Effects of water activity (aw) on the growth of some epiphytic micro-organisms isolated from grape berry

It is well known that wet weather often induces microbial deterioration of grape berries by Botrytis cinevea during the noble rot process, and that heavy rainfall increases the number of epiphytic micro-organisms. To better understand the influence of environmental conditions, we investigated the effects of water availabilty on the in vitro growth of 7 yeast strains, 10 strains of bacteria and one strain of the fungus Botrytis cinerea, isolated from grape berries. The results confirm that growth of Botrytis cinerea is inhibited at water activities (aw) < 0.93. Growth was highest if sucrose was added to the medium compared to other solutes (KCl, CaCl2), Most bacteria were more sensitive to water deficit than Botrytis cinerea. Bacteria were only able to grow at aw, ranging from 0.997 to 0.940. Yeasts were more resistant than bacteria. Most yeasts grow at aw between 0.96 and 0.88, The present results may contribute to control epiphytic micro-organisms in over-ripened fruit of grapevine.

Polygalacturonase isozymes produced during infection of the grape berry by Botrytis cinerea

This paper focuses on polygalacturonase activity during the early stages of infection of the grape berry by the fungus Botrytis cinerea. While a weak polygalacturonase activity was measured in healthy, ripe Semillon grape berries, in infected berries the activity increased rapidly with infection. Liquid isoelectrofocalisation was used to separate polygalacturonase isozymes in healthy and infected berries. In healthy berries, we found 4 isozymes of polygalacturonase with pI values of 4.2, 4.9, 6.0 and 8.0. In infected berries, we have separated up to 7 isozymes of polygalacturonase in infected berries. The first isozymes detected had acidic pIs; basic isozymes of polygalacturonase with considerable activity were separated. The most active isozyme had a pI of 8.8. At the onset of infection by B. cinerea, polygalacturonase activity consists of a large number of isozymes, most of which are identical with the isozymes previously described.

Calcium accumulation and redistribution during the development of grape berry

In this study, we investigated the evolution of calcium content during grape berry development (Vitis vinifera L.). In 5 years using several cultivars, the calcium content per berry was assessed in all compartments of the fruit. In the whole berry the calcium content increased from anthesis to ripeness. In the pericarp it decreased at the onset of ripening whereas it increased in seeds. Furthermore, during ripening, calcium was transported from the flesh to the skin. As calcium is a cation mobile in xylem, we compared our results with those on the functioning of xylem during the development of grape berries. We hypothesize that the calcium accumulation observed in the whole berry during ripening is due to its accumulation in the seeds.

Evolution et localisation des principaux cations au cours du développement du raisin

L'évolution des principaux cations de la baie de Cabernet Sauvignon a été étudiee de la floraison à la maturation. Les teneurs en calcium, potassium et magnesium ont été déterminées dans la pulpe et la pellicule et au niveau des parois et du contenu intracellulaire des cellules de ces deux tissus. Au cours du développement du raisin, les quantités de cations par baie augmentent; à maturite, les baies présentent 15 fois plus de potassium et deux fois plus de calcium et de magnesium par rapport aux baies vertes. En conséquence, le rapport K/Ca augmente et les proportions respectives de magnésium et de calcium restent relativement constantes. Au cours de la maturation, les cellules de la pellicule s'enrichissent en potassium et en calcium tandis que les cellules de la pulpe accumulent essentiellement du potassium. La repartition du magnésium dans les différentes parties de la baie varie peu. A maturité, les parois cellulaires de la pellicule sont riches en calcium; les cellules de la pulpe sont caracterisées par des quantités importantes de potassium intracellulaire et de faibles teneurs en calcium parietal.Evolution and localisation of the main cations during grape berry developmentThe evolution of the main cations was studied in developing grape berries (Vitis vinifera cv. Cabernet Sauvignon) from anthesis to ripeness. The calcium, potassium and magnesium contents of the skin and the fruit flesh and their distribution within cell wall and cell compartment were determined. The concentrations of these cations on per berry basis increased during the entire period of berry development. The ripe berry showed a potassium level 15 times more than green berries but calcium and magnesium increased only twofold. It resulted in an increase of the K/Ca ratio since Mg/Ca ratio remained constant during berry ontogeny. In contrast to the flesh cells which overall accumulated potassium, skin cells grew richer in potassium and calcium during ripening. There was little change in the magnesium distribution within the different parts of the berry. At maturity, a high calcium content characterised the skin cell wall; the flesh cells contained large quantities of potassium and little wall-calcium

