Significance of phenylpropanoid pathways in the response of two pomegranate cultivars to salinity and ozone stress

Secondary metabolites play a pivotal role in defense mechanisms, especially in plant-environment interactions. However, there are still difficulties in ascertaining the metabolic effect of their production due to individual and/ or combined stress, given the variety of simultaneous and interconnected effects of multiple stresses to metabolic processes in plants. Here, two pomegranate cultivars (Wonderful and Parfianka) were subjected to moderate levels of salt (i.e., 100 mM NaCl for 35 consecutive days) and sequentially exposed to a realistic O3 concentration (i.e., 100 ppb for 5 h) to evaluate how NaCl treatment and/or O3 fumigation alter the leaf polyphenolic composition, and what is the role of metabolites and enzymes involved in the phenylpropanoid pathway during sequential abiotic stresses. Wonderful leaves responded to NaCl or O3 treatments through the production/ accumulation of cinnamic acid derivatives (more than 3-fold higher than controls) and by exhibiting chemical composition plasticity against oxidative stress. The unchanged concentrations of benzoic acid derivatives indicate that treated Wonderful leaves could diversify the components of polyphenolic compounds and induce the biosynthesis of the components available (e.g., ellagitannins and punicalagin). During sequential abiotic stresses, Wonderful leaves needed few cellular adjustments to maintain oxidative stress under control (especially during the recovery time). On the other hand, Parfianka leaves had phenolics/polyphenolics amount (at constitutive level) suitable to face out the environmental changes (occurring singly or sequentially) so that no rearrangement of metabolites and enzymes involved in the phenylpropanoid pathway was required. Consequently, it is possible to conclude that Parfianka is more salt- and O3-tolerant than Wonderful.