Germination and post-germination development of Colletotrichum dematium f. circinans on Allium cepa

p6e production of aflatoxins by Aspergillus flavus SRRC-1000 growing on soybean (Forrest) and glandless cottonseed (Deltapine 16) meals was examined with respect to effects of zinc and phytate. Aflatoxins were not produced on unautoclaved soybean meal. Addition of zinc (as zinc sulfate) to autoclaved meal inhibited aflatoxin production and supplementation with sodium phytate relieved this inhibition. Addition of sodium phytate alone promoted production. When cottonseed meal was treated to release native phytate into the meal from phytate-sequestering globoids, aflatoxin production increased. However, the largest production on cottonseed meal occurred upon dialysis of the meal without releasing phytate, implying removal of a small molecular weight inhibitor.     

Degenerative changes in the epidermal cell wall of Allium cepa caused by Botrytis allii: Loss of dry mass,pectin, and cellulose in halos

Halos detected using interference microscopy (even- and fringle-field modes with monoand poly-chromatic light) around penetration sites of Botrytis allii in cell walls of normal and protoplast-free outer epidermal tissue of white, yellow, and red onions were alike. Halos in protoplast-free cell walls contained 33% less dry mass than areas of these walls adjacent to halos (quantitative interference miscroscopy with 546 nm light in the even-field mode). Halos were significantly larger in the white onion than in the yellow and red varieties. The loss of cell wall dry mass during the production of halos involved the loss of pectin and cellulose. We infer that this is caused by enzymes released from the pathogen. Cuticle degradation at penetration sites was not observed.     

Protoplast responses in the epidermis of Allium cepa induced by penetration by Botrytis allii

Penetration of Allium cepa epidermal cells (white, yellow, and red varieties) by Botrytis allii induced a response by host protoplasts in normal tissue which was not observed when penetrations were made in protoplast-free host cell walls. Callose and auto-fluorescing substances (possibly phenolic compounds) were located at the penetration sites only in normal host cells containing protoplasts. Lignin tests were negative. Halos were clearly visible in both types of tissue. Autofluorescence was observed at penetration sites in normal cells of all cultivars but general wall background autofluorescence was not observed in white onions. Autofluorescence was generally yellow green and when treated with ammonium hydroxide became green. Treatment with sodium hydroxide abolished autofluorescence. No attempt was made to isolate the autofluorescing material.     

Behavior of leucoplast nucleoids in the epidermal cell of onion (Allium cepa) bulb

Summary The behavior of nucleoids during the leucoplast division cycle in the epidermis of onion (Allium cepa) bulbs was investigated using DNA-specific fluorochrome 4'6-diamidino-2-phenylindole (DAPI) staining. The leucoplast was morphologically amoeboid and continuously changed its shape. A dumbbell-shaped leucoplast divided into two spherical daughter ones by constriction in the middle region of the body. Leucoplasts contained 4–10 mostly spherical, oval, partly rodand dumbbell-shaped nucleoids which were dispersed within the bodies. The proportion of one DNA molecule of a T4 phage particle to the small leucoplast nucleoid in the grain density of negative film was 1 to 0.91. Comparison of the present result and another groups' biochemical results suggested that a small leucoplast nucleoid contains one DNA molecule. The dumbbell-shaped leucoplast probably before division contained about twice as many nucleoids as the spherical leucoplast after division, and each half of the dumbbell contained about half the number of nucleoids. Nucleoids increased in number with growth of the leucoplast. The behavior of nucleoids during the leucoplast division cycle in onion bulbs was basically similar to that during the chloroplast division cycle in higher plants and green algae, which was previously reported (Kuroiwa et al. 1981 b).     

On the properties of fluorescing compounds in guard and epidermal cells of Allium cepa L.

