Identification of a new bioregulator acting in ultralow doses in bulb onion (<Emphasis Type="Italic">Allium cepa</Emphasis> L.)

A bioregulator that has physicochemical and biological properties similar to a group of bioregulators isolated from various animal tissues has been found in the bulb onion (Allium cepa L.). It was determined that the biological action of the plant bioregulator is determined by a peptide with molecular weight of 4036 ± 2 Da whose 18-C-terminal amino acid sequence consisted of 18 residues. On models of seed germination of some vegetable cultures, the ability of the bioregulator isolated from supernatant of onion extract in ultralow doses (10⁻¹³ mg of protein/ml) to inhibit growth and development was demonstrated.     

Bioregulator from rat liver tissue

It has been shown that the membranotropic homeostatic tissue-specific bioregulator isolated from rat liver tissue contains a nanosized peptide-protein complex consisting of low-molecular peptides (1–6.5 kDa) and a protein from the serum albumin family. This bioregulator modulated the peptide biological activity and determined the tissue specificity.     

Structural-functional characteristics of a new bioregulator isolated from bovine pigmented epithelium tissue

A new bioregulator operating in ultralow doses corresponding to 10^?17 mg/ml has been isolated from tissue of pigmented epithelium of bovine eyes. It has been established that the functional basis of this bioregulator is a complex of a low molecular weight regulatory peptide (4372 Da) and a modulator consisting of a mixture of proteins with molecular weights of 14.980–66.283 kDa. It has been shown that the regulatory peptide is responsible for membranotropic activity of the bioregulator, and the modulator proteins are responsible for biological action in ultralow doses. The data demonstrate an interrelation between nanocondition of the bioregulator and its ability to show activity in ultralow doses.     

Application of actinomycetes as biocontrol agents in the management of onion bacterial rot diseases

This study was conducted to achieve biological control for the post-harvest onion bacterial rot diseases with the aid of Egyptian isolates of actinomycetes. In this respect, 45 actinomycetes strains were isolated from Egyptian soils and screened for their antagonistic effect against onion bacterial rot pathogens; Erwinia carotovora subsp. carotovora and Burkholderia cepacia. The most two active strains were identified based on their cultural, morphological and molecular properties as Streptomyces lavendulae HHFA1 and Streptomyces coelicolor HHFA2, the latter was most potent and so was used in vivo (pots and field) for controlling onion bacterial rot. S. coelicolor HHFA2 application resulted in enhancement in the photosynthetic pigments and some foliar growth parameters of onion plants confirming its growth promoting effect. The results of the post-harvest estimation of the disease incidence (DI) of the onion bacterial rot throughout storage revealed that, the application of S. coelicolor HHFA2 reduced the DI pronouncedly comparing with the untreated control and confirm its successful role in the biological control of onion bacterial rot diseases.     

Studies on the structure of the bioregulator purified from the rat brain

From the brain tissue of Wistar rats, we purified a bioregulator, which is active at ultralow doses. Using reversed-phase HPLC, we prepared a homogenous polypeptide with a molecular weight of 4749 ± 2 Da, which is responsible for the biological activity of the bioregulator. Using the CD spectroscopy method, we calculated the percentage of canonical elements of the secondary polypeptide structure in a solution. Using the methods of proteomics, we revealed that the structure of the investigated polypeptide was similar to the N-terminal sequence of a fragment of guanine-nucleotide binding G₀-protein subunit α-1.     

The uptake,transport and metabolism of the bioregulator 2-(3,4-dichlorophenoxy) ethyldimethylamine in guayule

The bioregulator 2-(3,4-dichlorophenoxy) ethyldimethylamine was applied to five-month-old summer and winter guayule plants. Uptake of this molecule depended on the presence of viable trichomes and a well-developed cuticle, in the leaves. Winter plants absorbed the bioregulator more successfully than summer plants. The stem proved to be an active absorption site in young plants. Six days after bioregulator application, transport of the molecule was restricted to the lower stem in summer plants, and stem and leaves in winter plants. Transport was governed by the availability and development of conduits. The intact molecule was recovered two days after application but was not detectable after 4 and 6 days indicating that it is metabolized fairly rapidly. The significance of these findings is discussed in terms of the use of bioregulators to stimulate rubber production in guayule plants.     

