Protein changes in Lepidium sativum L. exposed to Hg during soil phytoremediation

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.

Role of phosphorus in Vallisneria natans and biofilm exposure to Pb2+ and Cd2+ stress

Phosphorus (P) could improve the stress resistance and adaptability of submerged macrophytes. This study investigated the physiological and biochemical responses of plants exposed to different P and Pb, Cd concentrations. Alterations of protein synthesis, the DNA methylation (5-mC) level, and the microbial community of biofilm were also evaluated. Results indicated that lower P (0.5 mg·L^-1) could promote plant growth and metal enrichment while mitigating the toxicity of metals. Higher P (5.0 mg·L^-1) induced a degree of oxidative stress, as confirmed by increased activity of superoxide dismutase, peroxidase, and acid phosphatase, as well as increased malondialdehyde contents. While the variation of metallothionein synthesis and DNA methylation level of the plant was dependent on the level of P and metals in the water. These responses indicated potential mechanisms of P detoxification and intoxication. In addition, more abundant microbial communities were observed in biofilms exposed to P and metals. These findings provide theoretical support for the metal detoxification of P in submerged plants.

Zincum Metallicum, a homeopathic drug, alleviates Zn-induced toxic effects and promotes plant growth and antioxidant capacity in Lepidium sativum L

In this study, we investigated the effect of the homeopathic drug Zincum Metallicum (ZM) on zinc (Zn) toxicity in the plant species Lepidium sativum L. We focused on growth parameters, Zn uptake and numerous biochemical parameters. Seedlings were hydroponically subjected during 7 days to 0.05, 500, 1000, 1500 and 2000 µM Zn²⁺, in the absence or presence of 15ch or 9ch ZM. In the absence of ZM, Zn induced negative effect on growth especially at the dose of 2 mM. Zn induced also chlorosis, reduced total chlorophyll and/or carotenoid content and increased the level of malondialdehyde (MDA). Under Zn toxicity (500, 1000 and 1500 µM), the superoxide dismutase (SOD), catalase (CAT), gaiacol peroxidase (GPX) and glutathione reductase (GR) activities were increased or not significantly affected, while at 2000 µM Zn affected the activity of these enzymes. At the highest Zn level (2 mM), proline and total polyphenol and flavonoid contents were markedly increased in leaves and roots of L. sativum. Additionally, ZM supply considerably ameliorated the plant growth, photosynthetic pigment contents and increased non-enzymatic antioxidant molecules and enzymatic activities against Zn-induced oxidative stress. Our data suggest that homeopathic properties of ZM may be efficiently involved in the restriction of Zn-induced oxidative damages, by lowering Zn accumulation and translocation in the leaves and roots of Lepidium sativum L.

C3 and C4 plant systems respond differently to the concurrent challenges of mercuric oxide nanoparticles and future climate CO2

Future climate CO₂ (eCO₂) and contamination with nano-sized heavy metals (HM-NPs) represent concurrent challenges threatening plants. The interaction between eCO₂ and HM-NPs is rarely investigated, and no study has addressed their synchronous impact on the metabolism of the multifunctional stress-related metabolites, such as sugars and amino acids. Moreover, the characteristic responses of C3 and C4 plant systems to the concurrent impact of eCO₂ and HM-NPs are poorly understood. Herein, we have assessed the impact of eCO₂ (620 ppm) and/or HgO-NPs (100 mg/Kg soil) on growth, physiology and metabolism of sugars and amino acids, particularly proline, in C3 (wheat) and C4 (maize) plant systems. Under Hg-free conditions, eCO₂ treatment markedly improved the growth and photosynthesis and induced sugars levels and metabolism (glucose, fructose, sucrose, starch, sucrose P synthase and starch synthase) in wheat (C3) only. In contrast, HgO-NPs induced the uptake, accumulation and translocation of Hg in wheat and to less extend in maize plants. Particularly in wheat, this induced significant decreases in growth and photosynthesis and increases in photorespiration, dark respiration and levels of tricarboxylic acid cycle organic acids. Interestingly, the co-application of eCO₂ reduced the accumulation of Hg and recovered the HgO-NPs-induced effects on growth and metabolism in both plants. At stress defense level, HgO-NPs induced the accumulation of sucrose and proline, more in maize, via upregulation of sucrose P synthase, ornithine amino transferase, ∆¹-pyrroline-5-carboxylate (P5C) synthetase and P5C reductase. The co-existence of eCO₂ favored reduced sucrose biosynthesis and induced proline catabolism, which provide high energy to resume plant growth. Overall, despite the difference in their response to eCO₂ under normal conditions, eCO₂ induced similar metabolic events in C3 and C4 plants under stressful conditions, which trigger stress recovery.

