Limnology and Oceanography
Molecular mechanisms that drive metabolic acclimation to environmental shifts have been poorly characterized in phytoplankton. In this laboratory study. the response of light- and N-limited Skeletonema costatum cells to an increase in light and NO3 availability was examined. C assimilation was depressed relative to N assimilation early in enrichment, and the photosynthetic quotient (O2: CO2) increased, consistent with the shunting of reducing equivalents from CO2 fixation to NO3- reduction. The concomitant increase in dark respiration was consistent with the increased energetic demand associated with macromolecular synthesis. The accelerations of N-specific rates of NO3- uptake and nitrate reductase activity (NRA) over the first 24 h were comparable to observations for coastal upwelling systems. Increases in cell-specific rates of these processes, however, were confined to the first 8 h of enrichment. The abundance of 18S ribosomal ribonucleic acid (rRNA) increased immediately after the environmental shift, followed by increases in levels of NR-specific mRNA that coincided with the acceleration in NO3- assimilation. NRA, however, exhibited a diurnal rhythm that did not correspond to changes in NR protein abundance, suggesting that enzyme activity was also regulated by direct modulation of existing NR protein by light and NO3- availability.
Original Publication Citation
Smith, G.J., Zimmerman, R.C., & Alberte, R.S. (1992). Molecular and physiological responses of diatoms to variable levels of irradiance and nitrogen availability: Growth of Skeletonema costatum in simulated upwelling conditions. Limnology and Oceanography, 37(5), 989-1007. doi: 10.4319/lo.1992.37.5.0989
Smith, G. Jason; Zimmerman, Richard C.; and Alberte, Randall S., "Molecular and Physiological Responses of Diatoms to Variable Levels of Irradiance and Nitrogen Availability: Growth of Skeletonema Costatum in Simulated Upwelling Conditions" (1992). OEAS Faculty Publications. 118.