Sulfate supply decreases barium availability, uptake, and toxicity in lettuce plants grown in a tropical Ba-contaminated soil.

Barium (Ba) is a non-essential element that can cause toxicity in living organisms and environmental contamination. Plants absorb barium predominantly in its divalent cationic form Ba2+. Sulfur (S) can decrease the availability of Ba2+ in the soil by causing its precipitation as barium sulfate, a compound known for its very low solubility. The objective of this study was to evaluate the effect of soil sulfate supply in soil Ba fractions, as well as on plant growth, and Ba and S uptake by lettuce plants grown in artificially Ba-contaminated soil under greenhouse conditions. The treatments consisted of five Ba doses (0, 150, 300, 450, and 600 mg kg-1 Ba, as barium chloride) combined with three S doses (0, 40, and 80 mg kg-1 S, as potassium sulfate). The treatments were applied to soil samples (2.5 kg) and placed in plastic pots for plant cultivation. The Ba fractions analyzed were extractable-Ba, organic matter-Ba, oxides associated-Ba, and residual-Ba. The results indicate that the extractable-Ba fraction was the main one responsible for Ba bioavailability and phytotoxicity, probably corresponding to the exchangeable Ba in the soil. The dose of 80 mg kg-1 of S reduced extractable-Ba by 30% at higher Ba doses while it increased the other fractions. Furthermore, S supply attenuated the growth inhibition in plants under Ba exposure. Thus, S supply protected the lettuce plants from Ba toxicity by reduction of Ba availability in soil and plant growth enhancement. The results suggest that sulfate supply is a suitable strategy for managing Ba-contaminated areas.

Design and test of a laser lighting device for plant growth.

Aiming at the problems of high energy consumption, complex wiring, high layout cost, limited use environment, and limited function of conventional plant lighting equipment such as fluorescent lamps, sodium lamps, etc., this paper develops a type of laser device for plant growth with nanometer lasers based on the design of an intelligent control system of an immune algorithm, constant current driving circuit of the laser, pulse power supply, and rotatable intelligent platform to make the device more stable, reliable, practical, and energy efficient, and provides a useful reference for the innovation and application of materials, processes, and methods of plant lighting. The effects of nanometer laser light supplementation on the growth of purple lettuce, romaine lettuce, Chinese cabbage, and you-mai vegetable have been studied with the vegetables mentioned above as experimental materials and with natural light as the control sample. The results show that the nanometer laser device significantly increases stem height, stem thickness, leaf area, leaf number, and chlorophyll content, effectively promotes plant growth, and achieves efficient cultivation. In the future, studies of the effects of laser treatment on plant physiology and biochemistry will be sped up to explore the molecular biological mechanism of lasers to promote application and technological innovation of lasers in lighting for plant growth and the laser device in productivity.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine.

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 µg g-1) were found in plant tissue compared to Pb (277.2 ± 18.0 µg g-1) and Cu (255.3 ± 25.6 µg g-1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

Similarity assessment of metallic nanoparticles within a risk assessment framework: A case study on metallic nanoparticles and lettuce.

Similarity assessment is one of the means of optimally using scarcely available experimental data on the fate and hazards of nanoforms (NFs) for regulatory purposes. For a set of NFs that are shown to be similar it is allowed in a regulatory context to apply the information available on any of the NFs within the group to the whole set of NFs. Obviously, a proper justification for such a similarity assessment is to be provided. Within the context of exemplifying such a justification, a case study was performed aimed at assessing the similarity of a set of spherical metallic NFs that different with regard to chemical composition (three metals) and particle size (three different sizes). The endpoints of assessment were root elongation and biomass increase of lettuce (Lactuca sativa L.) seedlings and exposure assessment was performed in order to express the actual exposure concentration in terms of time-weighted average particle concentrations. The results of the study show that for the specific endpoints assessed, chemical composition is driving NF toxicity and this is mostly due to impacts on the fate of the NFs. On the other hand, particle size of Cu NFs had a negligible impact on the dose-response relationships for the specific endpoints assessed. It is thus concluded that hazard data available on spherical Cu NF tested in our case can be used to inform on the hazards of any spherical Cu NF within the size range of 25-100 nm, but only applies for the certain endpoints. Also, toxicity data for the Cu2+-ion are suited for such a similarity assessment.

