Response of growth and Pb accumulation characteristics of plants with intercropping Arabis alpina-Zea mays to exogenous oxalic acid.

In order to study the effects of oxalic acids on plant growth and Pb accumulation in different parts of the plants of intercropping Arabis alpina and Zea mays, pot experiment was conducted to investigate the changes of oxalic acid contents of the plants and Pb accumulation through exogenous oxalic acid addition (0, 5, 25 and 50 mmol kg-1). The results showed the root biomass of intercropped A. alpina and total biomass of Z. mays increased by 3.22 folds and 2.97 folds with 5 mmol kg-1 oxalic acid treatment. The oxalic acid contents of shoots and root secretions decreased by 86.5% and 44.3%, respectively. The BCF (bio-accumulation factor) and TF (translocation factor) of intercropping A. alpina reduced under 25 - 50 mmol kg-1 oxalic acid treatments. There were relationships between exogenous oxalic acid treatment concentrations and oxalic acid contents of A. alpina shoots, Z. mays root secretions. The Pb contents of shoots of A. alpina and Z. mays were related to exogenous oxalic acid additions and oxalic acid contents of shoots. In general, 5 mmol kg-1 oxalic acid treatment, that can improve plant growth of intercropped A. alpina and Z. mays, which Pb translocation and accumulation of A. alpina were promoted, whereas Pb accumulation of A. alpina was inhibited with 25 - 50 mmol kg-1 concentrations addition. This study will provide a basis for promoting the application of phytoremediation techniques and efficient crop production in heavy metal contaminated areas.

Hyperaccumulators intercropped with crops will remediate heavy metal soils or mitigate the damage caused by heavy metals to plants through oxalic acid secretion by the root system. However, the effect of oxalic acid changes on plant growth and Pb accumulation is lacking. Our study investigated the changes in oxalic acid content at different concentrations and sites affected the ability of intercropped plants to grow and accumulate Pb. This work shown that under intercropping conditions, exogenous oxalic acid promotes intercropped plant growth as well as soil pH reduction, Pb content in shoots both Arabis alpina and Zea mays is influenced by exogenous oxalic acid content, while lower Z. mays roots Pb content is determined by a combination of exogenous addition and aboveground oxalic acid content. Low concentrations of oxalic acid promoted Pb enrichment in roots of A. alpina, while reducing the uptake of Pb content in Z. mays. This article gives us a better understanding for the response of intercropping plants to the use of organic acids under heavy metal stress and how to modify their environment so as to favor growth.

Effects of UV-B Radiation Exposure on Transgenerational Plasticity in Grain Morphology and Proanthocyanidin Content in Yuanyang Red Rice.

The effect of UV-B radiation exposure on transgenerational plasticity, the phenomenon whereby the parental environment influences both the parent's and the offspring's phenotype, is poorly understood. To investigate the impact of exposing successive generations of rice plants to UV-B radiation on seed morphology and proanthocyanidin content, the local traditional rice variety 'Baijiaolaojing' was planted on terraces in Yuanyang county and subjected to enhanced UV-B radiation treatments. The radiation intensity that caused the maximum phenotypic plasticity (7.5 kJ·m-2) was selected for further study, and the rice crops were cultivated for four successive generations. The results show that in the same generation, enhanced UV-B radiation resulted in significant decreases in grain length, grain width, spike weight, and thousand-grain weight, as well as significant increases in empty grain percentage and proanthocyanidin content, compared with crops grown under natural light conditions. Proanthocyanidin content increased as the number of generations of rice exposed to radiation increased, but in generation G3, it decreased, along with the empty grain ratio. At the same time, biomass, tiller number, and thousand-grain weight increased, and rice growth returned to control levels. When the offspring's radiation memory and growth environment did not match, rice growth was negatively affected, and seed proanthocyanidin content was increased to maintain seed activity. The correlation analysis results show that phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), dihydroflavonol 4-reductase (DFR), and 4-coumarate:CoA ligase (4CL) enzyme activity positively influenced proanthocyanidin content. Overall, UV-B radiation affected transgenerational plasticity in seed morphology and proanthocyanidin content, showing that rice was able to adapt to this stressor if previous generations had been continuously exposed to treatment.

