Abstract
The main effects of three different irrigation regimes, i.e., sustained deficit irrigation (SDI), regulated deficit irrigation (RDI) and non-irrigated (NI), on seed traits namely proanthocyanidins (PAs) were evaluated in the wine grape cultivar Aragonez (syn. Tempranillo) grown in Alentejo (Portugal) over two growing seasons. Results showed that while the number of seeds per berry was not affected by water availability, seed fresh weight differed among treatments, the NI treatment exhibiting the lowest values. The biosynthetic pathway of flavanols appeared to be modified by the irrigation treatment, and several genes responsible for PA synthesis were up-regulated in the most stressed seeds (RDI and NI). However, this effect had no impact on PA content, suggesting the influence of other factors such as oxidation and/or degradation of PAs at late stages of maturation in grape seeds. The seeds’ non-enzymatic antioxidant capacities (oxygen radical absorbance capacity (ORAC) and hydroxyl radical adverting capacity (HORAC)) were modulated by water deficit and correlated well with PA content. The impact of irrigation strategy on PA biosynthesis, content, and anti-radical activity during seed ripening is discussed in the context of increasing interest in the role of PAs in the color and taste of wine, and the potential health benefits relating to their antioxidant capacity.
Highlights
Proanthocyanidins (PAs), known as condensed tannins, are secondary metabolites synthesized via the flavonoid biosynthetic pathway
Tannin content in seeds is very relevant for wine production, few studies have dealt with the effect of watering in seed polyphenols, and their results seem to be contradictory [7,33,34]
In the present study we show the effect of three different irrigation systems—ranging from little stress, through mild to severe stress—on flavanol monomer and polymeric proanthocyanidin content and biosynthesis in grape seeds during ripening
Summary
Proanthocyanidins (PAs), known as condensed tannins, are secondary metabolites synthesized via the flavonoid biosynthetic pathway. Grape seed PAs have beneficial effects on human health due to anticancer activities, antioxidant, cardio-protective properties, anti-microbial, and anti-allergic proprieties [19] These compounds are extracted during winemaking and transmitted to the finished wine. Altering metabolite accumulation, and changing the expression of genes responsible for some grape berry compounds [26,31] It has not been established whether changes in seed proanthocyanidin composition and antioxidant activity result from different irrigation practices. Given the increasing interest in grape PAs due to their role in wine color and taste and their antioxidant capacity, we investigated the effect of irrigation strategy on seed flavanol monomers, and on PA accumulation, biosynthesis and anti-radical activity during berry ripening
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