Whole genome sequencing elucidates the species‐wide diversity and evolution of fungicide resistance in the early blight pathogen Alternaria solani

Early blight of potato is caused by the fungal pathogen Alternaria solani and is an increasing problem worldwide. The primary strategy to control the disease is applying fungicides such as succinate dehydrogenase inhibitors (SDHI). SDHI‐resistant strains, showing reduced sensitivity to treatments, appeared in Germany in 2013, shortly after the introduction of SDHIs. Two primary mutations in the SDH complex (SdhB‐H278Y and SdhC‐H134R) have been frequently found throughout Europe. How these resistances arose and spread, and whether they are linked to other genomic features, remains unknown. For this project, we performed whole‐genome sequencing for 48 A. solani isolates from potato fields across Europe to better characterize the pathogen's genetic diversity in general and understand the development and spread of the genetic mutations that lead to SDHI resistance. The isolates can be grouped into seven genotypes. These genotypes do not show a geographical pattern but appear spread throughout Europe. We found clear evidence for recombination on the genome, and the observed admixtures might indicate a higher adaptive potential of the fungus than previously thought. Yet, we cannot link the observed recombination events to different Sdh mutations. The same Sdh mutations appear in different, non‐admixed genetic backgrounds; therefore, we conclude they arose independently. Our research gives insights into the genetic diversity of A. solani on a genome level. The mixed occurrence of different genotypes, apparent admixture in the populations, and evidence for recombination indicate higher genomic complexity than anticipated. The conclusion that SDHI tolerance arose multiple times independently has important implications for future fungicide resistance management strategies. These should not solely focus on preventing the spread of isolates between locations but also on limiting population size and the selective pressure posed by fungicides in a given field to avoid the rise of new mutations in other genetic backgrounds.

Transcriptome Analysis of Potato Infected with the Necrotrophic Pathogen Alternaria solani

Potato early blight is caused by the necrotrophic fungus Alternaria solani and can result in yield losses of up to 50% if left uncontrolled. At present, the disease is controlled by chemical fungicides, yet rapid development of fungicide resistance renders current control strategies unsustainable. On top of that, a lack of understanding of potato defences and the quantitative nature of resistance mechanisms against early blight hinders the development of more sustainable control methods. Necrotrophic pathogens, compared to biotrophs, pose an extra challenge to the plant, since common defence strategies to biotic stresses such as the hypersensitive response and programmed cell death are often beneficial for necrotrophs. With the aim of unravelling plant responses to both the early infection stages (i.e., before necrosis), such as appressorium formation and penetration, as well as to later responses to the onset of necrosis, we present here a transcriptome analysis of potato interactions with A. solani from 1 h after inoculation when the conidia have just commenced germination, to 48 h post inoculation when multiple cell necrosis has begun. Potato transcripts with putative functions related to biotic stress tolerance and defence against pathogens were upregulated, including a putative Nudix hydrolase that may play a role in defence against oxidative stress. A. solani transcripts encoding putative pathogenicity factors, such as cell wall degrading enzymes and metabolic processes that may be important for infection. We therefore identified the differential expression of several potato and A. solani transcripts that present a group of valuable candidates for further studies into their roles in immunity or disease development.

Phosphite Integrated in Late Blight Treatment Strategies in Starch Potato Does Not Cause Residues in the Starch Product

Currently available fungicides against potato late blight are effective but there are concerns about the sustainability of frequent applications and the risks of fungicide resistance. Therefore, we investigated how potassium phosphite can be integrated into late blight control programs with reduced fungicides in field trials. Phosphite was somewhat less effective than the conventional fungicides at suppressing late blight in the foliage, and the tubers contained less starch. However, when we reduced the amount of phosphite and combined it with reduced amounts of conventional fungicides, we observed no differences in disease suppression, total yields, and tuber starch contents compared with the full treatments with conventional fungicides. The amount of phosphite detected in the harvested tubers was linearly associated with the amount of phosphite applied to the foliage. Our analyses indicate that phosphite could replace some fungicides without exceeding the current European Union standards for the maximum residue levels in potato tubers. No phosphite was detected in the starch from the tubers. In 1 of 2 years, early blight (caused by Alternaria solani) was less severe in the phosphite treatments than in the treatments without phosphite. The integration of phosphite into current treatment strategies would reduce the dependence on conventional fungicides.

Intact salicylic acid signalling is required for potato defence against the necrotrophic fungus Alternaria solani

KEY MESSAGE

Using disease bioassays and transcriptomic analysis we show that intact SA-signalling is required for potato defences against the necrotrophic fungal pathogen Alternaria solani.

