Home About us Contact
|
Home About us Contact | ||
|
|
||
Leaf Tissue (leaf + tissue)
Selected AbstractsBiochemical Changes in Leaf Tissues of Taro [Colocasia esculenta L. (Schott)] Infected with Phytophthora colocasiaeJOURNAL OF PHYTOPATHOLOGY, Issue 3 2010Manas Ranjan Sahoo Abstract The changes in some biochemical parameters due to Phytophthora leaf blight infection were assessed in leaf tissues of one resistant (DP-25), two moderately resistant (Duradim and Jhankri) and one susceptible (N-118) genotypes of taro [Colocasia esculenta (L.) Schott]. Phytophthora spore suspension (15 000 spore/ml water) was sprayed onto the in vitro raised taro plantlets at 30 days after establishment in pots to induce disease. In comparison with the uninoculated leaves, blight infected leaves showed reduction in protein content and activity of nitrate reductase and increase in total soluble sugar, reducing sugar content and activities of acid phosphatase and alkaline phosphatase among the studied genotypes. Changes in biochemical parameters under induced blight stress as compared with uninoculated control were less in resistant genotypes than that in susceptible genotype. The deviations in biochemical contents were highest in susceptible genotype N-118. Based on the variations of above parameters under stress and non-stress control among the four tested genotypes, the overall pattern of changes was N-118 > Duradim > Jhankri > DP-25, which is in accordance with the pattern of increasing resistance. The resistant genotypes could be used for commercial cultivation and genetic improvement programme to develop resistant varieties to Phytophthora leaf blight disease. [source] Tomato spotted wilt virus in peanut tissue types and physiological effects related to disease incidence and severity,PLANT PATHOLOGY, Issue 4 2005D. Rowland Three peanut cultivars, Georgia Green, NC-V11, and ANorden, were grown using production practices that encouraged the development of Tomato spotted wilt virus (TSWV). The progression of TSWV infection was examined through the season using enzyme-linked immunosorbent assay (ELISA) tests on different tissue types [roots, leaves, pegs (pod attachment stem structures) and pods] and the effect of TSWV infection on physiological functions was examined at three harvest dates. Plants were classed into three severity categories: (i) no TSWV symptoms or previous positive ELISA tests; (ii) less than 50% of leaf tissue exhibiting TSWV symptoms; and (iii) greater than 50% of leaf tissue affected. TSWV showed a slow rate of infection at the beginning of the season and a greater percentage of infection of the roots than in the leaves. Photosynthesis was reduced in virus-affected infected plants by an average of 30% at the mid-season harvest and 51% at the late season harvest compared with virus-free plants across all three cultivars. Leaf tissue with symptoms had lower photosynthetic rates than healthy leaves. There were small differences among cultivars, with cv. ANorden maintaining higher average photosynthetic levels than cv. Georgia Green and higher transpirational levels than cv. NC-V11. The ability to maintain high assimilation physiology in the presence of the virus may help cultivars withstand TSWV infection and maintain final yields. [source] Survey of the incidence and distribution of viruses infecting yam (Dioscorea spp.) in Ghana and TogoANNALS OF APPLIED BIOLOGY, Issue 2 2010A.O. Eni Yam leaves were collected during surveys of major yam producing agro-ecological zones (AEZs) in Ghana (n = 628) and Togo (n = 218) respectively, in 2005. Leaf tissues were tested for Cucumber mosaic virus (CMV), Dioscorea mottle virus (DMoV), Yam mild mosaic virus (YMMV), Yam mosaic virus (YMV) and badnaviruses by enzyme-linked immunosorbent assay (ELISA), immunocapture-polymerase chain reaction (IC-PCR) and/or IC-reverse transcription-PCR (IC-RT-PCR). Eighty-one percent (370/459) and 78.9% (127/161) of symptomatic leaf samples from Ghana and Togo, respectively and 56.2% (95/169) and 57.9% (33/57) of non-symptomatic leaf samples, reacted positive to CMV, YMMV, YMV and/or badnaviruses, but DMoV was not detected. The highest incidence of YMV and badnaviruses was observed in the forest,savannah transition and Guinea savannah AEZ respectively in Ghana. In Togo, incidence of badnaviruses across the four AEZ ranged from 50 to 57.9%; however, Savane Derivée Seche AEZ had the highest incidence of badnaviruses (57.9%), YMV (34.2%) and CMV (7.9%). Mixed infection of badnaviruses and YMMV was the most frequent (105 of 276 mixed infections) in the two countries and Dioscorea alata was more heavily infected than D. rotundata in both countries. [source] Contribution of fungal biomass to the growth of the shredder, Pycnopsyche gentilis (Trichoptera: Limnephilidae)FRESHWATER BIOLOGY, Issue 11 2009NAMIL CHUNG Summary 1.,1. It has been accepted that aquatic hyphomycetes colonising submerged leaves increase the nutritional value of leaf detritus and suggested that fungal biomass plays a greater role in the growth of shredders than leaf tissue itself. However, it is not clear what proportion of the nutritional needs of shredders is met by fungal biomass. 2.,We fed Pycnopsyche gentilis larvae with tulip poplar (Liriodendron tulipifera) leaf discs colonised by the aquatic hyphomycete, Anguillospora filiformis, which had been radiolabelled to quantify the contribution of fungal carbon to the growth of the shredder at different larval developmental stages. Instantaneous growth rates of larvae on this diet were also estimated. 3.,When provided with fungal-colonised leaves (14,16% fungal biomass), the third and the fifth instar larvae of P. gentilis grew at the rates of 0.061 and 0.034 day,1, respectively, but on a diet of sterile leaves, both larval instars lost weight. The incorporation rates of fungal carbon were 31.6 ,g C mg,1 AFDM day,1, accounting for 100% of the daily growth rate of the third instar larvae and 8.6 ,g C mg,1 AFDM day,1, accounting for 50% of the daily growth rate of the fifth instar larvae. 