Flavonol Profile Is a Reliable Indicator to Assess Canopy Architecture and the Exposure of Red Wine Grapes to Solar Radiation.

Johann Martínez-Lüscher,Luca Brillante,Sahap Kaan Kurtural

doi:10.3389/fpls.2019.00010

Abstract

Exposure to solar radiation is a determining factor of grape composition. Flavonol synthesis is upregulated by solar radiation leaving a fingerprint on flavonol profile. This study aimed to test the factors affecting flavonol accumulation and profile and their potential as an indicator to assess the overall exposure of red wine grape berry to solar radiation. We performed three experiments to study the response of flavonol accumulation and profile to (1) three different solar radiation exclusion treatments during berry development; (2) canopy porosity and leaf area index (LAI); and (3) spatial variability of water status, vigor and ripening and cultural practices in commercial vineyards. Results showed a strong relationship between global radiation, inverse dormant pruning weights or canopy porosity (inversely proportional to LAI) and % kaempferol or % quercetin. Furthermore, the increase in concentration of the above two flavonols was associated with a reduction of % myricetin. Total flavonol content, % kaempferol, % quercetin, and % myricetin had significant correlations with inverse dormant pruning weights, but these were less sensitive to over-ripening or water deficits. Flavonol profile was associated to site hydrology (wetness index) through changes in vigor, and to LAI; and responded to shoot thinning or fruit-zone leaf removal. These results support the reliability of the flavonol profile as an assessment parameter for studies aiming to discuss canopy architecture or the effect of solar radiation on grapevine berries.

Highlights

Flavonols are mainly accumulated in epidermal cells of plant tissues in response to solar radiation, especially UV-B, filtering the most harmful part of the solar spectrum to DNA (Kolb et al, 2001)
Regulatory and synthetic genes responsible for flavonol biosynthesis are upregulated by UV-B fraction of solar radiation (Carbonell-Bejerano et al, 2014; Liu et al, 2014), and grape flavonol content increases with exposure to UV-B radiation unequivocally (Berli et al, 2011; Martínez-Lüscher et al, 2014b; Del-Castillo-Alonso et al, 2016b; Matus, 2016)
We aimed to propose flavonol profile, and specially the proportion of kaempferol, as a validation tool for the accumulated solar radiation received by grapes and test its reliability and use

Summary

Introduction

Flavonols are mainly accumulated in epidermal cells of plant tissues in response to solar radiation, especially UV-B, filtering the most harmful part of the solar spectrum to DNA (Kolb et al, 2001). Flavonols are known to play a role complementary to xanthophylls, protecting the photosynthetic apparatus in situ from excess of solar radiation (Agati et al, 2013; Castagna et al, 2017). Due to their strong radical scavenging activity, flavonoids such as flavonols and anthocyanins are involved in the mitigation of drought-related oxidative damage (Nakabayashi et al, 2014). Flavonoids are one of the most versatile secondary metabolites in plants. Flaonol Profile, a Reliable Indicator (Koes et al, 1994) They play an important role in crosstalk between plants and microorganisms, as they are released as exudates into the rhizosphere (Cooper, 2004). Flavonoids are remarkable for their inhibitory activity on inter-species seed germination and on fungal pathogens (Kong et al, 2004)

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