THE EFFECT OF SHADING ON THE FLAVONOID PATHWAY DURING GRAPE BERRY RIPENING IN THREE AGLIANICO BIOTYPES

Abstract

Polyphenols play a crucial role in wine making: they are involved in the oxidation reactions and in the determination of the sensorial quality of wine, particularly the astringency and the structure (tannins) and the color of red wines (anthocyanins). Some polyphenols have nutraceutical properties and are responsible for the benefit of moderate consumption of red wine on human health. Anthocyanins are a very well known group of phenolic compounds responsible for red, blue and purple pigmentation in plants, particularly in some flowers (eg, Petunia) and in many fruits, including red grape berries. Anthocyanins are synthesised in the flavonoid pathway. Previous studies (Downey et al, 2004; Fujita et al 2007; Rustioni et al, 2006) have demonstrated that cluster shading may significantly influence anthocyanin synthesis and, in general, the whole flavonoid pathway. More studies are necessary to elucidate the role of shading in the regulation of the pathway. For this reason we have chosen to study the response to shading in very closely related biotypes of a red berry cultivar of Vitis vinifera. Aglianico is a very famous red cultivar traditionally grown in Southern Italy in many separated areas. Recent study (Costantini et al, 2005) have demonstrated that several byotipes of Aglianico, although showing clearly different phenotypes, they are originated from the same original genotype. For this reason, Aglianico is considered a good model for intra-variety variability. Three main biotypes of Aglianico (Vulture, Taurasi and Taburno) were selected to carry out this work. A vineyard collecting the three biotypes was chosen as experimental site. In the experimental vineyard the biotypes are grown in the same environmental and agronomic conditions. Before veraison, clusters from each biotype underwent two different treatments: 12 clusters were covered with a shading screen designed to exclude light without modifying temperature and relative humidity; other clusters were completely exposed to sunlight through defoliation of the bottom leaves of the canopy. Physiological and technological variables such as sugars, pH and titrable acidity, and the accumulation kinetics of the each polyphenol species were measured. The relative expression of CHS2, F3‘5‘H, F3’H, F3H, DFR1, LDOX1, UFGT, OMT, AM1, AM3, GST4, LAR2, FLS4, MYB5a, MYB5b, MYB12 and MYBA1 was analysed by means of Real Time PCR. This work describes the behaviour of the three biotypes regarding both the accumulation of primary and secondary metabolites as well as the differential expression of the flavonoid biosynthethic genes. In the mean time it describes the accumulation of primary and secondary metabolites and transcriptional expression of the genes of the flavonoid pathway in response to the grape berry shading treatment. This work is the first report about the effect of grape bunch exposure on the expression of the F3’5’H and F3’H genes, and on the AM1, AM3 and GST4 anthocyanin transporters.