Lettuce Roots Research Articles

Substrate Matters: Ionic Silver Alters Lettuce Growth, Nutrient Uptake, and Root Microbiome in a Hydroponics System.

Ionic silver (Ag+) is being investigated as a residual biocide for use in NASA spacecraft potable water systems on future crewed missions. This water will be used to irrigate future spaceflight crop production systems. We have evaluated the impact of three concentrations (31 ppb, 125 ppb, and 500 ppb) of ionic silver biocide solutions on lettuce in an arcillite (calcinated clay particle substrate) and hydroponic (substrate-less) growth setup after 28 days. Lettuce plant growth was reduced in the hydroponic samples treated with 31 ppb silver and severely stunted for samples treated at 125 ppb and 500 ppb silver. No growth defects were observed in arcillite-grown lettuce. Silver was detectable in the hydroponic-grown lettuce leaves at each concentration but was not detected in the arcillite-grown lettuce leaves. Specifically, when 125 ppb silver water was applied to a hydroponics tray, Ag+ was detected at an average amount of 7 μg/g (dry weight) in lettuce leaves. The increase in Ag+ corresponded with a decrease in several essential elements in the lettuce tissue (Ca, K, P, S). In the arcillite growth setup, silver did not impact the plant root zone microbiome in terms of alpha diversity and relative abundance between treatments and control. However, with increasing silver concentration, the alpha diversity increased in lettuce root samples and in the water from the hydroponics tray samples. The genera in the hydroponic root and water samples were similar across the silver concentrations but displayed different relative abundances. This suggests that ionic silver was acting as a selective pressure for the microbes that colonize the hydroponic water. The surviving microbes likely utilized exudates from the stunted plant roots as a carbon source. Analysis of the root-associated microbiomes in response to silver showed enrichment of metagenomic pathways associated with alternate carbon source utilization, fatty-acid synthesis, and the ppGpp (guanosine 3'-diphosphate 5'-diphosphate) stringent response global regulatory system that operates under conditions of environmental stress. Nutrient solutions containing Ag+ in concentrations greater than 31 ppb in hydroponic systems lacking cation-exchange capacity can severely impact crop production due to stunting of plant growth.

The dosage- and size-dependent effects of micro- and nanoplastics in lettuce roots and leaves at the growth, photosynthetic, and metabolomics levels

The occurrence of microplastics (MPs) and nanoplastics (NPs) in soils potentially induce morphological, physiological, and biochemical alterations in plants. The present study investigated the effects of MPs/NPs on lettuce (Lactuca sativa L. var. capitata) plants by focusing on (i) four different particle sizes of polyethylene micro- and nanoplastics, at (ii) four concentrations. Photosynthetic activity, morphological changes in plants, and metabolomic shifts in roots and leaves were investigated.Our findings revealed that particle size plays a pivotal role in influencing various growth traits of lettuce (biomass, color segmentation, greening index, leaf area, and photosynthetic activity), physiological parameters (including maximum quantum yield - Fv/Fmmax, or quantum yield in the steady-state Fv/FmLss, NPQLss, RfdLss, FtLss, FqLss), and metabolomic signatures. Smaller plastic sizes demonstrated a dose-dependent impact on aboveground plant structures, resulting in an overall elicitation of biosynthetic processes. Conversely, larger plastic size had a major impact on root metabolomics, leading to a negative modulation of biosynthetic processes. Specifically, the biosynthesis of secondary metabolites, phytohormone crosstalk, and the metabolism of lipids and fatty acids were among the most affected processes. In addition, nitrogen-containing compounds accumulated following plastic treatments.Our results highlighted a tight correlation between the qPCR analysis of genes associated with the soil nitrogen cycle (such as NifH, NirK, and NosZ), available nitrogen pools in soil (including NO3− and NH4), N-containing metabolites and morpho-physiological parameters of lettuce plants subjected to MPs/NPs. These findings underscore the intricate relationship between specific plastic contaminations, nitrogen dynamics, and plant performance.

