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Plant and Cell Physiology Advance Access published online on October 30, 2009
Plant and Cell Physiology, doi:10.1093/pcp/pcp151
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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 e-mail: journals.permissions@oxfordjournals.org

Raffinose in Chloroplasts is Synthesized in the Cytosol and Transported across the Chloroplast Envelope

Thomas Schneider and Felix Keller

Molekulare Pflanzenphysiologie, Institut für Pflanzenbiologie, Universität Zürich, Zollikerstr.107, 8008 Zürich, Switzerland

Corresponding author: Prof. Dr. Felix Keller Institute of Plant Biology University of Zürich Zollikerstr. 107 CH-8008 Zürich Switzerland Phone: +41 44 634 82 25 Fax: +41 44 634 82 04 E-mail: fkel{at}botinst.uzh.ch


  Abstract

In chloroplasts, several water-soluble carbohydrates have been suggested to act as stress protectants. The trisaccharide raffinose ({alpha}-1,6-galactosyl sucrose) is such a carbohydrate but has received little attention. We here demonstrate by compartmentation analysis of leaf mesophyll protoplasts that raffinose is clearly (to about 20%) present in chloroplasts of cold-treated common bugle (Ajuga reptans L.), spinach (Spinacia oleracea L.), and Arabidopsis [Arabidopsis thaliana (L.) Heynh.] plants. The two dedicated enzymes needed for raffinose synthesis, galactinol synthase and raffinose synthase, were found to be extrachloroplastic (probably cytosolic) in location, suggesting that the chloroplast envelope contains a raffinose transporter. Uptake experiments with isolated Ajuga and Arabidopsis chloroplasts clearly demonstrated that raffinose is indeed transported across the chloroplast envelope by a raffinose transporter, probably actively. Raffinose uptake into Ajuga chloroplasts was a saturable process with apparent Km and vmax values of 27.8 mM and 3.3 µmol mg-1 Chl min-1, respectively.

Keywords: abiotic stress - carbohydrate compartmentation - chloroplast - raffinose transport

(Received July 31, 2009; Accepted October 19, 2009)
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