Further Evidence for the Relationship between Light-Induced Changes of Plasmalemma Transport and Transthylakoid Proton Uptake

The simultaneous measurement of the induction curves of chlorophyllfluorescence, its responses to saturating flashes, light-scatteringat 532 nm, and plasmalemma voltage supports previous findings(Hansen, Kolbowski, and Dau, 1987), that light-induced uptakeof protons into the inner thylakoid space causes the rapid (5to 20 s) light-induced depolarization at the plasmalemma viasubstrate depletion of the electrogenic H⁺-pump. These conclusionsare based on kinetic studies which enable the separation ofindividual components in complex signals by means of their assignmentto different time-constants. In contrast to the previous investigation,binary noise was used for modulation of the actinic light. Thenew input signal not only increased the reliability of the previousresults obtained by sine-waves, but also led to the detectionof three additional time-constants. One of these is probablyrelated to the action of light on the potassium channel of theplasmalemma. The others are assigned to the quencher Q and toa still unknown process. Key words: Chlorophyll fluorescence, plasmalemma potential, proton fluxes, noise, scattering, spinach, state-transitions, thylakoid membrane     

Early effects of excess cadmium uptake in Phaseolus vulgaris

Abstract. Seedlings of Phaseolus vulgaris were exposed to solutions containing Cd²⁺ in the range 0 to 1 molm⁻³. Ethylene formation started following 3 h of exposure to 10⁻², 10⁻¹ and 1 mol m⁻³ Cd²⁺, peaked at 18 h and returned to a relatively low rate after 24 h. Cadmium-induced ethylene formation depended on the formation of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminoethoxyvinylglycine (AVG, 0.1 mol m⁻³) inhibited ACC accumulation and ethylene production during exposure to 0.2 mol m⁻³ Cd²⁺.
Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd²⁺ concentrations above 10⁻³ mol m⁻³ due to an increase in activity of cathodic isoperoxidases. Stimulation of soluble and ionically-bound peroxidase by 0.2 mol m⁻³ Cd²⁺ was reduced in the presence of 0.1 mol m⁻³ AVG.
Accumulation of soluble and insoluble ('ligninlike') phenolics was found in plants exposed to Cd²⁺ (10⁻² mol m⁻³ or above) in the presence or absence of AVG. Deposition of insoluble (autofluorescing) material occurred in cell walls around vessels and was associated with reduced expansion and water content of leaves.     

Template preferences of DNA polymerase and nuclease activities appearing during early development of Xenopus laevis.

The three DNA polymerase activities identified in early embryos of Xenopus laevis(Benbow et al., 1975) were further distinguished by their template preferences, pH optima and sensitivity to monovalent cations. In addition, endo and exonuclease activities at pH 7.5 were identified and monitored through early development. Endonuclease activity increased throughout early development while exonuclease activity remained nearly constant. These nuclease activities were not responsible for the different template preferences of the partially purified DNA polymerase activities.     

A procedure for the isolation and determination of deoxyribose derivatives

A method of determining deoxyribose derivatives in biological material is described. It has high sensitivity, and is particularly useful in that it can be applied to a large range of tissues for which the other available assays are unsuitable. This is because the method is applicable to complex mixtures of nucleotides in which such substances as ribonucleotides are present in very large excess over deoxyribonucleotides, and it is not necessary to equilibrate the nucleotide-precursor pool with radioactive phosphate. The method has mainly been developed with the object of determining deoxyribonucleoside triphosphates, but it can be used to assay ribonucleoside triphosphates, as well as the mono- and diphosphates of both types of nucleoside. The procedure used involves three basic techniques: (1) periodate oxidation and methylamine-induced cleavage of the sugar ring to destroy 2'- and 3'-unsubstituted ribonucleosides; (2) column chromatography to separate the deoxyribonucleotides from each other and from other substances, such as the products of the periodate oxidation; (3) fluorimetric determination of deoxyribose after labilization of the pyrimidine-glycosidic bond by bromination of the heterocyclic ring. Each of these three procedures can be used independently, in conjunction with other analytical procedures.     

Constitutive and growth factor-regulated phosphorylation of caveolin-1 occurs at the same site (Tyr-14) in vivo: identification of a c-Src/Cav-1/Grb7 signaling cassette

Caveolin-1 was first identified as a phosphoprotein in Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts. Tyrosine 14 is now thought to be the principal site for recognition by c-Src kinase; however, little is known about this phosphorylation event. Here, we generated a monoclonal antibody (mAb) probe that recognizes only tyrosine 14-phosphorylated caveolin-1. Using this approach, we show that caveolin-1 (Y14) is a specific tyrosine kinase substrate that is constitutively phosphorylated in Src- and Abl-transformed cells and transiently phosphorylated in a regulated fashion during growth factor signaling. We also provide evidence that tyrosine-phosphorylated caveolin-1 is localized at the major sites of tyrosine-kinase signaling, i.e. focal adhesions. By analogy with other signaling events, we hypothesized that caveolin-1 could serve as a docking site for pTyr-binding molecules. In support of this hypothesis, we show that phosphorylation of caveolin-1 on tyrosine 14 confers binding to Grb7 (an SH2-domain containing protein) both in vitro and in vivo. Furthermore, we demonstrate that binding of Grb7 to tyrosine 14-phosphorylated caveolin-1 functionally augments anchorage-independent growth and epidermal growth factor (EGF)-stimulated cell migration. We discuss the possible implications of our findings in the context of signal transduction.     

ISOLATED GRAPTOLITES FROM THE LITUIGRAPTUS CONVOLUTUS BIOZONE (SILURIAN, LLANDOVERY) OF DALARNA, SWEDEN

Abstract:  Isolated material of 13 graptolite species from the Aeronian (middle Llandovery) Lituigraptus convolutus Biozone is described. A considerable amount of late astogenetic peridermal thickening is revealed in Normalograptus scalaris and Rivagraptus bellulus . As a result, in the former, thecal morphology is modified from climacograptid to pseudoglyptograptid; in both species, the virgella becomes robust. In Metaclimacograptus minimus and Me. sp., it is shown that the dorsal metathecal wall forms the genicular hood, whereas in N. nikolayevi , the infragenicular wall of the succeeding theca forms the distal thecal apertural margin. Pribylograptus argutus exhibits typical pribylograptid thecae along the length of the available rhabdosome fragments. Characters differentiating Campograptus lobiferus from C. harpago include the greater dorso-ventral width and more rapid increase in dorso-ventral width of the former and the greater recurving of distal thecae and presence of thecal spines/processes on all thecae of the latter. Lituigraptus convolutus has rastritiform thecae proximally; thecal apertures throughout the rhabdosome are crescentic and laterally expanded.