PECTINS, EARLY MARKERS OF THE DEVELOPMENT OF FLAX HYPOCOTYL

Flax hypocotyls (Linum usitatissimum) showed different pectic metabolisms: after 3 days of germination, the cell walls were rich in acidic pectins, linked covalently. Using red ruthenium in transmission electronic microscopy allowed to localize these pectic acids in the primary cell walls. When the hypocotyls were etiolated, hydrosoluble polysaccharides were mainly neutral, including the pectins. Ferric hydroxylamine staining showed that the cell walls of the main tissues (cortex and liber) were enriched in methylated polygalacturonic blocks. On the contrary, when the plants were transfered in light, the acidic pectins were mainly found ionically linked in the intercellular junction, whereas the neutral pectins were mainly covalently linked to the primary cell walls. Then the cell wall composition appeared regulated in the mature zones, mainly via the cell wall enzymes, and in the elongation zones, via new syntheses. Besides, some particular pectins such as acetylated polygalacturonic acids, linked to some rhamnoglacturonan I, were localized in the cellular junctions of the mother fibre cells. All the results suggested that pectic polymers could be used in flax to mark the different steps of the cell wall developpement as well to mark very early the different tissues, especially the fibres.