Search Results (2)

Photosynthetic orchids associate with mycorrhizal fungi that can be mostly ascribed to the “rhizoctonia” species complex. Rhizoctonias’ phylogenetic diversity covers a variety of ecological/nutritional strategies that include, beside the symbiosis establishment with host plants, endophytic and pathogenic associations with non-orchid plants or saprotrophic soil colonization. In addition, orchid mycorrhizal fungi (OMF) that establish a symbiotic relationship with an orchid host can later proliferate in browning and rotting orchid tissues. Environmental triggers and molecular mechanisms governing the switch leading to either a saprotrophic or a mycorrhizal behavior in OMF remain unclear. As the sequenced OMF genomes feature a wide range of genes putatively involved in the degradation of plant cell wall (PCW) components, we tested if these transitions may be correlated with a change in the expression of some PCW degrading enzymes. Regulation of several genes encoding PCW degrading enzymes was evaluated during saprotrophic growth of the OMF Tulasnella calospora on different substrates and under successful and unsuccessful mycorrhizal symbioses. Fungal gene expression in planta was investigated in two orchid species, the terrestrial Mediterranean Serapias vomeracea and the epiphytic tropical Cattleya purpurata. Although we only tested a subset of the CAZyme genes identified in the T. calospora genome, and we cannot exclude therefore a role for different CAZyme families or members inside a family, the results showed that the degradative potential of T. calospora is finely regulated during saprotrophic growth and in symbiosis, often with a different regulation in the two orchid species. These data pose novel questions about the role of fungal PCW degrading enzymes in the development of unsuccessful and successful interactions. Full article

The volatile fractions from fresh inflorescences of naturally growing orchids Anacamptis coriophora (L.) R. M. Bateman, Pridgeon & M. W. Chase subsp. fragrans (Pollini), Anacamptis pyramidalis (L.) R. Ophrys holosericea (Burm.) Greuter and Serapias vomeracea (Burm. f.) B. were isolated by steam distillation and analyzed by GC/FID and GC/MS. Saturated hydrocarbons were quantified as the major constituents of the volatile fraction (47.87–81.57% of the total essential oil), of which long-chain monounsaturated hydrocarbons accounted from 9.20% to 32.04% of the total essential oil. Double bond position in linear alkenes was highlighted by dimethyl disulfide derivatization and MS fragmentation. Aldehydes (from 3.45 to 18.18% of the total essential oil), alcohols (from 0.19% to 13.48%), terpenes (from 0.98 to 2.50%) and acids (0.30 to 2.57%) were also detected. These volatiles compounds may represent a particular feature of these plant species, playing a critical role in the interaction with pollinators. DPPH assay evaluating the antioxidant activity of the essential oils was carried out, showing a dose-dependent antioxidant activity. Full article