Biomonitoring chromium III or VI soluble pollution by moss chlorophyll fluorescence

A Biorefinery Approach Integrating Lipid and EPS Augmentation Along with Cr (III) Mitigation by Chlorella minutissima

The quest for cleaner and sustainable energy sources is crucial, considering the current scenario of a steep rise in energy consumption and the fuel crisis, exacerbated by diminishing fossil fuel reserves and rising pollutants. In particular, the bioaccumulation of hazardous substances like trivalent chromium has not only disrupted the fragile equilibrium of the ecological system but also poses significant health hazards to humans. Microalgae emerged as a promising solution for achieving sustainability due to their ability to remediate contaminants and produce greener alternatives such as biofuels. This integrated approach provides an ambitious strategy to address global concerns pertaining to economic stability, environmental degradation, and the energy crisis. This study investigates the intricate defense mechanisms deployed by freshwater microalgae Chlorella minutissima in response to Cr (III) toxicity. The microalga achieved an impressive 92% removal efficiency with an IC50 value of 200 ppm, illustrating its extraordinary resilience towards chromium-induced stress. Furthermore, this research embarked on thorough explorations encompassing morphological, pigment-centric, and biochemical analyses, aimed at revealing the adaptive strategies associated with Cr (III) resilience, as well as the dynamics of carbon pool flow that contribute to enhanced lipid and extracellular polysaccharide (EPS) synthesis. The FAME profile of the biodiesel produced complies with the benchmark established by American and European fuel regulations, emphasizing its suitability as a high-quality vehicular fuel. Elevated levels of ROS, TBARS, and osmolytes (such as glycine-betaine), along with the increased activity of antioxidant enzymes (CAT, GR, and SOD), reveal the activation of robust defense mechanisms against oxidative stress caused by Cr (III). The finding of this investigation presents an effective framework for an algal-based biorefinery approach, integrating pollutant detoxification with the generation of vehicular-quality biodiesel and additional value-added compounds vital for achieving sustainability under the concept of a circular economy.

Surviving adversity: Exploring the presence of Lunularia cruciata (L.) Dum. on metal-polluted mining waste

The tailings dump of Barraxiutta (Sardinia, Italy) contains considerable concentrations of heavy metals and, consequently, is scarcely colonized by plants. However, wild populations of the liverwort Lunularia cruciata (L.) Dum. form dense and healthy-looking carpets on this tailing dump. L. cruciata colonizing the tailing dump was compared with a control population growing in a pristine environment in terms of: (i) pollutant content, (ii) photochemical efficiency, and (iii) volatile secondary metabolites in thalli extracts. L. cruciata maintained optimal photosynthesis despite containing considerable amounts of soil pollutants in its thalli and had higher sesquiterpene content compared to control plants. Sesquiterpenes have a role in plant stress resistance and adaptation to adverse environments. In the present study, we propose enhanced sesquiterpenes featuring Contaminated L. cruciata as a defence strategy implemented in the post-mining environment.

Melatonin alleviates Hg toxicity by modulating redox homeostasis and the urea cycle in moss

Mercury (Hg) is a highly toxic metal and can cause severe damage to many organisms under natural conditions. As an effective free radical scavenger and antioxidant, Melatonin (MT) has played important protective roles in alleviating oxidative damage caused by environmental cues including heavy metal stress in plants. However, the detailed mechanisms of melatonin in alleviating Hg toxicity still remain unclear in plants. Our results showed that the application of melatonin greatly reduced the concentrations of total and intracellular Hg in Taxiphyllum taxirameum. Meanwhile, melatonin significantly improved the antioxidant capacity and thus alleviated oxidative damage to the chloroplasts of T. taxirameum under Hg stress. Metabolic pathway analysis further revealed that melatonin-treated plants exhibited higher levels of 48 metabolites, including sugars, amino acids, and lipids, than non-melatonin-treated plants under Hg stress. Additionally, we further found that melatonin addition greatly improved the concentrations of four organic acids and three amino acids (Orn, Cit and Arg) related to the urea cycle, and thereby changed the levels of putrescine (Put) and spermidine (Spd) in T. taxirameum exposed to Hg stress. Further experiments showed that the high concentration of Put dramatically caused oxidative damage under Hg stress, while Spd effectively alleviated Hg toxicity in T. taxirameum. Taken together, this study provides new insight into the underlying mechanisms of melatonin in alleviating heavy metal toxicity in plants.