Enhanced UV-B Radiation Induced the Proanthocyanidins Accumulation in Red Rice Grain of Traditional Rice Cultivars and Increased Antioxidant Capacity in Aging Mice.

Proanthocyanidins are major UV-absorbing compounds. To clarify the effect of enhanced UV-B radiation on the proanthocyanidin synthesis and antioxidant capacity of traditional rice varieties in Yuanyang terraced fields, we studied the effects of enhanced UV-B radiation (0, 2.5, 5.0, 7.5 kJ·m-2·d-1) on the rice grain morphology, proanthocyanidins content, and synthesis. The effects of UV-B radiation on the antioxidant capacity of rice were evaluated by feeding aging model mice. The results showed that UV-B radiation significantly affected the grain morphology of red rice and increased the compactness of starch grains in the starch storage cells of central endosperm. The content of proanthocyanidin B2 and C1 in the grains was significantly increased by 2.5 and 5.0 kJ·m-2·d-1 UV-B radiation. The activity of leucoanthocyanidin reductase was higher in rice treated by 5.0 kJ·m-2·d-1 than other treatments. The number of neurons in the hippocampus CA1 of mice brain fed red rice increased. After 5.0 kJ·m-2·d-1 treatment, red rice has the best antioxidant effect on aging model mice. UV-B radiation induces the synthesis of rice proanthocyanidins B2 and C1, and the antioxidant capacity of rice is related to the content of proanthocyanidins.

Responses of antioxidant enzymes and key resistant substances in perennial ryegrass (Lolium perenne L.) to cadmium and arsenic stresses.

Cadmium (Cd) and arsenic (As) exist simultaneously in soil environment, which poses a serious threat to the safety of agricultural products and forage production. Four Perennial Ryegrass (Lolium perenne L.) cultivars with different accumulation characteristics ('Nicaragua', 'Venus', 'Excellent' and 'Monro') were selected as the material for pot experiment. The coupled responses of key components and related enzyme activities under combined stresses of Cd and As were investigated. key components contents include Non protein sulfhydryl (NPT), glutathione (GSH) and phytochelatins (PCs). The related enzyme includes (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), γ-glutamylcysteine synthetase (γ-ECS), glutathione synthetase (GSS), phytochelatin synthetases (PCSase) and arsenate reductase (AR). The results showed that Cd contents of perennial ryegrass were higher than those of As contents with TFCd/As < 1. Cd and As contents in roots were in the higher proportion than those in shoots. Compared to control, POD activities increased by 2.72 folds under 120 mg kg-1 As treatment. The contents of PCs increased by 5.68 folds under 120 mg kg-1 As treatment. Under combined Cd and As stress, the MDA contents and antioxidant enzyme activities of 'Venus' were higher than those of 'Nicaragua'. 'Nicaragua', a high accumulation cultivar. Under the combined stresses of Cd and As, the enzyme activities and the key components were significantly correlated (P < 0.05) with the contents of Cd and As. The tolerance to Cd and As was improved with increase in GSH and PCs contents and γ-ECS, GSS, PCSase and AR activities. In conclusion, the antioxidant enzyme system and key resistant substances of perennial ryegrass have important and antagonistic effects on Cd and As stresses.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Adsorption Characteristics of Modified Eucalyptus Sawdust for Cadmium and Arsenic and Its Potential for Soil Remediation.