4.,These results suggest that leaf material colonised by A. filiformis is a high quality food resource for P. gentilis larvae, and that fungal biomass can contribute significantly to the growth of these larvae. Differences in feeding behaviour and digestive physiology may explain the significantly greater assimilation of fungal biomass by the earlier instar than the final instar. To satisfy their nutritional needs the fifth instar larvae would have to assimilate detrital mass that may have been modified by fungal exoenzymes. [source] Plant functional group identity influences short-term peatland ecosystem carbon flux: evidence from a plant removal experimentFUNCTIONAL ECOLOGY, Issue 2 2009Susan E. Ward Summary 1Northern hemisphere peatlands are globally important stores of organic soil carbon. We examined effects of plant functional group identity on short-term carbon (C) flux in an ombrotrophic peatland in northern England, UK, by selectively removing one of each of the three dominant plant functional groups (ericoid dwarf-shrubs, graminoids and bryophytes). Carbon dynamics were quantified by a combination of CO2 flux measurements and 13CO2 stable isotope pulse labelling approaches. 2Significant effects of plant functional group removals on CO2 fluxes and tracer 13C uptake and turnover were detected. Removal of ericoid dwarf-shrubs had the greatest influence on gross CO2 flux, increasing rates of respiration and photosynthesis by > 200% relative to the undisturbed control. After pulse labelling with 13CO2, we found that turnover of recent photosynthate, measured as respired 13CO2, was also greatest in the absence of dwarf-shrubs. 3Analysis of 13C tracer enrichment in leaf tissues from all plant removal treatments showed that the rate of fixation of 13CO2 and turnover of 13C labelled photosynthate in leaf tissue was greatest in graminoids and lowest in bryophytes. Furthermore, graminoid leaf 13C enrichment was greatest when growing in the absence of dwarf-shrubs, suggesting that the presence of dwarf-shrubs reduced the photosynthetic activity of graminoids. 4We conclude that plant functional groups differentially influence the uptake and short-term flux of carbon in peatlands, suggesting that changes in the functional composition of vegetation resulting from global change have the potential to alter short-term patterns of carbon exchange in peatland. [source] Chlorophyll fluorescence, predawn water potential and photosynthesis in precipitation pulse-driven ecosystems , implications for ecological studiesFUNCTIONAL ECOLOGY, Issue 3 2008V. Resco Summary 1A major research focus in population and community ecology is to establish a mechanistic understanding of plant interactions and demographic responses. The first step towards this mechanistic approach relies on understanding the differences in stress caused by different environmental conditions. Leaf-level photosynthetic rate (A) within and among plant populations provides important insight into population and community processes, but is difficult to acquire with sufficient replication under field conditions. Instead, chlorophyll fluorescence (Fv/Fm) and predawn water potential (,pd) are often used in arid and semi-arid ecosystems. 2Fv/Fm reflects the photoactivation status of photosystem II (PSII), whereas ,pd indicates water availability in the rhizosphere. Here we compare these indices with A in two perennial C4 grasses (native Heteropogon contortus and invasive Eragrostis lehmanniana) and in seedlings of the C3 shrub Prosopis velutina growing on highly contrasting sandy loam and loamy clay soils in experimental plots. Measurements were made the day prior to and up to 7 days following a 39-mm rainfall pulse after 2 months of drought. 3A was more sensitive across a broad range of environmental conditions, whereas Fv/Fm and ,pd only responded to periods of protracted drought. The use of these measures was further complicated because their values varied daily and we observed different time-lags in their response to precipitation pulses. 4We suggest sampling schemes and a priori measurements to capture the value that is representative for the question of interest, and that match the pulsed biological activity in these ecosystems. Finally, we suggest the use of these measures in combination with measurements providing integration over longer time periods, such as ,13C, ,18O and N concentration in bulk leaf tissue. [source] Effects of climate change on labile and structural carbon in Douglas-fir needles as estimated by ,13C and Carea measurementsGLOBAL CHANGE BIOLOGY, Issue 11 2002ERIC A. HOBBIE Abstract Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2 but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar Carea (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (,13C) caused by inputs of 13C-depleted CO2 to estimate labile and structural C in needles of different ages in a four-year, closed-chamber mesocosm experiment in which Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO2 (ambient + 179 ppm). Declines in ,13C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The ,13C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second- and third-year needles, respectively, with higher proportions of new C in elevated than ambient CO2 chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second-year needles). Relative to ambient CO2, elevated CO2 increased labile C in both first- and second-year needles. Relative to ambient temperature, elevated temperature diminished labile C in second-year needles but not in first-year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant-soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations suggested that labile C was primarily determined by carbohydrates. Labile C was negatively correlated with concentrations of cellulose and protein. Elevated temperature increased foliar %C, possibly due to a shift of labile constituents from low %C carbohydrates to relatively high %C protein. Decreased sugar concentrations and increased nitrogen concentrations with elevated temperature were consistent with this explanation. Because foliar constituents that vary in isotopic signature also vary in concentrations with leaf age or environmental conditions, inferences of ci/ca values from ,13C of bulk leaf tissue should be done cautiously. Tracing of 13C through foliar carbon pools may provide new insight into foliar C constituents and turnover. [source] Poor host plant quality causes omnivore to consume predator eggsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2003Arne Janssen Summary 1Omnivorous arthropods are known to change their diet when host plant quality is low. Consequently, it has been suggested that decreased plant quality has a twofold negative effect on herbivore populations: (1) a decrease in growth rate of herbivores; (2) omnivores include more herbivores in their diet. We hypothesized that decreased host plant quality may also cause omnivores to feed on predators, including their own enemies. 