Carbon allocation and element composition in four

Authors: Francesco Memmola Bratati Mukherjee James V Moroney Mario Giordano

Publish Date: 2014/04/22

Volume: 121, Issue: 2-3, Pages: 201-211

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Abstract

Four mutants of Chlamydomonas reinhardtii with defects in different components of the CO2 concentrating mechanism CCM or in Rubisco activase were grown autotrophically at high pCO2 and then transferred to low pCO2 in order to study the role of different components of the CCM on carbon allocation and elemental composition To study carbon allocation we measured the relative size of the main organic pools by Fourier Transform Infrared spectroscopy Total reflection Xray fluorescence was used to analyze the elemental composition of algal cells Our data show that although the organic pools increased their size at high CO2 in all strains their stoichiometry was highly homeostatic ie the ratios between carbohydrates and proteins lipid and proteins and carbohydrates and lipids did not change significantly The only exception was the wildtype 137c in which proteins decreased relative to carbohydrates and lipids when the cells were transferred to low CO2 It is noticeable that the two wild types used in this study responded differently to the transition from high to low CO2 Malfunctions of the CCM influenced the concentration of several elements somewhat altering cell elemental stoichiometry especially the C/P and N/P ratios changed appreciably in almost all strains as a function of the growth CO2 concentration except in 137c and the Rubisco activase mutant rca1 In strain cia3 defective in the lumenal carbonic anhydrase CA the cell quotas of P S Ca Mn Fe and Zn were about 5fold higher at low CO2 than at high CO2 A Principle Components Analysis showed that mostly because of its elemental composition cia3 behaved in a substantially different way from all other strains at low CO2 The lumenal CA thus plays a crucial role not only for the correct functioning of the CCM but also for element utilization Not surprisingly growth at high CO2 attenuated differences among strainsCCM work in MG’s lab was funded by the Cariverona Foundation by the Italian Ministry for Agriculture MIPAF Bioforme project by the Italian Ministry of Foreign Affairs MAE Joint ItalianIsrael Cooperation Program and by the Assemble program of the European Union The work in JVM’s lab was funded by the National Science Foundation and a subcontract from the University of Illinois We wish to thank Elly Spijkerman for providing access to the instrumentation for the C and N quantification

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