A quantitative micromorphometric study of the cell compartment rearrangements was performed in a symbiotic chlorophyte Desmodesmus sp. 3Dp86E-1 grown on nitrogen (N) replete or N-free medium under 480 μmol PAR quanta m(-2) s(-1). The changes in the chloroplast, intraplastidial, and cytoplasmic inclusions induced by high light (HL) and N starvation were similar to those characteristic of free-living chlorophytes. The N-sufficient culture responded to HL by a transient swelling of the thylakoid lumen and a decline in photosynthetic efficiency followed by its recovery. In the N-starving cells, a more rapid expansion and thylakoid swelling occurred along with the irreversible decline in the photosynthetic efficiency. Differential induction of starch grains, oil bodies, and cell wall polysaccharides depending on the stress exposure and type was recorded. Tight relationships between the changes in the assimilatory and storage compartments in the stressed Desmodesmus sp. cells were revealed.