Carbohydrate composition of flax mucilage and its relation to morphological characters

Abstract

Mucilage of flax is a valuable product for food, medicine and biocomposites production. Each direction of use needs special characteristics of seeds, so it is necessary to describe flax polymorphism of mucilage carbohydrate composition to determine the effect of seed color and pleiotropic effects of genes controlling it on the mucilage chemical composition. The originality of the work consists in the use of lines genetic collection with identified seed color genes and methods of multivariate and nonparametric statistics to identify patterns of influence of seed color on the mucilage composition. Seed mucilage polysaccharide composition was evaluated in 29 lines and three cultivars of flax (15 lines had red-brown seeds of the wild type, 9 lines had yellow seeds and 7 lines had modified brown seeds). For some lines the genetic control of seed color was known (from 8 lines with yellow seeds 4 lines had gene s1, 4 ones had gene YSED1; 5 lines with yellow hue of seeds had gene pf1). Water extraction of mucilage performed for 2 hours at 20°C. After freeze drying monosaccharide composition was examined by gas chromatography. Generally, mucilage contained more pectin (pect = rhamnose (Rha) + galacturonic acid (GalA), 38-64 %) than arabinoxylans (AX = arabinose (Ara) + xylose (Xyl), 10-38 %). In the most of lines maximal and minimal percent of pectin was caused by rhamnogalacturonan (RG1b = 2 × Rha), except of the variety Orshanskii 2 which had an exceptionally high content of GalA and accordingly, homogalacturonan (HGA = GalA-Rha). Increase of AX was caused by extending of the core (Xyl), but there were lines with increased branching (Ara) or proportionally increased the whole molecule. Ratio Ara: Xyl was about 0.23 (0.05-0.30). Its extreme values did not always correspond to the AX content. Percent of RG1b was approximately twice higher than that of AX. But there were lines with more AX than RG1b. Galactose (Gal) was about 15 % of mucilage sugars, fucose (Fuc) was about 3.5 %. In average glucose (Glc) was 3.6 % of mucilage but it varied greatly (from 1.3 to 11.2 %, Cv = 79 %). Factor analysis revealed two main factors. The factor 1 showed antagonism of AX, Ara, Xyl with pectins, Gal, and GalA. The factor 2 showed antagonism of HGA with Fuc and Ara: Xyl. Mann-Whitney U rank test showed the significant decrease of AX, Ara, Xyl and conversely the increase of GalA, Gal, HGA, RG1b and RG1b: AX in brown seeds. Yellow seeds had significantly higher percent of AX, Xyl, Fuc and conversely lower percent of RG1b, HGA, GalA and Gal. Lines homozygous for the gene s1 contained significantly more Glc, AX, Ara, Xyl and less Gal, RG1b, Rha, GalA at lower RGb: AX. No significant differences in the composition of mucilage for lines carrying genes YSED1 and pf1 were identified. For the first time, by nonparametric and multivariate statistics we revealed a complete difference between lines groups with brown seeds having the greatest load on the factor 1 (much pect, GalA and Gal) and yellow seeds, and also homozygotes for the gene s1 having the lowest load on the factor 1 (much AX, Ara, Xyl).