Roger Bessis

Biological Activity of Resveratrol, a Stilbenic Compound from Grapevines, Against Botrytis cinerea, the Causal Agent for Gray Mold

The biological activity of resveratrol, a stilbenic compound synthesized by grapevines in response to various stresses, was reevaluated against Botrytis cinerea using a novel in vitro system that enabled direct observation of the fungus with an inverted microscope. We determined that 90 μg resveratrol/ml reduced germination of B. cinerea conidia by ca. 50%. Moreover, resveratrol was shown to significantly reduce mycelial growth of B. cinerea at concentrations ranging from 60 to 140 μg/ml. Exposure to resveratrol at concentrations ranging from 60 to 140 μg/ml resulted in cytological changes in B. cinerea, such as production of secondary or tertiary germ tubes by conidia, cytoplasmic granulations, protoplasmic retractation in the hyphal tip cells, and formation of curved germ tubes. These data reinforce the role played by this compound in the B. cinerea–grapevine interaction.

Metabolism of stilbene phytoalexins by Botrytis cinerea: 1. Characterization of a resveratrol dehydrodimer

Abstract Resveratrol, a grapevine phytoalexin, is metabolized by a laccase-like stilbene-oxidase of Botrytis cinerea, the causal organism for grey mould. Characterization of one major metabolite formed during this degradation process as a resveratrol dehydrodimer allowed us to precize the reaction mechanism of this enzyme on stilbenes.

Resveratrol Oxidation in Botrytis cinerea Conidia

ABSTRACT Observations using light microscopy showed that approximately 30% of Botrytis cinerea conidia treated with semi-lethal concentrations (i.e., 60 mug/ml) of the grapevine phytoalexin resveratrol possessed intracellular brown coloration. This coloration was never observed in the absence of resveratrol or in conidia treated with resveratrol together with sulfur dioxide (antioxidant compound) or sodium diethyldithiocarbamate (inhibitor of laccase action), suggesting that discoloration resulted from the laccase-mediated oxidation of resveratrol. Further studies using transmission electron microscopy enabled the observation of particular intravacuolar spherical vesicles and of granular material deposits along the tonoplast. These observations are likely to be related to the oxidation of resveratrol by an intracellular laccase-like stilbene oxidase of B. cinerea.

Characterization of a Pterostilbene Dehydrodimer Produced by Laccase of Botrytis cinerea.

ABSTRACT In the interaction between grapevines and Botrytis cinerea, one of the main aspects of pathogenicity is fungal ability to degrade phytoalexins synthesized by the plant in response to infection. Laccase-like stilbene oxidase activity in liquid cultures of B. cinerea has been shown to be related to the decrease of phytoalexin concentrations. Recent research and results presented in this paper determined the chemical structure of a pterostilbene metabolite produced by B. cinerea. Study of degradation of pterostilbene that has just one free hydroxy phenyl group function allowed us to determine the oxidative dimerization process undergone by grapevine phytoalexins after B. cinerea infection. The phytopathological significance of this degradation process in the B. cinerea interaction has also been discussed.

Use of carbon dioxide enrichment to obtain adult morphology of grapevinein vitro

A procedure has been developed forin vitro propagation ofVitis vinifera ‘Pinot noir’ from lateral-bud cuttings under high CO2 concentration (1200 µmol mol−1). Because of inhibition of rooting by CO2, this procedure requires a rooting pre-culture of explants on medium with sucrose before the CO2-enriched culture on sucrose-free medium. Shoot growth was enhanced by CO2 enrichment as a result of both a higher rate of leaf production and greater internode elongation. Leaf expansion and tendril growth were promoted and better rooting was obtained. The more significant effect of CO2 enrichment was to promote adult morphology with, in particular, the tendril pattern. Thus, for the first time, grapevine plants have been producedin vitro without typical juvenile characteristics. CO2 enrichment appears to be an interesting process to improve thein vitro propagation of grapevines.