ABSTRACT

Early blight, caused by the necrotrophic fungus Alternaria solani, is an increasing problem in potato cultivation. Studies of the molecular components defining defence responses to A. solani in potato are limited. Here, we investigate plant defence signalling with a focus on salicylic acid (SA) and jasmonic acid (JA) pathways in response to A. solani. Our bioassays revealed that SA is necessary to restrict pathogen growth and early blight symptom development in both potato foliage and tubers. This result is in contrast to the documented minimal role of SA in resistance of Arabidopsis thaliana against necrotrophic pathogens. We also present transcriptomic analysis with 36 arrays of A. solani inoculated SA-deficient, JA-insensitive, and wild type plant lines. A greater number of genes are differentially expressed in the SA-deficient mutant plant line compared to the wild type and JA- insensitive line. In wild type plants, genes encoding metal ion transporters, such as copper, iron and zinc transporters were upregulated and transferase-encoding genes, for example UDP-glucoronosyltransferase and Serine-glyoxylate transferase, were downregulated. The SA-deficient plants show upregulation of genes enriched in GO terms related to oxidoreductase activity, respiratory chain and other mitochondrial-related processes. Pathogenesis-related genes, such as genes encoding chitinases and PR1, are upregulated in both the SA-deficient and wild type plants, but not in the JA-insensitive mutants. The combination of our bioassays and the transcriptomic analysis indicate that intact SA signalling, and not JA signalling, is required for potato defences against the necrotrophic pathogen A. solani.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (10.1007/s11103-020-01019-6) contains supplementary material, which is available to authorized users.

Earlier occurrence and increased explanatory power of climate for the first incidence of potato late blight caused by Phytophthora infestans in Fennoscandia

BACKGROUND

Late blight (caused by Phytophthora infestans) is a devastating potato disease that has been found to occur earlier in the season over the last decades in Fennoscandia. Up until now the reasons for this change have not been investigated. Possible explanations for this change are climate alterations, changes in potato production or changes in pathogen biology, such as increased fitness or changes in gene flow within P. infestans populations. The first incidence of late blight is of high economic importance since fungicidal applications should be typically applied two weeks before the first signs of late blight and are repeated on average once a week.

METHODS

We use field observations of first incidence of late blight in experimental potato fields from five sites in Sweden and Finland covering a total of 30 years and investigate whether the earlier incidence of late blight can be related to the climate.

RESULTS

We linked the field data to meteorological data and found that the previous assumption, used in common late blight models, that the disease only develops at relative humidity levels above 90% had to be rejected. Rather than the typically assumed threshold relationship between late blight disease development and relative humidity we found a linear relationship. Our model furthermore showed two distinct responses of late blight to climate. At the beginning of the observation time (in Sweden until the early 90s and in Finland until the 2000s) the link between climate and first incidence was very weak. However, for the remainder of the time period the link was highly significant, indicating a change in the biological properties of the pathogen which could for example be a change in the dominating reproduction mode or a physiological change in the response of the pathogen to climate.

CONCLUSIONS

The study shows that models used in decision support systems need to be checked and re-parametrized regularly to be able to capture changes in pathogen biology. While this study was performed with data from Fennoscandia this new pathogen biology and late blight might spread to (or already be present at) other parts of the world as well. The strong link between climate and first incidence together with the presented model offers a tool to assess late blight incidence in future climates.

Plant Resistance Inducers against Pathogens in Solanaceae Species-From Molecular Mechanisms to Field Application

This review provides a current summary of plant resistance inducers (PRIs) that have been successfully used in the Solanaceae plant family to protect against pathogens by activating the plant's own defence. Solanaceous species include many important crops such as potato and tomato. We also present findings regarding the molecular processes after application of PRIs, even if the number of such studies still remains limited in this plant family. In general, there is a lack of patterns regarding the efficiency of induced resistance (IR) both between and within solanaceous species. In many cases, a hypersensitivity-like reaction needs to form in order for the PRI to be efficient. "-Omics" studies have already given insight in the complexity of responses, and can explain some of the differences seen in efficacy of PRIs between and within species as well as towards different pathogens. Finally, examples of field applications of PRIs for solanaceous crops are presented and discussed. We predict that PRIs will play a role in future plant protection strategies in Solanaceae crops if they are combined with other means of disease control in different spatial and temporal combinations.

