exposed to MPs are mainly metabolite interconversion enzymes, involved in cellular processes, indicating a severe alteration of the cellular metabolic pathways. Overall, these findings provide new insights on the mode of action of MPs in the sea urchin immune cells both at the molecular and cellular level.

Overexpression of the Phosphoserine Phosphatase-Encoding Gene (AtPSP1) Promotes Starch Accumulation in Lemna turionifera 5511 under Sulfur Deficiency

Duckweeds are well known for their high accumulation of starch under stress conditions, along with inhibited growth. The phosphorylation pathway of serine biosynthesis (PPSB) was reported as playing a vital role in linking the carbon, nitrogen, and sulfur metabolism in this plant. The overexpression of AtPSP1, the last key enzyme of the PPSB pathway in duckweed, was found to stimulate the accumulation of starch under sulfur-deficient conditions. The growth- and photosynthesis-related parameters were higher in the AtPSP1 transgenic plants than in the WT. The transcriptional analysis showed that the expression of several genes in starch synthesis, TCA, and sulfur absorption, transportation, and assimilation was significantly up- or downregulated. The study suggests that PSP engineering could improve starch accumulation in Lemna turionifera 5511 by coordinating the carbon metabolism and sulfur assimilation under sulfur-deficient conditions.

Aluminum phytotoxicity induced structural and ultrastructural changes in submerged plant Vallisneria natans

Aluminum (Al) is a concentration-dependent toxic metal found in the crust of earth that has no recognized biological use. Nonetheless, the mechanism of Al toxicity to submerged plants remains obscure, especially from a cell/subcellular structure and functional group perspective. Therefore, multiple dosages of Al³⁺ (0, 0.3, 0.6, 1.2, and 1.5 mg/L) were applied hydroponically to the submerged plant Vallisneria natans in order to determine the accumulation potential of Al at the subcellular level and their ultrastructural toxicity. More severe structural and ultrastructural damage was determined when V. natans exposed to ≥ 0.6 mg/L Al³⁺. In 1.2 and 1.5 mg/L Al³⁺ treatment groups, the total chlorophyll content of leaves significantly reduced 3.342, 3.838 mg/g FW, some leaves even exhibited chlorosis and fragility. Under 0.3 mg/L Al³⁺ exposure, the middle-age and young leaves were potent phytoexcluders, whereas at 1.5 mg/L Al³⁺, a large amount of Al could be transferred from the roots to other parts, among which the aged leaves were the most receptive tissues (7.306 mg/g). Scanning/Transmission electron microscopy analysis displayed the Al-mediated disruption of vascular bundle structure in leaf cells, intercellular space and several vegetative tissues, and demonstrated that Al in vacuole and chloroplast subcellular segregation into electron dense deposition. Al and P accumulation in the roots, stolons and leaves varied significantly among treatments and different tissues (P < 0.05). Fourier transform infrared spectroscopy of plant biomass also indicated possible metabolites (amine, unsaturated hydrocarbon, etc.) of V. natans that may bind Al³⁺. Conclusively, results revealed that Al³⁺ disrupts the cellular structure of leaves and roots or binds to functional groups of biological tissues, thereby affecting plant nutrient uptake and photosynthesis. Findings might have scientific and practical significance for the restoration of submerged vegetation in Al-contaminated lakes.

Potential of Lemna minor and Eichhornia crassipes for the phytoremediation of water contaminated with Nickel (II)

Phytoextraction of Nickel (II) in water by two types of aquatic macrophytes (Lemna minor and Eichhornia crassipes) was investigated using synthetic aqueous solutions of NiSO₄ at concentrations of 0.5, 1.5 and 2.5 mg/L. The toxic effects of nickel salt in plants were evaluated through the presence of necrosis and chlorosis. The bioconcentration factor, Nickel (II) removal efficiency and kinetics of removal were also calculated. Results of this study show bioconcentration factors higher than 1000, which categorize L. minor and E. crassipes as hyperaccumulators. Besides, L. minor presented a removal percentage higher than 68%, compared to E. crassipes that did not exceed 50% in any of the three concentrations studied. However, E. crassipes showed better resistance to the effects of nickel and obtained a greater removal capacity during the phytoremediation process that lasted for 10 days. In contrast, L. minor suffered necrosis and chlorosis in a concentration-dependent way. Consequently, both macrophytes are sustainable alternatives for nickel removal from contaminated water.

