bluuebunny/crossref_metadata_2025 huggingface dataset:
Water stress‐induced abscisic acid accumulation in relation to reducing agents and sulfhydryl modifiers in maize plant
Authors: Jia W. , Zhang J.
Published: March 2003

Signalling process of water stress‐induced abscisic acid (ABA) accumulation was investigated in maize (Zea mays L.) leaf and root tissues. Potent free‐radical scavengers and reducing agents, N‐acetyl cysteine (NAC) and cystein (Cys), significantly inhibited or nearly completely blocked dehydration‐induced ABA accumulation. Dithiothreitol (DTT), a reducing agent but not a free‐radical scavenger, also significantly inhibited such accumulation whereas solely free‐radical scavengers, dimethyl sulphoxide (DMSO) and melatonin (Mela), had no effects. Moreover, water stress‐induced ABA accumulation was not affected either by free radicals, such as superoxide anion and hydrogen peroxide, or by oxidants such as KIO4. These observations suggest that the blocking of water stress‐induced ABA accumulation resulted from the reducing effect, rather than from anything associated with free radicals. The disulphide bond might be crucial to the reactivity of some signal element(s) in the signalling process of water stress‐induced ABA accumulation. To test the hypothesis, we used a sulfhydryl modifier, iodoacetamide (IOA), and found that it nearly totally blocked the water stress‐induced ABA accumulation. Furthermore, an impermeable sulfhydryl modifier, p‐chloromercuriphenylsulphonic acid (PCMBS), could also inhibit the water stress‐induced ABA accumulation in the leaf tissues. These results indicate that water stress‐perception protein(s) or receptor(s) may be located on the plasmalemma and a sulfhydryl group in the extracellular domain is critical to the reactivity of the speculated water stress receptors. Cys, DTT and IOA did not lead to a decrease of the baseline ABA level, i.e. in non‐stressed roots. Result indicates that their blocking of water stress‐induced ABA accumulation occurred upstream of the ABA biosynthesis pathway, i.e. in the signalling process that initiates such accumulation.
Suramin inhibits oxidant signalling in tobacco suspension‐cultured cells
Authors: Miles G. P. , Samuel M. A. , Ellis B. E.
Published: March 2003

Plant cells respond to ultraviolet radiation and other oxidant‐generating agents by mobilizing cellular defences, but the signal network linking perception of redox perturbation with defence remains unknown. Irradiation of tobacco suspension‐cultured cells with UVC was found to induce the activation of a specific MAPK46 (salicylic acid‐induced protein kinase) within 1 min. To explore where UVC and other oxidants might initially act to trigger this signal response, we employed suramin, a non‐membrane‐permeable reagent that interferes with membrane receptor‐mediated signalling in mammalian cells. Pre‐treatment of tobacco cells with suramin strongly attenuated the UVC‐induced activation of MAPK46 in a concentration‐dependent manner. Suramin was also able to interdict both ozone‐ and hydrogen peroxide‐induced activation of MAPK46, indicating that reactive oxygen species (ROS) signalling to the MAPK cascade in general may be initiated at the cell membrane, perhaps through oxidative activation of membrane receptors.
Free amino acid, ammonium and nitrate concentrations in soil solutions of a grazed coastal marsh in relation to plant growth
Authors: Henry H. A. L. , Jefferies R. L.
Published: March 2003

Soluble free amino acids, ammonium and nitrate ions as sources of nitrogen for plant growth were measured in soils of a coastal marsh grazed by snow geese in Manitoba, Canada. Amounts of nitrogen, primarily ammonium ions, increased in the latter half of the growing season and over winter, but fell to low values early in the growing season. Free amino acid concentrations relative to ammonium concentrations were highest during the period of rapid plant growth in early summer, especially in soils in the intertidal zone, where the median ratio of amino acid nitrogen to ammonium nitrogen was 0·36 and amino acid concentrations exceeded those of ammonium ions in 24% of samples. Amino acid profiles, which were dominated by alanine, proline and glutamic acid, were similar to goose faecal profiles. In a continuous flow hydroponic experiment conducted in the field, growth of the salt‐marsh grass, Puccinellia phryganodes, on glycine was similar to growth on ammonium ions at an equivalent concentration of nitrogen. When supplies of soil inorganic nitrogen are low, amino acids represent a potentially important source of nitrogen for the re‐growth of plants grazed by geese and amino acid uptake may be as high as 57% that of ammonium ions.
Diurnal changes in the concentrations of 2‐phenylethyl β‐D‐glucopyranoside and the corresponding volatile aglycone in the tissue and headspace of Trifolium repens L. florets
Authors: Jakobsen H. B. , Christensen L. P.
Published: March 2003

Distinct synchronous diurnal rhythms were detected in the concentrations of phenethyl alcohol and phenethyl acetate in the tissue of blooming Trifolium repens florets. Corresponding rhythmic oscillations were observed for the same two compounds in the floral headspace. Maximum content of the volatiles in the tissue and headspace was observed 3–9 h after initiation of the photophase. The concentrations of phenethyl alcohol and phenethyl acetate in the tissue increased significantly during floral development. At full bloom the tissue contained amounts sufficient to support 2–3 h of emission. Several observations suggested that esterification of phenethyl alcohol was the source for phenethyl acetate. Trimethylsilyl derivatization and enzymatic hydrolysis of fractionated flower extracts identified 2‐phenylethyl β‐d‐glucopyranoside as the major glucoside in the florets. The pool of glucosides increased significantly during floral development and at full bloom 97% of the phenethyl alcohol was bound as glucoside. The concentration of 2‐phenylethyl β‐d‐glucopyranoside did not vary in a rhythmic diurnal manner. The dynamics among the diurnal rhythmic phenomena in the tissue and headspace and the fraction of volatiles bound as glucosides is discussed.
Effect of NO3‐ supply on N metabolism of potato plants (Solanum tuberosum L.) with special focus on the tubers
Authors: Mäck G. , Schjoerring J. K.
Published: March 2003

