N. europaea recovering from up to 7 days starvation showed no lag phase before nitrifying activity or growth could be measured. Cells starved for 1- 4 weeks had a lag phase of 20 - 40 min before activity. Cells starved for 0 - 7 d had no lag phase before growth. A lag phase before growth was initiated after 1 - 2 weeks starvation, which increased to 93 - 98 h after 6 weeks of starvation. Between 1 and 6 weeks starvation the nitrifying activity per ml of recovering cell suspension decreased significantly. N. europaea was also starved in continuous flow sand and soil columns. Cells recovering from starvation in sand columns resumed nitrifying growth and activity immediately at the same growth rate of cells initially inoculated into the column. Cells recovering from starvation in soil columns took longer to resume nitrifying activity than cells starved in sand. pH and nitrapyrin both had significant effects on nitrifying activity and the interaction between pH and nitrapyrin treatment was significant in the inhibition of both growth and activity. pH and PEX both significantly inhibited nitrifying activity but the interaction between pH and PEX was not significant. PEX completely inhibited growth at concentrations which only partially inhibited nitrifying activity. The optimum pH for nitrifying activity by N. europaea was between pH 8.5 and 9 and the optimum pH for growth was between 7.5 and 8.0. The optimum pH for activity increased as substrate concentration decreased. A previously published model quantifying the relationship between pH, substrate availability and ammonia oxidation (Quinlan, 1985) was tested. Data predicted using the model fitted experimental data when data from a limited pH range were used to calculate the coefficients (pH 7-9), but not when data from a wider range (6-9) were used.

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The pollution of agricultural land with heavy metals occurs as a result of industrial activities such-as metal mining and the application of sewage sludge to the land. Regulations concerning the maximum permissible levels of heavy metals in soils of agricultural use relate only to total concentrations, not to the chemical nature (speciation) of the metal. Bioavailability and toxicity of the metal to the plant are governed by speciation. The overall aim of the research was to investigate heavy metal plant uptake with respect to metal speciation in the growing media. Plants have been shown to possess a unique ability to adapt rapidly and evolve tolerance to toxic and potentially lethal levels of heavy metals. To alleviate the stress imposed by heavy metal exposure, plants synthesize metal-binding polypeptides termed 'Phytochelatins'. Phytochelatin synthesis is thought to act as the detoxification mechanism in plant forms, analogous to metallothionein synthesis in animals. The project involved growing Zea mays plants under carefu.lly controlled conditions - the first stage was to design and build a unit to provide a constant light and temperature source. Plant symptoms were monitored and extraction and storage procedures investigated. Various methods for the isolation and purification of phytochelatins were studied in order to determine the most effective process for their quantification. The equilibrium speciation of the aqueous growing media was computed using a sophisticated computer modelling program, after an extensive thermodynamic database was constructed for the nutrient solution components. The uptake of cadmium, and the resultant Phytochelatin synthesis, has been studied in relation to the equilibrium speciation of the growing media. Cadmium was used as the toxicant, since this has been shown to be the greatest inducer of Phytochelatins. Recently several different purification methods have been documented. Hence a major part of the study has been the development of the optimum procedures for extraction, isolation and separation of Phytochelatins from 'Zea mays' primary roots.

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