Ugni Blanc Research Articles

Two Paenibacillus spp. strains promote grapevine wood degradation by the fungus Fomitiporia mediterranea: from degradation experiments to genome analyses

Ascomycetes, basidiomycetes and deuteromycetes can degrade wood, but less attention has been paid to basidiomycetes involved in Esca, a major Grapevine Trunk Disease. Using a wood sawdust microcosm system, we compared the wood degradation of three grapevine cultivars inoculated with Fomitiporia mediterranea M. Fisch, a basidiomycete responsible for white-rot development and involved in Esca disease. The grapevine cultivar Ugni blanc was more susceptible to wood degradation caused by F. mediterranea than the cultivars Cabernet Sauvignon and Merlot. Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy showed that F. mediterranea preferentially degrades lignin and hemicellulose over cellulose (preferential, successive or sequential white-rot). In addition, co-inoculation of sawdust with two cellulolytic and xylanolytic bacterial strains of Paenibacillus (Nakamura) Ash (Paenibacillus sp. (S231-2) and P. amylolyticus (S293)), enhanced F. mediterranea ability to degrade Ugni blanc. The NMR data further showed that the increase in Ugni blanc sawdust degradation products was greater when bacteria and fungi were inoculated together. We also demonstrated that these two bacterial strains could degrade the wood components of Ugni blanc sawdust. Genome analysis of these bacterial strains revealed numerous genes predicted to be involved in cellulose, hemicellulose, and lignin degradation, as well as several other genes related to bacteria-fungi interactions and endophytism inside the plant. The occurrence of this type of bacteria-fungus interaction could explain, at least in part, why necrosis develops extensively in certain grapevine varieties such as Ugni blanc.

Highlighting the varietal origin of eugenol in Armagnac wine spirits from Baco blanc, a hybrid grape variety.

We report on the first evidence of a varietal origin of eugenol as a molecular marker in Baco blanc, one of the grape varieties used to produce Armagnac. Eugenol was identified and quantified by HS-SPME-GC-MS. For two separate vintages, the concentrations found in monovarietal wine spirits made from Baco blanc, were, on average, 10 times higher than those in other Vitis varieties, ranging from 31.0 to 174.7µg/L. Investigations were carried out to quantify eugenol in the wines used for distillation, in the musts and finally in several parts of the plant. For all matrices over both vintages, it was confirmed that eugenol is much more abundant in Baco blanc than in Ugni blanc and Folle blanche. Moreover, enzymatic hydrolysis made it possible to release a significant quantity of eugenol from precursors, demonstrating that more than 90% of eugenol is bound in the must and in the grape berry pulp.

Fungitoxic role of endogenous eugenol in the hybrid grapevine cultivar Baco blanc resistant to <i>Botrytis cinerea</i>

Eugenol (2-methoxy-4-(2-propenyl)-phenol), widely spread in various plants, notably clove, basil and bay, is a well-known antifungal and antibiotic molecule that is abundant in the hybrid grapevine cultivar Baco blanc (Vitis vinifera × Vitis riparia × Vitis labrusca). This variety, created by François Baco (19th century), is confirmed in this study as highly resistant to Botrytis cinerea by comparing fruit rot incidence and severity with two Vitis vinifera cultivars: Folle Blanche and Ugni Blanc. According to two major antibiosis modes of action, i.e., direct or volatile, this study demonstrated the efficiency of eugenol in vitro by also investigating precisely the effect on B. cinerea of small concentrations of eugenol, 3 to 4 ppm, corresponding to IC10. Moreover, the vapour-inhibiting effect was shown to be highly powerful. The total eugenol concentration peaked at the veraison stage, exceeding 1000 μg×kg-1 in the skin of Baco blanc berry under our conditions. At this point, leaf removal in the bunch zone induced a significant increase in eugenol (32 %), from 1118 to 1478 μg×kg-1, which was also associated with a significant decrease in B. cinerea infection in the vineyard. Thus, for the first time, eugenol, as an endogenous molecule of Baco blanc, was clearly demonstrated to be an inducible compound in the vineyard. Furthermore, significant intravarietal variability in eugenol concentrations according to the Baco blanc clone was demonstrated to be associated with significant differences in fruit susceptibility to the plant pathogen assessed in biotests. Interestingly, in keeping with fruit ontogenic resistance, a significant negative correlation was established between the technological maturity of berries and the total eugenol content in the berry skin. Finally, the time-progress study of the two biochemical forms of eugenol (bound vs. free eugenol) allowed us to hypothesise the effectiveness against the plant pathogen of some precursor forms of eugenol, and the corresponding biochemical structures are currently being investigated. Thus, eugenol appears to be a key biochemical marker of ontogenic resistance in the hybrid cultivar Baco blanc.

Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate

Maintaining wine production under global warming partly relies on optimizing the choice of plant material for a given viticultural region and developing drought-resistant cultivars. However, progress in these directions is hampered by the lack of understanding of differences in drought resistance among Vitis genotypes. We investigated patterns of xylem embolism vulnerability within and among 30 Vitis species and sub-species (varieties) from different locations and climates, and assessed the risk of drought vulnerability in 329 viticultural regions worldwide. Within a variety, vulnerability to embolism decreased during summer. Among varieties, we have found wide variations in drought resistance of the vascular system in grapevines. This is particularly the case within Vitis vinifera, with varieties distributed across four clusters of embolism vulnerability. Ugni blanc and Chardonnay featured among the most vulnerable, while Pinot noir, Merlot and Cabernet Sauvignon ranked among the most resistant. Regions possibly at greater risk of being vulnerable to drought, such as Poitou–Charentes, France and Marlborough, New Zealand, do not necessarily have arid climates, but rather bear a significant proportion of vulnerable varieties. We demonstrate that grapevine varieties may not respond equally to warmer and drier conditions, and highlight that hydraulic traits are key to improve viticulture suitability under climate change.

The aromatic profile of wine distillates from Ugni blanc grape musts is influenced by the nitrogen nutrition (organic vs. inorganic) of Saccharomyces cerevisiae

Although the impact of nitrogen nutrition on the production of fermentative aromas in oenological fermentation is well known today, one may wonder whether the effects studied are the same when winemaking takes place at high turbidities, specifically for the production of wines intended for cognac distillation. To that effect, a fermentation robot was used to analyze 30 different fermentation conditions at two turbidity levels with several factors tested: (i) initial addition of nitrogen either organic (with a mixture of amino acids - MixAA) or inorganic with di-ammonium phosphate (DAP) at different concentrations, (ii) variation of the ratio of inorganic/organic nitrogen (MixAA and DAP) and (iii) addition of different single amino acids (alanine, arginine, aspartic acid and glutamic acid). A metabolomic analysis was carried out on all resulting wines to have a global vision of the impact of nitrogen on more than sixty aromatic molecules of various families. Then, at the end of the alcoholic fermentation, the wines were micro-distilled. A first interesting observation was that the aroma profiles of both wines and distillates were close, indicating that the concentration factor is rather similar for the different aromas studied. Secondly, the fermentation kinetics and aroma results have shown that the nitrogen concentration effect prevailed over the nature of nitrogen. Although the lipid concentration was in excess, an interaction between the assimilable nitrogen and lipid contents was still observed in wines or in micro-distillates. Alanine is involved in the synthesis of acetaldehyde, isobutanol, isoamyl alcohol and isoamyl acetate. Finally, it was demonstrated that modifying the ratio of assimilable nitrogen in musts is not an interesting technological response to improve the aromatic profile of wines and brandies. Indeed, unbalance the physiological ratio of the must by adding a single source of assimilable nitrogen (organic or inorganic) has been shown to deregulate the synthesis of most of the fermentation aromas produced by the yeast. Wine metabolomic analysis confirmed the results that had been observed in micro-distillates but also in the other aromatic families, especially on terpenes. The contribution of solid particles, but also yeast biosynthesis (via sterol management in must) to wine terpenes is discussed. Indeed, the synthesis of terpenes in this oenological context seems to be favored, especially since the concentration of assimilable nitrogen (in addition to the lipid content) favor their accumulation in the medium. A non-negligible vintage effect on the terpene profile was also demonstrated with variations in their distribution depending on the years.Thus, the present study focuses on the metabolism of wine yeasts under different environmental conditions (nitrogen and lipid content) and on the impact of distillation on the fate of flavor compounds. The results highlight once again the complexity of metabolic fluxes and of the impact of nitrogen source (nature and amount) and of lipids. Furthermore, this study demonstrates that beyond the varietal origin of terpenes, the part resulting from the de novo synthesis by the yeast during the fermentation cannot be neglected in the context of cognac winemaking with high levels of turbidity.

