Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles

Bio-formulated chitosan nanoparticles enhance disease resistance against rice blast by physiomorphic, transcriptional, and microbiome modulation of rice (Oryza sativa L.)

Rice blast disease (RBD) caused by Magnaporthe oryzae, threaten food security by cutting agricultural output. Nano agrochemicals are now perceived as sustainable, cost-effective alternatives to traditional pesticides. This study investigated bioformulation of moringa chitosan nanoparticles (M-CsNPs) and their mechanisms for suppressing RBD while minimizing toxic effects on the microenvironment. M-CsNPs, sized 46 nm with semi-spherical morphology, significantly suppressed pathogen growth, integrity, and colonization at 200 mg L-1in vitro. Greenhouse tests with foliar exposure to the same concentration resulted in a substantial 77.7 % reduction in RBD, enhancing antioxidant enzyme activity and plant health. Furthermore, M-CsNPs improved photosynthesis, gas exchange, and the nutritional profile of diseased rice plants. RNA-seq analysis highlighted upregulated defense-related genes in treated rice plants. Metagenomic study showcased reshaping of the rice microbiome, reducing Magnaporthe abundance by 93.5 %. Both healthy and diseased rice plants showed increased microbial diversity, particularly favoring specific beneficial species Thiobacillus, Nitrospira, Nocardioides, and Sphingomicrobium in the rhizosphere and Azonexus, Agarivorans, and Bradyrhizobium in the phyllosphere. This comprehensive study unravels the diverse mechanisms by which M-CsNPs interact with plants and pathogens, curbing M. oryzae damage, promoting plant growth, and modulating the rice microbiome. It underscores the significant potential for effective plant disease management.

The Impact of Nanomaterials on Photosynthesis and Antioxidant Mechanisms in Gramineae Plants: Research Progress and Future Prospects

As global food security faces challenges, enhancing crop yield and stress resistance becomes imperative. This study comprehensively explores the impact of nanomaterials (NMs) on Gramineae plants, with a focus on the effects of various types of nanoparticles, such as iron-based, titanium-containing, zinc, and copper nanoparticles, on plant photosynthesis, chlorophyll content, and antioxidant enzyme activity. We found that the effects of nanoparticles largely depend on their chemical properties, particle size, concentration, and the species and developmental stage of the plant. Under appropriate conditions, specific NMs can promote the root development of Gramineae plants, enhance photosynthesis, and increase chlorophyll content. Notably, iron-based and titanium-containing nanoparticles show significant effects in promoting chlorophyll synthesis and plant growth. However, the impact of nanoparticles on oxidative stress is complex. Under certain conditions, nanoparticles can enhance plants' antioxidant enzyme activity, improving their ability to withstand environmental stresses; excessive or inappropriate NMs may cause oxidative stress, affecting plant growth and development. Copper nanoparticles, in particular, exhibit this dual nature, being beneficial at low concentrations but potentially harmful at high concentrations. This study provides a theoretical basis for the future development of nanofertilizers aimed at precisely targeting Gramineae plants to enhance their antioxidant stress capacity and improve photosynthesis efficiency. We emphasize the importance of balancing the agricultural advantages of nanotechnology with environmental safety in practical applications. Future research should focus on a deeper understanding of the interaction mechanisms between more NMs and plants and explore strategies to reduce potential environmental impacts to ensure the health and sustainability of the ecosystem while enhancing the yield and quality of Gramineae crops.

Mechanism of the adverse outcome of Chlorella vulgaris exposure to diethyl phthalate: Water environmental health reflected by primary producer toxicity

