Abstract
Na+ dependent stimulation of the growth and PSII-activity in the marine diatom Phaeodactylum tricornutum was previously reported. It was also reported that intercellular Na+ influx toward chloroplast under high Na+. These results suggest that P. tricornutum possesses a halophilic mechanism. In this study, effects of Na+ on PSII were investigated using isolated thylakoid-membrane.
Comparative analysis of isoelectric point of PSII-components indicates that psbO of P. tricornutum is acidic as compared with that of green algae. A tertiary-structure predicted on PsbO demonstrated that PSII-binding-loop of PsbO possesses a unique three tandem Asp-residues, which would give highly acidic spot in this region. These results suggested that Na+ might stabilize the binding between psbO-loop and PSII-core. At present, effects of Na+ on PSII activity is being investigated biochemically.
Additionally, many animal-type sodium-dependent-transporters were identified by genomic-analysis. This result also strongly suggests that P. tricornutum might share a similar halophilic mechanism with animal-type systems.
