Differential Aquaporin Response to Distinct Effects of Two Zn Concentrations after Foliar Application in Pak Choi (Brassica rapa L.) Plants

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

Foliar spraying of zinc oxide nanoparticles improves water transport and nitrogen metabolism in tomato (Solanum lycopersicum L.) seedlings mitigating the negative impacts of cadmium

The use of bio-nanotechnology in agriculture-such as the biological applications of metal oxide nanoparticles (NPs)-greatly improves crop yield and quality under different abiotic stress factors including soil metal contamination. Here, we explore the effectiveness of zinc oxide (ZnO)-NPs (0, 50 mg/L) foliar spraying to ameliorate the detrimental effects of cadmium (Cd) on the water transport and nitrogen metabolism in tomato (Solanum lycopersicum Mill. cv. Chibli F1) plants grown on a Cd-supplied (CdCl2; 0, 10, 40 μM) Hoagland nutrient solution. The results depicted that the individually studied factors (ZnO-NPs and Cd) had a significant impact on all the physiological parameters analyzed. Independently to the Cd concentration, ZnO-NPs-sprayed plants showed significantly higher dry weight (DW) in both leaves and roots compared to the non-sprayed ones, which was in consonance with higher and lower levels of Zn2+ and Cd2+ ions, respectively, in these organs. Interestingly, ZnO-NPs spraying improved water status in all Cd-treated plants as evidenced by the increase in root hydraulic conductance (L0), apoplastic water pathway percentage, and leaf and root relative water content (RWC), compared to the non-sprayed plants. This improved water balance was associated with a significant accumulation of osmoprotectant osmolytes, such as proline and soluble sugars in the plant organs, reducing electrolyte leakage (EL), and osmotic potential (ψπ). Also, ZnO-NPs spraying significantly improved NO3- and NH4+ assimilation in the leaf and root tissues of all Cd-treated plants, leading to a reduction in NH4+ toxicity. Our findings point out new insights into how ZnO-NPs affect water transport and nitrogen metabolism in Cd-stressed plants and support their use to improve crop resilience against Cd-contaminated soils.

Toxicity effects of zinc supply on growth revealed by physiological and transcriptomic evidences in sweet potato (Ipomoea batatas (L.) Lam)

Zinc toxicity affects crop productivity and threatens food security and human health worldwide. Unfortunately, the accumulation patterns of zinc and the harmful effects of excessive zinc on sweet potato have not been well explored. In the present research, two genotypes of sweet potato varieties with different accumulation patterns of zinc were selected to analyze the effects of excessive zinc on sweet potato via hydroponic and field cultivation experiments. The results indicated that the transfer coefficient was closely related to the zinc concentration in the storage roots of sweet potato. Excessive zinc inhibited the growth of sweet potato plants by causing imbalanced mineral concentrations, destroying the cellular structure and reducing photosynthesis. Furthermore, a total of 17,945 differentially expressed genes were identified in the two genotypes under zinc stress by transcriptomic analysis. Differentially expressed genes involved in the absorption and transport of zinc, defense networks and transcription factors played important roles in the response to zinc stress. In conclusion, this study provides a reference for the selection of sweet potato varieties in zinc contaminated soil and lays a foundation for investigating the tolerance of sweet potato to excessive zinc, which is meaningful for environmental safety and human health.

Study on nitrogen demand model in pakchoi (Brassica campestris ssp. Chinensis L.) based on nitrogen contents and phenotypic characteristics

INTRODUCTION

In precision agriculture, the diagnosis of the nitrogen (N) nutrition status based on the plant phenotype, combined effects of soil types, various agricultural practices, and environmental factors which are essential for plant N accumulation. It helps to assess the N supply for plants at the right time and optimal amount to ensure high N use efficiency thereby reducing the N fertilizer applications to minimize environmental pollution. For this purpose, three different experiments were performed.