As a ubiquitous contaminant in aquatic environments, diethyl phthalate (DEP) is a major threat to ecosystems because of its increasing utilization. However, the ecological responses to and toxicity mechanisms of DEP in aquatic organisms remain poorly understood. To address this environmental concern, we selected Chlorella vulgaris (C. vulgaris) as a model organism and investigated the toxicological effects of environmentally relevant DEP concentrations at the individual, physiological, biochemical, and molecular levels. Results showed that the incorporation of DEP significantly inhibited the growth of C. vulgaris, with inhibition rates ranging from 10.3 % to 83.47 %, and disrupted intracellular chloroplast structure at the individual level, while the decrease in photosynthetic pigments, with inhibition rates ranging from 8.95 % to 73.27 %, and the imbalance of redox homeostasis implied an adverse effect of DEP at the physio-biochemical level. Furthermore, DEP significantly reduced the metabolic activity of algal cells and negatively altered the cell membrane integrity and mitochondrial membrane potential. In addition, the apoptosis rate of algal cells presented a significant dose-effect relationship, which was mainly attributed to the fact that DEP pollutants regulated Ca2+ homeostasis and further increased the expression of Caspase-8, Caspase-9, and Caspase-3, which are associated with internal and external pathways. The gene transcriptional expression profile further revealed that DEP-mediated toxicity in C. vulgaris was mainly related to the destruction of the photosynthetic system, terpenoid backbone biosynthesis, and DNA replication. Overall, this study offers constructive understandings for a comprehensive assessment of the toxicity risks posed by DEP to C. vulgaris.

Combined analysis of transcriptomics and metabolomics on the cumulative effect of nano-titanium dioxide on mulberry seedlings

Introduction

Titanium dioxide nanoparticles (TiO₂ NPs) are among the most widely used inorganic nanomaterials in industry, medicine and food additives. There are increasing concerns regarding their potential risks to plants and the environment. Mulberry trees are widely grown in China due to their high survival rate and ability to aid ecological recovery.

Methods

Herein, the effects of TiO₂ NPs with different concentrations (100, 200, 400 and 800 mg/L) on the growth and physiology of the mulberry tree were systematically evaluated in aspects of physiology, transcriptomics and metabolomics.

Results

Results showed that TiO₂ NPs could be absorbed by the mulberry sapling root system and be transferred to the plant shoot. This results in the destruction of mulberry sapling root and leaf tissue. Furthermore, the number of chloroplasts and their pigment contents were reduced and the homeostasis of metal ions was disrupted. The toxic effects of TiO₂ NPs attenuated the mulberry sapling's stress resistance, the contents of malondialdehyde in 100 mg/L, 200 mg/L 400 mg/L and 800 mg/L treatment groups increased by 87.70%, 91.36%, 96.57% and 192.19% respectively compared with the control group. The transcriptomic data showed that TiO₂ NPs treatment mainly affected the expression of genes related to energy synthesis and transport, protein metabolism, and response to stress. Meanwhile, the results of metabolomics showed that 42 metabolites produced significant differences in mulberry, of which 26 differential metabolites were up-regulated in expression and 16 differential metabolites were down-regulated, mainly including metabolic pathways such as secondary metabolite biosynthesis, citric acid cycle, and tricarboxylic acid cycle, and was not conducive to the seed germination and or growth of the mulberry sapling.

Discussion

This study enriches the understanding of the effects of TiO₂ NPs on plants and provides a reference for the comprehensive scientific assessment of the potential risks of nanomaterials on plants.

Elevated CO2 altered the nano-ZnO-induced influence on bacterial and fungal composition in tomato (Solanum lycopersicum L.) rhizosphere soils

To investigate whether elevated CO₂ (eCO₂) changes the influence of nanoparticles (NPs) on soil microbial communities and the mechanisms, various nano-ZnO (0, 100, 300, and 500 mg·kg^-1) and CO₂ concentrations (400 and 800 µmol·mol^-1) were applied to tomato plants (Solanum lycopersicum L.) in growth chambers. Plant growth, soil biochemical properties, and rhizosphere soil microbial community composition were analyzed. In 500 mg·kg^-1 nano-ZnO-treated soils, root Zn content was 58% higher, while total dry weight (TDW) was 39.8% lower under eCO₂ than under atmospheric CO₂ (aCO₂). Compared with the control, the interaction of eCO₂ and 300 mg·kg^-1 nano-ZnO decreased and increased bacterial and fungal alpha diversities, respectively, which was caused by the direct effect of nano-ZnO (r =  - 1.47, p < 0.01). Specifically, the bacterial OTUs decreased from 2691 to 2494, while fungal OTUs increased from 266 to 307, when 800-300 was compared with 400-0 treatment. eCO₂ enhanced the influence of nano-ZnO on bacterial community structure, while only eCO₂ significantly shaped fungal composition. In detail, nano-ZnO explained 32.4% of the bacterial variations, while the interaction of CO₂ and nano-ZnO explained 47.9%. Betaproteobacteria, which are involved in C, N, and S cycling, and r-strategists, such as Alpha- and Gammaproteobacteria and Bacteroidetes, significantly decreased under 300 mg·kg^-1 nano-ZnO, confirming reduced root secretions. In contrast, Alpha- and Gammaproteobacteria, Bacteroidetes, Chloroflexi, and Acidobacteria were enriched in 300 mg·kg^-1 nano-ZnO under eCO₂, suggesting greater adaptation to both nano-ZnO and eCO₂. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2) analysis demonstrated that bacterial functionality was unchanged under short-term nano-ZnO and eCO₂ exposure. In conclusion, nano-ZnO significantly affected microbial diversities and the bacterial composition, and eCO₂ intensified the damage of nano-ZnO, while the bacterial functionality was not changed in this study.

