Towards understanding vacuolar antioxidant mechanisms: a role for fructans?

Abstract

Recent in vitro, in vivo, and theoretical experiments strongly suggest that sugar-(like) molecules counteract oxidative stress by acting as genuine reactive oxygen species (ROS) scavengers. A concept was proposed to include the vacuole as a part of the cellular antioxidant network. According to this view, sugars and sugar-like vacuolar compounds work in concert with vacuolar phenolic compounds and the ‘classic’ cytosolic antioxidant mechanisms. Among the biologically relevant ROS (H2O2, O2·–, and ·OH), hydroxyl radicals are the most reactive and dangerous species since there are no enzymatic systems known to neutralize them in any living beings. Therefore, it is important to study in more detail the radical reactions between ·OH and different biomolecules, including sugars. Here, Fenton reactions were used to compare the ·OH-scavenging capacities of a range of natural vacuolar compounds to establish relationships between antioxidant capacity and chemical structure and to unravel the mechanisms of ·OH–carbohydrate reactions. The in vitro work on the ·OH-scavenging capacity of sugars and phenolic compounds revealed a correlation between structure and ·OH-scavenging capacity. The number and position of the C=C type of linkages in phenolic compounds greatly influence antioxidant properties. Importantly, the splitting of disaccharides and oligosaccharides emerged as a predominant outcome of the ·OH–carbohydrate interaction. Moreover, non-enzymatic synthesis of new fructan oligosaccharides was found starting from 1-kestotriose. Based on these and previous findings, a working model is proposed describing the putative radical reactions involving fructans and secondary metabolites at the inner side of the tonoplast and in the vacuolar lumen.

Antioxidant Capacity and Bioaccessibility of Synergic Mango (cv. Ataulfo) Peel Phenolic Compounds in Edible Coatings Applied to Fresh-Cut Papaya

“…However, it was observed that the PC (gallic and protocatechuic acids) added into alginate solutions resulted in a slight increase of the AOXC of the protocatechuic acid measured by the DPPH assay (Figure 2(B)), whilst the AOXC by FRAP assay showed 2 fold increase (Figure 2(D)). These results, according to Peshev and Vergauwen [26], suggest that the antioxidant mechanism followed by the combination of alginate, gallic and protocathechuic acid are not entirely by hydrogen donation. As Peshev, Vergauwen [26] described, if double bonds are present in the antioxidant molecules they follow the radical addition mechanism, which is not considered as a possible mechanism for carbohydrates, but it is for PC [24].…”

“…These results, according to Peshev and Vergauwen [26], suggest that the antioxidant mechanism followed by the combination of alginate, gallic and protocathechuic acid are not entirely by hydrogen donation. As Peshev, Vergauwen [26] described, if double bonds are present in the antioxidant molecules they follow the radical addition mechanism, which is not considered as a possible mechanism for carbohydrates, but it is for PC [24]. It means that the capacity of the synergic combination to donate electrons is not restricted, but enhanced by the presence of alginate, following diverse possible antioxidant mechanisms.…”

Spatio-Temporal Dynamics of Fructan Metabolism in Developing Barley Grains

“…Recent experiments have suggested the direct participation of sugars in ROS detoxification (Nishizawa et al, 2008;Peshev et al, 2013;Falkeborg et al, 2014). In tobacco (Nicotiana tabacum), enhanced freezing tolerance has been correlated with the increased ROS scavenging capacity generated by the constitutive expression of a bacterial levansucrase gene producing fructans (Parvanova et al, 2004).…”

Anatomy and fructan distribution in vegetative organs of Dimerostemma vestitum (Asteraceae) from the campos rupestres

“…In addition, these compounds are thought to stabilize membranes, to function as osmoregulators (Carvalho et al 2007, Livingston et al 2009) and to protect plants against reactive oxygen species (Peshev et al 2013). Fructans are fructose polymers containing one internal or terminal glucose unit.…”