Speciation of macro- and nanoparticles of Cr2O3 in Hordeum vulgare L. and subsequent toxicity: A comparative study

Chromium (Cr) is reported to be hazardous to environmental components and surrounding biota when levels exceed allowable thresholds. As Cr is extensively utilized in different industries, thereby comprehensively studied for its toxicity. Along with Cr, the applications of nano-Cr or chromium oxide nanoparticles (Cr₂O₃-NPs) are also expanding; however, the literature is scarce or limited on their phytotoxicity. Thereby, the current work investigated the morpho-physiological insights of macro- and nanoparticles of Cr in Hordeum vulgare L. plants. The increased accumulation and translocation of Cr under the exposure of both forms disturbed the cellular metabolism that might have inhibited germination and growth as well as interfered with the photosynthesis of plants. The overall extent of toxicity was noticeably higher under nanoparticles' exposure than macroparticles of Cr. The potential cue for such phytotoxic consequences mediated by Cr nanoparticles could be an increased bioavailability of Cr ions which was also supported by their total content, mobility, and factor toxicity index. Besides, to support further these findings, synchrotron X-ray technique was used to reliably identify Cr-containing compounds in the plant tissues. The X-ray spectra of the near spectral region and the far region of the spectrum of K-edge of Cr were obtained, and it was established that the dominant crystalline phase corresponds to Cr₂O₃ (eskolaite) from the recorded observations. Thus, the obtained results would allow revealing the mechanism of macro- and nanoparticles of Cr induced impacts on plant at the tissue, cellular- and sub-cellular levels.

Does inorganic carbon species alter chromium reduction mechanism in sulfur-based autotrophic biosystem?

Sulfur-based autotrophic bioremediation is recognized as an environmentally-friendly and effective method for the treatment of Cr(VI) in groundwater. However, inorganic carbon (IC), especially IC-rich solid kitchen waste, has rarely been reported as an important factor in the autotrophic process. In China, kitchen waste containing IC is generated in large quantities, and in combination with Cr(VI) autotrophic treatment technology in groundwater can achieve a win-win situation. Herein, the efficiency of Cr(VI)-bioreduction coupling solid inorganic carbon (SIC) (e.g. marble, egg shell, oyster shell, and NSAD synthetic material) and liquid inorganic carbon (LIC) was compared for the first time. After 18 d incubation, there were significant differences in Cr(VI) reduction efficiency and microbial community between SIC-bioreactors and LIC-bioreactors. Higher electron transfer activity, greater bioavailability of organics, and multiple Cr(VI) reductases were detected in SIC-biosystems, which effectively promoted Cr(VI) energy metabolism and enzyme-mediated biological reduction. High-throughput 16S rRNA gene sequencing reveled multiple cooperative mechanism in different substrate biosystems. This study not only advances the understanding of SIC coupled with Cr(VI) autotrophic bioreduction, but also provides new insights for the treatment of solid kitchen waste and groundwater bioremediation.

Non-Protein Thiol Compounds and Antioxidant Responses Involved in Bryophyte Heavy-Metal Tolerance

Heavy-metal pollution represents a problem which has been widely discussed in recent years. The biological effects of heavy metals have been studied in both animals and plants, ranging from oxidative stress to genotoxicity. Plants, above all metal-tolerant species, have evolved a wide spectrum of strategies to counteract exposure to toxic metal concentrations. Among these strategies, the chelation and vacuolar sequestration of heavy metals are, after cell-wall immobilization, the first line of defence that prevent heavy metals from interacting with cell components. Furthermore, bryophytes activate a series of antioxidant non-enzymatic and enzymatic responses to counteract the effects of heavy metal in the cellular compartments. In this review, the role of non-protein thiol compounds and antioxidant molecules in bryophytes will be discussed.

Effect of nanobiochar (nBC) on morpho-physio-biochemical responses of black cumin (Nigella sativa L.) in Cr-spiked soil