The production of resveratrol (3,5,4'‐trihydroxystilbene) by grapevine in vitro cultures, and its application to screening for grey mould resistance

The ability of grapevine in vitro cultures to synthesise the phytoalexin precursor resveratrol in response to ultraviolet light irradiations is investigated in order to develop methods for screening for resistance to grey mould (Botrytis cinerea Pers.) in grapevines produced as a result of somatic embryogenesis. It is demonstrated that resveratrol formation can be reproducibly induced in leaves of in vitro plantlets. Differences in the production of resveratrol among the three varieties of Vitis vinifera tested (Pinot Noir, Chardonnay and Cabernet Sauvignon) were consistent with observations regarding their field susceptibility to grey mould. The use of phytoalexin induction and of in vitro methods as a tool for selection of Vitis resistant genotypes in early screening tests is discussed.

The Significance of Stilbene-Type Phytoalexin Degradation by Culture Filtrates of Botrytis Cinerea in the Vine-Botrytis Interaction

Phytoalexins, antimicrobial compounds, synthesized by a plant in response to infection or a variety of stresses are known to be the most efficient way by which grapevines withstand an attack by Botrytis cinerea Pers., the causal organism for grey mould. In that plant, such responses include the production of a simple stilbene, resveratrol, and the biosynthetically related compounds, viniferins and pterostilbene. If stilbene-type phytoalexins represent a contributory factor in the resistance of grapevines to B.cinerea, the capacity of the pathogen to metabolize antifungal compounds released by the host could also play a significant role in the outcome of the interaction between grapevines and B.cinerea.Indeed, the net accumulation of phytoalexins within plant tissues infected by various pathogens is probably controlled by a balance which may result, on the one hand, from the ability of the host cells to resist colonization by creating an inhibitory barrier for the parasite, and, on the other hand, from tolerance of the pathogen to antifungal compounds produced by the plant and from its ability to detoxify the phytoalexins to which it is exposed. Thus, the resistance of plants to infection depends on the phytoalexin production/degradation balance following attack by the pathogen. A variety of factors can alter this balance in favour of either the parasite or the host, resulting in non-compatible or compatible interactions. Among these, the capacity of B.cinerea to detoxify the phytoalexins produced by grapevines was investigated. We present here good evidence that this fungus produces a stilbene oxidase which can degrade resveratrol and pterostilbene. No detoxication of stilbenes is detected during the germination process in vitro, suggesting that stilbene-degrading activity does not seem to be constitutive in dormant conidia of Botrytis.

Evolution of the grapevine (Vitis vinifera L.) imprinted by natural and human factorsThis review is one of a selection of papers presented at the symposium on Vitis at the XVII International Botanical Congress held in Vienna, Austria, in 2005.

This paper is concerned with vegetative reproduction, which is the only mode of propagation in cultivated grapevines. After a brief summary of the systematics of the Vitaceae the question of the nomenclature of cultivated grapevines is discussed. Intra-varietal variability is discussed using morphological and molecular characteristics. The origins of variation are presented: mutations, foreign nucleic acids, and memory of previous environmental conditions. Grapevines provide characteristic products, leading viticulturalists to make selections among the diversity observed in the vineyard, thus decreasing diversity. Grapevines interact with various environmental agents. One example, the natural defence provided by resveratrol, is analysed, showing its direct effects against parasitic fungi and its indirect effects, both metabolic and genetic, on other organisms. Thus, the grapevine, viticulturalists, and their environment form a web of biological interactions.

Fertilité des rameaux anticipés de vigne (Vitis vinifera L.) : II. — Influence de la fertilité potentielle et de la vitesse de croissance

RÉSUMÉ Certains facteurs qui influent sur l’expression de la fertilité des rameaux anticipés obtenus après écimage sont analysés. La fertilité observée dépend de la fertilité potentielle des bourgeons anticipés au moment de leur entrée en croissance et des caractères de cette croissance. La fertilité maximale est obtenue au vignoble lorsque la fertilité potentielle vient d’atteindre sa valeur maximale dans les bourgeons anticipés. Les causes d’une perte de fertilité aux écimages précoces et tardifs sont abordées.