Hypersensitive response

Hypersensitive response

The hypersensitive response (HR) is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens. The HR is characterized by the rapid death of cells in the local region surrounding an infection. The HR serves to restrict the growth and spread of pathogens to other parts of the plant. The HR is analogous to the innate immune system found in animals, and commonly precedes a slower systemic (whole plant) response, which ultimately leads to systemic acquired resistance (SAR).cite book| last =Freeman| first =Scott|title =Chapter 37: Plant Defense Systems| booktitle = Biological Science.| publisher = Prentice Hall| date = 2003| url =http://wps.prenhall.com/esm_freeman_biosci_1/0,6452,500505-,00.html| id =]

Mechanism

The HR is triggered by the plant when it recognizes a pathogen. The identification of a pathogen typically occurs when virulence genes, secreted by a pathogen, bind to, or indirectly interact with the product of a plant resistance (R) gene. Plant R genes are highly polymorphic, and many plants produce several different types of R gene products, enabling them to recognize virulence products produced by many different pathogens.cite journal| last =Heath| first =MC. | title =Hypersensitive response-related death.| journal = Plant Molecular Biology| volume =44| issue = 3| pages =321–34 | date =2000| pmid = 11199391 | doi =10.1023/A:1026592509060]

In phase one of the HR, the activation of R genes triggers an ion flux, involving an efflux of hydroxide and potassium outside the cells, and an influx of calcium and hydrogen ions into the cell.cite web | last =Matthews| first = Ben | title =The Hypersensitive Response| work = Agricultural Research Service: Plant Science Institute| publisher = The United States Department of Agriculture.| url =http://bldg6.arsusda.gov/benlab/Soybean%20Defense%20Response/hypersensitive_response.htm| accessdate = 2007-01-12] In phase two, the cells involved in the HR generate an oxidative burst by producing reactive oxygen species (ROS), superoxide anions, hydrogen peroxide, hydroxyl radicals and nitrous oxide. These compounds affect cellular membrane function, in part by inducing lipid peroxidation and by causing lipid damage. The alteration of ion components in the cell, and the breakdown of cellular components in the presence of ROS, results in the death of affected cells and the formation of local lesions. Reactive oxygen species also trigger the deposition of lignin and callose, as well as the production of hydroxyproline-rich glycoproteins. These compounds serve to reinforce the walls of cells surrounding the infection, creating a barrier and inhibiting the spread of the infection. [cite journal| last = Pontier| first = D, | coauthors=Balague C, Roby D.|title =The hypersensitive response. A programmed cell death associated with plant resistance| journal = C R Acad Sci III| volume =321| issue = 9| pages = 721–34 | date = 1998| pmid = 9809204]

Mediators

Several enzymes have been shown to be involved in generation of ROS. For example, copper amine oxidase, catalyzes the oxidative deamination of polyamines, especially putrescine, and releases the ROS mediators hydrogen peroxide and ammonia. [cite journal| last = Koyanagi| first = T| coauthors= Matsumura K, Kuroda S, Tanizawa K. |title =Molecular cloning and heterologous expression of pea seedling copper amine oxidase.| journal = Biosci Biotechnol Biochem. | volume =64| issue = 4| pages = 717–22 | date = 2000| pmid = 10830482 |doi =10.1271/bbb.64.717] Other enzymes thought to play a role in ROS production include xanthine oxidase, NADPH oxidase, oxalate oxidase, peroxidases, and flavin containing amine oxidases.

In some cases, the cells surrounding the lesion synthesize antimicrobial compounds, including phenolics, phytoalexins, and pathogenesis related (PR) proteins, including β-glucanases and chitinases. These compounds may act by puncturing bacterial cell walls; or by delaying maturation, disrupting metabolism, or preventing reproduction of the pathogen in question.

Studies have suggested that the actual mode and sequence of the dismantling of plant cellular components depends on each individual plant-pathogen interaction, but all HR seem to require the involvement of cysteine proteases. The induction of cell death and the clearance of pathogens also requires active protein synthesis, an intact actin cytoskeleton, and the presence of salicylic acid.

Pathogen evasion

Pathogens have evolved several strategies designed to suppress plant defense responses. Host processes usually targeted by bacteria include; alterations to programmed cell death pathways, inhibiting cell wall-based defenses, and altering plant hormone signaling and expression of defense genes. [cite journal| last = Abramovitch | first = RB | coauthors=GB Martin |title =Strategies used by bacterial pathogens to suppress plant defenses.| journal = Curr Opin Plant Biol. | volume =7| issue = 4| pages = 356–64 | date = 2004| pmid = 15231256 |doi =10.1016/j.pbi.2004.05.002 ]

ee also

* Phytopathogen
* Plant hormones
* Systemic acquired resistance
* Antimicrobial peptide

References


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • hypersensitive response — Bot. An active response of plant cells to pathogenic attack in which the cell undergoes rapid necrosis and dies. Associated with the production of phytoalexins, lignin, and sometimes callose. The response is thought to prevent a potential… …   Dictionary of molecular biology

  • hypersensitive response — 1. A specific reaction of a plant to attack by a pathogen. The plant cells surrounding the point of infection rapidly die and dry out, so that pathogen spread within the plant is prevented. Often associated with the interaction of race specific R …   Glossary of Biotechnology

  • hypersensitive — adjective abnormally or excessively sensitive, either emotionally or in physical response. Derivatives hypersensitiveness noun hypersensitivity noun …   English new terms dictionary

  • Allergic response — An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury …   Wikipedia

  • allergic response — A hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury …   English dictionary of cancer terms

  • Immune system — A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and… …   Wikipedia

  • Arabidopsis thaliana — Scientific classification Kingdom: Plantae (unranked) …   Wikipedia

  • Inflammation — Toes inflamed by Chilblains Inflammation (Latin, īnflammō, “I ignite, set alight”) is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants …   Wikipedia

  • Innate immune system — See also: Immune system and Adaptive immune system Innate immune system The innate immune system, also known as non specific immune system and secondary line of defence,[1] comprises the cells and mechanisms that defend the host …   Wikipedia

  • Glossary of phytopathology — This is a glossary of some of the terms used in phytopathology.Phytopathology is the study of plant diseases. It is a multi disciplinary since prerequisites for disease development are the presence of a susceptible host species, a pathogen and… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”