Chromium is a highly toxic heavy metal. High concentrations of Cr (III) can affect metabolic processes in plants, resulting in different morphological, physiological, and biochemical defects. Agricultural practices such as sewage irrigation, over-fertilization, and sewage sludge application contribute significantly to Cr contamination. It can reduce the growth of plants by affecting the activity of antioxidant enzymes. The materials in nano form play an important role in nano-remediation and heavy metals absorption due to their high surface area and micropores. This research was conducted to study the potential of foliar application of nanobiochar/nBC (100 mg/L^-1 and 150 mg/L^-1) for mitigation of Cr (III) stress (200 mg/kg and 300 mg/kg) in black cumin (Nigella sativa) plants. The results showed that increased Cr stress (300 mg/kg) decreased the plant growth parameters, chlorophyll content, total soluble sugars, and proteins. However, increased the level of hydrogen peroxide (H₂O₂) and malondialdehyde acetate (MDA) as a result of the activity of antioxidant enzymes (Catalase, Superoxide dismutase, peroxidase dismutase, and ascorbic peroxidase) increased in Nigella sativa seedlings. Foliar application of the nBC (100 mg/L^-1) increased plant growth parameters, chlorophyll content, and osmoprotectants, while decreasing the levels of oxidative stress markers (H₂O₂ and MDA). Furthermore, with the application of nBC, the antioxidant enzyme activity considerably improved. Improved antioxidant activity shows that nBC helped to decrease oxidative stress, which in return improved the growth of Nigella sativa seedlings. Overall, present study findings concluded that foliar application of nBC in Nigella sativa seedlings improved growth, chlorophyll, and antioxidant enzymes. The nBC treatment of 100 mg/L^-1 showed better results compared to 150 mg/L^-1 under chromium stress.

Temporal and spatial biomonitoring of atmospheric heavy metal pollution using moss bags in Xichang

Heavy metal air pollution poses a serious threat to human health and the environment in Chinese tourist cities. In this study, we investigated the temporal and spatial variations of atmospheric heavy metal pollution using moss bags in Xichang, a tourist destination in Southwest China. The biomonitoring investigation used an indigenous moss (Taxiphyllum taxirameum) transplanted into bags. Moss bags were exposed to 22 sites including industrial, agricultural, urban/residential, tourist, and high-traffic sites, across four different seasons in 2019-2020. The results showed that T. taxirameum was a good biomonitor of air pollution in Xichang. Among the 22 sample points, air pollution was the worst along the G102 motorway. Heavy metal emissions varied in different regions and directions. Temporal changes significantly influenced the heavy metals accumulated in moss bags, with low deposition of most elements observed at nearly all sampling sites in summer. Different seasons and regions were important factors affecting atmospheric heavy metal pollution. Based on the correlation analysis and the positive matric factorization model, the results revealed that heavy metals in moss bags in Xichang were mainly derived from anthropogenic sources and atmospheric deposition. Overall, this research provides an important reference for air pollution monitoring in urban areas.

Chromium biogeochemical behaviour in soil-plant systems and remediation strategies: A critical review

Chromium (Cr) is a toxic heavy metal that is heavily discharged into the soil environment due to its widespread use and mining. High Cr levels may pose toxic hazards to plants, animals and humans, and thus have attracted global attention. Recently, much progress has been made in elucidating the mechanisms of Cr uptake, transport and accumulation in soil-plant systems, aiming to reduce the toxicity and ecological risk of Cr in soil; however, these topics have not been critically reviewed and summarised to date. Accordingly, based on available data-especially from the last five years (2017-2021)-this review traces a plausible link among Cr sources, levels, chemical forms, and phytoavailability in soil; Cr accumulation and translocation in plants; and Cr phytotoxicity and detoxification in plants. Additionally, given the toxicity and hazard posed by Cr(VI) in soils and the application of reductant materials to reduce Cr(VI) to Cr(III) for the remediation of Cr(VI)-contaminated soils, the reduction and immobilisation mechanisms by organic and inorganic reductants are summarised. Finally, some priority research challenges concerning the biogeochemical behaviour of Cr in soil-plant systems are highlighted, as well as the environmental impacts resulting from the application of reductive materials and potential research prospects.

Comparative Study of Cytotoxicity, DNA Damage and Oxidative Stress Induced by Heavy Metals Cd(II), Hg(II) and Cr(III) in Yeast

Wide range of applications of heavy metals and improperly discarded their castoffs possess serious threats to environment and human health. In this study, cytotoxicity, DNA damage and oxidative stress induced by Cd(II), Hg(II) and Cr(III) were comparatively studied in yeast Saccharomyces cerevisiae. Cd(II), Hg(II), and Cr(III) all produced strong cytotoxicity resulting in growth inhibition and cell mortality to varying degrees (Hg(II) > Cd(II) > Cr(III)). Hg(II) produced more oxidative stress. Cr(III) caused more serious DNA damage in vitro. Cd(II) also caused both obvious DNA damage and oxidative stress at higher concentration, but not as efficiently as Cd(II) and Hg(II). A further null mutation sensitivity assay showed that the relative sensitivity of rad1∆ to the metals was Cr(III) > Cd(II) > Hg(II), and that of trx1∆ to the metals was Hg(II) > Cd(II) > Cr(III). These data provide a clear evidence that the Cr(III) can cause significant DNA damage and potential genotoxicity; Hg(II) can strongly inhibit SOD activity, produce lipid peroxidation and cause serious membrane injury, suggesting these heavy metals can cause different toxic effects in different ways.

