Growth, Photosynthesis, Respiration, and Intracellular Free Amino-acid Profiles In the Unicellular Alga Cyanidium-caldarium - Effect of Nutrient Limitation and Resupply

Growth, intracellular free amino acid pools and photosynthetic and respiratory activities in nutrient sufficient cells and in N-, K- and P-limited cells of Cyanidium caldarium (Tilden) Geitler, and responses to nutrient resupply were investigated. Addition of ammonium to N-limited cells and of phosphate to P-limited cells resulted in a stimulation of dark respiration and in a decrease in photosynthetic oxygen evolution. Addition of K to K-limited cells had no effect on rates of photosynthesis and respiration. Nutrient limited cells and sufficient cells exhibited different free amino acid profiles. Upon resupply of ammonium to N-limited cells levels of glutamine, citrulline, arginine, alanine, and serine increased. Also the levels of delta-aminolevulinic acid (delta-ALA) and putrescine increased notably. On adding phosphate to P-limited cells the level of glutamate decreased significantly whereas the level of alanine increased and the concentrations of other amino acids remained unaffected. On adding potassium to K-limited cells there was an increase in glutamate and citrulline concentrations, and a decrease in putrescine concentration, whereas concentrations of arginine and alanine remained at the very high levels observed already before addition. Resuspension of N- and K-limited cells in a complete growth medium resulted in resumption of growth, but maximum growth rate was reached only after 25-30 h. In P-limited cells resumption of growth in complete medium occurred progressively and reached the maximum rate 30 h later. P-, K- and N-limited cells resuspended into sufficient media showed different rates of ammonium and phosphate assimilation. The pattern of recovery from nutrient limitation is discussed according to the cellular role fulfilled by the nutrient which was growth rate-limiting.