Abstract
Flax plantlets, cultivated from day 3 in liquid medium and under continuous light showed linear growth. Electron microscopy observations showed that treatment of the cell walls with cdta-Na2 cleared out the middle lamella and the cell junctions, whereas boiling water extracted pectic polysaccharides from the primary cell wall in each tissue (epidermis, cortical parenchyma and phloem). Pulse-chase experiments showed that there was during the growth of flax plantlets a continuous redistribution of radioactivity in all parts of the cell walls: 1) from pectins to hemicelluloses and even to the cellulosic residues. 2) from oligomers to polymers. 3) from neutral to acidic polymers in the core of the middle lamella. 4) from acidic to neutral pectins in the primary cell walls. The elongation zone which was restricted to a small zone back from the tip, involved strong synthesis of neutral pectins in all the cell walls. Conversely, the redistribution of radioactivity was related mainly to the plant cell maturation, and especially to the acidification of the cell wall. Demethylation of some neutral pectins occurred in the middle lamella whereas strongly acidic pectins were synthetized in the primary cell wall.