Peroxidase activity and induced lignification in rusted flax interactions varying in their degree of incompatibility

Abstract

A histological comparison of the L⁹, K, P, P¹, P², and P³ genotypes in flax revealed differences in their expression of incompatibility. K and P¹ were only moderately incompatible, whereas P, P², and P³ were highly incompatible, restricting fungal development completely by the 4th day after inoculation. Host cell necrosis was delayed until day 3 in P³ and day 2 in P²; it was present at day 1 in P. Peroxidase, using guaiacol as a proton donor, was detected in P after 2 days, in K at 5 days, and in L⁹ after 7 days. Soluble peroxidase activity increased in the rusted P genotype from day 3 and from day 7 in K. Gel electrophoresis of infected P revealed a new peroxidase isozyme at 6 days after inoculation. Three new protein bands were also detected at this stage. In 3- and 4-day-old rusted P, peroxidase was detected in the host cell walls of tissue surrounding necrotic infection sites. It was not located in the host cell walls of the compatible L⁹ genotype at this stage. Lignin was detected histochemically in P after 2 days, in K after 5 days, and in L⁹ after 9 days. The Wiesner, Maiile, and KMnO₄ tests gave equivalent results. Suberin was detected in P, K, and L⁹ at the same time that lignin became observable.