Auxin-Cytokinin Interactions in Wild-Type and Transgenic Tobacco

Cytokinins and auxins are important regulators of plant growthand development, but there is incomplete and conflicting evidencethat auxins affect cytokinin metabolism and vice versa. We haveinvestigated these interactions in Nicotiana tabacum L. by separatein planta manipulation of levels of the hormones followed byanalysis of the induced changes in the metabolism of the otherhormone. Cytokinin-overproducing plants (expressing the Agrobacte-riumtumefaciens ipt gene) had lower than wild-type levels of freeIAA, and reduced rates of IAA synthesis and turnover, but therewere no differences in the profiles of metabolites they producedfrom fed IAA. Similarly, auxin-overproducing plants (expressingthe A.tumefaciens iaaM and iaaH genes), had lower levels ofthe major cytokinins than wild-type plants and lower cytokininoxidase activity, but there were no differences in the profilesof metabolites they produced from fed cytokinins. The data demonstratethat cytokinin or auxin overproduction decreases the contentof the other hormone, apparently by decreasing its rate of synthesisand/or transport, rather than by increasing rates of turnoveror conjugation. Implications for the importance of cytokinin: auxin ratios in plant development are considered. (Received September 24, 1996; Accepted December 4, 1996)     

Individual Variation in Advertisement Calls of Territorial Male Green Frogs, Rana clamitans: Implications for Individual Discrimination

Individuals of many territorial species discriminate between familiar territorial neighbors and unfamiliar strangers based on individual differences in acoustic signals. Many anuran amphibians are territorial and use primarily acoustic communication during social interactions, but evidence for acoustically mediated individual discrimination is available only for one species. As a first step in research designed to investigate individual discrimination in a second species of territorial frog, we examined patterns of within-male and among-male variability in 198 advertisement calls of 20 male green frogs, Rana clamitans . The aim was to determine which acoustic properties could be used by males to recognize their territorial neighbors and to estimate limits of reliability afforded by these properties for identifying different neighbors. All of the call properties that we examined exhibited significant inter-individual variation. Discriminant function analyses assigned between 52% and 100% of calls to the correct individual, depending on sample size and the call properties included in the model. This suggests that there is sufficient among-male variability to statistically identify individuals by their advertisement calls. The call properties of fundamental frequency and dominant frequency contributed the most towards discrimination among individuals. Based on their natural history and behavior and the results reported here, we suggest that male green frogs likely discriminate between strangers and adjacently territorial neighbors based on individual variation in advertisement calls.     

Interactions between mucopolysaccharides and cationic polypeptides in aqueous solution: hyaluronic acid, heparitin sulfate, and keratan sulfate

Circular dichroism spectroscopy has been used to study the interactions of hyaluronic acid, heparitin sulfate, and keratan sulfate with cationic polypeptides. The results indicate that the presence of these mucopolysaccharides has an effect in the conformation of poly(L -lysine) and poly(L -arginine), such that the former adopts the “random” form and the latter takes up the α-helical conformation, rather than the “charged coil” form expected at neutral pH. The relative strengths of the interactions can be judged from the melting temperatures above which they are disrupted. Both the stoichiometry and the strength of the interactions depend on the position, number, and type of anionic groups attached to the polysaccharide backbone. Such considerations place the six common mucopolysaccharides in order of increasing strength of interaction: hyaluronic acid < chondroitin 4-sulfate < heparitin sulfate < chondroitin 6-sulfate < keratan sulfate ? dermatan sulfate. These differences should be paralleled by differences in the interaction of the mucopolysaccharides with collagen and fibrous proteins.     