METHODS

A critical N content (Nc) model was constructed based on cumulative photothermal effect (LTF), Napplications, and cultivation systems on yield and N uptake in pakchoi.

RESULTS AND DISCUSSION

According to the model, aboveground dry biomass (DW) accumulation was found equal or below to 1.5 t/ha, and the Nc value was observed at a constant of 4.78%. However, when DW accumulation exceeded 1.5 t/ha, Nc declined with the increase in DW accumulation, and the relationship between Nc and DW accumulation developed with the function Nc %=4.78 x DW-0.33. An N demand model was established based on the multi-information fusion method, which integrated multiple factors, including Nc, phenotypical indexes, temperature during the growth period, photosynthetically active radiation, and N applications. Furthermore, the model's accuracy was verified, and the predicted N contents were found consistent with the measured values (R2 = 0.948 and RMSE = 1.96 mg/plant). At the same time, an N demand model based on N use efficiency was proposed.

CONCLUSIONS

This study can provide theoretical and technical support for precise N management in pakchoi production.

Association studies of genes in a Pb response-associated network in maize (Zea mays L.) reveal that ZmPIP2;5 is involved in Pb tolerance

Lead (Pb) in the soil affects the growth and development of plants and causes damages to the human body through the food chain. Here, we identified and cloned a Pb-tolerance gene ZmPIP2;5 based on a weighted gene co-expression network analysis and gene-based association studies. We showed that ZmPIP2;5 encodes a plasma membrane aquaporin and positively regulated Pb tolerance and accumulation in Arabidopsis and yeast. Overexpression of ZmPIP2;5 increased root length and fresh weight of Arabidopsis seedlings under Pb stress. Heterologous expression of ZmPIP2;5 in yeast caused the enhanced growth speed under Pb treatment and Pb accumulation in yeast cells. A (T/A) SNP in the ZmPIP2;5 promoter affected the expression abundance of ZmPIP2;5 and thereby led to the difference in Pb tolerance among different maize lines. Our study helps to understand the mechanism underlying plant tolerance to Pb stress and provides new ideas for breeding Pb-tolerance maize varieties via molecular marker-assisted selection.

Grain yield and quality of wheat are improved through post-flowering foliar application of zinc and 6- benzylaminopurine under water deficit condition

INTRODUCTION

Zinc (Zn) as an essential micronutrient and cytokinin as phytohormone not only regulate plant growth but also play fundamental roles in plant tolerance against drought stress. Understating the function and the role of cytokinin in combined with an essential micronutrient, Zn, could improve the choice of a sustainable strategy for improvement of plant drought stress. The objective of this field research was to determine the effect of post-flowering foliar application of ZnSO4 and 6-benzylaminopurine (6-BAP) on grain yield and quality of winter wheat under water deficit condition.

METHODS

Experiments were conducted under filed condition. Drought was imposed by with holding irrigation at the beginning of flowering till the signs of temporary wilting/leaf rolling appeared, after which all plots were irrigated to field capacity. The foliar treatment consisted of (1) foliar application of water, as control treatment; (2) foliar application of 10 g ha-1 6-BAP; (3) Foliar application of 20 g ha-1 6-BAP; (4) Foliar application of 10 g ha-1 6-BAP plus foliar application of 6 kg ha-1 ZnSO4 solution and (5) foliar application of 10 g ha-1 6-BAP plus foliar application of 6 kg ha-1 ZnSO4 solution 2 days before drought imposition. Data were collected on grain and straw yield, yield attributes, harvest index, flag leaf fresh matter and dry matter weight, TaCKX6-D1 expression, phytic acid content in grains, mycorrhiza colonization rate and succinate dehydrogenase (SD) activity.

