Protein turnover in relation to maintenance metabolism at low photon flux in two marine microalgae
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abstract
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 mol photons m-2 s-1. The kinetics of pulse-chase labelling of the protein with 3H 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.