A Physiological behavior and tolerance of Lactuca sativa to lead nitrate and silver nitrate heavy metals / Comportamento fisiológico e tolerância de Lactuca sativa aos metais pesados nitrato de chumbo e nitrato de prata

This study goal to evaluate the effects of different concentrations of lead (Pb) and silver (Ag) on germination, initial growth and anatomical alterations of Lactuca sativa L. Plants use various mechanisms to reduce the impacts caused by anthropic action, such as xenobiotic elements of soils and water contaminated by heavy metals. These metals were supplied as lead nitrate and silver nitrate and the following treatments were established: control for both metals, maximum dose of heavy metals, for arable soils, allowed by the National Council of the Environment (Ag = 25 mg. Kg-¹, Pb = 180 mg. Kg-¹), double (Ag = 50 mg. Kg-¹, Pb = 360 mg. Kg-¹) and triple (Ag = 75 mg. Kg-¹, Pb = 540 mg. Kg-¹) of this dosage. Vigor and germination tests of the seeds and possible anatomical changes in the leaves and roots of lettuce plants were performed. The species showed a high capacity to germinate under Pb and Ag stress, and the germination was never completely inhibited; however, the germination decreased with increasing Pb concentrations, but not under Ag stress. The use of increasing doses of metals reduced seed vigor and increased chlorophyll content. An increase in biomass was also observed in plants from treatments submitted to Pb. The phytotoxic effects of metals were more pronounced at 15 days after sowing. Anatomically, L. sativa was influenced by metal concentrations, and had a reduction of up to 79.9% in root epidermis thickness at the highest Pb concentration, although some structures did not suffer significant changes. The results suggest that L. sativa presents tolerance to high concentrations of heavy metals, showing possible mechanisms to overcome the stress caused by these metals. In this research lettuce possibly used the mechanism of exclusion of metals retaining Pb and Ag in the roots preserving the photosynthetic apparatus in the aerial part of the plants. In general, the chemical element Pb was more toxic than Ag, in these experimental conditions.

Este estudo teve como objetivo avaliar os efeitos de diferentes concentrações de chumbo (Pb) e prata (Ag) na germinação, crescimento inicial e alterações anatômicas de Lactuca sativa L. As plantas utilizam vários mecanismos para reduzir os impactos causados pela ação antrópica, como elementos xenobióticos de solos e água contaminada por metais pesados. Esses metais foram fornecidos como nitrato de chumbo e nitrato de prata e foram estabelecidos os seguintes tratamentos:controle para ambos os metais, dose máxima de metais pesados, para solos cultiváveis, permitida pelo Conselho Nacional do Meio Ambiente (Ag = 25mg.Kg-¹, Pb = 180mg.Kg-¹), dobro (Ag = 50mg.Kg-¹, Pb = 360mg.Kg-¹) e triplo (Ag = 75mg.Kg-¹, Pb = 540 mg.Kg-¹) desta dosagem. Foram realizados testes de vigor e germinação das sementes e possíveis alterações anatômicas nas folhas e raízes das plantas de alface. A espécie apresentou alta capacidade de germinar sob estresse de Ag e Pb, e a germinação nunca foi completamente inibida; entretanto, a germinação diminuiu com o aumento das concentrações de Pb, mas não sob estresse de Ag. O uso de doses crescentes dos metais, reduziu o vigor das sementes e aumentou o teor de clorofila. Também foi observado aumento da biomassa nas plantas a partir dos tratamentos submetidos ao Pb. Os efeitos fitotóxicos dos metais foram mais acentuados aos 15 dias após a semeadura. Anatomicamente, L. sativa foi influenciada pelas concentrações de metais, e teve uma redução de até 79,9% na espessura da epiderme radicular na maior concentração de Pb, embora algumas estruturas não tenham sofrido alterações significativas. Os resultados sugerem que L. sativa apresenta tolerância a altas concentrações de metais pesados, mostrando possíveis mecanismos para superar o estresse causado por esses metais. Nesta pesquisa a alface possivelmente utilizou o mecanismo de exclusão de metais retendo Pb e Ag nas raízes preservando o aparato [...].

