Pb Stress Research Articles

Alleviating Role of Gibberellic Acid in Enhancing Plant Growth and Stimulating Phenolic Compounds in Carrot (Daucus carota L.) under Lead Stress

Toxicity of heavy-metals in soil is a major constraint for the production of carrots (Daucus carota L.). Different plant growth regulators are being used to overcome this problem. It has been found that plant growth regulators induce stress tolerance in plants. In this study, the role of exogenously applied plant growth regulator, gibberellic acid (GA3) was examined in soil grown two carrot cultivars under four different levels of lead (0, 50, 100, and 150 mg/kg) with one level of gibberellic acid (50 ppm). Results showed that Pb stress retarded the plant growth and reduced chlorophyll contents in the leaves of both carrot cultivars. A significant decrease was observed in photosynthetic attributes by Pb addition alone. However, exogenously applied GA3 ameliorated the plant growth and chlorophyll contents in the leaves of both carrot cultivars under Pb stressed conditions. Moreover, GA3 also decreased the uptake of Pb concentration in carrot leaves and roots. In addition, GA3 significantly regulated the phenolic compounds concentration in both carrot cultivars under Pb stress. In this study, cultivar T-29 was found to be more tolerant to Pb stress, however, cultivar Mevarick experienced higher damage regarding plant growth under Pb stress.

Antioxidant Enzyme Activities as Biomarkers of Cu and Pb Stress in Centella asiatica

The present study investigated the antioxidant enzyme activities (AEA) of ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) as biomarkers of Cu and Pb stress by using Centella asiatica grown in an experimental hydroponic condition. The results showed (i) higher accumulations of Cu and Pb in the roots of C. asiatica than those in the leaves, (ii) synergistic effects of Cu and Pb stress at higher metal-level exposures, and (iii) Cu and Pb stress triggered the increment of APX, CAT, GPX, and SOD levels in both the leaves and roots of C. asiatica. The increment of four AEA indicated that C. asiatica underwent oxidative stress caused by the production of reactive oxygen species when the plant was exposed to Cu and Pb. In order to prevent damages caused by Cu and Pb stress, the AEA system was heightened in C. asiatica, in which APX, CAT, GPX, and SOD can be used as biomarkers of Pb and Cu stress in the plant.

Bridging the gap: linking morpho-functional traits' plasticity with hyperaccumulation.

Plant species exhibiting heavy metal tolerance are instrumental in phytoremediation of metalliferous sites. Most of the time, variations in plant functional traits (PFTs) are overlooked while identifying hyperaccumulators. However, investigating morphological, physiological, and phenological variations can contribute to our knowledge about stress tolerance, and aid in identifying potential hyperaccumulators. In the present study, we investigated variation in morpho-functional traits in Solanum nigrum, a known hyperaccumulator, under lead (Pb) stress. Twenty-one PFTs including 9 above-ground (leaf count, leaf area, specific leaf area, leaf dry matter content, leaf thickness, leaf dry mass, shoot length, stem dry mass, stem diameter), 3 below-ground (root length, root dry mass, and root diameter), 4 reproductive (flower bud count, fruit count, flower count, and fruit dry mass), and 5 photosynthetic traits (total chlorophyll, total carotenoid, chlorophyll a, chlorophyll b, and photosynthetic efficiency) under varying Pb concentrations (500-2000mgkg-1) were assessed. Pillai's trace test (MANOVA) depicted significant variations in above-ground, below-ground, and photosynthetic traits, whereas reproductive traits did not vary significantly with progressive metal concentration. However, most of the studied traits except flower count, fruit dry mass, and chlorophyll b varied significantly under Pb stress. The study depicts that enhanced PFT's plasticity enables S. nigrum to grow in Pb-contaminated soil effectively without impacting plant fitness. Plasticity of morpho-functional traits, therefore, establishes itself as a resourceful approach in successful identification of phytoremediation capacity of a plant.

