JXB Advance Access originally published online on April 23, 2007
Journal of Experimental Botany 2007 58(8):1947-1956; doi:10.1093/jxb/erm056
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RESEARCH PAPER |
Protection mechanisms in the resurrection plant Xerophyta viscosa (Baker): both sucrose and raffinose family oligosaccharides (RFOs) accumulate in leaves in response to water deficit
1University of Cape Town, Department of Molecular and Cell Biology, Private Bag, Rhodes Gift, 7701, Cape Town, South Africa
2University of Zürich, Institute of Plant Biology, Molecular Plant Physiology, Zollikerstrasse 107, Zürich 8008, Switzerland
* To whom correspondence should be addressed. E-mail: fkel{at}botinst.uzh.ch
Changes in water-soluble carbohydrates were examined in the leaves of the resurrection plant Xerophyta viscosa under conditions of water deficit. Sucrose and raffinose family oligosaccharides (RFOs), particularly raffinose, increased under these conditions, with the highest concentrations evident at 5% relative water content [RWC; 23.5 mg g–1 dry weight (DW) and 17.7 mg g–1 DW, respectively]. Importantly, these effects were reversible, with concentrations returning to levels comparable with that of the full turgor state 7 d after water deficit conditions were alleviated, providing evidence that both sucrose and RFOs may play a protective role in desiccated leaf tissue of X. viscosa. Further, because the sucrose-to-raffinose mass ratio of 1.3:1 observed in the dehydrated state was very low, compared with published data for other resurrection plants (always >5), it is suggested that, in X. viscosa leaves, RFOs serve the dual purpose of stress protection and carbon storage. XvGolS, a gene encoding a galactinol synthase enzyme responsible for the first catalytic step in RFO biosynthesis, was cloned and functionally expressed. In leaf tissue exposed to water deficit, XvGolS transcript levels were shown to increase at 19% RWC. GolS activity in planta could not be correlated with RFO accumulation, but a negative correlation was observed between RFO accumulation and myo-inositol depletion, during water deficit stress. This correlation was reversed after rehydration, suggesting that during water deficit myo-inositol is channelled into RFO synthesis, but during the rehydration process it is channelled to metabolic pathways related to the repair of desiccation-induced damage.
Key words: Desiccation tolerance, galactinol synthase, raffinose family oligosaccharides, resurrection plants
Received 2 October 2006; Revised 19 February 2007 Accepted 21 February 2007
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