A digital sensor to measure real-time leaf movements and detect abiotic stress in plants.

Plant and plant organ movements are the result of a complex integration of endogenous growth and developmental responses, partially controlled by the circadian clock, and external environmental cues. Monitoring of plant motion is typically done by image-based phenotyping techniques with the aid of computer vision algorithms. Here we present a method to measure leaf movements using a digital inertial measurement unit (IMU) sensor. The lightweight sensor is easily attachable to a leaf or plant organ and records angular traits in real-time for two dimensions (pitch and roll) with high resolution (measured sensor oscillations of 0.36 ± 0.53° for pitch and 0.50 ± 0.65° for roll). We were able to record simple movements such as petiole bending, as well as complex lamina motions, in several crops, ranging from tomato to banana. We also assessed growth responses in terms of lettuce rosette expansion and maize seedling stem movements. The IMU sensors are capable of detecting small changes of nutations (i.e. bending movements) in leaves of different ages and in different plant species. In addition, the sensor system can also monitor stress-induced leaf movements. We observed that unfavorable environmental conditions evoke certain leaf movements, such as drastic epinastic responses, as well as subtle fading of the amplitude of nutations. In summary, the presented digital sensor system enables continuous detection of a variety of leaf motions with high precision, and is a low-cost tool in the field of plant phenotyping, with potential applications in early stress detection.

Quantitative Trait Loci and Candidate Genes Associated with Photoperiod Sensitivity in Lettuce (Lactuca spp.).

KEY MESSAGE: A population of lettuce that segregated for photoperiod sensitivity was planted under long-day and short-day conditions. Genetic mapping revealed two distinct sets of QTLs controlling daylength-independent and photoperiod-sensitive flowering time. The molecular mechanism of flowering time regulation in lettuce is of interest to both geneticists and breeders because of the extensive impact of this trait on agricultural production. Lettuce is a facultative long-day plant which changes in flowering time in response to photoperiod. Variations exist in both flowering time and the degree of photoperiod sensitivity among accessions of wild (Lactuca serriola) and cultivated (L. sativa) lettuce. An F6 population of 236 recombinant inbred lines (RILs) was previously developed from a cross between a late-flowering, photoperiod-sensitive L. serriola accession and an early-flowering, photoperiod-insensitive L. sativa accession. This population was planted under long-day (LD) and short-day (SD) conditions in a total of four field and screenhouse trials; the developmental phenotype was scored weekly in each trial. Using genotyping-by-sequencing (GBS) data of the RILs, quantitative trait loci (QTL) mapping revealed five flowering time QTLs that together explained more than 20% of the variation in flowering time under LD conditions. Using two independent statistical models to extract the photoperiod sensitivity phenotype from the LD and SD flowering time data, we identified an additional five QTLs that together explained more than 30% of the variation in photoperiod sensitivity in the population. Orthology and sequence analysis of genes within the nine QTLs revealed potential functional equivalents in the lettuce genome to the key regulators of flowering time and photoperiodism, FD and CONSTANS, respectively, in Arabidopsis.

The genetic basis of water-use efficiency and yield in lettuce.

