CHANGES IN INTRACELLULAR NITROGEN POOLS AND FEEDBACK CONTROLS ON NITROGEN UPTAKE IN <em>CHAETOMORPHA LINUM</em> (CHLOROPHYTA).

Changes in the size of intracellular nitrogen pools and the potential feedback by these pools on etaximum N uptake (NH[SUB4] and NO[SUB3]) rates were determined for Chaetomorpha linum (M&#252;ller) K&#252;tzing grown sequentially under nutrient-saturating and nutrient-limiting conditions. The size of individual pools in N-sufficient could be ranked as residual organic N (RON) comprised mainly of amino acids and compounds &gt; protein N &gt; NO[SUB3] &gt; NH[SUB4] 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 depletin 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 to days. Upon N resupply, the RON pool increased 3 &#215; faster that either the inogrance or protein pools, suggesting that prtein synthesis was the rate-limiting step in N assimilation and caused a buildup of intermediate storage compuinds. Maximum uptake rates for both NH[SUB4] And NO[SUB3,SUP-] varied inversely with macroalagal N status and appeared to be controlled by changes in small intracellular N pools. Uptake of NO[SUB3,SUP-] showed an initial lag phase, but the initial uptake of NH[SUB4,SUP+] Pool was depleted in the absence of an external N supply. A strong negative correlation between the RON pool the and maximum assimilation uptake rates for both NH[SUB4,SUP+] And NO[SUB3,SUP-] suggested a feedback control or assimilatin uptake to the buildup and depletin of organic compounds. Enhanced uptake and the accumulatin of N as simple organic compounds or nitrate both provide a temporary mechanism to buffer against the asynchrony of N supply and demans in C. linum. [ABSTRACT FROM AUTHOR]