The response of the tubers to NO3– was studied in comparison to the other organs of Solanum tuberosum var. Sava, with special focus on: (a) whether tubers are capable of primary N assimilation; (b) whether N assimilation is stimulated by NO3–; and (c) whether primary N assimilation in tubers is important for tuber growth. NO3– reduction via nitrate reductase (NR; EC 1.6.6.1) and NH4+ assimilation via glutamine synthetase (GS; EC 6.3.1.2) occurred predominantly in the shoots, but up to 20% was contributed by the tubers under low‐NO3– conditions. NR activation was highest in tubers (up to 90%) and declined in all organs with increasing NO3– supply. NR and GS activity responded with a decline in tubers and roots as opposed to an increase in the shoots. This corresponded to relative organ growth: growth of tubers and roots was stimulated relative to that of shoots at a limiting NO3– supply. Absolute growth of all organs was stimulated by NO3–, whereas tuber number declined. The concentration of N compounds increased with NO3– supply in all organs: NO3– increased most dramatically in the shoots (81‐fold), free amino acids most markedly in the tubers (three‐fold). The amount of patatin and of the 22 kDa protein complex in the tuber reached a minimum when the amount of Rubisco in the shoot reached maximum as a response to NO3– supply. Tuber sucrose and starch increased by 40%, whereas glucose and fructose declined two‐fold as plant N status increased. It is concluded that tubers are potentially N autotroph organs with capacity for de novo synthesis of amino acids. Primary N assimilation in tubers, however, declines with increasing NO3– supply and is not of major importance for tuber growth.
Grass cells ingested by ruminants undergo autolysis which differs from senescence: implications for grass breeding targets and livestock production
Authors: Beha E. M. , Theodorou M. K. , Thomas B. J. , Kingston‐Smith A. H.
Published: March 2003

It is widely believed that the initial degradation of proteins contained in grazed forage is mediated by rumen micro‐organisms, but the authors’ recent work suggests that the plant cells themselves contribute to their own demise. In the present study the responses of Lolium perenne leaves to the rumen environment were investigated by using an in vitro system which simulates the main stresses of the rumen but from which rumen micro‐organisms were excluded. Degradation of leaf protein and the accumulation of amino acids in tissue and bathing medium occurred over a time‐scale that is relevant to rumen function, and in a near 1 : 1 ratio. Significant loss of nuclear material was observed after 6 h incubation and chloroplasts became morphologically more spherical as the incubation progressed. In situ localization suggested that ribulose 1,5 bisphosphate carboxylase/oxygenase was broken down within chloroplasts which from cytology were judged to be intact. We conclude from these data that plant metabolism may play a significant role in breaking down plant proteins within relatively intact organelles in the rumen. The determinations of chlorophyll content and cell viability revealed that the plant processes occurring in the simulated rumen were similar but not identical to those of natural senescence.
Discrimination of genes expressed in response to the ionic or osmotic effect of salt stress in soybean with cDNA‐AFLP
Authors: UMEZAWA T. , MIZUNO K. , FUJIMURA T.
Published: March 2003

‘Ionic effects’ and ‘osmotic effects’ are major components of salt stress in plants. In this study these two parameters were clearly discriminated in soybean (Glycine max (L.) Merr.) using a modified cDNA‐amplified fragment length polymorphism (AFLP) technique. Soybean (cv. Lee) seedlings were exposed to iso‐osmotic treatment consisting of 100 mm NaCl and 12% (w/v) polyethylene glycol 6000 for 24 h. The NaCl treatment fully activated salt tolerance as confirmed by the expression of the inositol‐1‐phosphate synthase gene. Then, gene expression in each sample was examined by cDNA‐AFLP, and 140 differentially expressed cDNA fragments were obtained out of 13 000 amplicons. The percentage of transcripts dependent on ionic (NaCl‐specific) and osmotic effects (common with NaCl and polyethylene glycol) could be evaluated for 44 and 40% of them, respectively. cDNA‐AFLP also revealed the distribution of transcripts in shoots and roots. The ionic effect‐dependent gene expression was more abundant in roots indicating that they showed a greater response to ionic stress than shoots. Several ion transporters, transcription factors and redox enzymes that were specific to the ionic effect may play important roles in the salt tolerance of soybean. The technical advantages of this modified cDNA‐AFLP method are also discussed.
Expression of the early light‐induced protein but not the PsbS protein is influenced by low temperature and depends on the developmental stage of the plant in field‐grown pea cultivars
Authors: NORÉN H. , SVENSSON P. , STEGMARK R. , FUNK C. , ADAMSKA I. , ANDERSSON B.
Published: March 2003