BACKGROUND: Water supply limits agricultural productivity of many crops including lettuce. Identifying cultivars within crop species that can maintain productivity with reduced water supply is a significant challenge, but central to developing resilient crops for future water-limited climates. We investigated traits known to be related to water-use efficiency (WUE) and yield in lettuce, a globally important leafy salad crop, in a recombinant inbred line (RIL) lettuce mapping population, produced from a cross between the cultivated Lactuca sativa L. cv. Salinas and its wild progenitor L. serriola L. RESULTS: Wild and cultivated lettuce differed in their WUE and we observed transgressive segregation in yield and water-use traits in the RILs. Quantitative trait loci (QTL) analysis identified genomic regions controlling these traits under well-watered and droughted conditions. QTL were detected for carbon isotope discrimination, transpiration, stomatal conductance, leaf temperature and yield, controlling 4-23 % of the phenotypic variation. A QTL hotspot was identified on chromosome 8 that controlled carbon isotope discrimination, stomatal conductance and yield under drought. Several promising candidate genes in this region were associated with WUE, including aquaporins, late embryogenesis abundant proteins, an abscisic acid-responsive element binding protein and glutathione S-transferases involved in redox homeostasis following drought stress were also identified. CONCLUSIONS: For the first time, we have characterised the genetic basis of WUE of lettuce, a commercially important and water demanding crop. We have identified promising candidate genomic regions determining WUE and yield under well-watered and water-limiting conditions, providing important pre-breeding data for future lettuce selection and breeding where water productivity will be a key target.

Lighting Direction Affects Leaf Morphology, Stomatal Characteristics, and Physiology of Head Lettuce (Lactuca sativa L.).

Plants are exposed to numerous biotic and abiotic stresses, and light is one of the most important factors that influences the plant morphology. This study was carried out to examine how the lighting direction affected the plant morphology by investigating the growth parameters, epidermal cell elongation, stomatal properties, and physiological changes. Seedlings of two head lettuce (Lactuca sativa L.) cultivars, Caesar Green and Polla, were subjected to a 12 h photoperiod with a 300 µmol·m-2·s-1 photosynthetic photon flux density (PPFD) provided by light emitting diodes (LEDs) from three directions: the top, side, and bottom, relative to the plants. Compared with the top and side lighting, the bottom lighting increased the leaf angle and canopy by stimulating the epidermal cell elongation in leaf midrib, reduced the leaf number and root biomass, and induced large stomata with a low density, which is associated with reduced stomatal conductance and carbohydrate contents. However, the proline content and quantum yield exhibited no significant differences with the different lighting directions in both cultivars, which implies that the plants were under normal physiological conditions. In a conclusion, the lighting direction had a profound effect on the morphological characteristics of lettuce, where the plants adapted to the changing lighting environments.

Ozone uptake at night is more damaging to plants than equivalent day-time flux.

MAIN CONCLUSION: Plants exposed to equivalent ozone fluxes administered during day-time versus night-time exhibited greater losses in biomass at night and this finding is attributed to night-time depletion of cell wall-localised ascorbate. The present study employed Lactuca sativa and its closest wild relative, L. serriola, to explore the relative sensitivity of plants to ozone-induced oxidative stress during day-time versus night-time. By controlling atmospheric ozone concentration and measuring stomatal conductance, equivalent ozone uptake into leaves was engineered during day and night, and consequences on productivity and net CO2 assimilation rate were determined. Biomass losses attributable to ozone were significantly greater when an equivalent dose of ozone was taken-up by foliage at night compared to the day. Linkages between ozone impacts and ascorbic acid (AA) content, redox status and cellular compartmentation were probed in both species. Leaf AA pools were depleted by exposure of plants to darkness, and then AA levels in the apoplast and symplast were monitored on subsequent transfer of plants to the light. Apoplast AA appeared to be more affected by light-dark transition than the symplast pool. Moreover, equivalent ozone fluxes administered to leaves with contrasting AA levels resulted in contrasting effects on the light-saturated rate of CO2 assimilation (Asat) in both species. Once apoplast AA content recovered to pre-treatment levels, the same ozone flux resulted in no impacts on Asat. The results of the present investigation reveal that plants are significantly more sensitive to equivalent ozone fluxes taken-up at night compared with those during the day and were consistent with diel shifts in apoplast AA content and/or redox status. Furthermore, findings suggest that some thought should be given to weighing regional models of ozone impacts for extraordinary night-time ozone impacts.

