Plant defenses, phenylpropanoids

Phenylpropanoids in Plant Defense and Plant-Pathogen Interactions Flavonoids and the Rhizobium-Legume Symbiosis... 

Korkina, L.G. (2007) Phenylpropanoids as naturally occurring antioxidants from plant defense to human health. Cell Mol Biol. 53,15-25... 

Type 1 MTs, currently exclusive for oxygen atoms (OMTs), methylate hydroxyl moieties of phenylpropanoid-based compounds (Fig. 2.3). The phenylpropanoid scaffold is used as a building block for many other types of compounds in the plant. Modification of this basic unit by multiple condensation reactions yields chalcone, flavonoid, isoflavonoid, and pterocarpan skeletons, for example. Flavonoids are ubiquitous in higher plants, where they function as UV protectants,5 defense compounds,6 and stimulators of beneficial mutualistic interactions with microorganisms, insects, and other organisms.7 Isoflavonoid natural products are limited primarily to leguminous plants, where they function as pre-... 

Matern, U. (1991) Coumarins and other phenylpropanoid compounds in the defense response of plant cells. Planta Med., 57, S15-20. 

It has been detected that the plants increase the phenylpropanoids synthesis in different situations, like, defense against herbivores protection of microorganism attack or invasion by other species. Besides, some external factors that can increase the free radicals levels, such as stress, high light (more UV incidence), low temperatures, pathogen infections, nutrient deficiency [5], drought or ozone exposition [6], can induce a higher production of PPG by the plants. 

In the phenylpropanoid pathway, the first biosynthetic step leading to SA is a deamination of phenylalanine to CA which is catalyzed by phenylalanine ammonia lyase (PAL). This enzyme is induced by a range of biotic and abiotic stress conditions and is a key regulator in the phenylpropanoid pathway, which yields a variety of phenolics among others involved in structural and defense-related functions [42]. In recent years, PAL and its corresponding genes have been subject of numerous studies in various plant species [43 7]. 

A second class of defensive phytochemicals often found in poplar and aspen at substantial levels are the proanthocyanidins, or condensed tannins (CTs) (Fig. 5.1). Unlike the phenolic glycosides that are found exclusively in the Salicaceae, CTs are widespread in the plant kingdom. These flavonoid polymers consist of mostly 4,8-linked flavan-3,4-diols and flavan-3-ols, ranging in size from 1440 to over 4500 Da depending on the species. Flavonoids are derived from the general phenylpropanoid pathway by a series of enzymes beginning with the enzyme... 

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