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The role of external carbonic anhydrase in photosynthesis during growth of the marine diatom Chaetoceros muelleri
Author(s) -
SmithHarding Tamsyne Jade,
Beardall John,
Mitchell James Gordon
Publication year - 2017
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/jpy.12572
Subject(s) - photosynthesis , biology , total inorganic carbon , carbon dioxide , phytoplankton , diatom , carbonic anhydrase , botany , saturation (graph theory) , rubisco , photosystem ii , ecology , nutrient , biochemistry , enzyme , mathematics , combinatorics
Carbon dioxide concentrating mechanisms ( CCM s) act to improve the supply of CO 2 at the active site of ribulose‐1,5‐bisphosphate carboxylase/oxygenase. There is substantial evidence that in some microalgal species CCM s involve an external carbonic anhydrase ( CA ext ) and that CA ext activity is induced by low CO 2 concentrations in the growth medium. However, much of this work has been conducted on cells adapted to air‐equilibrium concentrations of CO 2 , rather than to changing CO 2 conditions caused by growing microalgal populations. We investigated the role of CA ext in inorganic carbon (C i ) acquisition and photosynthesis at three sampling points during the growth cycle of the cosmopolitan marine diatom Chaetoceros muelleri . We observed that CA ext activity increased with decreasing C i , particularly CO 2 , concentration, supporting the idea that CA ext is modulated by external CO 2 concentration. Additionally, we found that the contribution of CA ext activity to carbon acquisition for photosynthesis varies over time, increasing between the first and second sampling points before decreasing at the last sampling point, where external pH was high. Lastly, decreases in maximum quantum yield of photosystem II (F v /F m ), chlorophyll, maximum relative electron transport rate, light harvesting efficiency (α) and maximum rates of C i ‐ saturated photosynthesis (V max ) were observed over time. Despite this decrease in photosynthetic capacity an up‐regulation of CCM activity, indicated by a decreasing half‐saturation constant for CO 2 (K 0.5 CO 2 ), occurred over time. The flexibility of the CCM during the course of growth in C. muelleri may contribute to the reported dominance and persistence of this species in phytoplankton blooms.