Sexual dimorphism and resource allocation in male and female shrubs of Simmondsia chinensis

Summary Desert populations of the evergreen dioecious shrub Simmondsia chinensis exhibit sex-related leaf and canopy dimorphisms not present in populations from more mesic coastal environments. Leaves on female shrubs have characteristically larger sizes, greater specific weights, and greater water-holding capacity than male leaves in desert habitats. In coastal scrub environments no significant difference is present, with leaf characteristics of both sexes similar to those of desert male shrubs. Desert female shrub canopies are typically relatively open with little mutual branch shading. In male shrubs canopies are more densely branched with considerable mutual shading of branches. Female plants allocate a greater proportion of their vegetative resources to leaves than do male plants. Considering total biomass, male plants allocate 10–15% of their resources (biomass, calories, glucose-equivalents, nitrogen, phosphorus) to reproductive tissues. Female allocation is dependent on seed set. At 100% seed set females would allocate 30–40% of their resources to reproduction, while female reproductive investment would equal that of males at approximately 30% seed set. Sexual dimorphism and the associated physiological characteristics in Simmondsia act as an alternative to differential habitat selection by male and female plants. Female plants respond to limited water resources in desert areas by increasing their efficiency in allocating limited resources to reproductive structures.     

The combining site of the dinitrophenyl-binding immunoglobulin A myeloma protein MOPC 315

Magnetic-resonance techniques are used to refine the model of the combining site of the Fv fragment of the dinitrophenyl-binding mouse myeloma protein MOPC 315 constructed by Padlan, Davies, Pecht, Givol & Wright (1976) (Cold Spring Harbor Symp. Quant. Biol. 41, in the press). Light-absorption studies indicate a dinitrophenyl–tryptophan interaction in the Fv fragment of the type occurring in free solution. The Dnp-aspartate–tryptophan complex is therefore used as a starting point for the n.m.r. (nuclear-magnetic-resonance) analysis of the dinitrophenyl–Fv fragment interaction. Ring-current calculations are used to determine the geometry of the complex. The specificity of complex-formation between dinitrophenyl and tryptophan is confirmed by the lack of ring-current shifts of the dinitrophenyl resonances when tryptophan is replaced by any other aromatic amino acid. Proton n.m.r. difference spectra (at 270MHz), resulting from the addition of a variety of haptens to the Fv fragment, show that the combining site is highly aromatic in nature. Calculations on the basis of ring-current shifts define the geometry of the combining site, which involves a dinitrophenyl ring in van der Waals contact with four aromatic amino acid residues on the protein. The observation of a nuclear Overhauser effect on the H₍₃₎ resonance of the dinitrophenyl ring provides additional constraints on the relative geometry of the H₍₃₎ proton and an aromatic amino acid residue on the Fv fragment. The specificity of the Fv fragment for dinitrophenyl ligands arises from a stacking interaction of the dinitrophenyl ring with tryptophan-93_L, in an `aromatic box' of essentially tryptophan-93_L, phenylalanine-34_H and tyrosine-34_L; asparagine-36_L and tyrosine-34_L also contribute by forming hydrogen bonds with the nitro groups on the dinitrophenyl ring. The n.m.r. results also confirm that the antibody–hapten reaction may be visualized as a single encounter step. An Appendix shows the method of calculation of ring currents for the four aromatic amino acids and their use in calculating structures.     

Actin filaments in muscle: Pattern of myosin and tropomyosin/troponin attachments

X-ray patterns from lobster and crayfish muscles show very clear layer lines from the thin filaments, well separated from the myosin layer lines. The intensities in patterns from relaxed muscles include an important contribution from the regulatory proteins, and allow the arrangement of the troponin complexes to be deduced. Moreover, the troponin diffraction indirectly provides an accurate value for the pitch of the actin helix in relaxed muscle.In rigor, the attachment of cross-bridges modifies the intensities. These X-ray patterns support Reedy's (1968) concept that cross-bridges in rigor attach only to certain azimuths on the actin filaments (“target areas”); the 145 Å repeat of their origins on the thick filaments is not reflected in the pattern of attachment. Our calculations show that the observed intensities agree quantitatively with those expected for models based on such attachment, but depend significantly on the locations of the troponin complexes. The arrangement of the filament components is discussed in terms of design requirements. Our conclusions may be applicable to many other muscles, especially insect flight muscle and other invertebrate muscles.     

