Photoinhibition in outdoor Spirulina platensis cultures assessed by polyphasic chlorophyll fluorescence transients

摘要

Photoinhibition in outdoor cultures of Spirulina platensis was studied by measuring the polyphasic rise of chlorophyll fluorescence transients, which provide information on the primary photochemistry of PSII (photosystem II). The maximum efficiencyof PSII photochemistry (Fv/Fm) declined in response to daily increasing irradiance and recovered as daily irradiance decreased. The greatest inhibition (15%) in Fv/Fm was observed at 12:00 h which responded to the highest irradiance. The absorption flux,the trapping flux, and the electron transport flux per PSII reaction centre increased in response to daily increasing irradiance and decreased as irradiance decreased. The daily change in the concentration of PSII reaction centres followed the same pattern as Fv/Fm. However, no significant changes in the probability of electron transport beyond QA (PSIo) were observed during the day. The results suggest that the decrease in Fv/Fm induced by photoinhibition in outdoor Spirulina cultures was a result ofthe inactivation of PSII reaction centres. The results also suggest that the measurement of polyphasic fluorescence transients is a powerful tool to study the mechanism of photoinhibition in outdoor Spirulina cultures and to screen strains for photoinhibition tolerance.