IMMUNOLOCALIZATION OF PECTIN METHYLESTERASES IN THE HYPOCOTYL TISSUESOF FLAX

This paper is the first report on the direct visualization of pectin m ethylesterases (PMEs, EC 3.1.1.11) of flax (Linum usitatissimum) using immunofluorescence microscopy. PME localization is studied in the dif ferent tissues sampled along the hypocotyl of flax seedlings at differ ent 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 paren chyma, and the xylem. As expected from biochemical data reported in th e literature, PMEs are distributed along the hypocotyl axis whatever t he state of development, in the elongating as well as in the non-elong ating zones. However, we observe that, after NaCl treatment of the sam ples, the labelling remains higher in the lower than in the upper part of the hypocotyl. These data suggest that, in the basal part, some PM Es are more tightly associated or entangled in cell structures. A tota l extinction of the labelling is noticed when using cdta-Na-2, a chela tor of calcium, indicating a co-location of PMEs with polymers which a re calcium-bound to cell structures.