Bull. Spec. CORESTA Symposium, Kallithea, 1990, p. 183, PP01, ISSN.0525-6240

Biochemical study of tobacco tested under"test-cotyledon"conditions : Effects of magnesium, reactions of plants resistant and sensitive to Peronospora tabacina. Cytochemical study of Callose

Institute of Genetics, Sofia, Bulgaria; Institut Expérimental du Tabac, Bergerac, France
Tobacco obtained under cotyledon test conditions was inoculated with P. tabacina Adam conidia. The presence of callose deposits was detected in the cell walls of three genotypes. In the sensitive type, there was no formation of callose papillae in young plants cultivated on Knop's medium, whereas this phenomenon was weakly expressed on the magnesium-containing medium. In the resistant types, marked accumulation of callose on the cell walls appeared as a response to fungal invasion. This accumulation was weaker on Knop's medium than on the magnesium-containing medium, in which the resistance genes were fully expressed. In the latter situation, the callose-containing papillae were more numerous and had thicker walls in the resistant type than in the sensitive type. It is assumed that the callose deposits fulfill a morphological barrier function by limiting the progression of the pathogen. It is probable that the cell recognition systems play an important part in trigg ering the callose deposit formation reactions.