Evolution des polyosides des parois cellulaires au cours du développement du raisin

La composition en polyosides pariétaux des baies de raisin a été étudiée de la floraison à la maturité chez deux cépages bordelais, le Cabernet-Sauvignon et la Muscadelle. Les techniques histochimiques et densitométriques utilisées ont permis de suivre l'évolution de trois zones distinctes: la zone pelliculaire la plus externe, la zone pelliculaire sous-jacente et la pulpe. Au cours du développement des baies, les teneurs de la majorité des polyosides pariétaux diminuent, particulièrement chez la Muscadelle. Ce phénomène ne concerne pas la cellulose du tissu pelliculaire dont le taux reste constant lors de la maturation. Chez les deux cépages, les parois cellulaires de la pellicule sont toujours plus riches en polyosides que celles de la pulpe. A maturité, la proportion de pectines pariétales au niveau de la pellicule est plus importante chez le Cabernet Sauvignon. Evolution of cell wall polyosides during grape berry growth and ripeningThe content of cell wall polyosides of grape berries has been studied in two Bordeaux vine cultivars, Cabernet Sauvignon and Muscadelle. Three different zones were determined by histochemical and densitometric technics: external part of the skin, skin underlying cells and flesh. Their changes in polyosides have been followed from flowering to maturity. During the growth of the berries, the level of the cell wall polyosides decreases particularly in Muscadelle variety, whereas during ripening the berry skin cellulose levels remains constant. In the two cultivars, the cell walls of the skin are always richer than the flesh ones. At maturity, there are more pectins in the cell walls of the skin of Cabernet Sauvignon berries

Evolution de la composition en polyamines des baies de raisin au cours du processus d'infection par Botrytis cinerea

Evolution of polyamine composition in grape berries during infection with Botrytis cinereaPolyamines are growth regulators occurring naturally in grapevine(Vitis vinifera L.) and pathogenic fungi, e.g. Botrytis cinerea. Investigation of polyamines of in vitro-grown Botrytis cinerea mycelium and infected berries has shown modifications in the metabolism of the berries which are directly related to the development of the fungi in the berries. The abnormal polyamine concentrations in infected berries appear to be of fungal origin for free polyamines and of plant origin for conjugated polyamines. The specific role of each type of polyamine is discussed with regard to the host-parasite relation.

Occurrence and specificity of glucose oxidase (E.C: 1.1.3.4) in botrytized sweet white wine. Comparison with laccase (E.C: 1.10.3.2), considered as the main responsible factor for oxidation in this type of wine

Two types of oxidizing enzymes are present in botrytized white grapes and wines: laccase (PPO) and glucose oxidase (GOX). The evolution of these two enzymes is similar both during the over-ripening of grapes and during wine making. Yet, PPO is severely inhibited by the addition of SO2 following the alcoholic fermentation, and shows a marked instability in both the must and wine environments. GOX, however, remains free and active in solution and helps develop the main characteristics of the wine. In particular, as is to be expected from its activity, GOX oxidizes tartaric acid, ethanol and glycerol, the major components of must and wine, respectively to glyoxylic acid, acetaldehyde and glyceraldehyde. And then, by nucleophilic additions under acidic conditions, these products react with catechins and proanthocyanidins to form several new compounds, some of which appear in a colored form. These reactions can have an impact on the visual quality of the wine.