Response of phenolic metabolism to the application of carbendazim plus boron in tobacco

In view of the essential role of phenolic compounds in the development of pathogen resistance in plants, and given the influence that fungicides and boron (B) exert over phenolic metabolism, the aim of the present study was to determine the individual effect of the application of a fungicide, as well as to determine the joint effect of the fungicide and B on the metabolism of phenolic compounds in tobacco plants (Nicotiana tabacum L, cv, Tennessee 86), The fungicide applied was carbendazim (carb), a preventative fungicide, with a purity of 100% at a concentration of 2.6 mM, Boron was applied in the form of H(3)BO(3) at: 1.6 mM (B(1)), 4 mM (B(2)), 8 mM (B(3)), 16 mM (B(4)), 32 mM (B(5)), or 64 mM (B(6)). In all, there were eight treatments: one without carb and without B (control), one with only carb, and six combinations of carb with concentration of B. The results indicated that the foliar application with carb alone led to increases in phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) activity and a foliar accumulation of phenols, This effect of the carb alone could signify an additional tolerance mechanism to pathogenic infection, given the participation of phenolic compounds in the lignification of plant cell walls. The joint application of carb and B increased both the biosynthesis and the oxidation of the phenolic compounds, especially in carb plus B(3), while the application of carb plus B(5) or carb plus B(6) reduced these processes as well as the foliar biomass.