Tyloses and gels associated with cellulose accumulation in vessels are responses of plane tree seedlings (Platanus x acerifolia) to the vascular fungus Ceratocystis fimbriata f. sp platani

Stems of plane tree seedlings were cytological:ly investigated regarding th e involvement of tyloses and gels in defense reactions to Ceratocystis fimb riata f. sp platani, the canker stain disease agent. In the lumen of infect ed xylem vessels, cytochemical tests revealed the occurrence of compounds l abeled for cellulose and wh:ich seem to be involved in gel formation. Immun ogold methods indicated that pectin-rich material accumulated in the paramu ral area of vessel-associated parenchyma cells and around tylosis walls. Ty losis formation and deposition of pectin-containing gels were associated wi th metabolic changes of vessel-associated parenchyma cells. It is suggested that parenchyma cells play a key role in the defense of plane tree seedlin gs through plugging of xylem vessels leading to compartmentalization of the vascular fungus.