Drought increases chlorophyll content in stems of Vitis interspecific hybrids

Plants respond to drought stress through different physiological mechanisms. To highlight a specific adaptation strategy related to stem photosynthetic activity, woody tissue pigmentation was studied. In this work, 25 Vitis hybrids were studied in two experimental vineyards: one of them with sufficient water availability and the other showing drought stress. 1500 reflectance spectra of woody tissues were collected. Beside the spectral elaboration and interpretation, indexes for the pigment quantification were calculated. The content and the proportion in chlorophylls (a and b) in stems were significantly modified in response to water stress. Genotypes were classified based on their plasticity/elasticity and adaptive/susceptible behavior. The cluster analysis produced 4 main groups based on their average spectra and on the spectral variations between watered and stress conditions. The most interesting genotypes concerning this trait were pointed out. Nevertheless, this adaptation mechanism could also be due to an increased detoxification necessity related to other physiological disfunctions caused by water stress. A multi-parameter approach is encouraged for phenotyping of abiotic stress tolerant plant selection. In the next future, this work will support the release of new drought tolerant rootstocks for viticulture

Effect of anthocyanin absence on white berry grape (Vitis vinifera L.)

In grapevines, white berried cultivars are characterized by the absence of anthocyanins, which are the main pigments in V. vinifera fruits. These varieties produce berries with a yellowish color. The pigments responsible of this hue are still not well defined. In this paper, spectrophotometric analyzes were carried out using non-invasive methods (reflectance spectra) and destructive quantifications (chlorophyll and carotenoid quantifications) to describe the variation in color of three white grape varieties during ripening. A decrease in chlorophylls and carotenoids was found. Changes in the proportion of blue (450-500 nm) and red (630\u2011700 nm) absorption bands were underlined. The contribution of melanin-like pigments (oxidation products) is also discussed. In general, our results indicate that the yellow color of white cultivars is not related to the activation of specific biosynthetic pathways. It is most likely due to a series of catabolic processes (and to their relative intensity), which become visible and that are possibly stimulated by the anthocyanin absence

Effect of anthocyanin absence on white berry grape (Vitis vinifera L.)

In grapevines, white berried cultivars are characterized by the absence of anthocyanins, which are the main pigments in V. vinifera fruits. These varieties produce berries with a yellowish color. The pigments responsible of this hue are still not well defined. In this paper, spectrophotometric analyzes were carried out using non-invasive methods (reflectance spectra) and destructive quantifications (chlorophyll and carotenoid quantifications) to describe the variation in color of three white grape varieties during ripening. A decrease in chlorophylls and carotenoids was found. Changes in the proportion of blue (450-500 nm) and red (630‑700 nm) absorption bands were underlined. The contribution of melanin-like pigments (oxidation products) is also discussed. In general, our results indicate that the yellow color of white cultivars is not related to the activation of specific biosynthetic pathways. It is most likely due to a series of catabolic processes (and to their relative intensity), which become visible and that are possibly stimulated by the anthocyanin absence

Chlorophyll and carotenoid quantifications in white grape (Vitis vinifera L.) skins by reflectance spectroscopy

In white grapes, chlorophylls and carotenoids play important roles in berry color and environmental interactions (e.g. radiative stresses). In this paper, easy, fast and low cost non-invasive reflectance methods have been tested and developed. Previously published indexes showed good performances for chlorophyll quantifications. However, in this work, new formulas able to discriminate chlorophylls a and b were also proposed. The wavelengths of major interest for the absorption detection were identified. Formulas based on the Gaussians half heights were proposed. In general, chlorophyll quantifications were obtained directly from reflectance spectra, while carotenoid absorption bands did not allow good reflectance correlations. However, the chlorophyll/carotenoid ratio (due to the pigments physiological linked roles) could be used to estimate carotenoid content. Their proportion changes during berry development, thus the index coefficients should be adapted in relation to the BBCH phenological phase. The obtained indexes demonstrated good correlations with the destructive quantifications. These methods could support further researches concerning cultivar classification and physiological studies

The Effect of Copper Ions on Colour in Extracts of Cabernet Sauvignon and Sangiovese Skins Under Wine-like Conditions

Pigment-metal complexes are generally not considered to play significant roles in grape and wine colour. However, to the best of my knowledge, this hypothesis has never been investigated. In this work, grape skin extracts (cultivars Sangiovese and Cabernet Sauvignon) were allowed to react with copper sulphate aqueous solutions at different concentrations. High, and toxic, copper additions produced significant absorption increases in the green spectral region (corresponding to the typical absorption band of anthocyanins). Further studies will be necessary to characterise the nature of this interaction

Optical Properties of Berry Epicuticular Waxes in Four Georgian Grape Cultivars (Vitis vinifera L.)

