Sterol Accumulation and Composition in Developing Zea mays L. Kernels

Kernels were collected from three maize (Zea mays L.) inbreds from 10 days after pollination until kernel maturity. Sitosterol, campesterol, and stigmasterol were the major sterols at all stages of kernel development. Cholesterol was less than 1% of the dry weight. The three major sterols accumulated during kernel development, but at a rate slower than dry weight. The ratio of the sterols did not vary greatly among the inbreds. At maturity, the three inbreds, Wf9, Oh43, and Ky226, had sterol levels of 325, 228, and 173 micrograms per kernel, respectively. Sitosterol accounted for 75 to 85% of the sterol. The relative amount of stigmasterol decreased during the linear phase of development, while sitosterol increased in the free fraction and campesterol increased in the steryl ester fraction.     

Sterols,steryl esters and fatty acids in some Vicia faba seeds

Free and esterified sterol levels in seeds of five cultivars of Vicia faba were determined. Sitosterol was the most abundant free sterol, followed by stigmasterol and campesterol. Cholesterol could not be detected. Esters were generally present in greater quantities than the free form of the sterols. The fatty acid content of the plants is also reported.     

Sterols in hardening winter wheat

The main sterols in winter wheat crowns and roots were sitosterol and campesterol, with significant amounts of stigmasterol and traces of cholesterol. The main groups of sterol-containing lipids were free sterols, steryl glucosides, steryl esters and esterified steryl glucosides. Sterol analysis within each group showed little difference between them. Steryl esters were relatively rich in cholesterol and poor in stigmasterol. Free sterols were rich in stigmasterol. Low temperature caused an increase in sterol content but had little effect on sterol composition and sterol to lipid P ratio. There was some increase in steryl esters and some decrease in free sterols. Cholesterol and stigmasterol decreased in the steryl ester and free sterol fractions, respectively. There was little evidence for involvement of sterols in winter wheat frost hardening.     

Influence of Temperature on Sterol Biosynthesis in Triticum aestivum

Sitosterol, campesterol, stigmasterol, and cholesterol were isolated from green wheat (Triticium aestivum var. Monon) seedlings. Sitosterol was the predominant sterol extracted from the shoot, root, and crown tissue. Cholesterol accounted for less that 1% of sterol in shoot tissue with only trace amounts in the root. A temperature change from 10 to 1 C resulted in a general decrease in sitosterol, stigmasterol, and campesterol in the shoot tissue. The cholesterol level was not altered significantly by the temperature change. The sterols in the root responded in a manner very different from those in the shoots. With the reduction in temperature, sterols first decreased and then recovered over a period of 7 to 14 days to levels that were equal to or exceeded the original levels. From these experiments, it would appear that root tissue can acclimate to the lower temperatures and continue sterol synthesis at the normal rate. The level and response of sterols in the crown tissue were intermediate between the root and shoot tissue. At 10 C the crown response was similar to that of root tissue, whereas, at 1 C the response more closely resembled that of the shoot.     

Die quantitative verteilung der sterine und sterinderivate in organen von Solanum dulcamara

The following sterols were found in the roots, stems, leaves, unripe and ripe fruits of Solanum dulcamara: cholesterol, sitosterol, stigmasterol, campesterol, brassicasterol, isofucosterol and 24-methylenecholesterol. The most abundant components are cholesterol, sitosterol and stigmasterol (77–84%). In all parts of the plant the sterols are present in the free form and as esters, glycosides and acylated glycosides. The total sterol content and the content of combined forms were determined photometrically. In the leaves 58% of the sterols were found in the form of glycoside (26%), acylated glycoside (29%) and ester (2%). In the roots only 25% of the sterol were found in combined form. In the other organs the ratio of free and combined sterols was intermediate. In all cases, the ester fraction was the least.     

Biosynthesis of phytosterol esters: identification of a sterol o-acyltransferase in Arabidopsis

Fatty acyl esters of phytosterols are a major form of sterol conjugates distributed in many parts of plants. In this study we report an Arabidopsis (Arabidopsis thaliana) gene, AtSAT1 (At3g51970), which encodes for a novel sterol O-acyltransferase. When expressed in yeast (Saccharomyces cerevisiae), AtSAT1 mediated production of sterol esters enriched with lanosterol. Enzyme property assessment using cell-free lysate of yeast expressing AtSAT1 suggested the enzyme preferred cycloartenol as acyl acceptor and saturated fatty acyl-Coenyzme A as acyl donor. Taking a transgenic approach, we showed that Arabidopsis seeds overexpressing AtSAT1 accumulated fatty acyl esters of cycloartenol, accompanied by substantial decreases in ester content of campesterol and beta-sitosterol. Furthermore, fatty acid components of sterol esters from the transgenic lines were enriched with saturated and long-chain fatty acids. The enhanced AtSAT1 expression resulted in decreased level of free sterols, but the total sterol content in the transgenic seeds increased by up to 60% compared to that in wild type. We conclude that AtSAT1 mediates phytosterol ester biosynthesis, alternative to the route previously described for phospholipid:sterol acyltransferase, and provides the molecular basis for modification of phytosterol ester level in seeds.     

