Localization of methyltransferase activities throughout the endomembrane system of flax (Linum usitatissimum L) hypocotyls

Abstract

A microsomal fraction from flax hypocotyls (Linum usitatissimum L) showed a methylation ability from S-adenosyl-methionine on to the cell wall polysaccharides. Two kinds of methylation were found: (i) a methyl esterification of uronic acids in the oxalate extracts and (ii) an O-methylation of the hydroxyl groups in the NaOH extracts. The methyltransferase study showed a rapid decrease of the methyl esterification abilities, whereas the O-methylation on to the hydroxyl groups was maintained throughout the culture duration. The localization of such activities in the flax endomembrane system was performed using isopycnic centrifugation. Enzymic marker tests allowed us to identify the different membrane types. Methyltransferase activities in the different enriched fractions appeared to be associated with the Golgi apparatus for the O-methylation, and with the plasma membrane, Golgi apparatus and endoplasmic reticulum compartments for the carboxymethyl esterification.

Identification and Partial Characterization of the Pectin Methyltransferase “Homogalacturonan-Methyltransferase” from Membranes of Tobacco Cell Suspensions1

“…However, no sensitivity of the methylated product to cleavage by EPGase was reported and no subsequent work on the solubilization and purification of the mung bean PMT has been published. Putative PMT activity has also been detected in flax (Linum usitatissimum L.) hypocotyls (Vannier et al, 1992) and flax suspension-cultured cells (Schaumann et al, 1993). The PMT in flax was shown to synthesize a product from which [ 14 C]methanol was released after treatment with a high concentration of base (1 m NaOH) (Vannier et al, 1992).…”

“…Putative PMT activity has also been detected in flax (Linum usitatissimum L.) hypocotyls (Vannier et al, 1992) and flax suspension-cultured cells (Schaumann et al, 1993). The PMT in flax was shown to synthesize a product from which [ 14 C]methanol was released after treatment with a high concentration of base (1 m NaOH) (Vannier et al, 1992). However, further studies to prove that the enzyme transfers 14 CH 3 from SAM specifically to HGA have not been reported.…”

“…Tobacco cell suspensions were used, because the enzyme that synthesizes HGA, PGA-GalAT, has been identified and studied in these cells (Doong et al, 1995). A comparison of the characteristics of the HGA-MT from tobacco with the PMTs previously described from flax (Vannier et al, 1992) and mung bean ) is also presented.…”

“…This belief is supported by the observation that HGA in the walls of young cells is highly methylesterified, whereas HGA in the walls of older cells has a lower degree of esterification (Schaumann et al, 1993). The differences in the degree of methylesterification of pectins are believed to be controlled by the activities of PMT in the Golgi apparatus (Vannier et al, 1992) and PME in the cell wall (Gaffe et al, 1992).…”

The Import of S-Adenosylmethionine into the Golgi Apparatus Is Required for the Methylation of Homogalacturonan

“…In plants, SAM is also involved in other metabolic pathways, such as ethylene biosynthesis (Kende, 1993) and the methylation of pectins (Kauss and Hassid, 1967;Vannier et al, 1992;Boulard et al, 1997;Goubet et al, 1998). The pectins are a group of complex polysaccharides present in the primary cell wall in plants and are composed of homogalacturonan (HGA), rhamnogalacturonan I, and rhamnogalacturonan II (O'Neill et al, 1990;Albersheim et al, 1996).…”