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Plant and Cell Physiology Advance Access originally published online on July 8, 2009
Plant and Cell Physiology 2009 50(8):1522-1531; doi:10.1093/pcp/pcp097
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Physiological Regulation of Coccolith Polysaccharide Production by Phosphate Availability in the Coccolithophorid Emiliania huxleyi

Keisuke Kayano and Yoshihiro Shiraiwa*

Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8572 Japan

*Corresponding author: E-mail, emilhux{at}biol.tsukuba.ac.jp; Fax, +81-29-853-6614.


  Abstract

Coccoliths of the coccolithophorid Emiliania huxleyi are calcified biomineral scales composed of calcium carbonate and coccolith polysaccharide (CPs). Coccolith production is regulated by inorganic phosphate (Pi) availability, but no information currently exists on how this process occurs. In this study CP was experimentally characterized by HPLC analysis as an acid polysaccharide of mannose, galacturonic acid, xylose and rhamnose. Both calcification (estimated from 45Ca uptake) and CP production (estimated from uronic acid quantification) were stimulated under Pi-deficient conditions but strongly suppressed under Pi-sufficient conditions. When cells were transferred from Pi-sufficient to Pi-deficient conditions the production of neutral polysaccharides (NP)—storage glucans—ceased rapidly after a temporary increase in the presence of Pi, and CP production started to increase after Pi was almost depleted. Under Pi-sufficient conditions NP production increased, concomitant with stimulation of cell growth. Calcification increased gradually, but photosynthetic 14CO2 fixation was reduced by almost 40% for 5 d of culture during Pi depletion. [14C]CP production was maintained at almost constant, high levels under Pi-deficient conditions but gradually decreased under Pi-sufficient conditions in conjunction with cell growth. In contrast, [14C]NP production increased about 3-fold under Pi-sufficient conditions for 3 d. The present study indicates that E. huxleyi switches the direction of carbon flow toward CP and NP production under Pi-deficient and Pi-sufficient conditions, respectively.

Keywords: Acid polysaccharide - Calcification - Carbon metabolism regulation - Coccolith polysaccharide - Emiliania huxleyi - Phosphate deficiency

Abbreviations: ABEE, 4-aminobenzoic acid ethyl ester; AP, acid polysaccharide; BAS, bio-imaging analyzer system; CP, coccolith polysaccharide; IP, imaging plate; NP, neutral polysaccharide; TCA, trichloroacetic acid.

(Received March 4, 2009; Accepted June 25, 2009)
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