PECTIN CHANGES IN SAMPLES CONTAINING POPLAR CAMBIUM AND INNER BARK INRELATION TO THE SEASONAL CYCLE

Biochemical changes occurring during the transition between meristemat ic activity and rest were studied in samples containing cambial cells and their phloem derivatives from Populus x euramericana. Uronic acids represented around 9% of the cell-wall dry matter in spring and 7% in summer and winter. In contrast, a higher content of methylated galact uronic acids was observed during the rest period. The degree of esteri fication increased from 2% in spring to 35% in winter, indicating an i mportant accumulation of acidic pectins during the active season altho ugh the cation content was always very low. Nuclear magnetic resonance spectroscopy of neutral polysaccharides solubilized with boiling wate r showed that in winter arabinans and xylans were the main carbohydrat es. By contrast, in spring and in summer the xylans were very scarce, arabinans being the major neutral polysaccharide, indicating that impo rtant modifications occur during the autumn. Histochemical observation s of material treated with hot water and EDTA confirmed the low relati ve pectin content during the rest period. Calcium ions, detected as an timonate salt were scarce. In the cambium, they were located mainly in cell junctions whereas in phloem derivatives these cations were distr ibuted throughout the whole cell wall.