| Abstract: | Cucumber seedlings (Cucumis sativus L. cv Marketer), heat-shocked for 40 s at 50 °C, acquire disease resistance to the fungal pathogen Cladosporium cucumerinum E11. and Arth. The resistance develops 15 to 21 h after heat shock treatment and is associated with stimulated ethylene production and changes in the plant cell wall. There was a two-fold increase in the production of ethylene and in its precursor 1-aminocyclopropane-1-carboxylic acid by 6 h after the heat shock. Heat shock also enhanced the accumulation of insoluble extensin, a hydroxyproline-rich glycoprotein found in cell walls of seedlings. A heat shock treatment of seedlings 24 h before inoculation with C. cucumerinum resulted in a doubling of extensin content at 72 h after the inoculation. Cell walls from heat shocked seedlings were up to 55% more resistant to degradation by enzymes from C. cucumerinum than were cell walls from unshocked seedlings, but increased lignin depositions did not appear responsible. The accumulation of extensin after heat shock and its crosslinking by peroxidase is discussed as a possible mechanism of induced resistance to C. cucumerinum. |
