ElSayed A I, Rafudeen M S, Golldack D
Department of Biochemistry, Faculty of Agriculture, Zagazig University, Zagazig, Egypt.
Department of Molecular and Cell Biology, Science Faculty, University of Cape Town, Cape Town, South Africa.
Plant Biol (Stuttg). 2014 Jan;16(1):1-8. doi: 10.1111/plb.12053. Epub 2013 Aug 12.
Abiotic stresses resulting from water deficit, high salinity or periods of drought adversely affect plant growth and development and represent major selective forces during plant evolution. The raffinose family oligosaccharides (RFOs) are synthesised from sucrose by the subsequent addition of activated galactinol moieties donated by galactinol. RFOs are characterised as compatible solutes involved in stress tolerance defence mechanisms, although evidence also suggests that they act as antioxidants, are part of carbon partitioning strategies and may serve as signals in response to stress. The key enzyme and regulatory point in RFO biosynthesis is galactinol synthase (GolS), and an increase of GolS in expression and activity is often associated with abiotic stress. It has also been shown that different GolS isoforms are expressed in response to different types of abiotic stress, suggesting that the timing and accumulation of RFOs are controlled for each abiotic stress. However, the accumulation of RFOs in response to stress is not universal and other functional roles have been suggested for RFOs, such as being part of a carbon storage mechanism. Transgenic Arabidopsis plants with increased galactinol and raffinose concentrations had better ROS scavenging capacity, while many sugars have been shown in vitro to have antioxidant activity, suggesting that RFOs may also act as antioxidants. The RFO pathway also interacts with other carbohydrate pathways, such as that of O-methyl inositol (OMI), which shows that the functional relevance of RFOs must not be seen in isolation to overall carbon re-allocation during stress responses.
水分亏缺、高盐度或干旱期等非生物胁迫会对植物的生长发育产生不利影响，并且是植物进化过程中的主要选择压力。棉子糖家族寡糖（RFOs）由蔗糖通过依次添加由肌醇半乳糖苷提供的活化肌醇半乳糖基部分合成。RFOs被认为是参与胁迫耐受性防御机制的相容性溶质，尽管也有证据表明它们可作为抗氧化剂，是碳分配策略的一部分，并且可能作为应激反应的信号。RFO生物合成中的关键酶和调控点是肌醇半乳糖苷合酶（GolS），GolS表达和活性的增加通常与非生物胁迫相关。研究还表明，不同的GolS同工型会响应不同类型的非生物胁迫而表达，这表明每种非生物胁迫下RFOs的合成时间和积累量都是受到调控的。然而，RFOs在胁迫下的积累并非普遍现象，并且有人提出RFOs还具有其他功能作用，例如作为碳储存机制的一部分。肌醇半乳糖苷和棉子糖浓度增加的转基因拟南芥植物具有更好的活性氧清除能力，而许多糖类在体外已被证明具有抗氧化活性，这表明RFOs也可能作为抗氧化剂发挥作用。RFO途径还与其他碳水化合物途径相互作用，例如O-甲基肌醇（OMI）途径，这表明不能孤立地看待RFOs在胁迫反应中整体碳重新分配过程中的功能相关性。
