To cope with environmental fluctuations and to prevent invasion by pathogens, plant metabolism must be flexible and dynamic. Active oxygen species, whose formation is accelerated under stress conditions, must be rapidly processed if oxidative damage is to be averted. The lifetime of active oxygen species within the cellular environment is determined by the antioxidative system, which provides crucial protection against oxidative damage. The antioxidative system comprises numerous enzymes and compounds of low molecular weight. While research into the former has benefited greatly from advances in molecular technology, the pathways by which the latter are synthesized have received comparatively little attention. The present review emphasizes the roles of ascorbate and glutathione in plant metabolism and stress tolerance. We provide a detailed account of current knowledge of the biosynthesis, compartmentation, and transport of these two important antioxidants, with emphasis on the unique insights and advances gained by molecular exploration.

ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation o...

Chemistry and uses of pectin--a review.

Antioxidant Potential of Ferulic Acid

Using enzymes as decontaminating agents has received great attention. One of the most promising groups of enzymes, laccases, are used to decontaminate phenol-polluted systems and for bio technological applications. Higher plants and fungi, mostly wood-rotting fungi, are the main producers of laccases, but bacterial laccases also have been found. Belonging to the class of phenoloxidases, laccases catalyze the polymerization of several phenolic substances to polymeric products. In addition, they have transformed lignin and lignin-related compounds, showing a very broad substrate specificity. Specific compounds acting as protein-synthesis inducers historically have been used to improve the production of the enzyme. Recent success in fungal molecular and cellular engineering technology has contributed to significantly increase the industrial production of recombinant laccase. Kinetic (Michaelis-Menten parameters, optimum pH, kcat) and stability properties of laccases may vary according to the source of the en...

https://www.tandfonline.com/doi/pdf/10.1080/10889869991219163

Laccases: A Useful Group of Oxidoreductive Enzymes

When plants are attacked by pathogens, they defend themselves with an arsenal of defence mechanisms, both passive and active. The active defence responses, which require de novo protein synthesis, are regulated through a complex and interconnected network of signalling pathways that mainly involve three molecules, salicylic acid (SA), jasmonic acid (JA), and ethylene (ET), and which results in the synthesis of pathogenesis-related (PR) proteins. Microbe or elicitor-induced signal transduction pathways lead to (i) the reinforcement of cell walls and lignification, (ii) the production of antimicrobial metabolites (phytoalexins), and (iii) the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Among the proteins induced during the host plant defence, class III plant peroxidases (EC 1.11.1.7; hydrogen donor: H(2)O(2) oxidoreductase, Prxs) are well known. They belong to a large multigene family, and participate in a broad range of physiological processes, such as lignin and suberin formation, cross-linking of cell wall components, and synthesis of phytoalexins, or participate in the metabolism of ROS and RNS, both switching on the hypersensitive response (HR), a form of programmed host cell death at the infection site associated with limited pathogen development. The present review focuses on these plant defence reactions in which Prxs are directly or indirectly involved, and ends with the signalling pathways, which regulate Prx gene expression during plant defence. How they are integrated within the complex network of defence responses of any host plant cell will be the cornerstone of future research.

Class III peroxidases in plant defence reactions

Peroxidases (EC 1.11.1.7) from Populus x euramericana were investigated during the dormant and growing seasons using histochemical and biochemical methods. The activities of syringaldazine oxidase and p-paraphenylenediamine-pyrocatechol oxidase in sections of branches were maximal during spring in both phloem and young xylem. Cytoplasmic and cell-wall peroxidase activities from different lignified tissues were estimated in vitro. Pronounced differences were noticed between fractions isolated during spring and winter. Gel electrophoresis showed the presence of an anionic fast-migrating isoperoxidase group with a high syringaldazine-oxidase activity. The isoenzymes of this group were different in winter and in spring. The properties of these isoperoxidases (kinetic constants, pH optimum, resistance to heat) were investigated after isolation by ion-exchange chromatography.

Isolation and characterization of Populus isoperoxidases involved in the last step of lignin formation.

Some Properties of Syringaldazine Oxidase, a Peroxidase Specifically Involved in the Lignification Processes

Tetramethylbenzidine and p-phenylenediamine-pyrocatechol for peroxidase histochemistry and biochemistry: Two new, non-carcinogenic chromogens for investigating lignification process

Cytochemical Localization of Hydrogen Peroxide in Lignifying Cell Walls

To characterize the structural events associated with incompatibility of graft development, we conducted a histological study of compatible and incompatible pear/pear and pear/quince grafts that had been grown for five months in a greenhouse. Multivariate analysis of histological data describing the structure of the graft union allowed us to discriminate between compatible and incompatible combinations before either macroscopic examination or qualitative microscopic examination differences between graft combinations became evident. The histological variables responsible for the discrimination between incompatible and compatible unions were related to three typical symptoms of graft incompatibility: bark discontinuity, which was the main feature; cambial dysfunction; and accumulation of starch in the scion. Little cell necrosis was observed at the interface of incompatible grafts at the 5-month stage of graft development. Multivariate analysis of histological data provides a new tool for studying early structural events resulting from the graft incompatibility response and for diagnosing early graft incompatibility.

Localized graft incompatibility in pear/quince (Pyrus communis/Cydonia oblonga) combinations: multivariate analysis of histological data from 5-month-old grafts.

Anne-Marie Catesson

Papers

Isolation and characterization of Populus isoperoxidases involved in the last step of lignin formation.

Some Properties of Syringaldazine Oxidase, a Peroxidase Specifically Involved in the Lignification Processes

Tetramethylbenzidine and p-phenylenediamine-pyrocatechol for peroxidase histochemistry and biochemistry: Two new, non-carcinogenic chromogens for investigating lignification process

Cytochemical Localization of Hydrogen Peroxide in Lignifying Cell Walls

Localized graft incompatibility in pear/quince (Pyrus communis/Cydonia oblonga) combinations: multivariate analysis of histological data from 5-month-old grafts.