Plant cells exposed to photo‐inhibitory conditions respond by accumulation of the early light‐induced proteins (Elips) with a potential photoprotective function. Here we studied the expression of Elip in various pea cultivars grown under agricultural or climate‐chamber conditions. We demonstrated that the expression of Elip in all cultivars was developmentally regulated and its level decreased during flowering and post‐flowering periods. Surprisingly, significant amounts of Elip transcripts, but not proteins, accumulated in senescing leaves already under low light conditions and the exposure to light stress resulted in a 10‐times higher induction of Elip transcripts. Furthermore, the expression pattern of Elip transcript and protein significantly differed under field and growth‐chamber conditions. First, the expression level of Elip was much higher in field‐grown than in chamber‐grown cultivars. Second, substantial amounts of Elip transcripts and protein were detected during the night in field‐grown plants in contrast to chamber‐grown cultivars due to a synergistic effect of light stress occurring during the day and low temperature present during the following night. The expression of the PsbS protein related to Elips and involved in the photoprotection of the photosystem II was relatively constant under all conditions tested.
Identification and characterization of peanut stunt cucumovirus from naturally infected alfalfa in Iran
Authors: Bananej K. , Hajimorad M. R. , Roossinck M. J. , Shahraeen N.
Published: March 2003

A mechanically transmissible virus was isolated from a naturally infected alfalfa plant (Medicago sativa) in Karaj, Iran. It induced fern‐leaf symptoms in Lycopersicon esculentum, general chlorosis and stunting in Arachis hypogoea, local lesions and systemic infection in Chenopodium quinoa, Phaseolus vulgaris and Vigna unguiculata but only local lesions in C. amaranticolor. In gel‐immunodiffusion tests, it reacted strongly with an antiserum to peanut stunt cucumovirus (PSV), moderately with two of six antisera to cucumber mosaic cucumovirus (CMV) and with two of five antisera to tomato aspermy cucumovirus. Its spherical virions (28 nm in diameter) contained a coat protein of approximately 29 kDa and encapsidated four species of RNAs with similar electrophoretic mobilities to RNAs 1–4 of CMV strains Fny and LS and those of PSV strains J and W. Its encapsidated RNAs hybridized in slot‐blot hybridization assay with the complementary DNA probe of PSV‐W RNAs but not with those of CMV strains. Therefore, on the basis of biological, serological and physico‐biochemical properties, the virus was identified as PSV. No satellite RNA was associated with the virus. This is the first report of PSV in Iran.
Assessing the virulence of four bark beetle‐associated bluestain fungi using Norway spruce seedlings
Authors: Krokene P. , Solheim H.
Published: March 2003

The virulence of two isolates of each of four different bark beetle‐associated bluestain fungi was evaluated by wound‐inoculating 2‐ and 4‐year‐old Norway spruce seedlings. One isolate of Ceratocystis polonica killed 40% of the 2‐year‐old plants and 20% of the 4‐year‐old plants, whereas the other fungi (Ophiostoma piceae, Ophiostoma sp., an unidentified fungus with dark sterile mycelium) and the control treatments (inoculation with sterile agar and unwounded plants) did not kill any plants during the 11‐week incubation period. Only C. polonica and the Ophiostoma sp. caused any bluestain of the sapwood. The two C. polonica isolates caused significantly deeper bluestain penetration into the sapwood and longer necrotic lesions on the sapwood surface than all other isolates. The symptoms caused by the other fungi were similar to those on the sterile inoculated control plants. The virulence of the fungal isolates tested in this study agrees largely with results from a previous mass inoculation study using the same isolates inoculated into 40‐year‐old Norway spruce trees. Thus, inoculation of seedlings seems to be a reliable, inexpensive and convenient bioassay for determining the virulence of bark beetle‐associated bluestain fungi.
Genetic control of the resistance of Erysiphe graminis f.sp. hordei to five triazole fungicides
Authors: Blatter  , Brown  , Wolfe
Published: March 2003

The genetics of resistance to ergosterol demethylation inhibitor (DMI) fungicides of the triazole (conazole) group was examined in a cross between two isolates of the barley powdery mildew fungus, Erysiphe graminis (= Blumeria graminis) f.sp. hordei. One isolate, E1, was previously identified as being resistant to the triazole fungicide triadimenol, while the other, HL3/5, was sensitive. The 56 progeny tested were classified into two distinct groups, either being resistant to triadimenol, like E1, or sensitive, like HL3/5. The segregation ratio was not significantly different from 1:1, consistent with responses to triadimenol being controlled by a single gene. In further tests with cyproconazole, epoxiconazole, propiconazole and tebuconazole, all the progeny classified as resistant to triadimenol were also more resistant to each of these other triazole fungicides than were any of the triadimenol‐sensitive progeny. This is consistent with the triadimenol resistance allele also conferring cross‐resistance to the other triazoles. The ratio between the responses of the resistant and sensitive progeny (the resistance factor, RF) was greatest for triadimenol, followed by tebuconazole, propiconazole, epoxiconazole and cyproconazole, in that order. The RF for triadimenol was much greater when the fungicide was applied as a seed treatment than when it was sprayed. Five isolates, covering the five levels of responses to triadimenol identified previously in the UK population of E. graminis f.sp. hordei, were used as standards; a triadimenol‐sensitive isolate and one with the lowest level of resistance were sensitive to all four of the other fungicides, while three isolates with higher levels of triadimenol‐resistance were also more resistant to the other chemicals.
Genetic characteristics of Fusarium verticillioides isolates from maize in Costa Rica
Authors: Danielsen  , Meyer  , Funck Jensen
Published: March 2003

