Physiological of biochar and α-Fe2O3 nanoparticles as amendments of Cd accumulation and toxicity toward muskmelon grown in pots

BACKGROUND

Due to the severe cadmium (Cd) pollution of farmland soil, effective measures need to be taken to reduce the Cd content in agricultural products. In this study, we added α-Fe2O3 nanoparticles (NPs) and biochar into Cd-contaminated soil to investigate physiological responses of muskmelon in the whole life cycle.

RESULTS

The results showed that Cd caused adverse impacts on muskmelon (Cucumis melo) plants. For instance, the chlorophyll of muskmelon leaves in the Cd alone treatment was reduced by 8.07-32.34% in the four periods, relative to the control. The treatments with single amendment, α-Fe2O3 NPs or 1% biochar or 5% biochar, significantly reduced the soil available Cd content, but the co-exposure treatments (α-Fe2O3 NPs and biochar) had no impact on the soil available Cd content. All treatments could reduce the Cd content by 47.64-74.60% and increase the Fe content by 15.15-95.27% in fruits as compared to the Cd alone treatment. The KEGG enrichment results of different genes in different treatments indicated that single treatments could regulate genes related to anthocyanin biosynthesis, glutathione metabolism and MAPK signal transduction pathways to reduce the Cd toxicity.

CONCLUSIONS

Overall the combination of biochar and α-Fe2O3 NPs can alleviate Cd toxicity in muskmelon. The present study could provide new insights into Cd remediation in soil using α-Fe2O3 NPs and biochar as amendments.

Application of γ-aminobutyric acid demonstrates a protective role of polyamine and GABA metabolism in muskmelon seedlings under Ca(NO3)2 stress

The effects of exogenous γ-aminobutyric acid (GABA) application on growth, polyamine and endogenous GABA metabolism in muskmelon leaves and roots were measured. Plants were treated under control or 80 mM Ca(NO3)2 stress conditions with or without foliar spraying 50 mM GABA. Ca(NO3)2 stress significantly suppressed seedling growth and GABA transaminase activity, and enhanced glutamate decarboxylase (GAD) activity and endogenous GABA levels. Polyamine (PA) biosynthesis and degradation capacity increased in parallel with increasing GAD activity. Exogenous GABA application effectively alleviated the growth inhibition caused by Ca(NO3)2 stress, and significantly enhanced the activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), polyamine oxidase (PAO), and diamine oxidase (DAO). Exogenous GABA also significantly reduced the accumulation of free putrescine (Put) and increased the levels of free spermidine (Spd) and spermine (Spm) in leaves, which improved the capacity for polyamine biosynthesis. Application of exogenous GABA under Ca(NO3)2 stress enables the plants to maintain a higher ratio of free Spd and free Spm with respect to free Put. Our data suggest that exogenous GABA has an important role in improving muskmelon seedling tolerance to Ca(NO3)2 stress by improving biosynthesis of PAs and GABA, and by preventing PA degradation. There is a potential positive feedback mechanism that results from higher endogenous GABA content and the combined effects of Ca(NO3)2 stress and exogenous GABA, which coordinately alleviate Ca(NO3)2 stress injury by enhancing PA biosynthesis and converting free Put to an insoluble bound PA form, and reduce PA degradation in muskmelon seedlings.

The effects of sewage sludge and sewage sludge biochar on PAHs and potentially toxic element bioaccumulation in Cucumis sativa L

The presence of contaminants such as polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs), including As, Cd, Cu, Pb and Zn, restricts the application of sewage sludge (SS) to agricultural land. This research established that the conversion of SS to SS biochar (SSBC) significantly (p ≤ 0.01) decreased PAH and available PTE concentrations. Once added to soil both SS and SSBC significantly (p ≤ 0.05) decrease PAH availability. Bioaccumulation of PAHs into Cucumis sativa L. was reduced by both SSBC (44-57%) and (to a lesser extent 20-36%) by SS. Following addition to soil SSBC significantly (p ≤ 0.05) reduced available PTEs (except Cd), while SS significantly (p ≤ 0.05) increased PTE availability. As a consequence SSBC significantly (p ≤ 0.05) reduced PTE bioaccumulation (except Cd and Zn), while SS increased PTE bioaccumulation. These results suggest SSBC to be a candidate for soil amendment that offers advantages over SS in terms of PAH/PTE bioaccumulation mitigation.

Optimization of factors influencing in vitro flowering of gherkin (Cucumis anguria L.)

