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The use of NH 4 + rather than NO 3 − affects cell stoichiometry, C allocation, photosynthesis and growth in the cyanobacterium Synechococcus sp. UTEX LB 2380, only when energy is limiting
Author(s) -
Ruan Zuoxi,
Giordano Mario
Publication year - 2017
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/pce.12858
Subject(s) - photosynthesis , synechococcus , stoichiometry , assimilation (phonology) , nutrient , biology , limiting , carbon assimilation , cyanobacteria , biophysics , chemistry , botany , ecology , bacteria , mechanical engineering , engineering , linguistics , genetics , philosophy , organic chemistry
The assimilation of N‐NO 3 − requires more energy than that of N‐NH 4 + . 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 NH 4 + did not stimulate growth. When energy was limiting, however, Synechococcus grew faster in NH 4 + than in NO 3 − 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.