Membrane structures in the integumentary cell walls of the ovule of Nerium oleander

Summary Ultrastructural changes in the integumentary cell walls of Nerium oleander L. were observed, starting with the beginning of nucellus degeneration. The cell walls in direct contact with the nucellus, followed in a regular progression by those of the next 2–3 cell layers, were seen to increase rapidly in thickness and, in contact with the plasmalemma, to develop a peculiar layer characterized by the presence of numerous membrane-like structures. Morphological and cytochemical findings indicate a membraneous nature of these wall structures; the structures exhibit a marked affinity to potassium permanganate, ruthenium red and phosphotungstic acid, and possess a three-layered configuration. Moreover, the structures were found to be disorganized by phospholipase C. Some of the wall structures appear to be pitted, sac-shaped formations; others to be single sheets. Both types exhibit a direct continuity with the plasmalemma after digestion of the wall material by cellulase. The origin and development of these structures are discussed.     

Compositional and Thermal Properties of Thylakoid Polar Lipids of Nerium oleander L. in Relation to Chilling Sensitivity

The polar lipid classes from thylakoids of Nerium oleander L. were studied with the aim of relating changes in their composition and thermal behavior with reported changes in the transition temperature of their polar lipids and chilling sensitivity of their leaves. With an increase in growth temperature, the transition temperature of phosphatidylglycerol increased from 16°C to 26°C, and for sulfoquinovosyldiacylglycerol from 19°C to 24°C. Transitions in the other lipid classes were below −10°C for plants grown at both growth temperature. The major changes in the molecular species of phosphatidylglycerol, with increasing growth temperature, were an increase in 1-oleoyl-2-palmitoyl phosphatidylglycerol from 21 to 39% and a decrease in 1-oleoyl-2-trans-3-hexadecanoic phosphatidylglycerol from 51 to 25%. Although the disaturated species increased from 8 to 23%, the maximum was less than that reported for chilling-sensitive plants. There was no change in the sum of the palmitic, hexadeca-trans-3-enoic and stearic acids. Dipalmitoyl sulfoquinovosyldiacylglycerol increased from 12 to 20% and 1-linolenoyl-2-palmitoyl sulfoquinovosyldiacylglycerol decreased from 40 to 30%. It is concluded that the increase in the transition temperature of the polar lipids and the sensitivity of acclimated oleander plants to chilling could not be predicted by the absolute sum of the saturated fatty acids or disaturated molecular species in phosphatidylglycerol. The polar lipid transition appears to be a product of mixing of both high and low melting-point lipids.     

Somatic embryogenesis and plant regeneration of Nerium oleander

Leaf explants of Nerium oleander L. produced masses of callus when both an auxin and a cytokinin were included in the medium. Leaves cultured on the B5 medium of Gamborg et al. supplemented with 2,4-dichlorophenoxyacetic acid (2,4-d; 9.05 M) plus benzyladenine (BA; 4.4 M) produced callus and profuse rhizogenesis was observed from callus developed from older leaves. On Murashige & Skoog medium (MS) with the same concentration of 2,4-d and BA, explants from young and mature leaves produced callus, but only that from young leaves was embryogenically competent. Globular somatic embryos were obtained when embryogenic cells were cultured on MS medium without growth regulators. Both normal and anomalous development of embryos occurred in either liquid or gelled medium. Plantlets were produced faster when mature embryos were cultured on either solid medium or placed on Sorbarod plugs soaked with this same medium but with 1% sucrose. Plantlets with three nodes were transferred to pots and acclimatized in a growth chamber and afterwards transferred to garden beds.     

Low Temperature-Induced Changes in the Thermotropic Properties and Fatty Acid Composition of the Plasma Membrane and Tonoplast of Cultured Rice (Oryza sativa L.) Cells

The thermotropic transitions of the plasma membrane and tonoplastfrom cultured cells of chilling-sensitive (CS) and chilling-insensitive(CI) strains of rice (Oryza sativa L.) were analyzed by monitoringthe fluorescence polarization of an embedded fluorophore, 1,6-diphenyl-1,3,5-hexatriene(DPH), and their relationship to the degree of unsaturationof fatty acids in phospholipids was examined. Polarization values (P) for the tonoplast from cultured cellsof CI rice, in contrast to those from CS rice, exceeded thosefor the plasma membrane. The values for the tonoplast and plasmamembrane from CI cells were somewhat higher than those fromCS cell. Thus, the tonoplast of CI cells has the lowest fluidity,while the fluidity of the tonoplast and plasma membrane of CIcells shows greater dependence on temperature. Arrhenius plotsof the fluorescence anisotropy parameter {(r_o/r)–1}–1of DPH in the plasma membrane and tonoplast from CI cells gavea slope that was virtually linear throughout the entire rangeof temperatures from 50°C to 10°C. However, in the caseof CS cells, a discontinuity was sometimes noted in the curvebetween 35°C and 30°C for tonoplast membranes. The activationenergy (E_a) of the anisotropy parameter of DPH in both the plasmamembrane and tonoplast from CI cells was greater than that fromCS cells. E_a in both cases for CS cells increased with increasingduration of exposure to low tempera ture (5°C), becomingnearly the same as that for CI cells. The proportion of unsaturated fatty acids, such as linoleicacid (18:2) and linolenic acid (18:3), in the total phospholipidsof the plasma membrane and tonoplast from CI cells was muchhigher than that from CS cells. In membranes from CS cells,this proportion also increased with increasing duration of exposureto low temperature and reached the value for membranes fromCI cells. In particular, in CS cells, the most dramatic changewas the change in PE and PC that in volved a sharp decreasein levels of 18:1, accompanied by an increase in 18:3. The proportionof unsaturated fatty acids was increased by exposure to lowtemperature, with an accompanying in crease in values of E_a. (Received April 10, 1991; Accepted May 9, 1992)     

