Lewitus 9315663 The recognition that light can stimulate respiration has cast uncertainties in primary productivity measurements for years. Resolution of this often pronounced effect is complicated by the existence of several respiratory pathways in phytoplankton (e.g. "dark" respiration, photorespiration, mealier reaction), all driven by the cell in different ways. It was recently discovered in the laboratory that several estuarine phytoplankton contain another such pathway, "alternative respiration", that previously had been reported in few species and whose function in phytoplankton is poorly understood. The potential for expression of this pathway can be very high (up to 99% of the total light- stimulated respiration), and glucose enrichment in the light can this potential. Based on this preliminary findings and higher plant research, it is hypothesized that the alternative pathway has energy dissipating role in phytoplankton -- the pathway is engaged when the cellular energy supply exceeds the demands for growth, maintenance, and storage. This hypothesis will be tested by examining the effects of light, dissolved organic substrate, and nutrient supplies on the capacity and activity of alternative reparation in recently isolated phytoplankton clones and in field populations. This will be accomplished, in part, by the use of membrane inlet mass spectrometry and a newly developed antibody to the main enzyme of the alternative pathway. Understanding how alternative respiration works impacts our understanding of how primary productivity is controlled -- this process may be a rapid and efficient means by which phytoplankton can dissipate excess carbon and energy in the upper euphotic zone. ***
