Onion Bulb Tissue Research Articles

Development of an Untargeted Method for the Analysis of the Volatile Profile of Onions via Solid-Phase Microextraction Arrow-Headspace-Gas Chromatography-Mass Spectrometry Using Design of Experiments.

The distinctive aroma of onions, consisting primarily of sulfur-containing compounds, is one of the reasons for the popularity of the vegetable. The rapid enzymatic and chemical reactions that occur after the destruction of onion bulb tissue render the analysis of the volatile profile challenging. Therefore, sample preparation is a crucial step in the analysis of the onion volatilome, but it often does not receive the necessary attention in the literature. In this work, we focused on two aspects: Firstly, we compared different sample preparation approaches to maximize the volatile yield and to enable the description of the onion volatile profile as it would emerge after a solid-phase microextraction (SPME) Arrow sampling procedure. For headspace (HS)-gas chromatography-mass spectrometry analysis, onion juice with the addition of an ammonium sulfate solution proved to be the best option. Secondly, we optimized the HS sampling and desorption parameters (enrichment time, enrichment temperature, agitator speed, desorption time) for onion volatiles using the efficient design of experiments (DoE) approach. The optimal conditions for the analysis with HS-SPME Arrow were an enrichment time of 75min at 60°C with an agitator speed of 713rpm and a desorption time of 120s.

Thiosulfinate Tolerance Gene Clusters Are Common Features of Burkholderia Onion Pathogens.

Burkholderia gladioli pv. alliicola, B. cepacia, and B. orbicola are common bacterial pathogens of onion. Onions produce organosulfur thiosulfinate defensive compounds after cellular decompartmentalization. Using whole-genome sequencing and in silico analysis, we identified putative thiosulfinate tolerance gene (TTG) clusters in multiple onion-associated Burkholderia species similar to those characterized in other Allium-associated bacterial endophytes and pathogens. Sequence analysis revealed the presence of three Burkholderia TTG cluster types, with both Type A and Type B being broadly distributed in B. gladioli, B. cepacia, and B. orbicola in both the chromosome and plasmids. Based on isolate natural variation and generation of isogenic strains, we determined the in vitro and in vivo contribution of TTG clusters in B. gladioli, B. cepacia, and B. orbicola. The Burkholderia TTG clusters contributed to enhanced allicin tolerance and improved growth in filtered onion extracts by all three species. TTG clusters also made clear contributions to B. gladioli foliar necrosis symptoms and bacterial populations. Surprisingly, the TTG cluster did not contribute to bacterial populations in onion bulb scales by these three species. Based on our findings, we hypothesize onion-associated Burkholderia may evade or inhibit the production of thiosulfinates in onion bulb tissues. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The Genetic Requirements for HiVir-Mediated Onion Necrosis by Pantoea ananatis, a Necrotrophic Plant Pathogen.

Pantoea ananatis is an unusual bacterial pathogen that lacks typical virulence determinants yet causes extensive necrosis in onion foliage and bulb tissues. The onion necrosis phenotype is dependent on the expression of the phosphonate toxin, pantaphos, which is synthesized by putative enzymes encoded by the HiVir (high virulence) gene cluster. The genetic contributions of individual hvr genes in HiVir-mediated onion necrosis remain largely unknown, except for the first gene, hvrA (phosphoenolpyruvate mutase, pepM), whose deletion resulted in the loss of onion pathogenicity. In this study, using gene-deletion mutation and complementation, we report that, of the ten remaining genes, hvrB to hvrF are also strictly required for the HiVir-mediated onion necrosis and in-planta bacterial growth, whereas hvrG to hvrJ partially contributed to these phenotypes. As the HiVir gene cluster is a common genetic feature shared among the onion-pathogenic P. ananatis strains that could serve as a useful diagnostic marker of onion pathogenicity, we sought to understand the genetic basis of HiVir-positive yet phenotypically deviant (non-pathogenic) strains. We identified and genetically characterized inactivating single nucleotide polymorphisms in the essential hvr genes of six phenotypically deviant P. ananatis strains. Finally, inoculation of cell-free spent medium of the isopropylthio-β-galactoside (IPTG)-inducible promoter (Ptac)-driven HiVir strain caused P.ananatis-characteristic red onion scale necrosis as well as cell death symptoms in tobacco. Co-inoculation of the spent medium with essential hvr mutant strains restored in-planta populations of the strains to the wild-type level, suggesting that necrotic tissues are important for the proliferation of P. ananatis in onion. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification of Pseudomonas viridiflava, causal agent of onion (Allium cepa L.) bulb rot