2We tested this hypothesis, using the omnivorous western flower thrips. This species is known to feed on many plant species, but also on the eggs of another herbivore, the two-spotted spider mite. Previous research has shown that a decrease in plant quality leads to increased feeding on spider mite eggs by western flower thrips. Western flower thrips also kill the eggs of various predatory mites, including those of the specialist predator of spider mites and those of a predatory mite that attacks western flower thrips itself. 3In this paper we investigate whether thrips larvae kill predator eggs to feed on them and whether this predation depends on host plant quality. 4Larval survival as well as developmental rate increased when plant tissue of low quality (sweet pepper) was supplemented with eggs of two predatory mite species or when it was supplemented with pollen, a high-quality food type. 5Supplementing high quality leaf tissue (cucumber) with predator eggs did not lead to increased survival and developmental rate. Thrips larvae fed significantly less on predatory mite eggs when pollen was available. 6Thus, thrips larvae indeed feed on predator eggs, including those of their predator, and they feed more on predator eggs when host plants are of low quality. [source] Approaching risk assessment of complex disease development in horse chestnut trees: a chemical ecologist's perspectiveJOURNAL OF APPLIED ENTOMOLOGY, Issue 5 2008A. B. Johne Abstract The chemo-ecological predispositions were investigated for the development of a complex disease on the basis of an insect,fungus mutualism using the system of horse chestnuts (Aesculus hippocastanum and Aesculus x carnea), the horse chestnut leaf miner (Cameraria ohridella) and the biotrophic powdery mildew (Erysiphe flexuosa). Both C. ohridella and E. flexuosa can appear on the same horse chestnut leaf tissue simultaneously. The olfactory detection of fungal infection by the insect, its ability to discriminate the potentially mutualistic fungus from other fungi and the impact of fungal infection on insect oviposition were examined. Gas chromatography coupled with mass spectroscopic and electroantennographic detection by C. ohridella (GC-MS/EAD) was used to assess the olfactory detection of fungal-infected A. hippocastanum and A. x carnea leaves by C. ohridella. Infection-related compounds, such as benzyl alcohol, dodecane, tridecane and methyl salicylate as well as fungus-related C8 compounds, are perceived by C. ohridella. The discrimination of E. flexuosa from another phytopathogenic fungus, such as Guignardia aesculi, is based primarily on the differing pattern of C8 compounds of these fungi. Oviposition on fungal-infected leaves of A. hippocastanum and leaves treated with fungal-related compounds showed that C. ohridella is able to respond to the modifications in the leaf volatile profiles of horse chestnuts caused by the different fungal infections. Thus, from the perception point of view, the necessary predispositions for the development of a close insect,fungus relation between the biotrophic fungus E. flexuosa and the leaf-mining insect C. ohridella are fulfilled. However, decreased oviposition on infected leaves does not enhance the selective contact between the species. As a consequence, an important predisposition for forming an insect,fungus mutualism is not fulfilled by these two species and, according to this approach, the risk of forming a complex disease can be assessed as low. [source] Interactions of Salmonella enterica with lettuce leavesJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009Y. Kroupitski Abstract Aims:, To investigate the interactions of Salmonella enterica with abiotic and plant surfaces and their effect on the tolerance of the pathogen to various stressors. Methods and Results:,Salmonella strains were tested for their ability to form biofilm in various growth media using a polystyrene plate model. Strong biofilm producers were found to attach better to intact Romaine lettuce leaf tissue compared to weak producers. Confocal microscopy and viable count studies revealed preferential attachment of Salmonella to cut-regions of the leaf after 2 h at 25°C, but not for 18 h at 4°C. Storage of intact lettuce pieces contaminated with Salmonella for 9 days at 4°C resulted only in small changes in population size. Exposure of lettuce-associated Salmonella cells to acidic conditions (pH 3·0) revealed increased tolerance of the attached vs planktonic bacteria. Conclusions:, Biofilm formation on polystyrene may provide a suitable model to predict the initial interaction of Salmonella with cut Romaine lettuce leaves. Association of the pathogen with lettuce leaves facilitates its persistence during storage and enhances its acid tolerance. Significance and Impact of the Study:, Understanding the interactions between foodborne pathogens and lettuce might be useful in developing new approaches to prevent fresh produce-associated outbreaks. [source] Linking physiological traits to impacts on community structure and function: the role of root hemiparasitic Orobanchaceae (ex-Scrophulariaceae)JOURNAL OF ECOLOGY, Issue 1 2005G. K. PHOENIX Summary 1The hemiparasitic Orobanchaceae (ex-Scrophulariaceae) are characterized by a distinctive suite of ecophysiological traits. These traits have important impacts on host plants and non-host plants, and influence interactions with other trophic levels. Ultimately, they can affect community structure and functioning. Here, we review these physiological traits and discuss their ecological consequences. 