Onion guard cells, in contrast to those of Vicia and Pisum, do not require an alkaline treatment in order to fluoresce. Fluorescing compounds of Allium cepa L. were characterized using in-vivo microspectrophotometry; furthermore, invitro chemical analysis for epidermal tissue, intact guard and epidermal cells, and isolated guard-cell protoplasts was performed. The emission intensity (_max 520 nm) decreased when intact onion guard cells were excited with 436 nm light, but increased (_max 470 nm) when excited at 365 nm. This photodecomposition at 436 nm is typical of flavins or flavoproteins whereas an increase in fluorescence intensity with excitation at 365 nm may be explained by the presence of other substances. The presence of flavins could not be unambiguously confirmed from these results. Indeed, the absorption spectra of the vacuolar area of guard cells did not show the peak at 445 nm which is characteristic for flavins. Furthermore, there was no decrease of absorption at the excitation wavelengths of 440 and 330 nm. Since spectral data indicate the presence at high amounts of flavonoids in guard and epidermal cells, this may reduce the sensitivity for the detection of flavins in guard cells. Using thin-layer chromatography and high-performance liquid chromatography together with hydrolytic procedures, flavonol glycosides with kaempferol and quercetin as aglycones substituted with sulphate and glucuronate were identified. Further studies on guard-cell metabolism should consider the presence of flavonoids in stomata of onion and other plants.Abbreviations GCP guard-cell protoplast - HPLC high-performance liquid chromatography - TLC thin-layer chromatography     

Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L.

From compartmental analysis of radioisotope elutin measurements, fluxes of Ca²⁺ were estimated for cortical cells in root segments of onion, Allium cepa L., relative to complete nutrient solutions containing a range of calcium concentrations ([Ca₀]) from 2 eq l^-1 to 20 meq l^-1, increasing in 10-fold steps for Ca²⁺. Except for the calcium counter-ion (usually NO ₃ ^- , sometimes Cl^- at the highest [Ca₀]), the composition of the nutrient solution was other-wise the same at all calcium concentrations. Compartmental analysis indicated that the cytoplasm had a high content of exchangeable Ca²⁺ but, in the light of evidence from animal studies, ionic activity of calcium in the cytoplasm was assumed to be no greater than 0.002 eq ml^-1. With the Ussing-Teorell flux equation as the criterion, it was concluded that at all values of [Ca₀] tested, Ca²⁺ entered the cytoplasm passively and was actively pumped back into the external solution. Entry of calcium to the vacuole from the cytoplasm was active in all cases. The conclusions regarding the character of ion transport across the plasmalemma were the same as when the whole calcium content of the cytoplasm was taken to contribute to the ionic activity. However, the electrochemical activity gradient was very much steeper than formerly estimated. Calcium was transported to the stele in proportion to the calcium content of the cytoplasm and moved in the xylem almost exclusively in the basipetal direction.     

Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L.

Summary From compartmental analysis of radioisotope elution measurements, concentrations and fluxes of Mg²⁺ were estimated for cortical cells in root segments of onion, Allium cepa L., relative to a complete nutrient solution containing 0.25 mM Mg²⁺. Five compartments for Mg²⁺ in the cortex were found and, in order of increasing rates of exchange, identified with the vacuoles and the cytoplasm of the cortical parenchyma, the Donnan free space, the water free space, and the superficial film of solution on the segments. With the Ussing-Teorell flux ratio equation as the criterion, it was concluded that Mg²⁺ entered the cytoplasm passively and was actively pumped back across the plasmalemma. Mg²⁺ concentration in the vacuole could be estimated only as lying between wide limits (1.3 to 14.3 eq ml^-1), but whatever the concentration within this range, it was concluded that Mg²⁺ was passively distributed across the tonoplast. Net flux was zero and the vacuolar concentration commensurate with this was found to be 6.6 eq ml^-1. The transported fraction of total efflux, appearing at the segment cut ends, was estimated separately. Magnesium was found to be transported almost exclusively in the basipetal direction.     

