bluuebunny/crossref_metadata_2025 huggingface dataset:
Does an antagonistic relationship between ABA and ethylene mediate shoot growth when tomato (Lycopersicon esculentum Mill.) plants encounter compacted soil?
Authors: Hussain A. , Black C. R. , Taylor I. B. , Roberts J. A.
Published: March 2003

This study tested the hypothesis that antagonistic interactions between abscisic acid (ABA) and ethylene mediate the effects of soil compaction on shoot growth. Isogenic wild‐type (Ailsa Craig), ABA‐deficient (notabilis) and a transgenic (ACO1AS) tomato genotype with a reduced capacity to synthesize ethylene were examined. Exogenous ABA was also applied. Leaf area was comparable when Ailsa Craig and ACO1AS were grown in uncompacted (1·1 g cm−3) or compacted (1·5 g cm−3) soil, but was lower in notabilis. However, a 1·1/1·5 g cm−3 split‐pot treatment invoked marked genotypic differences, whereby leaf area was comparable to 1·1 g cm−3 control plants in ACO1AS but was intermediate between the 1·1 and 1·5 g cm−3 treatments in Ailsa Craig and notabilis. ABA may be discounted as the root‐sourced signal responsible for reducing leaf area when the roots encountered compacted soil as Ailsa Craig and ACO1AS showed differing responses despite similar increases in xylem sap ABA concentration; leaf area was invariably lower in notabilis. These genotypic differences were correlated with ethylene evolution; thus the greater leaf area in ACO1AS was associated with its reduced ability to synthesize ethylene, whereas the reductions in leaf expansion observed when Ailsa Craig and notabilis encountered compacted soil were accompanied by increased ethylene production. Application of ABA had little effect on ACO1AS, but promoted a recovery of leaf expansion in notabilis, and more surprisingly in Ailsa Craig. These results suggest that antagonistic interactions between ABA and ethylene may regulate leaf expansion when the root system simultaneously encounters uncompacted and compacted soil.
Stem hydraulic supply is linked to leaf photosynthetic capacity: evidence from New Caledonian and Tasmanian rainforests
Authors: Brodribb T. J. , Feild T. S.
Published: March 2003

A strong relationship between hydraulic supply of water to leaves and maximum photosynthetic capacity was found in a group of seven conifers and 16 angiosperm species, including two vessel‐less taxa, from similar rainforest communities in New Caledonia and Tasmania (Australia). Stem hydraulic supply was expressed as the hydraulic conductivity of branches in terms of leaf area supplied (KL) and leaf photosynthetic capacity was measured as the mean quantum yield of PSII (ØPSII) in leaves exposed to full sun, as determined by chlorophyll fluorescence analysis. A single, highly significant linear regression (r2= 0·74) described the relationship between hydraulic conductivity and quantum yield in all species. This suggests that the maximum photosynthetic rate of leaves is constrained by their vascular supply. In both rainforest locations, the KL of conifer wood overlapped broadly with that of associated vessel‐bearing and vessel‐less angiosperms indicating a degree of hydraulic convergence in these forests.
Patterns of pinitol accumulation in soybean plants and relationships to drought tolerance
Authors: Streeter J. G. , Lohnes D. G. , Fioritto R. J.
Published: March 2003

Previous studies indicate that methylated cyclitols are potentially important osmolytes in plants. In a search for genetic diversity for pinitol (D‐3‐O‐methyl‐chiro‐inositol) accumulation in soybean (Glycine max (L.) Merr.), two‐ to three‐fold differences in pinitol accumulation in leaf blades were found among Chinese plant introductions. Furthermore, it was found that genotypes that accumulated high concentrations of pinitol, when grown under well‐watered conditions, had been selected for performance in regions of China having low rainfall. Among the carbohydrates analysed, pinitol accumulation was uniquely associated with adaptation to dry areas of China. A detailed study of pinitol accumulation in the soybean plant showed two‐ to three‐fold gradients in pinitol concentration from the bottom to the top of the plant. The gradient shifted during plant development, with consistently higher concentrations of pinitol in the uppermost leaves. Pinitol accumulation was not correlated with activity of the key biosynthetic enzyme, inositol methyl transferase. This result and other lines of evidence indicated that shifting patterns of pinitol accumulation were due to translocation of the cyclitol from lower to upper nodes. Pinitol, proline, and sugars accumulated in leaf blades on soybean plants subjected to drought, but the molar concentration of pinitol in stressed plants was greater than the concentrations of proline or sugars. Although the mechanism by which pinitol participates in drought tolerance is not fully known, our results provide additional correlative evidence linking pinitol and drought tolerance in soybean.
Abscisic acid introduced into the transpiration stream accumulates in the guard‐cell apoplast and causes stomatal closure
Authors: Zhang S. Q. , Outlaw W. H.
Published: March 2003

Petioles of water‐sufficient intact Vicia faba L. plants were infused with 1 µm abscisic acid (ABA) to simulate the import of root‐source ABA. This protocol permitted quantitative ABA delivery, up to 300 pmol ABA over 60 min, to the leaf without ambiguities associated with perturbations in plant–water status. The ABA concentrations in whole‐leaf samples and in apoplastic sap increased with the amount infused; ABA degradation was not detected. The ABA concentration in apoplastic sap was consistent with uptake of imported ABA into the leaf symplast, but this interpretation is qualified. Our focus was quantitative cellular compartmentation of imported ABA in guard cells. Unlike when leaves are stressed, the guard‐cell symplast ABA content did not increase because of ABA infusion (P = 0·48; 3·0 ± 0·5 versus 4·0 ± 1·2 fg guard‐cell‐pair−1). However, the guard‐cell apoplast ABA content increased linearly (R2 = 0·98) from −0·2 ± 0·5 to 3·1 ± 1·3 fg guard‐cell‐pair−1 (≈ 3·1 µm) and was inversely related to leaf conductance (R2 = 0·82). Apparently, xylem ABA accumulates in the guard‐cell wall as a result of evaporation of the apoplast solution. This mechanism provides for integrating transpiration rate and ABA concentration in the xylem solution.
Ultraviolet‐B radiation reduces the rates of cell division and elongation in the primary leaf of wheat (Triticum aestivum L. cv Maris Huntsman)
Authors: Hopkins L. , Bond M. A. , Tobin A. K.
Published: March 2003

