Interaction of transition metal ions with Z form poly d(A-C).poly d(G-T) and poly d(A-T) studied by I.R. spectroscopy.

Interactions between Ni2+, Co2+ and purine bases have been studied by I.R. spectroscopy in the case of double stranded regularly alternating purine-pyrimidine polynucleotides poly d(A-T), poly d(A-C).poly d(G-T) and poly d(G-C). The spectra of polynucleotide films have been recorded in hydration and salt content conditions which correspond to the obtention of the classical right-handed (A,B) and left-handed (Z) helical conformations. Selective deuteration of the 8C site of purines has been obtained and is used to detect interactions between the transition metal ions and the adenine or guanine bases. The spectral region between 1500 and 1250 cm-1 corresponding to base in-plane vibrations and involving also the glycosidic linkage torsion is discussed in detail. The selective interaction between the transition metal ion and the 7N site of the purine base is considered to be partly responsible for the stabilization of the base in a syn conformation, which favours the adoption by the polynucleotide (poly d(G-C), poly d(A-C).poly d(G-T) or poly d(A-T)) of a Z type conformation.     

Olfactory responses of aquatic and terrestrial tiger salamanders to airborne and waterborne stimuli

Summary Electro-olfactograms (EOGs) were used to assess olfactory responding by aquatic larval and terrestrial adult tiger salamanders (Ambystoma tigrinum) to airborne volatile compounds, and volatile and non-volatile compounds in aqueous solution. Both forms of salamander showed saturation effects to presentations of airborne stimuli (Fig. 2). Saturation was not observed, however, to stimulus presentations in aqueous solution (Figs. 2, 3). When threshold values and concentration-response curve parameters were compared, non-volatile amino acids in solution were more potent stimuli for larvae while airborne volatiles were more potent stimuli for adults (Tables 1, 2). We infer that metamorphosis in the tiger salamander is accompanied by changes in olfactory response characteristics, due possibly to changes in receptor population, changes in perireceptor properties (e.g. mucus) or to changes in stimulus access.Abbreviations EOG electro-olfactogram - PPM (ppm) parts per million     

Isolation and Characterization of a Virus Inhibitor from Spinach (Spinacia oleracea L.)

A virus inhibiting protein (VI) was isolated from spinach (Spinacia oleracea L.). The VI inhibited infections of test plants with plus- and minus-strand RNA viruses. Inoculation of both local lesion and systemic hosts with TMV in the presence of varying amounts of the VI resulted in typical dose response curves for the number of local lesions or the amount of virus respectively. The lowest concentration of VI leading to a significant reduction in the number of local lesions was 0.06 μg/ml. The VI was found to inhibit local lesion formation only when applied within 2–3 h p.i. but still reduced the number of local lesions when applied up to 9 h prior to virus inoculation. The antiviral activity could be attributed to a protein of molecular weight 29,000 dalton with an isoelectric point of 10.3. Its activity was destroyed by heating for 30 min to 70°C. These characteristics resemble those of other virus inhibiting proteins described for members of the order Caryophyllales such as the Phytolacca inhibitor against which a serological relationship was obtained.     

Early morphological abnormalities in splotch mouse embryos and predisposition to gene- and retinoic acid-induced neural tube defects

Genetic and environmental factors contribute to an individual's neural tube defect liability. In the mouse, the gene mutation Splotch (Sp) causes a pigmentation defect in heterozygotes while homozygotes have spina bifida +/- exencephaly. Splotch homozygotes, heterozygotes, and wild-type embryos were examined for somite number, anterior neuropore closure, and posterior neuropore length. The aim was to distinguish potentially affected homozygotes early in pathogenesis and find a morphological basis for increased teratogen susceptibility in heterozygotes. Posterior neuropore closure as well as anterior neuropore closure was significantly delayed in potentially affected Sp as compared to wild-type litter embryos exceeding the incidence found in day-10-diagnosed homozygotes. Part of this excess was attributed to a transient delay in heterozygotes which in turn might predispose to retinoic acid-induced neural tube defects. This idea was supported by an outcross of Sp heterozygote males by inbred SWV females and wild-type males by SWV where a significant increase in retinoic acid-induced neural tube defects was found in Sp carrier litters.     

