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REGULATORY ASPECTS OF NH 4 + UTILIZATION IN THE ACIDOPHILIC THERMOPHILIC UNICELLULAR RED ALGA CYANIDIUM CALDARIUM
Author(s) -
MARTINO RIGANO VITTORIA,
VONA VINCENZA,
MARTINO CATELLO,
RIGANO CARMELO
Publication year - 1987
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1987.tb00861.x
Subject(s) - ammonium , chemostat , darkness , assimilation (phonology) , chemistry , incubation , thermophile , nitrogen , ammonia , biochemistry , nuclear chemistry , biology , botany , bacteria , enzyme , organic chemistry , linguistics , genetics , philosophy
S ummary Cyanidium caldarium is an acidophilic thermophilic red alga. At pH 1.9 with cells grown in batch culture with excess ammonium, removal of CO 2 or darkness caused immediate inhibition of ammonium assimilation. By contrast, with cells grown in chemostat culture with nitrogen limitation, assimilation of ammonium was not inhibited by darkness, but it was inhibited by CO 2 deprivation. In the case of these cells, inhibition was not immediate and behaved as a time‐dependent phenomenon. Ammonium assimilation was restored when CO 2 was supplied in either light or darkness. In contrast, at pH 7.4, ammonium assimilation decreased with time both in the presence and absence of CO 2 , and it ceased completely after about 90 min incubation at this pH. The inhibition was not due to the high pH per se. When resuspended at pH 2, these inhibited cells were unable to assimilate ammonium during a 25 min period in the presence of CO 2 . Thereafter, they become able to assimilate ammonium but at a rate which was only 30% of that of the control. If they were pre‐incubated at pH 2 in nitrogen‐free medium for 3 h, however, they then assimilated ammonium immediately after its addition. It is suggested that a reversible inactivation at pH 1.9 and a denaturation at pH 7.4 of the system for ammonium uptake occurs, and that this uptake system is stabilized by carbon compounds against inactivation at pH 1.9 but not against denaturation at pH 7.4.