The primary leaf of wheat (Triticum aestivum L. cv Maris Huntsman) was used as a model system to examine how elevated ultraviolet‐B (UV‐B; λ= 280–320 nm) radiation affected growth. A reduction in the rate and duration of growth of the primary leaf, in response to UV‐B, was the result of changes in both the rate and extent of cell division and elongation. UV‐B reduced the proportion of mitotically active cells (mitotic index) and increased the time taken for cell division (cell doubling time). Thus the supply of cells into the elongation zone was reduced, and this, coupled to a reduction in the rate of elongation, resulted in reduced leaf growth. This analysis of the spatial distribution of growth provided a means of calculating the age of cells within the leaves. Cells of UV‐B‐treated leaves were found to age more quickly than those of the controls. This analysis will enable future studies to take account of age‐related changes when interpreting the response of plants to any number of environmental stresses that affect leaf development.
Examination of the dehiscence zone in soybean pods and isolation of a dehiscence‐related endopolygalacturonase gene
Authors: Christiansen L. C. , Dal Degan F. , Ulvskov P. , Borkhardt B.
Published: March 2003

Microscopic examination of cross sections of dorsal and ventral sutures of soybean pods (Glycine max cv. TGx1835‐2E) at two different stages of maturity revealed that the dehiscence zone of soybean pods is functionally equivalent to the dehiscence zone known from crucifers. Enzymatic assays demonstrated the presence of endo‐1,4‐β‐glucanases and endopolygalacturonases, the activity of which accumulated in the dehiscence zone and peaked during maturation. A single partial cDNA encoding an endopolygalacturonase was isolated by polymerase chain reaction and this clone was used to isolate the complete gene encoding the endopolygalacturonase in question. Approximately 1·2 kb of 5′ upstream sequence was cloned in the plant transformation vector pCAMBIA1301 in front of the uidA (GUS) gene and transformed into Arabidopsis thaliana. Expression analysis of the soybean endopolygalacturonase transcript revealed that the endopolygalacturonase is primarily found in dehiscence‐related tissue and is presumably involved in the breakdown of the middle lamella prior to dehiscence. This result was corroborated by GUS stainings of the transgenic Arabidopsis lines
Changes in the acquisition and partitioning of carbon and nitrogen in the gibberellin‐deficient mutants A70 and W335 of tomato (Solanum lycopersicum L.)
Authors: Nagel O. W. , Lambers H.
Published: March 2003

Even though the growth‐promoting effects of gibberellins (GAs) in plants are well established, little is known about GA action on carbon metabolism and the available reports seem contradictory. We studied the effects of GA deficiency in mutants of tomato (Solanum lycopersicum L.) on rates of carbon acquisition and the allocation of acquired carbon to growth and respiration of leaves, stems and roots. Carbon budgets were calculated from 24 h measurements of photosynthesis and respiration. The partitioning of nitrogen compounds to leaves, stems and roots, which strongly influences carbon budgets, was also studied. The GA‐deficient mutants acquired less carbon per unit plant mass per day than did the wild type and used a larger fraction of it for root growth and root respiration. To find out to what extent these changes were just consequences of restriction of growth, the experiment was repeated at a low exponential nitrate addition rate, which forced all genotypes to grow at the same rate. Under these conditions, the low‐GA mutants still photosynthesized and respired faster and partitioned more carbon to root growth than the wild type did. The reasons for the observed differences in carbon economies between the wild type and the low‐GA mutants are discussed.
ATP citrate lyase: cloning, heterologous expression and possible implication in root organic acid metabolism and excretion
Authors: Langlade N. B. , Messerli G. , Weisskopf L. , Plaza S. , Tomasi N. , Smutny J. , Neumann G. , Martinoia E. , Massonneau A.
Published: March 2003

In order to cope with phosphate deficiency, white lupin produces bottle‐brushed like roots, so‐called cluster or proteoid roots which are specialized in malate and citrate excretion. Young, developing cluster roots mainly excrete malate whereas mature cluster roots mainly release citrate. Mature proteoid roots excrete four to six times more carboxylates compared with juvenile proteoid roots. Using a cDNA‐amplified restriction fragment length polymorphism (AFLP) approach we identified a gene coding for a putative ATP‐citrate lyase (ACL) up‐regulated in young cluster roots. Cloning of the lupin ACL revealed that plant ACL is constituted by two polypeptides (ACLA and ACLB) encoded by two different genes. This contrasts with the animal ACL, constituted of one polypeptide which covers ACLA and ACLB. The ACL function of the two lupin gene products has been demonstrated by heterologous expression in yeast. Both subunits are required for ACL activity. In lupin cluster roots, our results suggest that ACL activity could be responsible for the switch between malate and citrate excretion in the different developmental stages of cluster roots. In primary roots of lupin and maize, ACL activity was positively correlated with malate exudation. These results show that ACL is implicated in root exudation of  organic  acids  and  hence  plays  a  novel  role  in  addition to lipid synthesis. Our results suggest that in addition to lipid biosynthesis, in plants, ACL is implicated in malate excretion.
The relative impacts of daytime and night‐time warming on photosynthetic capacity inPopulus deltoides
Authors: TURNBULL M. H. , MURTHY R. , GRIFFIN K. L.
Published: March 2003

