When grown in alternating cycles of light and darkness, non-synchronous cultures of Gloeotkce fixed N2 mainly in the dark phase. This diumd pattern of N2 fixation was independent of the doubling time (69 & 16 h) of the organism and, since cell divisionwas asynchronous, N2 fixation does not seem to be confined to a specific phase in the cell cycle. Fluchrtltions in the rate of N2 fixation coincided with similar fluctuations in the rate of nitrogenase synthesis. Diurnal fluctuations also occurred in the utilization of &can and acid-soluble polyphosphate and in the ADP/ATP ratio. Based on these observations, it is pmposed that specific mcfabofic changes are involved in the regulation of the diurnal pattern of N2 fixation by Glcnmthece.

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Research into chemical bird repellents is reviewed. The feeding preferences of Bullfinches Pyrrhula pyrrhula for bud extracts of 26 pear cultivars were established in the laboratory and correlated with underlying biochemical differences between extracts. A group of phenolic compounds was identified as aversive. Some of these compounds proved to be powerful inhibitors of protease activity in uitro, supporting theories about the role of phenolics as plant defences against herbivores. A larger study, however, failed to demonstrate a correlation between their biochemical reaction with digestive enzymes and their ability to deter feeding by feral pigeons Columba livia. Nevertheless, cinnamamide was identified as a promising bird repellent, although its mechanism of action is unclear.