2The root hemiparasitic Orobanchaceae form a convenient subset of the parasitic angiosperms for study because: they are the most numerous and most widely distributed group of parasitic angiosperms; their physiological characteristics have been well studied; they are important in both agricultural and (semi)natural communities; and they are tractable as experimental organisms. 3Key traits include: high transpiration rates; competition with the host for nutrients and haustorial metabolism of host-derived solutes; uptake of host-derived secondary metabolites; dual autotrophic and heterotrophic carbon nutrition; distinct carbohydrate biochemistry; high nutrient concentrations in green leaf tissue and leaf litter; and small (often hairless and non-mycorrhizal) roots. 4Impacts on the host are detrimental, which can alter competitive balances between hosts and non-hosts and thus result in community change. Further impacts may result from effects on the abiotic environment, including soil water status, nutrient cycling and leaf/canopy temperatures. 5However, for non-host species and for organisms that interact with these (e.g. herbivores and pollinators) or for those that benefit from changes in the abiotic environment, the parasites may have an overall positive effect, suggesting that at the community level, hemiparasites may also be considered as mutualists. 6It is clear that through their distinctive suite of physiological traits hemiparasitic Orobanchaceae, have considerable impacts on community structure and function, can have both competitive and positive interactions with other plants, and can impact on other trophic levels. Many community level effects of parasitic plants can be considered analogous to those of other parasites, predators or herbivores. [source] Antisense-Mediated Depletion of Tomato Chloroplast Omega-3 Fatty Acid Desaturase Enhances Thermal ToleranceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2006Xun-Yan Liu Abstract A chloroplast-localized tomato (Lycopersicon esculentum Mill.) ,-3 fatty acid desaturase gene (LeFAD7) was isolated and characterized with regard to its sequence, response to various temperatures, and function in antisense transgenic tomato plants. The deduced amino acid sequence had four histidine-rich regions, of which three regions were highly conserved throughout the whole ,-3 fatty acid desaturase gene family. Southern blotting analysis showed that LeFAD7 was encoded by a single copy gene and had two homologous genes in the tomato genome. Northern blot showed that LeFAD7 was expressed in all organs and was especially abundant in leaf tissue. Meanwhile, expression of LeFAD7 was induced by chilling stress (4 °C), but was inhibited by high temperature (45 °C), in leaves. Transgenic tomato plants were produced by integration of the antisense LeFAD7 DNA under the control of a CaMV35S promoter into the genome. Antisense transgenic plants with lower 18:3 content could maintain a higher maximal photochemical efficiency (Fv/Fm) and O2 evolution rate than wild-type plants. These results suggested that silence of the LeFAD7 gene alleviated high-temperature stress. There was also a correlation between the low content of 18:3 resulting from silence of the LeFAD7 gene and tolerance to high-temperature stress. (Managing editor: Li-Hui Zhao) [source] Wheat Resistance to Spot Blotch Potentiated by SiliconJOURNAL OF PHYTOPATHOLOGY, Issue 5 2010Gisele Pereira Domiciano Abstract Spot blotch, caused by the fungus Bipolaris sorokiniana, is one of the most important diseases on wheat. The effects of silicon (Si) on this wheat disease were studied. Plants of wheat cultivars BR-18 and BRS-208 were grown in plastic pots containing Si-deficient soil amended with either calcium silicate (+Si) or calcium carbonate (,Si). The content of Si in leaf tissue was significantly increased by 90.5% for the +Si treatment. There was no significant difference between Si treatments for calcium content, so variations in Si accounted for differences in the level of resistance to spot blotch. The incubation period was significantly increased by 40% for the +Si treatment. The area under spot blotch progress curve, number of lesions per cm2 of leaf area, and real disease severity significantly decreased by 62, 36 and 43.5% in +Si treatment. There was no significant effect of Si on lesion size. The role played by total soluble phenolics in the increased resistance to spot blotch of plants from both cultivars supplied with Si was not clear. Plants from cultivar BR-18 supplied with Si showed the highest values for concentration of lignin-thioglycolic acid derivatives during the most advanced stages of fungus infection. Chitinase activity was high at the most advanced stages of fungus infection on leaves from both cultivars supplied with Si and may have had an effect on fungus growth based on the reduction of the components of resistance evaluated. Peroxidase activity was found to be high only at 96 h after inoculation of both cultivars supplied with Si. Polyphenoloxidase activity had no apparent effect on resistance regardless of Si treatments. Results revealed that supplying Si to wheat plants can increase resistance against spot blotch. [source] Occurrence of Alfalfa Bacterial Stem Blight Disease in Kurdistan Province, IranJOURNAL OF PHYTOPATHOLOGY, Issue 10 2007B. Harighi Abstract During spring and summer of 2004 and 2005, a new disease of alfalfa was observed for the first time in some areas of the Kurdistan province in Iran. Symptoms were initially yellowed area on leaves, within which water-soaked, irregular spots developed. These spots eventually coalesced to produce large necrotic areas. Symptoms on petiole and stem include water-soaked lesions, which later turned brown. Gram negative and rod-shaped bacteria were isolated from infected tissues. From the results of LOPAT tests (levan production, oxidase reaction, potato soft rot, arginine dihydrolase and tobacco hypersensitivity) and other phenotypic, biochemical and physiological properties investigated, the causal bacterium have been identified as Pseudomonas syringae pv. syringae. Pathogenicity of selected strains was confirmed by injecting a bacterial suspension into leaf tissue from the underside of leaves. [source] Components of Partial Disease Resistance in Wheat Detected in a Detached Leaf Assay Inoculated with Microdochium majus using