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

A galactomannan-driven enhancement of the in vitro multiplication rate for the Marubakaido apple rootstock (Malus prunifolia (Willd.) Borkh) is not related to the degradation of the exogenous galactomannan

Agar is a complex mixture of gel-forming polysaccharides. Gelling agents are very often used to provide proper support for plants grown in semisolid culture media. And agar is the most frequently used gelling agent in plant tissue culture media. Galactomannans, another group of gel-forming polysaccharides, consists of a (1 → 4)-linked β-D: -mannopyranosyl backbone partially substituted at O-6 with D: -galactopyranosyl side groups. In this work, we demonstrate that a statistically significant 2.7-fold increase on the multiplication rate (MR) for in vitro-grown Marubakaido (Malus prunifolia) shoots was associated with a 12.5% replacement of agar in the semi-solid culture media for a galactomannan obtained from seeds of Schizolobium paraybae. This increase on MR was due mainly to a 1.9-fold increase in the number of main branches and an 8.6-fold increase in the number of primary lateral branches. Gas liquid chromatography and thin layer chromatography analyzes demonstrated that the galactomannan-driven enhancement of the in vitro multiplication rate of the Marubakaido apple rootstock was not related to the galactomannan degradation. To the best of our knowledge, this is the first report on the successful use of partial replacement of high quality agar by a galactomannan from S. paraybae in a micropropagation system for a tree species.

Molecular order and dynamics of phosphatidylcholine bilayer membranes in the presence of cholesterol, ergosterol and lanosterol: a comparative study using 2H-, 13C- and 31P-NMR spectroscopy

We report the results of a comparative study of the molecular order and dynamics of phosphatidylcholine (PC) bilayer membranes in the absence and presence of cholesterol, ergosterol and lanosterol, using deuterium (2H) nuclear magnetic resonance (NMR) of deuterated phospholipid molecules, in addition to solid state 13C and 31P-NMR. Using dimyristoylphosphatidylcholines (DMPCs) specifically labeled at positions 2', 3', 4', 6', 8', 10' and 12' of the sn-2 chain together with the perdeuterated 2-[2H27]DMPC derivative, the order profile for 9 of the 13 methylene groups of the sn-2 chain was established at 25 degrees C for DMPC, DMPC/cholesterol, DMPC/ergosterol and DMPC/lanosterol membranes, at a fixed sterol/phospholipid mol ratio of 30%, and in the presence of excess water. The overall ordering effects were found to be ergosterol > cholesterol >> lanosterol. Transverse relaxation (T2e) studies of these systems indicated that while for DMPC, DMPC/cholesterol and DMPC/ergosterol the relative relaxation rates were in qualitative agreement with models which assume cooperative motions of the bilayer molecules as the main relaxation mechanism, those in DMPC/lanosterol were anomalously high, suggesting alterations of lipid packing. Using dipalmitoylphosphatidylcholine (DPPC) deuterated at the trimethylammonium group of the choline moiety, we found that the differential ordering and motional effects induced by the sterols in the acyl chains were also reflected in the headgroup, both in the gel (L beta) and liquid-crystalline phases. 13C and 1H spin dynamics studies of these systems, including cross-polarization, rotating frame longitudinal relaxation and dipolar echo relaxation rates showed that the mobility of the different regions of the phospholipid molecules in the binary lipid systems were inversely correlated with the ordering effects induced by the sterols. A novel combination of C-D bond order parameters (obtained by 2H-NMR) and 13C-1H cross polarization rates confirmed these results. The effects of the same sterols at the same molar proportion on the unsaturated lipid 1-[2H31]palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (2H31-POPC) at 25 and 35 degrees C were different from those observed on DMPC and showed ordering effects which are largest for cholesterol, while ergosterol and lanosterol produced significantly smaller effects. Transverse relaxation studies indicate that while cholesterol does not perturb cooperative motions in POPC, both ergosterol and lanosterol do. Again, high-resolution solid state 13C-NMR studies support the conclusions of the 2H-NMR experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of antimycotic azoles on growth and sterol biosynthesis of Leishmania promastigotes

Promastigotes of 36 World Health Organization reference (and other) strains of 6 species and 10 subspecies of Leishmania were cultured in the presence of 3 antimycotic azole drugs (ketoconazole, itraconazole, fluconazole) and their population growth determined. A representative of each subspecies was also analyzed for its sterol composition. For all strains the order of azole drug activity with respect to both growth and sterol biosynthesis inhibition was itraconazole greater than or equal to ketoconazole greater than fluconazole. The inhibitory actions of the three azole drugs were greater on L. donovani and L. braziliensis subspecies and on L. mexicana amazonensis than on L. aethiopica, L. major, L. tropica and L. mexicana mexicana. The nature of the changes in sterol composition caused by the drugs was the same for all strains. The normal, major endogenous sterols of the promastigotes (5-dehydroepisterol and ergosterol) were reduced in amount to 1-2% of the total free sterols and were replaced by endogenous 14 alpha-methyl sterols and exogenous cholesterol. The changes occurred rapidly, were drug concentration dependent and coincided with growth inhibition. Six strains of those Leishmania species less sensitive to the azole drugs could be subcultured indefinitely at reduced growth rates in the presence of a ketoconazole concentration causing the same extraordinary alterations in sterol composition. This suggested that the bulk membrane functions of sterols in leishmanias can be served by 14 alpha-methyl sterols and cholesterol, albeit imperfectly, while traces of 14 alpha-desmethyl sterols are needed for uncharacterized metabolic functions.