A celery transcriptional repressor AgERF8 negatively modulates abscisic acid and salt tolerance.

Ethylene response factors (ERFs) widely exist in plants and have been reported to be an important regulator of plant abiotic stress. Celery, a common economic vegetable of Apiaceae, contains lots of ERF transcription factors (TFs) with various functions. AP2/ERF TFs play positive or negative roles in plant growth and stress response. Here, AgERF8, a gene encoding EAR-type AP2/ERF TF, was identified. The AgERF8 mRNA accumulated in response to both abscisic acid (ABA) signaling and salt treatment. AgERF8 was proving to be a nucleus-located protein and could bind to GCC-box. The overexpression of AgERF8 in Arabidopsis repressed the transcription of downstream genes, AtBGL and AtBCH. Arabidopsis overexpressing AgERF8 gene showed inhibited root growth under ABA and NaCl treatments. AgERF8 transgenic lines showed low tolerance to ABA and salt stress than wild-type plants. Low increment in SOD and POD activities, increased accumulation of MDA, and significantly decreased plant fresh weights and chlorophyll levels were detected in AgERF8 hosting lines after treated with ABA and NaCl. Furthermore, the overexpression of AgERF8 also inhibited the levels of ascorbic acid and antioxidant-related genes (AtCAT1, AtSOD1, AtPOD, AtSOS1, AtAPX1, and AtP5CS1) expression in transgenic Arabidopsis. This finding indicated that AgERF8 negatively affected the resistance of transgenic Arabidopsis to ABA and salt stress through regulating downstream genes expression and relevant physiological changes. It will provide a potential sight to further understand the functions of ERF TFs in celery.

[Effect of Cd on autophagy-related genes of celery].

Autophagy is one of the most common protective mechanisms during plant stress response. We studied the effect of exogenous Cd on autophagy in celery, by using transcriptome sequencing technique to analyze the differentially expressed genes under different Cd concentrations (0, 2, 4 and 8 mg/L). Eight differentially expressed autophagy-related genes were screened and identified by qRT-PCR. Cd had obvious toxic effect on celery, in a dose-dependent manner. Eight differentially expressed autophagy-related genes were screened, among which ATG8a, ATG8f, ATG13, AMPK-1 and AMPK-2 were up-regulated, whereas ATG12, VPS30 and VPS34 were first up-regulated and then decreased. The up-regulated expression of differential genes may resist Cd toxicity by increasing autophagosome structures; however, 8 mg/L Cd exceeded the autophagosome tolerance limit of celery, resulting in decreased expression of multiple autophagy-related genes. The above results can provide help for subsequent functional study of autophagy-related genes, and provide a reference for further exploring the tolerance mechanism of celery to Cd toxicity.

Bioavailability of cadmium to celery (Apium graveolens L.) grown in acidic and Cd-contaminated greenhouse soil as affected by the application of hydroxyapatite with different particle sizes.

Cadmium contamination in greenhouse vegetable fields greatly limited the sustainable production especially of leafy vegetables. Hydroxyapatite (HAP), as a common soil amendment, has been widely used in the remediation of Cd-contaminated soils, while its remediation efficiency greatly depends on its particle sizes. In this study, a rhizobag pot experiment was conducted to investigate the effects of HAP (<60 nm, <12 µm and <80 µm) on bioavailability of Cd to celery grown in acidic and slightly Cd-contaminated greenhouse soil. The results suggested that HAP with the largest particle size (<80 µm) had the best effectiveness in reducing Cd uptake especially by the edible part of celery. Specifically, the increase in HAP (<80 µm) addition from 0.5% to 3% prominently reduced Cd concentrations in celery shoot by 19.6%-76.8% as compared with the untreated group. Also, adding HAP (<80 µm) especially at 3% significantly decreased translocation factor (TF) of Cd from celery root to shoot by 30.6% and reduced bioconcentration factor (BCF) of Cd from rhizosphere soil to celery shoot by 76.4%. These were predominantly associated with the significantly increased soil pH and the subsequently decreased soil CaCl2-Cd concentration after adding HAP (<80 µm). Overall, although rhizosphere soil pH was the key factor in controlling Cd uptake by edible celery and regulating BCF and TF of Cd, insignificant root-induced acidification had limited effect on the immobilization efficiency of Cd by HAP (<80 µm). In conclusion, HAP (<80 µm) has good potential for the remediation of Cd-contaminated greenhouse soils.

Comparative de novo transcriptomics and untargeted metabolomic analyses elucidate complicated mechanisms regulating celery (Apium graveolens L.) responses to selenium stimuli.