Thirty‐nine isolates of Fusarium verticillioides from maize seeds from three regions of Costa Rica were classified on fertility, fumonisin production, vegetative compatibility and pathogenicity. The identity of the isolates was verified by sexual crosses with standard tester strains and by isozyme analysis. Twenty‐three isolates (59%) were mating type A− and 16 (41%) were A+; 29 (74%) were female fertile. The isolates produced high amounts of fumonisin B1 when grown on sterilized maize grits, 32 isolates producing more than 1000 μg g−1, as determined by TLC, and 7 less than 1000 μg g−1. Vegetative compatibility tests by pairing nit mutants identified 34 vegetative compatibility groups (VCGs), of which 29 had one member and 5 had two members. Isolates belonging to the same VCG were obtained from the same seed sample. Two pathogenicity tests with different inoculation methods were performed: on toothpick inoculation of 7‐week‐old maize stalks, 71% of the isolates were pathogenic according to the length of the necrosis formed in the stalk, and on sand inoculation of maize seedlings all the isolates were pathogenic, according to shoot length and dry weight production. Differences in aggressiveness between some of the isolates were recorded. It is concluded that natural populations of F. verticillioides in Costa Rica consist of genetically diverse, highly fertile and pathogenic isolates that represent a potential risk for disease development and fumonisin accumulation in maize crops.
Effects of leaf wetness duration, relative humidity, light and dark on infection and sporulation by Didymella rabiei on chickpea
Authors: Jhorar O. P. , Butler D. R. , Mathauda S. S.
Published: March 2003

No infection occurred at less than 95% relative humidity (r.h.) when chickpea plants were dried after inoculation with conidia of Didymella rabiei. Infection was significant when the dry leaves were exposed to 98% r.h. for 48 h. When inoculated plants were subjected to different leaf wetness periods, some infection occurred with 4 h wetness, and disease severity increased with wetness duration according to an exponential asymptote, with a maximum value after about 18 h. Germination of conidia and germ tube penetration increased linearly with increasing wetness periods when recorded 42 h after inoculation. With a 24‐h wetness period, germination of conidia was first observed 12 h after inoculation and increased linearly with time up to 52 h (end of the experiment). Dry periods immediately after inoculation, followed by 24‐h leaf wetness, reduced disease severity; as the dry period increased the severity decreased. Disease severity increased with increasing periods of darkness after inoculation. The number of pycnidia and the production of conidia on infected leaves increased only slightly with high r.h. (either in the light or in the dark), but large increases occurred over an 8‐day period when the leaves were kept wet.
Induction of different pathogenesis‐related cDNAs in grapevine infected with powdery mildew and treated with ethephon
Authors: Jacobs  , Dry  , Robinson
Published: March 2003

Uncinula necator, the causal agent of grapevine powdery mildew, was found to elevate the activity of the pathogenesis‐related (PR) proteins, chitinase and β‐1,3‐glucanase in leaves and berries of a number of susceptible grapevine (Vitis vinifera) cultivars. The increase in hydrolytic activity was directly related to the severity of powdery mildew infection on both leaves and berries but no systemic induction was observed in uninfected tissues. A number of cDNA clones encoding various PR proteins, including chitinases (PR‐2), β‐1,3‐glucanases (PR‐3) and thaumatin‐like (TL) proteins (PR‐5), were isolated and their expression in response to powdery mildew infection examined. PR genes encoding extracellular proteins were most strongly induced in infected leaves, including an acidic class III chitinase (VvChi3), a basic class I glucanase (VvGlub) and a thaumatin‐like protein (VvTl2). A basic class I chitinase (VvChi1b) was also detected, but only in severely infected leaves. A similar pattern of PR gene induction was observed in mildew‐infected preveraison berries, with the exception of VvChi1b, which was not detected. Chitinase and β‐1,3‐glucanase enzyme activities were also found to be highly induced in leaves and preveraison berries by ethephon treatment. The pattern of chitinase gene induction by ethephon, however, was markedly different for mildew infection, with no apparent induction of VvChi3 but a marked increase in the transcript level of an acidic class IV chitinase, VvChi4. These results demonstrate that the leaves and preveraison berries of grapevine respond to environmental and stress‐related stimuli by the expression of specific PR genes but that the induction of these genes during pathogen invasion does not afford complete protection of these tissues against Uncinula necator.

The following abbreviations have been used: Tris: 2‐amino‐2‐(hydroxymethyl)‐1,3‐propanediol; EDTA: ethylenediaminetetra‐acetic acid; PVPP: polyvinylpolypyrrolidone. The GenBank accession numbers for VvChi1b and VvGlub are AF053341 and AF053750, respectively.
Races of Xanthomonas campestris pv. vesicatoria overcoming the gene Bs2 for bacterial spot resistance in pepper, prevalent on Capsicum chinense in Barbados and Grenada and weakly pathogenic on bell pepper and tomato in the field
Authors: O'Garro  , Gore  , Ferguson
Published: March 2003

A total of 404 isolates of Xanthomonas campestris pv. vesicatoria, obtained from Capsicum chinense cv. West Indian Red grown in Barbados and Grenada, were differentiated into pathogenic races, and of these, 96 were tested also for selected taxonomic group phenotypes. The response of C. chinense to infection by several X. campestris pv. vesicatoria races and the contribution of races isolated from this cultivar to severity of bacterial spot of bell pepper and tomato were also investigated. P4T2, P5T2 and P6T2 were the predominant races of X. campestris pv. vesicatoria isolated from C. chinense grown in Grenada, whereas nine races (T1, P4, P6, P0T2, P1T2, P4T1, P4T2, P6T1 and P6T2) were isolated in Barbados. Race P4T2 comprised 46.0 and 71.4% of the isolates from Barbados and Grenada, respectively. The 96 isolates, all of which overcame resistance conferred by the gene Bs2, shared taxonomic group B strain characteristics, including the presence of the β‐protein band, positive amylolytic activity and inability to oxidize cis‐aconitate. The C. chinense cv. West Indian Red was susceptible only to races of X. campestris pv. vesicatoria that can overcome Bs2 gene resistance. Of six such races identified in Barbados, only P4T1, P4T2 and P6T1 affected bacterial spot‐susceptible bell pepper or tomato in the field, and they amounted to only 1.5–2.1% of each sample of isolates from these plant species. Moreover, they were confined to the smallest bacterial spot lesions. Bell pepper was most severely affected by combinations of races T1 with P3T2 and T2 with P0T1, and tomato by race T1 only and combinations of races P0T1 with P0T2 and P1T1 with P1T0, all of which prevailed in the field despite selection against them by C. chinense cv. West Indian Red.
Interaction of virus‐infected celery and Septoria apiicola
Authors: Ataga  , Epton  , Frost
Published: March 2003

