Photophysiology of Bolidomonas pacifica
LE3 .A278 2012
Bachelor of Science
Bolidomonas pacifica is a cholorophyll a/c marine phytoplankter in a sister lineage to the more widely distributed diatoms. Marine diatoms thrive under conditions of fluctuating light, so this study sought to characterize the photophysiology of B. pacifica, and its responses to upward fluctuations in light. B. pacifica were grown under six photosynthesis photon flux (PPF) levels between 30 to 450 μmol m-2·s-1, a range spanning the bottom 10% of the photic zone up to the near-surface top 30% of the photic zone. The cells achieved maximum growth of 0.55 d-1 at 250 umol m-2·s-1, equivalent to the middle of the photic zone, with a light compensation point for growth of ~15 μmol m- 2·s-1. Light capture measures for Photosystem II (PSII) photochemistry were much greater than in marine diatoms, with a low growth PPF effective absorbance cross section of ~1071 A2·quanta-1 that decreased slightly under higher growth PPFs. Light response curves of PSII electron transport showed a transition point from light limited to light saturated that corresponded with growth PPF, thus electron transport rate showed PPF level acclimation. When analyzing B. pacifica responses to mixing through the water column, it was found that within 15 minutes of being shifted to a higher light, B. pacifica cultures induced PSII repair, thus stabilizing PSII function in the face of accelerated photoinactivation. When a chloroplast protein synthesis inhibitor (lincomycin) was used to block PSII repair, the cells suffered progressive loss of PSII function, with a susceptibility to photoinactivation of ~1 x 10-5 A2·quanta-1, about double that of marine diatoms under comparable conditions. Bolidomonas has a larger absorbance cross section serving PSII than diatoms, but must induce greater amounts of repair to account for higher susceptibility to photoinactivation.
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