Alleviating lead-induced phytotoxicity and enhancing the phytoremediation of castor bean (Ricinus communis L.) by glutathione application: new insights into the mechanisms regulating antioxidants, gas exchange and lead uptake

Heavy metals pollution represents a serious issue for cultivable lands and ultimately threatens the worldwide food security. Lead (Pb) is a menacing metal which induces toxicity in plants and humans. Lead toxicity reduces the photosynthesis in plants, resulting in the reduction of plant growth and biomass. The excessive concentration of Pb in soil accumulates in plants body and enters into food chain, resulting in health hazards in humans. The phytoremediation is eco-friendly and cost-efficient technique to clean up the polluted soils. However, to the best of our Knowledge, there are very few reports addressing the enhancement of the phytoremediation potential of castor bean plants. Therefore, the present study aimed to investigate the potential role of glutathione (GSH), as a promising plant growth regulator, in enhancing the lead stress tolerance and phytoremediation potential of castor bean plants grown under lead stress conditions. The results indicated that Pb stress reduced the growth, biomass, chlorophyll pigments and gas exchange attributes of castor bean plants, causing oxidative damage in plants. Pb stress induced the oxidative stress markers and activities of antioxidant enzymes. On the other hand, the application of GSH reduced oxidative stress markers, but enhanced the growth, biomass, photosynthetic pigments, gas exchange attributes, Pb accumulation and antioxidant enzymes activities of lead-stressed castor bean plants. Both Pb uptake and Pb accumulation were increased by increasing concentrations of Pb in a dose-additive manner. However, at high dose of exogenous GSH (25 mg L−1) further enhancements were recorded in the Pb uptake in shoot by 48% and in root by 46%; Pb accumulation was further enhanced in shoot by 98% and in root by 101% in comparison with the respective control where no GSH was applied. Taken together, the findings revealed the promising role of GSH in enhancing the lead stress tolerance and phytoremediation potential of castor bean (Ricinus communis) plants cultivated in Pb-polluted soils through regulating leaf gas exchange, antioxidants machinery, and metal uptake.

Relative morpho-physiological responses of millets and oats against lead toxicity

Lead (Pb) toxicity due to accumulation in pearl millet (Pennisetum glaucum (L.) R. Br.), finger millet (Eleusine coracana (L.) Gaertn.) and oat (Avena sativa L.) was investigated. Seeds were grown on MS medium supplemented with 0–40 mg/l Pb and their response was noted after 15 days of germination. Accumulation of Pb in all the 3 species increased with increasing Pb, and maximum accumulation (91.3 ± 1.8 mg/l) was noted in roots of finger millet at 40 mg/l Pb. Toxicity effect of Pb accumulation was determined in terms of seed germination, seedling growth, chlorophyll and proline content, and antioxidative activity. Maximum decline in seed germination (78.5 %) was noted in oats. Inhibition of shoot (∼75–78.3 %) and root (∼97–98 %) elongation was maximum in pearl millet and oat, while reduction in biomass accumulation was maximum in shoot (67 %) and root (∼74 %) in oat. Chlorophyll content decreased significantly and was minimum (1.01 ± 0.03 mg/g FW) in pearl millet at 40 mg/l Pb. Higher SOD and GPX activities were noted in all the plantlets, while CAT activity decreased with increasing Pb levels in the medium. At the highest Pb concentration, proline accumulation (13.1 ± 0.17 μM/g FW), MDA content (22.1 ± 0.20 μmol/g FW), SOD activity (58.73 ± 0.69 U/mg protein) and GPX activity (1.5 ± 0.01 U/g FW) were maximum in oat roots, while CAT activity (75.03 ± 2.37 mg H2O2 destroyed/5 min/g FW) was maximum in shoots of finger millet. Finger millet was more tolerant to Pb toxicity and showed significant accumulation potential in both above and below ground parts. This study provides an overview of toxicity and tolerance mechanism of millets and oats against Pb stress. The study helps in understanding the mechanism of detoxification of lead employed by the plants and to select tolerant plant variety which could be used to bioremediate the lead contaminated soils.

Alleviation of Lead Stress on Sage Plant by 5-Aminolevulinic Acid (ALA).