Presently, concern regarding the effects of selenium (Se) on the environment and organisms worldwide is increasing. Too much Se in the soil is harmful to plants. In this study, Illumina RNA sequencing and the untargeted metabolome of control and Se-treated celery seedlings were analyzed. In total, 297,911,046 clean reads were obtained and assembled into 150,218 transcripts (50,876 unigenes). A total of 36,287 unigenes were annotated using different databases. Additionally, 8,907 differentially expressed genes, including 5,319 up- and 3,588 downregulated genes, were identified between mock and Se-treated plants. "Phenylpropanoid biosynthesis" was the most enriched KEGG pathway. A total of 24 sulfur and selenocompound metabolic unigenes were differentially expressed. Furthermore, 1,774 metabolites and 237 significant differentially accumulated metabolites were identified using the untargeted metabolomic approach. We conducted correlation analyses of enriched KEGG pathways of differentially expressed genes and accumulated metabolites. Our findings suggested that candidate genes and metabolites involved in important biological pathways may regulate Se tolerance in celery. The results increase our understanding of the molecular mechanism responsible for celery's adaptation to Se stress.

Effect of lead on plant availability of phosphorus and potassium in a vegetable-soil system.

Two typical red soils were sequentially cultivated with celery (Apium graveolens L.) and Chinese cabbage (Brassica chinensis L.) in a greenhouse to determine the effect of lead (Pb) on plant availability of phosphorus (P) and potassium (K) in the soils. The concentrations of available P as estimated by the 0.05 mol L-1 HCl-0.025 mol L-1 (1/2 H2SO4) extraction and available K estimated by the NH4OAc extraction method in the crop-free soils were not affected by Pb treatment. Plant P concentrations in the above-ground part of celery and Chinese cabbage exposed to Pb were either lower or showed no significant difference to the control.

Effect of different organic fertilizers application on growth and environmental risk of nitrate under a vegetable field.

The effect of chicken manure after different disposal methods (water-logged composting, GOF; anaerobic digestion, BR; thermophilic composting, ROF) on vegetable growth and environmental risk was investigated under the tomato-celery-tomato field. Results showed that organic fertilizers significantly increased vegetable yield and quality, but with inappropriate application may cause serious environmental risk such as nitrate pollution. Maximum vegetable yield of 80.9, 68.3, 112.7 t·ha-1 (first, second and third rotation crop, respectively) with best vegetable quality was obtained in ROF treatment. The highest N use efficiency with the least nitrate enrichment in soil was also found in ROF treatment. Moreover, under this fertilization way, nitrate concentration in soil leachate dropped to 6.4 mg·L-1, which satisfied the threshold (<10 mg·L-1) for drinking water set by the US Environmental Protection Agency. Thus, ROF was suggested to be the optimal fertilizer with the best yield, quality and the least environmental risk under the "tomato-celery" rotation system.

Measurement and mitigation of nitrous oxide emissions from a high nitrogen input vegetable system.

The emission and mitigation of nitrous oxide (N2O) from high nitrogen (N) vegetable systems is not well understood. Nitrification inhibitors are widely used to decrease N2O emissions in many cropping systems. However, most N2O flux measurements and inhibitor impacts have been made with small chambers and have not been investigated at a paddock-scale using micrometeorological techniques. We quantified N2O fluxes over a four ha celery paddock using open-path Fourier Transform Infrared spectroscopy in conjunction with a backward Lagrangian stochastic model, in addition to using a closed chamber technique. The celery crop was grown on a sandy soil in southern Victoria, Australia. The emission of N2O was measured following the application of chicken manure and N fertilizer with and without the application of a nitrification inhibitor 3, 4-dimethyl pyrazole phosphate (DMPP). The two techniques consistently demonstrated that DMPP application reduced N2O emission by 37-44%, even though the N2O fluxes measured by a micrometeorological technique were more than 10 times higher than the small chamber measurements. The results suggest that nitrification inhibitors have the potential to mitigate N2O emission from intensive vegetable production systems, and that the national soil N2O emission inventory assessments and modelling predictions may vary with gas measurement techniques.

Uptake and phytotoxicity of anthracene and benzo[k]fluoranthene applied to the leaves of celery plants (Apium graveolens var. secalinum L.).