In order to investigate the relative impacts of increases in day and night temperature on tree carbon relations, we measured night‐time respiration and daytime photosynthesis of leaves in canopies of 4‐m‐tall cottonwood (Populus deltoidesBartr. ex Marsh) trees experiencing three daytime temperatures (25, 28 or 31 °C) and either (i) a constant nocturnal temperature of 20 °C or (ii) increasing nocturnal temperatures (15, 20 or 25 °C). In the first (day warming only) experiment, rates of night‐time leaf dark respiration (Rdark) remained constant and leaves displayed a modest increase (11%) in light‐saturated photosynthetic capacity (Amax) during the day (1000–1300 h) over the 6 °C range. In the second (dual night and day warming) experiment,Rdarkincreased by 77% when nocturnal temperatures were increased from 15 °C (0·36 µmol m−2 s−1) to 25 °C (0·64 µmol m−2 s−1).Amaxresponded positively to the additional nocturnal warming, and increased by 38 and 64% in the 20/28 and 25/31 °C treatments, respectively, compared with the 15/25 °C treatment. These increases in photosynthetic capacity were associated with strong increases in the maximum carboxylation rate of rubisco (Vcmax) and ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity mediated by maximum electron transport rate (Jmax). Leaf soluble sugar and starch concentration, measured at sunrise, declined significantly as nocturnal temperature increased. The nocturnal temperature manipulation resulted in a significant inverse relationship betweenAmaxand pre‐dawn leaf carbohydrate status. Independent measurements of the temperature response of photosynthesis indicated that the optimum temperature (Topt) acclimated fully to the 6 °C range of temperature imposed in the daytime warming. Our findings are consistent with the hypothesis that elevated night‐time temperature increases photosynthetic capacity during the following light period through a respiratory‐driven reduction in leaf carbohydrate concentration. These responses indicate that predicted increases in night‐time minimum temperatures may have a significant influence on net plant carbon uptake.
Spatial and temporal characteristics of dicarboximide‐resistant strains of Monilinia fructicola and brown rot incidence in stone fruit
Authors: Elmer P. A. G. , Gaunt R. E. , Frampton C. M.
Published: March 2003

The spatial and temporal distribution of dicarboximide‐resistant strains of Monilinia fructicola were investigated in six peach and nectarine orchard blocks in 1987–89 using a dispersion index (Lloyd's Patchiness Index, LPI), and spatial, temporal and spatio‐temporal autocorrelation analyses (Moran's Coefficient, I). The LPI values indicated that resistant strains were aggregated in all blocks in all years. Spatial correlations were not significant beyond one quadrat for any spatial proximity pattern in five of six blocks. Thus the spread of resistant strains was mostly restricted to the vicinity of the original focus. An absence of significant temporal correlation between years in five of the six blocks indicated poor persistence of resistant strains at specific locations. Only one significant temporal correlation was detected at one block and this could have arisen by chance. Significant spatio‐temporal correlation was not detected, suggesting that there was no focus expansion or carry‐over of resistant strain inoculum from the previous sampling date. Spatial, temporal and spatio‐temporal autocorrelation analyses were consistent with previously reported laboratory results that resistant strains had not acquired all the necessary characteristics to remain in, or dominate, field populations. The spatial pattern of brown rot incidence was investigated at one block in a separate study in 1988 and 1989. There were no significant spatial correlations for brown rot incidence in 1988 for any of the spatial proximity patterns analysed. In 1989, however, significant correlations indicated ellipsoid aggregates of brown rot orientated along the orchard rows.
Association of induction of protease and chitinase in chickpea roots with resistance to Fusarium oxysporum f.sp. ciceri
Authors: Giri  , Harsulkar  , Patankar  , Gupta  , Sainani  , Deshpande  , Ranjekar
Published: March 2003

To improve the breeding of chickpea varieties with resistance to Fusarium wilt, an attempt was made to analyse the biochemical basis of disease resistance by measuring levels of chitinase, β‐1,3‐glucanase, protease and proteinase inhibitor activities in dry and soaked seeds and in root and shoot tissues of wilt‐resistant and wilt‐susceptible cultivars. Marginal variation was observed in the levels of the candidate proteins in dry or soaked seeds. Chitinase activity was higher in roots than in shoots or cotyledons. No proteinase inhibitor activity was detected in root and shoot tissue of any of the cultivars. When the levels of these proteins were analysed in resistant (Vijay) and susceptible (JG‐62) cultivars during development of wilt by growing plants in soil infested with F. oxysporum f.sp. ciceri, race 1, both cultivars showed induction of chitinase activity in the roots. However, the induced activity in JG‐62 (3.82 U g−1) was equivalent to the constitutive level in Vijay (3.90 U g−1) and much lower than that induced in Vijay (5.18 U g−1). Induction of protease activity was observed only in root extracts of Vijay when challenged by the pathogen. The root extract of Vijay showed in vitro antifungal activity in a plate assay. Simultaneous induction of proteolytic and chitinolytic activities specifically in the resistant cultivar was correlated with antifungal properties of root extracts effective in conferring resistance.
The teleomorph stage, Mycosphaerella graminicola, in epidemics of septoria tritici blotch on winter wheat in the UK
Authors: Hunter  , Coker  , Royle
Published: March 2003