Objective: To phenotypically and molecularly characterize and identify the causal agent of onion (Allium cepaL.) bulb rot in Morelos, Mexico.Methodology: Fluorescent bacteria from onion bulb tissue with symptoms of rot were isolated; the LOPATtest was used to describe them and subsequently they were identified by partial 16S rRNA gene amplification.Pathogenicity in vegetables and plants was evaluated injecting a suspension with 108 CFU mL-1of the pathogen.Results: Phenotypic characterization and 16S rRNA nucleotide sequencing showed 100% identity withPseudomonas viridiflava as the causal agent of onion bulb rot. The pathogen caused infection in broccoli (Brassica oleracea L.), spring onion (Allium fistulosum L.), purple onion (Allium cepa L.), cauliflower (Brassica oleracea var. botrytis L.), leek (Allium porrum L.), and carrot (Daucus carota L.), as well as in plant species such as jalapeño pepper (Capsicum annuum var. annuum L.), bean (Phaseolus vulgaris L.), and tomato (Solanum lycopersicum L.).Implications: This information is important for agriculture in Mexico. Pseudomonas viridiflava is a bacterialpathogen with high potential to infect new hosts. This is the first report of P. viridiflava causing onion rot in Mexico.Conclusions: Pseudomonas viridiflava is the causal agent of onion bulb r

The role of organ - and daylength - specific gene expression in bulb development and resource management in onion (ALLIUM CEPA L.)

Onion development is a complex process with each developmental event depending on the adequate supply of resources. Also, these resource components themselves are crucial nutrients in onion when consumed as food. For higher yield and better quality in onion production, it is essential to not only have a high level of photosynthesis but also effective transportation of photosynthetic products. A comprehensive set of spatial and developmental time-course experiments detailed the gene expression in onion leaf and bulb tissues during the development of a long-day onion cultivar under long-day and short-day conditions. Candidates included well characterised functional clock genes in Arabidopsis flowering pathway, as well as some novel sequences differentially expressed in bulb tissues. Both AcFT1 and AcFT4 showed significant increasing expression level during plant development, with AcFT1 being expressed in long-days during bulb formation and AcFT4 in short-days where bulbs are not formed. The data further support the role of AcFT1 as a promoter and AcFT4 as inhibitor in onion bulb formation. A number of genes associated with onion carbohydrate metabolism, sulphur metabolism and bulb development were identified as having different tissue-specific expression and provide targets for future studies.

MALDI-TOF/TOF tandem mass spectrometry imaging reveals non-uniform distribution of disaccharide isomers in plant tissues

Mass spectrometry imaging (MSI) is a powerful technique for investigating the biomolecular locations within tissues. However, the isomeric compounds are rarely distinguished due to inability of MSI to differentiate isomers in the probing area. Coupling tandem mass spectrometry with MSI can facilitate differentiating isomeric compounds. Here MALDI-TOF/TOF tandem mass spectrometry imaging approach was applied to probing the spatial distributions of isomeric disaccharides in plant tissues. First, MS/MS imaging analysis of disaccharide-matrix droplet spots demonstrated the feasibility of distinguishing isomeric species in tissues, by measuring the relative intensity of specific fragments. Then, tandem MS imaging of disaccharides in onion bulb tissues indicated that sucrose and other unknown non-sucrose disaccharides exhibit heterogeneous locations throughout the tissues. This method enables us to image disaccharide isomers differentially in biological tissues, and to discover new saccharide species in plant. This work also emphasizes the necessity of considering isobaric compounds when interpreting MSI results.