First, Second and Third Expanding Seedling LeavesJOURNAL OF PHYTOPATHOLOGY, Issue 4 2006R. A. Browne Abstract The use of first, second and third expanding seedling leaves of wheat (L1, L2 and L3 respectively), inoculated with conidial suspensions of Microdochium majus (syn. Microdochium nivale var. majus) in a detached leaf assay, for detecting components of partial disease resistance (PDR) was investigated across a range of wheat cultivars. Incubation periods (period from inoculation to first appearance of symptoms; a dull grey,green water-soaked lesion) and latent periods (period from inoculation to the first appearance of sporodochia) were longest and lesions smallest on L3. The expression of PDR components on L2 was intermediate to those on L1 and L3. The longer latent periods on L3 typically occurred after leaf senescence contrasting with latent periods on L1 and L2 where sporulation most frequently occurred on relatively green leaf tissue. Cultivar differences in the first appearance of symptoms, incubation period, which occurred before any leaf senescence was observed, correlated significantly across all leaf positions. Similarly cultivar differences in latent period were correlated for L1 and L2. However, latent periods on L3, which were the least consistent between cultivars across experiments, were not correlated with those of L1 or L2 in any experiment. The results indicate that due to the delay in sporulation until after leaf senescence, observations on latent period in L3 are less representative of what occurs in the whole plant where infection of living tissue is of greatest interest. This work indicates that the selection of the first or second expanding leaf of wheat is optimal for the use in the detached leaf assay using M. majus for studying components of PDR. [source] Phenotypic Reaction and Genetic Analysis Using AFLP-derived SCARs for Resistance to Apple ScabJOURNAL OF PHYTOPATHOLOGY, Issue 5 2004E. M. Huaracha Abstract Six sequence-characterized amplified region (SCAR) markers linked to the apple scab resistance gene Vf were evaluated for their utility in marker-assisted selection (MAS) in apple breeding. Of the six SCARs used in this study, ACS-6 was located left of the Vf gene, ACS-7 and ACS-9 co-segregated with Vf, and ACS-8, ACS-4, ACS-5 were located right of the Vf gene. Three families derived from crosses between scab-resistant and scab-susceptible cultivars, including ,Liberty' × ,Deljub', ,Liberty' × ,Delcorf', and ,Florina' ×,Delcorf', previously screened for scab resistance following greenhouse inoculation with the fungal pathogen Venturia inaequalis, were genotyped and compared with phenotypic reactions to scab infection in the field. For each family, a subset progeny of 30 seedlings (propagated onto Malling 9 rootstock and of 7 years old) was selected based on fungal sporulation according to the following scheme. Ten seedlings with no visible scab sporulation on leaves were given phenotypic scores of 0 (deemed resistant); 10 seedlings with moderate scab sporulation were given phenotypic scores of 1.0 (deemed moderately resistant); and 10 seedlings with heavy sporulation were given phenotypic scores of 2.0 (deemed susceptible). DNA was isolated from leaf tissue collected from all 90 seedlings, parents and Malus floribunda 821, the original source of the Vf gene, and screened with all six SCARs. All six SCARs were present in the two scab-resistant parents, ,Liberty' and ,Florina', and M. floribunda 821; while, the two scab-susceptible parents, ,Deljub' and ,Delcorf', lacked all SCARs. All SCARs were either present or absent in varying numbers of seedlings in each progeny with phenotypic ratings of either 0 (resistant) or 1.0 (moderately resistant); while all seedlings with phenotypic ratings of 2.0 (susceptible) lacked all SCARs. The inconsistencies between phenotypic scab ratings and SCAR marker data are discussed. [source] Leaf Disc Inoculation, a Fast and Precise Test for the Screening of Metalaxyl Tolerance in Sunflower Downy MildewJOURNAL OF PHYTOPATHOLOGY, Issue 6 2001B. Rozynek A new method, based on leaf disc inoculation, was developed for the screening of metalaxyl tolerance in field isolates of Plasmopara halstedii. High-pressure liquid chromatography (HPLC) was used to determine the fungicide concentration in the inoculation medium and in the incubated leaf tissue over the test period. These measurements revealed that the fungicide concentration inside the leaf tissue within 24 h had adjusted to the concentration in the outer medium and remained constant for the time of cultivation over a period of more than 11 days. In contrast to whole seedling tests with application of the fungicide via seed dressing, the leaf disc method allows precise quantification of the effective fungicide concentration at the site of infection and is less space and time consuming. Metalaxyl tolerance of P. halstedii isolates was gradually determined according to the sporulation of the pathogen on sunflower leaf discs in the presence of increasing fungicide concentrations. Isolates collected in South Germany showed no tolerance and sporulation was prohibited when tests were carried out at 0.02 ,g (a.i.)/ml of metalaxyl or more. In contrast, a tolerant French isolate developed sporangia on leaf discs incubated in a metalaxyl solution of 100 ,g (a.i.)