Biosynthesis of Callose and Cellulose by Detergent Extracts of Tobacco Cell Membranes and Quantification of the Polymers Synthesized in vitro

The conditions that favor the in vitro synthesis of cellulose from tobacco BY-2 cell extracts were determined. The procedure leading to the highest yield of cellulose consisted of incubating digitonin extracts of membranes from 11-day-old tobacco BY-2 cells in the presence of 1 mM UDP-glucose, 8 mM Ca2+ and 8 mM Mg2+. Under these conditions, up to nearly 40% of the polysaccharides synthesized in vitro corresponded to cellulose, the other polymer synthesized being callose. Transmission electron microscopy analysis revealed the occurrence of two types of structures in the synthetic reactions. The first type consisted of small aggregates with a diameter between 3 and 5 nm that associated to form fibrillar strings of a maximum length of 400 nm. These structures were sensitive to the acetic/nitric acid treatment of Updegraff and corresponded to callose. The second type of structures was resistant to the Updegraff reagent and corresponded to straight cellulose microfibrils of 2-3 nm in diameter and 200 nm to up to 5 μm in length. In vitro reactions performed on electron microscopy grids indicated that the minimal rate of microfibril elongation in vitro is 120 nm/min. Measurements of retardance by liquid crystal polarization microscopy as a function of time showed that small groups of microfibrils increased in retardance by up to 0.047 nm/min per pixel, confirming the formation of organized structures.     

Inhibitory effects of the antiprogestin, RU 486, on progesterone actions and luteinizing hormone secretion in pituitary gonadotrophs

The effects of RU 486 on the modulation of LH release by progesterone were investigated in cultured anterior pituitary cells from ovariectomized adult female rats. The inhibitory effect of progesterone on LH secretion was demonstrable in estrogen-treated pituitary cells, in which addition of 10(-6) M progesterone to cells cultured in the presence of 10(-9) M estradiol for 52 h reduced the LH response to GnRH (10(-11) to 10(-7) M). When RU 486 was superimposed upon such combined treatment with estradiol and progesterone, the suppressive effect of progesterone on GnRH-induced LH release was completely abolished. The converse (facilitatory) effect of progesterone on LH secretion was observed in pituitary cells pretreated with 10(-9) M estradiol for 48 h and then with 10(-6) M progesterone for 4 h. When RU 486 was added together with progesterone during the 4 h treatment period, the facilitatory effect of progesterone was blocked and LH release fell to below the corresponding control value. The direct effect of RU 486 on LH secretion in the absence of exogenous progesterone was evaluated in cells cultured in the absence or presence of 10(-9) M estradiol and then treated for 4 to 24 h with increasing concentrations of RU 486 (10(-12) to 10(-5) M) and stimulated with GnRH (10(-9) M) during the last 3 h of incubation. In estrogen-deficient cultures, 4 h exposure to RU 486 concentrations of 10(-6) M and above decreased the LH response to GnRH by up to 50%. In cultures pretreated with 10(-9) M estradiol, GnRH-stimulated LH responses was inhibited by much lower RU 486 concentrations, of 10(-9) M and above. After 24 h of incubation the effects of RU 486 were similar in control and estradiol-pretreated pituitary cell cultures. Thus, RU 486 alone has a significant inhibitory effect on LH secretion that is enhanced in the presence of estrogen. The antiprogestin is also a potent antagonist of both the inhibitory and the facilitatory actions of progesterone upon pituitary gonadotropin release in vitro.     

Cytomechanical properties of papaver pollen tubes are altered after self-incompatibility challenge

Self-incompatibility (SI) in Papaver rhoeas triggers a ligand-mediated signal transduction cascade, resulting in the inhibition of incompatible pollen tube growth. Using a cytomechanical approach we have demonstrated that dramatic changes to the mechanical properties of incompatible pollen tubes are stimulated by SI induction. Microindentation revealed that SI resulted in a reduction of cellular stiffness and an increase in cytoplasmic viscosity. Whereas the former cellular response is likely to be the result of a drop in cellular turgor, we hypothesize that the latter is caused by as yet unidentified cross-linking events. F-actin rearrangements, a characteristic phenomenon for SI challenge in Papaver, displayed a spatiotemporal gradient along the pollen tube; this suggests that signal propagation occurs in a basipetal direction. However, unexpectedly, local application of SI inducing S-protein did not reveal any evidence for localized signal perception in the apical or subapical regions of the pollen tube. To our knowledge this represents the first mechanospatial approach to study signal propagation and cellular responses in a well-characterized plant cell system. Our data provide the first evidence for mechanical changes induced in the cytoplasm of a plant cell stimulated by a defined ligand.     