Gangliosides and Other Lipids of the Growth Cone Membrane

Growth cone membranes, derived from growth cone particles isolated from 16- to 18-day-old fetal rat brain, were found to be rich in overall lipid content with a lipid-to-protein ratio of 3.5. The phospholipid-to-cholesterol ratio indicated considerably less cholesterol than plasma membranes from mature neurons. All major classes of phospholipid were present in the usual proportions except sphingomyelin, which could not be detected. Gangliosides expressed in relation to protein were present at somewhat higher levels compared to previously reported values for synaptic plasma membranes (73 versus 44 micrograms/mg protein), but when related to phospholipid their level was well below that of the latter (26 versus 62 micrograms/mg phospholipid). The ganglioside pattern was generally similar to that of mature synaptic membranes except for the presence of relatively more GD3 and less GD1a, a phenomenon also observed in whole fetal brain of the same age. Several neutral glycosphingolipids were detected, glucosylceramide being the major one of this group. Their total level in growth cone membranes was roughly comparable to that of gangliosides, but unlike the latter their concentration in whole brain decreased with development. For comparison we analyzed the ganglioside composition of mixed membrane fractions from the same fetal brains and found no significant differences between these and growth cone membranes, suggesting that these glycoconjugates are not localized specifically in the growth cones. Neutral glycosphingolipids, on the other hand, appeared somewhat more concentrated in growth cones than in the mixed membranes.     

Isolation and structure of two cardiac glycosides from the leaves of Nerium oleander

Two new cardiac glycosides, kaneroside and neriumoside, have been isolated from the fresh, undried, winter leaves of Nerium oleander and their structures established as 3β-O-(D-diginosyl)-2α-hydroxy-8,14β-epoxy-5β-carda-16:17,20:22-dienolide and 3β-O-(D-diginosyl)-2α,14β-dihydroxy-5β-carda-16:17,20:22-dienolide, respectively, through chemical and spectral studies.     

Alterations of Red Cell Membrane Properties in Nneuroacanthocytosis

Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington’s disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an “acanthocytic state” of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration.     

Characterisation of recombinant thermostable manganese-superoxide dismutase (NeMnSOD) from Nerium oleander

Superoxide dismutase is one of the key antioxidant enzymes accountable for the eradication of free radicals generated during various metabolic processes. This is first study reporting a thermostable MnSOD obtained from a xerophytic plant, Nerium oleander. The full-length gene identified using Rapid amplification of cDNA ends revealed an open reading frame of 699 bp flanked by 5′UTR and 3′UTR of 134 bp and 198 bp respectively. The corresponding NeMnSOD protein was cloned and expressed in Escherichia coli. The purified protein yields a band of 25.4 kDa, which established a specific activity of 2617 units mg^?1 of protein and under native condition yield bands of 52 kDa and 110 kDa, confirming the dimeric and tetrameric state of the protein. The Km and V_max of 0.078?±?0.008 mM and 1052.3?±?33.59 units mg^?1 of protein, respectively. The purified enzyme demonstrated thermostability by retaining more than 20% activity at a temperature 70 ℃. The enzyme functioned at pH range of 4–9.0 with maximum activity at pH 7.4. Sodium azide, effectively inhibited the activity of enzyme confirming it to be MnSOD. The enzyme activity was least affected on treatment with strong denaturants (Urea, guanidine HCl and SDS) and harsh chemicals (DTT, CHAPS and β-mercapto-ethanol) These experimental data validated with Insilco analysis revealed that NeMnSOD possessed thermo as well as kinetically stable moiety which can be further exploited with its applications in the field of pharmaceutical, food and cosmetic industry, which urge for such thermostable enzyme.

Graphic Abstract

     

Low Temperature-Induced Alterations in the Chloroplast and Microsomal Membranes of Dunaliella salina

The metabolic regulation of membrane lipid composition has been examined using the cell wall-less, unicellular green alga Dunaliella salina (UTEX 1644) as a model system. Low temperature stress was employed to initiate and study the regulatory response.     

