Cell wall reinforcement in cotton hypocotyls in response to a Verticillium dahliae elicitor

Cotton (Gossypium hirsutum) hypocotyl tissue responded with increased lignification following treatment with a protein-lipopolysaccharide elicitor from Verticillium dahliae, the causative agent of vascular wilt disease in cotton. The induction of defence reactions was investigated over a period of 0 35 hr. Following exposure to the elicitor, increased synthesis and deposition of lignin and lignin-like phenolic polymers occurred. The induced phase of active lignification correlated with and was preceded by a transient increase in levels of enzyme activities; phenylalanine ammonia-lyase, cinnamyl alcohol dehydrogenase and cell wall associated peroxidase. The defence responses in two cultivars of G. hirsutum (cv. OR₁₉ and Acala_1517-70, resistant and susceptible to V. dahliae, respectively) were compared. The resistant cultivar exhibited higher and earlier induced levels of enzyme activity and lignin-like polymers compared to the susceptible cultivar. This indicates that the effectiveness of induced defence responses depends on their rapid initiation, development and accumulation and suggests a possible correlation between the timing and intensity of lignin-like polymer accumulation and resistance/tolerance of G.hirsutum seedlings against V. dahliae.