Small oligomers of galacturonic acid are endogenous suppressors of diseaseresistance reactions in wheat leaves

Citation
Bm. Moerschbacher et al., Small oligomers of galacturonic acid are endogenous suppressors of diseaseresistance reactions in wheat leaves, J EXP BOT, 50(334), 1999, pp. 605-612
Citations number
29
Categorie Soggetti
Plant Sciences","Animal & Plant Sciences
Journal title
JOURNAL OF EXPERIMENTAL BOTANY
ISSN journal
00220957 → ACNP
Volume
50
Issue
334
Year of publication
1999
Pages
605 - 612
Database
ISI
SICI code
0022-0957(199905)50:334<605:SOOGAA>2.0.ZU;2-Q
Abstract
Plants infected by a phytopathogenic fungus appear to recognize the presenc e of the pathogen by the molecular recognition of fungal cell wall fragment s, termed 'elicitors', or of breakdown products of their own cell walls, te rmed 'endogenous elicitors'. Successful pathogens are thought to counteract this elicitation of active resistance reactions by the production of 'supp ressors'. Evidence is presented here that fragments of the host cell wall, presumably produced enzymatically during fungal penetration, may act as 'en dogenous suppressors' of resistance reactions in wheat. Pectic fractions we re extracted from wheat cell walls by a variety of methods: Ca2+-chelators (CDTA and imidazole), a commercial mixture of pectic enzymes (Pectolyase Y2 3), a highly purified recombinant endopolygalacturonase (EPG), and solvolys es of the cell walls in anhydrous hydrogen fluoride at low temperatures fol lowed by imidazole extraction. All of these fractions suppressed elicitor-i nduced activities of phenylalanine ammonia-lyase and peroxidases when co-in jected with a glycoproteogalactanelicitor, isolated from germ tubes of the wheat stem rust fungus, into the intercellular spaces of wheat leaves. Supp ressor activity was correlated with the content of galacturonic acid in the extracts. of the oligogalacturonides tested (monomer to hexamer), the dime r and trimer proved to be most active. This was not only true for suppressi on of elicitor-induced responses, but also for suppression of the hypersens itive resistance reaction in infected, genetically resistant host plants. A s a consequence of reduced host cell necrosis in suppressor-treated leaves, the fungus developed larger colonies than in water-treated control leaves. Small oligomers of galacturonic acid, thus, are endogenous suppressors of resistance reactions in wheat leaves.