Fumonisin B1 production by Fusarium proliferatum strains isolated from Allium fistulosum plants and seeds in Japan

Aims:  To test the fumonisin B₁ - producing ability of Fusarium proliferatum strains isolated from Welsh onion ( Allium fistulosum ) plants and seeds of commercial cultivars in Japan and to examine the applicability of PCR-based assays to discriminate between fumonisin B₁-producing and nonproducing isolates.
Methods and Results:  Fumonisin B₁ levels in 20 Fusarium isolates obtained from Welsh onion plants and seeds of seven commercial cultivars were determined by HPLC. Thirteen of the 20 isolates produced fumonisin B₁. PCR assay with FUM1 gene-specific primers amplified a DNA fragment (700 bp) only from fumonisin-producing isolates.
Conclusions:  Fusarium proliferatum isolates that can produce fumonisin B₁ were often associated with wilted Welsh onion plants and seeds of some commercial cultivars. The PCR assay with FUM1 gene-specific primers has the potential to discriminate between fumonisin B₁-producing and nonproducing isolates.
Significance and Impact of the Study:  This study revealed that F. proliferatum producing fumonisin B₁ is associated with Welsh onion plants and that commercial cultivar seeds may be contaminated with the fungus. PCR amplification of FUM1 gene can be a useful tool for the rapid identification of fumonisin B₁-producing F. proliferatum isolates.     

Glu–Phe from onion (Allium Cepa L.) attenuates lipogenesis in hepatocytes

A Glu–Phe (EF) was isolated from onion (Allium cepa L. cv. Sunpower). The chemical structure of EF was determined by nuclear magnetic resonance and electrospray ionization–mass (ESI?MS) spectroscopy. We showed that EF reduced lipid accumulation in mouse hepatocytes by inhibiting the expression of sterol regulatory element-binding protein-1c (SREBP–1c) and its lipogenic target genes. We also found that AMP-activated protein kinase (AMPK) was required for the inhibitory effect of EF on lipid accumulation in mouse hepatocytes. Furthermore, EF was qualified in nine onion cultivars by selective multiple reaction-monitoring detection of liquid chromatography–ESI?MS. These results suggest that EF could contribute to the beneficial effect of onion supplement in maintaining hepatic lipid homeostasis.     

Atomic force microscopy of microfibrils in primary cell walls

Examination of angiosperm primary cell walls by transmission electron microscopy shows that they contain microfibrils that probably consist of cellulose microfibrils surrounded by associated non-cellulosic polysaccharides. Previous studies using solid-state (13)C NMR spectroscopy have shown that the cellulose is all crystalline with crystallites of cross-sectional dimensions of 2-3 nm. However, it is not known if each microfibril contains only one, or more than one crystallite because there is no agreement about the dimensions of the microfibrils. Partially hydrated primary cell walls isolated from onion ( Allium cepa L.) and Arabidopsis thaliana (L.) Heynh. were examined by atomic force microscopy and the microfibril diameters determined. The cell walls of both species contained tightly interwoven microfibrils of uniform diameter: 4.4+/-0.13 nm in the onion and 5.8+/-0.17 nm in A. thaliana. The effect was also examined of extracting the A. thaliana cell walls to remove pectic polysaccharides. The microfibrils in the extracted cell walls of A. thaliana were significantly narrower (3.2+/-0.13 nm) than those in untreated walls. The results are consistent with the microfibrils containing only one cellulose crystallite.     

Immobilization of microbial cells on inner epidermis of onion bulb scale for biosensor application

Inner epidermis of onion bulb scales was used as a natural support for immobilization of microbial cells for biosensor application. A bacterium Sphingomonas sp. that hydrolyzes methyl parathion into a chromophoric product, p-nitrophenol (PNP), has been isolated and identified in our laboratory. PNP can be detected by electrochemical and colorimetric methods. Whole cells of Sphingomonas sp. were immobilized on inner epidermis of onion bulb scale by adsorption followed by cross-linking methods. Cells immobilized onion membrane was directly placed in the wells of microplate and associated with the optical transducer. Methyl parathion is an organophosphorus pesticide that has been widely used in the field of agriculture for insect pest control. This pesticide causes environmental pollution and ecological problem. A detection range 4-80 μM of methyl parathion was estimated from the linear range of calibration plot of enzymatic assay. A single membrane was reused for 52 reactions and was found to be stable for 32 days with 90% of its initial hydrolytic activity. The applicability of the cells immobilized onion membrane was also demonstrated with spiked samples.     