Toxicogenetic of tebuconazole based fungicide through Lactuca sativa bioassays.

The rampant use of pesticides can cause serious environmental problems. They can be contaminating surface water and groundwater, affecting the surrounding micro and macro biota. In this sense, this work aimed to evaluate the effects of a tebuconazole-based fungicide through endpoints accessed in Lactuca sativa bioassays. Germinated-seeds with roots upon 2 mm were treated with a fungicide containing Tebuconazole (TBZ) as active compound. The final concentration of TBZ in the tested solutions were 0.025 (C1); 0.05 (C2); 0.1 (C3); 0.2 (C4) and 0.4 g/L (C5). L. sativa roots were exposed for 24 h to these solutions and Petri dishes containing the treated seeds were kept in incubation chamber at 24 °C. Two positive controls (PC,) the herbicide trifluralin (0.84 mg/L) and Methanesulfonate (4 ×10-4 mol/L), were applied. Distilled water was negative control (NC). The following endpoints were analyzed: root growth (RG), cytogenotoxic potential by cell cycle analysis, induction of DNA damage through TUNEL and comet assays. The obtained data were submitted to one-way variance analysis (ANOVA) and then to Tukey or Kruskal Wallis (P < 0.05) tests. The concentrations (C1, C2, C4 and C5) affected negatively the RG of L. sativa, in comparison with the NC. The mitotic index was reduced by 25% from NC to C1 and in the rest of treatments it did not present significant modifications. However, from C3 to C5 great amount of chromosome alterations were observed, in comparison with the NC. TBZ-based fungicide also induced DNA fragmentation as measured by TUNEL and comet assays. Thus, TBZ-based fungicide in some concentrations can have phytotoxic, cytotoxic and genotoxic effects in roots and meristematic cells of L. sativa.

Aquaporins and cation transporters are differentially regulated by two arbuscular mycorrhizal fungi strains in lettuce cultivars growing under salinity conditions.

The aim was to identify the effects of AM symbiosis on the expression patterns of genes associated with K+ and Na+ compartmentalization and translocation and on K+/Na+ homeostasis in some lettuce (Lactuca sativa) cultivars as well as the effects of the relative abundance of plant AQPs on plant water status. Two AM fungi species (Funneliformis mosseae and Claroideoglomus lamellosum) isolated from the hyper-arid Atacama Desert (northern Chile) were inoculated to two lettuce cultivars (Grand Rapids and Lollo Bionda), and watered with 0 and 60 mM NaCl. At 60 days of plant growth, the AM symbiotic development, biomass production, nutrient content (Pi, Na+, K+), physiological parameters, gene expressions of ion channels and transporters (NHX and HKT1), and aquaporins proteins abundance (phosphorylated and non-phosphorylated) were evaluated. Salinity increased the AM root colonization by both inocula. AM lettuce plants showed an improved growth, increased relative water content and improved of K/Na ratio in root. In Grand Rapids cultivar, the high efficiency of photosystem II was higher than Lollo Bionda cultivar; on the contrary, stomatal conductance was higher in Lollo Bionda. Nevertheless, both parameters were increased by AM colonization. In the same way, LsaHKT1;1, LsaHKT1;6, LsaNHX2, LsaNHX4, LsaNHX6 and LsaNHX8 genes and aquaporins PIP2 were up-regulated differentially by both AM fungi. The improved plant growth was closely related to a higher water status due to increased PIP2 abundance, as well as to the upregulation of LsaNHX gene expression, which concomitantly improved plant nutrition and K+/Na+ homeostasis maintenance.

Physiological and Oxidative Stress Responses of Lettuce to Cleomside A: A Thiohydroximate, as a New Allelochemical from Cleome arabica L.