RESULTS

According to ANOVA, the factor 'Zn' significantly affected leaf relative water content (p < 0.001). Relative water content for plants foliar applied with 6-BAP was not statistically significant. Applying Zn increased yield, straw dry weight, and kernel weight relative to plants sprayed with water alone. Increased grain yield due to foliar application of Zn was associated with decrease in cytokinin oxidase/dehydrogenase (TaCKX) and increase in kernel weight. Results showed that the drought stress significantly decreased 1000-grain weight that was accompanied with over-expression of cytokinin oxidase/dehydrogenase (TaCKX). Foliar application of Zn increased the concentration of Zn in grains. The experimental data on the zinc content of grain indicated no significant difference between the 6-BAP at 10 mg L-1 and control treatment. The phytate to Zn molar ratio was significantly affected by foliar applied Zn, but not significantly by applied 6-BAP. In the present study, SD activity of the hyphae of indigenous arbuscular mycorrhizal fungi (IAMF) associated with plant roots was also assayed. Results disclose that SD activity of IAMF was significantly affected by Zn treatments during grain filling stages.

DISCUSSION

In summary, both foliar applied Zn and 6-BAP had the significant effects on all measured parameters in winter wheat. However, spike number, harvest index and mycorrhizal colonization rate were neither significantly affected by Zn nor 6- BAP. Foliar application of Zn at 0.6% (6 kg ha-1) and higher 6-BAP (20 mg L-1 m-2) promoted wheat growth and performances under imposed drought stress condition. Plant that only foliar sprayed with water showed higher level of TaCKX6-D1 expression as compared to Zn treated plants, indicating these plants were more affected by imposed drought relative to those plants treated with Zn. The results of this study provides evidence that a combination of Zn and 6-BAP could be an effective in improvement of drought tolerance of wheat and prevents grain yield from further reduction in terms of quality and quantity due to drought stress.

Zn alleviated salt toxicity in Solanum lycopersicum L. seedlings by reducing Na+ transfer, improving gas exchange, defense system and Zn contents

Soil secondary salinization is a serious menace that has significant influence on the sustainability of agriculture and threatens food security around the world. Zinc (Zn) as an essential plant nutrient associated with many physio-biochemical processes in plants and improve resistance against various abiotic stresses. The role of Zn in acclimation of Solanum lycopersicum L. challenged with salt stress is miserly understood. A hydroponic study was performed with two tomato varieties (Riogrande and Sungold) exposed to the salinity stress (0 mM and 160 mM NaCl) under two Zn concentrations (15 μM and 30 μM ZnSO₄). The results revealed that salt stress exerted strongly negative impacts on root and shoot length, fresh and dry biomass, plant water relations, membrane stability, chlorophyll contents, Na⁺/K⁺ ratio along with inferior gas exchange attributes and activities of antioxidant enzymes. Moreover, Riogrande was found to be more resistant to salinity stress than Sungold. However, Zn supply significantly alleviated the hazardous effects of salinity by altering compatible solutes accumulation, photosynthetic activity, water relation, soluble sugar contents and providing antioxidant defense against salt stress. The salinity + Zn2 treatment more obviously enhanced RWC (19.0%), MSI (30.8%), SPAD value (17.8%), and activities of SOD (31.7%), POD (28.5%), APX (64.5%) and CAT (23.3%) in Riogrande than Sungold, compared with the corresponding salinity treatment alone. In addition, salinity + Zn2 treatment significantly (P > 0.05) ameliorated salinity stress due to the depreciation in Na⁺/K⁺ ratio by 63.3% and 40.8%, Na⁺ ion relocation from root to shoot by 10.4% and 6.4%, and thereby significantly reduced Na⁺ ion accumulation by 47.4% and 16.3% in the leaves of Riogrande and Sungold respectively, compared to the salinity treatment alone. Therefore, it was obvious that 30 μM Zn concentration was more effective to induce resistance against salinity stress than 15 μM Zn concentration. Conclusively, it can be reported that exogenous Zn application helps tomato plant to combat adverse saline conditions by modulating photosynthetic and antioxidant capacity along with reduced Na⁺ uptake at the root surface of tomato plant.