Removal of mercury(II), lead(II) and cadmium(II) from aqueous solutions using Rhodobacter sphaeroides SC01

Microorganisms and microbial products can be highly efficient in uptaking soluble and particulate forms of heavy metals, particularly from solutions. In this study, the removal efficiency, oxidative damage, antioxidant system, and the possible removal mechanisms were investigated in Rhodobacter (R.) sphaeroides SC01 under mercury (Hg), lead (Pb) and cadmium (Cd) stress. The results showed that SC01 had the highest removal rates (98%) of Pb among three heavy metals. Compared with Hg and Cd stress, Pb stress resulted in a lower levels of reactive oxygen species (ROS) and cell death. In contrast, the activities of four antioxidant enzymes in SC01 under Pb stress was higher than that of Hg and Cd stress. Furthermore, the analysis from fourier transform infrared spectroscopy indicated that complexation of Pb with hydroxyl, amid and phosphate groups was found in SC01 under Pb stress. In addition, X-ray diffraction analysis showed that precipitate of lead phosphate hydroxide was produced on the cell surface in SC01 exposed to Pb stress. Therefore, these results suggested that SC01 had good Pb removal ability by biosorption and precipitation and will be potentially useful for removal of Pb in industrial effluents.

A study on the protective effects of taxifolin on human umbilical vein endothelial cells and THP-1 cells damaged by hexavalent chromium: a probable mechanism for preventing cardiovascular disease induced by heavy metals

Taxifolin suppressed the toxicity and THP-1 cell adhesion to HUVECs induced by Cr(vi) via regulating the p38 MAPK and JNK pathways.

Noninvasive determination of toxic stress biomarkers by high-throughput screening of photoautotrophic cell suspension cultures with multicolor fluorescence imaging

BACKGROUND

With increasing pollution, herbicide application and interest in plant phenotyping, sensors capturing early responses to toxic stress are demanded for screening susceptible or resistant plant varieties. Standard toxicity tests on plants are laborious, demanding in terms of space and material, and the measurement of growth-inhibition based endpoints takes relatively long time. The aim of this work was to explore the potential of photoautotrophic cell suspension cultures for high-throughput early toxicity screening based on imaging techniques. The investigation of the universal potential of fluorescence imaging methods involved testing of three toxicants with different modes of action (DCMU, glyphosate and chromium).

RESULTS

The increased pace of testing was achieved by using non-destructive imaging methods-multicolor fluorescence (MCF) and chlorophyll fluorescence (ChlF). These methods detected the negative effects of the toxicants earlier than it was reflected in plant growth inhibition (decrease in leaf area and final dry weight). Moreover, more subtle and transient effects not resulting in growth inhibition could be detected by fluorescence. The pace and sensitivity of stress detection was further enhanced by using photoautotrophic cell suspension cultures. These reacted sooner, more pronouncedly and to lower concentrations of the tested toxicants than the plants. Toxicant-specific stress signatures were observed as a combination of MCF and ChlF parameters and timing of the response. Principal component analysis was found to be useful for reduction of the collected multidimensional data sets to a few informative parameters allowing comparison of the toxicant signatures.

CONCLUSIONS

Photoautotrophic cell suspension cultures have proved to be useful for rapid high-throughput screening of toxic stress and display a potential for employment as an alternative to tests on whole plants. The MCF and ChlF methods are capable of distinguishing early stress signatures of at least three different modes of action.

Perspective of Monitoring Heavy Metals by Moss Visible Chlorophyll Fluorescence Parameters

Chlorophyll fluorescence measurements have been mainly applied to investigate the functioning of the photosynthetic apparatus in the diagnosis of environmental stress. Moss is sensitive to several abiotic stresses and is considered an environmental indicator. Therefore, moss chlorophyll fluorescence can be as a visual parameter applicable for monitoring heavy metal contaminants in water. Different from previous studies with value changes of chlorophyll fluorescence in mosses, we suggest that phenotypes with anthocyanin accumulation pattern and chlorosis pattern and colors of chlorophyll fluorescence images of the maximum efficiency of PSII photochemistry (Fv/Fm) and the quantum yield of PSII electron transport (ΦPSII) could reflect metal species groups and concentrations roughly. And we further indicated that Cr(III) and Cr(VI) could be monitored distinguishably according to the non-photochemical quenching (NPQ) fluorescence of sporadic purple and sporadic lavender images, respectively. It is interesting that the fluorescence color patterns were nearly the same for all treatment concentrations. This perspective provides additional data of chlorophyll fluorescence changes in moss under cold, heat, salinity, high light or osmotic stress. Only heat stress and high light have significant effects on the fluorescence parameters of Fv/Fm and ΦPSII. In contrast, mosses are less sensitive to short-term cold, salinity, and osmotic stress. While NPQ decreases rapidly under the osmotic stress. Nevertheless, heat stress, high light or osmotic stress does not usually co-occur in the place where the moss grows. Estimation through moss chlorophyll fluorescence color patterns is still a rapid and non-invasive method to monitor heavy metal pollutions in water.