/ml. [source] Lipopolysaccharide mobility in leaf tissue of Arabidopsis thalianaMOLECULAR PLANT PATHOLOGY, Issue 6 2010DANA ZEIDLER SUMMARY Bacterial lipopolysaccharides (LPS) are triggers of defence responses in plants, and induce local as well as systemic acquired resistance. Arabidopsis thaliana plants pretreated with LPS show an increased resistance to the virulent bacterial plant pathogen Pseudomonas syringae pv. tomato DC3000. To investigate the mobilization and transport of LPS in Arabidopsis leaves, fluorescently labelled LPS (Alexa Fluor® 488 conjugate) from Salmonella minnesota was used. Leaves were pressure infiltrated with fluorescein-labelled LPS and fluorescence microscopy was used to follow the movement and localization of LPS as a function of time. The observation of leaves 1 h after supplementation with fluorescein-labelled LPS revealed a fluorescent signal in the intercellular space. Capillary zone electrophoresis was used for the detection and analysis of the labelled LPS in directly treated leaves and systemic leaves. In addition, gel electrophoresis was used to confirm LPS mobilization. The results indicated that LPS mobilization/translocation occurs through the xylem from local, treated leaves to systemic, untreated leaves. Consequently, care should be taken when ascribing the observed biochemical responses and induced resistance from LPS perception as being uniquely local or systemic, as these responses might overlap because of the mobility of LPS in the plant vascular system. [source] Over-expression of putative transcriptional coactivator KELP interferes with Tomato mosaic virus cell-to-cell movementMOLECULAR PLANT PATHOLOGY, Issue 2 2009NOBUMITSU SASAKI SUMMARY Tomato mosaic virus (ToMV) encodes a movement protein (MP) that is necessary for virus cell-to-cell movement. We have demonstrated previously that KELP, a putative transcriptional coactivator of Arabidopsis thaliana, and its orthologue from Brassica campestris can bind to ToMV MP in vitro. In this study, we examined the effects of the transient over-expression of KELP on ToMV infection and the intracellular localization of MP in Nicotiana benthamiana, an experimental host of the virus. In co-bombardment experiments, the over-expression of KELP inhibited virus cell-to-cell movement. The N-terminal half of KELP (KELPdC), which had been shown to bind to MP, was sufficient for inhibition. Furthermore, the over-expression of KELP and KELPdC, both of which were co-localized with ToMV MP, led to a reduction in the plasmodesmal association of MP. In the absence of MP expression, KELP was localized in the nucleus and the cytoplasm by the localization signal in its N-terminal half. It was also shown that ToMV amplified normally in protoplasts prepared from leaf tissue that expressed KELP transiently. These results indicate that over-expressed KELP interacts with MP in vivo and exerts an inhibitory effect on MP function for virus cell-to-cell movement, but not on virus amplification in individual cells. [source] The stem canker (blackleg) fungus, Leptosphaeria maculans, enters the genomic eraMOLECULAR PLANT PATHOLOGY, Issue 3 2005T. ROUXEL SUMMARY Leptosphaeria maculans is the most ubiquitous pathogen of Brassica crops, and mainly oilseed brassicas (oilseed rape, canola), causing the devastating ,stem canker' or ,blackleg'. This review summarizes our current knowledge on the pathogen, from taxonomic issues to specific life traits. It mainly illustrates the importance of formal genetics approaches on the pathogen side to dissect the interaction with the host plants. In addition, this review presents the main current research topics on L. maculans and focuses on the L. maculans genome initiative recently begun, including its main research issues. Taxonomy:,Leptosphaeria maculans (Desm.) Ces. & de Not. (anamorph Phoma lingam Tode ex Fr.). Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes (Loculoascomycetes), Order Pleosporales, Genus Leptosphaeria, Species maculans. Host range:, cultivated Brassicas such as Brassica napus (oilseed rape, canola), B. rapa, B. juncea, B. oleracea, etc., along with numerous wild crucifers species. Arabidopsis thaliana was recently reported to be a potential host for L. maculans. Primary disease symptoms are greyish-green collapse of cotyledon or leaf tissue, without a visible margin, bearing tiny black spots (pycnidia). The fungus then develops an endophytic symptomless growth for many months. Secondary symptoms, at the end of the growing season, are dry necroses of the crown tissues with occasional blackening (stem canker or blackleg) causing lodging of the plants. Pseudothecia differentiate on leftover residues. Seedling damping-off and premature ripening are also reported under certain environmental conditions. Useful websites:,Leptosphaeria maculans sequencing project at Genoscope: http://www.genoscope.cns.fr/externe/English/Projets/Projet_DM/organisme_DM.html; the SECURE site: http://www.secure.rothamsted.ac.uk/ the ,Blackleg' group at the University of Melbourne: http://www.botany.unimelb.edu.au/blackleg/overview.htm [source] Transient expression of a vacuolar peroxidase increases susceptibility of epidermal barley cells to powdery mildewMOLECULAR PLANT PATHOLOGY, Issue 6 2001Brian Kåre Kristensen summary The expression of genes encoding the peroxidases, Prx7 and Prx8, is induced in barley leaf tissue after inoculation with the barley powdery mildew fungus, Blumeria graminis f.sp. hordei (DC) Speer (Bgh). The role of these peroxidases in general barley defence responses against fungal attack was investigated using a transient expression system. Colonization frequencies of Bgh on cells transfected with Prx7 or Prx8 expression-, mutant- or fusion-DNA constructs were compared to the frequencies on cells expressing a ,-glucuronidase (GUS) control construct. Twice the number of powdery mildew colonies were observed on cells expressing Prx7 as compared to control cells. Introduction of either mutant or truncated versions of Prx7 showed that decreased resistance against Bgh was dependent on the presence of the C-terminal signal peptide required for correct subcellular targeting, but not affected significantly by mutations in the catalytic centre. No impact on Bgh performance was observed after the introduction of Prx8 or mutant constructs. An enhanced accumulation of the apoplastic Prx8 was verified by immunocytology. These results indicate a more complex role of peroxidases in defence responses than was previously suspected. [source] Mitochondrial morphology transition is an early indicator of subsequent cell death in ArabidopsisNEW PHYTOLOGIST, Issue 1 2008Iain Scott Summary ,,Mitochondrial morphology and dynamics were investigated during the onset of cell death in Arabidopsis thaliana. Cell death was induced by either chemical (reactive oxygen species (ROS)) or physical (heat) shock. ,,Changes in mitochondrial morphology in leaf tissue, or isolated protoplasts, each expressing mitochondrial-targeted green fluorescent protein (GFP), were observed by epifluorescence microscopy, and quantified. ,,Chemical induction of ROS production, or a mild heat shock, caused a