Genetic control of sterol esterification in developing wheat endosperm.

1. The action of gene Pln, previously characterized by the sterol ester patterns of mature whole wheat kernels, has been found to be restricted to the endosperm and not to affect the embryo, the pericarp or the seed coat. 2. The dominant allele Pln, which determines a sterol ester pattern with palmitate as the main ester, is also responsible for a low level of free sterol at maturity. A high level of free sterol is associated with the recessive allelet pln, which determines an ester pattern with linoleate as the main ester. 3. Divergence between the two phenotypes starts at about 21 days after anthesis, when cell proliferation has been completed, the aleurone layer has differentiated, and only cell enlargement is taking place. A marked increased in esterification, mainly by palmitate, which is controlled by the dominant allele, is concomitant with a sharp decrease in free sterol. 4. The increased net esterification is non-specific with respect to 4-demethyl sterols, because it affects the four main ones, namely sitosterol, stigmasterol, campesterol and cholesterol.     

Changes in Sterol Composition during Greening of Etiolated Barley Shoots

The following sterols were identified in barley shoots: stigmasterol, β-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 β-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 β-sitosterol in favor of stigmasterol; however, no correlation was observed between chlorophyll synthesis and shift in sterol composition.     

Sterol Changes during Germination of Nicotiana tabacum Seeds

The identity, composition, and concentration of the total, free, esterified, and glycosidic sterol fractions were determined during germination of tobacco seeds. The total, free, and esterified sterols increased, with stigmasterol and campesterol accounting for most of the increase. Steryl glycosides decreased during germination, and stigmasteryl and sitosteryl glycosides showed the largest decrease. During germination, sitosterol was the major sterol in all fractions but stigmasterol and campesterol showed the greatest changes. The fatty acid composition of the steryl esters and acylated steryl glycosides most closely resembled the di- and triglycerides.     

A dynamic role for sterols in embryogenesis of Pisum sativum

Molecular roles of sterols in plant development remain to be elucidated. To investigate sterol composition during embryogenesis, the occurrence of 25 steroid compounds in stages of developing seeds and pods of Pisum sativum was examined by GC-MS analysis. Immature seeds containing very young embryos exhibited the greatest concentrations of sterols. Regression models indicated that the natural log of seed or pod fr. wt was a consistent predictor of declining sterol content during embryonic development. Although total sterol levels were reduced in mature embryos, the composition of major sterols sitosterol and campesterol remained relatively constant in all 12 seed stages examined. In mature seeds, a significant decrease in isofucosterol was observed, as well as minor changes such as increases in cycloartenol branch sterols and campesterol derivatives. In comparison to seeds and pods, striking differences in composition were observed in sterol profiles of stems, shoots, leaves, flowers and flower buds, as well as cotyledons versus radicles. The highest levels of isofucosterol, a precursor to sitosterol, occurred in young seeds and flower buds, tissues that contain rapidly dividing cells and cells undergoing differentiation. Conversely, the highest levels of stigmasterol, a derivative of sitosterol, were found in fully-differentiated leaves while all seed stages exhibited low levels of stigmasterol. The observed differences in sterol content were correlated to mRNA expression data for sterol biosynthesis genes from Arabidopsis. These findings implicate the coordinated expression of sterol biosynthesis enzymes in gene regulatory networks underlying the embryonic development of flowering plants.     

Sterol distribution in intracellular organelles isolated from tobacco leaves

All membrane-containing fractions isolated from tobacco leaves contained free sterols, sterol glycosides, and sterol esters. The three sterol forms increased, on a dry weight basis, with a decrease in particle size. The supernatant fraction contained only trace amounts of sterol. The major sterols in all cellular fractions, in the order of decreasing amounts, were: stigmasterol, β-sitosterol, campesterol, and cholesterol. The 500g pellet contained the largest percentage of free sterol, while the 46,000g pellet contained the largest percentage of esterified sterol. The individual sterol composition of the free sterol and sterol glycoside fraction was very similar; however, the composition of the sterol ester fraction varied widely among intracellular fraction. The intracellular distribution pattern of cholesterol-¹⁴C added to the isolation medium provided evidence that the intracellular sterol distribution pattern is not an artifact. These results support the suggestion that sterols in plant cells may have a physiological function associated with membranes.     