Variety-specific response of bulk stomatal conductance of grapevine canopies to changes in net radiation, atmospheric demand, and drought stress.

In wine growing regions around the world, climate change has the potential to affect vine transpiration and overall vineyard water use due to related changes in daily atmospheric conditions and soil water deficits. Grapevines control their transpiration in response to such changes by regulating conductance of water through the soil-plant-atmosphere continuum. The response of bulk stomatal conductance, the vine canopy equivalent of stomatal conductance, to such changes were studied on Cabernet-Sauvignon, Merlot, Tempranillo, Ugni blanc, and Semillon vines in a non-irrigated vineyard in Bordeaux France. Whole-vine sap flow, temperature and humidity in the vine canopy, and net radiation absorbed by the vine canopy were measured on 15-minute intervals from early July through mid-September 2020, together with periodic measurements of leaf area, canopy porosity, and predawn leaf water potential. From these data, bulk stomatal conductance was calculated on 15-minute intervals, and multiple linear regression analysis was performed to identify key variables and their relative effect on conductance. For the regression analysis, attention was focused on addressing non-linearity and collinearity in the explanatory variables and developing a model that was readily interpretable.Variability of vapour pressure deficit in the vine canopy over the day and predawn water potential over the season explained much of the variability in bulk stomatal conductance overall, with relative differences between varieties appearing to be driven in large part by differences in conductance response to predawn water potential between the varieties. Transpiration simulations based on the regression equations found similar differences between varieties in terms of daily and seasonal transpiration. These simulations also compared well with those from an accepted vineyard water balance model, although there appeared to be differences between the two approaches in the rate at which conductance, and hence transpiration is reduced as a function of decreasing soil water content (i.e., increasing water deficit stress). By better characterizing the response of bulk stomatal conductance, the dynamics of vine transpiration can be better parameterized in vineyard water use modeling of current and future climate scenarios.

First Report of Grapevine Virus L Infecting Grapevine in Southeast France.

Grapevine virus L (GVL) is a recently described vitivirus (family Betaflexiviridae) with a positive-sense single-stranded RNA genome. It has so far been reported from China, Croatia, New-Zealand, the United States and Tunisia (Debat et al. 2019; Diaz-Lara et al. 2019; Alabi et al. 2020; Ben Amar et al. 2020). It has significant genetic variability (up to 26% of nucleotide divergence between isolates) and the existence of four phylogroups has been proposed (Alabi et al. 2020). In the frame of a project investigating the possible links between grapevine trunk diseases and grapevine virome, viral high throughput sequencing (HTS)-based testing was performed on symptomatic and asymptomatic grapevines collected in July 2019 in vineyards of four areas in France (Bourgogne, Charentes, Gard, Gironde) corresponding to five cultivars of Vitis vinifera (Cabernet franc, Cabernet Sauvignon, Chardonnay, Sauvignon, Ugni blanc). Total RNAs were purified from powder of 105 trunk wood samples using the Spectrum™ Plant Total RNA Kit (Sigma-Aldrich, Saint-Quentin-Fallavier, France) and RNA-seq libraries were prepared using Zymo-Seq RiboFree Total RNA Library Prep Kit (Ozyme, Saint Cyr l'Ecole, France). HTS was performed on a S4 lane of Illumina NovaSeq 6000 using a paired-end read length of 2x150 bp. The trimmed sequence reads obtained from Chardonnay plants CH30-75M (99.9 M) and CH37-19S (114 M) from a vineyard in Gard were analyzed using CLC Genomics Workbench v21 (Qiagen, Courtaboeuf, France) and revealed complex mixed infections. Besides contigs representing a complete GVL genome (average scaffold coverage: 6,197x and 2,970x, respectively), contigs from grapevine rupestris stem pitting virus (1,697x ; 1,124x), grapevine virus A (82x ; 95x), grapevine pinot gris virus (1,475x ; 866x), grapevine leafroll-associated virus 3 (5,122x ; 1,042x), hop stunt viroid (13,783x ; 29,514x) and grapevine yellow speckle viroid 1 (690x ; 1158x) were also identified. Plant CH37-19S was also co-infected by grapevine rupestris vein feathering virus (164x). The GVL contigs integrated respectively 320,000 and 152,000 reads (corresponding to 0.32% and 0.11% of filtered/trimmed reads, respectively). The GVL genomic sequences from each sample (7,616 nt) have been deposited in GenBank (Accession nos. OK042110 and OK042111, respectively). The two contigs are nearly identical (99.9% nt identity) and share respectively 97.5% and 95.9% with GVL-KA from the USA (MH643739) and GVL-RS from China (MH248020), the closest isolates present in GenBank. To confirm the presence of GVL, the original grapevines were resampled in the field and total RNAs were extracted as described above from cambial scrappings and leaves. Total RNAs were used for RT-PCR tests using primers targeting a 279-bp fragment corresponding to the 3' end of the coat protein gene and part of the nucleic acid binding protein gene (Debat et al. 2019). The Sanger-derived sequences from the amplicons shared 100% nt identities with the corresponding sequences of the HTS assembled genomes, confirming the presence of GVL in both tissues of both grapevine samples. To our knowledge, this represents the first report of the occurrence of GVL in vineyards in France. Given the complex mixed infection present in the two analyzed grapevines, no conclusions can be drawn on the pathogenicity of GVL. Further efforts are needed to better understand GVL distribution and its potential pathogenicity to grapevine. References Alabi, O J., et al. 2020. Arch. of Virol. 165:1905-1909. Ben Amar, A., et al. 2020. Plant disease 104:3274. Debat, H., et al. 2019. Eur J Plant Pathol. 155:319. Diaz-Lara, A., et al. 2019. Arch. of Virol. 164:2573. Acknowledgments The authors are grateful to the "Plan National Dépérissement du Vignoble" (Mycovir project) for the financial support.

