Effects of nitrogen‐deprivation, and recovery from it, on the metabolism of microalgae

Abstract

SUMMARYInitial rates of uptake of the ammonium analogue, [14C] methylammonium increased during N‐deprivation of the microalgae, Dunaliella primolecta Butcher, Tetraselmis subcordiformis Butcher (Wille), Chlomydomonas reinhardtii Dangeard. Amphidinium carterae Hulburt and Phaeodactylum tricornum Bohlin.The C:N ration of P. tricornutum increased from 7.4 to 19.8 during 48 h of N‐deprivation; the ability to take up [14C] methylammonium increased 50–fold during this time. Intracellular glutamate and glutamine were measured fluorimetrically; the contend of glutamate fell during N‐deprivation but that of glutamine was low and changed little. The activity of glutamine synthetase (transferase) in cells permeabilized by toluene treatment approximately doubled during the first 4 h of N‐deprivation, irrespective of whether the cells had been grown with NO2 or NH4+ as N cource: thereafter the activity of thia enzyme decreased slowly. The activity of nitrate reductase was high in NO3 grown cells and decreased during N‐deprivation. In NH4+ grown cells, nitrate reductase activity was low and increased markedly during 4 h of N‐deprivation; therefore it fell slowly.The addition of NH4+ to N‐deprived cells was followed by an immediate and large fall in the ability to take up [14C] methylammonium. In contrast, the addition of NO3 produced an initial small drop in the ability to take up [14C]methylammonium followed by another drop after 4.6 h; 8 h after NO3 addition the initial rate of [14C]methylammonium uptake was similar to that of N‐replate cells. These falls in ability to take up methylammonium were reversed when NH4+ or NO3 were removed; the reversals were not prevented by addition fo cycloheximide (an inhibitor of protein synthesis). Changes in intracellular glutamate and glutamine were followed during the periods following NO3 and NH4+ addition and removal. There was evidence fro a negative correlation between glutamine content and the rate of uptake of mehtylammonium