Do Galacturonic Acid Oligosaccharides Have a Role in the Resistance Mechanism of Cucumber towards Cladosporium Cucumerinum?

Abstract

Lignification was suggested to be a mechanism of disease resistance in cucumber by Hijwegen [1] who observed that lignin-like material was produced in resistant, but not in susceptible seedlings upon infection with the scab fungus Cladosporium cucumerinum. The lignin-like material was deposited in the walls and cytoplasm of the host tissue [1,2]. Hammerschmidt [3] reported that vanillin was released by cupric oxide oxidation of cell walls from infected resistant cucumber hypocotyls, but not from hypocotyl walls of control seedlings. This further supports the view that lignin is produced during infection of resistant plants. The work of Hammerschmidt and Kuć [4] indicates that lignification also has a role in the resistance mechanism of susceptible cucumber plants which have been systemically immunized against scab disease. Lignification has also been implicated in defence mechanisms of many other plants [5]. The available experimental evidence suggests that lignification may restrict fungal growth either because it makes the plant cell walls resistant to enzymatic degradation [6] or because some of the lignin precursors, like coniferyl alcohol, are toxic to fungi [4].