The epidermis of plant shoot organs is generally covered by epicuticular waxes. The role of this layer isrelated mainly to the protection of the inner tissues from biotic and abiotic stresses. In this study, attentionis focused on the optical properties of the berry epicuticular waxes of the grapevine (Vitis vinifera L.) atfruit ripening. The reflectance of the berry surface was measured before and after chloroform treatmentsin four Georgian grape cultivars grown in northern Italy. Epicarp optical properties were underlinedat different wavelengths (341 to 1025 nm) for each cultivar. The results show that the berry waxes haveseveral optical properties; it is possible that their main eco-physiological effect is to provide specificprotection against different types of radiation. Besides the physiological aspects, the results are interestingalso from a technical point of view in the field of interpretation of reflectance measurements carried out bynon-invasive instruments

Influence of bunch exposure on anthocyanins extractability from grapes skins (Vitis vinifera L.)

In relation to bunch exposure to solar irradiance (sun exposed vs. leaf shaded conditions), anthocyanin ripening and extractability were studied in two grape cultivars ('Croatina' and 'Pinot Noir') coming from three different vineyards in Northern Italy. Analysis of anthocyanin content were carried out by HPLC and spectrophotometry, and a simulated maceration process was developed. Pigments extraction occurred mainly in the first few hours of the maceration process. Anthocyanins with disubstituted B-ring showed a faster extractability than the trisubsituted ones. Bunch exposure to sunlight seemed to be important for pigment extractability timing in winemaking, showing a delay in pigments release. This delay was only partially explained by the different pigments profile, with higher percentage of disubstituted compounds in shaded berries, because all the molecules indicated a similar extraction trend during maceration.

Disfunctions in the anthocyanin accumulation of Vitis vinifera L. varieties studied by a targeted resequencing approach

BACKGROUND: The pathway of anthocyanin biosynthesis, and its alterations leading to berry colour modification, are well known in grape skin. This variability could affect both quantity and quality of pigment accumulation. OBJECTIVE: The present work is focused on 15 grapevine cultivars selected to represent a high variability in the phenotypical colour traits in order to highlight new polymorphisms related to the flavonoid pathway. METHODS: Twenty-one genes involved in the biosynthetic pathway of anthocyanins were studied via targeted resequencing and were correlated with phenotypic data ( anthocyanin profiles and spectroscopy indices). RESULTS: Single nucleotide polymorphism (SNP) and InDel (insertion/deletion) polymorphisms were detected. Out of 1751 polymorphic loci, 68% were SNPs and 32% were InDels (568). Cluster analysis and SPLS-DA were used to investigate the genetic relationships among the cultivars, confirming the large range of phenotypical variability. Statistically significant correlations were detected between accumulation of 3\u2019 anthocyanins and genetic polymorphisms in two structural genes and one transcription factor putatively involved in the anthocyanin biosynthetic pathway. CONCLUSIONS: The understanding of the polymorphisms related to the anthocyanin accumulation could support future selection of new pink table grape varieties with increased appeal on the consumers

Advances in grape phenotyping: pigment characterization by reflectance and theoretical chemistry

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Grape seed ripening evaluation by ortho-diphenol quantification

Two millennia of viticulture recognize the seed browning importance on tannin ripening and, thus, on grape and wine quality. This color change was recently attributed to phenolic oxidations. However an objective chemical index able to quantify the oxidation status of seed tannins was missing, probably due to the heterogeneous oxidation polymerizations. This work suggests the adoption of the ortho-diphenol quantification as indication of the tannin ripening process, because ortho-dihydroxylated substitutions are highly susceptible to oxidation. The method proposed is based on the ortho-diphenol characteristic complexation with molybdenum. Different cultivars (Merlot, Pinot noir, Croatina, Aladasturi, Alexandrouli, Odjaleshi and Tavkveri) were studied during three vintages in Oltrepo pavese, Italy. The color darkening correlated with the ortho-diphenol decrease. We believe this index could find useful applications in viticulture, supporting harvesting time decisions