No abstract

Grapevine is subject to a number of diseases that affect yield and wine quality. To limit the excessive use of phytochemicals in the vineyard, alternative strategies have to be developed. Plant treatment with signaling molecules like elicitors stimulates their natural defense mechanisms. To improve grapevine tolerance against fungal pathogens, Vitis vinifera plants were treated with a natural exogenous elicitor, methyl jasmonate (MeJA). MeJA-treated leaves (Cabernet Sauvignon foliar cuttings) reacted by increasing transcript levels coding pathogenesis-related proteins (acidic class IV chitinase, serine protease inhibitor, polygalacturonase-inhibiting protein, and beta-1,3-glucanase) and coding enzymes involved in phytoalexin biosynthesis (one phenylalanine ammonia lyase and one stilbene synthase). This was correlated with the accumulation of stilbenes (antimicrobial compounds). The eliciting activity of MeJA was confirmed by enhanced tolerance of grapevine foliar cuttings and vineyard against powdery mildew (75% and 73%, respectively). On the basis of these original results, MeJA can therefore act as an efficient elicitor in an alternative strategy of grapevine protection.

Tomato (Solanum lycopersicum) fruit ripening is characterized by a massive accumulation of carotenoids (mainly lycopene) as chloroplasts change to chromoplasts. To address the question of the role of sugars in controlling carotenoid accumulation, fruit pericarp discs (mature green fruits) were cultured in vitro in the presence of various sucrose concentrations. A significant difference in soluble sugar content was achieved depending on external sucrose availability. Sucrose limitation delayed and reduced lycopene and phytoene accumulation, with no significant effect on other carotenoids. Chlorophyll degradation and starch catabolism were not affected by variations of sucrose availability. The reduction of lycopene synthesis observed in sucrose-limited conditions was mediated through metabolic changes illustrated by reduced hexose accumulation levels. In addition, variations of sucrose availability modulated PSY1 gene expression. Taken together our results suggest that the modulation of carotenoid accumulation by sucrose availability occurs at the metabolic level and involves the differential regulation of genes involved in carotenoid biosynthesis.

The grapevine (Vitis vinifera) is susceptible to many pathogens such as Botrytis cinerea, Plasmopara viticola, Erysiphe necator, and Eutypa lata. Phytochemicals are used extensively in vineyards to reduce pathogen infections, but the appearance of pesticide-resistant pathogen strains and the need for environmental protection require the use of alternative strategies. The phytohormone ethylene is assumed to play a role in the development of disease resistance. In the present study, we have treated grapevine foliar cuttings (Cabernet Sauvignon) with ethylene-releasing ethephon. This resulted in an increase in the number of pathogenesis-related protein (CHIT4c, PIN, PGIP, and GLU) gene copies and in an enhancement of phytoalexin biosynthesis by inducing the PAL and STS genes that correlated with the accumulation of stilbenes (antimicrobial compounds). Moreover, ethephon treatment triggered the protection of grapevine detached leaves and grapevine foliar cuttings against Erysiphe necator, the causal agent of powdery mildew (64% and 70%, respectively). These studies emphasize the major role of ethylene in grapevine defense.