The assimilation of N-NO3- requires more energy than that of N-NH4+ . This becomes relevant when energy is limiting and may impinge differently on cell energy budget depending on depth, time of the day and season. We hypothesize that N-limited and energy-limited cells of the oceanic cyanobacterium Synechococcus sp. differ in their response to the N source with respect to growth, elemental stoichiometry and carbon allocation. Under N limitation, cells retained almost absolute homeostasis of elemental and organic composition, and the use of NH4+ did not stimulate growth. When energy was limiting, however, Synechococcus grew faster in NH4+ than in NO3- and had higher C (20%), N (38%) and S (30%) cell quotas. Furthermore, more C was allocated to protein, whereas the carbohydrate and lipid pool size did not change appreciably. Energy limitation also led to a higher photosynthetic rate relative to N limitation. We interpret these results as an indication that, under energy limitation, the use of the least expensive N source allowed a spillover of the energy saved from N assimilation to the assimilation of other nutrients. The change in elemental stoichiometry influenced C allocation, inducing an increase in cell protein, which resulted in a stimulation of photosynthesis and growth.

• MeSH
• adenosintrifosfát metabolismus   MeSH
• amoniové sloučeniny farmakologie   MeSH
• bakteriální proteiny metabolismus   MeSH
• biomasa MeSH
• dusičnany farmakologie   MeSH
• dusík metabolismus   MeSH
• energetický metabolismus * účinky léků   MeSH
• fosfor metabolismus   MeSH
• fotosyntéza účinky léků   MeSH
• kyslík metabolismus   MeSH
• lipidy analýza   MeSH
• sacharidy analýza   MeSH
• síra metabolismus   MeSH
• Synechococcus cytologie   účinky léků   růst a vývoj   metabolismus   MeSH
• uhlík metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH