Acylated steryl glycoside

Many changes in the lipid composition of the plasma membrane have been associated with hardening (Lynch Steponkus, 1987). In rye (cv. Puma) an increase of the total lipid content has been measured during hardening (Cloutier, 1987). Free sterols increased while steryl-glycoside and acylated steryl-glycoside decreased. In addition the phospholipid contents of the plasma membrane increased. 

Keywords Plant sterol phytosterol sterol conjugate steryl ferulate gamma-oryzanol steryl glycoside acylated steryl glycoside steryl ester free sterol. 

Figure 10.1 Examples of structural formulas of phytosterol and sterol conjugates. FS = free sterol alcohol, SE = sterol fatty acid ester, SF = steryl ferulate, SG = steryl glycoside, ASG = acylated steryl glycoside.

Phytosterols The relationship between total dietary phytosterol content and the fatty acid composition of the diet decreases with increasing saturated fatty acids, whereas the total dietary phytosterol content increases with increasing PUFA (86). Phytosterols consist of a mixture of cell membrane constituents that include free sterols, esterified steryls (e.g., esterified to phenolics), steryl glycosides, and acylated steryl glycosides (Table 2). 

Glycolipids of this type are synthesized in the chloroplast (Lawlor, 1993). Sulfoquinovosyl diglyceride (12) is widespread in leaves but usually occurs at low concentrations (Stumpf, 1976). This lipid is linked to S04 reduction in the chloroplast (Lawlor, 1993). Sterol esters and acylated steryl glycosides are also found in leaf lipids. 

Eichenberger, W., Steryl glycosides and acylated steryl glycosides, in Lipids and Lipid Polymers in Higher Plants (M. Tevini and H. K. Lichtenthaler eds.), 169-182, Springer-Verlag, Berlin, 1977. 

Sterols are substituted with an isoprenoid side chain at C-17 (Fig. 120). In plants they may be glycosylated (steryl glycosides) or acylated by fatty acids (steryl esters) at the C-3 hydroxy group. Acylated steryl glycosides, e.g., 6-0-palmitoyl-/8-D-glucosyl-sitosterol, also occur in plants. Sterols are grouped according to the pattern of methylation into 4,4-dimethylsterols, e.g., lanosterol and cycloartenol, 4a-methylsterols, e.g., obtusifoliol, and 4-demethylsterols, e.g., cholesterol. 

Phytosterols (PS) are plant sterols or stands found in plants. Plant sterols belong to the triterpene family and differ from cholesterol by having a methyl or ethyl group in C24. Plant stanols, on the other hand, are the saturated form of the plant sterols (Fig. 113.1). PS are present in free or conjugated form as fatty-acyl esters, hydroxycinnamate steryl esters, steryl glycosides, or acylated steryl glycosides. The main function of plant sterols/stanols is to stabilize plant membranes and serve as precursors in the synthesis of steroidal saponins, alkaloids, and other steroids [1]. 

Acylated steryl glycosides, e.g., 6-0-palmitoyl-P-D-glucosyl-sitosterol (Sticher 2007 and references therein)... 

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