INHIBITION BY GLUCOSE OF CHLOROPHYLL-A AND PHYCOCYANOBILIN BIOSYNTHESIS IN THE UNICELLULAR RED ALGA GALDIERIA-PARTITA AT THE STAGE OF COPROPORPHYRINOGEN-III FORMATION

The repression effect of D-glucose on the pigment apparatus of photosy nthesis in the unicellular acidophilic red alga Galdieria partita capa ble of heterotrophic growth was studied. The rate of cell growth under heterotrophic conditions was higher by more than one order of magnitu de than that in the autotrophic ones, and the size of those cells was larger. The addition of 1% D-glucose to the growth medium caused an in crease in the number of mitochondrion profiles in the cell and a decli ne of thylakoid number in the chloroplast of G. partita. The loss of t hylakoid membranes is accompanied by a reduction of the contents of ch lorophyll a, C-phycocyanin and allophycocyanin in the heterotrophic ce lls. Simultaneously, switching G. partita from autotrophic growth to h eterotrophic nutrition led to the excretion of coproporphyrin(ogen) II I into the growth medium. Thus, the presence of D-glucose caused a red uction of pigment contents in the eel, due to the inhibition of chloro phyll a and phycocyanobilin biosynthesis at the stage of the transform ation of their universal precursor, coproporphyrinogen III, to protopo rphyrinogen IX. In the mixotrophic culture of G. partita light induces both the biosynthesis of photosynthetic pigments and the excretion of coproporphyrin(ogen) III. It is supposed that light affects an earlie r stage in the biosynthetic pathway of chlorophyll a and phycocyanobil in than does D-glucose. (C) 1998 Elsevier Science Ireland Ltd. All rig hts reserved.