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

Biochemical changes occurring during the transition between meristematic 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 galacturonic acids was observed during the rest period. The degree of esterification increased from 2% in spring to 35% in winter, indicating an important accumulation of acidic pectins during the active season although the cation content was always very low. Nuclear magnetic resonance spectroscopy of neutral polysaccharides solubilized with boiling water showed that in winter arabinans and xylans were the main carbohydrates. By contrast, in spring and in summer the xylans were very scarce, arabinans being the major neutral polysaccharide, indicating that important modifications occur during the autumn. Histochemical observations of material treated with hot water and EDTA confirmed the low relative pectin content during the rest period. Calcium ions, detected as antimonate salt were scarce. In the cambium, they were located mainly in cell junctions whereas in phloem derivatives these cations were distributed throughout the whole cell wall.