Uptake rates of various nitrogen sources by nitrate-grown Tetraselmis (Platymonas) striata

Abstract

Cells of Tetraselmis striata, grown in a medium with nitrate as nitrogen source, were tested for their ability to remove a variety of other nitrogen sources from the growth medium in short term (6 h) experiments. There was no detectable removal of cytosine, thymine, uracil, adenine and allantoin. The purines guanine, xanthine, hypoxanthine and uric acid were all immediately removed at high rates (c. 1 pg N cell^-1 h^-1). The amino acids alanine, arginine, glutamic acid, glycine and tryptophan were initially either not removed significantly, or were removed at rates which were inadequate to sustain normal growth and reproduction. However, within 1–2 h of presentation of these nitrogen sources the rates of removal from the medium increased from zero to about 0·16 pg N cell^-1 h^-1 for arginine and glutamate, and from zero to 0·3 pg N cell^-1 h^-1 for alanine. The amino acid amides asparagine and glutamine were initially removed slowly, but much higher rates (0·5–0·7 pg cell^-1 h^-1) were found after 2·5 h from presentation. T. striata is known to be capable of growth and reproduction using a number of the nitrogen sources which were poorly utilized, or, in these short term experiments were not utilized at all. Therefore the enzymes involved in their uptake and/or assimilation are probably not constitutive but are induced by exposure to the new substrate after a time lag.