Ethanol sprays to release grapevine bud dormancy: a potential alternative to cyanamides

Aim: Grape growers sometimes use cyanamides (calcium or hydrogen) to release bud dormancy in warm climate regions, where the chilling requirement has not been met during winter. However, these products can cause damage to plants and are dangerous to handle, so alternatives would be welcomed by growers. Connections between metabolisms of ethanol, ethylene and cyanide revealed by previous studies led us to test the potential of ethanol sprays on bud break and early shoot growth.Methods and results: Trials were performed over three years on Vitis vinifera grapevines trained in Guyot or cordon, and on cuttings in growth chambers. Cultivars used in the studies included Cabernet-Sauvignon, Syrah and Ugni blanc. The results show that ethanol can advance bud break of all three cultivars at concentrations ranging from 2.5 to 10 % ethanol in water. Ethanol stimulates bud development in both Guyot and cordon training systems. However, the timing of ethanol application is crucial, and late spring season applications reduce the effectiveness of the treatment.Conclusions: Observations were performed over three different seasons. The trials revealed that ethanol sprays can advance bud break of different Vitis vinifera vines, trained with cane or spur systems.Significance and impact of the study: Climate change impacts dormancy release, making it an increasingly important issue over the next few decades. An alternative to the dangerous use of cyanamides to promote bud break would greatly help growers. These preliminary results with ethanol are promising but should lead to trials in various growing areas and with various cultivars in order to confirm their potential for viticulture.

English

The objective of this study was to optimize a protocol for in vitro micropropagation of selected grape vine varieties. Preliminary studies were conducted to optimize the duration of sterilization of the explants. For shoot initiation experiment nodes of the three varieties of grape vines were cultured on MS medium (Murashige-Skoog’s, 1962) supplemented with five different concentrations of 6-Benzylaminopurine (BAP) and the control. Various experiments were carried out to optimize shoot multiplication using MS medium supplemented with different concentrations of BAP alone or in combination with Indole-3-butyric acid (IBA). To optimize root induction, different concentrations of Indole-3-acetic acid (IAA) were used. Sterilization of explants using 1% of NaOCl for 7 min duration was optimum. Chenin blanc showed high percentage of survival rate (96%) followed by Ugni blanc and Canonannon (88%) at 0.5 mg/L BAP. Among the different concentrations and combination of Plant Growth Regulators (PGRs) used for multiplication, maximum mean number of shoots 7.2, 6.7, and 6.1 was achieved at 1 mg/L BAP combined with 0.1 mg/L IBA for Chenin blanc, Canonnanon and Ugni blanc, respectively. All varieties induced root for all the treatments used including the control but good roots were found on MS medium supplemented with 2 and 4 mg/L of IAA. The plantlets were acclimatized in the glasshouse and survival percentage was 92% for Chenin blanc followed by 78.6 and 73.9% for Ugni blanc and Canonannon, respectively. Thus, the achievements of this study will play a big role in the grape vine culture program. Key words: Vitis vinifera L., acclimatization, explant, cytokinin, auxin.