This study investigated the factors influencing in vitro flowering of gherkin (Cucumis anguria L.). Multiple shoots were efficiently regenerated from cotyledonary node and axillary bud explants of C. anguria within 15 days on MSB5 medium containing 3% sucrose and supplemented with 1.5 mg l-1 6-benzyladinine (BA). The elongated shoots were excised and transferred to MSB5 medium containing 4% sucrose supplemented with 0.5 mg l(-1) gibberellic acid (GA(3)) and 1.0 mg l(-1) indole-3-butyric acid (IBA) induced maximum number of flowers (9.5 flowers/plant) and root induction (16.5 roots/plant). Factors that influence the in vitro flowering were optimizing pH, photoperiod and temperature. In vitro flowering was significantly early and higher number of flowers produced at pH (5.8), photoperiod (12/12 h) and room temperature (28 °C). In vitro developed flowers were less viable (80 ± 1.0%) compared to control plants (90 ± 2.0%). Our in vitro flower induction procedures provide an extremely effective method for further research on flowering regulation mechanisms in C. anguria. These plantlets were successfully transferred to the soil where they grew well for 3 to 5 weeks with 90% survivability. Plants grew normally and produced flowers with viable pollen and fertile seeds.

Proteomics reveal cucumber Spd-responses under normal condition and salt stress

To investigate the effects of exogenous Spd on proteomic changes under normal condition and NaCl stress of 3 days in cucumber seedling leaves, a 2-DE gel electrophoresis and MALDI-TOF/TOF MS was performed. A total of 63 differentially expressed proteins responded to salt stress or exogenous Spd treatments, and they were all successfully identified by MALDI-TOF/TOF MS. Many changes were observed in the levels of proteins involved in energy and metabolic pathways, protein metabolic, stress defense, and other functional proteins. Increased salt tolerance by exogenous Spd would contribute to higher expressions of proteins involved in the SAMs metabolism, protein biosynthesis, and defense mechanisms on antioxidant and detoxification. Meanwhile, the regulation of Calvin cycle, protein folding assembly and the inhibition of protein proteolysis by Spd might play important roles in salt tolerance. This study provides insight that may facilitate a better understanding of the salt resistance by Spd in cucumber seedlings.

Effects of 24-epibrassinolide on nitrogen metabolism in cucumber seedlings under Ca(NO(3))(2) stress

Ca(NO(3))(2) accumulation is a major factor that limits greenhouse production in China. The present investigation was carried out to study the effect of 24-epibrassinolide (EBL) on nitrogen metabolism (including contents of NO(3)(-), NH(4)(+) and amino acids and related enzymes activities) in cucumber seedlings (Cucumis sativus L. cv. Jinyou No. 4) under 80 mM Ca(NO(3))(2) stress. This study found that exogenous EBL significantly reduced the accumulation of NO(3)(-) and NH(4)(+) by Ca(NO(3))(2), and enhanced the inactivated enzymes activities involved in the nitrogen metabolism. In addition, EBL alleviated the inhibition of photosynthesis nitrogen-use efficiency by Ca(NO(3))(2). Increased total amino acids by EBL under stress increased the precursor of proteins biosynthesis, thus promoting the biosynthesis nitrogen containing compounds. The presence of Ca(NO(3))(2) increased polyamines level, which might result from the increased content of free putrescine that is harmful to plant growth. However, exogenous EBL induced a further increase in total polyamines. The increase is likely caused by the elevated contents of conjugated and bound forms of polyamines. In summary, exogenously EBL compensated for the damage/losses by Ca(NO(3))(2) stress to some extent through the regulation of nitrogen metabolism and metabolites.

Effect of chromium on accumulation and antioxidants in Cucumis utillissimus L.: response under enhanced bioavailability condition

This study compares the accumulation of Cr(VI) and biochemical changes (total chlorophyll, carotenoid, protein, malondialdehyde (MDA) and cysteine contents) and roles of antioxidant enzymes (superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX)) in tolerance to metal induced stress in Cucumis utillissimus L. grown in Cr contaminated soil (CS) with garden soil (GS). Furthermore, Cr bioavailability was enhanced by ethylene diamine tetra-acetic acid (EDTA) addition to the soil to forecast the plant's accumulation pattern at elevated Cr environment. Accumulation of Cr in the leaves of the plant increased with increase in substrate metals concentration. It further increased with the addition of EDTA by 1437% and 487% in GS and CS, respectively at the highest treatment level. The lipid peroxidation increased proportionately with increase in Cr accumulation in the leaves. All the activity of antioxidant enzymes (SOD, GPX and APX) and the level of cysteine increased with dose dependant manner. SOD and cysteine were observed to be higher in the GS than in CS, but APX and GPX were found to be higher in CS than in GS. The increase in GPX and APX activities with the increase in Cr concentration could be assumed that these two enzymes have a major role in the defense mechanism towards stress induced by Cr in C. utillissimus.

