臨時生物科学セミナー（第１５９回）

　　日　時：平成１９年１１月２１日（水）　１６：３０〜１８：００

場　所：理学部２号館　第二講義室（２２３号室）

講演題目：CO₂ transfer in the mesophyll. A carbonic anhydrase perpective

講演者名：Bernard Genty

Laboratoire d’Ecophysiologie Moléculaire des Plantes, UMR 6191 CNRS-CEA,

Aix-Marseille II, SBVMe, IBEB, CEA Cadarache, 13108 St Paul-lez-Durance, France.

講演概要

Using ¹⁸O labelled CO₂ and mass spectrometry, estimations of the carbonic anhydrase (CA) activity and the CO₂ transfer conductance between the atmosphere and the site of CA have been obtained in various C₃ plants. Remarkably, the CO₂ concentration estimated at the site of catalysed hydration in folio was closer to the CO₂ concentration estimated at the evaporative site than to the CO₂ concentration predicted in the chloroplast contrary to the current view assuming catalysis by chloroplastic activity only. In order to dissect the basis of this observation, we analysed expression and function of genes encoding putative CA in Arabidopsis thaliana. Six b-CA genes were found to be expressed in leaf tissues. We provided evidence that each of the corresponding b-CAs is targeted to specific subcellular compartment (chloroplasts, cytosol, plasma membranes and mitochondria) (Fabre et al., 2007). By using null mutants depleted in various CA isoforms, the role of CA activity with respect to their specific cellular compartments has been addressed. We showed that CO₂ hydration in the mesophyll is not only catalysed by chloroplastic CA but also by extrachloroplastic CAs. In particular, the main cytosolic isoform represented up to a quarter of the whole leaf CA activity. For several null mutants, contrasting growth phenotypes which depended on CO₂ concentration during growth have been obtained. From CA-based estimations of mesophyll conductance together with estimations based on Rubisco in these mutants, the relationship between CAs (activity and cellular localisation) mesophyll CO₂ transfer, CO₂ uptake and growth will be discussed.

参考文献

Fabre N, Reiter IA, Becuwe-Linka N, Genty B, Rumeau D. (2007) Characterization and expression analysis of genes enocoding a and b carbonic anhydrase in Arabidopsis. Plant Cell Environ. 30: 617-629.

Havaux M, Triantaphylidès C, Genty B (2006) Autoluminescence imaging: a non-onvasive tool for mapping oxidative stress. Trends in Plant Science 11: 480-485.

　東京大学理学部生物学科植物学コース