Annual Variation in the Effect of Red Light on Sterol Biosynthesis in Digitalis purpurea L.

Abstract

The effect of varying sequences of red and far red light on sterol biosynthesis in etiolated seedngs of Digtalis pwprea L. was examined.Red lght caused a marked increase in the amounts of free and glycosidic sterols and a small decrease in esterifled sterols during the first 4 hours after Unminatin Far red light elicited the same response but to a lesser degree. Exposure The biosynthesis of many terpene derivatives has been shown to be influenced by light. R has been found to stimulate carotene synthesis in etiolated seedlings of oat, barley, maize, mustard, tomatoes, and radishes (2,5,19,23,26). Synthesis of gibberellic acid, a diterpene, is enhanced by red light in wheat leaves (21). The synthesis of several chloroplast-related isoprenoids (vitamin K, tocopherols, plastoquinone, and solanesol) is also influenced by light (28). The effect of R on promoting carotene synthesis has been shown to occur through the intermediacy of phytochrome (2,5,19,23,26). On the other hand, sterol content of light-grown Digitalis purpurea and other seedlings is one-half that of darkgrown controls (7, 13).Sterols and carotenes are synthesized in different compartments within the cell: carotenes in the chloroplasts, and sterols in the cytoplasm (10,22 ence on carotene synthesis, it was of interest to determine whether the pigment also regulates sterol biosynthesis. We have conducted experiments over a period of 2.5 years on the effect of light on sterol content of D. purpurea seedlings. The seeds were stored in the dark at constant temperatures and the seedlings were germinated in the dark in controlled temperature rooms. Considerable variability was experienced from experiment to experiment but when the data were examined over a period of years, the effects of light appeared to follow an annual pattern. We reported previously that the sterol content of dark-grown seedlings is highest during the winter and spring and lowest during the summer and fall (14). It has now been demonstrated that the response of sterol biosynthesis to R varies inversely with the endogenous sterol content.MATERIALS AND METHODS Seeds. D. purpurea seeds were purchased from Burnett Brothers Seedsmen, New York. Three separate batches of seeds were used in these experiments. One, received in May, 1971, was used through April, 1972. The second, received in May, 1972, was used through and including June, 1973. The third, received in July, 1973, was used subsequently. The seeds were stored at 22 to 24 C in a dark room, and were not exposed to light until preparation for seeding. All three batches of seeds exhibited a period of null germination in April and May in the year of their use, but would resume germination in late May or June.Procedures have been described previously for sowing and harvesting of seedlings as well as for the extraction and preliminary separation of sterols into esterified and free plus glycoside fractions (14).Light Sources. The light sources used in these experiments were identical to those of Hopkins and Bonnell (11). The R had ...

Correlation of side chain mobility with cholesterol retention by phospholipid vesicles

“…They are readily soluble in nonpolar solvents such as petroleum ether and benzene and should be extractable from an aqueous lipid suspension with these solvents. We were therefore surprised to find that neither solvent would extract even a trace of sterol from a total lipid extract prepared from seedlings of Digitalis purpurea (1,2). In reviewing the methods used in the Digitalis studies for extraction of lipids, it appeared that we may have prepared a crude suspension of multilamellar vesicles (MLV) and that free sterols could have been incorporated into phospholipid bilayers.…”

How is sterol synthesis regulated in higher plants?

“…In an early study on the effect of light on plant isoprenoid synthesis Goodwin & Mercer (1963) found that although illumination of etiolated maize seedlings initiated synthesis of carotenoids there was no marked stimulation of sterol synthesis. By contrast, dark grown Digitalis purpurea (Jacobsohn & Frey, 1968) and etiolated maize seedlings (Hirayama & Suzuki, 1968) have a considerably higher sterol content than light grown plants. Similarly, Bush et al (1971) found that the total sterol and free sterol concentrations of etiolated barley shoots were a little higher than in green shoots.…”

“…Illumination of etiolated seedlings of Digitalis purpurea with red light increased the free sterol and steryl glycoside content and this response was also seen to a lesser extent after exposure VOl. 11 to far red light (Jacobsohn et al, 1978). It appeared that the response to red light may be seasonal and the greater stimulation in sterol biosynthesis occurs when the endogenous sterol concentration is low.…”

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

“…Some of the metabolic effects which are caused by light have been linked to the phytochromemediated systems (17). R light causes a marked increase in the amounts of free and glycosidic sterols and a small decrease in esterified sterols (21). FR light exerts the same influence, but to a lesser degree.…”