Environmental exposure and nanotoxicity of titanium dioxide nanoparticles in irrigation water with the flavonoid luteolin

Different concentrations of titanium oxide nanoparticles (TiO2NPs) have been frequently reported in treated wastewater used for the irrigation of crops. Luteolin is a susceptive anticancer flavonoid in many crops and rare medicinal plants that can be affected by exposure to TiO2NPs. This study investigates the potential transformation of pure luteolin in exposure to TiO2NP-containing water. In an in vitro system, three replicates of 5 mg L-1 of pure luteolin were exposed to TiO2NPs (0, 25, 50, 100 ppm). After 48 h exposure, the samples were extensively analyzed by Raman spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, and dynamic light scattering (DLS). A positive correlation was found between TiO2NPs concentrations and the structural alteration of luteolin content, where over 20% of luteolin structure was allegedly altered in the presence of 100 ppm TiO2NPs. The increase of NPs diameter (∼70 nm) and dominant peaks in Raman spectra revealed that luteolin was adsorbed onto the TiO2NPs surface. Further, the second-order derivative analysis confirmed the transformation of luteolin upon exposure to TiO2NPs. This study provides fundamental insight into agricultural safety measures when exposed to air or water-borne TiO2NPs.

Elevated CO2 may increase the health risks of consuming leafy vegetables cultivated in flooded soils contaminated with Cd and Pb

Elevated CO₂ levels threat the crop quality by altering the environmental behavior of heavy metals (HMs) in soils. In reality, multiple HMs often co-exist in field, while details regarding coexisting HMs migration in flooded soil at elevated CO₂ levels remain unclear. A pot experiment in open-top chambers (CO₂ at 400 and 600 μmol mol^-1) was conducted to explore the uptake and transfer of cadmium (Cd) and lead (Pb) in water dropwort (Oenanthe javanica DC.) grown in flooded soils contaminated with Cd and Pb. Results showed that elevated CO₂ significantly reduced soil pH, promoting the release of Cd and Pb (by 63.64-106.90% and 10.66-30.99%, respectively) into soil porewater. In the harvested O. javanica, elevated CO₂ decreased the root uptake of Cd but promoted that of Pb. Further mechanism analysis showed that elevated CO₂ promoted the formation of iron plaque on root surface by 44.60-139.57%, with lower adsorption capacity to HMs (0-34.93% and 63.61-67.69% for Cd and Pb, respectively). Meanwhile, Pb showed lower adsorbability in iron plaque but higher transfer capacity when compared with Cd. Ultimately, elevated CO₂ increased the target hazard quotient values of Pb in O. javanica. These findings provide new insights on the effects of elevated CO₂ on the transfer of coexisting HMs in soil-plant system, and the risk of HMs pollution under climate changes needs to be more fully assessed.

Potential Effects of Metal Oxides on Agricultural Production of Rice: A Mini Review

The extensive usage of metal oxide nanoparticles has aided in the spread and accumulation of these nanoparticles in the environment, potentially endangering both human health and the agroecological system. This research describes in detail the hazardous and advantageous impacts of common metal oxide nanomaterials, such as iron oxide, copper oxide, and zinc oxide, on the life cycle of rice. In-depth analyses are conducted on the transport patterns of nanoparticles in rice, the plant's reaction to stress, the reduction of heavy metal stress, and the improvement of rice quality by metal oxide nanoparticles, all of which are of significant interest in this subject. It is emphasized that from the perspective of advancing the field of nanoagriculture, the next stage of research should focus more on the molecular mechanisms of the effects of metal oxide nanoparticles on rice and the effects of combined use with other biological media. The limitations of the lack of existing studies on the effects of metal oxide nanomaterials on the entire life cycle of rice have been clearly pointed out.