ROS mediate brassinosteroids-induced plant stress responses

Brassinosteroids (BRs) play important roles in the complex network of plant signal transduction that regulates plant growth and development. Field and greenhouse trials have shown that exogenous BRs can also improve plant tolerance to abiotic and biotic stress. We have recently shown that application of exogenous BR enhances while inhibition of endogenous BR biosynthesis compromises the tolerance to photo-oxidative and cold stresses and resistance to cucumber mosaic virus in cucumber plants. These results suggest a possible role of endogenous BRs in plant stress responses as well. We have further shown that BR-induced stress tolerance is associated with increased accumulation of reactive oxygen species (ROS), which, in turn, is important for BR-induced stress tolerance. BR-induced ROS accumulation is sensitive to inhibitor of plasma membrane-bound NADPH oxidases. ROS mediate BR-induced stress tolerance, most likely by regulating genes involved in plant stress response pathways. Given their established roles as second messengers, ROS may also participate in other BR-regulated biological processes including plant growth, development and photosynthesis.

Isolation and identification of rhizoxin analogs from Pseudomonas fluorescens Pf-5 by using a genomic mining strategy

The products synthesized from a hybrid polyketide synthase/nonribosomal peptide synthetase gene cluster in the genome of Pseudomonas fluorescens Pf-5 were identified using a genomics-guided strategy involving insertional mutagenesis and subsequent metabolite profiling. Five analogs of rhizoxin, a 16-member macrolide with antifungal, phytotoxic, and antitumor activities, were produced by Pf-5, but not by a mutant with an insertion in the gene cluster. The five rhizoxin analogs, one of which had not been described previously, were differentially toxic to two agriculturally important plant pathogens, Botrytis cinerea and Phytophthora ramorum. The rhizoxin analogs also caused swelling of rice roots, a symptom characteristic of rhizoxin itself, but were less toxic to pea and cucumber roots. Of the rhizoxin analogs produced by Pf-5, the predominant compound, WF-1360 F, and the newly described compound 22Z-WF-1360 F were most toxic against the two plant pathogens and three plant species. These rhizoxin analogs were tested against a panel of human cancer lines, and they exhibited potent but nonselective cytotoxicity. This study highlights the value of the genomic sequence of the soil bacterium P. fluorescens Pf-5 in providing leads for the discovery of novel metabolites with significant biological properties.

Model study on the effect of 15 phenolic olive mill wastewater constituents on seed germination and Vibrio fischeri metabolism

Olive mill wastewaters (OMW) can be a severe problem when disposed of as untreated because of their high organic load, elevated concentration of polyphenols, and moderately low biodegradability. In the present study, the acute toxicity of 15 compounds with low molecular weight (<350 Da), catechol, four benzoic acids, three phenylacetic acids, three phenylethanols, and four cinnamic acids, already isolated from the reverse osmosis in the fractionation of OMW, was assessed on the marine bacterium Vibrio fischeri and on the seeds of two dicotyledonous species Cucumis sativus and Lepidium sativum, and on one monocotyledon Sorghum bicolor. Results of phytotoxicity showed that the most toxic compounds were catechol (EC50s ranging from 0.40 mmol/L for S. bicolor to 1.09 for C. sativus) and hydroxytyrosol, (EC50s ranging from 0.47 mmol/L for S. bicolor to 1.55 for C. sativus) while the toxic potential on bacteria was particularly elevated with EC50 values 1 or 2 orders less than phytotoxicity. These results suggested that the risk of OMW disposal may be more elevated for the water compartment than for the soil.

Tobacco PR-2d promoter is induced in transgenic cucumber in response to biotic and abiotic stimuli

The PR-2d promoter/uidA (GUS) gene construct was introduced into the cucumber (Cucumis sativus L.) genome and several transgenic lines were produced. Activation of the PR-2d promoter was investigated in these plants in response to inoculation with fungal pathogens and after salicylic acid (SA) or cold treatments. Treatment with exogenous SA increased GUS activity 2 to 11 fold over that of the control. Endogenous SA and its conjugate salicylic acid glucoside (SAG) rose in parallel after inoculation with the fungal pathogen Pseudoperonospora cubensis, with SAG becoming the predominant form. The free SA levels increased 15 fold above the basal level at 5 dpi and preceded the induction of the PR-2d promoter by five days, which occurred at 10 dpi with a 12 fold increase over the control. Inoculation with another fungal pathogen, Erysiphe polyphage, increased GUS activity 4 to 44 fold over that of the control. During normal development of flowers in the cucumber, the PR-2d/uidA gene expressed in the floral organs was similar to that of the primary host. In addition, we present the first evidence that the PR-2d promoter was induced (624 fold) under cold stress. We demonstrate that in the heterologous state the gene construct was expressed according to the signalling pattern of the native species and was stably transmitted to progeny over four generations.

