Ethephon elicits protection against Erysiphe necator in grapevine.

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.

Effects of exogenous glucose on carotenoid accumulation in tomato leaves.

To investigate the effect of carbohydrate on carotenoid accumulation in leaves, excised plants of tomato (Lycopersicum esculentum var. cerasiformae, wva 106) were supplied with glucose through the transpiration stream for 48 h. We report here that sugar accumulation in leaves led to a decrease of carotenoid content, which was related to the reduction of Chl. The decrease in carotenoid amount correlated with a sugar-induced repression of genes encoding enzymes of the carotenoid and of the Rohmer pathways. The lower 1-deoxy-D-xylulose-5-phosphate synthase transcript level probably leads to a decreased metabolic flux through the methylerythritol pathway and subsequently to a lower amount of substrate available for plastidic isoprenoid synthesis. Differences between responses of young (sink) and mature (source) leaves to carbohydrate accumulation are discussed.

Effect of methyl jasmonate in combination with carbohydrates on gene expression of PR proteins, stilbene and anthocyanin accumulation in grapevine cell cultures.

Grapevine (Vitis vinifera L.) is subject to a number of diseases which affect yield and wine quality. After veraison, berries become strongly susceptible to pathogens due to different physiological changes including the accumulation of glucose and fructose, on the one hand, and to the decrease of anti-microbial compounds called stilbenes, on the other. To obtain berry protection, pesticides are excessively used leading to important cost to the grower and to undesirable environmental impact of the residues, especially in grape, soil and water. As a consequence, alternative strategies have to be developed. Exogenously applied biotic elicitors induce defense responses. We studied the effects of methyl jasmonate in combination with sucrose on defense-related gene expression, stilbene and anthocyanin production in grapevine cell suspensions. The methyl jasmonate/sucrose treatment was effective in stimulating phenylalanine ammonia lyase, chalcone synthase, stilbene synthase, UDP-glucose: flavonoid-O-glucosyltransferase, proteinase inhibitor and chitinase gene expression, and triggered accumulation of both piceids and anthocyanins in cells, and trans-resveratrol and piceids in the extracellular medium. Methyl jasmonate treatment might be an efficient natural strategy to protect grapevine berries in vineyard.

Methyl jasmonate induces defense responses in grapevine and triggers protection against Erysiphe necator.

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.

Sucrose deficiency delays lycopene accumulation in tomato fruit pericarp discs.

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.

Oxidation of ferulic acid or arabinose-esterified ferulic acid by wheat germ peroxidase.

The oxidation of ferulic acid (FA) or 5-O-(trans-feruloyl)-L-arabinose (EFA) by a purified wheat germ peroxidase was followed by UV spectrophotometry and high-performance liquid chromatography using an electrochemical detection. Wheat peroxidase (POD) exhibits a ping-pong bireactant mechanism forming phenoxy radicals more rapidly from FA than from EFA in routine assay conditions. When both the free and the esterified forms of FA are present, the reverse was found. This result could be due to a nonenzymatic cooxidation of FA by the phenoxy radicals of EFA leading to the formation of phenoxy radicals of FA and the EFA regeneration. Addition of ascorbic acid (AA) provokes a delay of FA consumption. AA reduced very rapidly the phenoxy radicals formed by POD back to initial phenol avoiding the formation of ferulate dimers until it was completely oxidized in dehydroascorbic acid. Conversely, cysteine addition slowed but did not delay the FA consumption. The thiol reduced a fraction of the phenoxy radicals produced by wheat POD and was oxidized into cystine, while the other part of phenoxy radicals formed ferulate dimers. These results could be of interest to understand the POD effect on the wheat dough rheological properties.