Effect of caffeoylshikimic acid of date palm roots on activity and production of Fusarium oxysporum f. sp. albedinis cell wall-degrading enzymes

The caffeoylshikimic acid (CSA), a major phenolic compound of date palm roots, represents one of the resistance factors of the host to Fusarium oxysporum f. sp. albedinis. The CSA was tested at various concentrations (0,25 to 3 μmol/ml) on the activity and the production of F. oxysporum f. sp. albedinis cell wall-degrading enzymes (CWDE): proteases, cellulases, pectinemethyl-esterases (PME), polygalacturonases (PG) and polygalacturonate trans-eliminases (PGTE). The results obtained show that CSA had very little effect on the activity of the various enzymes although it greatly reduced their production. The mycelial growth was also affected by CSA, but this does not explain why only the production of CWDE was noticeably reduced. In order to explain this differential effect of CSA on the activity and production of CWDE, in one group of experiments the effects of the products of hydrolysis of CSA (caffeic acid and shikimic acid) was tested and in another, the effect of the products of CSA (quinones) obtained by tyrosinase oxidation was investigated. The results obtained show that the shikimic acid did not have a significant effect on the activity of the CWDE but presented a weak inhibition of their production. The caffeic acid showed a larger inhibition of the activity of the various CWDE that was more than that of CSA and its inhibiting effect appeared to be more important during their production. The oxidation of CSA by tyrosinase was accompanied by a greater inhibition of the activity of the various CWDE. This inhibition was appreciable in comparison with that observed due to the effect of non-oxidized CSA on CWDE production. In the same way, oxidation of caffeic acid provoked a greater inhibiting effect on the activity of CWDE than unoxidized caffeic acid. These results suggests that CSA generates products of hydrolysis (in particular caffeic acid) and products of oxidation (quinones) which inhibit the activity of the proteolytic, cellulolytic and pectinolytic enzymes produced by F. oxysporum f. sp. albedinis in the culture medium.