Role of aminocyclopropane-l-carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1-aminocyclopropane-l-carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.     

Zur Charakterisierung neuronaler und gliöser Elemente im Epithel des Saccus vasculosus von Knochenfischen

Zusammenfassung Das Epithel des Saccus vasculosus des Flußbarsches Perca fluviatilis besteht aus Krönchenzellen, bipolaren Liquorkontaktneuronen (Zahlenverhältnis etwa 41) und Stützzellen. Im Bereich des Saccus kommen Macrophagen vor. Die Krönchenzellen wurden unter verschiedenen Fixierungsbedingungen untersucht. Die Globuli enthalten schlauchförmige Zisternen, die nicht mit den Zisternen des Zellapex in Verbindung stehen. Im Zytoplasma des Zellapex und der Globuli wird bei langdauernder OsO₄-Imprägnation Osmium gebunden. Die Krönchenzellen werden basal von Ausläufern der Stützzellen unterlagert. Sie werden nicht innerviert und entsenden keine Axone.Die bipolaren Neurone sind durch einen im Liquor endigenden Dendriten und ein Axon gekennzeichnet, das in eines der Faserbündel des Epithels eintritt. Der Dendrit trägt 1 bis 2 Zilien. Die Zelle ist reich an Vesikeln und kann am Perikaryon wie an den Ausläufern Synapsen tragen. Im extrazellulären Raum um die Neurone und in vesikulären Strukturen des Apex wird Acetylcholinesterase nachgewiesen.Der Nervus sacci vasculosi dürfte nur afferente Axone von Liquorkontaktneuronen und efferente Fasern, die diese innervieren, enthalten.

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Neuronal and glial cell elements within the epithelium of the Saccus vasculosus in teleosts

Summary The epithelium of the Saccus vasculosus of Perca fluviatilis consists of coronet cells and bipolar liquor contact neurones in a 41 ratio, and supporting cells. The organ also contains macrophages.The coronet cells have been studied after different kinds of fixation. The globules of these cells contain tubelike cisternae, which do not connect with cisternae in the cell's apical protrusion. The cytoplasm of the apical protrusion and to a greater extent of the globules, is stained by longlasting OsO₄-impregnation. The coronet cells have no direct contact with the basement membrane of the organ. They are neither innervated nor have axons.The dendrites of the bipolar nerve cells end with a bulbous structure protruding into the cerebrospinal fluid. The dendrites contain vesicles and each bears 1–2 cilia. The axons join the fiber bundles of the epithelium. There are synaptic contacts on the surface of the neurons and their processes. In some vesicular structures within the apices and more conspicuously within the extracellular space around these cells indications of acetylcholinesterase activity are found.It appears that the nervus sacci vasculosi contains only afferent axons of the bipolar liquor-contact neurons and efferent fibres which form synaptic contacts with these neurons.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Mutagen specificity in the induction of karyotic versus cytoplasmic respiratory deficient mutants in yeast by nitrous acid and alkylating nitrosamides

Summary In the haploid eukaryotic organism Saccharomyces cerevisiae the induction of cytoplasmic and genic (karyotic) RD mutants was studied, using nitrous acid, nitrosomethylurethane (NMU) and nitrosoimidazolidone (NIL).The cytoplasmic or genic origin of the induced RD mutants was determined by prescreening in complementation tests with ^– and wild type tester strains. Among the mutants of all three agents we could thus score the incidence of three RD mutant types: genic, suppressive and cytoplasmic (both primary and secondary). The final identification of the cytoplasmic type was only possible through tetrad analysis, performed in the cases of HNO₂ and NMU.A distinct difference in cytoplasmic versus genic mutagen specificity was observed between HNO₂ and NMU. HNO₂ was unable to induce cytoplasmic RD mutants but it proved to be highly efficient in the induction of genic RD mutants. In contrast, NMU induced more cytoplasmic effects was it possible to detect mutagenic specificities which, solely on the basis of karyotic action, were not detectable.     