Tartaric acid pathways in Vitis vinifera L. (cv. Ugni blanc): a comparative study of two vintages with contrasted climatic conditions.

BackgroundThe acid component of grape berries, originating in the metabolism of malate and tartrate, the latter being less well-known than the former, is a key factor at play in the microbiological stability of wines destined for distillation. Grape acidity is increasingly affected by climate changes. The ability to compare two vintages with contrasted climatic conditions may contribute to a global understanding of the regulation of acid metabolism and the future consequences for berry composition.ResultsThe results of the analyses (molecular, protein, enzymatic) of tartrate biosynthesis pathways were compared with the developmental accumulation of tartrate in Ugni blanc grape berries, from floral bud to maturity. The existence of two distinct steps during this pathway was confirmed: one prior to ascorbate, with phases of VvGME, VvVTC2, VvVTC4, VvL-GalDH, VvGLDH gene expression and abundant protein, different for each vintage; the other downstream of ascorbate, leading to the synthesis of tartrate with maximum VvL-IdnDH genetic and protein expression towards the beginning of the growth process, and in correlation with enzyme activity regardless of the vintage.ConclusionsOverall results suggest that the two steps of this pathway do not appear to be regulated in the same way and could both be activated very early on during berry development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0833-1) contains supplementary material, which is available to authorized users.

Bleeding Sap and Old Wood Are the Two Main Sources of Contamination of Merging Organs of Vine Plants byXylophilus ampelinus, the Causal Agent of Bacterial Necrosis

The spatial distribution of vine plants contaminated by Xylophilus ampelinus, the agent responsible for bacterial necrosis, was studied over a 5-year period within two vineyards in the Cognac area. Both vineyards were planted with Vitis vinifera cv. Ugni blanc but were different in age and agronomic location. The emission of X. ampelinus in contaminated bleeding sap was observed during vine sprouting. Contaminated bleeding sap is an important source of inoculum for external contamination due to the high susceptibility of young merging shoots to the pathogen. X. ampelinus emission by bleeding sap was not affected by the age of the plants or the location of the vineyards. However, its emission was irregular with time, and it varied between two fruit canes from individual plants and between plants as well as between years. Moreover, the two vineyards appeared to be entirely contaminated. Consequently, the behavior of the pathogen is not predictable. The distribution of the pathogen inside vine plant organs was analyzed through the four growing seasons. The old wood was contaminated throughout the year and constituted a stock inoculum for endophytic contamination of crude sap during the winter and the spring. Despite the fact that most of the young green shoots were contaminated in May, X.ampelinus was not found in green shoots in June and September, refuting the hypothesis of an epiphytic life of the pathogen under natural conditions. Although all plants were entirely contaminated in both vineyards, symptoms were rare and were observed on different plants each year.

Colonization of Vitis vinifera by a green fluorescence protein-labeled, gfp-marked strain of Xylophilus ampelinus, the causal agent of bacterial necrosis of grapevine.

The dynamics of Xylophilus ampelinus were studied in Vitis vinifera cv. Ugni blanc using gfp-marked bacterial strains to evaluate the relative importance of epiphytic and endophytic phases of plant colonization in disease development. Currently, bacterial necrosis of grapevine is of economic importance in vineyards in three regions in France: the Cognac, Armagnac, and Die areas. This disease is responsible for progressive destruction of vine shoots, leading to their death. We constructed gfp-marked strains of the CFBP2098 strain of X. ampelinus for histological studies. We studied the colonization of young plants of V. vinifera cv. Ugni blanc by X. ampelinus after three types of artificial contamination in a growth chamber and in a greenhouse. (i) After wounding of the stem and inoculation, the bacteria progressed down to the crown through the xylem vessels, where they organized into biofilms. (ii) When the bacteria were forced into woody cuttings, they rarely colonized the emerging plantlets. Xylem vessels could play a key role in the multiplication and conservation of the bacteria, rather than being a route for plant colonization. (iii) When bacterial suspensions were sprayed onto the plants, bacteria progressed in two directions: both in emerging organs and down to the crown, thus displaying the importance of epiphytic colonization in disease development.

