Genome relationship betweenPsathyrostachys huashanica andP. fragilis (Poaceae)

Hybrids between the Chinese endemic speciesPsathyrostachys huashanica Keng and the SW. Asian speciesP. fragilis (Boiss.)Nevski (all 2n = 14) developed normally but were completely sterile. Meiotic analyses revealed a high chiasma frequency indicating that the two species as well asP. juncea (Fisch.)Nevski share the same basic genome (called N). The hybrid nature of the plants was established through karyotype analysis and Giemsa C-banding.     

The effect of low- and high-density lipoprotein cholesterol on steroid hormone production and ACTH-induced differentiation of rat adrenocortical cells in primary culture

Summary The choroid plexus consists of the choroidal epithelium, a derivative of the neural tube, and the choroidal stroma, which originates from the embryonic head mesenchyme. This study deals with epithelio-mesenchymal interactions of these two components leading to the formation of the organ. Grafting experiments of the prospective components have been performed using the quail-chicken marker technique. Prospective choroidal epithelium of quail embryos, forced to interact with mesenchyme of the body wall of chicken embryos, gives rise to a choroid plexus showing normal morphogenesis and differentiation. The choroidal epithelium induces the differentiation of organtypical fenestrated capillaries, which are highly permeable to intravenously injected horseradish peroxidase. The choroidal epithelium of the grafts constitutes a blood-cerebrospinal fluid barrier. On top of the choroidal epithelium, there are epiplexus cells displaying a typical ultrastructure. The experimental results show that these cells do not originate from the transplanted neural epithelium. Prospective choroidal stroma of chicken embryos does not exert a choroid plexus-inducing influence upon a quail embryo's neural epithelium isolated from parts of the brain that normally do not develop a choroid plexus. The experiments show that the choroidal epithelial cells are determined at least three days before the first organ anlage is detectable.This work was supported by the Deutsche Forschungsgemeinschaft (grant Ch 44/7-1)     

Effects of endogenous and exogenous cholesterol on the ultrastructure and steroid secretion of undifferentiated rat adrenocortical cells in primary culture

Summary The present study was undertaken to define the effects of lipoprotein-derived cholesterol and endogenous, de novo synthesized cholesterol on the ultrastructure and function of undifferentiated rat adrenocortical cells [lipoprotein (HDL₃ and LDL) receptor-negative, zona glomerulosa-like adrenocortical cells] in primary culture. For this purpose human plasma high density lipoprotein (HDL₃) or low density lipoprotein (LDL) was added to culture medium devoid of cholesterol. Steroid secretion remained at the low basal level even after addition of lipoproteins, and the amount of intracellular lipid droplets did not increase. When mevinolin (0.96 µg/ml), an inhibitor of cholesterol synthesis, was added to the culture medium, a low secretion of corticosterone was measured both in serum-free and serum-containing media. Ultrastructurally, lipid droplets disappeared after treatment with mevinolin in both media used. At this concentration of mevinolin cell proliferation was similar to that in the controls, but at higher concentrations (4.8 or 9.6 µg/ml) proliferation was inhibited to 42% and 26% in serum-free medium, and 20% and 12% in serum-supplemented medium, respectively. This study demonstrates that cell proliferation and synthesis of corticosterone by undifferentiated rat adrenocortical cells is identical in the absence or presence of exogenous lipoprotein cholesterol. Inhibition of de novo cholesterol synthesis by mevinolin over a period of 7 days does not inhibit corticosterone secretion or proliferation of cells but decreases the amount of intracellular lipid droplets, thus suggesting utilization of intracellular cholesterol esters. However, higher concentrations of mevinolin inhibit proliferation of cells both in serum-free and serum-containing media.     

