Effects of carotenoid-depletion on the photosynthetic apparatus of a Galdieria sulphuraria (Rhodophyta) strain that retains its photosynthetic apparatus in the dark

摘要

A Galdieria sulphuraria (Galdieri) Merola strain that retains its photosynthetic apparatus in the dark was treated with the inhibitor of carotenoid biosynthesis, norflurazon, under autotrophic and heterotrophic conditions. Under autotrophic conditions cultures were not able to grow. The chlorophyll content of the cells decreased constantly and a partial decomposition of their chloroplast structure could be observed. In the dark, under heterotrophic conditions, the inhibitor caused a nearly total loss of carotenoids, a reduction of the chlorophyll content per cell, a slight increase of the ratio of phycocyanin to chlorophyll and an accumulation of a pheophorbide a-like pigment. The ultrastructure of the algae, however, was not affected. The polypeptides of the photosystem II core-complex and of the light-harvesting complex of photosystem I were dramatically reduced, indicating that carotenoids are essential for their assembly. The core-complex of photosystem I was present. Its fluorescence maximum, however, was blue-shifted from 725 to 717 nm. When excited at 580 nm norflurazon-treated cells exhibited a fluorescence maximum at 686 nm, indicating that phycobilisomes are energetically neither connected with photosystem II nor with photosystem I. Nevertheless, phycobilisomes of norflurazon-treated and control algae were not distinguishable.