Exogenous melatonin enhances salt stress tolerance in maize seedlings by improving antioxidant and photosynthetic capacity

Melatonin (N-acetyl-5-methoxytryptamine) is an important biological hormone in many abiotic stress responses and developmental processes. In this study, the protective roles of melatonin were investigated by measuring the antioxidant defense system and photosynthetic characteristics in maize under salt stress. The results indicated that NaCl treatment led to the decrease in plant growth, chlorophyll contents and photochemical activity of photosystem II (PSII). However, the levels of reactive oxygen species increased significantly under salt stress. Meanwhile, we found that application of exogenous melatonin alleviated reactive oxygen species burst and protected the photosynthetic activity in maize seedlings under salt stress through the activation of antioxidant enzymes. In addition, 100 μM melatonin-treated plants showed high photosynthetic efficiency and salinity. Immunoblotting analysis of PSII proteins showed that melatonin application alleviated the decline of 34 kDa PSII reaction center protein (D1) and the increase of PSII subunit S protein. Taken together, our study promotes more comprehensive understanding in the protective effects of exogenous melatonin in maize under salt stress, and it may be involved in activation of antioxidant enzymes and regulation of PSII proteins.

Metal-induced oxidative stress in terrestrial macrolichens

Short-term (24 h) responses of Cladonia arbuscula subsp. mitis and Cladonia furcata to copper (CuII) or chromium (CrIII) excess (10 or 100 μM) were compared. C. arbuscula accumulated more Cu and Cr at higher metal doses but both species revealed depletion of K and/or Ca amount. Not only Cu but also Cr typically elevated reactive oxygen species (ROS) formation (fluorescence microscopy detection of total ROS and hydrogen peroxide) and depleted nitric oxide (NO) signal, with Cu showing more negative impact on lipid peroxidation (BODIPY 581/591 C11 staining reagent). Metals and staining reagents also affected anatomical responses and photobiont/mycobiont visibility. Principally different impact of Cu and Cr was observed at antioxidative metabolites level, indicating various ways of metal-induced ROS removal and/or metal chelation: Cu strongly depleted glutathione (GSH) and stimulated phytochelatin 2 (PC2) content while ascorbic acid accumulation was depleted by Cu and stimulated by Cr. Subsequent experiment with GSH biosynthetic inhibitor (buthionine sulfoximine, BSO) revealed that 48 h of exposure is needed to deplete GSH and BSO-induced depletion of GSH and PC2 amounts under Cu or Cr excess elevated ROS but depleted NO. These data suggest close relations between thiols, NO and appearance of oxidative stress (ROS generation) under metallic stress also in lichens.

Assessment of Fv/Fm absorbed by wheat canopies employing in-situ hyperspectral vegetation indexes

Chlorophyll fluorescence parameter of F_v/F_m, as an important index for evaluating crop yields and biomass, is key to guide crop management. However, the shortage of good hyperspectral data can hinder the accurate assessment of wheat F_v/F_m. In this research, the relationships between wheat canopy F_v/F_m and in-situ hyperspectral vegetation indexes were explored to develop a strategy for accurate F_v/F_m assessment. F_v/F_m had the highest coefficients with normalized pigments chlorophyll ratio index (NPCI) and the medium terrestrial chlorophyll index (MTCI). Both NPCI and MTCI were increased with the increase in F_v/F_m. However, NPCI value ceased to increase as F_v/F_m reached 0.61. MTCI had a descending trend when F_v/F_m value was higher than 0.61. A piecewise F_v/F_m assessment model with NPCI and MTCI regression variables was established when F_v/F_m value was ≤0.61 and >0.61, respectively. The model increased the accuracy of assessment by up to 16% as compared with the F_v/F_m assessment model based on a single vegetation index. Our study indicated that it was feasible to apply NPCI and MTCI to assess wheat F_v/F_m and to establish a piecewise F_v/F_m assessment model that can overcome the limitations from vegetation index saturation under high F_v/F_m value.