In order to explore the utilization of Eucalyptus sawdust (C) and develop its remediation potential in cadmium and arsenic contaminated soil, Eucalyptus sawdust were modified by FeCl3 and NaOH coprecipitation (MC). Characterization technology and pot experiment were used to explore the adsorption mechanism of cadmium and arsenic by MC and the effect of soil remediation. The results showed that iron oxide was loaded on the surface of Eucalyptus sawdust and destroyed the semi fiber structure. The adsorption mechanisms of cadmium and arsenic included electrostatic attraction, precipitation, complexation, redox. The soil pH value reduced by 0.12-0.18 units with 0.25%-1% ratio of application rates of MC to soil weight treatment; The contents of available cadmium and arsenic were reduced by 18%-25% and 12%-18%; MC could promote the transformation of Cd and As from highly active formation to low active formation and had a good application prospect for Cd and As compound pollution remediation.

An arbuscular mycorrhizal fungus increased the macroaggregate proportion and reduced cadmium leaching from polluted soil.

NOVELTY STATEMENT: AMF significantly increased the GRSP content and the macroaggregate proportion in soil, which contributed to reducing the Cd concentration in pore water and its leaching loss from soil.

Plant Species Diversity of Plant Communities and Heavy Metal Accumulation in Buffer Zone of Momianhe Stream Along a Long-Term Mine Wastes Area, China.

The species composition of eight shrub communities were investigated in order to understand the species diversity of plant communities in buffer zone and wetland of Momianhe stream along a long-term mine waste area, Lanping county, Yunnan province, China. Dominant plant species and soil samples were collected to analysis heavy metal (Cu, Zn, Pb and Cd) accumulation characteristics. The results showed that 100% samples for Zn, Pb, Cd, and 87.5% samples for Cu in the investigated area exceeded the Yunnan geochemical background value of the heavy metals in the soil. There were 36 plants species in communities, among which Epilobium pyrricholophum, Elsholtzia argyi, Artemisia vestita, Tripogon chinensis were the dominant species. Plant species, the number of individuals, Ecological Dominance (Do), Shannon-Wiener index (H'), Simpson diversity index (Dsi) and Pielou evenness index (Epi) were affected by Cd and Cu contents of the soil and sediment. Therefore, the results indicate that Cu and Cd contents and ecological risk in the process of long-term vegetation restoration of small catchment in lead-zinc mine waste area should pay more attention.

Organic Acid Excretion in Root Exudates as a Mechanism of Cadmium Uptake in a Sonchus Asper-Zea Mays Intercropping System.

This study assessed how the Sonchus asper L.-Zea mays intercropping influenced the plant Cd level, as well as the organic acid (low molecular mass) types and concentrations in root secretions, which was accomplished by conducting pot experiments with soil that was collected from a farmland surrounding a mining area. The results showed that the oxalic and citric acids were the prevailing organic acids in the plant root secretions, and that the intercropping led to prominently elevated root exudate concentrations of the two acids for S. asper by 43.8 and 75.4%, respectively, while decreased such concentrations by 18.5 and 18.7% for Z. mays, compared to monoculture. According to observations, the root exudate concentrations of citric and oxalic acids were significantly positively related to the available rhizosphere soil Cd and plant Cd. The results indicate that changes in root exudation of oxalic acid and citric acid result in different available Cd contents of the rhizosphere soil, thereby affecting the bioavailability of soil Cd, which increases Cd uptake and accumulation in S. asper but inhibits Cd accumulation in Z. mays.

Accumulation and Transfer of Cadmium Isotope (112Cd) by Sonchus asper Intercropped with Vicia faba and Implications for Phytoremediation.

Accumulation and transfer of Cd by Sonchus asper intercropped with a legume crop, Vicia faba were determined via 112Cd as a tracer to assess the potential of Sonchus asper as a hyperaccumulator. In this study, Sonchus asper and Vicia faba were planted side by side in soils amended with arbuscular mycorrhizae, and 112Cd was applied to either Sonchus asper or Vicia faba planted soils while the neighboring plant received 112Cd across a nylon net impermeable to the roots. Mean concentration of 112Cd in the shoot of Sonchus asper was 7.0 times higher than Vicia faba. The translocation factor of 112Cd in Sonchus asper were 39 and 400 times higher than in Vicia faba under the 112Cd direct and indirect treatments, respectively. The results suggested that the intercropping of Sonchus asper as a hyperaccumulator with Vicia faba, might be a feasible approach for phytoremediation of Cd contaminated soil.