Elevated CO2 exacerbates effects of TiO2 nanoparticles on rice (Oryza sativa L.) leaf transcriptome and soil bacteria

Elevated CO₂ affects the plant rhizosphere and can therefore affect the fate and toxicity of soil contaminants. However, little is known about how the effects of nanoparticles on plants and soil bacteria will change under future CO₂ levels. A free-air CO₂ enrichment system with two CO₂ levels (ambient, 390 μmol mol^-1; elevated, 590 μmol mol^-1) was used to investigate the responses of rice (Oryza sativa L.) and soil bacteria to titanium dioxide nanoparticles (nano-TiO₂, 0 and 200 mg kg^-1). Results showed that nano-TiO₂ alone did not significantly affect rice growth but affected soil bacteria involved in the carbon and sulfur cycles. Elevated CO₂ alone increased rice plant biomass and up-regulated genes related to ribosomes, but its combination with nano-TiO₂ down-regulated genes related to photosynthesis and photosynthetic antennae. Elevated CO₂ also exacerbated the disturbance by nano-TiO₂ to soil bacteria involved in carbon and nitrogen cycles, and consequently inhibited the rice growth. These findings provide a reference for the comprehensive evaluation for the risk of soil pollution.

Toxicity of perfluooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS) to Scenedesmus obliquus: Photosynthetic characteristics, oxidative damage and transcriptome analysis

With the wide application as an alternative for perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate (PFBS) has been frequently detected in the aquatic environment. However, the aquatic toxicity of PFBS is still poorly understood. The present work studied the aquatic toxicity of PFBS using freshwater algae Scenedesmus obliquus (S. obliquus) as indicator, and the toxicity of PFOS was also examined for comparison. The results showed that PFBS exhibited much lower toxicity to S. obliquus than PFOS. The EC₅₀ value was higher than 1800 mg L^-1 after 7 days of exposure to PFBS. By contrast, a much lower EC₅₀ value of 136.69 mg L^-1 was obtained for PFOS. Photosynthetic efficiency analyzed by chlorophyll fluorescence also verified that PFOS induced a higher toxic effect on the algae than PFBS. The malondialdehyde, catalase and superoxide dismutase results indicate that PFOS exposure led to the accumulation of ROS, which caused oxidative damage to the algae, thereby resulting in the inhibition in the growth and photosynthesis of the algae. Furthermore, transcriptome analysis indicates that the significant down-regulation of key genes related to photosynthesis induced by PFOS was the fundamental mechanism for the inhibition in photosynthetic efficiency and biomass growth of S. obliquus.

Silver and copper-oxide nanoparticles prepared with GA3 induced defense in rice plants and caused mortalities to the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Nanoparticles have been employed as nanopesticides for pest control in agriculture. However, the harmful effects of their chemical synthesis on human and environmental health have resulted in increased use of green synthetic approaches, including the use of plant extracts. The brown planthopper, Nilaparvata lugens (Stål) (BPH), is a severe pest of rice plants (Oryza sativa L.), especially in Asia. It is usually controlled chemically but has developed resistance against many insecticides.

RESULTS

In this study, we synthesized metallic silver (Ag-NPs) and copper-oxide (CuO-NPs) nanoparticles using the exogenous phytohormone, gibberellic acid (GA₃), as a reducing agent. We then sprayed them separately on rice plants and BPH together and evaluated their effects on the plants and insects. SEM and TEM images showed that the synthesis was successful, indicated by the sizes (25-60 nm), uniform shape and spherical and cubical structures of Ag-NPs, as well as by the rugby sheet-like of CuO-NPs with lateral sizes of 150-340 nm and thickness of 30-70 nm. Independent applications of the nanoparticles and GA₃ on rice plants induced different volatile profiles, of which the highest number emitted was under Ag-NPs, including the highest emission of linalool. Transcriptome analysis showed that Ag-NPs-treated rice plants showed different transcriptome profiles compared to the control, 24 h after treatment, including the upregulation of the linalool synthase gene, genes of plants transcription factors such as WRKY, bHLH and NAC and other genes involved in plant defense responses. In all treatments, the mortality rate of BPH increased with an increase in NPs concentrations over time but was prominent under Ag-NPs treatment. The LC₅₀ values for Ag-NPs and CuO-NPs decreased with an increase in time. Also, the nanoparticles increased the activities of protective enzymes (POD, SOD and CAT), inhibited that of detoxification enzymes (A-CHE, ACP and AKP), and reduced total protein concentrations in the BPH.