A comparative study of several serotonin receptor antagonists on basal and stimulus induced release of insulin and glucagon in the intact rat.

Several commonly used serotonin receptor antagonists were studied for their ability to influence basal plasma insulin and glucagon (using 30K antibody) levels as well as the response of these hormones to a glucose or arginine challenge administered systematically to overnight fasted rats. Cyproheptadine, in contrast to other antagonists employed, induced large increases of insulin, glucagon and glucose, although this hyperinsulinemia was of a smaller magnitude when compared with hormone levels observed during an equivalent hyperglycemia resulting from glucose administration. The pancreatic response to a glucose load (increased insulin and decreased glucagon release) and an arginine load (increased insulin and glucagon release) were prevented by cyproheptadine pretreatment. Basal insulin levels were bot consistently altered by methysergide or cinanserin and were slightly elevated by metergoline. Basal glucagon levels were unaffected by these drugs. These three agents potentiated the insulinotropic effect of an arginine load whereas only metergoline exerted a similar effect on the response to glucose loading. Glucagon release in response to these stimuli was not significantly altered by drug pretreatment.     

Predation by a water mite (Piona exigua) on enclosed populations of zooplankton

Short term, replicated experimental alteration of densities of a predatory water mite Piona exigua Viets, inside 0.45–0.475 m³ litre enclosures, revealed little evidence of the effects of predation on the number and relative abundance of the enclosed zooplankton species. Predation rates more closely approximated those estimated from single prey functional response experiments in the second experimental period (December) than in the first (March). In December Daphnia was the only susceptible taxon present in large numbers, whereas in March, Ceriodaphnia and Chydorus were also present. This result is consistent with laboratory findings that predation rates are lowered in the presence of more than one prey type.The difficulty of obtaining evidence for significant effects of these planktonic predators is in part due to changes in the preferred prey species in the diet of Piona depending on stage and sex of the mite and to aspects of experimental design. The wide variability between replicate enclosures at each predator density reduced the power of the statistical analyses used to test the null hypothesis. Enclosures with no predators are necessary to investigate the effects of enclosure on the zooplankton prey, since these effects may outweigh those due to predator consumption.     

Efficient Lipid Staining in Plant Material with Sudan Red 7B or Fluoral Yellow 088 in Polyethylene Glycol-Glycerol

Polyethylene glycol (400) with 90% glycerol (aqueous) is introduced as an efficient solvent system for lipid stains. Various lipid-soluble dyes were dissolved in this solvent system and tested for their intensity, contrast, and specificity of staining of suberin lamellae in plant tissue. The stability (i.e., lack of precipitation) of the various staining solutions in the presence of fresh tissue was also tested. When dissolved in polyethylene glycol-glycerol, Sudan red 7B (fat red) was the best nonfluorescent stain and fluorol yellow 088 (solvent green 4) was an excellent fluorochrome. These two dyes formed stable staining solutions which efficiently stained lipids in fresh sections without forming precipitates. Estimations of the solubilities of these dyes in the solvent compared with their solubilities in lipids of various chemical types indicated that they should both be effective stains for lipids in general.     

