143 research outputs found
The influence of the ectomycorrhizal fungus Rhizopogon subareolatus on growth and nutrient element localisation in two varieties of Douglas fir (Pseudotsuga menziesii var. menziesii and var. glauca) in response to manganese stress
Acidification of forest ecosystems leads to increased plant availability of the micronutrient manganese (Mn), which is toxic when taken up in excess. To investigate whether ectomycorrhizas protect against excessive Mn by improving plant growth and nutrition or by retention of excess Mn in the hyphal mantle, seedlings of two populations of Douglas fir (Pseudotsuga menziesii), two varieties, one being menziesii (DFM) and the other being glauca (DFG), were inoculated with the ectomycorrhizal fungus Rhizopogon subareolatus in sand cultures. Five months after inoculation, half of the inoculated and non-inoculated seedlings were exposed to excess Mn in the nutrient solution for further 5Â months. At the end of this period, plant productivity, nutrient concentrations, Mn uptake and subcellular compartmentalisation were evaluated. Non-inoculated, non-stressed DFM plants produced about 2.5 times more biomass than similarly treated DFG. Excess Mn in the nutrient solution led to high accumulation of Mn in needles and roots but only to marginal loss in biomass. Colonisation with R. subareolatus slightly suppressed DFM growth but strongly reduced that of DFG (â50%) despite positive effects of mycorrhizas on plant phosphorus nutrition. Growth reductions of inoculated Douglas fir seedlings were unexpected since the degree of mycorrhization was not high, i.e. ca. 30% in DFM and 8% in DFG. Accumulation of high Mn was not prevented in inoculated seedlings. The hyphal mantle of mycorrhizal root tips accumulated divalent cations such as Ca, but not Mn, thus not providing a barrier against excessive Mn uptake into the plants associated with R. subareolatus
The genome of the emerging barley pathogen Ramularia collo-cygni
Background
Ramularia collo-cygni is a newly important, foliar fungal pathogen of barley that causes the disease Ramularia leaf spot. The fungus exhibits a prolonged endophytic growth stage before switching life habit to become an aggressive, necrotrophic pathogen that causes significant losses to green leaf area and hence grain yield and quality.
Results
The R. collo-cygni genome was sequenced using a combination of Illumina and Roche 454 technologies. The draft assembly of 30.3 Mb contained 11,617 predicted gene models. Our phylogenomic analysis confirmed the classification of this ascomycete fungus within the family Mycosphaerellaceae, order Capnodiales of the class Dothideomycetes. A predicted secretome comprising 1053 proteins included redox-related enzymes and carbohydrate-modifying enzymes and proteases. The relative paucity of plant cell wall degrading enzyme genes may be associated with the stealth pathogenesis characteristic of plant pathogens from the Mycosphaerellaceae. A large number of genes associated with secondary metabolite production, including homologs of toxin biosynthesis genes found in other Dothideomycete plant pathogens, were identified.
Conclusions
The genome sequence of R. collo-cygni provides a framework for understanding the genetic basis of pathogenesis in this important emerging pathogen. The reduced complement of carbohydrate-degrading enzyme genes is likely to reflect a strategy to avoid detection by host defences during its prolonged asymptomatic growth. Of particular interest will be the analysis of R. collo-cygni gene expression during interactions with the host barley, to understand what triggers this fungus to switch from being a benign endophyte to an aggressive necrotroph
Stressed out symbiotes:hypotheses for the influence of abiotic stress on arbuscular mycorrhizal fungi
Abiotic stress is a widespread threat to both plant and soil communities. Arbuscular mycorrhizal (AM) fungi can alleviate effects of abiotic stress by improving host plant stress tolerance, but the direct effects of abiotic stress on AM fungi are less well understood. We propose two hypotheses predicting how AM fungi will respond to abiotic stress. The stress exclusion hypothesis predicts that AM fungal abundance and diversity will decrease with persistent abiotic stress. The mycorrhizal stress adaptation hypothesis predicts that AM fungi will evolve in response to abiotic stress to maintain their fitness. We conclude that abiotic stress can have effects on AM fungi independent of the effects on the host plant. AM fungal communities will change in composition in response to abiotic stress, which may mean the loss of important individual species. This could alter feedbacks to the plant community and beyond. AM fungi will adapt to abiotic stress independent of their host plant. The adaptation of AM fungi to abiotic stress should allow the maintenance of the plant-AM fungal mutualism in the face of changing climates. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00442-016-3673-7) contains supplementary material, which is available to authorized users
UÄinak bakra na toksiÄnost i genotoksiÄnost kadmija u vodenoj leÄi (Lemna minor L.)