Genetic diversity and occurrence of the F129L substitutions among isolates of Alternaria solani in south-eastern Sweden

BACKGROUND

Early blight, caused by the fungus Alternaria solani, occurs on potato mainly in the south-eastern part of Sweden, but also in other parts of the country. The aim of this study was to investigate the genetic diversity of A. solani populations from different potato growing regions in south-eastern Sweden using AFLP marker analysis. In addition, the cultured isolates were examined for substitutions in the gene encoding cytochrome b, associated with loss of sensitivity against QoI fungicides.

RESULTS

Nei's gene diversity index for the Swedish populations of A. solani revealed a gene diversity of up to 0.20. Also genetic differentiation was observed among populations of A. solani from different locations in south-eastern Sweden. The mitochondrial genotype of the isolates of A. solani was determined and both known genotypes, GI (genotype 1) and GII (genotype 2), were found among the isolates. The occurrence of the F129L substitution associated with a loss of sensitivity to strobilurins was confirmed among the GII isolates. In vitro conidial germination tests verified that isolates containing the F129L substitution had reduced sensitivity to azoxystrobin and, at a lower extent, to pyraclostrobin.

CONCLUSIONS

Genetic diversity was relatively high among isolates of A. solani in south-eastern part of Sweden. F129L substitutions, leading to reduced sensitivity to strobilurins, have been established in field populations, which may have implications for the future efficacy of QoI fungicides.

Assessment of diversity and genetic relationships of Neonectria ditissima: the causal agent of fruit tree canker

BACKGROUND

Neonectria ditissima is one of the most important fungal pathogens of apple trees, where it causes fruit tree canker. Information about the amount and partitioning of genetic variation of this fungus could be helpful for improving orchard management strategies and for breeding apple cultivars with high levels of genetically determined resistance. In this study single-spore Neonectria isolates originating from both the same and from different perithecia, apple cultivars and apple orchards in Sweden and Belgium, were evaluated for AFLP- and SSR-based genetic similarity and for mating system.

RESULTS

Seven SSR loci produced a total of 31 alleles with an average of 4 alleles per locus, while 11 AFLP primer combinations produced an average of 35 fragments per primer combination and 71 % polymorphic fragments. An AFLP-based analysis of molecular variance (AMOVA) revealed that 89 % of the variation was found within orchards and 11 % between orchards. Genetic similarity among the studied isolates was illustrated with a principal coordinate analyseis (PCoA) and a dendrogram. AFLP-based Jaccard's similarity coefficients were the highest when single-ascospore isolates obtained from the same perithecium were compared, medium-high for isolates from different perithecia on the same tree, and lowest when isolates from different trees were compared.

CONCLUSIONS

Based on the results of PCoA and AMOVA analysis, isolates from the same or geographically close orchards did not group together. Since AFLP profiles differed also when single-ascospore isolates from the same perithecium were compared, the mating system of N. ditissima is most likely heterothallic.

Effector-driven marker development and cloning of resistance genes against Phytophthora infestans in potato breeding clone SW93-1015

We show the usefulness of integrating effector screening in a breeding program and in resistance gene cloning, with Phytophthora resistance in the Swedish potato breeding clone SW93-1015 as an example. Phytophthora infestans is one of the most devastating plant pathogens worldwide. We have earlier found that the SW93-1015 potato breeding clone has an efficient resistance against P. infestans under field conditions in Sweden, which has an unusually high local diversity of the pathogen. This potato clone has characteristics that are different from classical R-gene-mediated resistance such as elevated levels of hydrogen peroxide (H2O2) under controlled conditions. Analysis of 76 F1 potato progenies from two individual crosses resulted in nearly 50% resistant clones, from both crosses. This result suggests that the SW93-1015 clone has a simplex genotype for this trait. Screening with over 50 different P. infestans effectors, containing the conserved motif RXLR (for Arg, any amino acid, Leu, Arg), revealed a specific response to Avr2, which suggests that SW93-1015 might contain a functional homolog of the R2 resistance gene. We cloned eight R2 gene homologs from SW93-1015, whereof seven have not been described before and one gene encoded a protein identical to Rpi-ABPT. Expression of this gene in potato cultivar Désirée provided R2-specific resistance, whereas other homologues did not. Using RNAseq analyses we designed a new DNA marker for the R2 resistance in SW93-1015. In summary, we have demonstrated the use of effector screening in practical breeding material and revealed the key resistance mechanism for SW93-1015.

Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans

BACKGROUND

Potato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss. We investigated the transcriptome of Solanum tubersoum (cv. Desiree) and characterized the secretome by quantitative proteomics after foliar application of the protective agent phosphite. We also studied the distribution of phosphite in planta after application and tested transgenic potato lines with impaired in salicylic and jasmonic acid signaling.

RESULTS

Phosphite had a rapid and transient effect on the transcriptome, with a clear response 3 h after treatment. Strikingly this effect lasted less than 24 h, whereas protection was observed throughout all time points tested. In contrast, 67 secretome proteins predominantly associated with cell-wall processes and defense changed in abundance at 48 h after treatment. Transcripts associated with defense, wounding, and oxidative stress constituted the core of the phosphite response. We also observed changes in primary metabolism and cell wall-related processes. These changes were shown not to be due to phosphate depletion or acidification caused by phosphite treatment. Of the phosphite-regulated transcripts 40% also changed with β-aminobutyric acid (BABA) as an elicitor, while the defence gene PR1 was only up-regulated by BABA. Although phosphite was shown to be distributed in planta to parts not directly exposed to phosphite, no protection in leaves without direct foliar application was observed. Furthermore, the analysis of transgenic potato lines indicated that the phosphite-mediated resistance was independent of the plant hormones salicylic and jasmonic acid.

CONCLUSIONS

Our study suggests that a rapid phosphite-triggered response is important to confer long-lasting resistance against P. infestans and gives molecular understanding of its successful field applications.

Proteomics and transcriptomics of the BABA-induced resistance response in potato using a novel functional annotation approach

BACKGROUND

Induced resistance (IR) can be part of a sustainable plant protection strategy against important plant diseases. β-aminobutyric acid (BABA) can induce resistance in a wide range of plants against several types of pathogens, including potato infected with Phytophthora infestans. However, the molecular mechanisms behind this are unclear and seem to be dependent on the system studied. To elucidate the defence responses activated by BABA in potato, a genome-wide transcript microarray analysis in combination with label-free quantitative proteomics analysis of the apoplast secretome were performed two days after treatment of the leaf canopy with BABA at two concentrations, 1 and 10 mM.

RESULTS

Over 5000 transcripts were differentially expressed and over 90 secretome proteins changed in abundance indicating a massive activation of defence mechanisms with 10 mM BABA, the concentration effective against late blight disease. To aid analysis, we present a more comprehensive functional annotation of the microarray probes and gene models by retrieving information from orthologous gene families across 26 sequenced plant genomes. The new annotation provided GO terms to 8616 previously un-annotated probes.

CONCLUSIONS

BABA at 10 mM affected several processes related to plant hormones and amino acid metabolism. A major accumulation of PR proteins was also evident, and in the mevalonate pathway, genes involved in sterol biosynthesis were down-regulated, whereas several enzymes involved in the sesquiterpene phytoalexin biosynthesis were up-regulated. Interestingly, abscisic acid (ABA) responsive genes were not as clearly regulated by BABA in potato as previously reported in Arabidopsis. Together these findings provide candidates and markers for improved resistance in potato, one of the most important crops in the world.

Paranoid potato: phytophthora-resistant genotype shows constitutively activated defense

Phytophthora is the most devastating pathogen of dicot plants. There is a need for resistance sources with different modes of action to counteract the fast evolution of this pathogen. In order to better understand mechanisms of defense against P. infestans, we analyzed several clones of potato. Two of the genotypes tested, Sarpo Mira and SW93-1015, exhibited strong resistance against P. infestans in field trials, whole plant assays and detached leaf assays. The resistant genotypes developed different sizes of hypersensitive response (HR)-related lesions. HR lesions in SW93-1015 were restricted to very small areas, whereas those in Sarpo Mira were similar to those in Solanum demissum, the main source of classical resistance genes. SW93-1015 can be characterized as a cpr (constitutive expressor of PR genes) genotype without spontaneous microscopic or macroscopic HR lesions. This is indicated by constitutive hydrogen peroxide (H₂O₂) production and PR1 (pathogenesis-related protein 1) secretion. SW93-1015 is one of the first plants identified as having classical protein-based induced defense expressed constitutively without any obvious metabolic costs or spontaneous cell death lesions.