Soil ecotoxicity assessment using cadmium sensitive plants

Four crop plant species (sweet corn, Zea may; wheat, Triticum aestivum; cucumber, Cucumis sativus; and sorghum, Sorghum bicolor) were tested to assess an ecotoxicity in cadmium-amended soils. The measurement endpoints used were seed germination and seedling growth (shoot and root). The presence of cadmium decreased the seedling growth. The medium effective concentration values (EC50) for shoot or root growth were calculated by the Trimmed Spearman-Karber method. Due to the greater accumulation of Cd to the roots, root growth was a more sensitive endpoint than shoot growth. Bioavailability and transport of Cd within plant were related to concentration and species. The ratio of bioaccumulation factor (BAF) in the shoots to the roots indicated high immobilization of Cd in the roots. Seed germination was insensitive to Cd toxicity, and is not recommended for a suitable assay. Among the test plants and test endpoints, root growth of sorghum and cucumber appears to be a good protocol to assess ecotoxicity of soils contaminated by Cd.

Carvacrol and cinnamic acid inhibit microbial growth in fresh-cut melon and kiwifruit at 4 degrees and 8 degrees C

AIM

To establish whether or not carvacrol and cinnamic acid delay microbial spoilage of fresh-cut fruit.

METHODS AND RESULTS

Dipping of fresh-cut kiwifruit in carvacrol solutions at 5-15 mM reduced total viable counts from 6.6 to < 2 log cfu g-1 for 21 d at 4 degrees C; however, undesirable colour and odour changes were also observed. Treatment with 1 mM of carvacrol or cinnamic acid reduced viable counts on kiwifruit by 4 and 1.5 log cfu g-1 for 5 d at 4 degrees C and 8 degrees C, respectively. Treatment of fresh-cut honeydew melon with 1 mM of carvacrol or cinnamic acid extended the lag phase of the microbial flora from less than 1 d in the untreated controls to 3 d at 8 degrees C and 5 d at 4 degrees C. Viable counts on the treated melon were 6 log cfu g-1 lower on Day 3 at 8 degrees C and 4 log cfu g-1 lower on Day 5 at 4 degrees C, compared with the untreated controls.

IMPACT OF THE STUDY

Treatment with 1 mM of carvacrol or cinnamic acid delays spoilage of fresh-cut kiwifruit and honeydew melon at chill temperatures without adverse sensory consequences.

Effects of metals on seed germination, root elongation, and coleoptile and hypocotyl growth in Triticum aestivum and Cucumis sativus

A simple, fast, and easy-to-perform method was carried out for the quantification of the inhibitory effects of metals on wheat and cucumber. The method uses seed germination, root elongation, and hypocotyl and coleoptile growth in these plants as parameters in the presence of varying concentrations of metals. Metals selected for this study were Hg, Cd, Co, Cu, Pb, and Zn. Although effective concentrations of these metals for a certain degree of inhibition were different, both plants had a reduced seed germination rate, root, and hypocotyl or coleoptile length with increasing concentrations. Mercury was determined to be the most inhibitory metal on these parameters. This metal caused a complete inhibition of germination in wheat and cucumber seeds at certain concentrations-->or=1.5 mM in cucumber and at 1.7 mM in wheat. No other metal caused this kind of inhibition even at the highest concentration (8.0 mM) applied. Though this metal possessed a higher inhibition of germination in cucumber than in wheat seeds, the inhibitory effects of other metals used were the reverse, being higher in wheat. With some exceptions, all metals in selected concentrations caused a significant ( p < 0.01 or p < 0.05) decrease in germination rate of both plants compared to control group seeds.

Role of ethylene in the biosynthetic pathway of aliphatic ester aroma volatiles in Charentais Cantaloupe melons

Compared to other melon types, Cantaloupe Charentais melons are highly aromatic with a major contribution to the aroma being made by aliphatic and branched esters. Using a transgenic line in which the synthesis of the plant hormone ethylene has been considerably lowered by antisense ACC oxidase mRNA (AS), the aliphatic ester pathway steps at which ethylene exerts its regulatory role were found. The data show that the production of aliphatic esters such as hexyl and butyl acetate was blocked in AS fruit and could be reversed by ethylene. Using fruit discs incubated in the presence of various precursors, the steps at which ester formation was inhibited in AS fruit was shown to be the reduction of fatty acids and aldehydes, the last step of acetyl transfer to alcohols being unaffected. However, treating AS fruit with the ethylene antagonist 1-methylcyclopropene resulted in about 50% inhibition of acetyl transfer activity, indicating that this portion of activity was ethylene-dependent and this was supported by the low residual ethylene concentration of AS fruit discs (around 2 microl l(-1)). In conclusion, the reduction of fatty acids and aldehydes appears essentially to be ethylene-dependent, whilst the last step of alcohol acetylation has ethylene-dependent and ethylene-independent components, probably corresponding to differentially regulated alcohol acetyltransferases.