Effects of enhanced UV-B radiation on the interaction between rice and Magnaporthe oryzae in Yuanyang terrace.

Enhanced ultraviolet-B (UV-B) radiation affected the growth of rice and Magnaporthe oryzae, and changed the interactions between them. Increased UV-B radiation (5.0 kJ m-2 d-1) on rice leaves in a Yuanyang terrace was conducted before, during, and after infection of the leaves with Magnaporthe oryzae. The relationship between rice blast and UV-B radiation on the disease resistance of rice and the pathogenicity of M. oryzae was studied, and the effects of enhanced UV-B radiation on the interactions between rice and M. oryzae were analysed. The results indicated the following: (1) enhanced UV-B radiation significantly reduced the rice blast disease index, but as infection progressed, the inhibitory effect of UV-B radiation on the disease was weakened. (2) UV-B radiation treatment before infection with M. oryzae (UV-B + M.) significantly increased the activity of the enzymes related to disease resistance (phenylalanine ammonia lyase, lipoxygenase, chitinase, and ß-1,3-glucanase), and the plants exhibited light-induced resistance. (3) Exposure to UV-B radiation after M. oryzae infection (M. + UV-B) did not induce disease course-related protein (PR) activity, but the content of soluble sugar increased. The osmotic stress caused by pathogenic fungi infection was alleviated by active accumulation of soluble sugar; due to this lack of nutrients, it was difficult for the rice blast fungus to grow. (4) Enhanced UV-B radiation significantly inhibited the production of conidia by M. oryzae, and the expression of the pathogenic genes Chitinase, MGP1, MAGB, and CPKA was significantly downregulated. The pathogenicity of M. oryzae was reduced by UV-B radiation. The resistance of rice leaves was weakened by simultaneous exposure to UV-B radiation and M. oryzae (UV-B/M.). Hence, UV-B radiation can weaken the infectivity of M. oryzae, improve the resistance of traditional rice, and contain the disease.

Effect of root exudates of intercropping Vicia faba and Arabis alpina on accumulation and sub-cellular distribution of lead and cadmium.

A field experiment in which a hyperaccumulator (Arabis alpina) was intercropped with winter crop (Vicia faba), was conducted to understand effect of the root exudates on the content and accumulated amounts, sub-cellular distribution of Cd and Pb of the intercropped plants during the ripening period of V. faba (120 d after sowing). The results showed that contents of soluble sugars exuded from the roots of intercropped A. alpina were 67.6% less than that of the monocropped plant, whereas contents of free amino acids was 57.9% greater. The total contents of organic acids exuded from roots of intercropped A. alpina and V. faba were 578.8% and 37.8% greater than that of monocropped plants, respectively. The contents of tartaric acid and malic acid exuded by roots of intercropped A. alpina were greater 31.9 times and 15.9 times than those of monocropped A. alpina, respectively. The contents and accumulated amounts of Cd and Pb in intercropped A. alpina were greater than those of monocropped A. alpina. The contents of Pb bound to organic matter in cell walls, cytoplasm and organelles of intercropped plants were greater than those of monocropped plants. These results demonstrate that increases in accumulated amounts of Pb and Cd caused by intercropping were closely related to migration of Cd and Pb in plants mediated by the composition and content of the root exudates.

Effects of UV-B radiation on the infectivity of Magnaporthe oryzae and rice disease-resistant physiology in Yuanyang terraces.

