Molecular mechanisms of wheat acclimation to soil degradation: Insights into salt stress, heavy metal contamination, and nutrient deficiency

Plant acclimation to salt and alkali stress is closely linked to the ability of the antioxidant system to mediate the scavenging of reactive oxygen species (ROS). In this study, we investigated the effects of salt stress and alkali stress on ROS, antioxidant enzymes, transcriptome, and metabolome. The results showed that the levels of superoxide anions, hydrogen peroxide, malondialdehyde, and electrolyte leakage increased under salt and alkali stress, with higher concentrations observed under alkali stress than salt stress. The activities of superoxide dismutase (EC 1.15.1.1), peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11), glutathione reductase (EC 1.6.4.2), dehydroascorbate reductase (EC 1.8.5.1), and monodehydroascorbate reductase (EC 1.6.5.4) varied under salt and alkali stress. The transcriptome analysis revealed the induction of signal transduction and metabolic processes and differential expression of genes encoding antioxidant enzymes in response to salt and alkali stress. The metabolome analysis demonstrated increased ascorbic acid and glutathione under salt stress, while most phenolic acids, flavonoids, and alkaloids increased under salt and alkali stress. Integrative analysis of the metabolome and transcriptome data revealed that the flavonoid biosynthesis pathway played a key role in the grapevine's response to salt stress. The total flavonoid content increased under salt and alkali stress, but the accumulation of flavonoids was higher under salt stress than alkali stress. In conclusion, our findings indicate significant differences in the antioxidant defense of grapevines under these two stresses, providing insight into distinct acclimation mechanisms in grapevine under salt and alkali stress. This article is protected by copyright. All rights reserved.

Pollution and climate change degrade plant health. Plant stress can be decreased by application of salicylic acid, an hormone involved in plant signaling. Salicylic acid indeed initiates pathogenesis-related gene expression and synthesis of defensive compounds involved in local resistance and systemic acquired resistance. Salicylic acid may thus be used against pathogen virulence, heavy metal stresses, salt stress, and toxicities of other elements. Applied salicylic acid improves photosynthesis, growth, and various other physiological and biochemical characteristics in stressed plants. Salicylic acid antagonizes the oxidative damaging effect of metal toxicity directly by acting as an antioxidant to scavenge the reactive oxygen species and by activating the antioxidant systems of plants and indirectly by reducing uptake of metals from their medium of growth. We review here the use of exogenous salicylic acid in alleviating bacterial, fungal, and viral diseases, heavy metal toxicity, toxicity of essential micronutrients, and salt stress.

Heavy metal (HM) contamination in soils of greenhouse vegetable production (GVP) systems has drawn increasing attention in terms of food safety. In the present study, 64 surface soils were sampled, and the concentrations of select HMs were determined using atomic absorption spectroscopy. The results showed that the concentrations of cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), nickel (Ni) and chromium (Cr) in the soils were (0.2±0.2) mg/kg, (26.5±8.4) mg/kg, (101.4±43.2) mg/kg, (29.1±8.6) mg/kg, (24.5±3.3) mg/kg, and (56.5±6.3) mg/kg, and the corresponding accumulation index (AI) values were 2.30, 1.10, 1.43, 1.45, 1.07, and 0.97, respectively. The spatial distribution of the HMs suggested that Cd pollution displays a fractionation effect, which may be related to the source of Cd and its mobility. The concentration of Zn was significantly correlated with that of other HMs, implying that a comprehensive interactive effect might occur between Zn and other HMs. Furthermore, the values of the potential ecological risk index (RI) ranged from 41.23 to 185.91, meaning that attention should be paid to HM contamination of GVP soils to ensure food quality and safety. Keywords: heavy metal contamination, cold region, greenhouse vegetable production (GVP), distribution, ecological risk, food quality, food safety DOI: 10.25165/j.ijabe.20191202.4306 Citation: Lv P, Wei Z M, Yu Z M, Zhang J Z, Wang L M. Heavy metal contamination in soils of greenhouse vegetable production systems in a cold region of China. Int J Agric & Biol Eng, 2019; 12(2): 98–102.

Impact of heavy metal toxicity on the human health and environment.