Accumulation of quercetin conjugates in blood plasma after the short-term ingestion of onion by women

Quercetin is a typical flavonoid present mostly as glycosides in plant foods; it has attracted much attention for its potential beneficial effects in disease prevention. In this study, we examined human volunteers after the short-term ingestion of onion, a vegetable rich in quercetin glucosides. The subjects were served diets containing onion slices (quercetin equivalent: 67.6-93.6 mg/day) with meals for 1 wk. Quercetin was only found in glucuronidase-sulfatase-treated plasma, and its concentration after 10 h of fasting increased from 0.04 +/- 0.04 microM before the trial to 0.63 +/- 0.72 microM after the 1-wk trial. The quercetin content in low-density lipoprotein (LDL) after glucuronidase-sulfatase treatment corresponded to <1% of the alpha-tocopherol content. Human LDL isolated from the plasma after the trial showed little improvement of its resistance to copper ion-induced oxidation. It is therefore concluded that conjugated metabolites of quercetin accumulate exclusively in human blood plasma in the concentration range of 10(-7) approximately 10(-6) M after the short-term ingestion of vegetables rich in quercetin glucosides, although these metabolites are hardly incorporated into plasma LDL.     

Pyrenocine C,A phytotoxin-related metabolite produced by onion pink root fungus,Pyrenochaeta terrestris

The structure of pyrenocine C, a new metabolite isolated from onion pink root fungus, Pyrenochaeta terrestris (Hansen) has been elucidated as (±)-(2′E)-5-(1′-hydroxybut-2′-enyl)-4-methoxy-6-methyl-2-pyrone by spectroscopic methods and chemical correlation with pyrenocine A.     

Intraspecific metabolic diversity among strains ofBurkholderia cepacia isolated from decayed onions,soils, and the clinical environment

A collection of 218 strains ofBurkholderia cepacia (including 18% strain replicates) was assembled from organic soils, decayed onions, and clinical sources. Each strain was characterized for virulence to onion, catabolic ability using the Biolog GN microtiter plate, and several other behaviors. Overall test reproducibility was estimated at 98%. The results obtained using the Biolog GN system corresponded well to those obtained using standard methods. Three coefficients of resemblance (Gower similarity, pattern difference, and Jaccard similarity) were calculated and clustered by the group-average method. The sorted matrices and phenograms, while giving evidence of an underlying phenetic structure to theB. cepacia nomenspecies, gave little evidence of sorting by broad source of isolation. Strains isolated from within fields or samples were frequently found to be similar, however, strains isolated from fields with similar cropping histories were not. The Gower-transformed centroids of ordained clusters were projected in a principal coordinate system and estimates of disjunction were calculated. Strains ofB. cepacia were shown to be non-uniformly distributed in taxonomic space. Strains isolated by serial dilution on onion slices formed a tight phenetic cluster which includes the type strain of the nomenspecies and that of a synonymous group (Pseudomonas multivorans); the strains in this phenon were generally virulent to onion and were partially differentiated from others by pectolytic behavior and by the production of diffusible pigment on King's medium A. Further characterization should better resolve the taxonomy of the nomenspecies.     

Production of guard cell protoplasts from onion and tobacco

Guard cell protoplasts (GCP) from young cotyledons of onion and tobacco were isolated in culture microchambers where optimal isolating and culture conditions could be determined in situ. The digestion course was quantified by following under polarized light the loss of.retardation of the birefringent cellulose of the guard cells. The assay showed that driselase has a 5-fold higher cellulytic activity than cellulysin. Driselase is, however, harmful to the GCP. Calcofluor staining was less adequate for establishing digestion courses because it increases sharply after exposing guard cells to cellulysin.     

The aqueous garlic, onion and leek extracts release nitric oxide from S-nitrosoglutathione and prolong relaxation of aortic rings

Garlic, onion and leek have beneficial effects in treatment of numerous health disorders. The aim of the present study was to investigate underlying molecular mechanisms. To test the potency of the aqueous garlic, onion and leek extracts to release NO from GSNO we have measured NO oxidation product, NO(2)-, by the Griess reagent method. Further, we studied the ability of garlic extract to relax noradrenaline-precontracted rat aortic rings in the presence of GSNO and effects of garlic extract on electrical properties of rat heart intracellular chloride channels. We have observed that: i) garlic, onion and leek extracts released NO from GSNO in the order: garlic > onion > leek; ii) the ability of garlic extract to release NO was pH-dependent (8.0 > 7.4 > 6.0) and potentiated by thiols (Cys > GSH = N-acetyl-cysteine > oxidized glutathione) at concentration 100 μmol/l; iii) the garlic extract (0.045 mg/ml) prolonged relaxation time of aortic rings induced by GSNO (50 nmol/l) and inhibited intracellular chloride channels. We suggest that NO-releasing properties of the garlic, onion and leek extracts and their interaction with Cys and GSH are involved in NO-signalling pathway which contributes to some of its numerous beneficial biological effects.     