Induction of Reactive Oxygen Species and Phytoalexins in Onion (Allium cepa) Cell Culture by Biotic Elicitors Derived from the Fungus Botrytis cinerea

Metabolites of a phytopathogenic fungus Botrytis cinerea Pers. were analyzed for the presence of biotic elicitors. Three groups of elicitors competent in inducing defense responses inAllium cepa cells were identified and partly purified. The recognition of the elicitor signal in onion cells was shown to elevate the concentration of reactive oxygen species (ROS), namely, superoxide anion-radical (O₂^{\overset{-}.}) and hydrogen peroxide (₂₂). The intensity of ROS release depended on chemical identity of elicitor and its concentration. The most active ROS production in onion cells was induced by a protein fraction isolated from the medium for fungus culturing. The carbohydrate elicitors extracted from the fungus cytoplasm and cell walls of mycelia were much less effective. The dynamics of ROS generation comprised two stages. The first stage represented fast and low-amplitude changes that peaked in 15 min after the elicitor treatment. The second stage was more durable and extensive; it occurred in 1.5–6 h after the treatment.     

Production of inulinase by Xanthomonas campestris pv phaseoli using onion (Allium cepa) and garlic (Allium sativum) peels in solid state cultivation

AIMS: To access inulinase production by Xanthomonas campestris pv phaseoli using the submerged and solid state cultivation (SSC) methods. METHODS AND RESULTS: Various carbon sources, inulin-rich solid substrates and pure synthetic inulin were tested for their efficiency in inulinase induction. The highest inulinase production (17.42 IU ml(-1)) in submerged cultures of X. campestris was observed with inulin as a carbon source with an initial pH, temperature and agitation of 7.0, 37 degrees C and 150 rev min(-1) respectively. Among the various substrates, garlic peels (117 IU gds(-1)) and onion peels (101 IU gds(-1)) were found to be the best for inulinase production. CONCLUSION: The inulinase production level of X. campestris was 6.7-fold higher in garlic and 5.8-fold in onion, under optimized SSC conditions compared with the submerged culture. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on inulinase production from garlic and onion peels by X. campestris using SSC. SSC is an efficient method for inulinase production by X. campestris for commercial applications.     

In vitro,greenhouse and field assessments of cassava lines for resistance to anthracnose disease caused by Colletotrichum gloeosporioides f.sp. manihotis

Fifty-three cassava lines were selected from breeding populations at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and screened in vitro for resistance to cassava anthracnose disease (CAD). The in vitro inoculation of stem cuttings with the fungus Colletotrichum gloeosporioides f.sp. manihotis showed significant differences (p ± 0.05) in acervuli production and in the sensitivity of the cassava lines to the fungal infection after 7 days of incubation at 25 °C. Cassava lines 88/01084, 91/00595, 91/00475, 91/00344, 91/00684, 91/00313, 91/00422, and 91/00344 were highly resistant, with necrotic lesion sizes less than 7 mm. In contrast pedigree lines 88/02549, 89/0008, 91/00390 and 91/00402 were highly susceptible with the largest necrotic lesion size being greater than 20 mm. Ten cassava lines from the in vitro screening that showed varying levels of resistance to CAD were selected, based on their flowering abilities for diallel hydridization trials, and were further screened in greenhouse and field trials for CAD resistance. The greenhouse and field screening showed significant varietal differences (p ± 0.05) in sensitivity to the fungus. In all cases, the progeny lines showed correlated levels of resistance irrespective of the type of screening or assessments. Correlation analysis of the in vitro, greenhouse and field assessments showed that there was a good correspondence among all three methods of evaluating for CAD. This revised version was published online in June 2006 with corrections to the Cover Date.     

Recombinant chromosomes of advanced backcross plants between Allium cepa L. and A. fistulosum L. revealed by in situ hybridization

Cytological analysis of (Allium cepa L.×Allium fistulosum L.)×A. cepa L. F₁BC₃ plants revealed most plants were diploid with 16 chromosomes. Karyotypes of these plants showed recombinant chromosomes. Fluorescence and genomic in situ hybridization patterns of interspecific F₁ hybrid and F₁BC₃ plants revealed A. fistulosum chromosomes or chromosomal segments. A highly repetitive 376-bp DNA sequence and genomic DNA of A. fistulosum revealed similar telomeric hybridization sites when hybridized onto A. fistulosum chromosomes. Cytogenetic evidence showed that A. fistulosum DNA has recombined into the A. cepa genome. Received: 20 October 1999 / Accepted: 11 November 1999     

