Contrasting acclimation mechanisms of berry color variant grapevine cultivars (Vitis vinifera L. cv. Furmint) to natural sunlight conditions

The acclimation mechanisms of two berry color variant grapevine leaves, Furmint White (FW) and Furmint Red (FR), to natural sunlight conditions were investigated comparing leaves from two distinct locations: at canopy surface (sun-exposed leaves) and in the inner layers (shaded leaves). We found that in contrast to FR leaves, sun-exposed FW leaves were thicker than shaded leaves due to thicker palisade tissues. Confocal laser scanning microscopy of Naturstoff-treated leaf segments revealed that flavonoids were accumulated in nuclei, cell walls, cytoplasm, and chloroplasts of the adaxial epidermal and palisade layers of sun-exposed leaves in both cultivars. High-performance liquid chromatography analysis showed that the main phenolic components in both cultivars were caftaric acid and various glycosylated flavonols. Among the latter, the dominant component was quercetin glucuronide in both cultivars, unaffected by light conditions. However, caftaric acid and quercetin glucoside were present in significantly higher amounts in sun-exposed than in shaded leaves of both cultivars, but the effect of light conditions on caftaric acid contents was more pronounced in FR than in FW. Accordingly, the total polyphenol content of leaf extracts characterized by Folin-reagent reactivity was more enhanced in sun-exposed leaves of FR, than in FW. Our data suggest two different sunlight acclimation strategies to protect photosynthetic mesophyll tissues from potential photo-oxidative damage. One is realized in FW leaves as stronger shading by thicker palisade layer accompanied by enhanced chemical defense. The other is achieved in FR leaves via a more pronounced increase in caftaric acid and total polyphenol content but without morphological adjustments.