Evaluation of different QuEChERS-based methods for the extraction of 48 wastewater-derived organic contaminants from soil and lettuce root using high-resolution LC-QTOF with MRMHR and SWATH acquisition modes

The reuse of treated wastewater in agriculture is an important route of introducing a large number of organic contaminants into the agroecosystem. In this study, a modified QuEChERS-based approach was developed for rapid, simple, and simultaneous extraction of 48 organic wastewater-derived contaminants from soil and lettuce root. Twenty-two different (modification) scenarios of the known (or original) QuEChERS method have been tested, in order to obtain best and well-compromised recoveries for all target compounds for soil and roots. Finally, a common method was chosen for both matrices consisting of a single extraction step using EDTA-Mcllvaine buffer and the unbuffered Original QuEChERS salts. Method performance was accomplished by liquid chromatography coupled with high-resolution mass spectrometry on a QToF-MS system using two different acquisition modes, the ultra-fast high-resolution multiple reaction monitoring (MRMHR) mode and the innovative Sequential Window Acquisition of All Theoretical Fragment-Ion (SWATH) mode. Performance characterization was evaluated in terms of recovery, linearity, intra-day precision, method detection limits (MDLs), method quantification limits (MQLs), and matrix effect (ME). Recoveries in MRMHR mode ranged from 63 to 111% and 54 to 104% for lettuce root and soil, respectively, for most of compounds in MRMHR mode and from 56 to 121% and 54 to 104% for lettuce root and soil, respectively, for most of compounds in SWATH. Whereas, MQLs ranged from 0.03 to 0.92 ng g−1 in MRMHR and from 0.03 to 82 ng g−1 in SWATH for lettuce root, and from 0.02 to 0.44 ng g−1 in MRMHR and 0.02 to 0.14 ng g−1 in SWATH for soil. The method was then applied to follow the target compounds in soil and lettuce root, where the system lettuce-soil was irrigated with treated wastewater under real greenhouse conditions. Five and 17 compounds were detected in lettuce root and soil, respectively.Graphical

Bacterially enhanced plant-growing media for controlled environment agriculture.

Microbe-plant interactions in the root zone not only shape crop performance in soil but also in hydroponic cultivation systems. The biological and physicochemical properties of the plant-growing medium determine the root-associated microbial community and influence bacterial inoculation effectiveness, which affects plant growth. This study investigated the combined impact of plant-growing media composition and bacterial community inoculation on the root-associated bacterial community of hydroponically grown lettuce (Lactuca sativa L.). Ten plant-growing media were composed of varying raw materials, including black peat, white peat, coir pith, wood fibre, composted bark, green waste compost, perlite and sand. In addition, five different bacterial community inocula (BCI S1-5) were collected from the roots of lettuce obtained at different farms. After inoculation and cultivation inside a vertical farm, lettuce root-associated bacterial community structures, diversity and compositions were determined by evaluating 16S rRNA gene sequences. The study revealed distinct bacterial community structures among experimental replicates, highlighting the influence of raw material variations on root-associated bacterial communities, even at the batch level. However, bacterial community inoculation allowed modulation of the root-associated bacterial communities independently from the plant-growing medium composition. Bacterial diversity was identified as a key determinant of plant growth performance with green waste compost introducing Bacilli and Actinobacteria, and bacterial community inoculum S3 introducing Pseudomonas, which positively correlated with plant growth. These findings challenge the prevailing notion of hydroponic cultivation systems as sterile environments and highlight the significance of proper plant-growing media raw material selection and bacterial community inoculation in shaping root-associated microbiomes that provide stability through microbial diversity. This study supports the concept of creating bacterially enhanced plant-growing media to promote plant growth in controlled environment agriculture.

Polyethylene microplastic modulates lettuce root exudates and induces oxidative damage under prolonged hydroponic exposure

Root exudates are pivotal in plant stress responses, however, the impact of microplastics (MPs) on their release and characteristics remains poorly understood. This study delves into the effects of 0.05 % and 0.1 % (w/w) additions of polyethylene (PE) MPs on the growth and physiological properties of lettuce (Lactuca sativa L.) following 28 days of exposure. The release characteristics of root exudates were assessed using UV–vis and 3D-EEM. The results indicated that PE increased leaf number but did not significantly affect other agronomic traits or pigment contents. Notably, 0.05 % PE increased the total root length and surface area compared to the 0.1 % addition, while a non-significant trend towards decreased root activity was observed with PE MPs. PE MPs with 0.1 % addition notably reduced the DOC concentration in root exudates by 37.5 %, while 0.05 % PE had no impact on DOC and DON concentrations. PE addition increased the SUVA254, SUVA260, and SUVA280 values of root exudates, with the most pronounced effect seen in the 0.05 % PE treatment. This suggests an increase of aromaticity and hydrophobic components induced by PE addition. Fluorescence Regional Integration (FRI) analysis of 3D-EEM revealed that aromatic proteins (region I and II) were dominant in root exudates, with a slight increase in fulvic acid-like substances (region III) under 0.1 % PE addition. Moreover, prolonged PE exposure induced ROS damage in lettuce leaves, evidenced by a significant increase in content and production rate of O2·−. The decrease in CAT and POD activities may account for the lettuce's response to environmental stress, potentially surpassing its tolerance threshold or undergoing adaptive regulation. These findings underscore the potential risk of prolonged exposure to PE MPs on lettuce growth.

