Effects of Fusarium oxysporum culture filtrates on carnation callus cell ultrastructure and cytoplasmic calcium distribution

Abstract

Calli of Mediterranean carnation ( Dianthus caryophyllus L.) cvs. Corrida and Pulcino, susceptible and resistant respectively to Fusarium oxysporum f. sp. dianthi race 2, were exposed to fungus culture filtrates (FCF). The ultrastructure of cells from carnation callus was studied by transmission electron microscopy. Localization of intracellular Ca 2+ was achieved by a precipitation technique using potassium pyroantimonate. Cells from the resistant carnation cultivar exposed to 200 μl FCF for 15 min showed the presence of electron-dense granules in vacuolar and plasma membranes and marked ultrastructural changes. Treated or untreated cv. Corrida, as well as untreated cv. Pulcino callus cells, did not show any appreciable ultrastructural changes, and electron-dense precipitates were randomly distributed in the cytoplasm. The electron-dense granules, when analysed by electron probe microanalysis, appeared to be calcium precipitated with antimony. The involvement of calcium in the resistant carnation callus treated with FCF reported here, provides evidence of the possible involvement of this cation in the defence reaction. A fractal dimension study on the rough nature of the nuclei showed that nuclei of treated cv. Pulcino were highly invaginated and the arrangement of granular and fibrillar components of nucleoli were shown to be characteristic of high transcriptional activity. A quantitative ultrastructural study of the cytoplasmic organelles, performed on the micrographs, showed a significant ( P < 0·001) increase in dictyosome and endoplasmic cisternae in the resistant cultivar.