SUMMARYGlutamine synthetase (GSase), the enzyme that catalyses the conversion of glutamate and ammonia to glutamine, is present at high levels in vertebrate brain tissue and is thought to protect the brain from elevated ammonia concentrations. We tested the hypothesis that high brain GSase activity is critical in preventing accumulation of brain ammonia and glutamate during ammonia loading in the ammonia-intolerant rainbow trout. Trout pre-injected with saline or the GSase inhibitor methionine sulfoximine (MSOX, 6mgkg -1 ), were exposed to 0, 670 or 1000moll -1 NH 4 Cl in the water for 24 and 96h. Brain ammonia levels were 3-to 6-fold higher in ammonia-exposed fish relative to control fish and MSOX treatment did not alter this. Brain GSase activity was unaffected by ammonia exposure, while MSOX inhibited GSase activity by ~75%. Brain glutamate levels were lower and glutamine levels were higher in fish exposed to ammonia relative to controls. While MSOX treatment had little impact on brain glutamate, glutamine levels were significantly reduced by 96h. With ammonia treatment, significant changes in the concentration of multiple other brain amino acids occurred and these changes were mostly reversed or eliminated with MSOX. Overall the changes in amino acid levels suggest that multiple enzymatic pathways can supply glutamate for the production of glutamine via GSase during ammonia exposure and that alternative transaminase pathways can be recruited for ammonia detoxification. Plasma cortisol levels increased 7-to 15-fold at 24h in response to ammonia and MSOX did not exacerbate this stress response. These findings indicate that rainbow trout possess a relatively large reserve capacity for ammonia detoxification and for preventing glutamate accumulation during hyperammonaemic conditions.

The aim of this study was to assess the effect of cytokinins not commonly used for shoot induction from zygotic embryos of Pinus radiata D. Don. The influence of in vitro shoot and root induction treatments on the subsequent ex vitro development of the regenerated plants was also tested. Embryos were cultured with benzyladenine (BA), thidiazuron (T) and two cytokinins not previously assayed in radiata pine organogenesis (meta-topolin (m-T) and zeatin (Z)) in a range of concentrations and induction periods. Shoot induction treatments were assayed in seeds from different geographical origins to obtain wider conclusions. We analysed the effect of these cytokinin treatments on in vitro rooting with different auxins ((indole-3-butyric acid (IBA) and 1-naphtalene acetic acid (NAA)) and the traditionally used mixture. After in vitro rooting, the plantlets were acclimatized and their ex vitro behaviour was evaluated. Shoot induction treatments with 1 μM BA for 2 weeks, 4.4 μM BA for 3 weeks or 1 μM Z for 3 weeks were more effective than the other treatments. An interaction between in vitro shoot and root induction treatments was observed. IBA was more efficient for plant production because the explants rooted in this auxin had better survival rates in the greenhouse.

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We investigated whether abundant and relatively rare plants, either native or exotic, from an old-field site associate with different fungal communities and their symbiotic relationships with soil biota. Plant abundance and origin determined the fungal community. Fungal richness was higher for native abundant as opposed to relatively rare native plant species. This was not observed for exotics of contrasting abundance. Abundant exotics were the least mycorrhizal whereas rare natives were most susceptible to enemy attack. Our results suggest that compared to exotics, the relative abundance of native plant species in our old field-site is linked to the structure of belowground fungal communities.

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Little is known about the adaptive capacity of arbuscular mycorrhizal (AM) fungi to novel hosts. Here we assessed the possibility of two heterospecific AM fungal isolates to adaptively change, in terms of host biomass response, as a function of host plant identity, over the course of a growing season. First, we produced pure inocula of Rhizophagus clarus and Rhizophagus intraradices, each starting from a single spore. Second, we "trained" each isolate individually in a community with two plants, sudangrass (Sorgum bicolour subsp. drummondii) and leek (Aliium ampeloprasum var. porrum), using a dual-compartment system to allow the establishment of a common mycorrhizal network between the two hosts. Third, we conducted a greenhouse experiment to reciprocally test each "trained" clone, obtained from each compartment, either with the same (home), or the other host (away) under two contrasting phosphorus levels. Overall, results did not support adaptive responses of the AM fungi to their hosts (i.e., greater host biomass under "home" relative to "away" conditions), but the opposite (i.e., greater host biomass under "away" relative to "home" conditions) was more frequently observed. These changes in AM fungal symbiotic functioning open the possibility for relatively rapid genetic change of arbuscular mycorrhizal fungi in response to new hosts, which represents one step forward from in vitro experiments.

Citation: Sanderson LA, Antunes PM (2013) The exotic invasive plant Vincetoxicum rossicum is a strong competitor even outside its current realized climatic temperature range. NeoBiota 16: 1-16. doi: 10.3897/neobiota.16.4012 Abstract Dog-strangling vine (Vincetoxicum rossicum) is an exotic plant originating from Central and Eastern Europe that is becoming increasingly invasive in southern Ontario, Canada. Once established, it successfully displaces local native plant species but mechanisms behind this plant's high competitive ability are not fully understood. It is unknown whether cooler temperatures will limit the range expansion of V. rossicum, which has demonstrated high tolerance for other environmental variables such as light and soil moisture. Furthermore, if V. rossicum can establish outside its current climatic limit it is unknown whether competition with native species can significantly contribute to reduce fitness and slow down invasion. We conducted an experiment to test the potential of V. rossicum to spread into northern areas of Ontario using a set of growth chambers to simulate southern and northern Ontario climatic temperature regimes. We also tested plant-plant competition by growing V. rossicum in pots with a highly abundant native species, Solidago canadensis, and comparing growth responses to plants grown alone. We found that the fitness of V. rossicum was not affected by the cooler climate despite a delay in reproductive phenology. Growing V. rossicum with S. canadensis caused a significant reduction in seedpod biomass of V. rossicum. However, we did not detect a temperature x competition interaction in spite of evidence for adaptation of S. canadensis to cooler temperature conditions. We conclude that the spread of V. rossicum north within the tested range is unlikely to be limited by climatic temperature but competition with an abundant native species may contribute to slow it down.