Inoculation of celery plants with viruses CV036 (celery mosaic) and CV506 (parsnip yellow fleck) decreased blight on leaves inoculated later with Septoria apiicola by 17–39% and 54–91%, respectively. There was a significant negative correlation between the amount of blight and the furanocoumarin content of the celery petioles. The antifungal activity of these furanocoumarins was demonstrated by their in vitro inhibition of the germination of spores of S. apiicola and Botrytis cinerea. Scanning electron microscopy of virus‐infected leaves sprayed with spores of S. apiicola also showed slight but significant reductions in percentage germination and in germ‐tube length, and considerable reductions in the proportion of germ‐tubes which produced an appressorium, compared with spores on virus‐free leaves.
Identification and toxicity of Alternaria brassicicola, the causal agent of dark leaf spot disease of Brassica species grown in Thailand
Authors: Pattanamahakul  , Strange
Published: March 2003

Fungi, with spores characteristic of the genus Alternaria, were isolated from necrotic lesions on leaves of cabbage, cauliflower, Chinese kale and choi‐sum growing in Thailand, and were proved by Koch's postulates to be the causal agents of a disease known as dark leaf spot. All isolates corresponded in morphology to descriptions of Alternaria brassicicola and the identification was confirmed by analysis of the ITS1, 5.8S gene and ITS2 regions of rDNA, the nucleotide sequences of isolates from all four plants being identical to each other and to the published sequence of a known isolate of A. brassicicola. Culture filtrates of isolates of the fungus from each host, grown on a defined medium consisting of Czapek–Dox nutrients supplemented with cations, were toxic to cells isolated from the four host plants. Taking the data overall, filtrates from the cauliflower isolate were significantly less toxic than those from the other isolates. Although the filtrate from the cabbage isolate was most toxic to cabbage cells and that of the choi‐sum isolate most toxic to choi‐sum cells, filtrates of the Chinese kale and cauliflower isolates were most toxic to cells of plants other than those from which they were isolated.
Action of the fungicide phosphite onEucalyptus marginatainoculated withPhytophthora cinnamomi
Authors: Jackson  , Burgess  , Colquhoun  , Hardy
Published: March 2003

Although phosphite has been effective in the control ofP. cinnamomiinE. marginata(jarrah),the biochemical mechanisms behind phosphite protection are poorly understood. Using an aeroponics system, jarrah clones with moderate resistance toP.cinnamomiwere treated with foliar applications of phosphite (0 and 5 g L−1). The roots were inoculated with zoospores ofP. cinnamomiat 4 days before and 0, 2, 5, 8 and 14 days after phosphite treatment. Root segments were then analysed for activity of selected host defence enzymes (4‐coumarate coenzyme A ligase [4‐CL], cinnamyl alcohol dehydrogenase [CAD]) and the concentration of soluble phenolics and phosphite. Lesion development was most effectively reduced when phosphite concentrations within the roots were highest (i.e. days 8–14). During this time, the levels of host defence enzymes remained relatively unchanged. Lesion development was also effectively restricted when phosphite concentrations within the roots were lowest (i.e. days 2 and 5); a significant increase in host defence enzymes was associated with this decrease in lesion development. It was concluded from these studies that the effect of phosphite in controlling the pathogen is determined by the phosphite concentration at the host–pathogen interface. When phosphite concentrations within the roots are low, phosphite interacts with the pathogen at the site of ingress to stimulate host defence enzymes. At high phosphite concentrations, phosphite acts directly on the pathogen to inhibit its growth before it is able to establish an association with the host, and the host defences remain unchanged.
Suppression of clubroot andVerticilliumyellows in Chinese cabbage in the field by the root endophytic fungus,Heteroconium chaetospira
Authors: Narisawa  , Ohki  , Hashiba
Published: March 2003

Chinese cabbage seedlings inoculated with an isolate of the hyphomycete,Heteroconium chaetospira,were transplanted to the field. After 3 months, they showed a 52–97% reduction in clubroot and a 49–67% reduction inVerticilliumyellows compared with noninoculated controls.H. chaetospiracolonized the cortical cells, especially in the root tip region. Infected plants showed no disease symptoms. The infection process involves the formation of appressoria on the cell surface and the subsequent growth of hyphae within cells.H. chaetospiracolonized 18 plant species, indicating a wide range of hosts. It may have potential as a biocontrol agent for clubroot andVerticilliumyellows.
Biological control ofSclerotinia minorusing a chitinolytic bacterium and actinomycetes
Authors: El‐Tarabily K. A. , Soliman M. H. , Nassar A. H. , Al‐Hassani H. A. , Sivasithamparam K. , McKenna F. , Hardy G. E. ST. J.
Published: March 2003

