INFLUENCE OF D IFFERENT LIGHT I NTENSITIES AND D IFFERENT IRONNUTRITION ON THE PHOTOSYNTHETIC APPARATUS IN THE DIATOMCYCLOTELLA MENEGHINIANA (BACILLARIOPHYCEAE)

摘要

The diatom Cyclotella meneghiniana Kutz. (SAG1020-a) was cultured under high-light (HL) andlow-light (LL) conditions with either high (12 mu M)or low (1 mu M) iron in the media. Changes in cellmorphology, especially cell volume and chloroplastsize, were observed in cells grown under low iron.In contrast, HL had a much stronger influence onthe photosynthetic apparatus. PSII function wasunimpaired under lowered iron supply, but itsquantum efficiency and reoxidation rate werereduced under HL conditions. As reported before,HL induced changes in antenna polypeptide composition. Especially the amount of Fcp6, an antennaprotein related to LI818 and known to be involvedin photoprotection, was increased under HL butwas significantly reduced under lowered iron. Thediatoxanthin content correlated with the amount ofFcp6 in isolated FCPa antenna complexes and wasthus increased under HL and reduced under lowiron as well. While the diatoxanthin (Dt) content ofwhole cells was enhanced under HL, no decreasewas observed under lowered iron supply, ruling outthe possibility that the decreased amounts in FCPawere due to a hampered diadinoxanthin de-epoxidase activity under these conditions. Thus, diatoxanthin not bound to FCPa has to be responsiblefor protection under the slight reduction in ironsupply used here.