Collaborative Assessment and Health Risk of Heavy Metals in Soils and Tea Leaves in the Southwest Region of China

The collaborative assessment and health risk evaluation of heavy metals (HMs) enrichment in soils and tea leaves are crucial to guarantee consumer safety. However, in high soil HM geochemical background areas superimposed by human activities, the health risk associated with HMs in soil–tea systems is not clear. This study assessed the HMs concentration (i.e., chromium (Cr), cadmium (Cd), arsenic (As), and lead (Pb)) in tea leaves and their relationship with soil amounts in the southwest region of China to evaluate the associated health risk in adults. The results revealed that the average soil concentration of Cr was the highest (79.06 mg kg⁻¹), followed by Pb (29.27 mg kg⁻¹), As (14.87 mg kg⁻¹), and Cd (0.18 mg kg⁻¹). Approximately 0.71, 4.99, 7.36, and 10.21% of soil samples exceeded the threshold values (NY/T 853-2004) for Pb, Cr, As, and Cd, respectively. Furthermore, the average concentration of Pb, As, and Cd in tea leaves was below the corresponding residue limits, but Cr was above the allowed limits. Correlation analysis revealed that the Pb, Cr, As, and Cd amounts in tea leaves were positively correlated to their soil amounts (p < 0.01) with an R² of 0.203 **, 0.074 **, 0.036 **, and 0.090 **, respectively. Additionally, approximately 40.38% of the samples were found to be contaminated. Furthermore, spatial distribution statistical analysis revealed that Lancang was moderately contaminated, while Yingjiang, Zhenkang, Yongde, Zhenyuan, Lüchun, Jingdong, Ximeng, and Menglian were slightly contaminated areas. The target hazard quotients (THQ; health risk assessment) of Pb, Cr, As, and Cd and the hazard index (HI) of all the counties were below unity, suggesting unlikely health risks from tea consumption.

Evaluation of transcription factor and aquaporin gene expressions in response to Al2O3 and ZnO nanoparticles during barley germination

Aluminum oxide and zinc oxide nanoparticles (NPs) are two of the mostly produced engineered metal oxide NPs. Here, barley germination and root elongation as well as gene expressions of the selected aquaporins (HvTip1;1 and HvPip1;1) and transcription factors (HvERFs and HvNFX1) were investigated after exposure to Al₂O₃ and ZnO NPs for foreseeing the effect of NP exposure. ICP-MS analysis showed that the nanoparticles were taken up into root and leaves. Even the germination analysis and seedling establishment data indicate that the applied NPs do not have any observable inhibitory effects except on root length, the gene expression analysis revealed that these nanoparticle applications lead to a response at the molecular level. The gene expression profiling indicated that aquaporins and transcription factor genes were differentially regulated in leaves and roots in response to NPs treatments. The expressions of aquaporin genes were higher especially in leaves in compared to the control plants. Gradual decrease was obtained in roots by application of the increased levels of Al₂O₃ NPs. The effects of ZnO NPs on gene expression levels of barley TFs were dramatically more distinctive in comparison with that of Al₂O₃ NPs. The expression profiles of HvERFs and HvNFX1 transcription factors in response to the Al₂O₃ and ZnO NPs suggest that these selected TFs can play important roles in shaping abiotic stress tolerance in young barley roots and leaves. Outcomes of the study will allow us to predict complex stress response of barley in response to the nanoparticles.

Arbuscular Mycorrhiza-Mediated Regulation of Polyamines and Aquaporins During Abiotic Stress: Deep Insights on the Recondite Players