Oxidative stress is imparted by a varying range of environmental factors involving heavy metal stress. Thus, the mechanisms of antioxidant resistance may advance a policy to improve metal tolerance. Lead as a toxic heavy metal negatively affects the metabolic activities and growth of medicinal and aromatic plants. This investigation aimed to assess the function of 5-aminolevulinic acid (ALA) in the alleviation of Pb stress in sage plants (Salvia officinalis L.) grown either hydroponically or in pots. Various concentrations of Pb (0, 100, 200, and 400 µM) and different concentrations of ALA (0, 10, and 20 mg L−1) were tested. This investigation showed that Pb altered the physiological parameters. Pb stress differentially reduced germination percentage and protein content compared to control plants. However, lead stress promoted malondialdehyde (MDA) and H2O2 contents in the treated plants. Also, lead stress enhanced the anti-oxidative enzyme activities; ascorbate peroxidase superoxide, dismutase, glutathione peroxidase, and glutathione reductase in Salvia plants. ALA application enhanced the germination percentage and protein content compared to their corresponding controls. Whereas, under ALA application MDA and H2O2 contents, as well as the activities of SOD, APX, GPX, and GR, were lowered. These findings suggest that ALA at the 20 mgL−1 level protects the Salvia plant from Pb stress. Therefore, the results recommend ALA application to alleviate Pb stress.

Effects of heavy metal (Pb) stress on some growth parameters and chemical changes in the soybean plant (Glycine max L.)

Effects of heavy metal (Pb) stress on some growth parameters and chemical changes in the soybean plant (Glycine max L.)

Liquiritoside Alleviated Pb Induced Stress in Brassica rapa subsp. Parachinensis: Modulations in Glucosinolate Content and Some Physiochemical Attributes.

Current research was conducted to explore the effects of liquiritoside on the growth and physiochemical features of Chinese flowering cabbage (Brassica rapa subsp. parachinensis) under lead (Pb) stress. Lead stressed B. rapa plants exhibited decreased growth parameters, chlorophyll, and carotenoid contents. Moreover, Pb toxicity escalated the synthesis of malondialdehyde (MDA), hydrogen peroxide (H2O2), flavonoids, phenolics, and proline in treated plants. Nevertheless, foliar application of liquiritoside mitigated Pb toxicity by decreasing oxidative stress by reducing cysteine, H2O2, and MDA contents in applied plants. Liquiritoside significantly increased plant height, shoot fresh weight and dry weight, number of leaves, and marketable value of Chinese flowering cabbage plants exposed to Pb toxicity. This biotic elicitor also enhanced the proline, glutathione, total phenolics, and flavonoid contents in Chinese flowering cabbage plants exposed to Pb stress compared with the control. Additionally, total glucosinolate content, phytochelatins (PCs), and non-protein thiols were effectively increased in plants grown under Pb regimes compared with the control plants. Overall, foliar application of liquiritoside can markedly alleviate Pb stress by restricting Pb translocation in Chinese flowering cabbage.

Lead exposure induced inflammation in bursa of Fabricius of Japanese quail (C. japonica) via NF-κB pathway activation and Wnt/β-catenin signaling inhibition

Bursa of Fabricius (BF), one of primary lymphoid organ, is unique to birds. Meanwhile, lead (Pb) is well known for its high toxicology to birds. Therefore, this study aimed to examine the chronic toxic effects of lead exposure on BF in Japanese quails (C. japonica) and the underlying mechanism of lead immunotoxicity. One-week old male quails were exposed to 0 ppm, 50 ppm, 500 ppm and 1000 ppm Pb concentrations by drinking water for four weeks. The results showed that Pb accumulation in BF increased in a dose dependent way. The growth and development of BF was retarded in 500 ppm and 1000 ppm Pb groups. The number of lymphocytes was decreased and the release of immunoglobulin G and M (IgG, IgM), complement 3 and 4 (C3, C4) was inhibited by Pb exposure. Lead exposure also caused oxidative stress and increasing apoptosis in BF. Moreover, histopathological damages characterized by inflammatory hyperemia and inflammatory cell infiltration and ultrastructural injury featured by mitochondrial vacuole, cristae fracture and chromatin concentration were found in BF of 500 ppm and 1000 ppm Pb groups. Furthermore, RNA sequencing based transcriptomic analysis revealed that molecular signaling and functional pathways in BF were disrupted by lead exposure. In addition, the activation of Nuclear Factor kappa B (NF-κB) pathway while the inhibition of wingless integrated/catenin beta 1 (Wnt/β-catenin) signaling by Pb exposure were confirmed by quantitative real-time PCR (qPCR). Our study may benefit to understand potential mechanistic pathways of developmental immunotoxicology under Pb stress.