Promising Eco-Friendly Nanoparticles for Managing Bottom Rot Disease in Lettuce (Lactuca sativa var. longifolia)

Developing innovative, eco-friendly fungicide alternatives is crucial to mitigate the substantial threat fungal pathogens pose to crop yields. In this study, we assessed the in vitro effectiveness of SiO2, CuO, and γFe2O3 nanoparticles against Rhizoctonia solani. Furthermore, greenhouse experiments were conducted in artificially infested soil to evaluate the in vivo impact of nanoparticles under study. Two application methods were employed: soil drenching with 10 mL per pot at concentrations of 50, 100, and 200 mg L−1, and seedling dipping in nanoparticle suspensions at each concentration combined with soil drench. The combined treatment of 200 mg L−1 γFe2O3 or CuO nanoparticles showed the highest in vitro antifungal activity. Conversely, SiO2 nanoparticles demonstrated the lowest in vitro activity. Notably, the application of 200 mg/L SiO2 via the dipping and soil drenching methods decreased counts of silicate-solubilizing bacteria and Azospirillum spp. Whereas, application of 100 mg L−1 γFe2O3 nanoparticles via soil drenching increased soil bacterial counts, and CuO nanoparticles at 50 mg L−1 through dipping and soil drenching had the highest dehydrogenase value. γFe2O3 nanoparticles improved plant photosynthetic pigments, reduced malondialdehyde levels, and minimized membrane leakage in lettuce plants. A root anatomical study showed that 200 mg L−1 CuO nanoparticles induced toxicity, whereas 200 mg L−1 γFe2O3 or SiO2 nanoparticles positively affected root diameter, tissue structure, and various anatomical measurements in lettuce roots. γFe2O3 nanoparticles hold promise as a sustainable alternative for managing crop diseases.

Digging into the Lettuce Cold-Specific Root Microbiome in Search of Chilling Stress Tolerance-Conferring Plant-Growth-Promoting Bacteria

Growth of lettuce ( Lactuca sativa) is severely hampered by low temperatures, even when cultivated under greenhouse conditions. Root-associated bacteria might promote plant growth under stressful conditions. Therefore, we analyzed the effect of low temperatures on the lettuce root-associated microbiome to evaluate whether microbiome-based selection aids in identiying bacteria that stimulate plant growth in the cold. 16S ribosomal RNA gene amplicon sequencing was used to examine the compositional differences in the lettuce root-associated microbiome when grown under low- and control-temperature conditions. Chilling temperatures significantly altered the lettuce root endosphere composition, whereas their effects were less severe in the rhizosphere and absent in the bulk soil. Several cold-enriched families were found in both the rhizosphere and the root endosphere, nine of which were Oxalobacteraceae, Pseudomonadaceae, Flavobacteriaceae, Microscillaceae, Sphingobacteriaceae, Comamonadaceae, Devosiaceae, Methylophilaceae and env.OPS_17. Concurrently, a collection of lettuce root-colonizing bacteria was established and, based on correlation with these families, representative isolates were screened. None of the lettuce root isolates showed growth-promoting effects but three growth-promoting Flavobacterium strains from an available collection of grass root-colonizing bacteria were identified. Amplicon sequence variant (ASV) annotation of the lettuce and grass strains revealed that strains matching cold-enriched or highly abundant ASVs in at least one soil promoted growth in the cold. Overall, our data demonstrate that microbiome analyses, combined with high-throughput bacterial isolations might be a helpful tool to isolate effective cold growth-promoting strains.