Earlier studies have shown that primary infections of winter wheat crops by septoria tritici blotch are initiated in autumn by air‐borne ascospores of the teleomorph stage, Mycosphaerella graminicola, which originate from sources outside the crop. Subsequent disease development within the crop, and damage to the upper leaves in summer, were commonly ascribed to the anamorph stage, Septoria tritici, which first arises from primary, ascosporic lesions and develops to give rise to splash‐borne pycnidiospores produced in pycnidia. Trapping studies, using a Burkard volumetric trap sited adjacent to field trials of winter wheat, showed that ascospores are released from pseudothecia throughout the year; peak release is not restricted to the autumn and early winter when the primary infections occur. As M. graminicola ascospores can be confused with those of other species, their authenticity was established by incubating ascospores on trap tapes for 24–48 h before counting. Examination of wheat plants cv. Riband, removed from unsprayed crops just prior to harvest and exposed to external weather conditions over the winter in 1995 and 1996, showed that pseudothecia mature on residues of the upper leaf layers between August and March. However, peak development occurred in December/January, when there was a corresponding decline in pycnidial formation. On regenerated wheat in set‐aside (left uncultivated) fields, sources of pseudothecia of M. graminicola were exhausted by February of the following year. Natural development of the teleomorph stage was monitored in an unsprayed crop of winter wheat cv. Riband during the 1996–97 season, and was present on leaf 8 at growth stage 32 (24 April) and on leaf 3 at growth stage 85 (8 July), then a week later, on both leaf 2 and the flag leaf. The temporal development of M. graminicola asexual and sexual phases was also studied in inoculation experiments under external weather conditions on pot‐grown seedlings of winter wheat cv. Longbow, using inoculum from two single‐ascospore cultures.
Effects of soil moisture, organic matter and grass mulching on the carpogenic germination of sclerotia and infection of bean by Sclerotinia sclerotiorum
Authors: Ferraz  , Café Filho  , Nasser  , Azevedo
Published: March 2003

Microplot experiments were carried out during the autumn and winter of 1995 to determine the effects of soil moisture and levels of organic matter on the carpogenic germination of Sclerotinia sclerotiorum and subsequent infection of Phaseolus vulgaris. Soil moisture treatments were established by irrigation to field capacity: (a) when soil had dried to − 25 KPa, (b) when soil had dried to − 54 KPa, and (c) eight days after the soil had dried to − 54 KPa. Three levels of organic matter were established by mixing compost and yellow‐red latosol in the following proportions (by volume): (a) 0% compost and 100% soil, (b) 50% compost and 50% soil, and (c) 100% compost and 0% soil. More apothecia and diseased plants were observed in the plots with higher moisture levels. Drier treatments resulted in a reduction in number (in the winter experiment) or elimination (in the autumn experiment) of apothecia. Other experiments were designed to examine the effect of grass mulching and organic matter levels on the carpogenic germination of S. sclerotiorum. In one experiment, grass mulching was compared with no mulching, and in another, the effects of different depths of mulch on the soil surface (0, 1.5, 3, 6 and 9 cm) were examined. Fewer apothecia were formed in mulched soil and the effect was most pronounced with 6 and 9 cm of mulch. The highest level of mulch (9 cm) impaired the vigour and yield of bean plants. In these experiments, carpogenic germination was increased by high soil organic matter content. Control of soil moisture and grass mulching may reduce the production of apothecia of S. sclerotiorum even in soils rich in organic matter.
Parasitism of macroconidia, chlamydospores and hyphae of Fusarium culmorum by mycoparasitic Pythium species
Authors: Davanlou  , Madsen  , Madsen  , Hockenhull
Published: March 2003

Parasitism of macroconidia and endoconidial chlamydospores of Fusarium culmorum by Pythium oligandrum was studied on water agar (WA), corn‐meal agar (CMA) and glass slides. Loss of cytoplasmic content in F. culmorum spores was followed by complete degradation, and P. oligandrum produced an abundance of oogonia on the parasitized macroconidia. A simple method for assessing the relative aggressiveness of isolates is presented, based on the percentage of macroconidial cells devoid of cytoplasm. Parasitism of macroconidia by P. acanthophoron, P. oligandrum and P. periplocum, but not by the plant pathogenic species, P. tracheiphilum, was demonstrated by this method. Interactions between hyphae of P. oligandrum and F. culmorum on WA resulted in an increase in the number of oogonia of P. oligandrum and a decrease in the sporulation of F. culmorum. The ability of isolates of P. oligandrum, P. periplocum, P. acanthophoron and P. mycoparasiticum to suppress disease symptoms caused by F. culmorum on barley seedlings was demonstrated in a greenhouse test.
Induction of systemic resistance to Sclerotiniasclerotiorum by oxalic acid in oilseed rape
Authors: Toal  , Jones
Published: March 2003

Treatment of the lowermost leaf of flowering plants of oilseed rape cv. Linetta with 20 m m oxalic acid induced systemic disease resistance in the three next youngest leaves. Resistance was not caused by the translocation of fungitoxic concentrations of oxalic acid. Resistance was also expressed in the stem; in oxalic acid‐treated plants the vertical spread of stem lesions was halted and the signal travelled both acropetally and basipetally. Expression of resistance in the leaves was detected 6 h after treatment and continued for at least 5 weeks. Twenty‐four h after treatment, resistance was detectable in the leaves following the use of as little as 0.5 m
m oxalic acid. Local resistance in the oxalic acid‐sprayed leaf was detectable only at certain times (12 and 48 but not 24 h after treatment) and at very low (0.25 m
m) or high (≥40 m
m) oxalic acid concentrations. When oxalic acid was applied to a discrete area of the leaf, significant local resistance was expressed in the surrounding leaf tissue, maximum resistance being exhibited by the tissue closest to the site of petiole attachment.
Serological variability among European isolates of radish mosaic virus
Authors: Špak J. , Kubelková D.
Published: March 2003