Understanding the effect of Pulsed Electric Fields on multilayered solid plant foods: Bunching onions (Allium fistulosum) as a model system

While it is well known that the nature of the applied electric field and the heterogeneity of the tissue can influence the impact of PEF treatment on the plant tissues found in plant-based foods, few studies have investigated the influence of PEF on plant structures that are made up of multiple structurally similar organs. The aim of this study was to understand the effect of pulsed electric fields (PEF), at different electric field strengths (0, 0.3, 0.7 and 1.2 kV/cm) and specific energy (7, 21 and 52 kJ/kg), on a multilayered plant material, with bunching onion bulb tissues being used as a model system. The present study found that carbohydrates leakage was an appropriate index to assess PEF induced damage and that plasmolysis of epidermal cells was a good indicator of plasma membrane integrity after PEF. In addition, electric field strength had a greater impact on the cell integrity than specific energy applied. While other studies have shown that different cell types have different sensitivities to PEF, using plasmolysis as an indicator of cell damage, this study clearly showed that the same PEF treatment conditions had a greater effect on the epidermal cells of the outer scales compared to the inner scales. Hence, while different plant cell types vary in their sensitivities to PEF the spatial location of the same cell type within a complex plant material made up of multiple similar organs, i.e. an onion bulb, can also influence how cells respond to the PEF treatment. Despite PEF induced disruption at the cellular level being detected by carbohydrate leakage, the epidermal cell plasmolysis test and by cryo-scanning electromicroscopy (cryo-SEM), no gross structural changes at the organ level were observed using cryo-SEM or fluorescence microscopy. This study also reports for the first time that PEF treatment can enhance fructan leakage from onion bulbs, which means that PEF treatments have the potential to manipulate the fructan contents of some plant-based foods.

De Novo Transcriptome Analysis of Allium cepa L. (Onion) Bulb to Identify Allergens and Epitopes.

Allium cepa (onion) is a diploid plant with one of the largest nuclear genomes among all diploids. Onion is an example of an under-researched crop which has a complex heterozygous genome. There are no allergenic proteins and genomic data available for onions. This study was conducted to establish a transcriptome catalogue of onion bulb that will enable us to study onion related genes involved in medicinal use and allergies. Transcriptome dataset generated from onion bulb using the Illumina HiSeq 2000 technology showed a total of 99,074,309 high quality raw reads (~20 Gb). Based on sequence homology onion genes were categorized into 49 different functional groups. Most of the genes however, were classified under 'unknown' in all three gene ontology categories. Of the categorized genes, 61.2% showed metabolic functions followed by cellular components such as binding, cellular processes; catalytic activity and cell part. With BLASTx top hit analysis, a total of 2,511 homologous allergenic sequences were found, which had 37–100% similarity with 46 different types of allergens existing in the database. From the 46 contigs or allergens, 521 B-cell linear epitopes were identified using BepiPred linear epitope prediction tool. This is the first comprehensive insight into the transcriptome of onion bulb tissue using the NGS technology, which can be used to map IgE epitopes and prediction of structures and functions of various proteins.

