DETECTION AND CELLULAR-LOCALIZATION OF ELEMENTAL SULFUR IN DISEASE-RESISTANT GENOTYPES OF THEOBROMA-CACAO

DISEASE-RESISTANT genotypes are the basis for controlling many major m icrobial pathogens of economic plants. Resistance is often linked with organic, antimicrobial phytoalexins, produced de novo in cells surrou nding apoptotic or 'hypersensitive' cells that die rapidly after conta ct with incompatible pathogens(1-3). Here we report the production by resistant genotypes of Theobroma cacao of four phytoalexins in respons e to a xylem-invading fungal pathogen; these comprised two phenolics, a triterpenoid and, highly unusually in a higher eukaryote, elemental sulphur as cyclooctasulphur S-8. Energy dispersive X-ray microanalysis revealed a high accumulation of sulphur only in cells and structures in potential contact,vith the vascular pathogen; that is, xylem parenc hyma, xylem vessel cell walls and gels occluding vessels. Our data pro vide a rare example of cellular localization of an antimicrobial subst ance and evidence for the first time for accumulation of elemental sul phur in a plant Linked with a resistance response; this discovery come s centuries after man first used elemental sulphur as a potent fungici de(4,5).