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CHANGES IN INTRACELLULAR NITROGEN POOLS AND FEEDBACK CONTROLS ON NITROGEN UPTAKE IN CHAETOMORPHA LINUM (CHLOROPHYTA) 1
Author(s) -
McGlathery Karen J.,
Pedersen Morten Foldager,
Borum Jens
Publication year - 1996
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.1996.00393.x
Subject(s) - biology , nutrient , chlorophyta , nitrogen , nitrate , algae , photosynthesis , limiting , botany , zoology , biogeochemical cycle , dilution , intracellular , biochemistry , ecology , chemistry , mechanical engineering , organic chemistry , engineering , physics , thermodynamics
Changes in the size of intracellular nitrogen pools and the potential feedback by these pools on maximum N uptake (NH 4 + and NO 3 − ) rates were determined for Chaetomorpha linum (Müller) Kützing grown sequentially under nutrient‐saturating and nutrient‐limiting conditions. The size of individual pools in N‐sufficient algae could be ranked as residual organic N (RON) comprised mainly of amino acids and amino compounds > protein N > NO 3 − > NH 4 + > chlorophyll N. When the external N supply was removed, growth rates remained high and individual N pools were depleted at exponential rates that reflected both dilution of existing pools by the addition of new biomass from growth and movement between the pools. Calculated fluxes between the tissue N pools showed that the protein pool increased throughout the N depletion period and thus did not serve a storage function. RON was the largest storage reserve; nitrate was the second largest, but more temporary, storage pool that was depleted within 10 days. Upon N resupply, the RON pool increased 3 × faster than either the inorganic or protein pools, suggesting that protein synthesis was the rate‐limiting step in N assimilation and caused a buildup of intermediate storage compounds. Maximum uptake rates for both NH 4 + and NO 3 − varied inversely with macroalgal N status and appeared to be controlled by changes in small intracellular N pools. Uptake of NO 3 − showed an initial lag phase, but the initial uptake of NH 4 + was enhanced and was present only when the intracellular NH 4 + pool was depleted in the absence of an external N supply. A strong negative correlation between the RON pool size and maximum assimilation uptake rates for both NH 4 + and NO 3 − suggested a feedback control on assimilation uptake by the buildup and depletion of organic compounds. Enhanced uptake and the accumulation of N as simple organic compounds or nitrate both provide a temporary mechanism to buffer against the asynchrony of N supply and demand in C. linum .