Modelluntersuchungen zur Struktur des purpurnen Farbstoffkomplexes der Giemsa-Färbung

Summary Nuclei of Giemsa stained cells show a purple coloration, which is generated by a complex of DNA, azure B (AB) and eosin Y (EY). The structure of this complex is unknown. Its absorption spectrum shows a sharp and strong band at 18 100 cm^–1 (552 nm), the so called Romanowsky band (RB). It is possible to produce the complex outside of the cell, but it is cubersome to handle. Easier to handle is a purple complex composed of chondroitin sulfate (CHS), AB and EY, which also shows a sharp and strong RB at 18100 cm^–1 in the absorption spectrum. This CHS-AB-EY complex is a model for the DNA-AB-EY complex of Giemsa stained cell nuclei. We tried to investigate its structure.In the first step of the staining procedure CHS binds AB cations forming a stable CHS-AB complex. In the case of saturation each anionic SO ₄ ^– - and COO^–-binding site of CHS is occupied by one dye cation and the complex has 1:1 composition. It has a strong and broad absorption band with its maximum at ca. 18000 cm^–1 (556 nm). In the second step the CHS-AB complex additionally binds EY dianions forming the purple CHS-AB-EY complex with its RB at 18100 cm^–1. This band can be clearly distinguished from the broad absorption of the bound AB cations. RB is generated by the EY chromophore, whose absorption is shifted to longer wavelength by the interaction with the CHS-AB framework.The CHS chains of the CHS-AB and CHS-AB-EY complexes can be mechanically aligned in a preferred direction k. Fine films of highly orientated complexes were prepared with a special technique and studied with a microspectrophotometer equipped with a polarizer and an analyzer. They are birefringent and dichroic-the more birefringent, the better the mechanical orientation. The sites of best orientation within the film were selected according to the quality of the birefringence. We measured the absorption of these regions with linearly polarized light. By setting the polarizer (e _p parallel () or perpendicular () to k, we found that the transition moment m _AB of the long wave-length absorption of AB in the CHS-AB and the CHS-AB-EY complexes is polarized almost perpendicular to the preferred direction k, m _AB k. But the transition moment m _EY of EY in CHS-AB-EY is polarized parallel to k, m _EY k. The transition moments m _AB and m _EY lay in the molecular plane in the direction of the long axes of the AB and EY chromophores, respectively. Therefore, in both CHS-AB and CHS-AB-EY the long axes of the AB molecules are approximately perpendicular to the CHS chain; but in CHS-AB-EY the long axes of the EY chromophore are parallel to the chain of the biopolymer. This structure is somewhat surprising. In the CHS-AB-EY dye complex the chromophores of AB and EY are not parallel but approximately perpendicular to each other.     

Intra- and interspecies analyses of the carcinoembryonic antigen (CEA) gene family reveal independent evolution in primates and rodents

Summary Various rodent and primate DNAs exhibit a stronger intra- than interspecies cross-hybridization with probes derived from the N-terminal domain exons of human and rat carcinoembryonic antigen (CEA)-like genes. Southern analyses also reveal that the human and rat CEA gene families are of similar complexity. We counted at least 10 different genes per human haploid genome. In the rat, approximately seven to nine different N-terminal domain exons that presumably represent different genes appear to be present. We were able to assign the corresponding genomic restriction endonuclease fragments to already isolated CEA gene family members of both human and rat. Highly similar subgroups, as found within the human CEA gene family, seem to be absent from the rat genome. Hybridization with an intron probe from the human nonspecific cross-reacting antigen (NCA) gene and analysis of DNA sequence data indicate the conservation of noncoding regions among CEA-like genes within primates, implicating that whole gene units may have been duplicated. With the help of a computer program and by calculating the rate of synonymous substitutions, evolutionary trees have been derived. From this, we propose that an independent parallel evolution, leading to different CEA gene families, must have taken place in, at least, the primate and rodent orders.     