The traditional rice variety "Baijiaolaojing" was planted in Yuanyang terraces (1600 m altitude) under field conditions. The effects of enhanced UV-B radiation (0 kJ m-2, 2.5 kJ m-2, 5.0 kJ m-2 and 7.5 kJ m-2) on the rice-Magnaporthe oryzae system were studied with respect to the Magnaporthe oryzae infection, the disease-resistance physiology of the rice and the rice blast disease condition. The results showed that under enhanced UV-B radiation, the infectivity of Magnaporthe oryzae was decreased, which could significantly inhibit its growth and sporulation. The activities of rice leaf disease-resistance-related enzymes (phenylalanine ammonia-lyase, lipoxygenase, chitinase and ß-1,3-glucanase) were significantly increased under enhanced UV-B radiation. Following inoculation with Magnaporthe oryzae, levels of disease-resistance-related substances in the rice leaves were significantly increased. Among the results, it was found that leaves after UV-B radiation had a more significant resistance response. The level of UV-B irradiation showed a parabolic relationship with the rice blast index (r2 = 0.85, P < 0.01; in the control group, r2 = 0.88, P < 0.01). The disease index decreased with increase in irradiation. The DI was at a minimum with enhanced UV-B irradiance of 4 kJ m-2; thereafter, it increased with increasing irradiation. The enhanced UV-B radiation had a direct impact on the growth of rice and Magnaporthe oryzae, and it indirectly changed the rice-Magnaporthe oryzae system. UV-B radiation could reduce the harmful impact of rice blast.

Correction: Effects of UV-B radiation on the infectivity of Magnaporthe oryzae and rice disease-resistant physiology in Yuanyang terraces.

Correction for 'Effects of UV-B radiation on the infectivity of Magnaporthe oryzae and rice disease-resistant physiology in Yuanyang terraces' by Xiang Li et al., Photochem. Photobiol. Sci., 2018, 17, 8-17.

Effect of enhanced UV-B radiation on methane emission in a paddy field and rice root exudation of low-molecular-weight organic acids.

A local rice variety, "Baijiaolaojing", was grown in a paddy field in the Yuanyang rice terraces under ambient and supplemental levels of ultraviolet-B (UV-B, 280-315 nm) radiation. The effects of enhanced UV-B radiation (5 and 10 kJ m(-2) d(-1)) on methane emissions in the paddy field were evaluated using a closed-chamber gas chromatography-based system, and the contents of low-molecular-weight organic acids (LMWOAs) in root exudates were determined by high-performance liquid chromatography (HPLC). Peaks in methane emissions in the paddy field were detected at 60, 80 and 100 days after rice transplantation. The highest level of cumulative methane emissions occurred at the tillering stage, followed by the jointing-booting and maturity stages. The lowest level was found at the flowering stage. The enhanced UV-B radiation did not change the seasonal variation in methane emissions in the paddy field; however, it induced a significant increase in the flux of methane emissions at the jointing-booting and maturity stages, as well as a significant increase in the cumulative flux of methane emissions throughout the growth period. In addition, the enhanced UV-B radiation caused an increase in the contents of oxalic acid and succinic acid and a decrease in the contents of tartaric acid and malic acid in rice root exudates. Furthermore, a significant positive correlation (r = 0.725, p < 0.01) was found between the content of oxalic acid and the methane emissions in the paddy field. The results indicated that enhanced UV-B radiation promoted methane emissions in the paddy field, which was closely associated with its impact on the exudation of LMWOAs by rice roots.

Enhanced ultraviolet-B radiation alleviates structural damages on rice leaf caused by Magnaporthe oryzae infection.