Involvement of pectin methyl-esterase during the ripening of grape berries: partial cDNA isolation, transcript expression and changes in the degree of methyl-esterification of cell wall pectins

Grape berries ( Vitis vinifera L., cv Ugni blanc) were harvested at 12 different weeks of development in 1996 and 1997. Ripening was induced at veraison, the crucial stage of berry softening, and was followed by a rapid accumulation of glucose and fructose and an increase of pH. Total RNAs, crude proteins and cell wall material were isolated from each developmental stage. A partial length cDNA ( pme1, accession number AF159122, GenBank TM) encoding a pectin methyl-esterase (PME, EC 3.1.1.11) was cloned by RT–PCR with degenerate primers. Northern blots revealed that mRNAs coding for PME accumulate from one week before the onset of ripening until complete maturity, indicating that this transcript represents an early marker of veraison and could be involved in berry softening. However, PME activity was detected during all developmental stages. Total activity per berry increased, whereas “specific” activity, on a fresh weight basis, decreased during development. The amount of cell wall material (per berry and per g of berry) followed the same pattern as that of PME activity (total and “specific” respectively), indicating they were tightly correlated and that PME levels varied very little in the cell walls. Nevertheless, the degree of methyl-esterification of insoluble pectins decreased throughout the development from 68% in green stages to less than 20% for the ripe berries, and this observation is consistent with the induction of PME mRNAs during ripening. Relations between transcript expression, PME activity, the DE of insoluble pectic polysaccharides and their involvement in grape berry ripening are discussed.

Analysis of brandy aroma by solid-phase microextraction and liquid-liquid extraction

Headspace solid-phase microextraction (SPME) and continuous liquid–liquid extraction (LLX) with Freon were used to extract and analyse aroma volatiles in brandy. In general, SPME using a non-polar polydimethylsiloxane coating was more selective for esters and acids than was LLX. LLX using Freon 11 extracted the higher alcohols more efficiently than SPME. Relative differences in volatiles between brandies made from Vitis vinifera L cv Colombard and Vitis vinifera L cv Ugni blanc were observed, particularly for hexanol, 3-methylbutylacetate, 3-methylbutanol and 3-methylbutyloctanoate. In addition, a combination of SPME with GC–olfactometry was used to provide more detailed information on sensory characteristics of varietal brandies. © 2000 Society of Chemical Industry

Analysis of cell wall neutral sugar composition, β-galactosidase activity and a related cDNA clone throughout the development of Vitis vinifera grape berries

Fruit softening during ripening is accompanied by changes in cell wall composition due to the action of cell wall modifying enzymes. Moreover, the cell walls of grape berries form a barrier to the diffusion of aromatic and polyphenolic compounds which are important for wine quality. Samples of grape berries ( Vitis vinifera L., cv Ugni blanc) were harvested in 1996 and 1997 at twelve different developmental stages. The development of berries was characterized by physical, chemical and biochemical analysis. Isolated cell walls were analysed for their neutral sugar contents. The main changes during grape berry development were a large decrease in galactose parallel with glucose accumulation, while other neutral sugars (arabinose, rhamnose, xylose, fucose and mannose) showed no significant variations. For individual berries, galactose loss seemed to be softening-related, while galactose removal per mg of cell wall material was involved in a more general ripening process. β-Galactosidase (EC 3.2.1.23) activity was temporally associated with the loss of cell wall-linked galactosyl residues. A 545-base long partial cDNA ( ϐ-gal10, accession No. AF159124, GenBank) was isolated from first strand cDNA, and shared significant similarities with several β-gals in data banks. The pattern of transcript expression showed that β-gal10 was only detectable in the early stages of development, suggesting that β-gal10 may encode for a β-galactosidase active on cell walls during the early development of grape berries. Relationships between galactose content of the cell wall, β-galactosidase activity and expression of the corresponding transcripts, and their possible involvement in grape berry softening and ripening are discussed.

