Abstract
Flavonoids are specialized metabolites largely widespread in plants where they play numerous roles including defense and signaling under stress conditions. These compounds encompass several chemical subgroups such as flavonols which are one the most represented classes. The most studied flavonols are kaempferol, quercetin and myricetin to which research attributes antioxidative properties and a potential role in UV-defense through UV-screening mechanisms making them critical for plant adaptation to climate change. Despite the great interest in flavonol functions in the last decades, some functional aspects remain under debate. This review summarizes the importance of flavonoids in plant defense against climate stressors and as signal molecules with a focus on flavonols in Mediterranean plant species. The review emphasizes the relationship between flavonol location (at the organ, tissue and cellular scales) and their function as defense metabolites against climate-related stresses. It also provides evidence that biosynthesis of flavonols, or flavonoids as a whole, could be a crucial process allowing plants to adapt to climate change, especially in the Mediterranean area which is considered as one of the most sensitive regions to climate change over the globe.
Highlights
Plants possess thousands of plant secondary or specialized metabolites (PSMs) whose chemical diversity is species-specific
It is known that there exists a relationship between aglycone/glycone flavonols and the oxidative stress, the glycosylated forms of flavonols being less effective antioxidants [54,55]. Despite their contrasting antioxidant protection, an accumulation of quercetin 3-O-glucosides and a decrease in the antioxidant enzyme activity have been observed under water stress in leaves of the Mediterranean species Fraxinus ornus, suggesting that these glycoside forms of flavonols could act as H2O2 scavengers during water stress [38]
In shrub and a conifer species, recent studies have reported an effect of enhanced temperature which leads to a reduction in flavonoids in stems [133] and leaves [134,135], this being related to an increase in plant growth
Summary
Plants possess thousands of plant secondary or specialized metabolites (PSMs) whose chemical diversity is species-specific. Investigations have reported that flavonoids play a role in the modulation of reactive oxygen species (ROS) and possess UV-screening mechanisms [8,27,28,29,30] as described later in this review Their action as antioxidant is based on (i) their direct capacity to scavenge ROS [31], (ii) their role in inhibition of ROS formation by chelating ion of metals [32,33] and (iii) their ability to activate antioxidant enzymes [19,34]. We focus on the response and protection conferred by flavonols under climate stress in Mediterranean plants species All these sections are described by reviewing a number of interdisciplinary studies (biochemistry, ecology and ecophysiology studies) that have used genomic, transcriptomic, metabolomic and imaging approaches.
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