Leaf rust (Puccinia triticina) resistance in wheat (Triticum aestivum) cultivars grown in Northern Europe 1992-2002

Diversity of resistance to leaf rust caused by Puccinia triticina can be enhanced in wheat (Triticum aestivum) cultivars through a better knowledge of resistance genes that are present in important cultivars and germplasm. Multi-pathotype tests on 84 wheat cultivars grown in Denmark, Finland, Norway and Sweden during 1992-2002 and 39 differential testers enabled the postulation of nine known genes for seedling resistance to leaf rust. Genes Lr1, Lr2a, Lr3, Lr10, Lr13, Lr14a, Lr17, Lr23 and Lr26 were found singly or in combination in 47 of the cultivars (55.9%). The most frequently occurring genes in cultivars grown in Sweden were Lr13 (20.4%), Lr14a (14.8%) and Lr26 (14.8%). Lr14a was the most common gene in cultivars grown in Norway (18.7%), Lr13 in Denmark (35.5%) and Lr10 in Finland (20.0%). Although 28 cultivars (33.3%) exhibited a response pattern that could not be assigned to resistance genes or combinations present in the tester lines, several pathotypes carried virulence and hence these genes or combinations are of limited use. Nine cultivars (10.7%) lacked detectable seedling resistance. One cultivar was resistant to all pathotypes used in the study.

Sustained intravascular exposure to propofol does not prolong pain at the site of injection

BACKGROUND

Pain at the site of intravenous injection of propofol is a common clinical finding. This double-blind, randomized cross-over study was designed to evaluate whether venous occlusion applied during injection of a low dose of propofol reduces the intensity of pain at the site of injection compared with no occlusion.

METHODS

Bilateral 0.5-ml injections of an emulsion containing 10 mg/ml of propofol were given over 30 s in 75 adult surgical patients. Each patient was given one injection with and one without 60-s occlusion of the cannulated vein with a 10-min interval, and asked to score the maximal pain intensity on a visual analogue scale (VAS).

RESULTS

The maximal pain intensity [median (25th percentile; 75th percentile), range] at the site of injection was 0.5 (0; 3.5), 0-8.0 VAS units with venous occlusion and 0.5 (0; 1.4), 0-6.0 VAS units without occlusion (P= 0.042). Pain was first reported within 20 s regardless of the study regimen and was not prolonged by local venous occlusion.

CONCLUSION

Venous occlusion augments pain intensity at the site of propofol injection without prolonging pain, implying that propofol-induced pain is determined more by the blood concentration than by the duration of intravascular exposure. The low intensity of pain induced by low-dose propofol and the fading of pain despite sustained exposure suggest that initial low-dose administration of propofol should be evaluated for the attenuation of local pain induced by higher intravenous doses of propofol.

Low-dose propofol reduces the incidence of moderate to severe local pain induced by the main dose

BACKGROUND

Local pain on injection of propofol remains a considerable problem in clinical anaesthesiology. As slow infusion of a low dose of propofol induces little or no pain at the site of injection, and as propofol-induced pain fades during prolonged exposure, this randomized, double-blind, clinical cross-over study was designed to test whether pain on injection of propofol is attenuated by initial slow injection of a low dose of propofol by the same intravenous line.

METHODS

Seventy-seven adult surgical patients were cannulated in a dorsal vein on each hand. In each cannula, a 0.5-ml priming dose of either propofol 10 mg/ml dissolved in an emulsion of medium- and long-chain triglycerides or aqueous sodium chloride 9.0 mg/ml was injected over 30 s, and followed 120 s later by a main dose of 2.0 ml of the same propofol formula over 6 s. After each injection, the patients were asked by a blind investigator to score the maximal pain intensity on a visual analogue scale (VAS).

RESULTS

Although the decrease in maximal pain intensity did not reach statistical significance (P= 0.070), significantly fewer patients reported moderate or severe pain intensity (corresponding to 3.0 VAS units or more) after the main dose of propofol was preceded by a priming dose of propofol than by sodium chloride (P= 0.041).

CONCLUSIONS

The incidence of moderate to severe local pain induced by intravenous propofol can be decreased by a readily applicable technique in which a low dose of propofol emulsion is slowly administered by the same intravenous route 2 min in advance.

Stability of transgene integration and expression in subsequent generations of doubled haploid oilseed rape transformed with chitinase and beta-1,3-glucanase genes in a double-gene construct

A double-gene construct with one chitinase and one beta-1,3-glucanase gene from barley, both driven by enhanced 35S promoters, was transformed into oilseed rape. From six primary transformants expressing both transgenes 10 doubled haploid lines were produced and studied for five generations. The number of inserted copies for both the genes was determined by Southern blotting and real-time PCR with full agreement between the two methods. When copy numbers were analysed in different generations, discrepancies were found, indicating that at least part of the inserted sequences were lost in one of the alleles of some doubled haploids. Chitinase and beta-1,3-glucanase expression was analysed by Western blotting in all five doubled haploid generations. Despite that both the genes were present on the same T-DNA and directed by the same promoter their expression pattern between generations was different. The beta-1,3-glucanase was expressed at high and stable levels in all generations, while the chitinase displayed lower expression that varied between generations. The transgenic plants did not show any major impact on fungal resistance when assayed in greenhouse, although purified beta-1,3-glucanase and chitinase caused retardment of fungal growth in vitro.