The exogenous menadiol diacetate enhances growth and yield by reducing Pb uptake, translocation and its toxicity through tissue nutrients acquisition in cucumber (Cucumis sativus L.)

The experiment was conducted to assess whether exogenous application of menadiol diacetate (MD, vitamin K 4 ) could alter nutrients acquisition and mitigate lead (Pb) toxicity in cucumber ( Cucumis sativus L.) plants. The seeds of cucumber were surface sterilized with 0.1% solution of HgCl 2 and primed in three different concentrations (0, 10, 20 μ M) of MD solution for 24 h. The primed seeds were sown in pots filled with sand having different Pb regimes (0 and 4 mM). After 35 d of germination, plants were harvested for biochemical and physiological parameters while the yield attributes were collected from 80 d of germination. The exposure to Pb reduced biomass, increased oxidants such as malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) and caused nutrients imbalance by decreasing K + , Fe and Ca 2 + ions in the shoots. Further, cucumber accumulated Pb mostly in the roots. However, the exogenous MD reduced oxidative stress and enhanced growth and yield under Pb stress that was linked with MD-mediated increase in photosynthetic pigments and tissue accumulation of beneficial osmolytes (soluble sugars) and nutrients (K + , Fe and Ca 2 + ) while reduction in the uptake of Pb in the roots and transport to the shoots and fruits. The results showed that MD not only enhances growth and yield through nutrients acquisition in cucumber but also decreases Pb accumulation in shoot and fruit, and thus could reduce Pb-driven health hazards in agricultural systems.

FaHSP17.8-CII orchestrates lead tolerance and accumulation in shoots via enhancing antioxidant enzymatic response and PSII activity in tall fescue

Tall fescue (Festuca arundinacea Schreb.) shows huge potential for lead (Pb) phytoremediation, while little is known on the molecular mechanisms involved in Pb tolerance and accumulation. Here, genetic engineering strategy was firstly used to investigate Pb tolerance and accumulation in tall fescue. The transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII was generated. After exposure to 1000 mg/L Pb(NO3)2, two FaHSP17.8-CII overexpressing lines, OE#3 and OE#7, showed higher tolerance to Pb as illustrated by the reduced levels of electrolyte leakage (EL) and malondialdehyde (MDA) as compared to the wild-type (WT) plants under Pb stress. Moreover, the FaHSP17.8-CII overexpression lines, OE#3 and OE#7, exhibited 36.3% and 46.6% higher shoot Pb accumulation relative to the WT grasses. When the grasses were exposed to Pb stress, the two OE lines had higher CAT, POD and SOD activities as compared to WT. Additionally, overexpression of FaHSP17.8-CII improved the synthesis of chlorophyll and transcript abundance of FapsbC, FapsbD and FapsbE, and alleviated the photoinhibition of PSII in tall fescue under Pb stress. This study provides an initial genetic engineering strategy to improve Pb phytoremediation efficiency in tall fescue by FaHSP17.8-CII overexpression.

Biochar and exogenous calcium assisted alleviation of Pb phytotoxicity in water spinach (Ipomoea aquatica Forsk) cultivated in Pb-spiked soil.

The consumption of vegetables grown in Pb-polluted soils causes serious threats to human health around the globe. In this study, we evaluated the Pb toxicity alleviation in water spinach grown of pot experiments in Pb-spiked soil treated with biochar and exogenous calcium. The results showed that both biochar and exogenous calcium alleviated Pb stress in water spinach, which was mainly manifested on its improved soil health and increased growth and decreased Pb uptake. Incorporation of 3% biochar significantly reduced CaCl2 extracted Pb by 53.6% and decreased Pb accumulation in roots (67.1%) and shoots (80.8%). Our also findings indicated that Pb detoxification mechanism of biochar and exogenous calcium was totally different, while they can induce a synergistic impact on water spinach Pb stress alleviation. The combination of biochar and exogenous calcium in Pb-contaminated soil remediation may complement each other and reduce Pb entry into the human body through vegetables.

