Abstract
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 NO, availability was examined. C assimilation was depressed relative to N assimilation early in enrichment, and the photosynthetic quotient (0, : CO,) increased, consistent with the shunting of reducing equivalents from CO, fixation to NO; 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 NO,- uptake and nitrate rcductase activity (NRA) over the first 24 h were comparable to observations for coastal upwelling systems. Increases in cell-specific rates of these proccsscs, 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 NO,- 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 NO, - availability.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have