A mobile genetic element in Serratia marcescens, a causative agent of onion disease

Aim. To screen mobile genetic elements (MGE) in the bacterium which caused decay of field-grown onion bulb and to study an integron and gene cassettes associated. Methods. Polymerase chain reaction (PCR) and PCR products sequencing were used for both the bacterium and MGE identification. Terminally-labeled Restriction Fragment Length Polymorphism (TRFLP) analysis was performed for detection of any bacterium in the onion bulb tissue. Results. The bacterium, which caused field-grown onion decay, was identified by nucleotide sequence analysis of the 16S rRNA genes to be S. marcescens known as phytopathogen. However, this isolate did not respond to specific primers designed for pathogenic strains. Inoculation of onion (Allium cepa L.), Arabidopsis thaliana (L.) Heyhn, and lettuce (Lactuca sativa) seeds resulted in biomass promotion of symptomless plants. PCR revealed the presence of a class 1 integron in S. marcescens IMBG291 which represents the first isolation of this integron in phytopathogenic Serratia species. The gene cassettes harbored by the integron have been represented with the promoterless genes encoded formiminoglutamate deiminase and ascorbate-specific phosphotransferase system enzyme IIC, and with additional three senseless sequences flanked by a 59-bp element. Conclusion. S. marcescens IMBG291 exhibited plant growth promotion or pathogenicity, depending on the environmental situation, due to horizontally acquired new gene cassettes located in the integron.

Development of the Space-Resolved Solid-Phase Microextraction Technique and Its Application to Biological Matrices

To facilitate rapid in situ analyte monitoring within heterogeneous samples, a space-resolved solid phase microextraction (SR-SPME) technique was developed that utilized miniaturized segmented fibers. Initially, a multilayered agarose gel was used to determine the effects of diffusion-based mass transfer and fiber dimension on the space-resolving capability of SPME. For diazepam within agarose gel, the SR-SPME limit of detection was 2.5 ng/mL, with a linear dynamic range up to 500 ng/mL. The efficacy of the SR-SPME technique was further evaluated within diverse biological matrices (onion bulb, fish muscle, and adipose tissues) containing stratified pharmaceutical analytes. Empirically, the results agreed well with established techniques such as microdialysis and liquid extraction, but SR-SPME was simpler to implement, displayed higher spatial resolution, and was more cost-effective than traditional approaches. Additionally, the segmented design of the SPME fibers and stepwise desorption protocols offer potential advantages within high throughput applications.

Isolation and Structural Analysis In Vivo of Newly Synthesized Fructooligosaccharides in Onion Bulbs Tissues (Allium cepa L.) during Storage

Fructooligosaccharides are involved in physiological activities and quality attributes of onion bulbs. This work describes structures of newly synthesized oligosaccharides formed by fructose moieties in onion bulb tissues during storage. Onion bulbs were stored for four weeks at 10. HPAEC-PAD analysis showed that saccharide 1 was eluted after 1-kestose while saccharide 2 was eluted after nystose . Saccharides 1 and 2 have R-sucrose values of 1.55 and 2.15 by HPAEC, a reducing terminal, a reducing sugar-to-fructose ratio of 0.5 and 0.3, and a degree of polymerization of 2 and 3 by TOF-MS, respectively. GLC analysis of the methyl derivatives and NMR measurement of the saccharides confirmed the presence of two different structures: the structure of saccharide 1 is composed by two fructose moieties and linked by linkage and was identified as inulobiose [-D-fructofuranosyl---D-fructopyranose]. The structure of saccharide 2 consists of three units of fructose linked by linkage and was identified as inulotriose [-D-fructofuranosyl---D-fructofuranosyl---D-fructopyranose]. The spectra also showed that 70 to 80% of the terminal fructose residue of the two saccharides is of pyranosyl form, while 20 to 30% is of furanosyl form. This finding demonstrated that these newly produced saccharides, catalyzed by onion-purified 6G-FFT, were synthesized by the action of 1-FFT fructosyltransfer from 1-kestose to free fructopyranose yielding inulobiose and sucrose, while elongation of fructofuranosyl units occurs at this transferred fructofuranosyl residue to produce inulooligosaccharide having an additional unit of fructofuranose.