An acetyl esterase of Trichoderma reesei and its role in the hydrolysis of acetyl xylans

Summary An acetyl esterase was purified from Trichoderma reesei by cation and anion exchange chromatography. The enzyme had a molecular weight of 45 000 as determined by SDS-electrophoresis, or 67 000 as determined by gel filtration. In chromatofocusing the enzyme was shown to consist of two isoenzymes with isoelectric points of 6.8 and 6.0. The enzyme showed activity towards naphthyl acetate, triacetin and glucose-and xylose acetates. However, it liberated acetic acid from acetylated xylo-oligomers only to a small extent. The liberation of acetic acid from the oligomeric substrate was enhanced by addition of endoxylanase and -xylosidase.     

Endogenous cholesterol synthesis is sufficient for ACTH-induced differentiation of rat adrenocortical cells in primary culture

Summary To define the role of endogenously synthesized cholesterol in the differentiation of adrenocortical cells in primary culture, fetal rat adrenal cells were cultured in the presence of exogenous cholesterol (serum-supplemented medium) or in the absence of it (serum-free medium or lipoprotein-free medium). Ultrastructurally the cells had features of glomerulosa cells: mitochondria were oval or rod shaped with lamellar inner membranes. The amount of smooth endoplasmic reticulum was small, and lipid droplets were few. When the cells were cultured in serum-free medium some intracytoplasmic vacuoles were seen. The undifferentiated zona glomerulosa-like cells secreted low amounts of corticosterone and 18-OH-deoxycorticosterone (18-OH-DOC) in all three media (serum-supplemented medium, serum-free medium, and lipoprotein-free medium). Stimulation of the adrenocortical cells with ACTH induced the ultrastructural features of differentiated zona fasciculata-like cells. Mitochondrial inner membranes were well developed in lipoprotein-free medium, but not in serum-free medium. The amount of intracellular lipids was increased in both media devoid of cholesterol. In the ACTH stimulated cultures the presence of exogenous cholesterol resulted in increased secretions of corticosterone and 18-OH-DOC. In the absence of an exogenous source of cholesterol, the amounts of steroids secreted were only half of that secreted in the presence of serum-supplemented medium. Endogenously synthesized cholesterol is sufficient for the morphologic differentiation of fetal rat adrenocortical cells under ACTH stimulation. However, without exogenously provided cholesterol, the steroid production accounts only for half of the maximal output achieved using serum-supplemented medium. This work was supported by Finnish Culture Foundation.     

Membrane associated events during proliferative inhibition of granulocyte precursors

A new way of assessing the significance of intracellular signals that may regulate cellular proliferation, would be to analyze possible 'second messengers' when proliferation is slowed down, rather than stimulated. Therefore, we examined proliferating mononuclear blood cells from leukaemic patients which had been exposed to an inhibitory ox leucocyte extract. The extract decreased 3H-thymidine incorporation in leukaemic cells in short-term cultures. The inhibition was not cell-line specific, but was nevertheless non-toxic and not due to endotoxin. The K+ flux into the leukaemic cells was assessed with 86Rb+, a K+ analogue. An inverse relationship was found between 86Rb+ uptake and 3H-thymidine incorporation. The increased 86Rb+ influx was probably due to leakage or exchange mechanisms other than the Na+/K+ membrane pump, as suggested by ouabain inhibition experiments. However, the long lag time (greater than 45 min) between addition of inhibitor and a marked increase in 86Rb+ uptake does not support a role for the K+ flux as an early mediator of the inhibitory signal.     

Expression of genes for plastid membrane proteins in barley under intermittent light conditions

Barley plants grown under intermittent light show a plastid membrane composition intermediate between those of etioplasts and chloroplasts. In particular protochlorophyll reductase disappears from the membranes whereas the 32000 protein, coded for by chloroplast DNA, becomes integrated into the membranes. The light-harvesting chlorophyll a/b protein does not accumulate within the membranes even after 11 d of development, while the corresponding mRNA can already be observed after 4 d and is translated under in vivo conditions.Abbreviations LHCP light-harvesting chlorophyll a/b protein - IL intermittent light - LD light-dark (12-h day) - EGTA ethyleneglycol-bis(oxy-ethylenenitrile)tetraacetic acid