Role of Pili (Fimbriae) in Attachment of Bradyrhizobium japonicum to Soybean Roots

Pili (fimbriae) were observed on cells of each of the five strains of Bradyrhizobium japonicum and the one strain of Rhizobium trifolii examined. Pili on B. japonicum were about 4 nm in diameter and polarly expressed. Piliated cells were estimated by transmission electron microscopy and hydrophobic attachment to polystyrene to constitute only a small percentage of the total population. The proportion of piliated cells in these populations was dependent on culture age in some strains. Piliated B. japonicum cells were selectively and quantitatively removed from suspension when cultures were incubated with either soybean roots or hydrophobic plastic surfaces, indicating that pili were involved in the attachment of the bacteria to these surfaces. Pili from B. japonicum 110 ARS were purified and found to have a subunit molecular weight of approximately 21,000. Treatment of B. japonicum suspensions with antiserum against the isolated pili reduced attachment to soybean roots by about 90% and nodulation by about 80%. Pili appear to be important mediators of attachment of B. japonicum to soybean roots under the conditions examined.     

New Procedure for Extraction of Ammonium from Natural Waters for 15N Isotopic Ratio Determinations

A new method for extracting ammonium from natural waters for ¹⁵N isotopic ratio determination is described. The method employs the conversion of the ammonium nitrogen into indophenol, which is then concentrated onto an octadecylsilane column. The method shows accuracy and precision comparable to those of other methods described in the literature. Some results from field experiments on the Swedish west coast are presented.     

Characteristics of the β-Adrenoreceptor from Neuronal and Glial Cells in Primary Cultures of Rat Brain

The cellular characteristics of the beta-adrenoreceptor in glial and neuronal cells from the newborn rat brain were determined by (-)-[125I]iodocyanopindolol binding. In membranes from both cell types, the binding was saturable and from competition assays the potency series of (-)-isoproterenol greater than (-)-epinephrine = (-)-norepinephrine greater than (+)-isoproterenol was observed. 5'-Guanylyl-imidodiphosphate reduced the affinity of (-)-isoproterenol for the beta-adrenoreceptor from glial cells but had no effect on agonist affinity in neuronal cells. Chronic treatment of both cell types with (-)-isoproterenol reduced the receptor content and the capacity of the agonist to increase the cellular cyclic AMP content. However, the receptor recovery after chronic agonist treatment was faster in glial cells (72 h) than neuronal cells (120 h) and was blocked by cycloheximide. Treatment of both types with the irreversible beta-blocker bromoacetylalprenololmentane (2 microM) reduced the receptor content by 78% but no receptor recovery was observed for 120 h after the initial receptor loss. The data indicated that the majority of beta-adrenoreceptors in both cell types are the beta-1 subtype, but show some differences in receptor-agonist interactions. Furthermore, these CNS cells may be useful models for regulatory studies on the beta-adrenoreceptor.     

Cross-polarization/magic-angle spinning 13C-nmr of (1 → 6)-β-D-glucan (pustulan): Mechanism of gelation

¹³C-nmr has been employed to probe the molecular conformation and crystal structure of (1 → 6)-β-D -glucan (pustulan) in the solution, gel, and solid states. CP/MAS ¹³C-nmr spectra recorded for partially crystalline solid pustulan display a resonance near 82 ppm that is absent in solution spectra. The intensity and peak width of this resonance were found to depend on relative crystallinity as determined by x-ray diffraction. CP/MAS spectra of aqueous pustulan gels also exhibit the 82-ppm resonance, suggesting that the gelation mechanism may involve microcrystalline junction zones. Since the 82-ppm resonance is absent in the CP/MAS spectrum of the (1 → 6)-β-linked dimer gentiobiose, we tentatively conclude the crystal structure of this dimer does not adequately model the yet undetermined structure of pustulan.     

Replicating instabilities in yeast: occurrence in different mutational systems

Summary Following mutagenesis of yeast cells with nitrosoguanidine, primary mosaic colonies exhibiting prototrophic/auxotrophic phenotypes were obtained. Upon replating of these primary mosaics, numerous secondary mosaics were present in the progeny. This study shows that replicating instabilities occur at many different loci within the Schizosaccharomyces pombe genome. In addition, the ade-1 gene of Saccharomyces cerevisiae (causing red pigmentation) was used to show that the phenomenon also occurs in this yeast.NRCC#240/8     

Spatial variation in larval concentrations as a cause of spatial variation in settlement for the barnacle,Balanus glandula

Summary Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.     

