Mechanism of copper nanoparticle toxicity in rainbow trout olfactory mucosa.

Chemosensory perception is crucial for fish reproduction and survival. Direct contact of olfactory neuroepithelium to the surrounding environment makes it vulnerable to contaminants in aquatic ecosystems. Copper nanoparticles (CuNPs), which are increasingly used in commercial and domestic applications due their exceptional properties, can impair fish olfactory function. However, the molecular events underlying olfactory toxicity of CuNPs are largely unexplored. Our results suggested that CuNPs were bioavailable to olfactory mucosal cells. Using RNA-seq, we compared the effect of CuNPs and copper ions (Cu2+) on gene transcript profiles of rainbow trout (Oncorhynchus mykiss) olfactory mucosa. The narrow overlap in differential gene expression between the CuNP- and Cu2+-exposed fish revealed that these two contaminants exert their effects through distinct mechanisms. We propose a transcript-based conceptual model that shows that olfactory signal transduction, calcium homeostasis, and synaptic vesicular signaling were affected by CuNPs in the olfactory sensory neurons (OSNs). Neuroregenerative pathways were also impaired by CuNPs. In contrast, Cu2+ did not induce toxicity pathways and rather upregulated regeneration pathways. Both Cu treatments reduced immune system pathway transcripts. However, suppression of transcripts that were associated with inflammatory signaling was only observed with CuNPs. Neither oxidative stress nor apoptosis were triggered by Cu2+ or CuNPs in mucosal cells. Dysregulation of transcripts that regulate function, maintenance, and reestablishment of damaged olfactory mucosa represents critical mechanisms of toxicity of CuNPs. The loss of olfaction by CuNPs may impact survival of rainbow trout and impose an ecological risk to fish populations in contaminated environments.

Stomatal characteristics of riparian poplar species in a semi-arid environment.

Several native poplar species meet at the margins of their natural distributions in southern Alberta, Canada. In this semi-arid area, poplars are obligate riparian species but they occupy several intergrading ecoregions. Populus deltoides Bartr. ex Marsh predominates in the warmest and driest eastern prairie ecoregions; P. balsamifera L. occupies the cooler and wetter western parkland and montane ecoregions; and P. angustifolia James and hybrids between the species occur in the intermediate grassland ecoregions. We investigated stomatal characteristics of these poplars in 51 genotypes collected across the range of ecoregions and grown in a semi-arid common garden. Stomatal length differed among genotypes within species but did not differ among species, ranging from 19 to 22 microm. Total stomatal densities (adaxial plus abaxial) differed among genotypes within species but were similar among species (290-420 stomata mm(-2)). Single-surface stomatal densities differed among species and consequently, the ratio of adaxial:abaxial stomatal density also differed, ranging from 0.94 for P. deltoides to 0.27 for P. balsamifera, with intermediate stomatal density ratios in P. angustifolia and hybrids. In a subsequent study of a subset of the same genotypes, stomatal density was correlated with stomatal conductance (r2 = 0.75) and the conductance ratios differed among species in the same manner as the stomatal density ratios. We conclude that: (1) diverse poplar genotypes respond similarly to a semi-arid environment by producing comparatively small and dense stomata; (2) differences in stomatal density underlie differences in stomatal conductance and differences among species in stomatal density ratio or conductance ratio may reflect adaptation to climatic differences among ecoregions; and (3) there is substantial variation in stomatal characteristics within and among species and hybrids in this area that could be useful for the selection and breeding of poplars adapted to different climatic conditions.