Quantitative aspects of the interaction between chemical activators of systemic acquired resistance in plants and humic acids

Salicylic acid (SA) and its synthetic functional analogue acibenzolarS-methyl (BTH) are able to activate in plants the systemic acquired resistance (SAR) which is an effective natural defence against many parasites and pathogens. In this study, the quantitative aspects of the interaction between SA and BTH and four humic acids isolated from soil (S-HA), peat (P-HA), compost (C-HA) and a mixture of peat and compost (M-HA) were evaluated by constructing the adsorption kinetics and isotherms. The adsorption of SA and BTH at concentrations of 0.05 and 0.01 mM, respectively, onto S-HA resulted rapid and complete in few hours. SA adsorption onto S-HA, P-HA and M-HA followed a linear model with adsorption constants ranging between 150 e 200 ml g -1, whereas onto C-HA it followed the Freundlich model with a K f value of 44 ml g-1. BTH adsorption onto all HA followed the Freundlich model with Kf values ranging between 559 ml g -1for M-HA and 6460 ml g-1 for P-HA.