rapid and consistent change in mitochondrial morphology (termed the mitochondrial morphology transition) that preceded cell death. Treatment of protoplasts with a cell-permeable superoxide dismutase analogue, TEMPOL, blocked this morphology change. Incubation of protoplasts in micromolar concentrations of the calcium channel-blocker lanthanum chloride, or the permeability transition pore inhibitor cyclosporin A, prevented both the mitochondrial morphology transition and subsequent cell death. ,,It is concluded that the observed mitochondrial morphology transition is an early and specific indicator of cell death and is a necessary component of the cell death process. [source] Phenotypic plasticity in seedling defense strategies: compensatory growth and chemical inductionOIKOS, Issue 6 2008Kasey E. Barton Phenotypic plasticity in growth (leading to compensation) and secondary chemical production (leading to induction) in response to herbivory are key defense strategies in adult plants, but their role in seedling defense remains unclear. A pair of greenhouse studies was conducted to investigate compensation and induction in seedlings and juvenile plants, using Plantago lanceolata (Plantaginaceae) and the specialist buckeye caterpillar Junonia coenia (Nymphalidae) as a model system. Plants received 50% defoliation at two and four weeks of age, and groups of plants were harvested one week after herbivory and six to eight weeks after herbivory to investigate the duration of the responses. Plants damaged at two weeks showed no chemical induction and fully compensated for the lost leaf tissue by ten weeks of age. Plants damaged at four weeks showed a significant reduction in iridoid glycosides one week after herbivory and achieved full shoot compensation by ten weeks of age at the expense of root biomass. These results indicate that P. lanceolata seedlings use compensation, but not chemical induction, as a defense strategy. This research highlights the importance of considering ontogeny in studies of plant,herbivore interactions and suggests that seedling defense may differ markedly from adult plant defense. [source] Spatial association of photosynthesis and chemical defense in Arabidopsis thaliana following herbivory by Trichoplusia niPHYSIOLOGIA PLANTARUM, Issue 2 2009Jennie Tang Because they share common precursors and require significant amounts of energy, photosynthesis and defense against herbivores and pathogens may be inversely related. This relationship was examined in Arabidopsis thaliana exposed to herbivory by Trichoplusia ni neonates. The spatial pattern of photosynthesis was compared statistically with that of induction of the defense-related cinnamate-4-hydroxylase (C4H) gene across individual leaves exposed to herbivory in transgenic plants harboring a C4H:GUS gene fusion. In portions of the leaf where C4H:GUS expression was upregulated, photosynthesis was depressed, while non-photochemical quenching was increased, suggesting a trade-off between these two processes. However, photosynthetic damage spread further into surrounding areas than the induction of C4H:GUS expression. Photosynthetic depression was observed up to 1 mm from the edges of holes, whereas C4H:GUS induction typically was limited to about 0.5 mm or less from edges. Other mechanisms may be responsible for the spread of photosynthetic damage beyond where C4H-related defense was induced. Alternatively, C4H induction may reflect a subset of defensive responses more limited in their spatial distribution than the downregulation of photosynthesis. The suppression of photosynthesis in remaining leaf tissue represents a ,hidden cost' of herbivore damage. [source] Purification and characterisation of two ACC oxidases expressed differentially during leaf ontogeny in white cloverPHYSIOLOGIA PLANTARUM, Issue 1 2000Deming Gong Two isoforms of ACC oxidase (ACO) (EC 1.4.3), expressed differentially during leaf ontogeny in white clover (Trifolium repens L.), have been identified and purified to homogeneity. One isoform, designated MGI, was purified from mature green leaf tissue while the second isoform, designated SEII, was purified from senescent leaf tissue. The isolation and purification of these isoforms were achieved using a combination of hydrophobic interaction chromatography, anion exchange chromatography, chromatofocusing and gel filtration column chromatography. The Mr of both MGI and SEII was determined to be 37.5 kDa by gel filtration, and 37 kDa (MGI), 35 kDa (SEII) by SDS-PAGE, indicating that both isoforms are active as monomers. During purification, both isoforms were recognised by a polyclonal antibody directed against a recombinant polypeptide derived from a white clover ACO gene expressed in mature green leaf tissue, TR-ACO2. In addition to molecular mass, differences between the two isoforms were observed in terms of pH optima, isoelectric point (pI), Km for ACC, optimal requirements for the co-substrate ascorbate, and NaHCO3 and Fe2+ as co-factors. The identification of distinct ACC oxidases from the same tissue at different developmental stages shows that the now widely observed transcriptional regulation of the ACO gene family in higher plants is also expressed in terms of differential regulation of enzyme isoforms. [source] Leaf senescence is delayed in maize expressing the Agrobacterium IPT gene under the control of a novel maize senescence-enhanced promoterPLANT BIOTECHNOLOGY JOURNAL, Issue 2 2004Paul R. H. Robson Summary We have genetically modified maize plants to delay leaf senescence. A senescence-enhanced promoter from maize (PSEE1) was used to drive expression of the Agrobacterium cytokinin biosynthesis gene IPT in senescing leaf tissue. Three maize lines expressing IPT from PSEE1, Sg1, Sg2 and Sg3, were analysed in detail, representing mild, intermediate and extreme expression, respectively, of the delayed-senescence phenotype. Backcross populations segregating for the presence or absence of the PSEE1XbaIPTNOS transgene also simultaneously segregated for the senescence phenotype. At the time of ear leaf emergence, individuals of lines Sg1 and Sg2 segregating for the presence of the transgene carried about three fewer senescing leaves than control (transgene-minus) segregants, and