The inclination toward natural products have led the onset for the discovery of new bioactive metabolites that could be targeted for specific therapeutic or agronomic applications. This study aimed to isolate bioactive compounds from Cleome arabica L., and subsequently determine the unexplored mechanism of action of the newly identified compounds on Lactuca sativa L. Chemical investigation of the ethyl acetate fraction of methanolic silique extract of C. arabica afforded seven secondary metabolites belonging to different classes such as flavonoids, triterpene, and a new thiohydroximate derivative, named cleomside A. Among phytotoxic assays, the growth of lettuce was totally inhibited by cleomside A compared to the other identified compounds. This effect was associated with the increased levels of electrolyte leakage, malondialdehyde, and hydrogen peroxide indicating disruption of membrane integrity and induction of oxidative stress. Activities of the antioxidant enzymes SOD, CAT, and APX were also elevated, thereby demonstrating the enhanced generation of reactive oxygen species upon identified allelochemical exposure. Thus, the changes caused by cleomside A described herein can contribute to better understanding the allelochemical actions of thiohydroximate and the potential use of these substances in the production of natural herbicides compared to the other identified flavonoids and triterpene.

Proteomics Analysis Indicates Greater Abundance of Proteins Involved in Major Metabolic Pathways in Lactuca sativa cv. Salinas than Lactuca serriola Accession US96UC23.

Lettuce (Lactuca sativa), cultivated mainly for its edible leaves and stems, is an important vegetable crop worldwide. Genomes of cultivated lettuce (L. sativa cv. Salinas) and its wild relative L. serriola accession US96UC23 are sequenced, but a clear understanding of the genetic basis for divergence in phenotypes of the two species is lacking. Tandem mass tag (TMT) based mass spectrometry is used to quantitatively compare protein levels between these two species. Four-day old seedlings is transplanted into 500 mL pots filled with soil. Plants are grown for 8 weeks under 250 µmol m-2 sec-1 continuous light, 20 °C and relative humidity between 50-70%. Leaf discs (1 cm diameter) from three individuals per biological replicate are analyzed. A total of 3000 proteins are identified, of which the levels of 650 are significantly different between 'Salinas' and US96UC23. Pathway analysis indicated a higher flux of carbon in 'Salinas' than US96UC23. Many essential metabolic pathways such as tetrapyrrole metabolism and fatty acid biosynthesis are upregulated in 'Salinas' compared with US96UC23. This study provides a reference proteome for researchers interested in understanding lettuce biology and improving traits for cultivation.

Foliar graphene oxide treatment increases photosynthetic capacity and reduces oxidative stress in cadmium-stressed lettuce.

The application of graphene oxide (GO) in the environment can have a positive or negative effect on the toxicity of pollutants, but the effect of GO on cadmium (Cd2+)-stressed lettuce has not yet been thoroughly studied. Therefore, we assessed the potential effects of foliar GO sprays on photosynthesis and antioxidant systems in Cd-stressed lettuce. We found that the foliar application of 30 mg L-1 of GO could significantly reduce signs of Cd2+ toxicity in lettuce. We observed increased net photosynthetic rates, stomatal conductance, transpiration rates, chlorophyll content, primary maximum photochemical efficiency of photosystem II, actual quantum yield, photosynthetic electron transport rates, ribulose-1,5-bisphosphate carboxylase and oxygenase concentrations, and biomass in Cd2+-stressed lettuce treated with GO. In addition, the foliar application of 30 mg L-1 of GO reduced the accumulation of the reactive oxygen species O·Ì„2 and H2O2, malondialdehyde content, and the activity of antioxidant enzymes. The decreased antioxidant enzyme activity could have been due to the decrease in reactive oxygen species. Cd2+ pollution is highly destructive to agricultural products, and the foliar application of GO provides a new potential tactic to improve the tolerance of plants to heavy metals.

