The biogeochemical cycle of the adsorbed template

Experimental results are presented for the verification of the first adsorption step of the ‘adsorbed template’ biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently.     

Soluble minerals in chemical evolution

The adsorption of 5-AMP and 5-CMP was studied in saturated solutions of several soluble mineral salts (NaCl, Na₂SO₄, MgCl₂·6H₂O, MgSO₄·7H₂O, CaCl₂·2H₂O, CaSO₄·2H₂O, SrCl₂·6H₂O, SrSO₄, and ZnSO₄·7H₂O) as a function of pH, ionic strength, and surface area of the solid salt. The adsorption shows a pH dependence; this can be correlated with the charge on the nucleotide molecule which is determined by the state of protonation of the N-1 nitrogen of 5-AMP or N-3 nitrogen of 5-CMP and the phosphate oxygens. The adsorption which results from the binding between the nucleotide molecule and the salt surface is proposed as being due to electrostatic forces. It was concluded that the adsorption was reversible in nature. The adsorption shows a strong dependence upon ionic strength and decreases with increasing ionic strength. Surface area is shown to be an important factor in evaluating and comparing the magnitude of adsorption of nucleotides onto various mineral salts. The implications of the results of the study are discussed in terms of the importance of soluble mineral salts as adsorption sites in the characterization of the adsorption reactions of an adsorbed template in biogeochemical cycles.     

Oxidation of γ-Hydroxybutyrate to Succinic Semialdehyde by a Mitochondrial Pyridine Nucleotide-Independent Enzyme

An antibody that inhibits over 95% of the cytosolic NADP+-dependent gamma-hydroxybutyrate (GHB) dehydrogenase activity of either rat brain or kidney was found to inhibit only approximately 50% of the conversion of [1-14C]GHB to 14CO2 by rat kidney homogenate. A similar result was obtained with sodium valproate, a potent inhibitor of GHB dehydrogenase. The mitochondrial fraction from rat brain and kidney was found to catalyze the conversion of [1-14C]GHB to 14CO2. The dialyzed mitochondrial fraction also catalyzed the oxidation of GHB to succinic semialdehyde (SSA) in a reaction that did not require added NAD+ or NADP+ and which was not inhibited by sodium valproate. The enzyme from the mitochondrial fraction which converts GHB to SSA appears to be distinct from the NADP+-dependent cytosolic oxidoreductase which catalyzes this reaction.     

Dominant pleiotropy controls enzymes co-segregating with paraquat resistance in Conyza bonariensis

Summary The genetics of paraquat-resistance in Conyza bonariensis was studied. Reciprocal crosses were prepared between resistant and sensitive individuals. The enzymes of the pathway that detoxifies superoxide to innocuous oxygen species involved in resistance were evaluated in the F₁ and F₂ generations. All F₁ plants were as resistant as the resistant parent, irrespective of parental sex, demonstrating dominance and excluding maternal inheritance. The activities of superoxide-dismutase, ascorbate-peroxidase and glutathione-reductase in the F₁ were constitutively as high as in the resistant parent. Resistance in the F₂ generation was distributed in a 31 ratio (resistant to sensitive). Leaves from F₂ plants were removed for a resistance assay and enzyme immuno-assays of single plants were performed. The high levels of superoxide-dismutase and glutathione-reductase, the two enzymes for which antibodies were available, were similar in resistant individuals to the levels in the resistant parent; the levels were low in the susceptible individuals. These results indicate either a very tight linkage, or more probably, that one dominant nuclear gene controls resistance by pleiotropically controlling the levels of enzymes of the activeoxygen detoxification pathway.     

COMMENTARY ON KHAN'S “GENETIC HARM: BITTEN BY THE BODY THAT KEEPS YOU?”

Several important issues are raised and illuminated in "Genetic Harm"; not least, in its detailed discussion of specific genetic disorders. In particular, it focuses on a type of disorder whose ill effects are not manifested at birth, but only at a later stage in life. The conclusion, with its significant implications for practice, seems quite valid: a moral duty should be recognized to genetically (or otherwise, if feasible) cure an embryo of that which is expected to (later) cause such prospective suffering. Yet the reasons given for that conclusion, as well as much of the argument throughout, concentrate on a debatable notion of "harm". On an alternate account -- drawn in terms of personal identity -- what makes the moral difference in this type of case is rather that the genotype manifests itself, and that a life-history begins, prior to (and thus independently of) any effects of the gene(s) we are called to alter.     

The determination of chlorophylls a and b together with 14CO2 fixation in the same plant tissue samples

A simple, efficient, and inexpensive method for measuring radioactivity as well as chlorophylls a and b in a large number of plant tissue samples is presented. Chlorophyll is determined following extraction with dimethyl sulfoxide or N-N'-dimethylformamide. The solvent is then evaporated on glass-fiber filters and bleached under light. The filter disks are counted together with the cleared plant material.     

The RNA-world and co-evolution hypotheses and the origin of life: Implications,research strategies and perspectives

The applicability of the RNA-world and co-evolution hypotheses to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficulties. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work.A central element in the proposed experimental strategies is the study of the catalytic activities of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypotheses under consideration. It is suggested that the noveldirected molecular evolution technology, andmolecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a Primordial Darwinian entity.     

Electric Currents around Growing Trichoderma Hyphae, before and after Photoinduction of Conidiation

Electric currents were measured around Trichoderma harzianum (Rifai) hyphae using an extracellular vibrating electrode. A steady current enters growing hyphal tips and along the side of the apical millimeter. In addition, outward currents were detected at about one-ninth of the locations tested, 60 to 150 minutes after illumination but not in dark controls. This sporadic, localized outward current pattern might be an early biophysical response to blue light.     

Cell suspensions for kinetic studies of inhibitor action

Because of uniformity and small distances for transport, cell suspensions offer a system for rapid measurements of initial reactions of phytotoxic compounds. We had previously shown that a growth regulator, dikegulac (2,3:4,6 di-o-isopropylidine-2-keto-L-gulonate) inhibits amino acid incorporation into proteins. Using Solanum nigrum suspension cultures, it was found that dikegulac rapidly inhibits amino acid uptake into cells, before inhibiting incorporation, with time points starting at a few minutes, and kinetics that can be extrapolated back to time zero. With more rapid kinetics this compound induces leakage of a preloaded dye. The rate of leakage was less with stationary cells in suspension, reiterating that they are more resistant to the effects of this compound. It was thus concluded that at the concentrations used, the first effect of dikegulac (or one very close to the first effect) is on the cell membrane.Abbreviation FDA fluorescein diacetate     

Cell cultures vs. whole plants for measuring phytotoxicity II. Correlations between phytotoxicity in seedlings and calli

The effects of a broad range of compounds were assessed usingboth seedlings and callus cultures of five species. An experimentallyjustified ranking procedure was used to facilitate the comparisonof the inhibitory characteristics at multiple concentrations.When the effects on seedlings of Lycopersicon esculentum, Solanumnigrum, Chrysanthemum segetum and Cirsium arvense were comparedto those on white calli of the same species, some positive correlationswere obtained; photosynthesis inhibitors affected seedlingsmuch more than calli and some compounds affected calli muchmore than seedlings. Better correlations were obtained betweenthe effects on Rumex obtusifolius seedlings and on green Rumexcalli; the only exceptions being those compounds affecting mainlythe calli. Thus callus cultures, especially green ones, havea potential for use to assess possible phytotoxicity as wellas to detect potential toxicity of compounds not penetratinginto or being translocated in whole plants. (Received January 13, 1977; )