Proteome and physiological analyses reveal tobacco (Nicotiana tabacum) peroxidase 7 (POD 7) functions in responses to copper stress

Copper is a micronutrient essential for plant growth and development. However, Cu is also a heavy metal element that has deleterious impacts on plants when excessively accumulated in the environment. To understand the molecular mechanism underlying tobacco in response to Cu stress, iTRAQ based technology was used to identify differentially expressed proteins (DEPs) and important metabolic pathways in tobacco plants treated with excessive CuSO4. The results showed that 180 DEPs were detected between the treatment and control, among which 78 were upregulated and 102 were downregulated. These DEPs can be functionally divided into 65 categories and are closely related to metabolic pathways, carbon metabolism, secondary metabolite biosynthesis, biosynthesis of antibiotics, glyoxylate and dicarboxylate metabolism, and glycolysis/gluconeogenesis. Peroxidase7 was significantly upregulated and was selected and overexpressed in tobacco. Then, positive transgenic lines and wild type plants were exposed to a Cu stress environment. The results showed that Peroxidase7 transgenic tobacco plants exhibited enhanced Cu stress resistance with decreased malondialdehyde and Cu contents, and increased shoot dry weight, root length, secondary root number, SOD, POD and CAT activity. The present study suggests that the ROS scavenging mechanism is essential for tobacco plants in response to Cu stress and that Peroxidase7 functions in tobacco plant resistance to excessive Cu environment.

Over-Expression of Phosphoserine Aminotransferase-Encoding Gene (AtPSAT1) Prompts Starch Accumulation in L. turionifera under Nitrogen Starvation

It has been demonstrated that the phosphorylation pathway of L-serine (Ser) biosynthesis (PPSB) is very important in plant growth and development, but whether and how PPSB affects nitrogen metabolism and starch accumulation has not been fully elucidated. In this study, we took the energy plant duckweed (strain Lemna turionifera 5511) as the research object and used a stable genetic transformation system to heterologously over-expressing Arabidopsis AtPSAT1 (the gene encoding phosphoserine aminotransferase, the second enzyme of PPSB). Our results showed that, under nitrogen starvation, the transgenic plants grew faster, with higher values of Fv/Fm, rETR, and Y(II), as well as fresh and dry weight, than the wild-type. More promisingly, the accumulation of starch was also found to be significantly improved when over-expressing AtPSAT1 in the transgenic plants. qRT-PCR analysis results showed that the expression of genes related to nitrogen assimilation, carbon metabolism, and starch biosynthesis was up-regulated, while the expression of starch degradation-related genes was down-regulated by AtPSAT1 over-expression. We propose that the increased starch accumulation caused by AtPSAT1 over-expression may result from both elevated photosynthetic capacity and nitrogen utilization efficiency. This research sheds new light on the mechanism underlying the ability of PPSB to coordinate nitrogen and carbon metabolism, and provides a feasible way to improve starch production, that is, through engineering PPSB in crops.

Toxic mechanism of two cyanobacterial volatiles β-cyclocitral and β-ionone on the photosynthesis in duckweed by altering gene expression

Volatile organic compounds (VOCs) promote cyanobacteria dominating eutrophicated waters, with aquatic plant decrease and even disappearance. To uncover the toxic mechanism of cyanobacterial VOCs on aquatic plants, we investigated the growth, photosynthetic pigment levels, photosynthetic abilities and related gene expression in duckweed treated with β-cyclocitral and β-ionone, 2 main components in the VOCs. The levels of chlorophylls and carotenoids gradually declined with raising the concentration of the 2 compounds and prolonging the treatment time. Their decline should result from the down-regulation of 8 genes associated with photosynthetic pigment biosynthesis and up-regulation of 2 genes involved in carotenoid degradation. The reduction was also found in the photosystem II (PSII) efficiency and O₂ evolution rate, which should result from the lowered photosynthetic pigment levels and down-regulation of 38 genes related with photosynthetic process. The frond numbers, total frond area and fresh weight gradually decreased with raising the 2 compound concentration, which may result from the lowered photosynthetic abilities as well as down-regulated expression of 7 genes associated with growth-promoting hormone biosynthesis and signal transduction. It can be speculated that cyanobacterial VOCs may poison aquatic plants by lowering the photosynthesis and growth through altering related gene expression.

Effects of hydrogen peroxide on Scenedesmus obliquus: Cell growth, antioxidant enzyme activity and intracellular protein fingerprinting

Hydrogen peroxide (H₂O₂) is an environmental-friendly algicide and it is widely used to control algal blooms in aquatic ecosystems. However, the response of algal cell metabolic characteristics and intracellular protein profile under H₂O₂ stress is still not well understood. In the present study, the green alga Scenedesmus obliquus was exposed to different concentrations of H₂O₂ (0, 2, 6, 8 and 10 mg L^-1) to evaluate the changes in algal morphological, physiological, and proteomic features to H₂O₂ exposure. The results showed that 8 mg L^-1 of H₂O₂ could effectively inhibit the cell growth and photosynthetic activity of S. obliquus including chlorophyll-a content and chlorophyll fluorescence parameters. The increased activities of superoxide dismutase (SOD) and catalase (CAT) observed in this study indicate that cells exposure to H₂O₂ caused oxidative stress. The metabolic activity of S. obliquus was significantly decreased by H₂O₂ treatment. In terms of proteomic analysis, 251 differentially expressed proteins (DEPs) were successfully identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed significant protein enrichment in the metabolic pathways, photosynthesis, ascorbic acid, and alginate metabolism and phenylpropane biosynthesis of S. obliquus. The analysis of protein-protein interaction system shows that the pathways of photosynthesis and metabolic pathways of S. obliquus were essential to resist oxidative stress. Taking together, these results shed new lights on exploring the cell physiological metabolism and intracellular protein mechanisms of H₂O₂ inhibition on algal blooms.

