Enhancement of Cytochrome b 559 Indicates Its Possible Involvement in Long-Term High Light Stress Tolerance in Intertidal Macroalgae

The effects of high light (HL) stress on the photosynthetic proteins of green tide-forming macroalga were studied. The naturally grown Ulva prolifera was collected from an intertidal habitat and subjected to 1000 mu E m super(-2) s super(-1) HL for 12 h. The thylakoid membrane proteins were subsequently extracted and qualitatively analyzed using LC/MS. Quantitative analysis of the thylakoid membrane proteins showed that both PSII reaction center proteins and PSII chlorophyll antenna proteins were decreased. Comparatively, the main PSI reaction center proteins were well preserved. The cytochrome f subunit was significantly decreased, while the other subunits of cytochrome b 6 /f complex were maintained. These results demonstrated that the HL-induced cytochrome b 559 might play a role in photoacclimation of U. prolifera by involving in cyclic photosynthetic electron transfer (PET) flow around PSII. The LhcSR and PsbS proteins were also identified in U. prolifera, and PsbS was noted to be significantly increased under HL stress. The long-term photoacclimation mechanism of U. prolifera under HL stress might not depend on cyclic PET flow around PSI.