Variability of content of HGA regions in Arabidopsis mutants affected in pectin composition. The levels of HGA domains were determined by immunodot assay on ChASS fraction extracted from leaves of 4-week-old Arabidopsis WT (Col-0), mutants (qua2-1 and pme3), and transgenic plants (PG and PMEI). Equal amounts of ChASS were hybridized with the monoclonal antibody PAM1. PAM1 epitope levels were normalized with respect to the standard polygalacturonic acid (PGA). Bars represent means of PAM1 level ± SD (n = 3). Different letters indicate statistically significant differences, according to ANOVA followed by Tukey’s test (P <0.05). Similar results were obtained in at least three other experiments. ChASS, chelating agent-soluble solids; Col-0, Columbia-0; HGA, de-methyl-esterified homogalacturonan; PG, polygalacturonase; PGA, polygalacturonic acid; pme3, pectin methylesterase 3; PMEI, pectin methylesterase inhibitor; qua2-1, quasimodo2-1; WT, wild type.