Intrusive growth of flax phloem fibers is of intercalary type

Flax (Linum usitatissimum L.) phloem fibers elongate considerably during their development and intrude between existing cells. We questioned whether fiber elongation is caused by cell tip growth or intercalary growth. Cells with tip growth are characterized by having two specific zones of cytoplasm in the cell tip, one with vesicles and no large organelles at the very tip and one with various organelles amongst others longitudinally arranged cortical microtubules in the subapex. Such zones were not observed in elongating flax fibers. Instead, organelles moved into the very tip region, and cortical microtubules showed transversal and helical configurations as known for cells growing in intercalary way. In addition, pulse-chase experiments with Calcofluor White resulted in a spotted fluorescence in the cell wall all over the length of the fiber. Therefore, it is concluded that fiber elongation is not achieved by tip growth but by intercalary growth. The intrusively growing fiber is a coenocytic cell that has no plasmodesmata, making the fibers a symplastically isolated domain within the stem. Electronic Supplementary Material Supplementary material is available for this article at     

Modulatory actions of the new antiprogestins ZK 98.299 and ZK 98.734 and of RU 486 on luteinizing hormone secretion and progesterone effects in pituitary gonadotrophs

The effects of the antiprogestins (APs) ZK 98.299, ZK 98.734 and RU 486 on GnRH-stimulated LH secretion and their antagonistic activity on progesterone (P) actions were investigated in cultured pituitary cells from adult female Wistar rats. P (100 nM) was able to exert a facilitatory effect on GnRH (1 nM)-induced LH secretion after short-term (4 h) treatment of estradiol-primed (1 nM, 48 h) rat pituitary cells. When the APs (10 pM-10 microM) were introduced during the 4 h incubation period with P the facilitatory effect of P was totally abolished at concentrations greater than 10 nM (ZK 98.299, ZK 98.734) and greater than 1 nM (RU 486). Also the APs were shown to block the inhibitory action of P which occurs after long-term incubation of pituitary cells with this steroid. However at concentrations greater than 10 nM (ZK 98.734, RU 486) and greater than 100 nM (ZK 98.299) this antagonistic action of the APs was lost. To evaluate whether the APs have direct effects on GnRH-induced LH secretion in the absence of exogenous P pituitary cells cultivated for 48 h with or without 1 nM estradiol were incubated for 4 or 24 h with increasing concentrations of the APs (10 pM-10 microM). Four hour treatment of non-estradiol-primed cells with ZK 98.299 or ZK 98.734 was without any effect on the LH response to a 1 nM GnRH-stimulus. Only the highest concentration of RU 486 (10 microM) reduced the LH response. Twenty-four hour treatment of the cultures with the APs led to enhancement of GnRH-stimulated LH secretion by up to 113, 37 and 33% for ZK 98.734, ZK 98.299 and RU 486, respectively. When estradiol-primed cells were used for the same experiments we observed exclusively inhibitory effects on GnRH-induced LH secretion after 4 and 24 h treatment periods. It is concluded that these new APs are potent inhibitors of P-actions, but also per se they induce diverse effects on GnRH-stimulated LH secretion in cultured rat pituitary cells which have to be taken into account.     

Immunodetection and immunolocalization of globulin storage proteins during zygotic and somatic embryo development in Zea mays

Globulins (GLB) are storage proteins that accumulate to high levels during zygotic embryo development of Zea mays L. We visualized the distribution of GLB during zygotic embryo development by immunolabelling of polyethylene glycol sections with a GLB-specific antiserum and a fluorescent secondary antibody. In sections of embryos at 10 days after pollimation (DAP), GLB were detected in the scutellar node only. Sections of embryos of 17 DAP showed, besides the presence of GLB in the scutellar node, the presence of a low amount of GLB in the coleoptile and the leaf primordia. In 30-DAP embryos GLB were localized in the root, the coleorhiza, the leaf primordia, the coleoptile and in all cells of the scutellum with the exception of the epidermis and the pro-vascular tissues. The subcellular location of GLB was visualized by immunolabelling of ultrathin sections with anti-GLB and a gold-conjugated secondary antibody. Scutellum cells and root cortex cells of 30-DAP embryos were packed with protein storage vacuoles (PSV), which differed in electron density. GLB were either evenly distributed throughout the PSV or were localized in electron-dense inclusions within the PSV. SDS-PAGE and immunoblot analysis of total protein extracts indicated the presence of a low amount of the GLB1 processing intermediate proGLB1'in globular as well as mature somatic embryos. After maturation on an ABA-containing medium, somatic embryos showed the additional presence of the next GLB1 processing intermediate GLB1. By immuno-electron microscopy it was possible to localize GLB in globular deposits in PSV in scutellum cells of these somatic embryos.     