Role of magnesium oxide nanoparticles in the mitigation of lead-induced stress in Daucus carota: modulation in polyamines and antioxidant enzymes

During the current study, the effects of magnesium oxide nanoparticles (5 mmol/L) were observed on the growth and mineral nutrients of Daucus carota under lead (Pb) stress. The results demonstrated that Pb stress decreased the growth and photosynthetic rate of D. carota plants. Furthermore, Pb stressed plants showed decreased uptake of mineral nutrients including Zn, Na, Fe, K, Ca, Mg, K, and Cu. Similarly, Pb stressed plants showed enhanced electrolyte leakage (EL) and malondialdehyde (MDA) content. However, magnesium oxide nanoparticles detoxified ROS to mitigate Pb stress and improved the growth of plants. Magnesium oxide nanoparticles also escalated the activity of antioxidant enzymes including superoxide dismutase (SOD) and Catalase (CAT). A higher amount of Pb content was observed in the roots as compared to the shoot of plants. Lead toxicity reduced manganese accumulation in D. carota plants. The increased concentration of iron, manganese, copper, and zinc advocates stress the ameliorative role of Pb stress in plants. Novelty statement The role of MgONPs in the alleviation of Pb-toxicity in Daucus carota has never been exploited. In addition, the potential of MgONPs to enhance nutritional content in D. carota via modulation in antioxidant system and polyamines have never been reported.

Genotypic screening of wheat and their physiological responses under lead toxicity

Lead (Pb) is the second most harmful heavy metal contaminant in the environment and toxic for plant growth and development. Therefore, the identification and selection of plant genotypes tolerant to Pb stress are of great significance. In this study, twenty-six wheat lines (Triticum aestivum) were screened for Pb tolerance based on their morpho-physiological variations at the seedling stage with a rapid hydroponic technique using lead nitrate (Pb(NO3)2) at two concentrations (500 ?M and 1 mM) along with control. Wheat genotypes showed distinct variations in plant height, plant biomass and chlorophyll concentration in response to different concentrations of Pb. Considering all parameters, Akbar was found most tolerant (T) with minimum RS (2.97) to Pb stress, followed by BARI Gom-31 (3.45), Barkat (3.54) and Sufi (3.65), while BARI Gom-26 (10.14) was most sensitive (S) followed by Khude Gom (9.69), BARI Gom-30 (8.79), LalGom (8.76) and BARI Gom-32 respectively. More scores were seen in the remaining genotypes and were graded as moderately tolerant/resistant (MT) to Pb stress. Results showed that the resistant line had less damage to root and shoot characteristics along with chlorophyll score, thereby providing a hint about the Pb tolerance capacity of wheat genotypes at the seedling stage. Furthermore, findings indicate that Pb susceptibility in wheat is predominantly associated with a decrease in the Pb components of the root and shoot. We suggest Akbar as an elite genotype to cultivate or use in downstream studies on the basis of our findings to ensure an improved crop production relative to other varieties evaluated. These findings provide the necessary background for Pb cleansing and Pb-free wheat development for environment and health safety.

Indole Acetic Acid (IAA) Mediated Amelioration of Lead (Pb) Stress- Physiological Indices of Mung Bean [Vigna radiata (L.) Wilczek

Background: Heavy metals have their adverse effects on growth and physiology of plant. Plant growth regulators help in improving the growth and physiological phenomenon in plants. A pot culture experiment was devised to explore the ameliorative potential of Indole Acetic Acid (IAA) for toxicity of rhizospheric lead (Pb) on two varieties of Mung bean [Vigna radiate (L.) Wickzek]. Methods: Seeds of two varieties i.e., M- 8 and MN-92 were grown in earthen pots filled with sandy loam soil and were arranged under complete randomization. Fifteen days after germination, the lead (Pb) was added @ 10mg/kg and 20mg/kg soil as solution Pb NO3. Indole Acetic Acid @100.0mM was foliarly sprayed twice at 15 and 30 days of plants emergence. Physiological parameters i.e., Photosynthetic Rate, Transpiration Rate, Stomatal conductance, Sub Stomatal CO2 Concentration and biomass production in the form of stem, root and leaf dry weights were determined at the age of physiological maturity for three replicates. Result: By application of IAA, photostnthetic rate reduction was declined from 24.61% to 17.78% under 10mg Pb stress and from 55.54% to 27.35% under 20mg Pb stress. Stomatal conductance reduction was declined from 0.56% to 0.28% under 10mg Pb stress and from 3.37% to 1.68% under 20mg Pb stress. Alleviation of Pb stress by IAA for transpiration rate was non significant. Similarly, the role of IAA for alleviation of Pb stress in term of dry weights of stem,root and leaves were non significant statistically.

