The determination of nitrogen status in microalgae

Present methods used for the determination of N-status in microalgae typically involve testing for the existence of gross metabolic changes which develop in response to N-stress. Such approaches have 2 problems. First, the experimental tech~uques may be inappropriate for the species present and may perturb the organisms, possibly creating artifacts. Second, these gross changes, such as changes in rates of CO2-fixation and N-source uptake, may be affected by factors other than N-stress. There is a need to develop methods to detect metabolic changes which themselves trigger the genetic response to N-stress rather than to detect the products of that response. Such changes are likely to be in relative proportions of key metabolites of C and N metabolism, as In bacteria. It is suggested that only in the presence of excess NH: are the processes of cellular response to N-stress fully suppressed. As a consequence, microalgae throughout the oceans may show some symptoms of N-stress. The level of derepression of the N-stress responses which corresponds to growth-limitation, and hence is of ecological significance, needs to b e determined.