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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