CONCLUSIONS

These results show that synthesizing nanoparticles using phytohormones may be a safer and environmentally friendly option, which also holds promise for controlling the BPH in rice production.

CeO2 nanoparticles improved cucumber salt tolerance is associated with its induced early stimulation on antioxidant system

Salinity is a global issue limiting efficient agricultural production. Nano-enabled plant salt tolerance is a hot topic. However, the role of nanoparticles induced possible early stimulation on antioxidant system in its improved plant salt tolerance is still largely unknown. Here, poly (acrylic) acid coated nanoceria (cerium oxide nanoparticles) (PNC, 7.8 nm, -31 mV) with potent ROS (reactive oxygen species) scavenging ability are used. Compared with control, no significant difference of H₂O₂ and O₂^•─ content, MDA (malondialdehyde) content, relative electric conductivity, and Fv/Fm was found in leaves and/or roots of cucumber before onset of salinity stress, regardless of leaf or root application of PNC. While, before onset of salinity stress, compared with control, the activities of SOD (superoxide dismutase, up to 1.8 folds change), POD (peroxidase, up to 2.5 folds change) and CAT (catalase, up to 2.3 folds change), and the content of GSH (glutathione, up to 3.0 folds change) and ASA (ascorbic acid, up to 2.4 folds change) in leaves and roots of cucumber with PNC leaf spray or root application were significantly increased. RNA seq analysis further confirmed that PNC foliar spray upregulates more genes in leaves over roots than the root application. These results showed that foliar sprayed PNC have stronger early stimulation effect on antioxidant system than the root applied one and leaf are more sensitive to PNC stimulation than root. After salt stress, cucumber plants with foliar sprayed PNC showed better improvement in salt tolerance than the root applied one. Also, plants with foliar sprayed PNC showed significant higher whole plant cerium content than the root applied one after salt stress. In summary, we showed that foliar spray of nanoceria is more optimal than root application in terms of improving cucumber salt tolerance, and this improvement is associated with better stimulation on antioxidant system in plants.

Novel approach to enhance Bradyrhizobium diazoefficiens nodulation through continuous induction of ROS by manganese ferrite nanomaterials in soybean

BACKGROUND

The study of symbiotic nitrogen fixation between (SNF) legumes and rhizobia has always been a hot frontier in scientific research. Nanotechnology provides a new strategy for biological nitrogen fixation research. However, how to construct abiotic nano-structure-biological system, using the special properties of nanomaterials, to realize the self-enhancement of biological nitrogen fixation capacity is important.

RESULTS

In order to construct a more efficient SNF system, in this study, we applied manganese ferrite nanoparticles (MF-NPs) with sustainable diatomic catalysis to produce reactive oxygen species (ROS), thus regulating the nodulation pathway and increasing the number of nodules in soybean (Glycine max), eventually enhancing symbiotic nitrogen fixation. Symbiosis cultivation of MF-NPs and soybean plants resulted in 50.85% and 61.4% increase in nodule weight and number, respectively, thus inducing a 151.36% nitrogen fixation efficiency increase, finally leading to a 25.70% biomass accumulation increase despite no substantial effect on the nitrogenase activity per unit. Transcriptome sequencing analysis showed that of 36 differentially expressed genes (DEGs), 31 DEGs related to soybean nodulation were upregulated in late rhizobium inoculation stage (12 d), indicating that the increase of nodules was derived from nodule-related genes (Nod-R) continuous inductions by MF-NPs.

CONCLUSIONS

Our results indicated that the nodule number could be effectively increased by extending the nodulation period without threatening the vegetative growth of plants or triggering the autoregulation of nodulation (AON) pathway. This study provides an effective strategy for induction of super-conventional nodulation.

