Variations in pigmentation, ultrastructure and lipid composition of photosynthetic membranes in two species of cyanobacteria in response to variations in growth light intensity and spectral quality

Growth of the filamentous cyanobacteria Fremyella diplosiphon and Anabaena flos-aquae under conditions of varying light quantity and quality resulted in variations in chlorophyll content and in the ultrastructure and lipid con-tent of the thylakoid membranes in these cells. Cells of both species grown in three intensities of white light (66, 17, and 3 W/m², PAR) showed an inverse relationship between growth light intensity and chlorophyll content. Total thylakoid content (as visualized by electron microscopy) and total membrane lipid content of these cells also varied inversely with growth light intensity, supporting the contention that cellular thylakoid and membrane lipid contents are directly related to the chlorophyll contents of these cells.

Growth in broad-band red light (16 W/m², PAR) resulted in slightly lower cellular contents of chlorophyll, thylakoids and membrane lipids than in cells grown in equivalent intensity white light. Cells grown in far red light (3 W/m², PAR) contained substantially less total chlorophyll, thylakoids, and membrane lipids than did cells grown in equivalent intensity white light.

These data suggest that development of the thylakoid membrane is an integrated process involving light-controlled syntheses of the lipid components (chlorophyll and acyl lipids) of the membrane, and that light-induced variations in thylakoid membrane content in these two species is due in part to differential rates of synthesis and incorporation of individual lipids into thylakoid membranes.

In both species, the degree of unsaturation of fatty acids was found to be related to the chlorophyll content of the cells, those cells with the highest chlorophyll content having the highest unsaturation percentage.

Light intensity and quality also affected the morphology of these cells. As a result of growth in low and medium intensity white light, cells were cylindrically shaped and grew in filaments containing ca. 60-80 cells. Cells grown in medium intensity red and high intensity white light were roughly isodiametric, and grew in filaments containing ca. 12-20 cells. Surface area/volume ratio was specific for each species and remained constant through all the light treatments.

Contents of certain cytoplasmic inclusion granules (cyanophycin, polyphosphate, and polyglucoside) were found to vary, depending upon light treatment. However, no con-sistent relationships between individual light regimes and cellular contents of these granules were found.

These findings are discussed in the context of differential responses to various light regimes by F. Diplosiphon, which is capable of complementary chromatic adaptation, and A. flos-aquae, which lacks this capacity.