光合膜膜脂的结构、特性与分子组装

本文就叶绿体光合膜中主要膜脂的分子结构及其特性和在膜中的分子组装进行了综述,并指出了目前膜脂研究的趋势和存在的问题。     

光合膜膜脂的结构、特性与分子组装

本文就叶绿体光合膜中主要膜脂的分子结构及其特性和在膜中的分子组装进行了综述,并指出了目前膜脂研究的趋势和存在的问题     

Membrane Lipids and the Conformations of Membrane Proteins

The general relations between protein conformation and the optical activity of peptide chromophores are outlined and applied to the analysis of the optical rotatory dispersion and circular dichroism of the plasma membranes of human erythrocytes and Ehrlich ascites carcinoma cells. It is concluded that the proteins of these membranes are "globular" and that they have considerable helical content. The spectroscopic consequences of perturbing the membranes with phospholipase C, phospholipase A, lysolecithin, and sodium dodecyl sulfate are examined in the light of the effects of these agents upon certain enzymatic and physical properties of the membranes and upon their proton magnetic resonance spectra. The data suggest that the architecture of membrane proteins is strongly dependent upon apolar lipid-protein and/or lipid-sensitive protein-protein interactions.     

Thermal Tolerance of Zymomonas mobilis: Temperature-Induced Changes in Membrane Composition

The membrane composition of Zymomonas mobilis changed dramatically in response to growth temperature. With increasing temperature, the proportion of vaccenic acid declined with an increase in myristic acid, the proportion of phosphatidylcholine and cardiolipin increased with decreases in phosphatidylethanolamine and phosphatidylglycerol, and the phospholipid/protein ratio of the membrane declined. These changes in membrane composition were correlated with changes in thermal tolerance and with changes in membrane fluidity. Cells grown at 20°C were more sensitive to inactivation at 45°C than were cells grown at 30°C, as expected. However, cells grown at 41°C (near the maximal growth temperature for Z. mobilis) were hypersensitive to thermal inactivation, suggesting that cells may be damaged during growth at this temperature. When cells were held at 45°C, soluble proteins from cells grown at 41°C were rapidly lost into the surrounding buffer in contrast to cells grown at lower temperatures. The synthesis of phospholipid-deficient membranes during growth at 41°C was proposed as being responsible for this increased thermal sensitivity.     

Temperature-Induced Phase Transitions in Nematode Lipids and Their Influence on Respiration

Temperature-induced phase transitions estimated by electron spin resonance (ESR) technique were ohscrved in the lipids of several nematode species. In both Meloidogyne javanica and Caenorhahditis elegans, there was a phase transition in their phospholipids from a liquid-crystalline state to a solid gel state at about 10 C. Aphelenchus avenae also had a phase transition, but at about 20 C. With this species, the spin-label motion parameters indicated the transition was from the liquid-crystalline state below 20 C to a more liquid or disordered state above 20 C. Anguina tritici and Meloidogyne hapla, in contrast, had no phase transitions over the entire temperature range studied. Each phase transition detected by ESR was reflected in the respiratory rates of the nematodes, and the temperature of the transition coincides with the environmental adaptation of these species.     

Alterations in Membrane Lipids and Nutrient Uptake during Root Development of Rape-Seed (Brassica napus L.)

Diepenbrock, W. 1988. Alterations in membrane lipids and nutrientuptake during root development of rape-seed (Brassica napusL.). J. exp. Bot. 39: 193–198. Oil-seed rape was grown hydroponically in two experiments. Inthe first one, the effects of root development on phosphorusbound in lipids (lipid-P) and on nutrient uptake were tested.The content of lipid-P in root tissue decreased markedly withtime. This decline was accompanied by reduced rates of nitrogenaccumulation in the shoot. In the second experiment, plantswere grown in a split-root system with two chambers per pot.A part of the root system was harvested at 28 d after seedlingtransfer (DAS) referring to ‘continuous growth’.The other part was cut at 14 DAS and roots from the same chamberwere gathered at 14 d after root cutting (DAR) referring to‘re-growth’ Not only at 14 DAS but also at 14 DARhigh concentrations of lipid-P were detected whereas at 28 DASthe lipid-P content decreased dramatically. Changes in lipid-Pwere reflected in the fluctuation of fatty acid compositionof phosphatidyl choline, a major phospholipid in root tissue.It was clearly demonstrated that during re-growth, nutrientuptake was intensified as compared to continuous growth. Generally,membrane lipids and nutrient uptake were closely related. Key words: Root, lipids, nutrient uptake     

Composition and Thermal Properties of Membrane Lipids in Cryptoendolithic Lichen Microbiota from Antarctica

In Antarctica there exists a cryptoendolithic microbiota which survives extremely low temperatures. Fatty acid analysis of the membrane phospholipids of this microbial community showed a predominance of polyunsaturated fatty acids. Artificial membranes made from the purified community phospholipids remained fluid to below −20°C and had unusual hydration properties.