Free sterols,steryl esters,glucosides, acylated glucosides and water-soluble complexes in Calendula officinalis

In 3- and 14-day-old seedlings and in the leaves of Calendula officinalis the following sterols were identified: cholestanol, campestanol, stigmastanol, cholest-7-en-3-β-ol, 24-methylcholest-7-en-3β-ol, stigmast-7-en-3β-ol, cholesterol, campesterol, sitosterol, 24-methylcholesta-5,22-dien-3β-ol, 24-methylenecholesterol, stigmasterol and clerosterol. Sitosterol was predominant in young and stigmasterol in old tissues. Young tissues contained relatively more campesterol but in old tissues a C₂₈Δ^5,22 diene was present suggesting transformation of campesterol to its Δ^5,22 analog, similar to that of sitosterol to stigmasterol. All the identified sterols were present as free compounds and also in the steryl esters, glucosides, acylated glucosides and water-soluble complexes. The variations in the amounts of these fractions in the embryo axes and cotyledons of 3- and 14-day-old seedlings and the distribution of individual sterols among the fractions are discussed.     

Foliar sterols in soybeans exposed to chronic levels of ozone

Soybeans (Glycine max) exposed to chronic levels of ozone showed a linear decrease in biomass with increasing concentration. The foliar free sterols increased while the steryl ester, and the steryl glycosides, a minor component, decreased with increasing pollutant concentration. Of the free sterols, stigmasterol showed the largest increase, followed by sitosterol; campesterol, however, decreased. All steryl esters decreased; sitosterol showed the largest decrease and campesterol the least.     

α-Onocerin and sterol content of twelve species of Ononis

The sterols and triterpenoids of 12 species of the genus Ononis were analysed by GLC. α-Onocerin was found in all but one of these species, although in some others its concentration was low. In all species examined, sitosterol was the major sterol; stigmasterol, campesterol, cholesterol and the triterpenoids cycloartenol and 24-methylene cycloartanol also occurred. The patterns of α-onocerin and sterols found seem to be consistent with the accepted classification of species within the genus.     

Sterol composition of dwarf and tall Pisum sativum seedlings in relation to gibberellic-acid-enhanced shoot growth

Gibberellic acid (GA₃) stimulated shoot elongation in both dwarf and tall cultivars of pea, but more so in the dwarf cultivar. The sterol composition of shoots of both cultivars was similar, with sitosterol being the most abundant compound, followed by stigmasterol and campesterol. Cholesterol could not be detected. Following GA₃ application, levels of free sterols in whole shoots increased whereas glycoside levels tended to fall. The magnitudes of the changes in both classes of sterol were similar in both cultivars. Analyses of stems and leaves separately revealed a greater growth response to GA₃ in the former but no effect of the hormone on the sterol composition of either organ. It is concluded that GA₃ enhancement of shoot growth in pea is not mediated through quantitative changes in cell sterols.     

Sterols of soybeans differing in insect resistance and maturity group

Eight soybean varieties and lines representing insect-susceptible and -resistant genotypes, and differing in plant maturity group, showed no difference in leaf dry wt. Over the growing season the total and bound sterols increased while the free sterols decreased. Sitosterol, stigmasterol and campesterol were the major sterols. Over the season sitosterol increased while stigmasterol decreased. No difference due to insect resistance could be established but early maturing plants showed a larger change in sterols.     

Triterpenes and sterols of Buxus sempervirens and local variations in their levels

The leaves of Buxus sempervirens L. contain sitosterol, stigmasterol, cycloartenol, lupeol, germanicol and β-amyrin in the free state. All of these compounds, except stigmasterol, were also found in the esters fraction, as were obtusifoliol, 24-methylenelophenol, and 24-ethylidenelophenol, The triterpene diois betulin and moradiol were isolated, the latter for the first time from a plant source. In nineteen Buxus samples from England, Wales and Scotland, the sterol compositions were quite similar while those of the triterpene monols varied considerably.     

Paclobutrazol inhibition of sterol biosynthesis in a cell suspension culture and evidence of an essential role for 24-ethylsterol in plant cell division

Growth of a celery (Apium gravidens) cell suspension culture was inhibited by the synthetic plant growth regulator paclobutrazol. Paclobutrazol caused a reduction in the incorporation of [2-14C]acetate into the 4-demethyl sterols (campesterol, sitosterol, stigmasterol) but radioactivity accumulated in the 4 alpha-methylsterols. The accumulating 4 alpha-methylsterols were identified as obtusifoliol and cycloeucalenol indicating that paclobutrazol was inhibiting sterol biosynthesis by blocking 14 alpha-demethylation. The inhibition of celery cell growth by paclobutrazol could be partially overcome by addition of cholesterol to the culture medium. However, addition of stigmasterol restored growth to the control value suggesting an essential role for a 24-ethylsterol to support plant cell division.     

Chilling and age related changes in the free sterol composition of Phaseolus vulgaris L. primary leaves

Chill-stressed or aged bean (Phaseolus vulgaris cv. 194) plants showed relative increase in the campesterol content of the primary leaves. Sitosterol/stigmasterol ratio declined significantly 24 h following transfer of chilled plants to warmer conditions. Sitosterol/stigmasterol varied markedly according to plant age, showing a decline during the leaf greening phase but an increase by the senescent (leaf-yellowing) phase.