Environmental stresses of (a)biotic origin induce the production of multitudinous compounds (metabolites and proteins) as protective defense mechanisms in plants. On account of the regulation of some of these compounds, arbuscular mycorrhizal fungi (AMF) reinforce the inherent tolerance of plants toward the stress of different origins and kind. This article reviews two specific fundamental mechanisms that are categorically associated with mycorrhiza in alleviating major abiotic stresses, salt, drought, and heavy metal (HM) toxicity. It puts emphasis on aquaporins (AQPs), the conduits of water and stress signals; and polyamines (PAs), the primordial stress molecules, which are regulated by AMF to assure water, nutrient, ion, and redox homeostasis. Under stressful conditions, AMF-mediated host AQP responses register distinct patterns: an upregulation to encourage water and nutrient uptake; a downregulation to restrict water loss and HM uptake; or no alterations. The patterns thereof are apparently an integrative outcome of the duration, intensity, and type of stress, AMF species, the interaction of fungal AQPs with that of plants, and the host type. However, the cellular and molecular bases of mycorrhizal influence on host AQPs are largely unexplored. The roles of PAs in augmenting the antioxidant defense system and improving the tolerance against oxidative stress are well-evident. However, the precise mechanism by which mycorrhiza accords stress tolerance by influencing the PA metabolism per se is abstruse and broadly variable under different stresses and plant species. This review comprehensively analyzes the current state-of-art of the involvement of AMF in "PA and AQP modulation" under abiotic stress and identifies the lesser-explored landscapes, gaps in understanding, and the accompanying challenges. Finally, this review outlines the prospects of AMF in realizing sustainable agriculture and provides insights into potential thrust areas of research on AMF and abiotic stress.

Zinc toxicity in plants: a review

This review highlights the most recent updated information available about Zn phytotoxicity at physiological, biochemical and molecular levels, uptake mechanisms as well as excess Zn homeostasis in plants. Zinc (Zn) is a natural component of soil in terrestrial environments and is a vital element for plant growth, as it performs imperative functions in numerous metabolic pathways. However, potentially noxious levels of Zn in soils can result in various alterations in plants like reduced growth, photosynthetic and respiratory rate, imbalanced mineral nutrition and enhanced generation of reactive oxygen species. Zn enters into soils through various sources, such as weathering of rocks, forest fires, volcanoes, mining and smelting activities, manure, sewage sludge and phosphatic fertilizers. The rising alarm in environmental facet, as well as, the narrow gap between Zn essentiality and toxicity in plants has drawn the attention of the scientific community to its effects on plants and crucial role in agricultural sustainability. Hence, this review focuses on the most recent updates about various physiological and biochemical functions perturbed by high levels of Zn, its mechanisms of uptake and transport as well as molecular aspects of surplus Zn homeostasis in plants. Moreover, this review attempts to understand the mechanisms of Zn toxicity in plants and to present novel perspectives intended to drive future investigations on the topic. The findings will further throw light on various mechanisms adopted by plants to cope with Zn stress which will be of great significance to breeders for enhancing tolerance to Zn contamination.

Targeting aquaporins to alleviate hazardous metal(loid)s imposed stress in plants

Uptake of hazardous metal(loid)s adversely affects plants and imposes a threat to the entire food chain. Here, the role of aquaporins (AQPs) providing tolerance against hazardous metal(loid)s in plants is discussed to provide a perspective on the present understanding, knowledge gaps, and opportunities. Plants adopt complex molecular and physiological mechanisms for better tolerance, adaptability, and survival under metal(loid)s stress. Water conservation in plants is one such primary strategies regulated by AQPs, a family of channel-forming proteins facilitating the transport of water and many other solutes. The strategy is more evident with reports suggesting differential expression of AQPs adopted by plants to cope with the heavy metal stress. In this regard, numerous studies showing enhanced tolerance against hazardous elements in plants due to AQPs activity are discussed. Consequently, present understanding of various aspects of AQPs, such as tertiary-structure, transport activity, solute-specificity, differential expression, gating mechanism, and subcellular localization, are reviewed. Similarly, various tools and techniques are discussed in detail aiming at efficient utilization of resources and knowledge to combat metal(loid)s stress. The scope of AQP transgenesis focusing on heavy metal stresses is also highlighted. The information provided here will be helpful to design efficient strategies for the development of metal(loid)s stress-tolerant crops.