An isozyme-specific selective system for the recovery of mammalian cells deficient in hepatic alcohol dehydrogenase activity

A selective system toxic towards mammalian cells expressing the liver-specific isozyme of alcohol dehydrogenase (L-ADH) has been developed. A number of alpha-unsaturated primary and secondary alcohols were assayed for their ability to serve as substrates for rat liver ADH and were screened for cytotoxicity towards L-ADH+ and L-ADH- cells. 1-Propen-3-ol and 1-penten-3-ol were identified as agents showing selective cytotoxicity. Reconstruction experiments demonstrated that 1-propen-3-ol at a concentration of 15 microM could be used to recover L-ADH- clones from mixed populations of L-ADH+ and L-ADH cells. Cells expressing the non-allelic S-ADH isozyme were not killed under these conditions. The selective system defined in this report is thus isozyme-specific.     

Mycorrhizae and forest ecosystems

Summary Mycorrhizae play an important role in regulating patterns of energy and nutrient flux in terrestrial ecosystems. To conceptualize this role I develop the theory behind a simple index of the efficiency of soil resource acquisition by plant root systems (E). The morphological, physiological and demographic characteristics of mycorrhizae that define E appear to vary with environment and with plant community composition. This theory is elaborated with examples drawn from forest ecology literature. Some inconsistencies among observations of fine root dynamics are particularly revealing: (1) belowground carbon allocation vs soil fertility; (2) causes of root mortality; (3) root longevity vs decomposition rates. A comprehensive theory of mycorrhizal and ecosystem dynamics must await resolution of these inconsistencies and better quantitative information on mycorrhizal features affecting E.     

Evaluation of statistical precision and design of efficient sampling for the population estimation based on frequency of occurrence

The binomial sampling to estimate population density of an organism based simply upon the frequency of its occurrence among sampled quadrats is a labour-saving technique which is potentially useful for small animals like insects and has actually been applied occasionally to studies of their populations. The present study provides a theoretical basis for this convenient technique, which makes it statistically reliable and tolerable for consistent use in intensive as well as preliminary population censuses. Firs, the magnitude of sampling error in relation to sample size is formulated mathematically for the estimate to be obtained by this indirect method of census, using either of the two popular models relating frequency of occurrence (p) to mean density (m), i.e. the negative binomial model, p=1−(1+m/k)^−k, and the empirical model, p=1−exp(−am^b). Then, the equations to calculate sample size and census cost that are necessary to attain a given desired level of precision in the estimation are derived for both models. A notable feature of the relationship of necessary sample size (or census cost) to mean density in the frequency method, in constrast to that in the ordinary census, is that it shows a concave curve which tends to rise sharply not only towards lower but also towards higher levels of density. These theoretical results make it also possible to design sequential estimation procedures based on this convenient census technique, which may enable us with the least necessary cost to get a series of population estimates with the desired precision level. Examples are presented to explain how to apply these programs to acutal censuses in the field.     

Genetics of salt tolerance in higher plants: theoretical and practical considerations

Summary An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments.     

Diversity in the immune system: “Preconceived ideas” or ideas preconceived?

Two concepts of the evolution and regulation of expression of the combining site repertoire of the immune system, are compared. One view is based on the Associative Recognition Theory as formulated by the author and the other is based on the Idiotype Network Idea as conceived by Jerne. The two concepts are analyzed from the point of view of their logic, internal consistency and factual support.     

Concordant variation in thermal tolerance and allozymes of the red shiner,Notropis lutrensis,inhabiting tailwater sections of the Brazos River,Texas

Synopsis Critical thermal maxima (CTM) and genetic variation were compared for red shiners, Notropis lutrensis, from regulated and unregulated sites on the Brazos River in northcentral Texas. Tailwater fish acclimated to 25°C had significantly lower CTM's than those from a site upstream from the dam and unregulated downstream sites. Significantly different intrasite variances were observed, with two- and four-fold larger CTM variances in fish from within 1 km and 30 km of the dam. Genetic variation was determined from electrophoretic comparisons at 21 structural gene loci. Mean heterozygosity was greatest at regulated sites. Tests for locus heterogeneity at five variable loci indicated that regulated and unregulated populations are not homogeneous. Fish under regulation were genetically more similar to each other than they were to those not affected by regulation. The proportions of the gene variance attributable to habitat alteration were partitioned, and fully one-third of the gene variation was attributed to stream regulation. Patterns of variation in thermal tolerance and metabolic enzymes in the red shiner correlated closely with temperature regimes associated with hypolimnion release from the dam. These adaptive responses have occurred in less than 40 years.     

