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Abstract Detail



Wood: Biology of a Living Tissue

Blaedow, Ryan [1], Park, Ji-Hyun [2], Juzwik, Jennifer [3].

The Role of Xylem Parenchyma in Pathogen Defense.

The xylem, while considered to be nutritionally poor in comparison to other plant tissues, is constantly confronted with a wide range of pathogens and wood decay organisms. Vascular wilt diseases caused by fungi, bacteria, and oomycetes are among the most destructive diseases of woody perennials. Xylem-invading pathogens in particular can cause catastrophic disruptions in hydraulic conductivity through the production of phytotoxins, physical occlusion of tracheary elements, and the elicitation of excessive tylose production that results in severe tree decline or death. In addition, many of the most destructive tree diseases such as oak wilt, dutch elm disease, and laurel wilt are caused by pathogens capable of rapid systemic invasion of plants via spread through xylem vessels. Wood-inhabiting microorganisms such as decay fungi enter through tree wounds and derive energy from the degradation of cellulose, hemicelluloses, and lignin into simple organic substances. This activity can interfere with the transport of water and mineral nutrients, cause wood discoloration and decay, and destroy the sapwood leading to structural failure or death. Due to the imminent threat posed by xylem-invading pathogens, plants have developed the capacity to defend themselves using both pre-existing and inducible defense responses. Xylem parenchyma, which are among the only living cells in the sapwood, are key components of the physical and chemical barriers which constitute a plant’s pre-existing defenses. More importantly however, parenchyma are essential for the induction of defense responses when successful invasion of the xylem occurs. Specifically, the extra- and intracellular receptors responsible for the recognition of pathogen elicitors are believed to reside mainly within the paratracheal parenchyma cells that are closely associated with tracheary elements. Induced defense responses include the production of tyloses, gels, and gums by parenchyma that physically restrict pathogen movement. Recognition of vascular pathogens also leads to metabolic changes in the xylem parenchyma which result in the excretion into and accumulation of defense proteins and secondary metabolites in vessels including chitinases, peroxidases, proteases, phenolic compounds, pectic substances, and phytoalexins among others. The combination of pre-formed and induced defense responses executed by xylem parenchyma can enable a plant to physically restrict pathogen movement via physical and chemical barriers, and subsequently inhibit or eliminate the pathogen via the production of antimicrobial compounds. Specific examples of the role of xylem parenchyma in pathogen defense will be discussed including recent investigations of the host-pathogen interactions of hickory decline.


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1 - USDA Forest Service, Forest Health Protection, 200 WT Weaver Blvd., Asheville, NC, 28806, USA
2 - Korea Forest Research Institute, Seoul, Korea
3 - USDA Forest Service, Northern Research Station, 1561 Lindig Ave, St. Paul, MN, 55108, USA

Keywords:
xylem
Parenchyma
defense
pathogen.

Presentation Type: Symposium Presentation
Session: SY09, Wood: Biology of a Living Tissue
Location: Oglethrope Auditorium/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 9:15 AM
Number: SY09004
Abstract ID:326
Candidate for Awards:None


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