Comparison of Mono‐ and Di‐Saccharides Release in Aqueous Solutions by Raw or Fried Dice of Onion (Allium Cepa L.) Bulbs using Quantitative Nuclear Magnetic Resonance (qNMR)

Although onion bulb tissues, either raw or thermally processed, are widely used as culinary ingredients in homes, in restaurants, and in the food industry, especially for sauces, little is known about the chemical constituents released from such systems. To get a straightforward and fast analysis of sugars released from onion dice soaked in model aqueous solutions, quantitative nuclear magnetic resonance (qNMR) spectroscopy was applied, and the effect of a preliminary thermal processing in oil was investigated. Soaking of raw or fried onion bulb dice at room temperature was followed for 11 d as a model of long-term storage. For the Armstrong cultivar, the extracted dry matter (in milligrams per gram of fresh weight) as well as the content in 3 sugars (glucose, fructose, and sucrose) increased up to a maximum after about 48 h of soaking. Frying induces no measurable new water-soluble compounds. However, extraction kinetics are different (about 3 times faster with frying). Using additional microscopic studies, a possible extraction mechanism is proposed: compounds from sap-including sugars-would diffuse through conductive tissue channels.

(179) Using Quantitative Real Time PCR to Predict Levels of Botrytis allii in Stored Onion

Onion (Allium cepa L.) is an economically important vegetable in the United States. Though considered a minor crop in terms of total acreage, onions have high value when compared to other crops and, nationally, their value approaches $800 million. Because harvested onions are routinely stored for long periods, disease can be a major obstacle to the industry. The primary disease reported in stored onions is botrytis neck rot caused by the fungus Botrytis allii (syn. B. aclada). Losses from neck rot can approach 35% of the stored crop. In order to accurately quantify the level of B. allii inoculum in bulbs at harvest to be able to predict potential botrytis neck rot in storage, a quantitative real-time PCR test to quantify levels of B. allii DNA present in onion bulb tissue has been developed. We have employed the TaqMan real time PCR assay and report log-linear (R2= 0.9915) relationship between B. allii DNA concentration and cycle threshold (Ct) value with a detection limit of 5 pico gram/microliter DNA. In addition, a log-linear standard curve plotting mycelial dry weight against Ct value has been developed to allow prediction of mycelial weight in onion tissue at harvest. Currently, the ability of this test to predict botrytis neck rot during storage is being tested.

Hydrolysis Kinetic Parameters of DP 6, 7, 8, and 9−12 Fructooligosaccharides (FOS) of Onion Bulb Tissues. Effect of Temperature and Storage Time

The objective of this study was to report on the variation of DP 6 isomers (6b, 6c + 6d1 + 6d2), 7a, 8, and 9-12 fructooligosaccharides (FOS) and their hydrolysis parameters [percent hydrolysis, consumption rate, hydrolysis rate constant (k(obsd)), and half-life time (t(1/2))] in onion bulb tissues stored for 6 months at 10, 15, or 20 degrees C. The hydrolysis of DP 6 isomers, 7a, and 8 ranged from 74 to 85%, whereas that of DP 9-12 averaged 86%. The consumption rate of 6b, 6c + 6d1 + 6d2, 7a, 8, and -12 averaged 25, 58, 38, 26, and 48 microg/g of fresh weight per week, respectively. The k(obsd) showed large variation from 53 x 10(-3) week(-1) (lowest value) to 92 x 10(-3) week(-1) (highest value), whereas the half-life t(1/2) of the different FOS ranged between 7.5 and 13.1 weeks. DP 6b isomers increased during the first month, and then the content decreased sharply during the second month at 20 degrees C but remained stable during the last 4 months, whereas at 10 and 15 degrees C, 6b decreased progressively from the first to the six month. In contrast, DP 6c + 6d1 + 6d2 decreased abruptly within the first 3 months at 10, 15, and 20 degrees C; however, during the last 3 months they remained stable, ranging between 0.32 and 0.39. Variation of DP 7a, 8, and 9-12 FOS was close to that of DP 6 FOS isomers. DP 7a increased slightly during the first month, and afterward 7a started decreasing progressively during the last 5 months. DP 8 FOS showed a similar pattern independent of temperature regime: they increased slightly within the first month, but from the second month, DP 8 began decreasing progressively and continued decreasing to the sixth month. DP 9-12 FOS also varied similarly to DP 6c + 6d1 + 6d2. They decreased sharply within the first 2 months, and during the last 4 months, they continued to decrease slowly. Surprisingly, these variations occurred independently of temperature regimes and were affected only by storage duration. It was concluded that highly polymerized FOS are preferably hydrolyzed rather than low DP FOS isomers because they have a relatively high content of fructosyl end chains.

