Effects of Salinity on the Extensibility and Ca Availability in the Expanding Region of Growing Barley Leaves

The growth of barley (Hordeum vulgare L.) leaves is reduced by salinity. We used the Instron extensometric technique to measure the reversible and irreversible compliance of the expanding regions of growing barley leaves from plants exposed to 1, 40, 80 and 120 mM NaCl in nutrient solution. Two barley cultivars differing in salinity resistance (cv ‘Arivat’ and cv ‘Briggs’) were compared over 5d of leaf growth. During the period of most active leaf expansion, salinity reduced reversible compliance and increased compliance in the leaf segments, although responses to salinity were complex and changed over the course of leaf expansion. Salinity increased irreversible compliance more in the salt-sensitive cultivar Arivat than in the more salt-tolerant cultivar Briggs. Elemental analysis of the basal leaf segments used for extensometry revealed an accumulation of Na and a depletion of Ca in segments from salinized plants, resulting in very high Na: Ca ratios in salinized expanding tissue. The concentrations of K and Mg in basal leaf tissue were elevated by salinity. Our data do support the hypothesis that the inhibition of leaf expansion by salinity stress is mediated by a decline in irreversible extensibility. We suggest that reduced Ca availability in expanding leaf tissue may contribute to growth reduction in salt-stressed barley seedlings.     

Cardenolides from Asclepias asperula subsp. Capricornu and A. Viridis

6′-O-(E-4-hydroxycinnamoyl) Desglucouzarin, the first cardenolide containing a cinnamoyl ester moiety, has been isolated from the ethanolic extract of the milkweed, Asclepias asperula. In addition, five known cardenolides were isolated and identified from A. asperula and A. viridis.     

Science in the age of mechanical reproduction: moral and epistemic relations between diagrams and photographs

Sociologists, philosophers and historians of science are gradually recognizing the importance of visual representation. This is part of a more general movement away from a theory-centric view of science and towards an interest in practical aspects of observation and experimentation. Rather than treating science as a matter of demonstrating the logical connection between theoretical and empirical statements, an increasing number of investigations are examining how scientists compose and use diagrams, graphs, photographs, micrographs, maps, charts, and related visual displays. This paper focuses on diagrams in biology, and tries to demonstrate how diagrams are an integral part of the production of scientific knowledge. In order to disclose some of the distinctive practical and analytical uses of diagrams, the paper contrasts the way diagrams and photographs are used in biological texts. Both diagrams and photographs are shown to be “constructions” that separately and together mediate the investigation of scientific phenoman.     

Inhibition of adenine nucleotide synthesis: effect on tight junction structure and function of clone 4 MDCK cells.

The formation and maintenance of tight junctions as a barrier to the diffusion of ions and other water-soluble across epithelia is an energy-dependent process. The administration of N-formyl-hydroxyaminoacetic acid (Hadacidin), an analog of aspartate and a competitive inhibitor of adenylosuccinate synthetase, has been shown to inhibit the multiplication of clone 4 MDCK cells and concomitantly reduce the levels of ATP and cAMP (J. Cell. Physiol. 140, 186-194 (1989)). When added to mitotically quiescent confluent cultures of clone 4 MDCK cells, millimolar concentrations of Hadacidin inhibited the generation of transepithelial electrical resistance (TER). In such cultures passive Na+ permeability was similar to controls indicating that the effect of Hadacidin was not on the transcellular pathway. That these cells were viable was demonstrated by their ability to exclude Trypan Blue, and the fact that they remained competent to develop steady state TER upon removal of the inhibitor. Suppression of TER was completely reversed within 48 h of replacing the Hadacidin-supplemented medium with one containing aspartate. Adenosine, but not aspartate, when added simultaneously with the drug, obviated the latter's effect on TER. A mixture of dibutyryl cAMP (db-cAMP) and theophylline was only partially effective in overcoming the effects of Hadacidin on the development of TER and, in fact, markedly delayed its development in control cultures not treated with the drug. When monolayers with established steady state TER were exposed to Hadacidin, no change was noted during the first 24 h. By 48 h, however, TER had decreased to very low values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression of circadian rhythmicity in Djungarian hamsters under constant light: Effects of light intensity and the circadian system's state

