The ratio of glutamine:glutamate in microalgae: a biomarker for N-status suitable for use at natural cell densities

Abstract
A measure of the N-status of phytoplankton at natural cell densities may be made by determining the ratio of intracellular glutamine:glutamate (GLN:GLU). The intracellular pool of free amino acids from 104.sbd.106 cells is extracted in ultraclean conditions and analysed by reverse phase HPLC. A GLN:GLU ratio of > 0.5 indicates N-replete and < 0.2 N-deplete cells.