Stress signaling convergence and nutrient crosstalk determine zinc-mediated amelioration against cadmium toxicity in rice

Exogenous Hydrogen sulfide attenuates cadmium toxicity to Chrysanthemum (Chrysanthemum indicum) by modulating glutathione synthesis and cadmium adsorption capacity in the cell wall

Soil cadmium (Cd) contamination leads to plant toxicity and poses a risk to human health both directly and indirectly through the food chain. Hydrogen sulfide (H2S), a novel gaseous signaling molecule, has been shown to enhance plant tolerance to various abiotic stresses. In this study, the potential of H2S in mitigating Cd toxicity in chrysanthemum (Chrysanthemum indicum) was investigated through physiological, biochemical and transcriptomic analyses. Results showed that the application of exogenous H2S resulted Cd accumulation in the roots by 21.15 %, while reducing Cd in the aboveground parts by 13.21 %. It was further found that H2S increased the pectin and hemicellulose content by 50.09 % and 49.79 %, respectively, through the regulation of cell wall polysaccharide synthesis-related genes, leading to changes in root functional group content and cell wall adsorption capacity for cadmium ions (Cd2+). Additionally, H2S also promoted the synthesis of GSH and PCs by regulating the expression of genes related to sulfur metabolism, chelating free Cd2+ in the cytoplasm, and reducing their harmful effects on the organelles. It was also found that exogenous H2S may have regulated the expression of transporter proteins by modulating the expression of transcription factors (MYB, AP2/ERF, and WRKY), thereby affecting the uptake, transport, and accumulation of Cd2+. In conclusion, exogenous H2S reduced the free Cd2+ content in the cytoplasm by promoting the adsorption of Cd2+ in the root cell walls and facilitating the synthesis of GSH and PCs in the cells, which in turn alleviated the toxic effects of Cd2+ on chrysanthemum.

Transcriptome analysis reveals the role of microbial volatile 3-methyl-1-butanol-induced salt stress tolerance in rice (Oryza sativa L.) seedlings through antioxidant defense system

Microorganisms produce volatile organic compounds (VOCs) that have biological impacts on plants; however, it is unknown how these molecules participate in plants' responses to abiotic stress. This study aimed to determine the potential benefit of 3-methyl-1-butanol (3 MB), a microbial VOC, in helping rice (Oryza sativa) seedlings suffering from salinity stress. Our study revealed that rice seedlings primed with microbial volatile 3 MB for 12 h before exposure to salinity stress could decrease reactive oxygen species (ROS) generation and cell damage in rice roots. Additionally, antioxidant systems such as peroxidase (POD) isozymes 4 and 5 and catalase 1 (CAT1) increased after treatment with 3 MB + NaCl. The microbial volatile 3 MB fumigation also raised the proline content and activated the proline-related genes under 3 MB + NaCl treatment. To further elucidate the molecular mechanisms by which 3 MB assists rice in tolerating salinity stress, transcriptomic analysis was used to investigate the genome-wide gene expressions. Totally, 287 up-regulated differentially expressed genes (DEGs) were found. They are associated with phytohormone regulation, transcription factors, redox signaling, and defense responses. Through Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and MapMan enrichment results of DEGs revealed that 3 MB could activate antioxidant systems, jasmonic acid (JA) pathway, and starch biosynthesis to generate more ATP, thus building a line of defense in response to salinity stress. This study provides valuation information indicating that microbial volatile 3 MB vapor can enhance salt stress tolerance in rice seedlings and clarify its underlying mechanism.

Advances of the mechanism for copper tolerance in plants

Copper (Cu) is a vital trace element necessary for plants growth and development. It acts as a co-factor for enzymes and plays a crucial role in various physiological processes, including photosynthesis, respiration, antioxidant systems, and hormone signaling transduction. However, excessive amounts of Cu can disrupt normal physiological metabolism, thus hindering plant growth, development, and reducing yield. In recent years, the widespread abuse of Cu-containing fungicides and industrial Cu pollution has resulted in significant soil contamination. Therefore, it is of utmost importance to uncover the adverse effects of excessive Cu on plant growth and delve into the molecular mechanisms employed by plants to counteract the stress caused by excessive Cu. Recent studies have confirmed the inhibitory effects of excess Cu on mineral nutrition, chlorophyll biosynthesis, and antioxidant enzyme activity. This review systematically outlines the ways in which plants tolerate excessive Cu stress and summarizes them into eight Cu-tolerance strategies. Furthermore, it highlights the necessity for further research to comprehend the molecular regulatory mechanisms underlying the responses to excessive Cu stress.

