Twenty L of the exudates, and of the final aqueous extract for the determination in tissues were injected into a HPLC (Metrohm) fitted with an anion exclusion column(250 mm × 7.8 mm, 6.1005.200 Metrosep Organic Acids, Metrohm).The mobile phase was a mixture of 0.2 mM H2SO4 with 5% acetone,and the flow was set at 0.6 mL/min. Organic anions were identi-fied by comparison with the elution times of standards of citric,malic and succinic acids (Fluka) using a conductivity detector, theamounts of each one in the samples were determined from the peakareas in the samples with those for the standards using MagIC Net software (Metrohm).