Isolates of 85 bacteria and 94 streptomycete and 35 nonstreptomycete actinomycetes were obtained from a lettuce‐growing field in Al‐Ain, United Arab Emirates, on colloidal chitin agar, and screened for their ability to produce chitinase. Twenty‐three bacteria and 38 streptomycete and 15 nonstreptomycete actinomycete isolates produced high levels of chitinase and were examinedin vitrofor their ability to suppress the growth ofSclerotinia minor, a pathogen causing basal drop disease of lettuce. The three most suppressive isolates were examined further for their production of β‐1,3‐glucanase and antifungal activity as well as their ability to colonize the roots and rhizosphere of lettucein vitroandin planta. The three isolates,Serratia marcescens, Streptomyces viridodiasticusandMicromonospora carbonacea, significantly reduced the growth ofS. minor in vitro, and produced high levels of chitinase and β‐1,3‐glucanase.Streptomyces viridodiasticusalso produced antifungal metabolite(s) that significantly reduced the growth of the pathogenin vitro. When the pathogen was presented as the sole carbon source, all three isolates caused extensive hyphal plasmolysis and cell wall lysis.Serratia marcescens and St. viridodiasticuswere competent to varying degrees in colonizing the roots of lettuce seedlings after 8 days on agar plates and the rhizosphere within 14 days in pots, with their competency being superior to that ofM. carbonacea. All three isolates, individually or in combination, were antagonistic toS. minorand significantly reduced incidence of disease under controlled glasshouse conditions.
Pathotypes of Melampsora rust on Salix in short‐rotation forestry plantations
Authors: Ramstedt M. , Hurtado S. , Åström B.
Published: March 2003

Melampsora epitea, the causal agent of leaf rust on willow (Salix spp.) in short‐rotation forestry, was sampled over four consecutive years (1993–96) in Sweden. The pathotype patterns of 332 single‐spore isolates were examined for virulence characteristics using a defined set of willow hosts. Thirty‐seven pathotypes of M. epitea were identified and grouped into three formae speciales. No race or morph subdivision was observed among the isolates, other than the three formae speciales. For monitoring and studying the ecological and evolutionary dynamics of virulence for M. epitea, an internationally useful naming system for pathotypes is proposed, with a three‐digit code referring to virulence on a specified set of standard test clones.
Effects of calcium on biocontrol activity of yeast antagonists against the postharvest fungal pathogen Rhizopus stolonifer
Authors: Tian S. P. , Fan Q. , Xu Y. , Jiang A. L.
Published: March 2003

Calcium chloride (2% w/v) significantly inhibited the growth of the pathogen Rhizopus stolonifer, but did not affect the colony‐forming units (CFU) of yeasts Candida guilliermondii and Pichia membranefaciens in potato dextrose broth. The concentration of yeast suspension influenced spore germination and germ tube growth of R. stolonifer in vitro, as well as disease incidence and lesion development in fruits. There were significant negative relationships between the suspension concentrations of the yeasts and the growth as well as infectivity of the pathogen. The addition of calcium resulted in lower spore germination rates and slower growth of germ tubes in vitro, as well as in lower disease incidences and smaller lesion diameters compared with treatments with yeast antagonists alone. When yeast cell suspensions reached a concentration of 5 × 108 CFU mL−1, growth of the pathogen was completely limited in vitro, and no infection was found in peach and nectarine fruits treated with or without calcium.
Detection of Colletotrichum coccodes and Helminthosporium solani in soils by bioassay
Authors: Carnegie S. F. , Choiseul J. W. , Roberts A. M. I.
Published: March 2003

The sensitivity of a bioassay in detecting soil inoculum of Colletotrichum coccodes and Helminthosporium solani was examined using potato minitubers and microplants. Tests were conducted on soils which were collected from fields in which the interval after a previous potato crop differed, and which were also artificially infested with conidia or microsclerotia. For C. coccodes, determining plant infection based on the occurrence of infected roots after 9–12 weeks was a sensitive method for detecting and quantifying the amount of inoculum in soil. Infestations of less than 0·4 microsclerotia per g soil were detected in artificially infested soils. A semiselective medium, developed for isolating C. gloeosporioides from pepper, detected soil infestations by C. coccodes as low as nine conidia or one microsclerotium per g soil in artificially infested soil. For H. solani, infection on minitubers was a sensitive measure, with soil inoculum of fewer than 10 conidia per g soil being detected. Soil infestation could be quantified by assessing the percentage surface area of minitubers covered by sporulating lesions, which was strongly related to the amount of soil infestation. The results of these bioassay tests were compared with published results for real‐time quantitative PCR assays on the same soils. The two methods were in good agreement in artificially infested soils, but the bioassay appeared to be more sensitive with naturally infested soils.
Allergen‐Induced Migration of Human Cells in Allergic Severe Combined Immunodeficiency Mice
Authors: Duez  , Akoum  , Marquillies  , Cesbron  , Tonnel  , Pestel
Published: March 2003