Serological variability of radish mosaic virus (RaMV) isolates from white mustard, winter turnip rape, Camelina sativa and Chinese cabbage, collected in the Czech Republic and Russia, was studied using antisera against the Czech isolate RaMV1. In contrast to previous studies, reasonable serological differences were found between isolates from different locations and hosts, and even between neighbouring mustard plants in the field. Serological variability of European isolates was confirmed in extended experiments involving an Italian isolate, the American Type Strain (ATS) and its homologous antiserum. The results indicate that, in Europe, RaMV isolates may occur which differ both serologically and in host plant response, but no typical strains can be defined with the methods and isolates employed so far. Camelina sativa is reported as a new host of the virus.
Infection of onion leaves by Alternaria porri and Stemphylium vesicarium and disease development in controlled environments
Authors: Suheri H. , Price T. V.
Published: March 2003

Infection of onion by Alternaria porri and Stemphylium vesicarium was investigated under a range of controlled temperatures (4–25°C) and leaf wetness periods (0–24 h). Conidia of A. porri and S. vesicarium germinated within 2 h when incubated at 4°C. Terminal and intercalary appressoria were produced at similar frequencies at or above 10°C. The maximum number of appressoria was produced after 24 h at 25°C. Penetration of leaves by both pathogens was via the epidermis and stomata, but the frequency of stomatal penetration exceeded that of epidermal penetration. There was a strong correlation (R2 > 90%) between appressorium formation and total penetrations at all temperatures. Infection of onion leaves occurred after 16 h of leaf wetness at 15°C and 8 h of leaf wetness at 10–25°C, and infection increased with increasing leaf wetness duration to 24 h at all temperatures. Interruption of a single or double leaf wetness period by a dry period of 4–24 h had little effect on lesion numbers. Conidia of A. porri and S. vesicarium separately or in mixtures caused similar numbers of lesions. Alternaria porri and S. vesicarium are both potentially important pathogens in winter‐grown Allium crops and purple leaf blotch symptoms were considered to be a complex caused by both pathogens.
Inheritance of partial resistance to black stem (Phoma macdonaldii) in sunflower
Authors: Roustaee A. , Barrault G. , Dechamp‐Guillaume G. , Lesigne P. , Sarrafi A.
Published: March 2003

Two programmes to investigate the inheritance of resistance to black stem in sunflowers were undertaken in a controlled‐environment growth chamber. In the first, an experiment was performed using a randomized complete block design with 24 lines, six male‐sterile (A lines), six maintainers (B lines), six restorers (R lines) and their six F1 hybrids in six replications. Each treatment consisted of 12 seedlings. Twelve‐day‐old seedlings were inoculated with a suspension of pycniospores, and 7 days later the two cotyledon petioles of each seedling were scored on a 1–9 scale for the percentage of necrotic area. Some alloplasmic lines (which have the same nucleus and different cytoplasms) gave a significant cytoplasmic effect for improved partial resistance to the disease. Deviation of F1 hybrids from the mean of the parent values was significant for partial resistance to Phoma macdonaldii in three of the six F1 hybrids. Two further experiments with eight lines (resistant and susceptible) at the fifth leaf‐pair and flowering stages were carried out under the same conditions. At both growth stages the previous classification of lines at the seedling stage was confirmed. In the second programme, five male‐sterile sunflower lines were crossed with five fertility‐restorers in a factorial mating design. The 10 inbred lines and their 25 F1 hybrids were studied in two successive experiments under the same conditions and with the same experimental design and isolate of Phoma as in the seedling‐stage experiment in the first programme. Analysis of variance showed that male‐sterile and restorer lines possessed general combining abilities, and also that specific combining abilities of F1 hybrids were significant. The estimates of general combining ability for partial resistance were significant in AS617A, AS618A and AS614R inbred lines. These lines are available for developing F1 hybrids with improved resistance to Phoma in sunflower‐breeding programmes.
Occurrence of Fusarium‐produced naphthazarins in citrus trees and sensitivity of rootstocks to isomarticin in relation to citrus blight
Authors: Janse van Rensburg J. C. , Labuschagne N. , Nemec S.
Published: March 2003

Fusarium solani, the causal fungus of root and crown rot of citrus, produces naphthazarin toxins that were shown to be toxic to citrus plants. It was found that citrus trees in South Africa had varying levels of naphthazarins in their xylem. Significantly higher concentrations of these toxins were detected in trees with blight symptoms than in symptomless trees. Citrus seedlings grown in hydroponic culture containing isomarticin showed inhibition of growth, shortening of roots and accumulation of zinc in the trunk wood. Zinc deficiency symptoms were also observed on certain rootstocks. A procedural ranking of rootstocks indicated that trees with observed tolerance to blight in the field generally had higher tolerance to isomarticin in hydroponic culture, whereas trees susceptible to blight were more sensitive to the toxin. These findings indicate that Fusarium‐produced isomarticin is involved in the induction of some of the symptoms associated with citrus blight syndrome.
Occurrence and distribution of Raspberry bushy dwarf virus in commercial Rubus plantations in England and Wales
Authors: Barbara D. J. , Morton A. , Ramcharan S. , Cole I. W. , Phillips A. , Knight V. H.
Published: March 2003