Analysis of Cadmium-Stress-Induced microRNAs and Their Targets Reveals bra-miR172b-3p as a Potential Cd2+-Specific Resistance Factor in Brassica juncea

The contamination of soil with high levels of cadmium (Cd) is of increasing concern, as Cd is a heavy metal element that seriously limits crop productivity and quality, thus affecting human health. (1) Background: Some miRNAs play key regulatory roles in response to Cd stress, but few have been explored in the highly Cd-enriched coefficient oilseed crop, Brassica juncea. (2) Methods: The genome-wide identification and characterization of miRNAs and their targets in leaves and roots of Brassica juncea exposed to Cd stress was undertaken using strand specific transcript sequencing and miRNA sequencing. (3) Results: In total, 11 known and novel miRNAs, as well as 56 target transcripts, were identified as Cd-responsive miRNAs and transcripts. Additionally, four corresponding target transcripts of six miRNAs, including FLA9 (Fasciclin-Like Arabinogalactan-protein 9), ATCAT3 (catalase 3), DOX1 (dioxygenases) and ATCCS (copper chaperone for superoxide dismutase), were found to be involved in the plant’s biotic stress pathway. We further validated the expression of three miRNA and six target genes in response to Cd, hydrargyrum (Hg), manganese (Mn), plumbum (Pb) or natrium (Na) stress and Mucor infection by qRT-PCR, and show that ATCCS and FLA9 were significantly and differentially regulated in the Cd-treated leaves. In addition, our results showed that DOX1 was obviously induced by Pb stress. Among the respective target miRNAs, bra-miR172b-3p (target for ATCCS) and ra-miR398-3p (target for FLA9) were down-regulated in Cd-treated leaves. (4) Conclusions: We identified bra-miR172b-3p as a potential Cd-specific resistant inhibitor, which may be negatively regulated in ATCCS in response to Cd stress. These findings could provide further insight into the regulatory networks of Cd-responsive miRNA in Brassica juncea.

Effects of Lead (Pb) and Benzo [a] Pyrene (B[a]P) and their Combined Exposure on Element Accumulation in Ryegrass (Lolium perenne L.).

It was observed in this work that application of Pb and B[a]P co-exposure significantly (p < 0.05) reduced Pb content in ryegrass leaves and roots. The effect of Pb dominated the change of N, P, K, Cu, and Cr content in leaves and roots of ryegrass under joint stress of Pb and B[a]P. Principal component analysis showed that the foliar spraying of 400μmol L-1 Pb and 80μmol L-1 B[a]P had the best effect on improving the mineral element absorption under combined pollution. Ryegrass has strong resistance and certain Pb and B[a]P absorptive capacities, and can resist combined contamination by transferring N, P, K, Zn, Cu, and Cr contents between the overground and the root. These results highlight the potential capacity of ryegrass for use in the phytoremediation of soils contaminated by Pb and B[a]P.

Application of hydrogen-rich water modulates physio-biochemical functions and early growth of fragrant rice under Cd and Pb stress.