IPT transcript levels were higher in leaves at incipient senescence than in young leaves. Leaves of transgenic Sg3 plants were significantly greener than controls and progressed directly from fully green to bleached and dead without an intervening yellowing phase. IPT transcript abundance in this line was not related to the initiation of senescence. Extended greenness was accompanied by a delay in the loss of photosynthetic capacity with leaf age. The delayed-senescence trait was associated with relatively minor changes in morphology and development. The phenotype was particularly emphasized in plants grown in low soil nitrogen. The reduced ability of the extreme transgenic line Sg3 to recycle internal nitrogen from senescing lower leaves accounted for significant chlorosis in emerging younger leaves when plants were grown in low nutrient conditions. This study demonstrates that the agronomically important delayed-senescence (,stay-green') trait can be engineered into a monocot crop, and is the first example outside Arabidopsis of senescence modification using a homologous senescence-enhanced promoter. [source] Ice recrystallization inhibition proteins (IRIPs) and freeze tolerance in the cryophilic Antarctic hair grass Deschampsia antarctica E. Desv.PLANT CELL & ENVIRONMENT, Issue 4 2009ULRIK P. JOHN ABSTRACT Antarctic hair grass (Deschampsia antarctica E. Desv.), the only grass indigenous to Antarctica, has well-developed freezing tolerance, strongly induced by cold acclimation. Here, we show that in response to low temperatures, D. antarctica expresses potent recrystallization inhibition (RI) activity that, inhibits the growth of small ice crystals into potentially damaging large ones, is proteinaceous and localized to the apoplasm. A gene family from D. antarctica encoding putative homologs of an ice recrystallization inhibition protein (IRIP) has been isolated and characterized. IRIPs are apoplastically targeted proteins with two potential ice-binding motifs: 1,9 leucine-rich repeats (LRRs) and c. 16 ,IRIP' repeats. IRIP genes appear to be confined to the grass subfamily Pooideae and their products, exhibit sequence similarity to phytosulphokine receptors and are predicted to adopt conformations with two ice-binding surfaces. D. antarctica IRIP (DaIRIP) transcript levels are greatly enhanced in leaf tissue following cold acclimation. Transgenic Arabidopsis thaliana expressing a DaIRIP has novel RI activity, and purified DaIRIP, when added back to extracts of leaves from non-acclimated D. antarctica, can reconstitute the activity found in acclimated plants. We propose that IRIP-mediated RI activity may contribute to the cryotolerance of D. antarctica, and thus to its unique ability to have colonized Antarctica. [source] The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)PLANT CELL & ENVIRONMENT, Issue 8 2007EUN-YOUNG CHOI ABSTRACT Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity. [source] Functional characterization and expression analysis of a glutathione transporter, BjGT1, from Brassica juncea: evidence for regulation by heavy metal exposurePLANT CELL & ENVIRONMENT, Issue 10 2003J. BOGS ABSTRACT Glutathione and its derivatives play an important role in the tolerance of plants against heavy metals. A glutathione transporter, BjGT1 (AJ561120), was cloned and functionally characterized from Brassica juncea, a plant which may be used for phytoremediation. The full-length BjGT1 cDNA showed homology with the high affinity glutathione transporter HGT1 from Saccharomyces cerevisiae and shares 92% identity with a putative glutathione transporter from A. thaliana (At4g16370). When expressed in the S. cerevisiae hgt1, strain, BjGT1 complemented the mutant on medium with glutathione as the only sulphur source and mediated the uptake of [3H]GSH. Immunoblot analysis with a peptide-specific antiserum directed against a C-terminal sequence revealed high BjGT1 expression in leaf tissue and relatively low expression in stem tissue, whereas BjGT1 protein was not detectable in root tissue. The amounts of BjGT1 mRNA and protein were analysed during a 6 d exposure of B. juncea to 25 µm Cd(NO3)2. BjGT1 mRNA was strongly induced by cadmium in stems and leaves. Unexpectedly, the amount of BjGT1 protein in leaves showed a pronounced decrease with a minimum after 96 h of Cd exposure, followed by partial recovery. The strong regulation of BjGT1 by cadmium suggests a role of this glutathione transporter during heavy metal exposure. [source] Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profilesPLANT CELL & ENVIRONMENT, Issue 12 2000T. C. Vogelmann ABSTRACT Profiles of chlorophyll fluorescence were measured in spinach leaves irradiated with monochromatic light. The characteristics of the profiles within the mesophyll were determined by the optical properties of the leaf tissue and the spectral quality of the actinic light. When leaves were infiltrated with 10,4M DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethyl-urea] or water, treatments that minimized light scattering, irradiation with 2000 ,mol m,2 s,1 green light produced broad Gaussian-shaped fluorescence profiles that spanned most of the mesophyll. Profiles for chlorophyll fluorescence in the red (680 ± 16 nm) and far red (, > 710 nm) were similar except that there was elevated red fluorescence near the adaxial leaf surface relative to far red fluorescence. Fluorescence profiles were narrower in non-infiltrated leaf samples where light scattering increased the light gradient. The fluorescence profile was broader when the leaf was irradiated on its adaxial versus abaxial surface due to the contrasting optical properties of the palisade and spongy mesophyll. Irradiation with blue, red and green monochromatic light produced profiles that peaked 50, 100 and 150 ,m, respectively, beneath the irradiated surface. These results are consistent with previous measurements of the light gradient in spinach and they agree qualitatively with measurements of carbon fixation under monochromatic blue, red and green light. These results suggest that chlorophyll fluorescence profiles may be used to estimate the distribution of quanta that are absorbed within the leaf for photosynthesis. [source] | ||||||||||||||||||||||||||||