外源NO和H2O2对洋葱鳞片外表皮气孔开度的调控

以洋葱(Allium cepa L.)肉质鳞片外表皮为材料,研究不同浓度及不同处理时间的外源NO和H2O2对洋葱鳞片外表皮上气孔开度的调节作用,并结合NO清除剂血红蛋白(Hb)和H2O2清除剂过氧化氢酶(CAT)研究调控过程中NO和H2O2的相互关系.结果显示:单独施用不同浓度的NO和H2O2均可诱导洋葱鳞片外表皮气孔不同程度关闭,并且浓度越大时间越长,其诱导气孔关闭效应越明显;NO和H2O2共同施用所诱导气孔关闭的效应大于其单独施用效应;Hb和CAT能明显减弱NO和H2O2诱导的气孔关闭.研究表明,NO和H2O2能有效诱导洋葱鳞片上气孔关闭,存在明显的浓度效应和时间效应,且两者可能互相依赖,具有协同效应.     

Alterations in the carbohydrate composition of the cytosol of fungal spores caused by temperature variations and the storage process

Differences in the carbohydrate composition were revealed among spores of fungi belonging toZygomycetes, Ascomycota, Basidiomycota, andOomycota, part of the novel kingdomChromista. It was shown for the first time thatPhytophthora infestons contains arabitol in addition to glucose and trehalose. Sucrose was detected inPleurotus ostreatus basidiospores. It was established thatBlakeslea trispora stylospores contain inositol. The dependence of the spore carbohydrate composition on the temperature of the habitat of the corresponding species is discussed. It was shown that the cytosol of the conidia is dominated by trehalose and inositol under hypothermic conditions and by mannitol and glucose under hyperthermic conditions.Neomycota andEomycota were shown to differ in their responses to stress (starvation), which correlated with the differences in the carbohydrate composition of the spore cytosols. Assuming that cytosol carbohydrates perform a protective function, we explain the higher viability of conidia compared to stylo- and sporangiospores.     

Differential distribution of ascorbic acid,peroxidase activity,and hydrogen peroxide along the root axis in Allium cepa L. and its possible relationship with cell growth and differentiation

Summary.  In this paper we show an asymmetrical distribution of apoplastic and symplastic ascorbic acid content, peroxidase activities and hydrogen peroxide along the root axis in Allium cepa L. For most of these metabolites, a marked gradient from the root apex to the onion base was observed and was different for apoplastic and symplastic compartments. In total homogenates, ascorbic acid content was higher in the zones closer to the apex and decreased towards the root base. However, an opposite pattern was observed in the apoplastic fraction. Peroxidase activities with guaiacol, ferulic acid, ascorbic acid, and coniferyl alcohol were also different depending on the evaluated zone and the fraction used (apoplastic or symplastic). In general, each activity had a specific and unique pattern. Immunodetection of peroxidase proteins in Western blots using anti-horseradish peroxidase and anti-ascorbate peroxidase antibodies revealed different bands at the different zones of the root. Hydrogen peroxide was detected by electron microscopy and was mainly found in cell walls of epidermis (or rhizodermis), meristem, and elongating cells. The number of cell walls showing hydrogen peroxide decreased dramatically towards the root base. The results suggest that the different zones of the root show specific requirements for ascorbic acid and hydrogen peroxide. Also, each fragment of the root seems to express specific peroxidase proteins. Different processes that take place at every part of the root, as cell proliferation and elongation near the root apex and gradual lignification and differentiation towards the root base are the key to explain the results. Received May 10, 2002; accepted September 20, 2002; published online May 21, 2003 RID="*" ID="*" Correspondence and reprints: Departamento de Biología Celular, Fisiología e Inmunología, Edificio C-6, Campus de Rabanales, Universidad de Córdoba, 14014 Córdoba, Spain.     

