FLAVONOIDS ACCUMULATE IN CELL-WALLS, MIDDLE LAMELLAE AND CALLOSE-RICHPAPILLAE DURING AN INCOMPATIBLE INTERACTION BETWEEN XANTHOMONAS-CAMPESTRIS PV MALVACEARUM AND COTTON

Interactions between cotton cotyledons and Xanthomonas campestris pv. malvacearum were examined. During an incompatible interaction, fluores cence microscopy revealed that flavonoid compounds accumulated within 10 h after inoculation. Electron micrographs showed ultrastructural mo difications of cells that exhibited an intense fluorescence suggesting the presence of flavonoids. Phenol-like molecules were produced by ce lls of infection sites and were found in paramural areas within papill ae enriched with callose and in host cell walls and middle lamellae. H istochemistry showed that peroxidase activity and terpenoids were dete cted in the infected resistant plants, 4 and 48 h after inoculation, r espectively. In contrast, no changes in the deposits of lignin, suberi n, and catechin were seen in either the infected susceptible or resist ant lines. We suggest that early flavonoid accumulation is associated with the hypersensitive reaction of cotton cotyledons to X. campestris pv. malvacearum. The activity of wall-bound peroxidases may play a ro le in the incorporation of flavonoids in cell walls and paramural papi llae. (C) 1996 Academic Press Limited.