CYTOLOGICAL AND BIOCHEMICAL ASPECTS ASSOCIATED WITH THE HYPERSENSITIVE REACTION IN COFFEE PLANTS INFECTED WITH ORANGE RUST, HEMILEIA VASTATRIX
MC SILVA1, M NICOLE2, L GUERRA-GUIMARAES1, E BRESSON2, L RIJO1, JP GEIGER2 and CJ RODRIGUES JR1
1IICT - Centro de lnvestigacao das Ferrugens do Cafeeiro (CIFC), Quinta do Marques, 2780 Oeiras, Portugal; 2ORSTOM, Plant Pathology - BP 5045, 34032, Montpellier, France
Background and objectives
Results and conclusions
Around 5 days after inoculation, another increase in peroxidase activity and stimulation of enzymes of the phenylpropanoid pathway (PAL and TAL) was found, which could be responsible for the lignification observed histologically in the host cell walls. From 7 days after inoculation, the accumulation of an acicular material was seen in the intercellular spaces around the senescent hyphae, next to the dead host cells and in close association with the middle lamella. That material was autofluorescent, stained positively for lignin and polysaccharides and labelled for pectins. Cellulose, hemicellulose, extensins, hydroxyproline-rich glycoproteins and proteins were not detected. Hypertrophy and wall thickness of the host cells in the infection area were also observed around 12 days after inoculation, corresponding macroscopically to the reaction flt. Thus in resistant coffee plants the HR was associated with an increase in peroxidase activity, precocious haustorium encasement, early arrest of fungal growth, stimulation of the phenylpropanoid pathway, accumulation of an acicular material of heterogeneous composition, and by cell hypertrophy.