Serological surveys for Raspberry bushy dwarf virus (RBDV) made between 1995 and 1997 and covering ≈ 10% of the commercial farms growing Rubus (red raspberry and hybrid berries) in England and Wales showed that this virus was present on approximately one‐quarter of all farms and in approximately one‐sixth of all plots tested. RBDV was found in all of the four main raspberry cultivars being grown at that time (Autumn Bliss, Glen Moy, Glen Prosen and Leo), in Loganberry and in Tayberry. Fifteen RBDV genotypes (including two that appeared to be mixed) were identified using RT‐PCR/RFLPs, but the majority of genotypes were found only rarely. Of the RBDV isolates tested, two genotypes each comprised 12·5% and another 46·4%. None of the three most common genotypes was associated solely with single Rubus cultivars and vice versa. It is suggested that two separate outbreaks of RBDV are occurring in England and Wales. One outbreak comprises the most frequent genotype combined with one of the moderately frequent genotypes; this outbreak is largely confined to the main growing areas and is either spreading between farms or coming from multiple local sources. Circumstantial evidence suggests that these isolates (and hence this first outbreak) are of the RB pathotype. The second outbreak consists of the other moderately frequent genotype and those genotypes which are less common. These genotypes appear to be more scattered across England and Wales and seem more likely to be coming from local sources and not to be spreading naturally between commercial farms.
Novel in vivo use of a polyvalent Streptomyces phage to disinfest Streptomyces scabies‐infected seed potatoes
Authors: McKenna F. , El‐Tarabily K. A. , Hardy G. E. ST. J. , Dell B.
Published: March 2003

A highly virulent and polyvalent Streptomyces phage was isolated from a potato field near Albany, Western Australia. The efficacy of the isolated phage to disinfest seed potato tubers artificially inoculated with a common scab‐causing streptomycete was evaluated. The phage suspension was prepared in a mini‐bioreactor. Diseased potatoes were bathed in a phage suspension (1 × 109 plaque‐forming units per mL) for 24 h. The suspension was constantly circulated within a novel 25 L phage bath by means of an air‐sparging pipe driven from an air compressor. Phage‐treated scab‐affected seed potatoes planted into free‐draining polystyrene boxes containing steam‐pasteurized field soil produced tuber progeny with significantly (P < 0·05) reduced levels of surface lesions of scab (1·2%) compared with tubers harvested from nonphage‐treated tubers (23%). The number of scab lesions was also significantly reduced (P < 0·05) by phage treatment of mother tubers. No significant differences were recorded in weight, size or number of harvested tubers from phage‐treated or nontreated mother tubers. This is the first in vivo study that has used Streptomyces phage to significantly disinfest seed potatoes of Streptomyces scabies and thereby reduce contamination of soil from seed‐tuber‐borne inoculum and reduce infection of daughter tubers.
Comparison of viral RNA populations of pathogenically distinct isolates of Citrus tristeza virus : application to monitoring cross‐protection
Authors: Sambade A. , Rubio L. , Garnsey S. M. , Costa N. , Müller G. W. , Peyrou M. , Guerri J. , Moreno P.
Published: March 2003

The population of sequence variants of Citrus tristeza virus (CTV) isolates of different geographic origins and pathogenicity properties was characterized by single‐strand conformation polymorphism (SSCP) analysis of cDNA of the genes p18, p13, p20 and p23. The mild isolates analysed here usually yielded a SSCP profile with two DNA bands, suggestive of a predominant sequence variant, whereas the SSCP profile of the most virulent isolates contained more than two DNA bands, indicating that their viral populations are likely to be more complex. The set of SSCP profiles of the four genes allowed identification of individual isolates, but no profile characteristic of a geographic area or a biogroup was found. Sweet orange plants singly inoculated with a mild or with a severe isolate yielded the SSCP profile characteristic of each isolate, whereas the SSCP profile of plants successively inoculated with both isolates was a composite of the two individual profiles. The SSCP profile of plants singly inoculated remained constant, but the profile of doubly inoculated plants varied with time. Plants in which the SSCP profile of the severe isolate became predominant showed stem pitting, and those in which the predominant profile corresponded to the mild isolate remained symptomless. The results indicate that SSCP analysis can be used to study changes in RNA populations of doubly inoculated plants and to monitor cross‐protection between mild and severe isolates.
Detection of airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae in oilseed rape crops by polymerase chain reaction (PCR) assays
Authors: Calderon C. , Ward E. , Freeman J. , Foster S. J. , McCartney H. A.
Published: March 2003

The potential use of DNA‐based methods for detecting airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae, both damaging pathogens of oilseed rape, was investigated. A method for purifying DNA from spores collected using Hirst‐type spore samplers and detecting it using polymerase chain reaction (PCR) assays is described. For both pathogens, the sensitivities of the DNA assays were similar for spore‐trap samples and pure spore suspensions. As few as 10 spores of L. maculans or P. brassicae could be detected by PCR and spores of both species could be detected against a background of spores of six other species. The method successfully detected spores of P. brassicae collected using spore traps in oilseed rape crops that were infected with P. brassicae. Leptosphaeria maculans spores were detected using spore traps on open ground close to L. maculans‐infected oilseed rape stems. The potential use of PCR detection of airborne inoculum in forecasting the diseases caused by these pathogens is discussed.
Crosses between isolates of Phytophthora infestans from potato and tomato and characterization of F1 and F2 progeny for phenotypic and molecular markers
Authors: Knapova G. , Schlenzig A. , Gisi U.
Published: March 2003

