Helmut Baltruschat

Salt tolerance of barley induced by the root endophyte Piriformospora indica is associated with a strong increase in antioxidants.

The root endophytic basidiomycete Piriformospora indica has been shown to increase resistance against biotic stress and tolerance to abiotic stress in many plants. Biochemical mechanisms underlying P. indica-mediated salt tolerance were studied in barley (Hordeum vulgare) with special focus on antioxidants. Physiological markers for salt stress, such as metabolic activity, fatty acid composition, lipid peroxidation, ascorbate concentration and activities of catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase and glutathione reductase enzymes were assessed. Root colonization by P. indica increased plant growth and attenuated the NaCl-induced lipid peroxidation, metabolic heat efflux and fatty acid desaturation in leaves of the salt-sensitive barley cultivar Ingrid. The endophyte significantly elevated the amount of ascorbic acid and increased the activities of antioxidant enzymes in barley roots under salt stress conditions. Likewise, a sustained up-regulation of the antioxidative system was demonstrated in NaCl-treated roots of the salt-tolerant barley cultivar California Mariout, irrespective of plant colonization by P. indica. These findings suggest that antioxidants might play a role in both inherited and endophyte-mediated plant tolerance to salinity.

The mutualistic fungus Piriformospora indica protects barley roots from a loss of antioxidant capacity caused by the necrotrophic pathogen Fusarium culmorum.

Fusarium culmorum causes root rot in barley (Hordeum vulgare), resulting in severely reduced plant growth and yield. Pretreatment of roots with chlamydospores of the mutualistic root-colonizing basidiomycete Piriformospora indica (subdivision Agaricomycotina) prevented necrotization of root tissues and plant growth retardation commonly associated with Fusarium root rot. Quantification of Fusarium infections with a real-time polymerase chain reaction assay revealed a correlation between root rot symptoms and the relative amount of fungal DNA. Fusarium-infected roots showed reduced levels of ascorbate and glutathione (GSH), along with reduced activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, GSH reductase, dehydroascorbate reductase, and monodehydroascorbate reductase. Consistent with this, Fusarium-infected roots showed elevated levels of lipid hydroperoxides and decreased ratios of reduced to oxidized forms of ascorbate and GSH. In clear contrast, roots treated with P. indica prior to inoculation with F. culmorum showed levels of ascorbate and GSH that were similar to controls. Likewise, lipid peroxidation and the overall reduction in antioxidant enzyme activities were largely attenuated by P. indica in roots challenged by F. culmorum. These results suggest that P. indica protects roots from necrotrophic pathogens, at least partly, through activating the plants antioxidant capacity.

Expression of barley BAX Inhibitor‐1 in carrots confers resistance to Botrytis cinerea

SUMMARY BAX Inhibitor-1 (BI-1) is a protein that controls heterologous BAX-induced cell death, the hypersensitive reaction and abiotic stress-induced cell death in plants. When over-expressed in epidermal cells of barley, barley BI-1 induces susceptibility to the biotrophic fungal pathogen Blumeria graminis. When we expressed barley BI-1 in carrot susceptible to the necrotrophic fungus Botrytis cinerea, we obtained BI-1-mediated resistance to fungus-induced leaf cell death and less fungal spreading on the leaves. Barley BI-1 also mediated resistance to Chalara elegans in carrot roots. The results support the idea that cell death inhibition is an applicable approach to control cell-death-inducing pathogens in crop plants.

Soil engineering ants increase grass root arbuscular mycorrhizal colonization

The role of edaphic factors in driving the relationship between plant community structure and ecosystem processes is a key issue of the current debate on functional implications of biodiversity. In this study, we draw a direct link between aboveground/belowground relationships, vegetation structure, and aboveground management. We used ground nesting ants and arbuscular mycorrhizal fungi (AMF) as an example for quantifying the role of biotic interactions in soil. Although both groups are known to have a major impact on grasslands, the interactive effect of these taxa on vegetation structure and its sensitivity to grassland management is poorly understood. We show that the ant Lasius flavus increases the root arbuscular mycorrhizal colonization (AMC) of grasses by modifying biotic and abiotic soil properties. As a possible consequence, the shoot length of grass growing on ant mounds was shorter and shoot N and P concentrations were higher than in grass growing off of the mounds. In addition, management affected ant nest architecture and soil and, in turn, AMC. These results emphasize the need to consider the interactions between plants, soil microorganisms, soil fauna, and aboveground management to increase the understanding of the drivers of biodiversity and ecosystem functioning in grasslands both aboveground and belowground.

Impact of arbuscular mycorrhiza on the St. John’s wort (Hypericum perforatum) wilt disease induced by Colletotrichum cf. gloeosporioides

The importance of herbal plants is evident in the prevalent use as flavoring ingredients in food. However, meeting the growing demand for organic grown spices and ‘medicinal plants’ of regional origin is often hampered by technical difficulties during cultivation. Arbuscular mycorrhizal fungi (AMF) can support their host, by helping them to adapt to prevailing local conditions and thus increase the health of the plants.The aim of the present work was to evaluate the effects of arbuscular mycorrhiza (AMF) on the plant’s health, using St. John’s wort (Hypericum perforatum) - Colletotrichum cf. gloeosporioides (Cfg) as the model plant pathosystem.Following inoculation with AMF, the attack of St. John’s wort with Cfg led to a clear reduction in wilting of the two St. John’s wort cultivars. Furthermore, the yield of mycor-rhizal plants increased compared to non-mycorrhizal plants, irrespective of whether they were pathogen-infected or not. Compared to non-mycorrhizal plants, in mycorrhizal plants levels of ascorbic acid were elevated and activity of antioxidant enzymes increased after inoculation with Cfg. Furthermore, in mycorrhizal plants the progress in lipid peroxidation following pathogen attack was reduced, suggesting that the reduction of lipid peroxidation and the induction of antioxidants may play a crucial role in the plant’s defense against Cfg.