Neighborhood predictors of plant performance

Summary We developed models of inter-individual interference to predict the fecundity of individuals in populations of the annual plant species, Arabidopsis thaliana. An individual plant is modeled as having a neighborhood which is a circular area of fixed radius with the plant at its center. Other plants which share the circle with the focal plant are termed neighbors of the focal plant. We developed an index of neighborhood interference which is the independent variable in a non-linear regression model that predicts individual plant fecundity. We present methods of exploratory data analysis that are useful in determining a best neighborhood radius, defined as that radius which minimizes residual sum of squares, and in deciding on the functional form of the interference index. In developing the interference index for Arabidopsis, we focus on aspects of the spatial distribution of neighbors: their number, distance and angular dispersion.We found that a best (or optimal) neighborhood radius can be resolved, which provides the best predictor of plant performance. Fecundity predictors based on adult neighbors were noticeably better than those based on neighbors at the seedling stage. Rosettes of Arabidopsis may change location during development (they fall over) and the new fallen positions do provide some improvement in the predictor. Taking into account distance to neighbors within the neighborhood provided only negligible improvement in the model. Finally, the incorporation of angular dispersion in the crowding index produced a considerably better fit. The fecundity predictor that included number of neighbors and angular dispersion in the crowding index explained about 70% of the variation in individual seed set.     

Temporal Profiles of Proteins Responsive to Transient Ischemia

The responses of long and short half-lived proteins to ischemia were measured in rat brain during 6 days of recovery from 30 min of transient forebrain ischemia produced by four-vessel occlusion. At the end of the ischemic interval, the neocortical activities of four vulnerable enzymes [ornithine (ODC) and S-adenosylmethionine (SAMDC) decarboxylases, and RNA polymerases I and II] were unchanged, but within 30 min of reperfusion, their activities dropped by 25-50%. The loss of substance P in the striatum and substantia nigra was slower, reaching about 50% by 12 h. On the other hand, the activities of 5 long half-lived enzymes did not change in the neocortex at 5 and 15 h of reperfusion and regional protein concentrations were essentially unaffected over 6 days survival. The rate and extent of normalization of the amounts or activities of the vulnerable proteins varied. RNA polymerase II and ODC activities were restored within 4 h, and ODC showed a biphasic increase in activity, with peaks at 10 h and 2-3 days. RNA polymerase I and SAMDC activities were restored by 18 h and 5 days, respectively, whereas substance P concentrations did not completely recover, even at 6-15 days. The greater the regional reduction of blood flow during ischemia, the larger the net change (gain or loss) of SAMDC or ODC activity and the longer the time required to normalize the activities of these enzymes. The average rate of proteolysis, assessed by measuring the rate of clearance of 14C from protein prelabeled with [14C]bicarbonate, was abnormal during the first 2 days of reperfusion. Postischemic changes in both protein synthesis and degradation could affect the amounts of some of the proteins responsive to transient ischemia.     

Multiple pathways for amino acid transport inMytilus gill

Summary The epidermal tissues of marine mussels can accumulate amino acids from surrounding sea water. In the present study, gill tissue isolated from the California coastal mussel,Mytilus californianus, was used in conjunction with intact, actively pumping mussels to study epidermal transport processes. There appeared to be at least four pathways for this uptake: i) a -neutral pathway which transports taurine; ii) an -acidic pathway specific for substrates such as aspartate; iii) an -neutral pathway having a general specificity for this class of compound, but which also accepts the basic amino acid, lysine; and iv) a second -neutral pathway, also of broad specificity, capable of accepting the imino acid, proline, as a substrate. Replacement of Na in sea water with choline reduced uptake of leucine, taurine, aspartate, and proline by more than 95%, and reduced lysine uptake by 75%, suggesting that Na-independent pathways play no significant role in epidermal transport in the gill. Isolated gill tissue was used to estimate the maximum transport capacities (J _max's) of the pathways, which ranged from approximately 5 to 25 mol/(g·hr). Apparent Michaelis constants (K _t ^*'s) of the epidermal transporters were estimated using a convection-diffusion model introduced previously (Wright and Secomb, Am J Physiol 247:R346–R355, 1984). TheseK _t ^*'s ranged from 1 to 5 M. The characteristics of the epidermal transporters are such that they can play a significant role in both animal nutrition and in the reacumulation of endogenous amino acids lost from surface cells through passive diffusion.Abbreviation ASW artificial sea water