Nineteen crosses were carried out in vitro between seven and nine isolates of Phytophthora infestans originating from potato and tomato, respectively. Oospores were produced abundantly in all but two crosses, but oospore germination was generally low (a few per cent) and depended on the combination of parental isolates. The highest fertility in F1 progeny was observed when at least one parental isolate originated from tomato, and the lowest in crosses of isolates from potato; half the crosses were not fertile. Forty‐three F1 and 51 F2 single‐oospore progeny of a selected cross, along with the 16 field isolates, were analysed phenotypically and with molecular markers. Phenotypic characterization included mating type; sensitivity to the phenylamide fungicide metalaxyl‐M; specific virulence on potato R‐gene differentials; and aggressiveness (infected leaf area) on potato and tomato leaf discs (host preference). Isolates and progeny were also assessed for mitochondrial DNA haplotype with RFLP–PCR (restriction fragment length polymorphism–polymerase chain reaction), and characterized with AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeats, microsatellites). Parental isolates were sensitive and resistant to metalaxyl‐M, whereas all F1 were intermediate phenotypes. In the F2 progeny, the majority of isolates (43 of 51) were intermediate in sensitivity and four each were sensitive and resistant to metalaxyl‐M, respectively. In both F1 and F2 progeny, four isolates emerged through selfing. The A1 : A2 ratio was 25 : 18 in F1 and 24 : 21 (plus six self‐fertiles) among the F2 progeny. Many F1 progeny isolates were highly aggressive on both hosts, but 15 and 23% of isolates preferred tomato and potato, respectively. Among F2 progeny, few highly aggressive isolates were recorded and a quarter of isolates lost pathogenicity almost completely. Isolates preferring tomato increased, and those preferring potato significantly decreased in the F2 progeny. Inheritance of mitochondrial haplotype in F1 progeny was uniparental and mostly (25 of 27) from one parent only. Six and four different SSR genotypes were identified in F1 and F2 progeny, respectively, of which two were identical to the parents. The two microsatellite loci, 4B and 4G, segregated in the ratios 15 : 22 : 2 and 22 : 17 in F1 and 24 : 17 and 26 : 15 in F2 progeny, respectively, while the majority of AFLP markers segregated in either a 1 : 0, 1 : 1, 3 : 1 or 1 : 2: 1 ratio. There was no obvious association between AFLP and SSR genotypes, nor between genotypic and phenotypic traits.
T‐Cell Reactivity to Wheat Gluten in Patients with Insulin‐Dependent Diabetes Mellitus
Authors: Klemetti  , Savilahti  , Ilonen  , Åkerblom  , Vaarala
Published: March 2003

Dietary wheat gluten has been associated with the risk of diabetes in animal models of human insulin‐dependent diabetes mellitus (IDDM). To evaluate the role of wheat gluten as a T cell antigen in human IDDM, we studied the cell‐mediated immune response to wheat gluten in patients with IDDM and in control subjects. The cellular response to gluten was measured by the peripheral blood mononuclear cell (PBMC) proliferation test, and the results were expressed as a stimulation index (SI). We observed an enhanced cellular immune response to gluten (SI ≥ 3) in seven of 29 patients with newly diagnosed IDDM (24.1%), in six of 39 patients with a longer duration of IDDM (15.4%), and in two of 37 non‐diabetic controls (5.4%). Reactivity of T cells to gluten was associated with IDDM at diagnosis (P = 0.03), whereas patients with longer duration of IDDM did not differ from controls (P = 0.16). Responses of T cells to gluten were low in general: the median SI (range) was 2.0 (1–8.6) in patients with newly diagnosed IDDM and 1.5 (1–5.8) in control subjects (P = 0.03). Cellular responsiveness to gluten was not associated with HLA‐DQB1 risk alleles for IDDM in patients. Although T cell responses to gluten were slightly increased in newly diagnosed patients the responsiveness was rare, and thus our results do not support a major role of gluten in the pathogenesis of human IDDM.
Staphylococcal Enterotoxin‐A‐Induced In‐Vitro Adhesion of HL‐60 Cells to Endothelial Cells Involves both Selectin and Integrin Families of Cell Adhesion Molecules
Authors: Srinivas  , Dohlsten  , Kalland T , Lundblad
Published: March 2003

In‐vivo exposure to the bacterial superantigen Staphylococcal enterotoxin‐A (SEA) induces an inflammatory response characterized by rapid extravasation of leucocytes and release of excessive amounts of cytokines. We have utilized an in‐vitro adhesion assay to understand the molecular mechanisms responsible for SEA‐induced extravasation of leucocytes. Stimulation of human umbilical cord endothelial cells (HUVEC) with increasing concentrations of recombinant SEA (rSEA) did not influence the in‐vitro adhesion of HL‐60 cells to HUVEC, whereas stimulation of HUVEC by interleukin (IL)‐1β supported adhesion of HL‐60 cells. Increased adhesion of HL‐60 cells to HUVEC was noted upon stimulation of endothelium with culture medium obtained from human peripheral blood mononuclear cells (PBM) stimulated with recombinant SEA for 24 (CM–SEA 24 h), 72 (CM–SEA 72 h) and 120 h (CM–SEA 120 h), but not after stimulation with culture medium obtained from control human peripheral blood mononuclear cells (CM), suggesting that soluble factors present in the supernatants play a major role in SEA‐induced cell adhesion. While CM–SEA 24 and 72 h induced both a rapid (4 h) and delayed type of adhesion, CM–SEA 120 h only induced a delayed type of adhesion. Stimulation of PBM by SEA resulted in increased levels of IL‐1β, IL‐2 and interferon (IFN)‐γ after 24 h. Further stimulation for 72–120 h resulted in a significant increase in the levels of IL‐1β, IFN‐γ and tumour necrosis factor (TNF). Stimulation of PBM with SEA also resulted in increased levels of soluble and L‐selectin in the cell supernatants. Increased cell‐surface expression of E‐selectin, ICAM‐1, HLA‐DR and VCAM‐1 was detected on HUVEC stimulated with CM–SEA media. While E‐selectin and VCAM were induced on HUVEC within a few hours, induction of ICAM and HLA‐DR required a longer induction period. Adhesion of HL‐60 cells to HUVEC treated with CM–SEA was inhibited by monoclonal antibodies (MoAbs) against both the selectin and integrin families of cell adhesion molecules, suggesting that multiple pathways contribute to SEA‐induced leucocyte extravasation. The results suggested that selectin‐dependent adhesion was more prominent during the early phase while integrin‐induced adhesion occurred at a later stage.
An Immunoaffinity‐Purified Trypanosoma cruzi Antigen Suppresses Cellular Proliferation through a TGF‐β‐Mediated Mechanism
Authors: Hansen  , Villacres‐Eriksson  , Åkerblom  , Hellman  , Segura  , Carlomagno  , Morein
Published: March 2003