Tetra- and penta-fructooligosaccharide (FOS) isomers assessment in onion bulb tissues: effect of temperature and storage time

Tetra- and penta-fructooligosaccharide (FOS) isomers and their hydrolysis parameters––% hydrolysis, hydrolysis rate constant ( k obs) and half-lifes ( t 1/2) in onion bulb tissues kept for 6 months at 10, 15, and 20 °C, were investigated. The hydrolysis of the tetra- and pentaFOS isomers ranged between 67% and 86% and isomers of b type 4b and 5b were hydrolyzed preferentially. The k obs showed large variation from 51 × 10 −3 week −1 (lowest value) to 82 × 10 −3 week −1 (highest value), while the half-life t 1/2 of the isomers ranged between 8.5 and 16.6 weeks. DP 4 content showed close correlation at 15 and 20 °C but different at 10 °C. At 10 °C, DP 4 isomers decreased sharply during the first 2 months but remained stable during the last 4 months. At 15 and 20 °C, DP 4 increased slightly within the first month, and then decreased during the second month. During the last 4 months, the 4a isomer remained stable, while 4b and 4c increased slightly. PentaFOS isomers varied in a similar fashion to tetraFOS isomers. At 10 °C, DP 5 isomers decreased sharply during the first 2 months and remained stable during the last 4 months except for a slight increase observed during month 3 for 5b and 5c + 5d. At 15 and 20 °C, they showed a similar pattern to those of the tetra-isomers. It was concluded that pentaFOS isomers are preferentially hydrolyzed with respect to tetraFOS isomers, because they have a relatively high content of fructosyl ends chain. Results also allow us to distinguish that the DP xb (type b) isomers are preferentially hydrolyzed.

PCR Detection and RFLP Differentiation of Botrytis Species Associated with Neck Rot of Onion.

Botrytis aclada and other Botrytis spp. can cause neck rot on onions, a storage disease that normally is very difficult to detect at harvest using traditional isolation techniques. Sequence characterized amplified region primers (BA2f/BA1r) were designed based on a previously cloned and amplified DNA fragment for direct amplification of isolates of Botrytis spp. associated with neck rot of onions. Digestion of the polymerase chain reaction (PCR) amplification product with the restriction enzyme ApoI makes it possible to distinguish the five groups: Botrytis aclada types AI and AII (B. allii); B. byssoidea; B. squamosa; and B. cinerea. The detection limit was 1 to 10 pg of pure fungal DNA. It was possible to detect B. aclada with the PCR method in artificially inoculated onion bulb tissue and in mature onion leaves showing no symptoms of the disease. The availability of a sensitive and specific PCR detection and identification method for Botrytis onion neck rot pathogens should facilitate ecological studies of this group of onion pathogens.

Phenylalanine Ammonia-lyase, Peroxidase, Pyruvic Acid and Total Phenolics Variations in Onion Bulbs During Long-term Storage