Novel nanocomposite and biochar insights to boost rice growth and alleviation of Cd toxicity

Cadmium (Cd) is an unessential and pervasive contaminant in agricultural soil, eventually affecting the food and instigating health issues. The implication of nanocomposites in agriculture attained significant attention to drive food security. Nanocomposites possess exceptional characteristics to stun the challenges of chemical fertilizers that can enhance plant yield and better nutrient bioavailability. Similarly, biochar has the ability to immobilize Cd in soil by reducing mobility and bioavailability. Rice husk biochar is produced at high temperature pyrolysis under anoxic conditions and a stable carbon-rich material is formed. To strive against this issue, rice plants were subjected to Cd (15, 20 mg kg- 1) stress and treated with alone/combined Ca + Mg (25 mg L- 1) nanocomposite and rice husk biochar. In our study, growth and yield traits showed the nurturing influence of Ca + Mg nanocomposite and biochar to improve rice defence mechanism by reducing Cd stress. Growth parameters root length 28%, shoot length 34%, root fresh weight 19%, shoot fresh weight 16%, root dry weight 9%, shoot dry weight 8%, number of tillers 32%, number of grains 20%, and spike length 17% were improved with combined application of Ca + Mg and biochar, with Cd (20 mg kg- 1), rivalled to alone biochar. Combined Ca + Mg and biochar application increased the SPAD 23%, total chlorophyll 26%, a 19%, b 18%, and carotenoids 15%, with Cd (20 mg kg- 1), rivalled to alone biochar. MDA 15%, H2O2 13%, and EL 10% were significantly regulated in shoots with combined Ca + Mg and biochar application with Cd (20 mg kg- 1) compared to alone biochar. POD 22%, SOD 17%, APX 18%, and CAT 9% were increased in shoots with combined Ca + Mg and biochar application with Cd (20 mg kg- 1) compared to alone biochar. Cd uptake in roots 13%, shoots 14%, and grains 21% were minimized under Cd (20 mg kg- 1) with combined Ca + Mg and B. pumilus application, compared to alone biochar. Subsequently, combined Ca + Mg and biochar application is a sustainable solution to boost crop production under Cd stress.

Investigating the combined effects of β-sitosterol and biochar on nutritional value and drought tolerance in Phaseolus vulgaris under drought stress

Climate change-induced drought stress decreases crop productivity, but the application of β-sitosterol (BS) and biochar (BC) boosts crop growth and yield. A pot experiment was conducted to examine the effects of the alone and combined application of BS and BC on the growth and yield of Phaseolus vulgaris under drought stress. The synergistic application of BS and BC increased plant height (46.9cm), shoot dry weight (6.9g/pot), and root dry weight (2.5g/pot) of P. vulgaris plants under drought stress. The trend of applied treatments for photosynthetic rate remained as BC (15%) Collapse

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MESH Headings

• Sitosterols/pharmacology
• Phaseolus/drug effects
• Phaseolus/physiology
• Phaseolus/growth & development
• Droughts
• Charcoal/pharmacology
• Nutritive Value
• Stress, Physiological/drug effects
• Photosynthesis/drug effects
• Hydrogen Peroxide/metabolism
• Malondialdehyde/metabolism
• Drought Resistance

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Affiliation(s)

Marwa A Fakhr Botany Department, Faculty of Science, Fayoum University, Fayoum 63514, Egypt; and Green Materials Technology Department, Environment and Natural Materials Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab City, Alexandria 21934, Egypt
Abdelghafar M Abu-Elsaoud Department of Botany and Microbiology, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt; and Department of Biology, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11623, Kingdom of Saudi Arabia
Khadiga Alharbi Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia
Muhammad Zia-Ur-Rehman Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Punjab 38000, Pakistan
Muhammad Usman Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Punjab 38000, Pakistan
Mona H Soliman Botany and Microbiology Department, Faculty of Science, Cairo University, Giza 12613, Egypt; and Biology Department, Faculty of Science, Taibah University, Al-Sharm, Yanbu El-Bahr, Yanbu 46429, Kingdom of Saudi Arabia

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Insights into the alleviation of cadmium toxicity in rice by nano-zinc and Serendipita indica: Modulation of stress-responsive gene expression and antioxidant defense system activation