We investigated interactions between copper (in the concentrations of 2.5 ÎŒmol L-1 and 5 ÎŒmol L-1) and cadmium (5 ÎŒmol L-1) in common duckweed (Lemna minor L.) by exposing it to either metal or to their combinations for four or seven days. Their uptake increased with time, but it was lower in plants treated with combinations of metals than in plants treated with either metal given alone. In separate treatments, either metal increased malondialdehyde (MDA) level and catalase and peroxidase activity. Both induced DNA damage, but copper did it only after 7 days of treatment. On day 4, the combination of cadmium and 5 ÎŒmol L-1 copper additionally increased MDA as well as catalase and peroxidase activity. In contrast, on day 7, MDA dropped in plants treated with combinations of metals, and especially with 2.5 ÎŒmol L-1 copper plus cadmium. In these plants, catalase activity was higher than in copper treated plants. Peroxidase activity increased after treatment with cadmium and 2.5 ÎŒmol L-1 copper but decreased in plants treated with cadmium and 5 ÎŒmol L-1 copper. Compared to copper alone, combinations of metals enhanced DNA damage after 4 days of treatment but it dropped on day 7. In conclusion, either metal given alone was toxic/genotoxic and caused oxidative stress. On day 4 of combined treatment, the higher copper concentration was more toxic than either metal alone. In contrast, on day 7 of combined treatment, the lower copper concentration showed lower oxidative and DNA damage. These complex interactions can not be explained by simple antagonism and/or synergism. Further studies should go in that direction.U svrhu istraĆŸivanja interakcija izmeÄu bakra kao esencijalnog elementa te kadmija kao neesencijalnog i toksiÄnog metala, vodenu leÄu Lemna minor L. uzgajali smo na podlogama s kadmijem (5 ÎŒmol L-1) odnosno s bakrom (2,5 ÎŒmol L-1 i 5 ÎŒmol L-1) te s njihovim kombinacijama. Unos metala u biljke poveÄavao se s trajanjem pokusa, a kod kombinacije metala u biljkama je izmjerena niĆŸa koliÄina kadmija nego u onima uzgajanima samo na kadmiju. U biljkama tretiranim pojedinaÄnim metalom doĆĄlo je do poveÄanja
sadrĆŸaja malondialdehida (MDA) te aktivnosti katalaze i peroksidaze u odnosu na kontrolne biljke. TakoÄer, primijeÄeno je oĆĄteÄenje DNA iako kod bakra tek sedmog dana tretmana. KoliÄina MDA i aktivnost obaju enzima dodatno se poveÄala na tretmanu kombinacijom kadmija i bakra (5 ÎŒmol L-1) nakon Äetvrtog dana pokusa, dok se koliÄina MDA smanjila nakon sedmog dana kod kombinacije kadmija i 2,5 ÎŒmol L-1 bakra. U tim biljkama primijeÄena je i veÄa aktivnost katalaze, dok je aktivnost peroksidaze porasla na tretmanu kadmijem i 2,5 ÎŒmol L-1 bakrom, ali se smanjila na tretmanu kadmijem i 5 ÎŒmol L-1 bakrom. OĆĄteÄenje DNA koje je bilo veÄe kod kombinacije metala nakon Äetvrtog dana, osobito u usporedbi sa samim bakrom, smanjilo se nakon sedmog dana pokusa. Iz ovih rezultata moĆŸe se zakljuÄiti da su oba metala u istraĆŸivanim koncentracijama toksiÄna i genotoksiÄna za vodenu leÄu i da uzrokuju oksidacijski stres. Kadmij u kombinaciji s bakrom viĆĄe koncentracije bio je toksiÄniji od pojedinaÄnih metala nakon
Äetvrtog dana pokusa, dok su u biljaka tretiranih kombinacijom kadmija i bakra niĆŸe koncentracije toksiÄni uÄinci bili manji. BuduÄi da su primijeÄene interakcije vrlo kompleksne i ne ukljuÄuju samo antagonizam odnosno sinergizam potrebna su daljnja istraĆŸivanja
- âŠ