Recently, we have shown that severe combined immunodeficiency (SCID) mice, intraperitoneally reconstituted with peripheral blood mononuclear cells (PBMC) from Dermatophagoides pteronyssinus (Dpt)‐sensitive patients, produced human IgE and developed a pulmonary inflammatory‐type reaction after exposure to allergen aerosol. In order to understand the potential mechanisms involved in the human cell migration in SCID mice, we analysed their phenotypic profile in the lungs, spleen and thymus, 2 months after Dpt inhalation. The human cell recruitment in these organs was found to be allergen‐dependent as CD45+ human cells were only detected in hu‐SCID mice after Dpt exposure. The composition of the pulmonary human T‐cell infiltrate, preferentially memory (CD45RO), activated (human leucocyte antigen (HLA)‐DR) and CD4+ cells, was similar to that described in asthmatic patients. However, CD20+ B cells were predominately recruited in the spleen and thymus and may be IgE‐producing cells in the spleen. In the lungs, the percentage of human leucocytes expressing the α‐chain of the lymphocyte function‐assiciated antigen‐1 (LFA‐1) (CD11a) was higher than those of CD49d+ or CD54+ cells, in contrast to the spleen and thymus, suggesting a potential role of LFA‐1 in the human cell migration towards SCID mice lung. In conclusion, this model could be useful in the study of factors implicated in the cellular migration towards the lymphoid organs during an allergic reaction.
Improved Humoral and Cellular Immune Responses Against the gp120 V3 Loop of HIV‐1 Following Genetic Immunization with a Chimeric DNA Vaccine Encoding the V3 Inserted into the Hepatitis B Surface Antigen
Authors: Fomsgaard  , Nielsen  , Bryder  , Nielsen  , Machuca  , Bruun  , Hansen  , Buus
Published: March 2003

The gp120‐derived V3 loop of HIV‐1 is involved in co‐receptor interaction, it guides cell tropism, and contains an epitope for antibody neutralization. Thus, HIV‐1 V3 is an attractive vaccine candidate. The V3 of the MN strain (MN V3) contains both B‐ and T‐cell epitopes, including a known mouse H‐2d‐restricted cytotoxic T lymphocyte (CTL) epitope. In an attempt to improve the immunogenicity of V3 in DNA vaccines, a plasmid expressing MN V3 as a fusion protein with the highly immunogenic middle (pre‐S2 + S) surface antigen of hepatitis B virus (HBsAg) was constructed. Epidermal inoculation by gene gun was used for genetic immunization in a mouse model. Antibody and CTL responses to MN V3 and HBsAg were measured and compared with the immune responses obtained after vaccination with plasmids encoding the complete HIV‐1 MN gp160 and HBsAg (pre‐S2 + S), respectively. DNA vaccination with the HIV MN gp160 envelope plasmid induced a slow and low titred anti‐MN V3 antibody response at 12 weeks post‐inoculation (p.i.) and a late appearing (7 weeks), weak and variable CTL response. In contrast, DNA vaccination with the HBsAg‐encoding plasmid induced a rapid and high titred anti‐HBsAg antibody response and a uniform strong anti‐HBs CTL response already 1 week p.i. in all mice. DNA vaccination with the chimeric MN V3/HBsAg plasmid elicited humoral responses against both viruses within 3–6 weeks which peaked at 6–12 weeks and remained stable for at least 25 weeks. In addition, specific CTL responses were induced in all mice against both MN V3 and HBsAg already within the first 3 weeks, lasting at least 11 weeks. Thus, HBsAg acts as a ‘genetic vaccine adjuvant’ augmenting and accelerating the cellular and humoral immune response against the inserted MN V3 loop. Such chimeric HIV–HBsAg plasmid constructs may be useful in DNA immunizations as a ‘carrier’ of protein regions or minimal epitopes which are less exposed or poorly immunogenic.
The Frequent Expansion of a Subpopulation of B Cells that Express RF‐Associated Cross‐Reactive Idiotypes: Evidence from Analysis of a Panel of Autoreactive Monoclonal Antibodies
Authors: Melero  , Aguilera  , Mageed  , Jefferis  , Tarragó  , Núñez‐Roldán  , Sánchez
Published: March 2003

Preferential expression of VH gene segments is evident within the adult human primary B‐cell repertoire. The repertoire may be influenced by genetic factors, e.g. VH gene segment polymorphisms, or in a temporal manner due to the exposure to environmental antigens. The molecular characteristics of 15 autoreactive human monoclonal antibodies (MoAbs) are reported. All antibodies were of the IgM isotype, and 12 of the 15 were polyreactive and included rheumatoid factor type specificity, i.e. reactivity with IgG. Nine of the 15 MoAbs are products of VH3 gene segments, as evidenced by staphylococcal protein A binding; four of these express the cross‐reactive idiotype recognized by the mouse MoAb 3H7 and are thus products of the VH26 gene segment. One of the five remaining VH3 gene products expresses the cross‐reactive idiotypes recognized by the mouse MoAbs B6 and D12. V‐gene family usage, determined by polymerase chain reaction (PCR) amplification of cDNA and further hybridization with family‐specific oligonucleotide probes, confirmed the cross‐reactive idiotype studies and showed that only VH3‐gene‐encoded proteins bound staphylococcal protein A. Five of the six non‐VH3 gene segment products express the cross‐reactive idiotype recognized by the mouse MoAb LC1 and could be assumed to be products of the VH4.21 gene segment; however, one human MoAb is shown to be the product of a VH2 gene segment. This is interesting because it turns LC1 from being an anti‐cross‐reactive idiotype antibody into an anticlan reagent.
T‐Cell Clonal Change after Allo‐Kidney Transplantation in Humans
Authors: Hagihara  , Hiraga  , Tsuchida  , Morita  , Kanai  , Balgansuren  , Munkhbat  , Masuko  , Yamamoto  , Kato  , Tsuji
Published: March 2003