In natural environments, plants often experience different stresses simultaneously, and adverse abiotic conditions can weaken the plant immune system. Interactome mapping revealed that the LOW SULPHUR UPREGULATED (LSU) proteins are hubs in an Arabidopsis protein interaction network that are targeted by virulence effectors from evolutionarily diverse pathogens. Here we show that LSU proteins are up-regulated in several abiotic and biotic stress conditions, such as nutrient depletion or salt stress, by both transcriptional and post-translational mechanisms. Interference with LSU expression prevents chloroplastic reactive oxygen species (ROS) production and proper stomatal closure during sulphur stress. We demonstrate that LSU1 interacts with the chloroplastic superoxide dismutase FSD2 and stimulates its enzymatic activity in vivo and in vitro. Pseudomonas syringae virulence effectors interfere with this interaction and preclude re-localization of LSU1 to chloroplasts. We demonstrate that reduced LSU levels cause a moderately enhanced disease susceptibility in plants exposed to abiotic stresses such as nutrient deficiency, high salinity, or heavy metal toxicity, whereas LSU1 overexpression confers significant disease resistance in several of these conditions. Our data suggest that the network hub LSU1 plays an important role in co-ordinating plant immune responses across a spectrum of abiotic stress conditions.

Due to poor hygiene, handling, and food safety education, street food poses a substantial public health risk. Foods wrapped in ink-printed papers have been related to cancer, neurological, reproductive, and renal and liver harm. Objective of this study was to assess community awareness regarding potential microbiological and heavy metal contamination in ready-to-eat fried foods wrapped in printed paper in Dar es Salaam, Tanzania. The structured questionnaire was used to assess the awareness of 293 street food vendors in three districts: Kinondoni, Temeke, and Kigamboni. The findings from this study indicated that most (67.8%) of vendors were female, primarily aged 31-40 years (58.0%), and mostly possessing a primary level education (47.7%). Approximately 67.5% of vendors were owners of their businesses, and 36.7% possessed more than four years of experience. Findings revealed printed paper to be the primary wrapping material (44.5%), followed by plastic bags (41.3%). Hygiene practices were was reported to be inadequate in which 88.0% of vendors did not cover their hair while 62.2% wore unclean clothing, and 95.1% failed to wash their hands before handling food. It was further revealed that awareness on heavy metal (71.1%) and microbial contamination (67.5%) was markedly inadequate and that the vendors were unaware of these risks, respectively. Although the finding showed poor awareness, 63.6% of vendors favoured the need for regulations on heavy metal contamination, while 56.5% favoured the reinforcement of regulations on the use of printed papers as wrapping materials for foods. These findings highlight the need to educate vendors about the risks associated with using ink-printed paper and personal hygiene practices to reduce microbial and heavy metal contamination.

Heavy metal (s) contamination of vegetables is an alarming and significant concern due to its potential health risks for consumers. Heavy metal contamination of vegetables has threatened both food security and human health. Contaminants like lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg) and others can be added to vegetable tissues when present in the soil, water, or through other sources. Anthropogenic activities such as mining, industrialization and agricultural practices like pesticide, fungicide, as well as fertilizer use release heavy metals into the soil, water and atmosphere. Vegetables are essential to the human nutrition, which provide vitamins, minerals and fibres and also have beneficial anti-oxidative properties to maintain normal physiological functions. Vegetables absorb heavy metal(s) and store them in their bodies at levels that can lead to health issues. Even at low concentrations, heavy metals can be highly detrimental to the human body due to the lack of an efficient excretion mechanism. The research on review of heavy metal contamination of vegetable crops and their amelioration have been conducted from various secondary sources of published data. Heavy metal polluted soil leads to reduction in growth due to changes in physiological and biochemical activities which affect the growth and yield of vegetable crops. To mitigate heavy metal contamination, various strategies are soil testing, remediation of contaminated sites, improving agricultural practices and monitoring of water sources, etc. Remediation techniques for reducing heavy metal contamination in vegetables include immobilization using low-cost absorbents (soil amendments), physical and chemical approaches, phytoremediation/bioremediation, chelating agents, microorganisms, transgenic plants, nanotechnology and grafting, etc.