Regulation of insulin receptor kinase activity by insulin mimickers and an insulin antagonist

Three agents which mimic insulin action in intact cells (concanavalin A, wheat germ agglutinin, and polyclonal insulin receptor antibody), mimicked insulin's ability to stimulate the kinase activity of purified insulin receptors. In contrast, monoclonal insulin receptor antibody, an antagonist of insulin action, did not stimulate the phosphorylation of the insulin receptor either in intact IM-9 cells or in purified receptor preparations. This antibody, however, antagonized the ability of insulin to stimulate the phosphorylation of the receptor both in intact cells and in the purified receptor. These studies with insulin mimickers and an insulin antagonist are consistent with a role for the kinase activity of the receptor mediating the actions of insulin.     

Somatostatin mydriasis in mice

Administration of somatostatin intracerebroventricularly to mice produced a dose-dependent mydriasis, whereas intravenous injections were ineffective. Naloxone could prevent or abolish this effect. It is suggested that somatostatin either directly excites opiate receptors or activates endopioid pathways involved in the regulation of pupillary size.     

Teleonomical optimization of a fractal model of the pulmonary arterial bed

Modeling the pulmonary arterial tree (PAT) is considered here as an optimal synthesis problem. Firstly, a class of candidate models is specified: the three-dimensional symmetric dichotomous fractal trees of elastic tubes described by Womersley's equations. Secondly, the parameters are shown to be constrained by interactions of PAT with the rest of the body; these constraints are used to limit the volume of the parametric space to which attention will be directed in the synthesis step. Thirdly, a teleonomical hypothesis is proposed: a naturally selected PAT must have a minimal input impedance under conditions keeping total arterial volume and distensibility as small as possible. This hypothesis is translated in mathematical terms and the resulting cost-function minimized in the limited parametric volume. The optimal model has parameter values and an impedance spectrum corresponding satisfactorily with real data. Moreover this model gives a clear picture of the internal hemodynamic behavior of PAT as an impedance matching device.     

Target influences on [3H]ACh synthesis and release by ciliary ganglion neurons in vitro

The developmental influence of neuron-target interaction upon transmitter synthesis from labeled precursor and the capacity to release labeled transmitter were examined in dispersed cell cultures of embryonic ciliary ganglion neurons by comparing cultures of neurons plated alone and neurons plated upon pectoral myotubes. Of the total ACh synthesized from radiolabeled choline by neurons plated alone, more than half is via a Na+-dependent path, but a larger fraction of the synthesis is Na+ insensitive in culture than in mature neurons in vivo. In addition, at 1 week in culture the neurons lacking target failed to significantly increase ACh synthesis from the labeled choline in response to a previous high [K+]0 depolarization. Synthetic responsiveness to depolarization is a characteristic of mature nerve terminals in this preparation. One week after plating neurons onto myotube cultures, synthesis of ACh from the exogenous precursor is double that of sibling cultures lacking muscle, and prior depolarization with [K+]0 results in an increase in labeled product. Release from the labeled transmitter pool by the neurons with myotubes was also enhanced. [3H]ACh release elicited by depolarization via a Ca2+-dependent mechanism was more than fivefold higher in the cocultures. The influence of coculture with myotubes upon neuronal development is not duplicated by the neurons themselves despite formation of apparent interneuronal synapses (G. Crean, G. Pilar, J. Tuttle, and K. Vaca, 1982, J. Physiol. (London). 331, 87-104), by "fibroblasts" or medium conditioned over myotube cultures. Neurons under these conditions neither increase synthesis of [3H]ACh in response to a prior depolarization nor demonstrate enhanced basal [3H]ACh synthesis and release. Thus, coculture of embryonic ciliary ganglion neurons with a striated muscle target has a somewhat specific inductive effect, enhancing the capacity for neuronal [3H]ACh synthesis and release toward mature levels. This influence of a readily accessible target upon ciliary neuron cholinergic development in vitro may reflect a normal neuromuscular interaction occurring during embryogenesis.