Comparative measurements of the xylem pressure ofNicotiana plants by means of the pressure bomb and pressure probe

Determination of the pressure in the water-conducting vessels of intactNicotiana rustica L. plants showed that the pressure probe technique gave less-negative values than the Scholander-bomb method. Even though absolute values of the order of −0.1 MPa could be directly recorded in the xylem by means of the pressure probe, pressures between zero and atmospheric were also frequently found. The data obtained by the pressure probe for excised leaves showed that the Scholander bomb apparently did not read the actual tension in the xylem vessles ofNicotiana plants. The possibility that the pressure probe gave false readings was excluded by several experimental controls. In addition, cavitation and leaks either during the insertion of the microcapillary of the pressure probe, or else during the measurements were easily recognized when they occurred because of the sudden increase of the absolute xylem tension to that of water vapour or to atmospheric, respectively. Tension values of the same order could also be measured by means of the pressure probe in the xylem vessels of pieces of stem cut from leaves and roots under water and clamped at both ends. The magnitude of the absolute tension depended on the osmolarity of the bathing solution which was adjusted by addition of appropriate concentrations of polyethylene glycol. Partial and uniform pressurisation of plant tissues or organs, or of entire plants (by means of the Scholander bomb or of a hyperbaric chamber, respectively) and simultaneous recording of the xylem tension using the pressure probe showed that a 1∶1 response in xylem pressure only occurred under a few circumstances. A 1∶1 response required that the xylem vessels were in direct contact with an external water reservoir and/or that the tissue was (pre-)infiltrated with water. Corresponding pressure-probe measurements in isolated vascular bundles ofPlantago major L. orP. lanceolata L. plants attached to a Hepp-type osmometer indicated that the magnitude of the tension in the xylem vessels was determined by the external osmotic pressure of the reservoir. These and other experiments, as well as analysis of the data using classical thermodynamics, indicated that the turgor and the internal osmotic pressure of the accessory cells along the xylem vessels play an important role in the maintenance of a constant xylem tension. This conclusion is consistent with the cohesion theory. In agreement with the literature (P.E. Weatherley, 1976, Philos. Trans. R. Soc. London Ser. B23, 435–444; 1982, Encyclopedia of plant physiology, vol. 12B, 79-109), it was found that the tension in the xylem of intact plants under normal and elevated ambient pressure (as measured with the pressure probe) under quasi-stationary conditions was independent of the transpiration rate over a large range, indicating that the conductance of the flow path must be flow-dependent.     

Bioavailability of selenium accumulated by selenite-reducing bacteria

The bioavailability of selenium (Se) was determined in bacterial strains that reduce selenite to red elemental Se (Se^o). A laboratory strain ofBacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Microbacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na₂SeO₃). After harvest, the washed, lyophilizedB. subtilis andM. arborescens samples contained 2.62 and 4.23% total Se, respectively, which was shown to consist, within error, entirely of Se^o. These preparations were fed to chicks as supplements to a low-Se, vitamin E-free diet. Three experiments showed that the Se in both bacteria had bioavailabilities of approx 2% that of selenite. A fourth experiment revealed that gray Se^o had a bioavailability of 2% of selenite, but that the bioavailability of red Se^o depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray Se^o and bacterial Se; when ascorbate was the reductant, bioavailability was twice that level (3–4%). These findings suggest that aerobic bacteria such asB. subtilis andM. arborescens may be useful for the bioremediation of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.     

A microsomal ATP-binding protein involved in efficient protein transport into the mammalian endoplasmic reticulum.

Protein transport into the mammalian endoplasmic reticulum depends on nucleoside triphosphates. Photoaffinity labelling of microsomes with azido-ATP prevents protein transport at the level of association of precursor proteins with the components of the transport machinery, Sec61alpha and TRAM proteins. The same phenotype of inactivation was observed after depleting a microsomal detergent extract of ATP-binding proteins by passage through ATP-agarose and subsequent reconstitution of the pass-through into proteoliposomes. Transport was restored by co-reconstitution of the ATP eluate. This eluate showed eight distinct bands in SDS gels. We identified five lumenal proteins (Grp170, Grp94, BiP/Grp78, calreticulin and protein disulfide isomerase), one membrane protein (ribophorin I) and two ribosomal proteins (L4 and L5). In addition to BiP (Grp78), Grp170 was most efficiently retained on ATP-agarose. Purified BiP did not stimulate transport activity. Sequence analysis revealed a striking similarity of Grp170 and the yeast microsomal protein Lhs1p which was recently shown to be involved in protein transport into yeast microsomes. We suggest that Grp170 mediates efficient insertion of polypeptides into the microsomal membrane at the expense of nucleoside triphosphates.