Amino acid pools in nutrient limited Cyanidium caldarium and responses to resupply

Abstract

Amino acid pools in Cyanidium caldarium (Tilden) Geitler, growing under conditions of sufficiency of nutrients (sufficient cells), or under conditions of nitrogen, potassium or phosphorus limitation (N-, K- or P-limited cells), and responses upon nutrient resupply were investigated. Glutamate was the dominant amino acid in sufficient cells [11.2 μmol ml −1 packed cell volume (pcv)], in N-limited cells (7.71 μmol ml −1 pcv) and in P-limited cells (7.46 μmol ml −1 pcv), whereas in K-limited cells the dominant amino acid was alanine (8.83 μmol ml −1 pcv). Other amino acids detected occurring at significantly high concentrations were: citrulline, alanine, aspartate, glutamine and δ-aminolevulinic acid in sufficient cells, alanine in N-limited cells; alanine, citrulline, serine, arginine and asparagine in P-limited cells; glutamate, arginine, glutamine, citrulline, asparagine, serine, aspartate and putrescine in K-limited cells. On adding NH 4 + to N-limited cells the level of glutamate decreased and then increased to the starting value; there occurred an increase in the level of glutamine, aspartate, citrulline, arginine, alanine, serine, as well as of δ-ALA and putrescine. Resupply of Pi to P-limited cells caused a significant decrease of glutamate and a concomitant increase of alanine, but was without efrect on the concentration of other amino acids. On adding K + to K-limited cells there was an increase of glutamate and citrulline, and a decrease of putrescine, whereas arginine and alanine remained unvaried at the very high level occurring before addition.