Effects of naturally aged microplastics on the distribution and bioavailability of arsenic in soil aggregates and its accumulation in lettuce

Naturally aged microplastics (NAMPs) and arsenic (As) have been reported to coexist in and threaten potentially to soil-plant ecosystem. The research explored the combined toxic effects of NAMPs and As to lettuce (Lactuca sativa L.) growth, and the distribution, accumulation and bioavailability of As in soil aggregates. The As contaminated soil with low, medium and high concentrations (L-As, M-As, H-As) were treated with or without NAMPs, and a total of six treatments. The results displayed that, in comparison to separate treatments of L-As and M-As, the presence of NAMPs increased the total biomass of lettuce grown at these two As concentrations by 68.9 % and 55.4 %, respectively. Simultaneous exposure of NAMPs and L-As or M-As led to a decrease in As content in shoot (0.45–2.17 mg kg−1) and root (5.68–14.66 mg kg−1) of lettuce, indicating an antagonistic effect between them. In contrast, co-exposure to H-As and NAMPs showed synergistic toxicity, and the leaf chlorophyll and nutritional quality of lettuce were also reduced. NAMPs altered the ratio of different soil aggregate fractions and the distribution of bioavailable As within them, which influenced the absorption of As by lettuce. In conclusion, these direct observations assist us in enhancing the comprehend of the As migration and enrichment characteristics in soil-plant system under the influence of NAMPs.

Optimal design of the response surface for the root cutting of a hydroponic lettuce harvesting tool

A new type of continuous harvester is designed to address the problems of high labor cost and low efficiency in the process of harvesting lettuce in greenhouse hydroponics. The designed harvester is mainly composed of three parts, namely, reciprocating cutter, driving mechanism, and belt conveyor. The response surface method is used to establish the mathematical model between the force acting on the lettuce roots and the reciprocating speed of the cutter, the inclination angle of the cutter, and the conveying speed of lettuce. The reliability of the mathematical model is verified, and the optimal parameter combination of the force on the lettuce root is obtained. Considering the actual harvesting method, the destruction rate, damage rate, and success rate of lettuce are used as the design indexes in the experiment. Results showed that the force on the lettuce stem is the smallest under the optimal parameter combination of the reciprocating motion speed of the cutting blade (100 mm/s), the inclination angle of the cutting blade (2.31°), and the conveying speed of the lettuce (64.49 mm/s). When the minimum force is 1.91 N, the destruction rate of lettuce harvest is 1.85%, the damage rate of lettuce is 3.71%, and the success rate of lettuce harvest is 94.44%. This study offers a potential solution for the automatic harvesting of hydroponic lettuce in a greenhouse.

Assessing performance of simplified bioassays for soil-borne pathogens in smallholder systems of western Kenya.

Soil-borne pathogens cause considerable crop losses and food insecurity in smallholder systems of sub-Saharan Africa. Soil and crop testing is critical for estimating pathogen inoculum levels and potential for disease development, understanding pathogen interactions with soil nutrient and water limitations, as well as for developing informed soil health and disease management decisions. However, formal laboratory analyses and diagnostic services for pathogens are often out of reach for smallholder farmers due to the high cost of testing and a lack of local laboratories. To address this challenge, we assessed the performance of a suite of simplified soil bioassays to screen for plant parasitic nematodes (e.g., Meloidogyne, Pratylenchus) and other key soil-borne pathogens (Pythium and Fusarium). We sampled soils from on-farm trials in western Kenya examining the impact of distinct nutrient inputs (organic vs. synthetic) on bean production. Key soil health parameters and common soil-borne pathogens were evaluated using both simple bioassays and formal laboratory methods across eleven farms, each with three nutrient input treatments (66 samples in total). The soil bioassays, which involved counting galls on lettuce roots and lesions on soybean were well correlated with the abundance of gall forming (Meloidogyne) and root lesion nematodes (e.g., Pratylenchus) recovered in standard laboratory-based extractions. Effectiveness of a Fusarium bioassay, involving the counting of lesions on buried bean stems, was verified via sequencing and a pathogenicity test of cultured Fusarium strains. Finally, a Pythium soil bioassay using selective media clearly distinguished pathogen infestation of soils and infected seeds. When examining management impact on nematode communities, soils amended with manure had fewer plant parasites and considerably more bacterivore and fungivore nematodes compared to soils amended with synthetic N and P. Similarly, Pythium presence was 35% lower in soils amended with manure, while the Fusarium assays indicated 23% higher Fusarium infection in plots with amended manure. Our findings suggest that relatively simple bioassays can be used to help farmers assess soil-borne pathogens in a timely manner, with minimal costs, thus enabling them to make informed decisions on soil health and pathogen management.