Application of hydrogen-rich water (HRW) could improve plant growth under stress conditions; however, its effects on early growth and related physiological functions of fragrant rice under cadmium (Cd) and lead (Pb) toxicity are unknown. The present study was composed of two HRW treatments, i.e., H0: without H2 and HRW: with 500ppb H2 gas, three treatments with two metals, i.e., M0: without heavy metal, Cd: 75 μmol l-1 of Cd, Pb: 750 μmol l-1 of Pb applied to two popular fragrant rice cultivars, i.e., Yuxiangyouzhan and Xiangyaxiangzhan. The growth and physio-biochemical attributes of fragrant rice at 5 and 10 days after treatment (DAT) were assessed. Results showed that HRW treatment promoted the growth of rice seedlings in terms of increased dry biomass of shoot, root, and the whole seedling at 10 DAT. Moreover, HRW also improved early growth of fragrant rice under Pb stress with substantial increase in fresh and dry weight of roots and the whole seedling at 5 and 10 DAT. Application of HRW slightly alleviated the root inhibition caused by Cd toxicity in rice seedlings at 10 DAT. In addition, antioxidant activities, i.e., catalase (CAT) and peroxidase (POD), were increased with HRW application at 10 DAT while decreased root Pb and Cd contents of both rice cultivars. Overall, HRW alleviated the inhibitory effects of Cd and Pb toxicity by regulating the antioxidant defense response in growing rice plants.

Dynamic study of the lead (Pb) tolerance and accumulation characteristics of new dwarf bamboo in Pb-contaminated soil

Dwarf bamboo is a woody plant with potential for use in the remediation of Pb-contaminated soil. Due to its clonal growth habit, there are two keys to its application for continuous soil Pb remediation: 1) its ability to form shoots and grow into new bamboo normally under Pb stress and 2) the Pb tolerance and accumulation characteristics of this new bamboo. Here, 5 species of dwarf bamboo were treated with 2 levels of soil Pb stress (0 and 1500 mg kg−1). In the roots of 3 of the species (Sasa argenteostriata, Sasaella glabra, and Indocalamus decorus), Pb tended to be distributed along the cell wall and transported to vacuoles. In the other 2 species (Sasa auricoma and Sasa fortunei), Pb was arranged linearly along the cell wall. Under Pb treatment, the new bamboo of all species showed gradual physiological adaptation to Pb stress. Correlations of the net photosynthetic rate, superoxide dismutase activity, and free proline levels with Pb content in new leaves in November were all higher than those in July, though that of malondialdehyde content decreased, suggesting that new dwarf bamboo exhibits good soil Pb stress tolerance. Sasa argenteostriata and Indocalamus decorus consistently maintained higher antioxidant enzyme activities and free proline levels than the other species under Pb treatment, and the total biomass per pot of the new bamboo decreased the least compared to that in the Pb-free treatment for these two species. Therefore, these bamboo species may be used in the long-term continuous remediation of Pb-contaminated soil.

Melatonin-induced DNA demethylation of metal transporters and antioxidant genes alleviates lead stress in radish plants

Melatonin (MT) is a tryptophan-derived natural product that plays a vital role in plant response to abiotic stresses, including heavy metals (HMs). However, it remains elusive how exogenous MT mediates lead (Pb) accumulation and detoxification at the methylation and transcriptional levels in radish. In this study, decreased Pb accumulation and increased antioxidant enzyme activity were detected under MT treatment in radish. Single-base resolution maps of DNA methylation under Pb stress (Pb200) and Pb plus MT treatment (Pb_50MT) were first generated. The genome-wide methylation level was increased under Pb stress, while an overall loss of DNA methylation was observed under MT treatment. The differentially methylated region (DMR)-associated genes between Pb_50MT and Pb200 were uniquely enriched in ion binding terms, including cation binding, iron ion binding, and transition metal ion binding. Hyper-DMRs between Pb200 and Control exhibited a decreasing trend of methylation under Pb_50MT treatment. A few critical upregulated antioxidant genes (e.g., RsAPX2, RsPOD52 and RsGST) exhibited decreased methylation levels under MT treatment, which enabled the radish plants to scavenge lead-induced reactive oxygen species (ROS) and decrease oxidative stress. Notably, several MT-induced HM transporter genes with low methylation (e.g., RsABCF5, RsYSL7 and RsHMT) and transcription factors (e.g., RsWRKY41 and RsMYB2) were involved in reducing Pb accumulation in radish roots. These findings could facilitate comprehensive elucidation of the molecular mechanism underlying MT-mediated Pb accumulation and detoxification in radish and other root vegetable crops.