Less local pain on intravenous infusion of a new propofol emulsion

BACKGROUND

Local pain at the site of intravenous (iv) injection of propofol remains a considerable problem in clinical anaesthesiology, and particularly so in infants. The aim of the present study was to compare the influence of two different emulsions of propofol on local pain following iv administration.

METHODS

Eighty adult patients (ASA I-II) scheduled for ear-nose-throat or plastic surgery were randomly allocated into two study groups: A and B. A 1.0-mm teflon cannula (BD, Helsingborg, Sweden) was inserted into a dorsal vein on each hand. Each patient was given two 3.0-ml iv bolus injections of two different propofol emulsions of 10 mg ml(-1) over 2 s, one in each cannula, at 5-min intervals. The first study drug administered was Diprivan (AstraZeneca, Södertälie, Sweden) in group A (n = 34) and Propofol-Lipuro (Braun, Melsungen, Germany) in group B (n = 39). Each patient was then asked by a blinded investigator to score maximal pain intensity on a visual analogue scale (VAS).

RESULTS

The maximal intensity of propofol-induced local pain was significantly (P < 0.0001) lower after Propofol-Lipuro than after Diprivan--median 1 (25th percentile: 0; 75th percentile: 2) range 0-6 vs. 3 (0; 5) 0-9 VAS units.

CONCLUSION

The considerably lower intensity of local pain found to be associated with iv administration of the new drug formula Propofol-Lipuro indicates that emulsions of propofol based on medium- and long-chain triglycerides have a clinical advantage over traditional ones for induction of anaesthesia.

Earlier onset of DNA fragmentation in leaves of wheat compared to barley and rye

We have found extensive nucleosomal fragmentation of native DNA extracted from leaves of healthy cereal plants, as indicated by ladder patterns on agarose gels and TUNEL staining. The time of first appearance of fragmentation differed among cereals. Native DNA from the first leaf of 10-day-old plants formed a clear ladder pattern of multiples of 180 bp fragments in wheat and triticale but not in barley and oats. In one cultivar of rye a weak ladder pattern occurred but not in another. Freezing and thawing of samples before DNA extraction resulted in much more extensive DNA fragmentation in wheat but not in rye and barley, indicating that DNA-degrading enzymes are present in the cytoplasm of wheat, but not in barley and rye, at this stage. In barley, nucleosomal fragmentation was first detected in 25-day-old plants. These results indicate that programmed cell death takes place in developing leaves of young cereal plants, but that the time of onset differs among cereal species.

Propofol infusion rate does not affect local pain on injection

BACKGROUND

Local pain at the site of an i.v. injection of propofol is a well-known problem, particularly in infants. This randomised investigator-blinded crossover study was designed to assess the effect of the i.v. bolus infusion rate on propofol-induced pain at the site of injection.

METHODS

Thirty unpremedicated patients scheduled for ear-nose-throat or plastic surgery at Malmö University Hospital, Sweden, were given two consecutive 2.0 ml injections of propofol 10 mg/ml (Diprivan, AstraZeneca, Sweden/UK), at different infusion rates (0.2 or 1.0 ml/s), immediately before induction of general anesthesia. Half of the patients (n=15) received the first bolus of propofol over 2 s and the second bolus over 10 s, and the other half (n=15) had their injections in reversed order. After each injection, the patient was asked by an investigator to indicate pain intensity on a visual analog scale (VAS) and to report the times of the appearance, maximum point and disappearance of pain. The injections were given approximately 2 min apart. The investigators scoring pain intensity, as indicated by the patients on a 10-point numerical rate scale, were blinded to the order in which the injections were given, as were the patients themselves.

RESULTS

There were no statistically significant differences in the incidence (both 86%) of intensity (median; 25th; 75th percentiles, in VAS units: 3.1; 1.0; 5.3 and 3.3; 1.4; 5.0, respectively) or duration (66+/-31 and 73+/-26 s, respectively) of pain between the faster (1.0 ml/s) and slower (0.2 ml/s) bolus infusion rates of propofol studied.

