APOPLASTIC ENZYMES AND BIOLOGICAL ACTIVE OLIGOSACCHARIDES AS MARKERS OF EARLY PATHOGENESIS

Obiettivo

EARLY DETECTION OF DISEASES, BEFORE VISIBLE SYMPTOMS APPEAR, WILL BE MADE POSSIBLE BY THE IDENTIFICATION OF MARKER SUBSTANCES FORMED DURING INFECTION THAT WOULD PREDICT THE OUTCOME OF SPECIFIC RACE/CULTIVAR ENCOUNTERS. AN ADEQUATELY SENSITIVE ASSAY WILL BE DEVELOPED FOR DISTINCTION BETWEEN SUBSTANCES FORMED IN COMPATIBLE AND IN INCOMPATIBLE INTERACTIONS. MARKERS SUITABLE AS DIAGNOSTIC TESTS FOR EARLY PATHOGENESIS IN THE FIELD WILL THEN BE DEFINED, ALLOWING THE RAPID IMPLEMENTATION BY THE FARMER OF OPTIMAL COUNTERMEASURES TO SAVE THOSE CROPS PRESENTING A SIGNIFICANT MOLECULAR RESPONSE.

IN THE LONG TERM, THE KNOWLEDGE OF MOLECULES THAT GOVERN RACE/CULTIVAR RELATIONS WILL PROVIDE A BASIS FOR THE RATIONAL ENGINEERING OF CROPS TOWARDS DISEASE-RESISTANCE.
When a potential pathogen attacks a crop plant, considerable molecular activity occurs which determines if the invader will cause disease or the crop plant will successfully resist it. This process has been studied in tomato plants infected with Cladosporium fulvum.

By studying biochemical events at the cellular interface between the plant and its pathogen during infection, new information was found on the factors determining disease resistance and susceptibility. Extracellular proteins and oligosaccharides were in tomato leaves challenged with a race of the fungus which they can resist and succumbing to a fungal race to which they are susceptible. Healthy leaves were also examined. Proteins were analysed from infected leaves and the enzymic activity of some of these proteins was also investigated.

Races of the fungus with avirulence gene A9 produced a peptide which, when purified and applied to tomato leaves that were resistant to these races, caused localized necrosis, an essential part of the defence mechanism. Therefore, the peptide is central to the mechanism whereby certain tomato varieties can resist these races of the fungus. The peptide's precise structure was determined.

Several other proteins accumulated in tomato leaves infected with the fungus. Some of these (produced in large amounts and known as pathogenesis related (PR) proteins) were shown to be the enzymes chitinase and beta (1 to 3)-glucanase, which can attack fungal cell walls. Others (produced in much smaller amounts) were identified as enzymes that can lightly degrade the tomato's own cell walls; the early production of one such enzyme, endoarabinanase, was correlated with disease resistance. Both groups of enzymes can release soluble oligosaccharides from their respective target cell walls, and this may be important in active plant target.
A MOLECULAR TEST FOR THE EARLY INFECTION OF TOMATO BY A FUNGAL PARASITE, CLADOSPORIUM FULVUM, WILL BE DEVELOPED AT THE LEVEL OF APOPLASTIC FLUID FROM LEAF MATERIAL.

TWO TYPES OF BIOLOGICAL MARKERS WILL BE SCREENED FOR :
- ELICITORS OF PHYTOALEXIN SYNTHESIS,
- TRIGGERS OF THE HYPERSENSITIVE RESPONSES.

THE CHEMICAL ANALYSIS WILL FOCUS ON ENZYME ACTIVITIES AND BIOLOGYCALLY-ACTIVE CARBOHYDRATES. SPECIFIC HYDROLYTIC ENZYMES, PRODUCED EITHER BY THE FUNGUS OR BY THE PLANT IN RESPONSE TO THE FUNGUS, HYPOTHESISED TO SOLUBILISE, FROM WALL POLYMERS OLIGOSACCHARIDES WHICH EVOKE DEFENCE RESPONSE. THE BIOLOGICAL AND ENZYMATIC MARKERS WILL BE COMPARED WITH THE AIM OF BUILDING A COHERENT UNDERSTANDING OF THE ENZYME/SUBSTRATE RELATIONS WHICH DIRECT THE COURSE OF EARLY PATHOGENESIS.

Campo scientifico

Programma(i)

FP1-BAP - Multiannual research action programme (EEC) in the field of biotechnology (BAP), 1985-1989

Argomento(i)

Data not available

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

CSC - Cost-sharing contracts

Coordinatore

AGRICULTURAL UNIVERSITY OF WAGENINGEN

Contributo UE

Nessun dato

Indirizzo

LABORATORY OF PHYTOPATHOLOGY BINNENHAVEN 9
6709 PD WAGENINGEN
Paesi Bassi

Costo totale