Induced defence responses in cotton leaf disks by elicitors from Verticillium dahliae

Cotton (Gossypium hirsutum) leaf tissue responded with symptoms of chlorosis and necrosis to treatment with heat-released soluble cell-wall fragments from Verticillium dahliae. The induction of defence responses in leaf disks by the elicitor led to increased synthesis of anti-fungal lasinilene and cadalene stress metabolites, as well as the rapid deposition of phenolic polymers in the lignin fraction. The coordinated induction and accumulation of chitinases and 1,3-β-glucanases were observed following elicitation; selective low pH extracts of pathogenesis related-proteins revealed a bi-phasic defence hydrolase response that reached a peak within 12 hr, followed by a gradual increase up to 120 hr. Electrophoretic analysis and enzyme staining revealed differences in constitutive and inducible proteins. Three acidic isozymes of chitinase with isoelectric points in the range 3.7-4.2, but only one β-1,3-glucanase isozyme with an isoelectric point of 4.5 were found in the intercellular fluid. The results obtained indicate that the elicitation of cotton leaf disks by V. dahliae derived signal molecules exhibits some properties of a multicomponent dynamic system where different protective mechanisms have complementary roles in the overall expression of the defence response.