Heparin-polypeptide interactions in aqueous solution

Circular dichroism spectroscopy has been used to study the interactions between heparin and cationic polypeptides in dilute aqueous solution at neutral pH. The results indicate that poly(l-lysine), poly(l-arginine), and poly(l-ornithine) adopt the α-helical conformation in the presence of heparin, rather than the “charged coil” form observed for the polypeptide alone under the same conditions. Maximum interaction for the poly(l-lysine) and poly(l-ornithine) systems occur at an amino acid: disaccharide residue ratio of 2.3 ± 0.1:1, which correlates with the analytical data of 2.3 sulfates per heparin disaccharide. For poly(l-arginine), maximum interaction occurs at a residue ratio of 3.3 ± 0.1:1, and indicates that all the anionic groups (sulfate and carboxyl) of the heparin are involved in this case.The interactions of heparin are analogous to those observed previously for six connective tissue mucopolysaccharides, except that none of the latter had any effect on the conformation of poly(l-ornithine). The poly(l-ornithine)-heparin system shows a thermal “melting” transition at T_m = 56.0 ± 1.0 °C, at which point the polypeptide reverts to the “charged coil” form; the interactions with poly(l-lysine) and poly(l-arginine) are stable up to temperatures > 90 °C. The high thermal stability of these conformation-directing effects indicate a stronger interaction for heparin than the other mucopolysaccharides, which is probably due to the high sulfate content.     

A review of growth and life-history traits of native and non-native European populations of black bullhead <Emphasis Type="Italic">Ameiurus melas</Emphasis>

North American black bullhead, Ameiurus melas, which were introduced to Europe in the nineteenth and twentieth centuries, have received relatively little study. With focus on growth and reproduction, this extensive review, which includes new European data, aims to inform the risk analysis process concerning this non-native species in Europe. Surprisingly, the new data for Europe were more comprehensive than for native populations, with data available mainly from Oklahoma, and North and South Dakota (USA). In terms of relative growth, juvenile A. melas were found to have a relatively uniform body shape regardless of the population’s origin, whereas adults developed different phenotypes depending upon location. Overall growth trajectory was significantly faster for native than for non-native populations. Growth index values decreased significantly with increasing latitude in non-native but not native populations—the latter decreasing weakly with increasing altitude in the populations located at latitudes <40°. Mean general condition (slope ‘b’), mean sex ratio and mean egg diameter did not differ significantly between native and non-native populations. Absolute fecundity was slightly (but not significantly) higher in non-native than native populations. GSI data, which were very scarce for native populations, suggest gonad production may be slightly higher in native than in non-native populations. Precise data on age at maturity (AaM) are lacking for the native range, where 2–5 years is reported. Whereas, in the introduced range the greatest AaM was 3.5 years, and AaM decreases with increasing juvenile growth (TL at age 3). The populations with fastest juvenile growth tended to be from warmer water bodies where they are considered to be invasive. The great growth and life-history plasticity of black bullhead affords the species great potential to invade and establish viable populations in new areas.     

Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life

Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus.     

Cadmium accumulation and its effects on intracellular ion pools in a brewing strain of Saccharomyces cerevisiae

The presence of glucose resulted in a two- to three-fold increase in levels of Cd²⁺accumulated by Saccharomyces cerevisiae after 5 h compared with those observed in the absence of glucose. However, time-dependent Cd²⁺ uptake continued in the absence of glucose over 5 h, resulting in an appreciable increase in cellular Cd²⁺levels. Substantial K⁺ efflux but little Mg²⁺ and negligible Ca²⁺release was observed. Cell fractionation revealed that the bulk of intracellular Cd²⁺ was located in the vacuolar (25%) and bound (60%) fractions. Accumulation of Cd²⁺ ions impacted most noticeably on K⁺ rather than Mg²⁺ levels in intracellular compartments. Cytoplasmic and particularly vacuolar K⁺ levels decreased as Cd²⁺ sequestration continued resulting in increased extracellular levels. In contrast, corresponding intracellular Mg²⁺ pools were only modestly affected with a slight increase and decrease observed in the cytoplasmic and vacuolar fractions respectively. However, levels of bound Mg²⁺ decreased in response to continued Cd²⁺ accumulation. Received 07 March 1999/ Accepted in revised form 26 June 1999