The above-ground parts of celery plants were exposed to two polycyclic aromatic hydrocarbons (PAHs): 3-ring anthracene (ANT) and 5-ring benzo[k]fluoranthene (BkF), and the combination of ANT and BkF. After 43 days of exposure (overall dose of 1325µg/plant), celery plants retained only 1.4% of the total dose of ANT and 17.5% of the total dose of BkF. After exposure to a combination of ANT and BkF (1325µg of each compound per plant), the average ANT concentrations were more than twofold higher in/on leaf blades, whereas BkF levels were insignificantly higher. Under natural photoperiod conditions equivalent to a normal day, the combined application of ANT and BkF to the above-ground parts of celery plants slowed down physicochemical transformations of ANT. A similar effect was observed when PAHs were applied to glass surfaces. The combination of both PAHs probably led to stacking interactions, which decreased volatilization, in particular of ANT. Phytotoxicity of ANT and BkF could not be unambiguously established based on the results of this study. In all analyzed treatments, the chlorophyll content of leaf blades remained unchanged. Foliar application of ANT reduced ascorbic acid levels in all analyzed plant parts and increased the total acidity of celery leaves. In all experimental treatments, the total phenolic content of leaves increased up to 15%. Interestingly, ANT and BkF did not produce cumulative effects when applied in combination (when total PAH concentrations per plant were twofold higher).

CorA, the magnesium/nickel/cobalt transporter, affects virulence and extracellular enzyme production in the soft rot pathogen Pectobacterium carotovorum.

Pectobacterium carotovorum (formerly Erwinia carotovora ssp. carotovora) is a phytopathogenic bacterium that causes soft rot disease, characterized by water-soaked soft decay, resulting from the action of cell wall-degrading exoenzymes secreted by the pathogen. Virulence in soft rot bacteria is regulated by environmental factors, host and bacterial chemical signals, and a network of global and gene-specific bacterial regulators. We isolated a mini-Tn5 mutant of P. carotovorum that is reduced in the production of extracellular pectate lyase, protease, polygalacturonase and cellulase. The mutant is also decreased in virulence as it macerates less host tissues than its parent and is severely impaired in multiplication in planta. The inactivated gene responsible for the reduced virulent phenotype was identified as corA. CorA, a magnesium/nickel/cobalt membrane transporter, is the primary magnesium transporter for many bacteria. Compared with the parent, the CorA(-) mutant is cobalt resistant. The mutant phenotype was confirmed in parental strain P. carotovorum by marker exchange inactivation of corA. A functional corA(+) DNA from P. carotovorum restored exoenzyme production and pathogenicity to the mutants. The P. carotovorum corA(+) clone also restored motility and cobalt sensitivity to a CorA(-) mutant of Salmonella enterica. These data indicate that CorA is required for exoenzyme production and virulence in P. carotovorum.

Data-independent liquid chromatography/mass spectrometry (LC/MS(E)) detection and quantification of the secreted Apium graveolens pathogen defense protein mannitol dehydrogenase.

Plant cells secrete a wide variety of defense-related proteins into the extracellular space or apoplast in response to pathogen attack. One of these, mannitol dehydrogenase (MTD), is normally a cytoplasmic enzyme whose primary role is the regulation of intracellular levels of the sugar alcohol mannitol in plants. Recent immunological and biochemical evidence, however, suggests that MTD is also secreted into the apoplast in response to pathogen attack, despite lacking a known peptide signal sequence for Golgi-mediated secretion. Because many plant pathogenic fungi secrete mannitol to overcome pathogen-induced generation of reactive oxygen species (ROS) by the plant, extracellular localization of MTD is hypothesized to have a defensive role of catabolizing pathogen-secreted mannitol. In the current study, LC/MS(E) was used to analyze proteins in the secretome of Apium graveolens (celery) following treatment with salicylic acid (SA), an endogenous elicitor of defense responses in plants. Levels of MTD in the secretome of SA-treated celery cell cultures were found to be induced at least 18-fold over secretome samples from cell cultures not exposed to SA. This value is in close agreement with published immunological and biochemical observations. Overall, this report provides the first mass spectrometry identification and quantification measurements supporting the hypothesis that MTD is secreted in response to simulated pathogen attack via a non-classical secretion mechanism. As demonstrated with MTD secretion, LC/MS(E) can be implemented as a discovery-driven MRM-based quantitative approach which can be used to reveal potential post-translational modifications, thus providing a new method in the area of gel-free and label-free proteomic analysis.

Effects of foliar surfactants on host plant selection behavior of Liriomyza huidobrensis (Diptera: Agromyzidae).