Phenylalanine ammonia-lyase (PAL) and peroxidase (POD) enzyme activities, total phenolics and pyruvic acid (PA) (as pungency indicator) were measured in onion bulb tissues (c.v. Rouge Amposta) during storage at 4 and 20 °C. After 2 wk, PAL activity increased at 4 °C, but decreased at 20 °C, and after 4 wk, PAL activity at 20 °C was higher than activity observed at 4 °C. Peroxidase activity was high during the first weeks of storage, but at 4 °C this high activity lasted longer and a decrease was noted at both temperatures, coinciding with sprouting appearance. Total phenolics, which rose during the first 12 wk but fell during last weeks of storage, appeared to be linked to PAL activity. An inverse relationship was observed between phenolic content and the amount of sprouting development of bulbs. Pyruvic acid production appeared to be influenced by temperature, but in the last period of storage, the effect of temperature on PA production was less. The data demonstrate that PAL activity, which is linked to phenolic metabolism, and POD are highly involved in the sprouting of onion bulbs and these two enzymatic activities are much influenced by low temperature.

PHYSICAL CHARACTERIZATION OF ALLIINASE, THE FLAVOR GENERATING ENZYME IN ONIONS

The characteristic flavor of onions occurs when the enzyme alliinase (EC 4.4.1.4) hydrolyses the S-alk(en)yl-L-cysteine sulfoxides to form sulfur containing volatiles, pyruvate and ammonia. In this paper we have new evidence on the molecular mass of native onion alliinase, its subunit size and its relationship to the predicted size from translation of the gene. Alliinase from bulbs was purified to homogeneity. Two isoforms of alliinase were detected on ion-exchange chromatography. Both isoforms were analyzed by gel filtration FPLC. Alliinase activity was detected at molecular masses of 59, 166 kDa and 59, 170 and 393 kDa for isoforms 1 and 2, respectively. When analyzed by SDS-PAGE subunit sizes were determined to be 53.3 kDa for isoform 1 and 53.3 and 51.6 kDa for isoform 2. Amino terminal sequencing of both subunits confirmed they were alliinase. Alliinase was deglycosylated and the subunits migrated as a single band indicating a common protein backbone and varying glycosylation. Thus native alliinase is a monomer, trimer and multimer of the subunits. Molecular analysis of alliinase cDNA indicated that two genes and thus two protein subunits were expressed in onion bulb tissue. Translation is likely to have initiated from the third methionine of the leader sequence of the cDNA to give a protein backbone of 53.5 kDa in gradient SDS-PAGE. The functional significance of heterogenous subunits, from different genes, and multimeric native alliinase remains unknown.

Onion Umbel Tissue Induces Threefold Greater in Vitro Antiplatelet Activity than Onion Bulb Tissue

Onion consumption promotes cardiovascular health by inhibiting platelet activity. Bulbs are the only onion plant organ thus far examined for antiplatelet activity. The inbred line W420B was grown in replicated field trials at four United States locations in 1994. At bulb maturity, samples from each plot were tested for antiplatelet activity using human blood plasma. The remaining portion of the bulbs from each plot was stored, vernalized, and planted in a breeding nursery in 1995. Umbels were excised from 20 randomly selected plants when >50% of the flowers had opened and tested for antiplatelet activity. Inducement of antiplatelet activity was 336% higher by onion umbels than by bulbs. This finding indicates onion umbels are a more potent source of antiplatelet activity than onion bulbs. In addition, these data suggest that onion umbels may be a richer source of bioactive organosulfur compounds in onion tissue.

Protoplasmic Swelling as a Symptom of Freezing Injury in Onion Bulb Cells

Freezing injury, in onion bulb tissue, is known to cause enhanced K(+) efflux accompanied by a small but significant loss of Ca(2+) following incipient freezing injury and swelling of protoplasm during the postthaw secondary injury. The protoplasmic swelling of the cell is thought to be caused by the passive influx of extracellular K(+) into the cell followed by water uptake. Using outer epidermal layer of unfrozen onion bulb scales (Allium cepa L. cv Big Red), we were able to stimulate the irreversible freezing injury symptoms, by bathing epidermal cells in 50 millimolar KCl. These symptoms were prevented by adding 20 millimolar CaCl(2) to the extracellular KCl solution. Our results provide evidence that loss of cellular Ca(2+) plays an important role in the initiation and the progression of freezing injury.