Egert Aurélie, Eicher Barbara, Keller Felix, Peters Shaun
Institute of Plant Biology, Molecular Plant Physiology, University of Zürich Zürich, Switzerland.
Department of Genetics, Institute for Plant Biotechnology, University of Stellenbosch Stellenbosch, South Africa.
Front Physiol. 2015 Jul 22;6:206. doi: 10.3389/fphys.2015.00206. eCollection 2015.
The leaves of the resurrection plant Craterostigma plantagineum accumulate sucrose during dehydration, via a conversion from the unusual C8 ketose-sugar 2-octulose. However, raffinose family oligosaccharides (RFOs) have been shown to be major photosynthetic products in this plant. The tetrasaccharide stachyose is the major phloem-mobile carbohydrate and is used as a carbon store in roots. It has been suggested that this carbon store is remobilized during rehydration, presumably for cellular repair processes. We examined the effects of water deficit on the leaf water-soluble carbohydrate profiles of three Craterostigma species. Apart from the classical 2-octulose-to-sucrose interconversion, there was a strong water deficit-associated mass increase of RFOs up to the pentasaccharide verbascose. However, the activities of three dedicated RFO biosynthetic enzymes (raffinose, stachyose, and verbascose synthase) was not correlated with RFO accumulation, suggesting that biosynthetic enzyme activities measured in the early stages of water-deficit were sufficient to synthesize enough galactinol and lead to RFO accumulation in the leaves. Our findings are suggestive of RFOs providing additional carbohydrate-based stress protection to the leaves of these plants during the desiccated state.
复苏植物车前叶蓝蓟的叶片在脱水过程中会通过由特殊的C8酮糖-2-辛酮糖转化来积累蔗糖。然而，棉子糖家族寡糖（RFOs）已被证明是这种植物主要的光合产物。四糖水苏糖是主要的韧皮部可运输碳水化合物，并且在根中用作碳储存。有人提出，这种碳储存在复水过程中会被重新调动，大概用于细胞修复过程。我们研究了水分亏缺对三种车前叶蓝蓟属植物叶片水溶性碳水化合物谱的影响。除了经典的2-辛酮糖到蔗糖的相互转化外，还存在与水分亏缺密切相关的RFOs大量增加，直至五糖毛蕊花糖。然而，三种专门的RFO生物合成酶（棉子糖、水苏糖和毛蕊花糖合酶）的活性与RFO积累不相关，这表明在水分亏缺早期测量的生物合成酶活性足以合成足够的肌醇半乳糖苷并导致叶片中RFO积累。我们的研究结果表明，RFOs在这些植物叶片处于干燥状态时提供了额外的基于碳水化合物的胁迫保护。
