Interactive effects of PAR and UV-B radiation on PSII electron transport in the marine alga Dunaliella tertiolecta (Chlorophyceae)

To better understand the interactions between PAR and UV-B radiation in microalgae, the marine chlorophyte alga Dunaliella tertiolecta was subjected to a UV-B flux of 4.1 W.m(-2) (unweighted) with varying PAR fluxes. Rate constants for damage and repair processes during UV-B exposure increased with PAR flux. However, recovery after UV-B exposure increased with PAR up to 300 mumol quanta.m(-2).s(-1), beyond which photoinhibition of PSII electron transport was found to decrease recovery rates. In the absence of PAR during the post UV-B exposure period, no recovery was seen, indicating that perhaps the lack of light available for photosynthesis depresses repair either directly or indirectly by affecting ATP synthesis. Possible mechanisms for the observed interactions between PAR and UV-B exposure are discussed.