The adversities of cadmium (Cd) contamination are quite distinguished among other heavy metals (HMs), and so is the efficacy of zinc (Zn) nutrition in mitigating Cd toxicity. Rice (Oryza sativa) crop, known for its ability to absorb HMs, inadvertently facilitates the bioaccumulation of Cd, posing a significant risk to both the plant itself and to humans consuming its edible parts, and damaging the environment as well. The use of nanoparticles, such as nano-zinc oxide (nZnO), to improve the nutritional quality of crops and combat the harmful effects of HMs, have gained substantial attention among scientists and farmers. While previous studies have explored the individual effects of nZnO or Serendipita indica (referred to as S.i) on Cd toxicity, the synergistic action of these two agents has not been thoroughly investigated. Therefore, the gift of nature, i.e., S. indica, was incorporated alongside nZnO (50 mg L-1) against Cd stress (15 μM L-1) and their alliance manifested as phenotypic level modifications in two rice genotypes (Heizhan43; Hz43 and Yinni801; Yi801). Antioxidant activities were enhanced, specifically peroxidase (61.5 and 122.5% in Yi801 and Hz43 roots, respectively), leading to a significant decrease in oxidative burst; moreover, Cd translocation was reduced (85% for Yi801 and 65.5% for Hz43 compared to Cd alone treatment). Microstructural study showed a decrease in number of vacuoles and starch granules with ameliorative treatments. Overall, plants treated with nZnO displayed gene expression pattern (particularly of ZIP genes), different from the ones with alone or combined S.i and Cd. Inferentially, the integration of nZnO and S.i holds great promise as an effective strategy for alleviating Cd toxicity in rice plants. By immobilizing Cd ions in the soil and promoting their detoxification, this novel approach contributes to environmental restoration and ensures food safety worldwide.

Derivation and validation of soil cadmium thresholds for the safe farmland production of vegetables in high geological background area

Excessive dietary intake of cadmium (Cd) poses toxicity risks to human health, and it is therefore essential to establish accurate and regionally appropriate soil Cd thresholds that ensure the safety of agricultural products grown in different areas. This study investigated the differences in the Cd accumulation in 32 vegetable varieties and found that the Cd content ranged from 0.01 to 0.24 mg·kg^-1, and decreased in the order of stem and bulb vegetables > leafy vegetables > solanaceous crops > bean cultivars. A correlation analysis and structural equation model showed that pH, soil organic matter, and the cation exchange capacity had significant effects on Cd accumulation in the vegetables and explained 72.1 % of the variance. In addition, species sensitivity distribution (SSD) curves showed that stem and bulb vegetables were more sensitive to Cd than other types of vegetables. Using the Burr Type III function for curve fitting, we derived Cd thresholds of 6.66, 4.15, and 1.57 mg·kg^-1 for vegetable soils. These thresholds will ensure that 20 %, 50 %, and 95 % of these vegetable varieties were risk-free, respectively. The predicted threshold of soil Cd was more than twice that of China's current National Soil Quality Standard (GB 15618-2018) for Cd values. Therefore, soil scenarios and cultivars should be considered comprehensively when determining farmland soil thresholds. The present results provide a new model for setting soil Cd criteria in high geological background areas.

Genome-Wide Identification of R2R3-MYB Transcription Factor and Expression Analysis under Abiotic Stress in Rice

The myeloblastosis (MYB) family comprises a large group of transcription factors (TFs) that has a variety of functions. Among them, the R2R3-MYB type of proteins are the largest group in plants, which are involved in controlling various biological processes such as plant growth and development, physiological metabolism, defense, and responses to abiotic and biotic stresses. In this study, bioinformatics was adopted to conduct genome-wide identification of the R2R3-MYB TFs in rice. We identified 190 MYB TFs (99 R2R3-MYBs), which are unevenly distributed on the 12 chromosomes of rice. Based on the phylogenetic clustering and protein sequence characteristics, OsMYBs were classified into five subgroups, and 59.6% of the Os2R_MYB genes contained two introns. Analysis of cis-acting elements in the 2000 bp upstream region of Os2R_MYB genes showed that all Os2R_MYB genes contained plant hormones-related or stress-responsive elements since 91.9%, 79.8%, 79.8%, and 58.6% of Os2R_MYB genes contain ABRE, TGACG, CGTCA, and MBS motifs, respectively. Protein–protein network analysis showed that the Os2R_MYBs were involved in metabolic process, biosynthetic process, and tissue development. In addition, some genes showed a tissue-specific or developmental-stage-specific expression pattern. Moreover, the transcription levels of 20 Os2R_MYB genes under polyethylene glycol (PEG) and cadmium chloride (CdCl₂) stress inducers were dissected by qRT-PCR. The results indicated genes with an altered expression upon PEG or CdCl₂ stress induction. These results potentially supply a basis for further research on the role that Os2R_MYB genes play in plant development and stress responses.