Two subfractions with opposite immunological properties were obtained from the flagellar antigens (FF) of Trypanosoma cruzi epimastigotes by immunoaffinity chromatography. The ligand‐bound material (Ag 123) contained four polypeptide bands of 97, 55, 38 and 14 kDa. The nonretained flow‐through (FT), induced a potent proliferation of murine naive splenocytes. In contrast, Ag 123 inhibited the proliferative capacity of the FT as well as the proliferation mediated by the mitogen Concanavalin A (Con A). The suppressive effect of Ag 123 on the Con A‐mediated proliferation was neutralized by an anti‐TGF‐β monoclonal antibody. Both Ag 123 and FF stimulated high serum levels of TGF‐β in injected mice. Ag 123 also induced in vitro secretion of TGF‐β by murine splenocytes. These results demonstrate that Ag 123 is a potent stimulator of TGF‐β both in vivo and in vitro. Oligopeptides derived from the 38 kDa protein present in Ag 123 showed homology with human and rat alpha‐fetoproteins (AFP). Ag 123 seems to have a key role in the immunosuppression that develops during early stages in the infection with T. cruzi.
Cloning and Expression of Ragweed Allergen Amb a 6
Authors: Hiller  , Lubahn  , Klapper
Published: March 2003

We have cloned the protein coding region of an isoform of short ragweed allergen Amb a 6 (Ra6) and expressed the secreted product in Pichia pastoris at mg/l levels. 5′ RACE was performed using sequence obtained from a partial Amb a 6 clone. This yielded a product whose deduced protein sequence has a characteristic signal sequence motif at the N‐terminus followed by sequence consistent with that previously published for highly purified Amb a 6 [Roebber et al. J Immunol 1983;131:706–11]. The region encoding the secreted product was amplified by PCR and cloned into pPICZαa, an expression vector for the yeast Pichia pastoris. Yeast transformed with this vector secrete a protein which migrates near Amb a 6 in SDS–PAGE. This secreted protein reacts with polyclonal anti‐Amb a 6 antisera as well as an anti‐Amb a 6 monoclonal antibody, and has the N‐terminal sequence of Amb a 6. By time‐of‐flight mass spectrometry, recombinant Amb a 6 has a molecular weight of 9884 ± 0.2%. In addition to the deduced amino acid sequence of an Amb a 6 clone, the amino acid sequence of Amb a 6 protein is reported for comparison. The amino acid sequence was obtained by aligning overlapping tryptic and chymotryptic peptides from enzymatic digests of extensively reduced and alkylated Amb a 6. Sequences from at least three closely related Amb a 6 isoforms are present among these peptides. The amino acid sequence closely matches the deduced amino acid sequence of the Amb a 6 clone.
γδ T‐Cell Precursor‐Derived CD4− CD8−αβ T Cells Retain γδ Cell Function
Authors: Fritsch  , Ivars
Published: March 2003

We have previously shown that some of the DNαβ+ T cells arising in TcRα‐chain transgenic mice are of γδ T cell origin, based on phenotypic data and on their status of TcR gene rearrangements. In the present report we investigated the impact of αβ TcR expression on the functional programme of the mature γδ precursor‐derived DNαβ+ T cells. Our results demonstrate that both their proliferative capacity and their cytokine production profile are similar to that of γδ T cells. Furthermore, both transgenic DNαβ+ T cells and DNγδ+ T cells up‐regulate CD8α expression after activation, but, in contrast to CD4+αβ T cells, are unable to induce proliferation of naive B cells. Thus, our results suggest that the effector functions of mature T cells are determined independently of the TcR isotype, probably at an early stage of differentiation, and thereby have important implications for current models of T‐cell lineage commitment.
Release of the Soluble Co‐Receptor (Protein Fv) of Secretory Immunoglobulins after Colonization of Axenic Rats by the Human Gut Microflora
Authors: Andrieux  , Pires  , Moreau  , Bouvet
Published: March 2003

The presence of protein Fv (pFv), a soluble co‐receptor of human gut antibodies, was investigated in heteroxenic rats as a function of the presence of the human digestive microflora. This endogenous molecule was not detected in the stools of axenic rats but was found in those of heteroxenic animals. The release was delayed for 1 week after colonization and found to be independent from the kinetics of bacteria‐induced short‐chain fatty acids issued from the catabolism of carbohydrates and of proteins. The similar bacterial composition of pFv‐positive and of pFv‐negative stools, and the lack of induction by different dominant bacterial genera, suggest that non‐dominant species must be involved. These results indicate that human colonic flora is a major inducer of pFv and thus participates in increasing the efficiency of the intestinal immunity by this additional mechanism known to maintain and augment the polymeric status of secretory immunoglobulin (Ig)A.