Signal transduction of the melatonin receptor MT1 is disrupted in breast cancer cells by electromagnetic fields

The growth of estrogen‐receptor positive breast cancer cells is inhibited by the pineal gland hormone, melatonin. Concern has been raised that power‐line frequency and microwave electromagnetic fields (EMFs) could reduce the efficiency of melatonin on breast cancer cells. In this study we investigated the impact of EMFs on the signal transduction of the high‐affinity receptor MT1 in parental MCF‐7 cells and MCF‐7 cells transfected with the MT1 gene. The binding of the cAMP‐responsive element binding (CREB) protein to a promoter sequence of BRCA‐1 after stimulation with melatonin was analyzed by a gel‐shift assay and the expression of four estrogen‐responsive genes was measured in sham‐exposed breast cancer cells and cells exposed to a sinusoidal 50 Hz EMF of 1.2 µT for 48 h. In sham‐exposed cells, binding of CREB to the promoter of BRCA‐1 was increased by estradiol and subsequently diminished by treatment with melatonin. In cells exposed to 1.2 µT, 50 Hz EMF, binding of CREB was almost completely omitted. Expression of BRCA‐1, p53, p21^WAF, and c‐myc was increased by estradiol stimulation and subsequently decreased by melatonin treatment in both cell lines, except for p53 expression in the transfected cell line, thereby proving the antiestrogenic effect of melatonin at molecular level. In contrast, in breast cancer cells transfected with MT1 exposed to 1.2 µT of the 50 Hz EMF, the expression of p53 and c‐myc increased significantly after melatonin treatment but for p21^WAF the increase was not significant. These results convincingly prove the negative effect of EMF on the antiestrogenic effect of melatonin in breast cancer cells. Bioelectromagnetics 31:237–245, 2010. © 2009 Wiley‐Liss, Inc.     

Distribution of callose synthase, cellulose synthase, and sucrose synthase in tobacco pollen tube is controlled in dissimilar ways by actin filaments and microtubules

Callose and cellulose are fundamental components of the cell wall of pollen tubes and are probably synthesized by distinct enzymes, callose synthase and cellulose synthase, respectively. We examined the distribution of callose synthase and cellulose synthase in tobacco (Nicotiana tabacum) pollen tubes in relation to the dynamics of actin filaments, microtubules, and the endomembrane system using specific antibodies to highly conserved peptide sequences. The role of the cytoskeleton and membrane flow was investigated using specific inhibitors (latrunculin B, 2,3-butanedione monoxime, taxol, oryzalin, and brefeldin A). Both enzymes are associated with the plasma membrane, but cellulose synthase is present along the entire length of pollen tubes (with a higher concentration at the apex) while callose synthase is located in the apex and in distal regions. In longer pollen tubes, callose synthase accumulates consistently around callose plugs, indicating its involvement in plug synthesis. Actin filaments and endomembrane dynamics are critical for the distribution of callose synthase and cellulose synthase, showing that enzymes are transported through Golgi bodies and/or vesicles moving along actin filaments. Conversely, microtubules appear to be critical in the positioning of callose synthase in distal regions and around callose plugs. In contrast, cellulose synthases are only partially coaligned with cortical microtubules and unrelated to callose plugs. Callose synthase also comigrates with tubulin by Blue Native-polyacrylamide gel electrophoresis. Membrane sucrose synthase, which expectedly provides UDP-glucose to callose synthase and cellulose synthase, binds to actin filaments depending on sucrose concentration; its distribution is dependent on the actin cytoskeleton and the endomembrane system but not on microtubules.     

EXO70A1-Mediated Vesicle Trafficking Is Critical for Tracheary Element Development in Arabidopsis

Exocysts are highly conserved octameric complexes that play an essential role in the tethering of Golgi-derived vesicles to target membranes in eukaryotic organisms. Genes encoding the EXO70 subunit are highly duplicated in plants. Based on expression analyses, we proposed previously that individual EXO70 members may provide the exocyst with functional specificity to regulate cell type– or cargo-specific exocytosis, although direct evidence is not available. Here, we show that, as a gene expressed primarily during tracheary element (TE) development, EXO70A1 regulates vesicle trafficking in TE differentiation in Arabidopsis thaliana. Mutations of EXO70A1 led to aberrant xylem development, producing dwarfed and nearly sterile plants with very low fertility, reduced cell expansion, and decreased water potential and hydraulic transport. Grafting of a mutant shoot onto wild-type rootstock rescued most of these aboveground phenotypes, while grafting of a wild-type shoot to the mutant rootstock did not rescue the short root hair phenotype, consistent with the role of TEs in hydraulic transport from roots to shoots. Histological analyses revealed an altered pattern of secondary cell wall thickening and accumulation of large membrane-bound compartments specifically in developing TEs of the mutant. We thus propose that EXO70A1 functions in vesicle trafficking in TEs to regulate patterned secondary cell wall thickening.