Low levels of TiO2-nanoparticles interact antagonistically with Al and Pb alleviating their toxicity

The contamination and bioavailability of deleterious metals in arable soils significantly limits crop development and yield. Aiming at mitigating Pb- and Al-induced phytotoxicity, this work explores the use of P25 titanium dioxide nanoparticles (nTiO₂) in soil amendments. For that, Lactuca sativa L. plants were germinated and grown in the presence of 10 ppm Pb or 50 ppm Al, combined or not with 5 ppm nTiO₂. Growth parameters, as well as endpoints of the redox state [cell relative membrane permeability (RMP), thiobarbituric acid reactive substances content, total phenolic content and photosynthesis (sugars and pigments levels, chlorophyll a fluorescence and gas exchange), were evaluated. Concerning Al, nTiO₂ treatment alleviated the impairments induced in germination rate, seedling length, water content, RMP, stomatal conductance (g_s), intercellular CO₂ (C_i), and net CO₂ assimilation rate (P_N). It increased anthocyanins contents and effective efficiency of photosystem II (Φ_PSII). In Pb-exposed plants, nTiO₂ amendment mitigated the effects in RMP, P_N, g_s, and C_i. It also increased the pigment contents and the transpiration rate (E) comparatively to the control without nTiO₂. These results clearly highlight the high potential of low doses of nTiO₂ in alleviating metal phytotoxicity, particularly the one of Pb. Additionally, further research should explore the use of these nanoparticles in agricultural soil amendments.

Mechanisms underlying the phytotoxicity and genotoxicity of aluminum and their alleviation strategies: A review

Aluminum (Al) is considered as a potential limiting factor for plant growth in acidic environment. At lower concentration, Al promotes plant growth by facilitating the phosphorous availability, while, at higher concentration, it causes rhizotoxicity by inhibiting the nutrient transportation system. Cellular membrane is identified as the first site of Al toxicity, which is consequent to Al-induced reactive oxygen species prompted lipid catabolism. Among all the soluble forms, the trivalent cationic form (Al³⁺) of Al is most toxic. Though, the ability to ascribe Al-tolerance is very complex, exclusion is an extensively established process contributing to Al³⁺ detoxification. Alteration in pH at root apex/rhizosphere, exudation of chelating agents, cell wall immobilization, and Al efflux have been recognized as probable methods for exclusion of Al, which is highly dependent on concentrations of organic acids, and plant species. Additionally, exogenous applications of boron, silicon, calcium, etc., in Al-stressed plant species can form a conjugate with it, thereby reducing its bioavailability/toxicity. Moreover, nanoparticles (NPs) are emerging tools in agricultural sector, which are found to be relatively more effective in mitigation of metal stress compared to their bulk materials. This review exhibits the fundamental approaches of Al phytotoxicity and endows with a comprehensive knowledge of the cellular and metabolic processes underlying toxic impacts along with ameliorative efficiencies of various potential agents including NPs. Additionally, it also elucidates the molecular mechanisms, future research prospects and challenges in effective alleviation mechanisms for enhancing plant Al-tolerance, to improve the growth and yields of susceptible-species on acidic soil.

Metabolic modifications to Ni excess in L. minor: Role of organic-, amino- and fatty acid profiles

In this study, the effects of excess nickel (Ni) (100 μM and 200 μM) on growth, antioxidant production, fatty acid, organic and amino acids profiles were examined in Lemna minor L. After 7 days of Ni treatment, chlorosis, growth inhibition and ROS overproduction were observed, accompanied by Ni accumulation. Interestingly, decreased malondialdehyde (MDA) levels were recorded in fronds upon Ni exposure. Fatty acid profiles in Ni-treated L. minor were characterized by increases in saturated- and decreases in unsaturated fatty acids. Ni excess increased the activities of antioxidant enzymes such as superoxide dismutase (SOD), guiacol peroxidase (GPX), and glutathione reductase (GR), and non-enzymatic antioxidants such as glutathione (GSH) and ascorbic acid (AsA); however, deactivation of ascorbate peroxidase (APX) and catalase (CAT) activities were also observed. Disruption of amino acid metabolism in Ni-exposed fronds was evidenced by the accumulation of cysteine, arginine, threonine, valine, isoleucine, leucine, lysine and phenylalanine, as well as reduced levels of tyrosine, alanine, aspartate and proline. Approximately 299%-396%, 139%-254% and 56%-97% concentration increments in citric, malic and oxalic acids, respectively, were concomitantly observed with significant decreases in tartaric, acetic, and fumaric acids in fronds subjected to Ni stress. Taken together, these results indicated that Ni stress induced negative effects on plant physiological, biochemical and morphological processes; however, it is likely that the coordination of metabolites and antioxidants may ameliorate the damaging effects of Ni accumulation.