Histochemical analysis of rat testicular glycoconjugates. 1. Subsets of N-linked saccharides in seminiferous tubules

Summary The distribution of N-linked glycans in rat testis has been probed using a panel of lectins derived fromGalanthus nivalis (snowdrop, GNA),Canavalia ensiformis (jack bean, Con A),Lens culinaris (lentil, LCA),Pisum sativum (garden pea, PSA) andPhaseolus vulgaris, erythro- and leucoagglutinins (kidney bean, ePHA and IPHA). Several classes of N-linked glycan were identified in the spermatogenic series, and during differentiation into spermatozoa they altered in both their pattern of distribution and relative abundance. A population of tetra-antennary, non-bisected, complex glycans, detected by IPHA, was lost during the transition from spermatogonia to spermatocytes, while high-mannose structures were acquired; these were most abundant in spermatocytes, as were bi- and tri-antennary complex, non-bisected glycans, the latter becoming increasingly abundant on acrosomes and spermatozoa. Their bisected counterparts were more generally expressed throughout spermatogenic cells, although marked localization onto acrosomes and nuclear caps was again seen. Transition from spermatocytes to spermatids involved mainly changes of the acrosomal granule and nuclear cap, which were carried through to the final stages of differentiation. Sertoli cell surfaces and cytoplasmic granules showed a high level of N-glycan expression.     

Histochemical analysis of rat testicular glycoconjugates. 2. Beta-galactosyl residues in O- and N-linked glycans in seminiferous tubules.

Summary Rat testes have been examined with a panel of lectins that bind specifically to oligosaccharide sequences having terminal or subterminal -galactosyl residues in O-linked glycans, or in the outer chains of complex N-linked glycans:Arachis hypogaea (peanut, AHA),Erythrina cristagalli (coral tree, ECA),Ricinus communis (castor bean, RCA120) andAbrus precatorius (jequirity bean, APA) agglutinins. Pretreatment of sections with neuraminidase, -galactosidase and removal of alkali-labile O-linked sequences by -elimination allowed the structure of these glycans to be further explored. In spermatogonia and spermatocytes there was little evidence of glycans terminating in -galactosyl residues, although these were present at non-reducing terminals as sialylgalactosides. The acrosome contained two subsets of O-linked glycans terminating in sialylgalactosides, while the nuclear cap showed at least two subsets of N-linked sialylgalactosyl as well as O-linked glycans. Spermatozoa exhibited minor changes in the pattern of glycosylation, although the overall pattern of -galactosyl expression was similar. Binding to Sertoli cells showed the presence of some unsubstituted -galactosyl terminals on O-linked glycans but few such N-linked residues, while terminal -galactosides were scanty in tubular basement membranes.     

Location of the origin of replication for the 7.5-kbChlamydia trachomatis plasmid

The hypothetical origin of replication for the 7.5-kb plasmid common toChlamydia trachomatis is believed to be in a region of the plasmid that contains four 22-bp tandem repeats preceded by an A-T-rich region. To test this hypothesis, replication of plasmid DNA in metabolically active reticulate bodies of the Lymphogranuloma venereum biovar ofC. trachomatis was examined by electron microscopy. The results presented show that the origin of replication appears to be near the tandem repeats of pCHL2. In addition, replication of the 7.5-kb plasmid is unidirectional, and the copy number during replication is 7–10. The evidence presented suggests thatC. trachomatis has a homologue to theEscherichia coli dnaA gene and that this homologue might be involved in replication of theC. trachomatis 7.5-kb plasmid.     

Differential expression of heat shock proteins in Drosophila embryonic cells following metal ion exposure

Drosophila embryonic cells were exposed to a number of metal ions that have been previously reported to act as teratogens in mammalian systems, including some known to induce heat shock (stress) proteins in a variety of model systems. This study examined the effects of these ions both on differentiation of muscles and neurons and on the induction of heat shock proteins. Metals such as arsenate, cadmium, and mercury all inhibited neuron and/or muscle differentiation in Drosophila embryonic cultures, while they also induced the entire set of heat shock proteins. Two metal ions, nickel and zinc, were shown to induce only the 22-and 23-K proteins, a pattern similar to that seen in “classical” teratogens reported previously. None of the metals tested induced only the 26-and 27-K proteins. These results suggest that there exist different regulatory mechanisms responsible for the heat shock response.