Phytoalexins in defense against pathogens

Role of organic amendments on enhanced bioremediation of heavy metal(loid) contaminated soils

Plant in vitro cultures represent an attractive and cost-effective alternative to classical approaches to plant secondary metabolite (PSM) production (the "Plant Cell Factory" concept). Among other advantages, they constitute the only sustainable and eco-friendly system to obtain complex chemical structures biosynthesized by rare or endangered plant species that resist domestication. For successful results, the biotechnological production of PSM requires an optimized system, for which elicitation has proved one of the most effective strategies. In plant cell cultures, an elicitor can be defined as a compound introduced in small concentrations to a living system to promote the biosynthesis of the target metabolite. Traditionally, elicitors have been classified in two types, abiotic or biotic, according to their chemical nature and exogenous or endogenous origin, and notably include yeast extract, methyl jasmonate, salicylic acid, vanadyl sulphate and chitosan. In this review, we summarize the enhancing effects of elicitors on the production of high-added value plant compounds such as taxanes, ginsenosides, aryltetralin lignans and other types of polyphenols, focusing particularly on the use of a new generation of elicitors such as coronatine and cyclodextrins.

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Elicitation, an Effective Strategy for the Biotechnological Production of Bioactive High-Added Value Compounds in Plant Cell Factories.

Polyphenol oxidase, a copper-containing metalloprotein, catalyzes the oxidation of phenolic compounds to quinones, which produce brown pigments in wounded tissues. This enzymatic mechanism causes post harvest losses and mainly affects tropical fruits. In this article, some characteristics of polyphenol oxidase from different plants are reviewed and information about conventional and alternative methods to inactivate this enzyme is presented. Characterization of the polyphenol oxidase could help to develop or to choose more effective methods for controlling browning of vegetables and products.

Polyphenol Oxidase: Characteristics and Mechanisms of Browning Control

Tomato (Solanum lycopersicum) is a model plant for studying fleshy fruit development. Several genetic and molecular approaches have been developed to increase our knowledge about the physiological basis of fruit growth, but very few data are yet available at the proteomic level. The main stages of fruit development were first determined through the dynamics of fruit diameter and pericarp cell number. Then, total proteins were extracted from pericarp tissue at six relevant developmental stages and separated by two-dimensional gel electrophoresis. Protein patterns were markedly different between stages. Proteins showing major variations were monitored. We identified 90 of 1,791 well-resolved spots either by matrix-assisted laser-desorption ionization time-of-flight peptide mass fingerprinting or liquid chromatography-mass spectrometry sequencing and expressed sequence tag database searching. Clustered correlation analysis results pointed out groups of proteins with similar expression profiles during fruit development. In young fruit, spots linked to amino acid metabolism or protein synthesis were mainly expressed during the cell division stage and down-regulated later. Some spots linked to cell division processes could be identified. During the cell expansion phase, spots linked to photosynthesis and proteins linked to cell wall formation transiently increased. In contrast, the major part of the spots related to C compounds and carbohydrate metabolism or oxidative processes were up-regulated during fruit development, showing an increase in spot intensity during development and maximal abundance in mature fruit. This was also the case for spots linked to stress responses and fruit senescence. We discuss protein variations, taking into account their potential role during fruit growth and comparing our results with already known variations at mRNA and metabolite-profiling levels.

Major Proteome Variations Associated with Cherry Tomato Pericarp Development and Ripening

In grapevine (Vitis vinifera L.), defense responses after microbial infection or treatment with elicitors involve accumulation of phytoalexins, oxidative burst, and the synthesis of pathogenesis-related proteins. Oligosaccharide fractions from fungal or algal cell walls efficiently induce the defense responses, but a detailed analysis of the elicitor−plant cell surface interaction at the molecular level is precluded by the lack of chemically pure oligosaccharide elicitors. A grapevine liquid cell culture system was used to examine the properties of cyclodextrins (CDs) as inducers of defense responses. This work shows that the chemically pure heptakis(2,6-di-O-methyl)-βCD caused a dramatic extracellular accumulation of the phytoalexin resveratrol and changes in peroxidase activity and isoenzymatic pattern. Other modified CDs tested on several grapevine cell lines resulted in different eliciting capacities of CDs and different sensibilities of the cell lines. The spent medium of elicited cultures was shown ...

Modified cyclodextrins are chemically defined glucan inducers of defense responses in grapevine cell cultures

Effect of composted sewage sludge application to soil on sweet pepper crop (Capsicum annuum var. annuum) grown under two exploitation regimes.

Evaluation of composted sewage sludge as nutritional source for horticultural soils.

Tobacco mosaic virus (TMV) is a widespread plant virus from the genus Tobamovirus that affects tobacco and tomato plants causing a pathology characterised by cell breakage and disorganisation in plant leaves and fruits. In this study we undertook a proteomic approach to investigate the molecular and biochemical mechanisms potentially involved in tomato fruit defence against the viral infection. The comparison of 2-D gels from control and TMV-infected but asymptomatic tomato fruits revealed changes in several proteins. The differential expression of peptidases, endoglucanase, chitinase and proteins participating in the ascorbate-glutathione cycle in infected fruits suggests that pathogenesis-related proteins and antioxidant enzymes may play a role in the protection against TMV infection. TMV coat protein appeared as a prominent spot in 2-D gels from TMV-infected asymptomatic fruits. A Triton X-114 phase-partitioning step of tomato protein extracts favoured the solubilisation of TMV coat protein and the enrichment of two aminopeptidases not present in control fruits. PMF and MS/MS data of the 2-D gel-isolated TMV coat protein is proposed as a powerful analysis method for the simultaneous tobamovirus detection, species determination and strain differentiation in virus-infected fruit commodities.

Proteomic analysis of tobacco mosaic virus-infected tomato (Lycopersicon esculentum M.) fruits and detection of viral coat protein.

Blossom-end rot (BER) is a physiopathy that affects tomato fruits causing disorganisation, cell breakage and darkening of the tissues. In this study we describe a tomato fruit protein extraction protocol that includes polyvinyl polypyrrolidone, ascorbic acid and protease inhibitors to promote depletion of phenolics and to avoid protein degradation. The temperature-induced phase separation of plant extracts with nonionic detergent Triton X-114 favours the solubilisation of partially-hydrophobic species in the low-detergent upper phase, making them suitable for further analysis using two-dimensional gel electrophoresis. The analysis of two-dimensional images revealed differences in number and expression levels of several proteins from the control and BER-affected tomato fruits. Although the appearance of BER in tomato is primarily attributed to a lack of calcium supply to fruits, very little is known about the molecular and biochemical mechanisms involved. The identification of differential proteins from affected fruits with matrix-assisted laser desorption/ionisation-time of flight and peptide mass fingerprinting analysis revealed the induction of proteins participating in antioxidant processes (ascorbate-glutathione cycle) and the pentose phosphate pathway. We suggest that these two biochemical pathways, acting as reactive oxygen species scavengers in BER-affected fruits, restrain the spread of the blackening to the whole fruit.

Susana Sellés

Papers

Modified cyclodextrins are chemically defined glucan inducers of defense responses in grapevine cell cultures

Effect of composted sewage sludge application to soil on sweet pepper crop (Capsicum annuum var. annuum) grown under two exploitation regimes.

Evaluation of composted sewage sludge as nutritional source for horticultural soils.

Proteomic analysis of tobacco mosaic virus-infected tomato (Lycopersicon esculentum M.) fruits and detection of viral coat protein.

Proteomic approach to blossom-end rot in tomato fruits (Lycopersicon esculentum M.): antioxidant enzymes and the pentose phosphate pathway.