Superfície de resposta para quantificação dos efeitos de NaCl e pH em alface

Abstract The objective of this work was to evaluate the response surface methodology (RSM), with a large sample size, to investigate the effects of NaCl and pH on the root elongation of lettuce (Lactuca sativa) in vitro. For this, 20 lettuce seeds were placed in sterile Petri dishes with two filter papers at the bottom and 3.0 mL of the sample being tested. A rotatable 2x2 factorial arrangement was used, with two factors and a two-level matrix, incorporating two center points and ±1.41 α axial points. Each treatment group consisted of 40 replicates, resulting in 400 experimental observations. Increasing NaCl concentration from 0.0065 to 2,700 g L-1 caused a 19.3% decrease in lettuce root elongation. When pH decreased from 7.0 to 1.5, there was a 68.8% decrease in root elongation, but, when it increased from 7.0 to 12.5, there was a 44.9% decrease. The analysis of combined effects showed that the increase in NaCl concentration reduced the ability of the plant to resist changes in pH. The RSM was effective in evaluating the statistical significance of the NaCl and pH factors, including their second-order effects and interactions, as well as in quantifying their effects on the root elongation of lettuce under the experimental conditions. Therefore, the RSM is a valuable tool for interpreting the results and evaluating the sensitivity of multi-factor research, even when dealing with a large sample size.

First report of Pythium root rot of hydroponic lettuce (Lactuca sativa) in Greece, caused by Pythium Cluster B2a sp.

Pythium root rot has been reported in several countries, but in Greece this disease was first detected in 2021, causing severe yield losses in a hydroponic lettuce crop. Isolations, morphological and molecular characterization, as well as pathogenicity assays identified a Pythium Cluster B2a species causing the disease in hydroponically grown lettuce. This is the first report of Pythium Cluster B2a sp. causing lettuce root rot in Greece.

Fast and reliable determination of phthalic acid esters in soil and lettuce samples based on QuEChERS GC–MS/MS

Phthalates are commonly used as plasticizers, and solvents in industry and households. We propose an application of the QuEChERS method for the determination of six PAEs in the soil and lettuce (roots and leaves) by GC–MS/MS. The QuEChERS method validation procedure was performed and good linearity (>0.997), recovery (97.2–99.1 %), very low detection limits (0.09–0.43 ng/g), and satisfactory inter- and intraday precision (∼4%) were obtained confirming that QuEChERS GC–MS/MS applied for PAEs determination in the environmental samples is a cheap and environmentally friendly method. In general, the higher the number of carbon atoms in PAEs, the higher the percentage noted in the lettuce roots. At higher PAEs concentration (60 ng/g) the main bis(2-ethylhexyl) phthalate (DEHP) sink were roots whereas at lower concentrations (30 ng/g) most of DEHP was noted in lettuce leaves implying that the fate of PAEs was governed not by the chemical structure of PAEs but rather partitioning (logKow).

Plants Wilt Disease of Red Leaf Lettuce (Lactuca sativa L.) After Colonized by Trichoderma longibrachiatum

Trichoderma longibrachiatum rarely reported can cause disease in plants. The present study investigates the pathogenicity of T. longibrachiatum isolate UPMT14 on the red leaf lettuce (Lactuca sativa L.) plants grown in sterile soil under a controlled growth room environment. The fungal isolate was initially characterized morphologically as Trichoderma sp. and was then further characterized by (ITS) region sequencing and BLAST comparison identified as T. longibrachiatum. To observe the response of Trichoderma isolate UPMT14 when imposed on lettuce plants. The injection was made and repeated five times, and then the lettuce growth followed for 36 days. On day 36, the present study found that the red leaf lettuce plants expressed foliar symptoms that began as chlorotic, reduced plant height, reduced leaf length and diameter, wilt, and dried up before it collapsed at day 45 compared to untreated control lettuce plants. Microscopic observation on lettuce roots showed that the Trichoderma spores invading the root system by mass sporulation and spatial competition possibly impaired plant water uptake and eventually caused plant wilting. Therefore, this study indicates that T. longibrachiatum is among the causal agents of wilt disease in the lettuce plant.