Integration of subcellular partitioning and chemical forms to understand silver nanoparticles toxicity to lettuce (Lactuca sativa L.) under different exposure pathways.

The current understanding of the biological impacts of silver nanoparticles (AgNPs) is restricted to the direct interactions of the particles with biota. Very little is known about their intracellular fate and subsequent toxic consequences. In this research we investigated the uptake, internal fate (i,e., Ag subcellular partitioning and chemical forms), and phytotoxicity of AgNPs in lettuce following foliar versus root exposure. At the same AgNP exposure concentrations, root exposure led to more deleterious effects than foliar exposure as evidenced by a larger extent of reduced plant biomass, elevated oxidative damage, as well as a higher amount of ultrastructural injuries, despite foliar exposure leading to 2.6-7.6 times more Ag bioaccumulation. Both Ag subcellular partitioning and chemical forms present within the plant appeared to elucidate this difference in toxicity. Following foliar exposure, high Ag in biologically detoxified metals pool (29.2-53.0% by foliar exposure vs. 12.8-45.4% by root exposure) and low Ag proportion in inorganic form (6.1-11.9% vs. 14.1-19.8%) potentially associated with AgNPs tolerance. Silver-containing NPs (24.8-38.6 nm, 1.5-2.3 times larger than the initial size) were detected in lettuce plants exposed to NPs and to dissolved Ag+, suggesting possible transformation and/or aggregation of AgNPs in the plants. Our observations show that the exposure pathway significantly affects the uptake and internal fate of AgNPs, and thus the associated phytotoxicity. The results are an important contribution to improve risk assessment of NPs, and will be critical to ensure food security.

PBAT biodegradable mulch films: Study of ecotoxicological impacts using Allium cepa, Lactuca sativa and HepG2/C3A cell culture.

Biodegradable mulch films are an alternative to polyethylene films used in agriculture for weed control, improving crop productivity. This change could minimize the residue production and costs related to the final disposal. Nevertheless, the environmental safety of these biodegradable products is scarcely investigated. In this work, samples of poly(butylene adipate-co-terephthalate)-PBAT mulch films, with and without UV stabilizer additives, were prepared. Aqueous extracts of soil samples, where mulch films were disposed, were investigated using bioassays with Lactuca sativa, Allium cepa, and cell culture HepG2/C3A. As PBAT is expected to suffer photodegradation and biodegradation, soil samples mixed with films before and after these processes were evaluated. Soil aqueous extracts promoted root grown (mainly hypocotyl) of L. sativa, probably due to presence of nutrients. So, to evaluate toxicity potential, in this case it was necessary to use aqueous extract prepared with soil instead of ultrapure water as the control. After doing this analysis it was observed that no adverse impacts due to PBAT films occurred. No chromosomal abnormalities were observed in A. cepa bioassay for any of tested samples. The absence of genotoxic potential was confirmed by comet assay and micronucleus test using human hepatocarcinoma cell line HepG2/C3A. These results showed that the soil did not induce damage to the tested organisms, before and after degradation of PBAT films.

Antarctic root endophytes improve physiological performance and yield in crops under salt stress by enhanced energy production and Na+ sequestration.

Climatic change is pointed as one of the major challenges for global food security. Based on current models of climate change, reduction in precipitations and in turn, increase in the soil salinity will be a sharp constraint for crops productivity worldwide. In this context, root fungi appear as a new strategy to improve plant ecophysiological performance and crop yield under abiotic stress. In this study, we evaluated the impact of the two fungal endophytes Penicillium brevicompactum and P. chrysogenum isolated from Antarctic plants on nutrients and Na+ contents, net photosynthesis, water use efficiency, yield and survival in tomato and lettuce, facing salinity stress conditions. Inoculation of plant roots with fungal endophytes resulted in greater fresh and dry biomass production, and an enhanced survival rate under salt conditions. Inoculation of plants with the fungal endophytes was related with a higher up/down-regulation of ion homeostasis by enhanced expression of the NHX1 gene. The two endophytes diminished the effects of salt stress in tomato and lettuce, provoked a higher efficiency in photosynthetic energy production and an improved sequestration of Na+ in vacuoles is suggested by the upregulating of the expression of vacuolar NHX1 Na+/H+ antiporters. Promoting plant-beneficial interactions with root symbionts appears to be an environmentally friendly strategy to mitigate the impact of climate change variables on crop production.