Soluble Polysaccharide Content at Initial Time of Experimental Must Preparation

The diversity of procedures used for the analysis of polysaccharides in musts obtained at laboratory scale did not allow their accurate quantification and characterization. Soluble polysaccharides have been isolated from musts at the initial time of preparation of Sauvignon blanc and Ugni blanc cultivars and the influence of the mode of preparation has been investigated. Heat treatment, commonly used for the inactivation of endogenous glycosylhydrolases, led to an overestimation of polysaccharide contents. Consequently, the characterization of must polysaccharides requires their isolation from crushed and pressed grapes, a procedure representative of the typical process used for white winemaking. Glycosyl residue, determined by GC of their per-<i>O</i>trimethylsilylated methyl glycosides, and glycosyl linkage, determined by GC of their partially methylated and carboxyl-reduced alditol acetates, composition analyses showed that polysaccharides were a complex mixture of pectic (galacturonans, type I and II arabinogalactans, arabinans), cellulosic and hemicellulosic (xyloglucans and mannans) polysaccharides. Type II arabinogalactan proteins, which are soluble proteoglycans, are the most abundant polysaccharides, whereas the others, that are structural components of cell walls, are present in lower amounts. The significant difference concerning the polysaccharide composition of musts and wines is discussed. Furthermore total polysaccharides were separated in calcium- and ethanol-precipitated polysaccharides. Their respective glycosyl-composition analyses, determined by GC of their per-<i>O</i>-trimethylsilylated methyl glycosides, revealed that neutral "gums" and acidic "pectins" could not be separated by specific precipitation.

Concentration and compositional changes of procyanidins in grape seeds and skin of whiteVitis vin�fera varieties

Grapes from Semillon and Ugni blanc varieties have been sampled over the periods just before coloration (stage I), veraison (stage II) and harvest (stage III), during the seasons 1991–92 and 1992–93. The content of total extractable proanthocyanidins, catechins ((+)-catechin, (−)-epicatechin and (−)-epicatechin gallate), procyanidin dimers B1 to B8 and trimer C1 in skin and grape seeds were further determined. The quantitative determination was performed through Fractogel TSK chromatography followed by HPLC analysis. The highest concentration of procyanidins is present in the grapes in the early stages of development. (+)-Catechin was the major constituent of flavan-3-ols in skin and grape seeds. Procyanidin dimers B1, B4 and B6 represent the majority of dimers in the early stage of grape seeds development, while in the last stage of maturation dimers B2 and B4 were predominant. Curiously, the decrease in the procyanidins concentration goes along with a corresponding increase of dimer B2 synthesis during grape ripening. Dimer B1 was always the major dimer in skin. The differences between the two seasons were more significant than those between the Ugniblanc and Semillon varieties. However, Semillon contains a higher concentration of total proanthocyanidins. © 1999 Society of Chemical Industry

Trocas gasosas em videira sob regime de estresse hídrico. II. fotorrespiração e comportamento varietal

Analisou-se a fotorrespiração em folhas de videira (Vitis vinifera L.) submetidas a um regime de estresse hídrico, com o objetivo de caracterizar o comportamento de diferentes cultivares. Foram utilizadas plantas de dois anos, enxertadas sobre o porta-enxerto Fercal, plantadas em vasos plásticos e cultivadas em ambiente controlado. A fotorrespiração foi calculada a partir de medidas das trocas gasosas foliares. Os valores absolutos da fotorrespiração variaram pouco entre cultivares e nível de irrigação; já a eficiência da carboxilação e o ponto de compensação ao CO2 foram bastante afetados pelo estresse hídrico, o que revela diferentes níveis de sensibilidade varietal. Foi verificada a ocorrência de inibição não-estomática da fotossíntese, afetando diferencialmente as cultivares analisadas. Destacou-se, ainda, a maior adaptação da Chardonnay às condições de estresse hídrico, em oposição à grande sensibilidade da Sémillon e da Ugni blanc.

Attemps to improve the grape seed germination

&lt;p style="text-align: justify;"&gt;Using the« standard» germination method (dehydration, hydration before conserving at 5°C during several weeks or several months and rehydration followed by the germination at 27°C/28°C), it is possible to conserve grape seeds of &lt;em&gt;Vitis vinifera&lt;/em&gt; c.v. Ugni blanc more than one year and preserve a high ability of germination. However, to be able to work on young seedlings rapidly after harvesting, this method requiring a too long breaking dormancy treatment (conserving at 5°C), we tried to change these treatments and to speed up the breaking dormancy using an anoxic treatment finalized at the laboratory. Even if this system does not allow to obtain the best rate of germination, it aIlows to save 50 days for Ugni blanc treatment and more than 150 days for Merlot avoiding breaking dormancy with cold treatment. To improve the grape seed ability of germination following the « standard» method, we used a solution of etephon in external supply, releasing ethylene in tissues. Seeds conserved 90 days at 5°C and hydrated with this solution have a better rate of germination (+ 10 p. cent in comparison with a standard sample treated with the same method without ethylene). Finally, non conserved at 5°C grape seed lyophilization can be a rapid method for breaking dormancy and improving (at least 40 p. cent) the ability of germination.&lt;/p&gt;