Emerging applications of nanosized iron oxides in nanotechnology introduce vast quantities of nanomaterials into the human environment, thus raising some concerns. Here we report that the surface of γ-Fe(2)O(3) nanoparticles 20-40 nm in diameter mediates production of highly reactive hydroxyl radicals (OH(•)) under conditions of the biologically relevant superoxide-driven Fenton reaction. By conducting comparative spin-trapping EPR experiments, we show that the free radical production is attributed primarily to the catalytic reactions at the nanoparticles' surface rather than being caused by the dissolved metal ions released by the nanoparticles as previously thought. Moreover, the catalytic centers on the nanoparticle surface were found to be at least 50-fold more effective in OH(•) radical production than the dissolved Fe(3+) ions. Conventional surface modification methods such as passivating the nanoparticles' surface with up to 935 molecules of oleate or up to 18 molecules of bovine serum albumin per iron oxide core were found to be rather ineffective in suppressing production of the hydroxyl radicals. The experimental protocols developed in this study could be used as one of the approaches for developing analytical assays for assessing the free radical generating activity of a variety of nanomaterials that is potentially related to their biotoxicity.

The phytohormones, abscisic acid and cytokinin, once were thought to be present uniquely in plants, but increasing evidence suggests that these hormones are present in a wide variety of organisms. Few studies have examined fungi for the presence of these "plant" hormones or addressed whether their levels differ based on the nutrition mode of the fungus. This study examined 20 temperate forest fungi of differing nutritional modes (ectomycorrhizal, wood-rotting, saprotrophic). Abscisic acid and cytokinin were present in all fungi sampled; this indicated that the sampled fungi have the capacity to synthesize these two classes of phytohormones. Of the 27 cytokinins analyzed by HPLC-ESI MS/MS, seven were present in all fungi sampled. This suggested the existence of a common cytokinin metabolic pathway in fungi that does not vary among different nutritional modes. Predictions regarding the source of isopentenyl, cis-zeatin and methylthiol CK production stemming from the tRNA degradation pathway among fungi are discussed.

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Ustilago maydis is the causative agent of common smut of corn. Early studies noted its ability to synthesize phytohormones and, more recently these growth promoting substances were confirmed as cytokinins (CKs). Cytokinins comprise a group of phytohormones commonly associated with actively dividing tissues. Lab analyses identified variation in virulence between U. maydis dikaryon and solopathogen infections of corn cob tissue. Samples from infected cob tissue were taken at sequential time points post infection and biochemical profiling was performed using high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI MS/MS). This hormone profiling revealed that there were altered levels of ABA and major CKs, with a marked reduction in CK glucosides, increases in methylthiol CKs and a particularly dramatic increase in cisZ CK forms, in U. maydis infected tissue. These changes were more pronounced in the more virulent dikaryon relative to the solopathogenic strain suggesting a role for cytokinins in moderating virulence during biotrophic infection. These findings highlight the fact that U. maydis does not simply mimic a fertilized seed but instead reprograms the host tissue. Results underscore the suitability of the Ustilago maydis– Zea mays model as a basis for investigating the control of phytohormone dynamics during biotrophic infection of plants.

Phytohormones derived from fungi play a key role in regulating plant-pathogen interactions; however, deciphering the separate contributions of pathogen and plant during infection has been difficult. Here, the Ustilago maydis-Zea mays pathosystem was used to investigate this chemical exchange. Ustilago maydis, the causative agent of maize smut, produces cytokinins (CK), which are a group of phytohormones responsible for directing plant development. The characteristic symptom of smut disease is the formation of tumours composed of plant and fungal tissue. Isopentenyltransferase (IPT) catalyses the rate-limiting step in CK biosynthesis, and U. maydis strains in which the sole tRNA-ipt gene was deleted no longer produced CKs. These deletion strains elicited fewer, smaller tumours than the pathogenic strain SG200. High performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI MS/MS) was used to detect and quantify phytohormone levels in infected tissue. This revealed that key hormone changes in SG200 infections were not present in infections by deletion strains, suggesting that CK production by U. maydis is required for the altered phytohormone profile in infected tissue relative to uninfected tissue. Separate analyses indicated that U. maydis tRNA-ipt mutants might be altered in their ability to metabolize CKs taken up from the environment. Mining the U. maydis genome identified genes encoding putative CK signalling and biosynthesis proteins.