Enhanced ultraviolet-B (UV-B) radiation can change the interaction between crops and pathogens. The effects of single and compound stresses of enhanced UV-B radiation (5.0 kJ·m-2) and Magnaporthe oryzae on the morphology, anatomy, and ultrastructure of rice leaves were investigated. M. oryzae infection decreased the leaf area and thickness, reduced the stomatal area and density, and caused damages to the leaf ultrastructure, such as cytoplasm-cell wall separation, atrophy and sinking of fan-shaped bulliform cells, and chloroplast deformation. The enhanced UV-B radiation supplied before or during M. oryzae infection remarkably decreased the mycelia number of M. oryzae in leaf epidermis, increased the leaf area, leaf thickness, stomatal density, and mastoid number; and alleviated the ultrastructural damages induced by M. oryzae to keep an integral chloroplast. While the UV-B radiation was supplied after M. oryzae infection, its alleviation effects on the damages induced by M. oryzae infection on the morphology and structure of rice leaf were attenuated. Thus, the alleviation of enhanced UV-B radiation on damages induced by M. oryzae infection on rice leaves was related to its application period. The enhanced UV-B radiation supplied before or during M. oryzae infection allowed the rice leaf to resist M. oryzae infection.

Appropriate supply of sulfur alleviates lead toxicity and stimulates its accumulation in hyperaccumulator Arabis alpina.

Widespread lead (Pb) contamination of agricultural soils is a global issue stemming from human activities. The remediation of Pb-contaminated soils used for agricultural purposes is critically important to safeguard food crop safety. Despite the modulating effects of sulfur (S) on plant responses to toxic heavy metals, the ecological, physiological, and molecular mechanisms driving such modulation in the Pb hyperaccumulator Arabis alpina L. remain unclear. Here, we investigated the effects of five S concentrations (0, 50, 100, 150, and 200 mg kg-1) on A. alpina grown in Pb-contaminated soil from a lead-zinc mining area. Under S50 (i.e., 50 mg kg-1) and S100 treatments, the Pb concentration in both shoots and roots of A. alpina significantly decreased compared to the control (S0). Specifically, the S50 treatment significantly enhanced Pb accumulation, plant biomass, and plant height, indicating that low S applications facilitate Pb accumulation from the soil and alleviate Pb toxicity. Additionally, S50, S100, and S150 treatments significantly improved photosynthetic rate, stomatal conductance, and intercellular CO2 concentration in A. alpina. Transcriptomic analysis showed that S50 and S100 treatments increased the expression of the LHCA, LHCB, psa, and psb genes, which had a significant impact on photosynthetic efficiency. S50 and S100 boosted glutathione (GSH) levels in A. alpina roots, and the increased expression of GST gene enhanced tolerance to environmental stress. In summary, these results suggest that an appropriate supply of S (S50 and S100) not only alleviates Pb toxicity by enhancing plant biomass, height, photosynthetic features, and sulfur metabolites but also stimulates Pb accumulation in the hyperaccumulator A. alpina. Our study elucidated the specific concentrations of sulfur that optimally enhance both Pb accumulation and stress tolerance in the hyperaccumulator A. alpina, providing novel insights into the practical application of sulfur in phytoremediation strategies and advancing our understanding of the underlying molecular mechanisms.

Organic Materials Promote Rhododendron simsii Growth and Rhizosphere Soil Properties in a Lead-Zinc Mining Wasteland.

The mining of metal minerals generates considerable mining wasteland areas, which are characterized by poor soil properties that hinder plant growth. In this study, a field plot experiment was carried out in the mining wasteland of the Lanping lead-zinc mine in Yunnan Province to study the effects of applying three organic materials-biochar (B), organic fertilizer (OF), and sludge (S)-at concentrations of 1% (mass fraction), on promoting the soil of mining wasteland and the growth of two plant varieties (Huolieniao and Yingshanhong). The results showed that the amount of available nutrients in the surface soil of a mining wasteland could be considerably increased by S and OF compared to the control check (CK). In the rhizosphere soils of two Rhododendron simsii varieties, the application of S increased the available phosphorus (P) content by 66.4% to 108.8% and the alkali-hydrolyzed nitrogen (N) content by 61.7% to 295.5%. However, the contents of available cadmium (Cd) and available lead (Pb) were reduced by 17.1% to 32.0% and 14.8% to 19.0%, respectively. Moreover, three organic materials increased the photosynthetic rate and biomass of two R. simsii varieties. Specifically, OF and S were found to significantly increase the biomass of R. simsii. Organic materials have direct impacts on the increased plant height and biomass of R. simsii. Additionally, organic materials indirectly contribute to the growth of R. simsii by reducing the content of available Cd and available Pb in rhizosphere soil while increasing the content of available nutrients according to the structural equation model (SEM). Overall, S can stabilize Cd and Pb, increase soil nutrient contents, and promote the growth of R. simsii effectively, and has great potential in the vegetation reconstruction of mining wasteland.