Whether T cells circulating peripherally express changes at a clonal level after renal transplantation is uncertain. To clarify this issue, we analyzed T‐cell clonality of peripheral blood lymphocytes (PBLs) in 12 renal transplant recipients by a novel polymerase chain reaction–single‐strand conformation polymorphism (PCR–SSCP) method that can discriminate T‐cell clones with different T‐cell receptor (TCR) Vβ motifs. The PCR–SSCP study showed that after transplantation, only a few distinct T‐cell clonotypes accumulated in the absence of clinical episodes, irrespective of the compatibility of HLA antigens. In contrast, various T‐cell clones appeared in cases of acute rejection (AR) and infection. These subsided immediately after the AR was resolved; however, they remained long after the resolution of the infection. In a case of AR followed by an infectious episode, distinct T‐cell clones appeared concomitantly with each episode. Several of them disappeared or remained thereafter. In one case, significant numbers of accumulating bands were observed by in‐vitro stimulation by mixed lymphocyte reaction (MLR); several were identical to those found in vivo. However, some of those that did not appear in vitro were apparent in vivo. In conclusion, the appearance of T‐cell clonotypes at a peripheral level indicates the existence of immunologically activated T‐cell clones, which were significantly affected by immunosuppressive therapy. It was also determined that the T‐cell immune system is much more complicated in vivo than in vitro.
Analysis of the T‐Cell Receptors Utilized for Allogeneic HLA‐DR Recognition: Comparison of Different Responder‐Cell Donors Possessing an Identical HLA‐DR Allele
Authors: Obata  , Tsunoda‐Iizuka
Published: March 2003

We examined whether individuals with an identical HLA‐DR type utilized the same T‐cell receptors (TCRs) to recognize a given allogeneic HLA‐DR molecule. CD4+ T cells from three responder‐cell donors possessing the DRB1*0901 allele were stimulated with HLA‐DRB1*0406 molecules, subjected to the primary mixed lymphocyte reaction (MLR) and the TCRs of the activated CD4+ T cells were analysed using single strand conformation polymorphism (SSCP) and random cDNA clone sequencing. The responder cells of each donor yielded many dominant SSCP bands in several TCRAV and TCRBV segments, but none of these dominant SSCP bands derived from two or three responders. Random cDNA sequence analysis demonstrated that the alloreactive TCRs were diverse, but each of the three responder‐cell donors showed some dominant cDNA clones. However, no amino acid sequence identities or similarities among the dominant cDNAs of these donors were detected. These results indicate that certain T‐cell clones from each individual's TCR repertoire pool expand preferentially as a result of allogeneic HLA‐DR recognition but these clones are not necessarily common to different individuals, even when their responder cells possess identical DR alleles and are stimulated with the same alloantigen.
90 Years On: A Therapy to ‘Stimulate the Phagocytes’?
Authors: Turner
Published: March 2003

The collectins (collagenous lectins) constitute a major element of the innate immune system and mannan‐binding lectin (or mannose‐binding lectin, MBL) is now recognized as a serum constituent with many of the attributes of both antibody and C1q. A common opsonic deficiency recognized more than 20 years ago is known to be a functional manifestation of MBL deficiency. This is largely explained by three single point mutations in exon 1 of the MBL gene, each of which disrupts the collagenous region and probably prevents assembly of higher order oligomers. Several independent studies suggest that deficiency of the protein increases significantly the risk of infection with a range of different pathogens and also predisposes such individuals to autoimmune disease. The first description of MBL replacement therapy [Valdimarsson et al., Scand J Immunol 1998;48:116–123] provides evidence that administration of this purified plasma protein is safe, practical and possibly efficacious. These preliminary observations in two recipients now need to be extended in large‐scale trials.
Chemokine Receptors and their Crucial Role in Human Immunodeficiency Virus Infection: Major Breakthroughs in HIV Research
Authors: Kristiansen  , Knudsen  , Eugen‐Olsen
Published: March 2003

Within the last three years, major progress in the understanding of acquired immune deficiency syndrome pathogenesis has been achieved. The discovery that human immunodeficiency virus (HIV), in addition to the CD4 receptor, requires the presence of a coreceptor in order to infect cells has led to a series of breakthroughs in HIV research and knowledge. These include an increased understanding of viral entry, a connection of viral phenotype to specific coreceptor use, and an unequivocal linkage of a single human gene to host susceptibility. All in all these achievements provide a number of promising new strategies for combating HIV.
Antithymocyte Globulin and Cyclosporin A are Synergistic in an Experimental Transplantation Tolerance Model in the Rat
Authors: OLAUSSON  , LUKES  , NORRBY  , QI  , EKBERG  , GANNEDAHL  , TUFVESON  , MJÖRNSTEDT
Published: March 2003

The aim of the present investigation was to study the possible synergistic effect between cyclosporin A (CsA) and antithymocyte globulin (ATG), using the potent immunostimulator, Linomide®. DA rats were transplanted with a PVG/c heart to the neck vessels, and the recipients were treated for 10 days with oral CsA (10 mg/kg), oral Linomide® (160 mg/kg) and/or ATG, which was given as a single dose of either 0.02 ml, 0.1 ml or 0.2 ml prior to transplantation. Rats given a combination of ATG and Linomide® or CsA and Linomide® were used as controls. Synergism between CsA and ATG was tested using the two immunosuppressive drugs given in combination in order to override the challenge of Linomide®. CsA or ATG treatment alone resulted in rats with long‐term surviving grafts. Addition of Linomide® to CsA‐treated recipients was followed by early graft rejection. Similarily, Linomide® triggered rejection in rats given a low dose of ATG and in recipients given a high dose of ATG if Linomide® treatment was prolonged to 21 days. The combination of ATG, CsA and 21 days of Linomide® resulted in a significantly prolonged graft survival compared with either ATG + Linomide® or CsA + Linomide®. These findings demonstrate the synergistic capacity of ATG and CsA in combined immunosuppressive therapy.