Differential induction of phenylalanine ammonia-lyase activity in date palm roots in response to inoculation with Fusarium oxysporum f. sp albedinis and to elicitation with fungal wall elicitor

The inoculation of the roots of resistant (BSTN) and susceptible (JHL) cultivars of date palm seedlings by Fusarium oxysporum f, sp. albedinis (Foa) induces an increase in activity of phenylalanine ammonia-lyase (E.C. 4. 3. 1.5., PAL). The post-infectional response in the PAL activity in the resistant cultivar roots was faster and higher than that in the susceptible cultivar. However, the elicitation of the seedlings by the hyphal wall preparation (HWP) of Foa induces an identical PAL response in the resistant and the susceptible cultivars. The elicitor activity of HWP was dose-dependent, the optimal concentration which induces a maximum PAL activity was 10 mg of mycelium per mt. The elicitor present in the HWP was thermostable since its elicitor activity was maintained after heat treatment (121 degreesC for 45 min). The treatment of the HWP with protease (Pronase E) does not have an effect on the HWP elicitor activity. However, the treatment of the HWP with sodium periodate inhibits its elicitor activity. This data suggests that the HWP elicitor is a carbohydrate compound. In addition, the HWP elicitor is non-specific since it induces identical responses of the PAL activity in two cultivars showing different behaviors to the pathogen. The absence of specificity of HWP elicitors and the differential response of the PAL activity to the infection by Foa and to the elicitation by the HWP are discussed. An explanation of the general interactions between plant and parasite is proposed.