Isolation and characterization of photosystem II from the filamentous sporophyte of Porphyra yezoensis.

Thylakoid membranes were isolated and purified from diploid filamentous sporophytes of Porphyra yezoensis Ueda using sucrose density gradient ultracentrifugation (SDGUC). After thylakoid membranes were solubilized with SDS, the phtosystem II (PSII) particles with high 2, 6-dichloroindophenol (DCIP) photoreduction activity were isolated by SDGUC. The absorption and fluorescence spectra, DCIP photoreduction activity and oxygen evolution activity of the thylakoid membranes and PSII particles were determined. The polypeptide composition of purified PSII particles was distinguished by SDS-PAGE. Results showed that PSII particles of sporophytes differed from the gametophytes in spectral properties and polypeptide composition. Apart from 55 kDa D1-D2 heterodimer, CP47, CP43, 33 kDa protein, D1, D2, cyt b559 and 12 kDa protein were identified from PSII particles from sporophytes; a new 102 kDa protein was also detected. However, cyt c-550, 20 kDa, 14 kDa and 16 kDa proteins found in PSII particles from gametophytes were not detected in the sporophytes.

Relationship of fluorescence and thermal emission from isolated thylakoids under light stress conditions.

Simultaneous measurements of fluorescence and thermal emission have been made by a combined fluorescence and photoacoustic techniques on isolated thylakoids pretreated by a prolonged illumination of saturating light. The traces of the signals are used to calculate four characteristic parameters, energy storage, half-saturation intensity, number of photons to close reaction center, and a constant for quasi-equlibria between (re)oxidized and reduced quinone acceptors. These parameters are used to study the response of photosynthetic apparatus functioning under photoinhibition stress. The defense mechanism seems to possess an efficient cooperativity of reaction centers under stress conditions.