Summary Djungarian hamsters (Phodopus sungorus), were exposed to constant light with increasing intensities (20, 60, 350 lux), and wheel running activity was recorded. With increasing light intensity the percentage of hamsters showing a split in their daily activity pattern increased and the free running period was lengthened for both the unsplit and the split state. The fact that the free running period of both states depended on the light intensity together with the observation that the highest incidence of acircadian activity occurred under 350 lux, provoked the idea that the emergence of splitting or acircadian rhythmicity is a direct consequence of the light induced lengthening of the free running period. However, analysis of the data failed to support the idea that emergence of a split or acircadian activity is a threshold phenomenon with respect to the free running period.Due to differences in circadian function some Djungarian hamsters do not exhibit photoinduction following short day exposure. In these individuals splitting also occurred but required exposure to a higher light intensity than in photo-responsive hamsters. This observation is in accordance with the idea that the two phenotypes differ in the interaction of the two component oscillators underlying circadian rhythmicity.Abbreviations LD long day photoperiod - LL constant light - SD short day photoperiod - free running period     

Design and analysis of experiments on random drift and inbreeding depression

While the genetic consequences of inbreeding and small population size are of fundamental importance in many areas of biology, empirical research on these phenomena has proceeded in the absence of a well-developed statistical methodology. The usual approach is to compare observed means and variances with the expectations of Wright's neutral, additive genetic model for quantitative characters. If the observations deviate from the expectations more than can be accounted for by sampling variance of the parameter estimates, the null hypothesis is routinely rejected in favor of alternatives invoking evolutionary forces such as selection or nonadditive gene action. This is a biased procedure because it treats sequential samples from the same populations as independent, and because it ignores the fact that the expectations of the neutral additive genetic model will rarely be realized when only a finite number of lines are studied. Even when genes are perfectly additive and neutral, the variation among the properties of founder populations, the random development of linkage disequilibrium within lines, and the variance in inbreeding between lines reduce the likelihood that Wright's expectations will be realized in any particular set of lines. Under most experimental designs, these sources of variation are much too large to be ignored. Formulas are presented for the variance-covariance structure of the realized within- and between-line variance under the neutral additive genetic model. These results are then used to develop statistical tests for detecting the operation of selection and/or inbreeding depression in small populations. A number of recommendations are made for the optimal design of experiments on drift and inbreeding, and a method is suggested for the correction of data for general environmental effects. In general, it appears that we can best understand the response of populations to inbreeding and finite population size by studying a very large number (>100) of self-fertilizing or full-sib mated lines in parallel with one or more stable control populations.     

In vitro neurite extension by granule neurons is dependent upon astroglial-derived fibroblast growth factor

When grown in the absence of astroglial cells, purified mouse cerebellar granule neurons survive less than 36 hr and do not extend neurites. Here we report that low concentrations of basic fibroblast growth factor (bFGF, 1-25 ng/ml) maintained the viability and promoted the differentiation of purified granule neurons. The effect of bFGF on granule cell neurite outgrowth was dose dependent. Neurite outgrowth was stimulated markedly in the presence of 1-25 ng/ml bFGF, but effects were not seen below 1 ng/ml or above 50 ng/ml. When affinity-purified antibodies against bFGF (1-5 micrograms/ml) were added either to purified granule cells or to co-cultures of neurons and astroglial cells, process extension by granule neurons was severely impaired. The inhibition of neurite outgrowth in the presence of anti-bFGF antibodies was reversed by the addition of 25 ng/ml of exogenous bFGF. In addition to neuronotrophic effects, bFGF influenced the rate of growth of the astroglial cells. This result depended on whether the astroglia were grown in isolation from neurons, where low doses of bFGF (10-25 ng) stimulated glial growth, or in coculture with neurons, where much higher doses of bFGF (100-250 ng/ml) were needed for glial mitogenesis. Immunoprecipitation of lysates from 35S-labeled cerebellar astroglial cells with anti-bFGF antibodies revealed a single band after SDS-PAGE at 18,000 Da, the molecular weight of bFGF. These results indicate that glial cells synthesize bFGF and are possibly an endogenous source of bFGF in cerebellar cultures. Thus, astroglial cells synthesize soluble factors needed for neuronal differentiation.     