Correlative changes in sucrose uptake, ATPase activity and membrane fluidity in carnation petals during senescence

Apparent sucrose uptake. ATPase activity and membrane fluidity changes were studied during the development and senescence of carnation flowers ( Dianthus caryophyllus L., cv. Cerise Royallette). Typical changes associated with senescence of a cut flower, such as respiration, ethylene production and fresh weight, were measured. Concomitant with a rise in respiration and ethylene production and a decline in fresh weight, a sharp decrease in apparent sucrose uptake was observed. Sucrose uptake was pH dependent (pH optimum, 5.5) and influenced by membrane integrity. Apparently, the activity of ATPase is related to sucrose uptake, because similar changes occurred during flower development. In addition, the activity of ATPase was well correlated with membrane fluidity.
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed.     

Development and differentiation of the brain ventricular system in tadpoles of Xenopus laeris (Daudin) (Amphibia, Anura)

The development and the differentiation of the ventricular system of the brain of tadpoles of the South African Clawed Toad, Xenopus laevis (Daudin), is studied by light microscopy (stages 45 to 66) and scanning and transmission electron microscopy (stages 50 to 66). Special interest is paid to the ependymal structures of the foramen of Monroe, the ventricles of the diencephalon, the mesencephalon, and the rhombencephalon, and to the ependymal of the central canal and the choroid plexus of the third and fourth ventricle. At early developmental stages the lower two thirds of the ventricles are dominated by blebs, cytoplasmatic protrusions of the ependymal cells. During the development they become reduced and replaced by cilia. The number of cilia and microvilli increases strongly towards the end of the metamorphosis. The surface structures demonstrated by scanning electron microscopy are discussed in respect to morphology and physiology.     

Sequence interrelationships of the subunits of vicilin from pea seeds

Serological studies and comparison of N-terminal amino acid sequences with the amino acid sequence deduced from a cDNA clone have been used to establish the sequence relationships between the subunits of the pea seed storage protein, vicilin. Subunits smaller than M_r～50 000 (i.e., M_r 34 000, 30 000, 25 000, 18 000, 14 000, 13 000 and 12 000) show extensive homology with molecules within M_r～50 000 group. Both the sequencing and serological data confirm earlier evidence from studies on vicilin synthesisin vivo andin vitro which indicated that the vicilin subunits smaller than M_r～50 000 arose by endoproteolytic cleavage of parent molecules within the M_r～50 000 group. Cleavage in different M_r 50 000 parent molecules containing either one or both of two susceptible processing sites accounts for the formation of all the vicilin subunits smaller than M_r～50 000, with the possible exception of the M_r34 000 polypeptide. The position of these sites in the putative parents were defined by reference to a complete amino acid sequence deduced from the sequence of DNA complementary to mRNA for one member of the M_r～50 000 group.     

Role of vitamin B 6 biosynthetic rate in the study of vitamin B 6 synthesis in Escherichia coli

Nutritional auxotrophs of Escherichia coli synthesize vitamin B(6) compounds at a rate of 1 x 10(-10) to 2 x 10(-10) moles per hr per mg (dry weight) of cells when they are suspended in minimal medium lacking their required nutrients. A few auxotrophs have been found to stop or reduce vitamin B(6) synthesis during such an experiment. These include thiamineless, citrate synthaseless, and pyridoxineless mutants as well as mutants which require four carbon compounds for growth. Glycolaldehyde was found to restore vitamin B(6) synthesis in the last named of these mutants without restoring normal growth. A class of pyridoxineless mutants which responded with normal growth to 0.4 mm glycolaldehyde or 0.15 x 10(-3) mm pyridoxol was also found. The results suggest that a thiamine pyrophosphate-requiring step as well as glycolaldehyde may be involved in pyridoxal phosphate biosynthesis.     

Extinction of an appetitive operant response after administration of MSH

Hungry rats were trained to press a lever in order to obtain food on a fixed ratio (FR) or variable ratio (VR) of reinforcement. Rats trained on the FR schedule and injected with synthetic α-MSH had delayed extinction of the task as compared with control rats injected with diluent. The results show that MSH affects the behavior of rats in another type of behavioral situation involving an appetitive operant response.