Immunolocalization of pectin methylesterases in the hypocotyl tissues of flax

This paper is the first report on the direct visualization of pectin methylesterases (PMEs, EC 3.1.1.11) of flax (Linum usitatissimum) using immunofluorescence microscopy. PME localization is studied in the different tissues sampled along the hypocotyl of flax seedlings at different states of development. Our results indicate that, at the tissular level, PMEs are not evenly distributed, but preferentially located in the epidermis, the corners of the cell junctions of the cortical parenchyma, and the xylem. As expected from biochemical data reported in the literature, PMEs are distributed along the hypocotyl axis whatever the state of development, in the elongating as well as in the non-elongating zones. However, we observe that, after NaCl treatment of the samples, the labelling remains higher in the lower than in the upper part of the hypocotyl. These data suggest that, in the basal part, some PMEs are more tightly associated or entangled in cell structures. A total extinction of the labelling is noticed when using cdta-Na-2, a chelator of calcium, indicating a co-location of PMEs with polymers which are calcium-bound to cell structures.