CONCLUSIONS

We conclude that the i.v. bolus infusion rate of propofol does not influence drug-induced local pain on injection, at least not within the infusion rate interval studied. Therefore, adjusting i.v. injection speed does not seem to be a clinically useful tool for reducing the intensity or duration of propofol-induced pain at the site of administration.

Pain on injection of propofol with or without infusion of carrier fluid

BACKGROUND

Propofol, a popular intravenous (iv) anaesthetic induction agent for brief cases or day surgery, is associated with smooth induction, pleasant sleep, rapid recovery and little postoperative nausea. A major disadvantage is pain at the site of injection. The aim of the present study was to examine the influence of simultaneous iv infusion of carrier fluid on propofol-induced local pain.

METHODS

Thirty patients, scheduled for ear-nose-throat or plastic surgery under general anaesthesia, were randomly allocated into two groups. Each patient had two 2 ml iv bolus injections of propofol given at two minutes' interval. In group I (n=15) the first bolus injection was given with no iv carrier fluid and the second one given with a 10 ml iv carrier fluid infused over 10 s. Correspondingly, the patients in group II (n=15) had their first injection with and their second one without the iv carrier fluid. Following each injection of propofol the patients were asked by a blinded investigator to score their pain on a 10-point visual analogue scale, and to report the appearance, maximum and disappearance of pain. After the second assessment of pain, general anaesthesia was induced with more propofol.

RESULTS

Pain intensity at the site of propofol injection was found not to be influenced by simultaneous iv infusion of carrier fluid.

CONCLUSION

It seems, from the results obtained here, that simultaneous iv infusion of carrier fluid has no particular effect on local pain following iv administration of propofol.

DNA fragmentation in cereal roots indicative of programmed root cortical cell death

In cereals, a progressively increasing root cortical cell death (RCD) occurs from the root tip and upwards when measured with vital staining methods. In this study, nuclear DNA fragmentation was studied in seminal root segments of wheat and barley in order to investigate if the cell death resembled apoptosis. The fraction of cells with TUNEL-positive nuclei increased gradually with increasing root age in both the cortex and the stele. Southern analysis showed a typical ladder pattern, indicating nucleosomal fragmentation already in 2-day-old root segments, and this became more pronounced in older root segments. DNA fragmentation appeared to be more extensive in wheat than in barley roots. These results confirm earlier studies, where RCD has been found to be earlier initiated and to proceed at a faster rate in wheat. The characteristic DNA fragmentation found in the roots indicates programmed cell death with mechanistic similarities to apoptosis. Ultrastructural examination of nuclei in cortex cells with transmission electron microscopy revealed an increased chromatin condensation in older roots, particularly in wheat. In addition, we found nucleosomal DNA ladders in young leaf tissue from wheat but not from barley.

Comparisons of early root cortical senescence between barley cultivars, Triticum species and other cereals

The natural rate of root cortical death (RCD) in seminal roots was investigated in different cereals by staining the roots with acridine orange. In all cereals investigated the part of the cortex having stainable nuclei gradually decreased with increased age of the root. Wheat differed from barley, oats and rye in having a much faster rate of RCD In 15-d-old root regions of wheat grown in soil, only 10-20% of the radius of the root had stainable nuclei. In barley, oats and rye the amount of cortex with stainable nuclei varied between 65 and 80% Minor differences in RCD were found between different barley cultivars or accessions. Large variation in RCD was found between different Triticum species: T. monococcum, T. dicoccum and different Aegilops species had much slower RCD than did hexaploid wheat. These results are discussed in relation to microbial colonization of roots and susceptibility to root pathogens.

Effect of prehelminthosporol, a phytotoxin produced by Bipolaris sorokiniana, on barley roots

The effects of prehelminthosporol, a toxin produced by Bipolaris sorokiniana, were investigated on barley roots. A concentration of 30 μg∙mL−1 prehelminthosporol or higher in nutrient solution significantly increased the rate of nuclear disintegration in the root cortex cells. The toxin also increased leakage of ATP from intact roots of barley seedlings grown in nutrient solution, but the growth rate of the seedlings was not significantly affected. However, diluted filtrate from liquid shake cultures of the fungus inhibited the growth of the seedlings by 21 – 73% over a 5-day period. The results indicate that the toxin may play an important role in pathogenesis by killing or weakening plant cells in advance of the growing hyphae and facilitating nutrient uptake and further growth of the fungus in plant tissue. Different cultivars of barley differed in sensitivity to prehelminthosporol, but sensitivities were not correlated with known levels of resistance to B. sorokiniana. Key words: Cochliobolus sativus, Hordeum vulgare, root cortex, toxin, prehelminthosporol, ATP.