Distribution of Burkholderia cepacia phenotypes by niche, method of isolaiton and pathogenicity of onion

Several proposals have been made for the subdivision of the bacterial species Burkholderia cepacia. Data applying these schemes to a collection of 188 strains of B. cepacia, isolated using a variety of methods, from soils, decayed onions, and nosocomial sources are presented. None of the schemes could be shown to be associated with the method of isolation, niche from which a strain was isolated, pectolytic activity, or pathogenicity to onion. Strains isolated by serial dilution on onion slices were much more uniform than were strains isolated using semiselective media. The nutritionally stringent medium of Lumsden and Sasser (US Patent No. 4 588 584) was judged better for the collection of a phenotypically broad sample of B. cepacia than those of Hagedorn, Gould, Bardinelli & Gustavson (1987) and Wu & Thompson (1984), which are based on antibiotic insensitivity. Pectolytic activity and pathogenicity to onion were shown to be highly correlated characters. None of the strains of clinical origin was capable of macerating onion tissue.     

Variation of RBE between p(75) + Be and d(50) + Be neutrons determined for chromosome aberrations in Allium cepa.

The RBE of p(75) + Be neutrons relative to d(50) + Be neutrons has been determined for chromosome aberrations induced in Allium cepa (onion) roots. Two biological criteria were selected: the average number of aberrations (mainly fragments) per cell in anaphase and telophase, and the percentage of aberration-free cells. The influence of sampling time (3 to 7 h incubation) between irradiation and fixation was investigated systematically. This factor did not significantly influence the results. The RBE values of p(75) + Be neutrons compared to those of d(50) + Be neutrons were 0.85 (0.79-0.91) and 0.87 (0.80-0.95) for the first and the second criteria, respectively. In previous experiments for the same beams, we found an RBE of 0.90 (0.86-0.94) for survival of V79 cells (D0 ratio), 0.96 (0.93-0.99) for the intestinal crypt cell system, and 0.83 (0.70-0.96) for Vicia faba growth delay.     

Cloning and characterization of the lectin cDNA clones from onion,shallot and leek

Characterization of the lectins from onion (Allium cepa), shallot (A. ascalonicum) and leek (A. porrum) has shown that these lectins differ from previously isolated Alliaceae lectins not only in their molecular structure but also in their ability to inhibit retrovirus infection of target cells.cDNA libraries constructed from poly(A)-rich RNA isolated from young shoots of onion, shallot and leek were screened for lectin cDNA clones using colony hybridization. Sequence analysis of the lectin cDNA clones from these three species revealed a high degree of sequence similarity both at the nucleotide and at the amino acid level.Apparently the onion, shallot and leek lectins are translated from mRNAs of ca. 800 nucleotides. The primary translation products are preproproteins (ca. 19 kDa) which are converted into the mature lectin polypeptides (12.5–13 kDa) after post-translational modifications.Southern blot analysis of genomic DNA has shown that the lectins are most probably encoded by a family of closely related genes which is in good agreement with the sequence heterogeneity found between different lectin cDNA clones of one species.     

Exogenous ethylene inhibits sprout growth in onion bulbs

Background and Aims

Exogenous ethylene has recently gained commercial interest as a sprouting inhibitor of onion bulbs. The role of ethylene in dormancy and sprouting of onions, however, is not known.

Methods

A cultivar (Allium cepa ‘Copra’) with a true period of dormancy was used. Dormant and sprouting states of onion bulbs were treated with supposedly saturating doses of ethylene or with the ethylene-action inhibitor 1-methylcyclopropene (1-MCP). Initial sprouting was determined during storage at 18 °C by monitoring leaf blade elongation in a specific size class of leaf sheaths. Changes in ATP content and sucrose synthase activity in the sprout leaves, indicators of the sprouting state, were determined. CO₂ and ethylene production of onion bulbs during storage were recorded.

Key results

Exogenous ethylene suppressed sprout growth of both dormant and already sprouting onion bulbs by inhibiting leaf blade elongation. In contrast to this growth-inhibiting effect, ethylene stimulated CO₂ production by the bulbs about 2-fold. The duration of dormancy was not significantly affected by exogenous ethylene. However, treatment of dormant bulbs with 1-MCP caused premature sprouting.

Conclusions

Exogenous ethylene proved to be a powerful inhibitor of sprout growth in onion bulbs. The dormancy breaking effect of 1-MCP indicates a regulatory role of endogenous ethylene in onion bulb dormancy.Key words: Bulb dormancy, Allium cepa, onion, sprout growth, ethylene, CO₂ production, respiration, 1-methylcyclopropene