The incorporation of mannoproteins in the cell wall of S. cerevisiae and filamentous Ascomycetes

In yeast, glucanase extractable cell wall proteins are anchored to the plasma membrane at an intermediate stage in their biogenesis via a glycosylphosphatidylinositol (GPI) moiety before they become anchored to the wall glucan via a 1,6-glucan linkage. The mechanism of the membrane processing step of cell wall proteins is not known. Here, we report that Ascomycete filamentous fungi involved in food spoilage such as Aspergillus, Paecilomyces and Penicillium, also contain GPI membrane-anchored proteins some of which are processed by an endogenous phospholipase C activity. Furthermore, similar to the situation in yeast, their cell walls contain mannoproteins which are linked to the glucan backbone through a 1,6-glucan linkage. Interestingly, one mould which contains a significant amount of non covalently linked 1,6-glucosylated cell wall proteins, is much more sensitive towards 1,3-glucanases and membrane perturbing peptides than the others.     

Biological Control of Fusarium Wilt in Tomato Caused by Fusarium oxysporum f. sp. lycopersici by AMF Glomus intraradices and some Rhizobacteria

In the present study, the effects of the arbuscular mycorrhizal fungus (AMF) Glomus intraradices Schenck & Smith and four rhizobacteria (RB; 58/1 and D/2: Pseudomonas fluorescens biovar II; 17: P. putida; 21: Enterobacter cloacae), which are the important members of the rhizosphere microflora and biological control agents against plant diseases, were examined in the pathosystem of Fusarium oxysporum f. sp. lycopersici [(Sacc) Syd. et Hans] (FOL) and tomato with respect to morphological parameters (fresh and dry root weight) and phosphorous (P) concentration in the roots. Treatments with single and dual inoculation with G. intraradices and RB strains reduced disease severity by 8.6–58.6%. Individual bacteria inoculations were more effective than both the single AMF and dual (G. intraradices + RB) inoculations. In addition, the RB and G. intraradices enhanced dry root weight effectively. Significant increases in root weights were recorded particularly in the triple inoculations compared with single or dual inoculations. Compared with the non‐treated controls all biological control agents increased P‐content of treated roots of plants. Colonization with RB increased especially in triple (FOL + G. intraradices + RB) inoculations whereas colonization of G. intraradices was significantly decreased in treatment of FOL + G. intraradices compared with triple inoculations. The results suggest that suitable combinations of these biocontrol agents may ameliorate plant growth and health.     

Auxin stimulates both deposition and breakdown of material in the pea outer epidermal cell wall,as measured interferometrically

The effect of auxin on the mass per area in the outer epidermal walls of third internodes of Pisum sativum L. cv. Alaska grown in dim red light was investigated using interference microscopy, and rates of net deposition of wall material were calculated. Examination of these net rates under different growth conditions showed that there is no simple relationship between the deposition of mass and growth. Net deposition can be proportional to growth when sufficient substrate for wall synthesis is available, as in intact plants, and in segments treated with indole-3-acetic acid (IAA) plus glucose. Net deposition can cause thickening of the walls when growth is small, as in the case of segments kept without IAA in the presence or absence of glucose, or segments whose growth is inhibited with mannitol. When substrate is limited and growth is large, however, wall expansion can occur with no net deposition, or an actual net loss of wall material can even take place. Auxin appears to induce a breakdown in the walls of segments treated in the absence of glucose, although it promotes synthesis when glucose is present. It is likely that IAA always induces a breakdown of wall material, but that the breakdown is masked when substrate is available for synthesis. Our results indicate that pea epidermal cells have two different auxin-stimulated mechanisms, wall synthesis and wall breakdown, potentially available to loosen their outer epidermal walls to bring about cell enlargement, alternatives which could be employed to different extents depending on substrate conditions.Abbreviation IAA indole-3-acetic acid M.S. Bret-Harte would like to thank Drs. Peter M. Ray, Stanford University, Winslow R. Briggs, Carnegie Institute of Washington, Stanford, Calif. USA, and Wendy K. Silk, of the University of California Davis USA, for helpful discussions, Dr. Briggs and the Carnegie Institute of Washington for the use of experimental facilities, and Dr. Ray for editorial assistance. This work was supported by a National Science Foundation Graduate Fellowship to M.S.B.-H., a National Science Foundation Postdoctoral Fellowship to T.I.B., and National Science Foundation grant DCB8801493 to P.B.G.