Toxicity mechanism of Nylon microplastics on Microcystis aeruginosa through three pathways: Photosynthesis, oxidative stress and energy metabolism

Nylon has been widely used all over the world, and most of it eventually enters the aquatic environment in the form of microplastics (MPs). However, the impact of Nylon MPs on aquatic ecosystem remains largely unknown. Thus, the long-term biological effects and toxicity mechanism of Nylon MPs on Microcystis aeruginosa (M. aeruginosa) were explored in this study. Results demonstrated that Nylon MPs had a dose-dependent growth inhibition of M. aeruginosa at the initial stage, and the maximum inhibition rate reached to 47.62% at the concentration of 100 mg/L. Meanwhile, Nylon MPs could obstruct photosynthesis electron transfer, reduce phycobiliproteins synthesis, destroy algal cell membrane, enhance the release of extracellular polymeric substances, and induce oxidative stress. Furthermore, transcriptomic analysis indicated that Nylon MPs dysregulated the expression of genes involved in tricarboxylic acid cycle, photosynthesis, photosynthesis-antenna proteins, oxidative phosphorylation, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism. According to the results of transcriptomic and biochemical analysis, the growth inhibition of M. aeruginosa is inferred to be regulated by three pathways: photosynthesis, oxidative stress, and energy metabolism. Our findings provide new insights into the toxicity mechanism of Nylon MPs on freshwater microalgae and valuable data for risk assessment of MPs.

Impact of engineered nanomaterials on rice (Oryza sativa L.): A critical review of current knowledge

After use, a large number of engineered materials (ENMs) are directly or indirectly released into the environment. This may threaten the agricultural ecosystem, especially with crops under high demand for irrigation water, such as rice (Oryza sativa L.), a crop that feeds nearly half of the world's population. However, consistent and detailed information on the effects of nanoparticles in rice is limited. This review is a systematic exploration of the effects of ENMs on rice, with a critical evaluation of the mechanisms reported in the literature by which different nanomaterials cause toxicity in rice. The physiological and biochemical effects engendered by the nanoparticles are highlighted, focusing on rice growth and development, ENMs uptake and translocation, gene expression changes, enzyme activity modifications, and secondary metabolite alterations.

Copper accumulation and physiological markers of soybean (Glycine max) grown in agricultural soil amended with copper nanoparticles

Copper-based nanoparticles (NPs) display a strong potential to replace copper salts (e.g., CuSO4) for application in agricultures as antimicrobial agents or nutritional amendments. Yet, their effects on crop quality are still not comprehensively understood. In this study, the Cu contents in soybeans grown in soils amended with Cu NPs and CuSO4 at 100-500 mg Cu/kg and the subsequent effects on the plant physiological markers were determined. The Cu NPs induced 29-89% at the flowering stage (on Day 40) and 100-165% at maturation stage (on Day 100) more Cu accumulation in soybeans than CuSO4. The presence of particle aggregates in the root cells with deformation upon the Cu NP exposure was observed by transmission electron microscopy. The Cu NPs at 100 and 200 mg/kg significantly improved the plant height and biomass, yet significantly inhibited at 500 mg/kg, compared to the control. In leaves chlorophyll-b was more sensitive than chlorophyll-a and carotenoids to the Cu NP effect. The Cu NPs significantly decreased the root nitrogen and phosphorus contents, while they significantly increased the leaf potassium content in comparison with control. Our results imply that cautious use of Cu NPs in agriculture is warranted due to relatively high uptake of Cu and altered nutrient quality in soybeans.

Downregulation of the photosynthetic machinery and carbon storage signaling pathways mediate La2O3 nanoparticle toxicity on radish taproot formation

The molecular and physiological mechanisms of how rare earth oxide nanoparticles (NPs) alter radish (Raphanus sativus L.) taproot formation and cracking were investigated in the present study. We compared plants that received suspensions of 10, 50, 100, 300 mg L^-1 of La₂O₃ NPs, 300 m L^-1 La₂O₃ bulk-particles (BPs), 0.8 m L^-1 La³⁺, or only water for six days during their tuber formation period. 100 and 300 mg L^-1 La₂O₃ NPs exposure decreased storage root biomass by 38% and 60%, respectively, and they both induced visible root cracking. Physiological analyses showed that La₂O₃ NPs exposure (>100 mg L^-1) significantly inhibited leaf net photosynthetic rate, cell wall pectin synthesis of both storage root epidermis and xylem parenchyma tissues, but increased the contents of cellulose and hemicellulose 1 in root epidermis cell walls. Moreover, transcriptome analysis further found that La₂O₃ NPs changed root cell wall structure by down-regulating core genes involved in cell wall pectin and IAA biosynthesis, which coincided with the observed La₂O₃ NPs-induced root cracking. Our results revealed the molecular mechanisms related to cell wall carbohydrate metabolism in response to NPs stress, providing a step forward for understanding the causes of NPs phytotoxicity on edible plant taproot formation and cracking.

