Biochemistry of Plant Steroids

On the 7th day after soaking, 10-mm sections were cut from the third stem internode immediately below apical hooks which had just reached a 900 angle. Such sections were randomized by floating on water in a large Petri dish and 10 were later added to 20 ml of solution in a 10-cm Petri dish for each test. The sections were incubated in a basal medium composed of 1.5% sucrose, 5 mm KH2PO,, pH 5.5, and 50 jM CoCl, with emulsion stabilizer as noted below. When 1.8 /-M IAA and 0.3 /M GA are added, this medium supports maximal extension of pea stem sections under our conditions. After 20 to 24 hr of slow rotation on a shaker at 25 C in the dark room, the length of the sections was measured to the nearest tenth of a millimeter. Average lengths and standard deviations obtained for each dish were later correctly combined via addition of sum of the squares to obtain the average values in the tables which were usually based on three assays of each substance.Emulsification.

Section: Resultsmentioning

confidence: 99%

Probing a Membrane Matrix Regulating Hormone Action

Stowe

Dotts

1971

“…(12) suggested that sterodls in plants are merely waste products. This asstumption had not been qtuestioned uinitill recently when Heftmannii (9) expressed the view that steroids in plants may act much the same way as in anim,als. Steroids are said to act as hormones oni ceills and( cell constituients (16).…”

mentioning

confidence: 99%

Effect of Sterols on the Permeability of Alcohol-Treated Red Beet Tissue

Grünwald

1968

Abstract. Alcohols and hydrogen peroxide altered the permeability of membranes of Beta vulgaris root cells. Generally alcohols increased the permeability of membranes without going through an induction period except methanol which required a 10-to 15-hour induction period. The membrane effect of methanol could be inhibited with CaCl.,, cholesterol, /3-sitosterol, and stigmasterol. Cholesterol was the most effective inhibitor, foilowed by /3-sitosterol and stigmasterol; and at the same concentration, the sterols were more effective than CaCl,, the classic membrane stabilizer.Ergosterol increased the methanol-initiated betacyanin leakage. It has been suiggested that the transformation of the biological membrane from the open to closed Configultration is mainily due to the micella.r transfo-rmation of the lipidl componentis, which in tuirn is dependent tipioni the distribution o,f cations andl the natuire of the micelles (10). Leathes (ll) reported that cholesterol cauises a decrease of the area occ11-pied by the pho,spho-lipid (lecithin) molecufle anid WVinkle,r et al. (19)

“…only two hypotheses have any experimental support. The first hypothesis proposes that sterols, directly or indirectly, act in some way as plant hormone(s) (1,2,14,19,20). The second hypothesis considers sterols as structural components of plant membranes (3, 9-11, 14, 15, 18).…”

Section: Resultsmentioning

confidence: 99%

“…The results suggest that the cholesterol concentration of the tissue is critical, and that slight changes in sterol content could result in changes in permeability and function of membranes. The physiological picture is further complicated by the fact that in higher plants cholesterol is generally only a minor sterol component and the major sterols are sitosterol and stigmasterol (14). For ex- ample, in barley roots, cholesterol accounts for only 0.3% of the free sterols (11), which is about 1 jug of cholesterol per g of fresh weight, whereas sitosterol and campesterol are the major sterols in this tissue (1 1).…”

Section: Resultsmentioning

confidence: 99%

“…6B). The latter two sterols are the major higher plant sterols (14), and their inability to influence membrane permeability was at first disturbing, especially because both sterols were active in a red beet system (9) and in the pea bioassay oleanimin test (17 (16,21) depends upon the fatty acid composition and pairing in the lecithin molecule (5). As previously pointed out (9), if sterols in higher plants actually play a role in the structure and function of membranes then the particular sterol, or combination of sterols, that are involved in any specific case will be determined by all the functions of the membranes and not by only one function.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Sterol Molecular Modifications Influencing Membrane Permeability

Grünwald¹

1974

Various sterols and related steroids were tested for their ability to influence ethanol-induced electrolyte leakage fron Hordeunm vulgare roots. Cholesterol had the greatest influence and, depending on concentration, it stimulated or inhibited the loss of electrolyte. Cholesterol, however, was ineffective if the roots were pretreated with ethanol. These data suggest that sterols protect rather than restore membrane structure. First, modifications in the cholesterol perhydrocyclopentanophenanthrene ring system suggest that at least one double bond is required for membrane activity. Second, increasing the bulkiness of the C1 side chain of cholesterol, as shown with campesterol, stigmasterol, and sitosterol, decreased its activity. Apparently for maximum effectiveness the sterol molecule should have a relatively flat configuration. Third, the C3-hydroxyl group is required for membrane activity since cholesteryl methyl ether, cholest-5-ene-3g-thiol and cholesteryl halogens were without activity. Exception to the foregoing rule was cholestane which was slightly active but which has neither a C3-hydroxyl group nor a double bond in the ring system. In previous publications it was reported that exogenously applied cholesterol, and certain other higher plant sterols, modified the permeability of plant cells (9,11,15). To explain the action of sterols on plant membranes, a hypothesis which incorporated the results of animal and phospholipid film experiments (5-7, 13, 16, 21, 26, 27) was proposed. Briefly, it was suggested that cholesterol, or other sterols, insert themselves into the phospholipid layer of the membrane, with the C.-hydroxyl group interacting by weak ion-dipole-and hydrogen-bonding with the polar nitrogenous base moiety of the phospholipid. In this model, the C, side chain of cholesterol would align itself along the nonpolar terminal of the phospholipid, filling the phospholipid cavity and in turn stabilizing the lipid configuration. According to this hypothesis, the Chydroxyl group of the sterol molecule is an important functional group. This hypothesis would explain why only the free sterols were active and not the steryl esters and steryl glycosides (9,11), all of which are common higher plant constituents. However, sterol analogs with a small polar group in the C. posi- tion, other than a hydroxyl, have never been tested. The foregoing hypothesis of sterol action also assumes that for effectiveness, the sterol molecule must have a flat configuration similar to that of cholesterol (7,26). This requirement was confirmed partially with sterols that differed in branching in the C17 side chain (9, 1 1), but in this respect sterols with modifications in the perhydrocyclopentanophenanthrene ring system have not been studied.For purposes of studying the mechanism of sterol action on plant membranes, cholesterol can be taken as the basic molecule, and this molecule can be divided into three sites of possible physiological importance (Fig. 1). The cholesterol nucleus consisting of ring A, B, C, and D with...