Interactive impacts of microplastics and arsenic on agricultural soil and plant traits

The ability of microplastics (MPs) to interact with environmental pollutants is currently of great concern due to the increasing use of plastic. Agricultural soils are sinks for multipollutants and the safety of biodegradable MPs in field conditions is questioned. However, still few studies have investigated the interactive effects between MPs and metals on the soil-plant system with agricultural soil and testing crops for human consumption. In this work, we tested the effect on soil and plant parameters of two common MPs, non-degradable plastic low-density polyethylene and biodegradable polymer polylactic acid at two different sizes (<250 μm and 250–300 μm) in association with arsenic (As). Lettuce (Lactuca sativa L.) was used as a model plant in a small-scale experiment lasting 60 days. Microplastics and As explained 12 % and 47 % of total variance, respectively, while their interaction explained 21 %, suggesting a higher toxic impact of As than MPs. Plant growth was promoted by MPs alone, especially when biodegradable MPs were added (+22 %). However, MPs did not affect nutrient concentrations in roots and leaves. The effect of MPs on enzyme activities was variable depending on the time of exposure (with larger effects immediately after exposure), the type and size of the MPs. On the contrary, the co-application of MP and As, although it did not change the amount of bioavailable As in soil in the short and medium term, it resulted in a significant decrease in lettuce biomass (−19 %) and root nutrient concentrations, especially when polylactic acid was applied. Generally, MPs in association with As determined the plant-soil toxicity. This work provides insights into the risk of copollution of MPs and As in agricultural soil and its phytotoxic effect for agricultural crops. However, the mechanisms of the joint effect of MP and As on plant toxicity need further investigation, especially under field conditions and in long-term experiments.

Microbiome study of a coupled aquaponic system: unveiling the independency of bacterial communities and their beneficial influences among different compartments

To understand the microbiome composition and interplay among bacterial communities in different compartments of a coupled freshwater aquaponics system growing flathead grey mullet (Mugil cephalus) and lettuces (Lactuca sativa), 16S rRNA gene amplicon sequencing of the V3–V4 region was analysed from each compartment (fish intestine, water from the sedimentation tank, bioballs from the biological filter, water and biofilm from the hydroponic unit, and lettuce roots). The bacterial communities of each sample group showed a stable diversity during all the trial, except for the fish gut microbiota, which displayed lower alpha diversity values. Regarding beta diversity, the structure of bacterial communities belonging to the biofilm adhering to the hydroponic tank walls, bioballs, and lettuce roots resembled each other (weighted and unweighted UniFrac distances), while bacteria from water samples also clustered together. However, both of the above-mentioned bacterial communities did not resemble those of fish gut. We found a low or almost null number of shared Amplicon Sequence Variants (ASVs) among sampled groups which indicated that each compartment worked as an independent microbiome. Regarding fish health and food safety, the microbiome profile did not reveal neither fish pathogens nor bacterial species potentially pathogenic for food health, highlighting the safety of this sustainable food production system.

Foliar spraying of lanthanum activates endocytosis in lettuce (Lactuca sativa L.) root cells, increasing Cd and Pb accumulation and their bioaccessibility

Cadmium (Cd) and lead (Pb) accumulate easily in leafy vegetables and can harm human health. Lanthanum (La) have been used to improve agricultural yield and quality, but the effect of La application on Cd/Pb enrichment in leafy vegetables remains incomplete currently. A previous study reported that the endocytosis in lettuce leaf cells can be activated by La, leading to an increase in Pb accumulation in lettuce leaves. However, it has not been investigated whether foliar application of La enhances root cellular endocytosis and promotes its uptake of Cd and Pb. In this study, the influence of La on the uptake of Cd and Pb, Cd bioaccessibility, and the safety risks of cultivating lettuce under Cd and Pb stress were explored. It was found that La increased Cd (16–30 % in shoot, 16–34 % in root) and Pb (25–29 % in shoot, 17–23 % in root) accumulation in lettuce. The increased accumulation of Cd and Pb could be attributed to La-enhanced endocytosis. Meanwhile, La enhanced the toxicity of both Cd and Pb, inhibited lettuce growth, and aggravated the damage to the photosynthetic and antioxidant systems. Finally, gastrointestinal simulation experiments showed that La increased the Cd bioaccessibility in both gastric and intestinal phase by 7–108 % and 9–87 %, respectively. These results offer valuable insights into the safety of REEs for agricultural applications.

Employing a Plant Probiotic Actinomycete for Growth Promotion of Lettuce (Lactuca sativa L. var. longifolia) Cultivated in a Hydroponic System under Nutrient Limitation.