Heavy metal (HM) contamination in soils of greenhouse vegetable production (GVP) systems has drawn increasing attention in terms of food safety. In the present study, 64 surface soils were sampled, and the concentrations of select HMs were determined using atomic absorption spectroscopy. The results showed that the concentrations of cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), nickel (Ni) and chromium (Cr) in the soils were (0.2±0.2) mg/kg, (26.5±8.4) mg/kg, (101.4±43.2) mg/kg, (29.1±8.6) mg/kg, (24.5±3.3) mg/kg, and (56.5±6.3) mg/kg, and the corresponding accumulation index (AI) values were 2.30, 1.10, 1.43, 1.45, 1.07, and 0.97, respectively. The spatial distribution of the HMs suggested that Cd pollution displays a fractionation effect, which may be related to the source of Cd and its mobility. The concentration of Zn was significantly correlated with that of other HMs, implying that a comprehensive interactive effect might occur between Zn and other HMs. Furthermore, the values of the potential ecological risk index (RI) ranged from 41.23 to 185.91, meaning that attention should be paid to HM contamination of GVP soils to ensure food quality and safety. Keywords: heavy metal contamination, cold region, greenhouse vegetable production (GVP), distribution, ecological risk, food quality, food safety DOI: 10.25165/j.ijabe.20191202.4306 Citation: Lv P, Wei Z M, Yu Z M, Zhang J Z, Wang L M. Heavy metal contamination in soils of greenhouse vegetable production systems in a cold region of China. Int J Agric & Biol Eng, 2019; 12(2): 98–102.

Heavy metal (HM) contamination caused by mining and smelting activities can be harmful to soil microbiota, which are highly sensitive to HM stress. Here, we explore the effects of HM contamination on the taxonomic composition, predicted function, and co-occurrence patterns of soil bacterial communities in two agricultural fields with contrasting levels of soil HMs (i.e., contaminated and uncontaminated natural areas). Our results indicate that HM contamination does not significantly influence soil bacterial α diversity but changes the bacterial community composition by enriching the phyla Gemmatimonadetes, Planctomycetes, and Parcubacteria and reducing the relative abundance of Actinobacteria. Our results further demonstrate that HM contamination can strengthen the complexity and modularity of the bacterial co-occurrence network but weaken positive interactions between keystone taxa, leading to the gradual disappearance of some taxa that originally played an important role in healthy soil, thereby possibly reducing the resistance of bacterial communities to HM toxicity. The predicted functions of bacterial communities are related to membrane transport, amino acid metabolism, energy metabolism, and carbohydrate metabolism. Among these, functions related to HM detoxification and antioxidation are enriched in uncontaminated soils, while HM contamination enriches functions related to metal resistance. This study demonstrated that microorganisms adapt to the stress of HM pollution by adjusting their composition and enhancing their network complexity and potential ecological functions.

Salinity and nutrient-depleted soil are major constraints to crop production, especially for vegetable crops. The effects of salinity and nutrient deficiency on spinach (Spinacia oleracea L.) were evaluated in sand cultures under greenhouse conditions. Plants were watered every day with Hoagland nutrition solution, deprived of nitrogen (N), phosphorous (P), or potassium (K) for nutrient deficiency, either with or without 20/10 mm sodium chloride (NaCl)/calcium chloride (CaCl2) for salinity treatment. Salinity significantly decreased shoot fresh weight (FW) and dry weight (DW), leaf relative water content (RWC), and specific leaf area (SLA) relative to controls after 4 weeks of treatment and increased chlorophyll content, maximum photochemical efficiency (Fv/Fm), and photochemical yield [Y(II)]. Nitrogen deficiency greatly reduced shoot FW and DW, SLA, and chlorophyll content, regardless of salt treatment. Y(II) and Fv/Fm were reduced by N deficiency and salinity treatment. Phosphorous and K deficiencies, similarly, decreased shoot FW and DW irrespective of salinity treatment and increased chlorophyll content without salt stress. Phosphorous deficiency increased Y(II) under control and Fv/Fm under both control and salt treatment. Salinity and nutrient deficiency also affected the nutritional value of spinach. Salt stress increased carotenoid and flavonoid contents, and reducing power in full-strength Hoagland solution, and decreased leaf ferrous ion chelating ability (FICA). Nutrient deficiency increased reducing power regardless of salinity treatment. Nitrogen deficiency increased anthocyanin and total phenolic contents, decreased carotenoids and flavonoids regardless of salinity treatment, and increased antioxidant capacity under no-salt conditions. Phosphorous deficiency increased carotenoid and flavonoid contents under no-salt condition and enhanced total phenolic content and reduced FICA and amino acid content under salt stress. Potassium deficiency increased total phenolic, carotenoid, and flavonoid contents and antioxidant capacity under non-salt condition, but decreased FICA regardless of salinity treatment. These results suggest that spinach nutritional value could be improved with only moderately or slightly reduced yield through cultural practices that impose either low fertilizer levels or slight salt stress.