Genome-wide association mapping reveals loci for shelf life and developmental rate of lettuce.

KEY MESSAGE: Two major QTL, one for shelf life that corresponds to qSL4 and one, qDEV7, for developmental rate, were identified. Associated markers will be useful in breeding for improved fresh-cut lettuce. Fresh-cut lettuce in packaged salad can have short shelf life, and visible deterioration may start within a week after processing. Yield and developmental rate are an important aspect of lettuce production. Genetic diversity and genome-wide association studies (GWAS) were performed on 493 accessions with the genotypic data of 4615 high-quality single nucleotide polymorphism markers. Population structure (Q), principal component (PC), and phylogenetic analyses displayed genetic relationships associated with lettuce types and geographic distribution. Data for shelf life, yield, developmental rate, and their stability indices were used for statistical analysis, and GWAS was performed by general and mixed linear models. The genetic relationship among the individuals was incorporated into the models using kinship matrix, PC, and Q. Broad-sense heritability (H2) across environments was 0.43 for shelf life, 0.36 for yield, and 0.60 for developmental rate. There was a negative correlation between yield and developmental rate. Significant marker-trait association (SMTA) was detected for shelf life on chromosome 4. The most significant quantitative trait locus (QTL,  qSL4, P = 2.23E-17) explained 24% of the total phenotypic variation (R2). The major QTL for developmental rate was detected on chromosome 7 (qDEV7, P = 2.43E-16, R2 = 17%), while additional QTLs with smaller effect were found in all chromosomes. No SMTA was detected for yield. The study identified lettuce accessions with extended and stable shelf life, stable yield, and desirable developmental rate. Molecular markers closely linked to traits can be applied for selection of preferable genotypes and for identification of genes associated with these traits.

Efficiency of two arbuscular mycorrhizal fungal inocula to improve saline stress tolerance in lettuce plants by changes of antioxidant defense mechanisms.

BACKGROUND: Arbuscular mycorrhizal (AM) fungi establish symbioses with most agricultural plants and improves growth under soil stress conditions. The present study aimed to evaluate the functional contribution of 2 AM fungal inocula (a native consortium isolated from saline soils of the Atacama Desert, 'HMC', and a reference inoculum Claroideoglomus claroideum, 'Cc') on the growth and antioxidant compounds of two cultivars of lettuce (Lactuca sativa cvs. 'Grand Rapids' and 'Lollo Bionda') at increasing salt stress conditions (0, 40, and 80 mmol L-1 NaCl). At 60 days of plant growth, the symbiotic development, biomass production, lipid peroxidation, proline content, antioxidant enzymes, phenolic compound profiles and antioxidant activity were evaluated. RESULTS: The 2 AM inocula differentially colonized the roots of Grand Rapids and Lollo Bionda lettuce plants. The AM symbioses increased proline synthesis and superoxide dismutase, catalase and ascorbate peroxidase activities and diminished phenolic compound synthesis and oxidative damage in lettuce, which was related positively to a higher growth of inoculated plants under salt exposure. The higher concentration of phenolic compounds induced by salinity in non-inoculated plants was associated with high oxidative stress and low fresh biomass production. CONCLUSION: Modulation of salinity stress in lettuce by AM root colonization is a result of changes of antioxidant enzymatic systems that reduce oxidative damage and sustain growth. The application of AM fungi to improve crop production by means of directed inoculation with efficient AM fungal strains may enhance lettuce production on soils plagued with salinity worldwide. © 2019 Society of Chemical Industry.