Effect of NaHCO3 treatments on the activity of cell-wall-degrading enzymes produced by Penicillium digitatum during the pathogenesis process on grapefruit

BACKGROUND: The present study was performed to clarify the strategies of Penicillium digitatum during pathogenesis on citrus, assessing, on albedo plugs, the effects of treatment with NaHCO3, at two different pH (5 and 8.3), on cell wall-degrading enzymes activity, over a period of 72 h. RESULTS: The treatment with NaHCO3, under alkaline pH, delayed the polygalacturonase activity for 72 h, or 48 h in the case of the pectin lyase, if compared to the control or the same treatment at pH 5. On the contrary, the pectin methyl esterase activity rapidly increased after 24 h, in plugs dipped in the same solution. In this case, the activity remained higher than untreated or pH 5 treated plugs up to 72 h. CONCLUSION: The rapid increase in pectin methyl esterase activity, under alkaline conditions, is presumably the strategy of the pathogen to lower the pH, soon after the initiation of infection, in order to restore an optimal environment for the subsequent polygalacturonase and pectin lyase action. In fact at the same time, a low pH delayed the enzymatic activity of polygalacturonase and pectin lyase, the two enzymes that actually cleave the ?-1,4-linkages between the galacturonic acid residues.