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 p athogen resistance in plants, and given the influence that fungicides and b oron (B) exert over phenolic metabolism, the aim of the present study was t o determine the individual effect of the application of a fungicide, as wel l as to determine the joint effect of the fungicide and B on the metabolism of phenolic compounds in tobacco plants (Nicotiana tabacum L, cv, Tennesse e 86), The fungicide applied was carbendazim (carb), a preventative fungici de, with a purity of 100% at a concentration of 2.6 mM, Boron was applied i n the form of H3BO3 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 witho ut carb and without B (control), one with only carb, and six combinations o f carb with concentration of B. The results indicated that the foliar appli cation 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 pathogen ic infection, given the participation of phenolic compounds in the lignific ation of plant cell walls. The joint application of carb and B increased bo th 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.