The ability of plants to protect themselves from stress-related damages is termed "adaptability" and the phenomenon of showing better performance in subsequent stress is termed "stress memory". This phenomenon has been reported in various stresses such as drought, heat, salinity, cold, and heavy metal toxicity. Histone modification leading to chromatin remodeling and accumulation of phosphorylated RNA polymerase on the promoters of memory genes is a well-known mechanism of plant stress memory. Recent studies have revealed the role of non-coding RNAs (ncRNAs) and alternative splicing (AS) in memory-specific gene expression and transgenerational inheritance of stress memory. MicroRNAs (miRNAs) inhibit specific genes to enable plants to respond better in subsequent drought and heat stress, while long non-coding RNAs (lncRNAs) play roles in epigenetic regulation of memory gene expression in cold and salt stress. Small interfering RNAs (siRNAs) lead to DNA methylation during the memory response of biotic, salt, and heavy metal stress. Simultaneously, stress-responsive isoforms of tolerant genes are found to be expressed as a memory response in subsequent heat stress. This review highlights the stress-type-specific roles of ncRNAs and AS in establishing, maintaining, and transmitting stress memory, offering insights into their potential for improving crop resilience through genetic and epigenetic priming strategies.

Microplastic and heavy metal contamination in sediments of the high-altitude Nundkol Lake of northwestern Himalayas-Kashmir

Artificial islands construction can significantly influence the spatial distribution of heavy metals in inshore sediments. In this study, the distribution and contamination of heavy metals (Cd, Co, Cr, Cu, Ni, Pb, Zn, As and Hg) in inshore sediments of the Longkou Bay and artificial island adjacent areas were investigated in 2013 and 2014, respectively. Results showed that the contents of heavy metals increased in the Longkou Bay and decreased in the west of the artificial island in 2014 compared with 2013. The contamination and potential eco-risk of heavy metals in the sediments were higher in 2014 than those in 2013. Cd and Hg showed a high potential eco-risk in LK02, and other metals were in the lower level. The results indicated that after the construction of artificial islands in the Longkou Bay, the contamination and eco-risk of heavy metals in the sediments markedly increased in the Longkou Bay.

A modified indexing approach for assessment of heavy metal contamination in Deepor Beel, India

To clarify the characteristics of heavy metal (Hg, As, Cd, Cu, Zn, Pb, Ni, Cr) contamination in farmland within mountainous basin areas and investigate the influence mechanisms of soil nutrient factors (organic carbon SOC, pH, total nitrogen TN, total phosphorus TP, total potassium TK) and the C:N:P ratio on heavy metal pollution, This study selected a typical mountainous valley area within the Huangshan section of the Xin’anjiang River basin. A total of 300 soil samples were collected. Kriging interpolation was employed to assess the spatial distribution of heavy metal contamination. A positive definite factor matrix model was used for source analysis of soil heavy metals. Combined with redundancy analysis, correlation analysis, and structural equation modeling, the study investigated the influence mechanisms and distribution drivers of soil factors on soil heavy metal contamination. Results indicate: (1) Overall, heavy metal contamination in farmland across the study area was predominantly mild or below (>75%). Contamination was concentrated in the lower-elevation areas east of Xidi Town and west of Lantian Town, with notably elevated Cr, Cu, Zn, and Cd concentrations in these zones; (2) Atmospheric sources contributed most to Hg (72.8%); As was primarily influenced by industrial sources (73.9%); natural sources were the main contributors for Cr, Ni, and Cu, accounting for 52.5%, 51.7%, and 41.8%, respectively; soil Zn primarily originated from natural and transportation sources (31.0% and 42.8%); Agricultural sources dominate Cd contributions (83.9%); Pb is primarily influenced by natural sources and solid waste sources (40.9% and 43.1%, respectively); (3) Redundancy analysis indicates soil nutrient factors explain 21.5% of heavy metal pollution, with TN contributing the most at 63.4%; Both linear regression and structural equation modeling results indicate a significant negative correlation (p < 0.05) between the C:P ratio and the comprehensive soil heavy metal pollution index. This may be due to the fact that farmland in mountainous basin areas has a higher proportion of P compared to the average C:N:P ratio of subtropical farmland, and P can effectively bind with heavy metals (Cu, Cd, Pb, Ni, Zn) to form a stable state. This study systematically evaluates the heavy metal pollution in the Huangshan section of the Xin’an River from contamination assessment, source analysis, and impact mechanisms, offering a theoretical basis for preventing and controlling heavy metal pollution and ensuring land safety in similar regions.