Analysis of soil solution from forest sites dominated byEucalyptus grandis and Eucalyptus maculata indicates that soluble forms of organic nitrogen (amino acids and protein) are present in concentrations similar to those of mineral nitrogen (nitrate and ammonium). Experiments were conducted to determine the extent to which mycorrhizal associations might broaden nitrogen source utilization in Eucalyptus seedlings to include organic nitrogen, ln isolation, species of ectomycorrhizal fungi from northern Australia show varying abilities to utilize mineral and organic forms of nitrogen as sole sources. Pisolithus sp. displayed .strongest growth on NH4, glutamine and asparagine, but grew poorly on protein, while Amanita sp. grew well both on mineral sources and on a range of organic sources (e.g. arginine, asparagine, glutamine and protein). In sterile culture, non-mycorrhizal seedlings of Eucalyptus grandis and Eucalyptus maculata grew well on mineral sources of nitrogen, but showed no ability to grow on sources of organic nitrogen other than glutamine. In contrast, mycorrhizal seedlings grew well on a range of organic nitrogen sources. These observations indicate that mycorrhizal associations confer on species of Eucalyptus the ability to broaden their resource base substantially with respect to nitrogen. This ability to utilize organic nitrogen was not directly related to that of the fungal symhiont in isolation. Seedlings mycorrhizal with Pisolithus sp. were ahle to assimilate sources of nitrogen (in particular histidine and protein) on which the fungus in pure culture appeared to grow weakly. Experiments in which plants were fed ''^N-lahelled ammonium were undertaken in order to investigate the influence of mycorrhizal colonization on the pathway of nitrogen metabolism. In roots and shoots of all seedlings, '^N was incorporated into the amide group of glutamine, and label was also found in the amino groups of glutamine, glutamic acid, }^aminobutyric acid and alanine. Mycorrhizal colonization appeared to have no effect on the assimilation pathway and metabolism of ['^NIH/; labelling data were consistent with the operation of the glutamate synthase cycle in plants infected with either Pisolithus sp. (which in isolation assimilates via the glutamate synthase cycle) or Elaphomyces sp. (which assimilates via glutamate dehydrogenase). It is likely that the control of carhon supply to the mycorrhizal fungus from the host may have a profound effect on hoth the assimilatory pathway and the range of nitrogen sources that can he utilized hy the association.

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The plasma enzyme butyrylcholinesterase (BChE) is of clinical interest because of the occurrence of genetic variants with decreased ability to hydrolyse, and therefore inactivate, muscle-relaxant drugs such as suxamethonium. Analysis of BChE involves the determination of both enzyme activity and biochemical phenotypes which are used to determine the risk of so-called 'scoline apnoea'. Problems in analysis arise from both the lack of a universally accepted reference method and the variety of substrates and conditions employed for the determination of activity and phenotypes. Phenotype is determined by the use of speci c enzyme inhibitors that produce phenotype-speci c patterns of 'inhibitor numbers'. DNA analysis is now possible, and true genotypes can be obtained. The nomenclature in use for cholinesterase studies can cause problems in interpretation and reporting as there is poor understanding of the difference between phenotype and genotype, and terms are often, inappropriately, transposed. Techniques for both biochemical and molecular analysis of the enzyme are discussed.

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