The consumption of lettuce is associated with an increased risk of ingesting nitrate, a naturally occurring and potentially harmful compound that can have adverse effects on human health. Hydroponic cultivation systems serve as effective tools for regulating nutrient solutions and nitrogen availability, which are essential for controlling nitrate levels. However, the techniques for reducing nutrient levels need to be appropriately calibrated based on lettuce growth responses and their interactions with the environment and growing conditions. Previous studies have demonstrated that plant probiotic actinomycetes can alleviate nutritional stress in various crops. However, there is a noticeable gap in research concerning the effects of actinomycetes on hydroponically grown lettuce, particularly under nutrient-limiting conditions. This study aimed to evaluate the effectiveness of the actinomycete Streptomyces thermocarboxydus S3 in enhancing lettuce growth in a nutrient-restricted hydroponic system. The results indicated that the detrimental effects of nutrient stress on lettuce were mitigated by the inoculation of lettuce with S. thermocarboxydus S3. This mitigation was evident in various growth parameters, including leaf count, shoot length, and the fresh and dry weights of both shoots and roots. In the presence of nutritional stress, S. thermocarboxydus S3 likely mitigated the negative effects on lettuce by reducing hydrogen peroxide levels, presumably through the synthesis of H2O2-scavenging enzymes. Furthermore, S. thermocarboxydus S3 successfully survived and colonized lettuce roots. Therefore, the inoculation of lettuce with S. thermocarboxydus S3 offers significant advantages for promoting lettuce growth in nutrient-limited hydroponic systems.

Bioassay to characterise the effects of nematicidal compounds on Meloidogyne species

Summary A bioassay was developed to characterise the effects of nematicidal compounds and tested using low concentrations (0.125 and 0.25 mg l−1) of three nematicides: fluensulfone, fluopyram and fluazaindolizine. Germinating lettuce seeds with ca 2-3 mm roots were planted in a 5.5-cm-diam. Petri dish on agar containing the nematicides. Second-stage juveniles (J2) of Meloidogyne javanica and M. incognita were introduced to the agar plate immediately after planting. Alternatively, lettuce seeds were planted 48 h after introducing J2 to the plate. The number of J2 attracted to a root tip and J2 mobility were recorded 19 h after inoculation or planting, and infection rate and root length were recorded 5 days after planting. The three nematicides showed different effects on J2 of the Meloidogyne species. Fluensulfone did not inhibit infection by either species if the lettuce was planted immediately after inoculation, but their infection rates, and especially those of M. incognita, were reduced when lettuce seeds were planted 2 days later. Fluopyram reduced infection with M. javanica J2 at higher rates (&gt;83.3%) than for M. incognita J2 (&lt;58.4%) compared to the control, even without 48 h exposure before planting. Fluazaindolizine reduced M. incognita infection at high rates (&gt;83.3%), although the J2 were attracted to the lettuce roots. Root lengths also showed differences in infection severity. This assay distinguished the effects of the three nematicides on the two Meloidogyne species and can also serve to screen compounds that inhibit nematode infection without killing Meloidogyne J2.

Toxicity of decabromodiphenyl ethane on lettuce: Evaluation through growth, oxidative defense, microstructure, and metabolism

Decabromodiphenyl ethane (DBDPE) as the most widely used novel brominated flame retardants (NBFRs), has become a ubiquitous emerging pollutant in the environment. However, its toxic effects on vegetable growth during agricultural production have not been reported. In this study, we investigated the response mechanisms of hydroponic lettuce to DBDPE accumulation, antioxidant stress, cell structure damage, and metabolic pathways after exposure to DBDPE. The concentration of DBDPE in the root of lettuce was significantly higher than that in the aboveground part. DBDPE induced oxidative stress on lettuce, which stimulated the defense of the antioxidative system of lettuce cells, and the cell structure produced slight plasma-wall separation. In terms of metabolism, metabolic pathway disorders were caused, which are mainly manifested as inhibiting amino acid biosynthesis and metabolism-related pathways, interfering with the biosyntheses of amino acids, organic acids, fatty acids, carbohydrates, and other substances, and ultimately manifested as decreased total chlorophyll content and root activity. In turn, metabolic regulation alleviated antioxidant stress. The mechanisms of the antioxidative reaction of lettuce to DBDPE were elucidated by IBR, PLS-PM analysis, and molecular docking. Our results provide a theoretical basis and research necessity for the evaluation of emerging pollutants in agricultural production and the safety of vegetables.