POLYSACCHARIDE DISTRIBUTION IN THE CELLULAR JUNCTIONS OF IMMATURE FIBER CELLS OF FLAX SEEDLINGS

The characteristic features of the pectins present in the walls of imm ature fibre cells of the hypocotyl of flax seedlings have been studied by a combination of three subtractive methods (treatment with boiling water, calcium chelator, and free endopolygalacturonase), three stain ing reactions (periodic acid-thiocarbohydrazide-silver, Ruthenium Red, and ferric hydroxylamine) and labelling with an endopolygalacturonase -gold probe. The primary wall and the periphery of the tricellular jun ctions were shown to contain pectic molecules made of blocks either wi th free acidic functions or methyl-esterified, these molecules being r emoved from the wall by splitting alpha(1-4) linkages. On the contrary , the pectic molecules in the core of the tricellular junctions were m ainly with free acidic groups, but with an appreciable acetylesterific ation of their hydroxyl groups; and they were linked with one another chiefly by calcium bonds. This unexpected constitution of the core of the tricellular junctions may be considered to be an early marker of t he cells destined to give rise to the fibre bundles of the mature plan t.