Physiological aspects of raffinose family oligosaccharides in plants: protection against abiotic stress

Abstract

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.

Metabolite Profiling and Integrative Modeling Reveal Metabolic Constraints for Carbon Partitioning under Nitrogen Starvation in the Green Algae Haematococcus pluvialis

“…Raffinose showed a pattern similar to that of the TCH, peaking after the first 12 h of stress exposure. This sugar has been suggested to be associated with stress tolerance, defense mechanisms, and carbon partitioning in the cell, serving as an antioxidant signaling stress (64). These observations indicate that as long as Chl content is relatively high (9 -12 mg liter Ϫ1 ), the cell devotes its energy and carbon reserves to maintaining a carbon pool in the form of free sugars and starch.…”

Leaf Growth Response to Mild Drought: Natural Variation in Arabidopsis Sheds Light on Trait Architecture

“…Raffinose and other members of the raffinose family oligosaccharides are involved in stress tolerance and act as antioxidants. Furthermore, raffinose family oligosaccharides are part of the carbon storage system (ElSayed et al, 2014), possibly explaining why SIP2 is downregulated. The other four core response genes are involved in the synthesis of wax esters (FOLDED PETAL1) (Takeda et al, 2013), primary metabolism (PHOSPHOENOLPYRUVATE CARBOXYLASE KINASE1), stress-induced chloroplast disruption (CHLOROPLAST VESICULATION) (Wang and Blumwald, 2014), and Zn/Fe transport (IRON REGULATED TRANSPORTER3).…”

Seed-Specific Expression of a Feedback-Insensitive Form of CYSTATHIONINE-γ-SYNTHASE in Arabidopsis Stimulates Metabolic and Transcriptomic Responses Associated with Desiccation Stress

“…It has been demonstrated that certain sugars (such as Suc, Tre, and Raf) play a central role in the protection from drought stress in a wide range of organisms by helping to maintain the structure of the cytoplasm and to stabilize certain proteins when the amount of water is reduced (for review, see Ingram and Bartels, 1996). Galactinol, which increased up to 2.3-fold and is used for Raf synthesis, also plays an important role in abiotic stress tolerance (Elsayed et al, 2014). The higher levels of sugars in SSE seeds are apparently not the result of starch degradation, since the levels of starch increased in these seeds.…”