Carbon Fluxes in Plant-Soil Systems at Elevated Atmospheric CO2 Levels

The flow of carbon from photosynthesizing tissues of higher plants, through the roots and into the soil is one of the key processes in terrestrial ecosystems. An increased level of CO₂ in the atmosphere will likely result in an increased input of organic carbon into the soil due to the expected increase in primary production. Whether this will lead to accumulation of greater amounts of organic carbon in soil depends on the flow of carbon through the plant into the soil and its subsequent transformation in the soil by microorganisms. In this paper the major controls of carbon translocation via roots into the soil as well as the subsequent microbial turnover of root-derived carbon are reviewed. We discuss possible consequences of an increased CO₂ level in the atmosphere on these processes.

Influence of different application rates of nitrogen to soil on rhizosphere bacteria

The bacterial populations in the rhizosphere of wheat were investigated under different soil nitrogen regimes. Two different levels of nitrogen (250 and 50 mg N per plant) were added as a single application or split in time during growth, and consequently smaller amounts were given each time. The different application methods enabled the study of the bacterial populations in relation to nitrogen concentrations in the roots and in the soil with comparable rates of plant biomass production. When the nitrogen was applied as a single dose at the start of the experiment significantly larger numbers of bacteria (colony forming units) were found in the rhizosphere than in the other treatments. This was correlated with higher nitrogen concentrations in the roots and with higher levels of extractable mineral nitrogen in the soil. In contrast, the numbers of fluorescent pseudomonads were smaller when a high nitrogen rate was applied once. Possible mechanisms for the observed changes in the microbial populations are discussed. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Fluctuations in the fluorescent pseudomonad and actinomycete populations of rhizosphere and rhizoplane during the growth of spring wheat

The total bacterial populations, fluorescent pseudomonads, and actinomycetes in the rhizosphere, rhizoplane, and endorhizosphere of two wheat lines (C-R5B and C-R5D) were investigated weekly during plant growth. The total numbers of bacteria (colony-forming units) were counted on a low-nutrient agar medium, while the numbers of fluorescent pseudomonads and actinomycetes were determined by means of selective media. Fluorescent pseudomonads generally constituted less than 0.5% of the total bacterial numbers and the percentage significantly decreased with time in the rhizosphere, rhizoplane, and root-free soil. The percentages of fluorescent pseudomonads were lower in the rhizoplane than in the rhizosphere, and in the endorhizosphere they were barely detectable. The rapid decline of fluorescent pseudomonads frequently observed in survival studies may be explained by the inability of the plant to support this group of bacteria during later development of its rhizosphere. Actinomycetes generally represented no more than 7% of the total bacterial numbers. Actinomycete percentages were highest in the rhizosphere and root-free soil and lowest in the endorhizosphere. Only minor differences were found in total bacterial numbers and in the numbers of fluorescent pseudomonads between the two wheat lines. However, numbers of actinomycetes were significantly different over the whole experiment between wheat line C-R5B and C-R5D in the rhizosphere, rhizoplane, and endorhizosphere. Key words: actinomycetes, bacteria, fluorescent pseudomonads, rhizosphere, sampling time.

Pathogenic variation and sexual reproduction in Swedish populations of Bremia lactucae

The host-pathogen interaction between lettuce (Lactuca sativa) and downy mildew (Bremia lactucae) is mainly differential and the resistance so far utilized in the host is vertical. As in many other obligate parasites, the introduction of cultivars with new vertical resistance has exerted a strong selection pressure on the pathogen resulting in significant changes in virulence frequencies and in the establishment of races with new combinations of virulence. Genetic diversity in pathogen populations may arise through mutation and gene flow, and new virulence genotypes may then be established through parasexuality and sexual recombination. In Swedish populations of Bremia lactucae, the pattern of variation in the parasite agrees well with that which might be expected in a diploid, outcrossing organism with frequent sexual reproduction. This is supported by: two or more isolates, different in virulence and mating type, may occur together on the same lettuce leaf; zygotes (oospores) are formed in all populations investigated and the frequency varies from 22% to 98%; oospores germinate rather frequently under suitable conditions. To breed for resistance in dynamic host-pathogen systems such as this one is difficult and the program should preferably be based on race-non-specific resistance.