Journal
PLANT AND CELL PHYSIOLOGY
Volume 50, Issue 12, Pages 2174-2182Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcp151
Keywords
Abiotic stress Carbohydrate compartmentation Chloroplast Raffinose transport
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Funding
- Swiss National Foundation [31-103681]
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In chloroplasts, several water-soluble carbohydrates have been suggested to act as stress protectants. The trisaccharide raffinose (-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 extra-chloroplastic (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 K-m and v(max) values of 27.8mM and 3.3molmg(1) Chl min(1), respectively.
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