Glycosides steryl

Cell suspension cultures of Gypsophila paniculata and Saponaria officinalis produce very closely related triterpenoid saponins. Pretreatment of cell suspension cultures of G. paniculata with gypsogenin 3,0-glucuxonide (a triterpenoid saponin precursor in G. paniculata) followed by administration of [ C] acetate resulted in a marked reduction in incorporation of radioactivity into saponins and their precursors, but not into sterols and steryl glycosides [26]. Measurements of OSC activities revealed that there was no effect of elicitor treatment on CS levels in either species, but in G. paniculata AS levels went down while in S. officinalis they increased. This suggests that in these two species OSCs are regulating steps in the isoprenoid pathway and control the flux to sterols and triter-penes. 

The main problem in this approach is the very low permeability of mevalonic acid to membranes, resulting in very low incorporation. Positive results have been obtained by the use of cell-free systems incubated with [14C]-mevalonic acid,26,27 [14C]isopentenyl diphosphate,28 or [32P]orthophos-phate.29 Incubation of these radioactive lipids with glycosyl nucleotides labelled in the glycosyl group with a different isotope, followed by extraction and cochromatography in different solvent systems, may indicate that both compounds are present in the same molecule. When the lipid moiety becomes labelled from mevalonic acid or isopentenyl diphosphate, chromatography on DEAE-cellulose columns should be performed, in order to avoid confusion with steryl glycosides. 

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.

Gutierrez, A. del Rio, J.C. 2001. Gas chromatography/mass spectrometry demonstration of steryl glycosides in eucalypt wood, Kraft pulp and process liquids. Rapid Comm. Mass Spectrom. 15 2515-2520. 

Kesselmeier, J. Eiehenberger, W. Urban, B. 1985. High performance liquid chromatography of molecular species from free sterols and steryl glycosides isolated from oat leaves and seeds. Plant Cell Physiol. 26 463-471. 

Nystrom, L. Lampi, A.-M. Rita, H. Aura, A.-M. Oksman-Caldentey, K.-M. Piironen, V. 2007h. Effects of processing on availability of total plant sterols, steryl ferulates and steryl glycosides from wheat and rye bran. J. Agric. Food Chem. 55 9059 9065. 

Nystrom, L. Moreau, R.A. Lampi, A.-M. Hicks, K.B. Piironen V. 2008. Enzymatic hydrolysis of steryl ferulates and steryl glycosides. Eur. Food Res. Tech. 227 727-733. 

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. 

In Chapter 15, the biosynthesis of phytosterols was described. Briefly some of the major sterols found in plants are shown in Fig. 1. Principal differences are in the side chain (C20-CJ7) which has different degrees of substitution and unsaturation. The sterol derivatives, also shown in Fig. 1, are (1) steryl esters (SEs), in which a long-chain fatty acid is esterified at the 3-OH of the sterol, (2) steryl glycosides (SGs) in which the 3-OH of the sterol forms a glycosidic linkage to the 1-position of a monosaccharide, usually glu-... 

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. 

---