Effects of phosphorous fertilizers on growth, Cu phytoextraction and tolerance of Leersia hexandra swartz under different Cu stress levels

In this study, the effects of Ca(H₂PO₄)₂, KH₂PO₄ and (NH₄)₂HPO₄ on growth, Cu phytoextraction and tolerance of Leersia hexandra swartz (L. hexandra) under different Cu stress levels were investigated. The results showed that KH₂PO₄ could most significantly increase the plant height of L. hexandra (p < 0.05), while (NH₄)₂HPO₄ had the most significant promoting effect on its biomass (p < 0.05) by enhancing photosynthesis (chlorophyll content) (p < 0.01). The application of Ca(H₂PO₄)₂ could most significantly improve the Cu contents in roots, stems and leaves of L. hexandra (p < 0.05). In addition, (NH₄)₂HPO₄ could enhance the tolerance of L. hexandra to Cu by obviously reducing the content of MDA and increasing the contents of SP and MTs (p < 0.05), while Ca(H₂PO₄)₂ could evidently improve the activity of antioxidant enzymes (SOD, POD, CAT and APX) to reduce the damage of Cu to L. hexandra (p < 0.05). Although KH₂PO₄ could increase the contents of SP and MTs, the L. hexandra in KH₂PO₄ treatment groups had the highest MDA contents, which was unfavorable to the resistance to Cu stress. These suggested that the application in combination of Ca(H₂PO₄)₂ and (NH₄)₂HPO₄ may be more advantageous for Cu phytoextraction by L. hexandra.

Dactylis glomerata L. cultivation on mercury contaminated soil and its physiological response to granular sulphur aided phytostabilization

Most mercury (Hg) deposition in the environment results from anthropogenic inputs, Chlor-Alkali Plants (CAPs) particularly had a significant Hg impact on the environment at a regional scale. Exposure to mercury compounds resulting in various toxic effects for living organisms. The aim of this study was to investigate the capacity of granular sulphur (S) soil amendment and cultivation of Dactylis glomerata to decrease gaseous mercury emission to the atmosphere and mercury mobility in soils affected by CAP activity in the past. The effect of this approach on D. glomerata physiological status was also assessed (Hg concentration in biomass, chlorophyll a fluorescence, pigment contents and oxidative stress). Stabilization of mercury in soil and reduction of root and shoot concentration did not influence biomass production. Despite similar yields, photosynthetic efficiency was higher for plants grown in sulphur amended soil compared to unamended soil, particularly observed in phenomenological energy fluxes. Relative chlorophyll content was 30% lower for amended soil plants, however based on chlorophyll fluorescence data those were in high portion ineffective. Oxidative stress products and catalase activity did not differ significantly between experimental treatments. Sulphur amendment was a key factor for reduction of Hg mobility in soil (reduced by about 30%) while plant cover was significant for the reduction of Hg atmospheric emission (emissions were 2-times higher in sulphur amended soil without plant cover). Due to the very high concentration of Hg in soil (798.2 ± 7.3 mg kg^-1), growth inhibition was consistent regardless of treatment, demonstrated in the overload Reactive Oxygen Species scavenging mechanism and similar biomass yields. This leads to the conclusion that Hg may have greater impact on Calvin-Benson cycle associated enzymes than on the light-dependent photosynthesis phase. Despite these limitations this approach may still decrease environmental risks by reducing Hg emission to the atmosphere and reducing groundwater contamination.

Menadione sodium bisulphite mediated growth, secondary metabolism, nutrient uptake and oxidative defense in okra (Abelmoschus esculentus Moench) under cadmium stress

Menadione sodium bisulphite (MSB) mediates plant defense responses under abiotic stresses. In present experiment, Cd stress (1 mM) resulted in significant reduction in growth, relative water contents, chlorophyll and uptake of essential nutrients in two okra cultivars (Shabnum and Arka Anamika). Cd-induced reduction in these variables was more in cv. Arka Anamika compared with cv. Shabnum 786. Cd caused oxidative damage in the form of higher cellular levels of MDA and H₂O₂. MSB applications (0, 50, 100, 150 and 200 μM) had differential effect on growth and key physio-biochemical attributes. Higher MSB dose (200 μM) was lethal as it further aggravated damages under Cd toxicity. However, plants treated with 100 μM MSB exhibited lesser oxidative damage due to better oxidative defense in the form of stimulated activities of antioxidant enzymes (SOD, POD, CAT and APX) and increased concentration of non-enzymatic antioxidants (phenolics, flavonoids and ascorbic acid). Moreover, 100 μM MSB mitigated Cd effect on the uptake of Ca, K, and Mg. MSB also reduced the uptake and transport of Cd to aerial parts of plants. The results of present study revealed MSB-induced slight oxidative burst that induced the accumulation of reactive oxygen species (ROS) scavenging defense proteins under Cd stress.