Changes in Sterol Composition during Greening of Etiolated Barley Shoots

Abstract

The following sterols were identified in barley shoots: stigmasterol, 8-sitosterol, campesterol, and cholesterol. The total sterol content of green and etiolated tissue was 2.84 and 3.20 milligrams per gram dry weight, respectively. The free sterols accounted for most of the difference in total sterol content. The sterol ester, sterol glycoside, and acylated sterol glycoside contents of green and etiolated barley shoots were essentially the same. Etiolated tissue had twice as much total 8-sitosterol as stigmasterol, while green tissue had equal amounts of these two sterols. The campesterol and cholesterol content was the same in green and etiolated tissue. This same sterol composition pattern held true for the free, glycosidic, and acylated glycosidic sterols; however, the sterol ester fraction had a completely different composition pattern. The esterified stigmasterol content was quite low in green and etiolated tissue, and campesterol was the second largest esterfied sterol component in etiolated tissue. Etiolated barley seedlings exposed to light had a shift in the ratio of free stigmasterol to 6-sitosterol in favor of stigmasterol; however, no correlation was observed between chlorophyll synthesis and shift in sterol composition. Goodwin and Mercer (8) The barley shoots were homogenized in twice the amount of acetone (w/v) and extracted in a Soxhlet apparatus for 24 hr. A measured aliquot of acetone extract (about 5 g dry weight equivalent) was taken to dryness under vacuum and applied in n-hexane to a silica gel column for serial elution (7,22). A 1.5-cm diameter column was packed with 30 g of silica gel (70-325 mesh) as a slurry in n-hexane. Serial elution was carried out as follows: 150 ml of n-hexane followed by 150 ml of 10% benzene in n-hexane (discard); 700 ml of 40% benzene in nhexane (sterol esters); 150 ml of 100% benzene followed by 800 ml of chloroform (free sterols); 700 ml of 2% methanol in chloroform (acylated sterol glycosides); and 600 ml of 5% methanol in chloroform (sterol glycosides). The four sterolcontaining fractions were taken to dryness under vacuum. Added to the sterol ester fraction were 30 ml of 5% KOH in 95% methanol, and the fraction was refluxed for 30 min to hydrolyze the ester linkage. The free sterol fraction was dissolved in 30 ml of 95% methanol and heated for a few minutes. Added to the acylated sterol glycoside and sterol glycoside fraction were 30 ml of 95% methanol containing 0.15 ml H2SO4, and the fraction was refluxed for 12 hr to hydrolyze the glycosides.Analysis for total sterols was carried out by a modified method of Stedman and Rusaniwskyj (24). A measured aliquot (about 5 g dry weight equivalent) of acetone extract was taken to dryness and 25 ml of 95% ethanol containing 0.13 ml H2SO4 were added to the sample, refluxed for 12 hr, and cooled; then 15 ml of 10% KOH in 95% ethanol were added and the fraction was refluxed for 30 min. This sample gave total sterols since all glycosides and esters had been hydrolyzed.The sterols were extracted from all the ...

Effects of Free Sterols, Steryl Ester, and Steryl Glycoside on Membrane Permeability

“…Furthermore, it has been reported that the steryl ester composition of greening barley shoots was quite different from the free sterols (1). However, in this same study the steryl glycosides were very similar in composition to the free sterols, making this sterol form the more likely for translocation.…”

Sterol Composition and Accumulation in Glycine max (L.) Merr Leaves under Different Filtered Sunlight Conditions

“…This higher sterol content in mature tobacco and in Solanum andigena leaves was mainly due to an increase in free sterols (1,15), whereas, in Solanum tuberosum, glycosidic sterols accounted for most of the increase (10). In the experiment presented here, the free sterols are the dominant form and this agrees with other authors (6,15,25) and our own previous work (26) with other plant leaves. During this experiment, however, this fraction did not show an increase with plant age.…”

“…In the experiment presented here, the amounts of esterified and glycosidic sterols are lower than those observed by Bush et al (6) in barley shoots and by Grunwald (15,16) in tobacco leaves. In tobacco, the steryl esters decreased slightly with plant age and the quantities of esterified and glycosidic sterols were of the same magnitude (15).…”

“…The total sterol content was always higher than the summation of free, esterified, and glycosidic sterols (Table II) as we reported previously with Vicia sativa leaves (26) and as other authors have found with barley shoots (6) and Nicotiana tabacum seedlings (4).…”

“…Recent studies carried out with green seedlings show that sterol synthesis from mevalonic acid is greatly influenced by light (4,5) and the accumulation of the sterols is higher in dark grown dlings (6). However, not all reports agree.…”