The pea leafminer, Liriomyza huidobrensis (Diptera: Agromyzidae), is a highly polyphagous insect pest of global distribution. L. huidobrensis feeds and lays its eggs on leaf tissue and reduces crop marketability because of stippling and mining damage. In field insecticide trials, it was observed that stippling was reduced on plants treated with surfactant alone. The objectives of this study were to determine the effect of surfactants on host selection behaviors of female L. huidobrensis and to assess the phytotoxicity of two common surfactants to test plants. The application of the surfactant Sylgard 309 to celery (Apium graveolens) caused a significant reduction in stippling rates. The application of Agral 90 to cucumber leaves (Cucumis sativus) resulted in changes to the amount of effort invested by females in specific host plant selection behaviors, as well as causing a significant reduction in the amount of stippling damage. The recommended dose of Sylgard 309 does not induce phytotoxicity on celery over a range of age classes nor does Agral 90 cause a phytotoxic effect in 35-d-old cucumber. Thus, reductions in observed stippling and changes to host selection behaviors were caused by an antixenotic effect of the surfactant on L. huidobrensis rather than a toxic effect of the surfactant on the plant. The presence of surfactant on an otherwise acceptable host plant seems to have masked host plant cues and prevented host plant recognition. Results indicate that surfactants may be used to reduce leafminer damage to vegetable crops, potentially reducing the use of insecticides.

[Effects of metolachlor on biological activities in celery rhizophere and non-rhizosphere soil].

The study with rhizobag showed that in celery rhizophere and non-rhizosphere soil, metolachlor had a certain inhibitory effect on catalase activity, but stimulated dehydrogenase activity. Generally, the enzyme activities in rhizosphere soil were higher than those in non-rhizosphere soil. After 45 days of metolachlor treatment, the numbers of bacteria and fungi in rhizosphere soil were higher than those in non-rhizosphere soil, and the R/S was 1.76 to approximately 2. 51. The numbers of actinomycetes were relatively stable, and the rhizosphere effect was not significant. The degradation rate of metolachlor in rhizosphere and nonrhizosphere soil was 0. 0217 and 0.0176, and the corresponding half-live was 31.9 and 39.4 days, respectively. The degradation of metolachlor was enhanced greatly in rhizosphere soil.

Uptake and toxicity of Cr(III) in celery seedlings.

The present study shows that in celery Cr(III) induces deleterious effects on seedling development and morphology, and a number of metabolic responses related to stress. Exogenous CrCl3 from 0.01 to 1 mM increasingly inhibited seed germination and hypocotyl elongation, or completely blocked it (10 mM), while the root apparatus was dramatically damaged even at the lowest dose. Seedlings took up exogenous Cr(III) in a dose-dependent manner, roots being the site of major metal accumulation; translocation towards the hypocotyl and cotyledonary leaves was also detected. Either total or chlorophyll a content was significantly reduced by chromium as low as 0.01 mM. A large accumulation of free and, to a lesser extent, conjugated polyamines occurred in all segments of treated plants. A dose-dependent relationship linking actual amounts of Cr(III) recovered in the entire seedling or organ and the respective polyamine titre was evidenced. Free putrescine, in particular, was the polyamine exhibiting the highest rate of increase, and cotyledonary leaves the organ where the major response occurred. A marked increase in ubiquitin-protein conjugates after Cr(III) treatment was also observed, particularly in roots. Thus, the study suggests for the first time a possible relationship between ubiquitination and Cr(III)-stress. The putative function of polyamines as a stress response, and the recruitment of the ubiquitin pathway to remove damaged or aberrant proteins which might have been produced in metal-treated seedlings are discussed.

Structure of the complex of beta-cyclodextrin with beta-naphthyloxyacetic acid in the solid state and in aqueous solution.

The structure of the complex of beta-cyclodextrin (cyclomaltoheptaose) with beta-naphthyloxyacetic acid was studied in solid state by X-ray diffraction and in aqueous solution by 1H NMR spectroscopy. The complex crystallizes in the channel mode, space group C2, with a stoichiometry of 2:1; two beta-cyclodextrin molecules related by a twofold crystal axis form dimers, in the cavity of which one guest molecule is found on average. The above stoichiometry indicates one guest per beta-CD dimer statistically oriented over two positions or two guest molecules in pi-pi interactions in half of the beta-CD dimers and the rest of the beta-CD dimers empty. In addition, occupancy of 0.5 for the guest per every beta-CD dimer is in accord with the occupancy of the two disordered primary hydroxyls. These two hydroxyl groups, to which the carboxylic oxygen atoms of the guest are hydrogen bonded, point towards the interior of the beta-CD cavity. In aqueous solution, the 1H NMR spectroscopic study indicated that there is a mixture of complexes with host-guest stoichiometries both 1:1 and 2:1.