An endogenous Ca2+-sensitive proteinase converts the hepatic alpha 1-adrenergic receptor to guanine nucleotide-insensitive forms

An iodoazido[125I]prazosin analogue was employed to photoaffinity label alpha 1-adrenergic receptors in rat liver plasma membranes. Labeled proteins were separated by gradient polyacrylamide gel electrophoresis in sodium dodecyl sulfate, and (-)-epinephrine displacement of [3H]prazosin binding was concurrently measured in the presence or absence of guanosine 5'-O-(gamma-thiotriphosphate) (GTP[gamma S]). Inclusion of EGTA and/or proteinase inhibitors during membrane preparation and incubation increased the effect of GTP[gamma S] on alpha 1-adrenergic agonist binding and this could be correlated with increased concentrations of a 78 kDa photoaffinity labeled protein. In contrast, omission of EGTA or addition of exogenous Ca2+ diminished or abolished the effect of GTP[gamma S] on binding and caused loss of the 78 kDa form and the appearance of lower molecular weight labeled proteins. Age-dependent differences in GTP[gamma S] effects on alpha 1-adrenergic agonist binding were abolished when membranes were prepared and incubated in the presence of EGTA and proteinase inhibitors. However, the 78 kDa photoaffinity labeled protein observed in adult rats (over 225 g body weight) was not apparent in membranes from younger rats (50-75 g), even when the membranes were prepared and incubated in the presence of EGTA and proteinase inhibitors. Instead, a 68 kDa species was the major labeled protein. These data suggest that GTP effects on alpha 1-adrenergic agonist binding in rat liver membranes require the presence of either a 68 or 78 kDa alpha 1-adrenergic binding protein. Failure to inhibit proteolysis in the membranes leads to the generation of lower-molecular-weight binding proteins and the loss of GTP effects on alpha 1-adrenergic agonist binding, although [3H]prazosin binding characteristics are not changed. It is suggested that either the proteolyzed forms of the alpha 1-adrenergic receptor are unable to couple to a putative guanine nucleotide-binding regulatory protein, or that such a protein is concurrently proteolyzed and is thus unable to couple to the receptor.     

Increased T gamma and T mu cells in BALB/c mice with IgG and IgM plasmacytomas and hybridomas

The results of previous studies in our laboratory have shown that mice bearing plasmacytomas and hybridomas that secrete IgA or IgE are accompanied by increased frequencies of Lyt-1-2+ T lymphocytes bearing Fc receptors (FcR) for IgA (T alpha) or IgE (T epsilon), respectively. The present study was undertaken to examine whether IgG- or IgM-secreting tumors influenced the frequency of T lymphocytes that express FcR for IgG or IgM. We studied mice bearing IgG- and IgM-secreting plasmacytomas and hybridomas. BALB/c mice injected subcutaneously with the IgG-secreting hybridoma HDP1 (gamma 1 kappa, anti-TNP) were sequentially examined for the frequencies and Lyt phenotypes of splenic lymphocytes bearing FcR for IgG (T gamma), IgM (T mu), and IgA (T alpha). A threefold increase in the frequency of T gamma lymphocytes that were Lyt-1-2+, L3T4- was seen. The frequencies of T mu and T alpha lymphocytes in these mice were not significantly altered. Similarly, mice injected subcutaneously with the IgM-secreting plasmacytoma MOPC 104E (mu lambda, anti-dextran) or the IgM-secreting hybridoma C1D1 (mu kappa, anti-ox RBC) were examined sequentially for the frequencies of T gamma, T mu, and T alpha lymphocytes. Mice with established IgM subcutaneous tumors showed a twofold increase in splenic, nylon wool-nonadherent T mu lymphocytes. This was associated with a relative increase in Lyt-2+ splenic T lymphocytes and a relative decrease in Lyt-1+ splenic T lymphocytes. No changes were observed in the frequencies of either T gamma or T alpha lymphocytes. These studies extend to IgG and IgM the observation that plasmacytomas and hybridomas secreting immunoglobulins of a specific isotype cause an expansion of T lymphocytes bearing FcR specific for the corresponding isotype. The expansion of FcR+ Lyt-1-2+ T lymphocytes likely represents an exaggerated, but otherwise normal, immunoregulatory response of the host. These cells may be an important element in the regulation of isotype expression.