Phytotoxic effect and molecular mechanism induced by nanodiamonds towards aquatic Chlorella pyrenoidosa by integrating regular and transcriptomic analyses

The growing diverse applications of nanodiamonds (NDs), especially as adsorbents and catalysts for wastewater treatment, have significantly increased their discharge and potential risk towards aquatic ecosystems. Although NDs have been certified for superior biocompatibility and lower toxicity towards numerous human cell lines, the characteristic response and underlying mechanism of aquatic microalgal response remains unclear. Here, the response of Chlorella pyrenoidosa to five concentrations of NDs was thoroughly investigated by comprehensive phenotypic and transcriptional examinations. Results indicated that higher concentration of NDs (50 mg/L) induced 75.4% growth inhibition, exacerbated oxidative stress and malformed morphology of microalgae after 48 h exposure. Meanwhile, the aggregated microalgae formed several flocs, apparently under 50 mg/L NDs. Noticeably, photosynthesis was susceptible to the NDs exposure. Although, the chlorophyll content and genes involved in photosynthesis were significantly improved by NDs, the results obtained from the photochemical parameters indicated that the excessive electrons during photosynthesis might be a pivotal reason for oxidative stress generation. Additionally, the genes included in amino acids metabolism and protein synthesis were up-regulated to alleviate the oxidative stress. Collectively, this work discloses the explicit molecular mechanisms of aquatic microalgae and provides comprehensive insights of potential aqueous environmental risk of gradually emergent NDs.

Elevated CO2 concentration modifies the effects of organic fertilizer substitution on rice yield and soil ARGs

Antibiotic resistance and rising CO2 levels are considered among the most significant challenges we will face in terms of global development over the following decades. However, the impact of elevated CO2 on soil antibiotic resistance has rarely been investigated. We used a free-air CO2 enrichment system to investigate the potential risks posed by applying mineral and organic fertilizers to paddy soil at current CO2 concentration (370 ppm) and future elevated CO2 (eCO2, 570 ppm predicted for 2100). Organic fertilizer substitution (substituting the mineral fertilizer by 50% N) alone increased the plant uptake and soil residue of sulfamethazine, and enriched sulfonamide resistance genes (sul1, sul2), tetracycline resistance genes (tetG, tetM) and class 1 integron (intl1). But it decreased the rice grain yield (by 7.6%). Comparatively, eCO2 decreased the sul2, tetG and intl1 gene abundances by organic fertilizer substitution, and meanwhile increased grain yield (by 8.4%). Proteobacteria and Nitrospirae were potential hosts of antibiotic resistance genes (ARGs). Horizontal gene transfer via intl1 may play an important role in ARGs spread under eCO2. Results indicated that future elevated CO2 concentration could modify the effects of organic fertilizer substitution on rice yield and soil ARGs, with unknown implications for future medicine and human health.

Nanotechnology: an efficient approach for rejuvenation of aged seeds

Modern agricultural efforts are now in search of an efficient, eco-friendly and sustainable approach for enhanced crop production. Nearly 50-60% of seeds lost occurs due to improper technical handling. Seed deterioration manifests itself as reduction in the rate of germination and growth with increased susceptibility to biotic and abiotic stresses. Furthermore, seed ageing is another economic and scientific issue that is associated with an array of internal (structural, physiological and genetic) and external (storage temperature and relative humidity) factors. Reactive oxygen species (ROS) are believed to be a key player in ageing phenomenon. However, hydrated storage, or ROS blockers are a few of the conventionally used methods to minimize the ageing process. Recently, exogenous applications of different inorganic nanoparticles (metal and metal oxide) are suggested to revitalize and revive aged seeds. Owing to their special properties of nano-size with high surface area they easily penetrate the seed coat. Exposure of nanoparticles has been suggested to neutralize the excess of ROS to a level that initiates hormonal signaling to support early emergence of radicles from the seeds. Nanotechnology has been well explored to enhance the crops nutritional quality, livestock productivity, plant protection from various stressors and in enhancement of seed quality via nanopesticides and nanofertilizers. Aiming at sustainable agriculture practices with fewer inputs, maximum benefits, ecologically safe and compatible technique the nanotechnology is an efficient approach to counteract problems of seed ageing incurring during storage, which is relatively less explored and unresolved conventionally, in general.

