Protein turnover in relation to maintenance metabolism at low photon flux in two marine microalgae

Acclimation to very low photon fluxes involves adjusting a suite of physiological characteristics that collectively elicit a physiological response. Facilitating such changes is protein turnover. Dunaliella tertiolecta (Butcher) and Phaeodactylum tricornutum (Bohlin) were grown in turbidostats at a range of photon fluxes between 2 and 300 m mol photons m 2 s 1 . The kinetics of pulse-chase labelling of the protein with 3 H showed that (1) two protein pools were present, one of which turned-over rapidly (hours), and a second which turned over more slowly (days); and (2) protein turnover rates were slower in P. tricornutum than in D. tertiolecta . Phaeodactylum tricornutum had a lower maintenance coefficient for protein turnover than D. tertiolecta , and correspondingly a smaller proportion of its respiratory demands (30%) were associated with protein turnover than in D. tertiolecta (36%). There appears to be a correlation between lower metabolic activity, requiring lower protein concentrations, and an associated decreased cost of maintenance processes in P. tricornutum compared to D. tertiolecta . Differences between protein turnover rates and maintenance metabolic costs may be one of the photo-acclimation strategies that determine which photon niches microalgae can successfully exploit. Key-words : Dunaliella tertiolecta ; Phaeodactylum tricornutum ; maintenance metabolic rate; photo-acclimation; protein turnover; respiration.