Pectic metabolism in suspension-cultured cells of flax, Linum usitatissimum

Flax cells in suspension culture continuously synthesize two types of pectin (i) highly methylated pectin that is covalently linked to the cell wall (ii) and low methylated pectin that is ionically linked to the cell wall. A maximal activity of pectin methyltransferase (PMT) in microsomes was recorded at the beginning of the elongation phase, while, two maximal activities of pectin methylesterase (PME) in cell walls were recorded at the end of the elongation phase and during the maturation phase. The differences between the PMT and PME activities, not only in terms of their location but also in terms of the time course of the culture, may explain the variations in the cation-exchange capacity (CEC) of the cell walls, which is mainly due to the negative charges of the less methylated pectins. The minimal value of the CEC during the elongation phase was due to high-level synthesis of neutral, hemicellulose-like polysaccharides and also to the PMT activity into the highly methylated, covalently linked pectins. Conversely, the large increase of the CEC during the maturation phase, might be due to the low level of PMT activity that is responsible for the limited methylation of the pectins synthesized at that time.