Electron transport, light energy conversion and proteomic responses of periphyton in photosynthesis under exposure to AgNPs

Silver nanoparticles (AgNPs) including a mix of intact nanoparticle-Ag and 'free' Ag⁺ pose high risks to benthic photoautotrophs, but the photosynthetic responses of benthic microbial aggregates to AgNPs still remain largely unknown. Here, periphyton and Nostoc were used to elucidate the photosynthetic responses of benthic algae community to intact nanoparticle-Ag and Ag⁺. During exposure, both intact nanoparticle-Ag and Ag⁺ imposed negative effects on photosynthesis of benthic algae, but via different pathways. Specifically, Ag⁺ had stronger effects on damaging the oxygen-evolving complex (OEC) and thylakoid membrane than intact nanoparticle-Ag. Ag⁺ also suppressed electron transfer from Q_A to Q_B, and impaired phycobilisome. Intact nanoparticle-Ag inhibited the expression of PsbD and PsbL in PSII, but prompted the ROS scavenging capacity. In response to the stress of AgNPs, the benthic algae increased light energy absorption to maintain the electron transport efficiency, and up-regulated PSI reaction center protein (PsaA) to compensate the degraded PSII. These results reveal how intact nanoparticle-Ag and Ag⁺ influence electron transport, energy conversion and protein expression in the photosynthesis of periphyton, and provide deep insights into the responses of benthic photoautotrophs to different components of AgNPs.

Photosynthetic responses of Arabidopsis to SO2 were related to photosynthetic pigments, photosynthesis gene expression and redox regulation

Sulfur dioxide (SO₂) is one of the most common and harmful air pollutants. High concentrations of SO₂ can induce a series of defensive responses in Arabidopsis plants. However, the role of photosynthesis in the plant response to SO₂ stress is not clear. Here, we report the photosynthetic responses of Arabidopsis plants to SO₂ stress. Exposure to 30 mg/m³ SO₂ decreased stomatal conductance (Gs) and transpiration rate (Tr) but increased photosynthetic pigments and net photosynthetic rate (Pn). The contents of carbohydrates and sucrose were not altered. The transcript levels of most genes related to photosystem II (PSII), cytochrome b6/f (Cytb6f), photosystem I (PSI) and carbon fixation were upregulated, revealing one important regulatory circuit for the maintenance of chloroplast homeostasis under SO₂ stress. Exposure to SO₂ triggered reactive oxygen species (ROS) generation, accompanied by increases in superoxide dismutase (SOD) activity and the contents of cysteine (Cys), glutathione (GSH) and non-protein thiol (NPT), which maintained cellular redox homeostasis. Together, our results indicated that chloroplast photosynthesis was involved in the plant response to SO₂ stress. The photosynthetic responses were related to photosynthetic pigments, photosynthesis gene expression and redox regulation.

Effects of Decabromodiphenyl Ether and Elevated Carbon Dioxide on Rice (Oryza sativa L.)

We assessed the effects of carbon dioxide (CO₂) and decabromodiphenyl ether (BDE-209, 0, 3 and 30 mg/kg) on rice (Oryza sativa L. cv. Wuyunjing) in field free-air CO₂ enrichment system. Rice at elevated (580 ppm) CO₂ had increased net photosynthetic rate, intercellular CO₂ concentration, shoot biomass, yield and phosphorus content in grains. However, there were no significant changes in such parameters observed on rice at elevated CO₂ combined with BDE-209 (3 and 30 mg/kg). Elevated CO₂ alone had no significant effects on sugar or starch content in rice grains, whereas its combination with BDE-209 (3 mg/kg) significantly decreased grain sugar and starch content. In conclusion, rice reared in soil polluted by BDE-209 under elevated CO₂ modulates the effects in grain feature.