Effects of Different Sulfur Compounds on the Distribution Characteristics of Subcellular Lead Content in Arabis alpina L. var. parviflora Franch under Lead Stress.

Sulfur plays a vital role in the phytoremediation of lead-contaminated soil. The effects of different sulfur forms (S Na2S, and Na2SO4) on lead (Pb) absorption in hyperaccumulator Arabis alpina L. var. parviflora Franch were studied in a soil pot experiment. The subcellular sulfur and lead enrichment characteristics in A. alpina were studied by adding sulfur in different forms and concentrations (0, 75, and 150 mg·kg-1) to Pb-contaminated soil. The results show that the root and shoot biomass increased by 1.94 times under Na2S and Na2SO4 treatment, and the root-shoot ratio of A. alpina increased 1.62 times under the three forms of sulfur treatments, compared with the control. Sulfur content in cell walls and soluble fractions of the root and shoot of A. alpina significantly increased 3.35~5.75 times and decreased 5.85 and 9.28 times in the organelles under 150 mg·kg-1 Na2SO4 treatment. Meanwhile, Pb content in the root and shoot cell walls of A. alpina significantly increased by 3.54 and 2.75 times, respectively. Pb content in the shoot soluble fraction increased by 3.46 times, while it significantly reduced by 3.78 times in the shoot organelle. Pb content in the root organelle and soluble fraction decreased by 2.72 and 2.46 times. Different forms and concentrations of sulfur had no regularity in the effect of Pb and sulfur content in the subcellular components of A. alpina, but the bioconcentration and translocation factors of A. alpina increased compared with the control. Under different concentrations of Na2SO4, there was a significant positive correlation between the contents of sulfur and Pb in the subcellular components of the root of A. alpina (p < 0.05). These results indicate that sulfur application can enhance the Pb resistance of A. alpina by strengthening the cell wall fixation and vacuolar compartmentalization.

Response of Cd, Zn Translocation and Distribution to Organic Acids Heterogeneity in Brassica juncea L.

In order to investigate the translocation, distribution, and organic acid heterogeneity characteristics in Brassica juncea L., a pot experiment with the exogenous application of Cd and Zn was conducted to analyze the effects of Cd, Zn, and organic acid contents and heterogeneity on the translocation and distribution of Cd and Zn. The results showed that the Cd and Zn contents of B. juncea were mainly accumulated in the roots. The Cd content in the symplast sap was 127.66-146.50% higher than that in the apoplast sap, while the opposite was true for Zn. The distribution of Cd in xylem sap occupied 64.60% under 20 mg kg-1 Cd treatment, and Zn in xylem sap occupied 60.14% under 100 mg kg-1 Zn treatment. The Cd was predominantly distributed in the vacuole, but the Zn was predominantly distributed in the cell walls. In addition, oxalic and malic acids were present in high concentrations in B. juncea. In the vacuole, correlation analysis showed that the contents of Cd were negatively correlated with the contents of oxalic acid and succinic acid, and the contents of Zn were positively correlated with the contents of malic acid and acetic acid. The contents of Cd and Zn were negatively related to the contents of oxalic acid and citric acid in xylem sap. Therefore, Cd in B. juncea was mainly absorbed through the symplast pathway, and Zn was mainly absorbed through the apoplast pathway, and then Cd and Zn were distributed in the vacuole and cell walls. The Cd and Zn in B. juncea are transferred upward through the xylem and promoted by oxalic acid, malic acid, and citric acid.