Phytoalexins interactions

Plant-Environment Interactions, edited by Robert E. Wilkinson Handbook of Plant and Crop Physiology, edited by Mohammad Pessarakli Handbook of Phytoalexin Metabolism and Action, edited by M. Daniel and R. P. Purkayastha... 

The functions of phenylpropanoid derivatives are as diverse as their structural variations. Phenylpropanoids serve as phytoalexins, UV protectants, insect repellents, flower pigments, and signal molecules for plant-microbe interactions. They also function as polymeric constituents of support and surface structures such as lignins and suberins [1]. Therefore, biosynthesis of phenylpropanoids has received much interest in relation to these functions. In addition, the biosynthesis of these compounds has been intensively studied because they are often chiral, and naturally occurring samples of these compounds are usually optically active. Elucidation of these enantioselective mechanisms may contribute to the development of novel biomimetic systems for enantioselective organic synthesis. 

Morandi, D., Occurrence of phytoalexins and phenolic compounds in endomycorrhizal interactions, and their potential role in biological control, Plant Soil, 185, 241, 1996. 

Fig. (1). Interaction between invading fungi and host plants in the elicitation of phytoalexin production...

Aguero, M. E., Gevens, A., and Nicholson, R.L., 2002, Interaction of Cochliobolus heterostrophus with phytoalexin inclusions in Sorghum bicolor. Physiol. Mol. Plant Pathol. 61 267-271. 

Dereks W, Creasy LL. 1989. Influence of fosetyl-Al on phytoalexin accumulation in the Plasmopara viticola-grapevine interaction. Physiol Mol Plant Pathol 34 203-13. 

Tal, B. and Robeson, D.J., The metabolism of sunflower phytoalexins ayapin and scopoletin. Plant-fungus interactions, Plant Physiol., 82, 167-172, 1986b. 

Figure 10.5 Plant cell cultures have proven to be very useful for studying plant-pathogen interactions and isoprenoid metabolism. Tobacco cell cultures respond rapidly to the addition of fungal elicitors (0.5 pg cellulase/ml of culture) by browning (A) (analogous to a hypersensitive response) and the production of phytoalexins (B). Media was collected from elicited cell cultures at the indicated times, partitioned against an organic solvent, and concentrated aliquots run on a silica TLC plate. The plates were then sprayed with a suspension of Cladosporium cucumerinum spores and incubated in a humid environment for 5 days before viewing (B). The compound released from the elicitor-treated tobacco cells that inhibits spore germination is capsidiol, a sesquiterpene.

GLAZEBROOK, J., AUSUBEL, F.M., Isolation of phytoalexin-deficient mutants of Arabidopsis thaliana and characterization of their interactions with bacterial pathogens, Proc. Natl. Acad. Sci., USA, 1994,91, 8955-8959. 

We can distinguish between secondary metabolites that are already present prior to an attack or wounding, so-called constitutive compounds, and others that are induced by these processes and made de novo. Inducing agents, which have been termed elicitors by phytopathologists, can be cell wall fragments of microbes, the plant itself, or many other chemical constituents (4,17,22-24). The induced compounds are called phytoalexins, which is merely a functional term, since these compounds often do not differ in structure from constitutive natural products. In another way this term is misleading, since it implies that the induced compound is only active in plant-microbe interactions, whereas in reality it often has multiple functions that include antimicrobial and antiherbivoral properties (see below). 

PAL Induction and phytoalexin accumulation Is common to a wide range of host-parasite Interactions when plants are treated with ellcitors (41). Studies with several plant cell cultures also Indicated that PAL activities are readily Increased by ellcitors (11). 

NADPH oxidase. This defense mechanism has not received much attention, but has been implicated in some host-pathogen interactions. NADPH oxidase in potato tuber tissue was shown to be activated immediately after invasion by an incompatible race of PhvtoDhthora infestans. causing simultaneous superoxide production, hypersensitive ce11 death, and phytoalexin production (70-72). This enzyme system was not activated by a compatible . infestans race... 

Phytoalexins are an Important component of the plant disease defense reaction called the hypersensitive response. Successful pathogens have evolved methods for dealing with plant phytoalexins. Including suppressors of their production, detoxification of the phytoalexins and In some cases avoiding elaboration of substances, called elicitors, that would otherwise Initiate the defense reaction. Elicitors obtained from pathogens are of considerable utility for study of various aspects of plant biology because of their interaction with the products of plant disease resistance genes. Substantial information has been obtained on how elicitors are perceived by plant cells and how they function, but much remains to be done. Finally, elicitors may prove of value for the economic production of exotic plant secondary metabolites and as specific herbicides. 

Yang, Q., Trinh, H.X., Imai, S., Ishihara, A., Zhang, L., Nakayashiki, H., Tosa, Y, Mayama, S. (2004) Analysis of the involvement of hydroxyanthranilate hydroxycin-namoyltransferase and caffeoyl-Co A 3-O-methyltransferase in phytoalexin biosynthesis in oat. Mol. Plant Microbe Interact., 17, 81-9. 

Over 20,000 terpenoids have been identihed (1), and more are being discovered continuously. Plant terpenoids are important in both primary and secondary (speciahzed) metabolism. Their importance in primary metabolism includes physiological, metabolic, and stmctural roles such as plant hormones, chloro-plast pigments, roles in electron transport systems, and roles in the posttranslational modihcation of proteins. In secondary metabolism, the roles of plant terpenoids are incredibly diverse but are associated most often with defense and communication of sessile plants interacting with other organisms. Examples include terpenoid chemicals that form physical and chemical barriers, antibiotics, phytoalexins, repellents and antifeedants against insects and other herbivores, toxins, attractants for pollinators or fruit-dispersing animals, host/nonhost selection cues for herbivores, and mediators of plant-plant and mycorrhiza interactions (2, 3). 

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