Visual optics in toads (Bufo americanus)

Aspects of visual optics were investigated in the American toad (Bufo americanus). The development of the refractive state of the eye during metamorphosis was followed with IR photoretinoscopy. Frozen sections documented the changes in optical parameters before and after metamorphosis. There is a difference in light sensitivity between juvenile and adult toads. Binocular accommodation in adult toads was observed. 1. IR photoretinoscopic measurements showed that the refractive state of the eye changed very rapidly during metamorphosis, about 10 D/h while the animal entered the terrestrial habitat. 2. Frozen sections showed that the almost spherical lens in a tadpole eye had flattened in a just metamorphosed toad's eye while at the same time the distance of the lens to the retina had decreased. However, the morphological measurements were not sufficiently sensitive to record the relatively small changes in ocular dimensions that were responsible for the rapid changes in refractive state during metamorphosis. 3. Schematic eyes, with homogeneous and non homogeneous lenses, were constructed for tadpoles, juvenile toads, and adult toads. 4. Nonparaxial raytracing studies in schematic eyes suggested that the lenses of animals of the three developmental stages tadpole, juvenile toad, and adult are not homogeneous but have a refractive index gradient. The raytracing studies indicated that the refractive index gradient is different for the different developmental stages, being highest in the tadpole lens. 5. The observations of toads during feeding behavior at different light levels showed an increased light sensitivity in the adult nocturnal toads in contrast to the juvenile animals, which are diurnal. The increased light sensitivity could partly be explained with an increase in aperture and an increase in red rod outer segments. To fully explain the higher light sensitivity in adult toads, changes in neuronal parameters had to be assumed. 6. Retinoscopic measurements of the resting refractive state in the adult toad showed a hyperopic defocus of about +8 D. By subtracting the measurement artefact for retinoscopy, the true resting focus was found to be nearly emmetropic. 7. The amount of natural accommodation in adult toads during normal feeding behavior was investigated with IR photoretinoscopy. Binocular accommodation of about 8 D was observed.     

Influence of blood parasites on the body mass of passeriform birds

Body masses of 3,739 birds representing immature and adult males and females of 15 species of passeriforms (both uninfected and infected with Haemoproteus spp. and Leucocytozoon spp.) were compared. There was some interaction among year, month and area of capture for several host species, but there was no discernible effect of either parasite genus on body mass. There were no effects due to high intensity parasitemia for eight host species examined. Either parasitism does not cause loss of body mass, or the techniques used were too insensitive to separate effects of parasitism from other natural causes.     

Microbial hydroxylation of quinoline in contaminated groundwater: evidence for incorporation of the oxygen atom of water

Studies conducted in an aquifer contaminated by creosote suggest that quinoline is converted to 2(1H)quinolinone by an indigenous consortium of microorganisms. Laboratory microbial experiments using H218O indicate that water is the source of the oxygen atom for this hydroxylation reaction under aerobic and anaerobic conditions.     

Social organization and ecology of proboscis monkeys (Nasalis larvatus) in mixed coastal forest in Sarawak

Data are presented from a 16-month study of proboscis monkeys in an area of mixed coastal forest in Sarawak. The population density, social organization, and feeding and ranging behavior are described in detail. Results are compared with those from other primates in an attempt to understand why females of certain species (including proboscis monkeys) transfer between social groups. The scarcity of available food and reasons for the limited habitat preferences of proboscis monkeys are also discussed.     

Effects of lignin on the anaerobic degradation of (ligno) cellulosic wastes by rumen microorganisms

Summary There appeared to be a clear correlation between the lignin content (% of TS) of several waste and natural materials and their degradability by rumen microorganisms. Materials with lignin contents higher than 25% were not degraded within 72 h. The effects of Kraft pine lignin and some lignin monomers on filter paper degradation, methane production and CMCase activity were tested. Testing these compounds in concentrations comparable to natural conditions showed minor effects. At higher concentrations p-coumaric acid strongly inhibited cellulose degradation and methane production in batch cultures. Influence of lignin compounds on degradation is discussed in relation to structural effects and enzyme or growth inhibition.     

Mutations in human lymphocytes studied by an HLA selection system

Human lymphocytes mutated at the HLA-A2 or HLA-A3 alleles were enumerated and studied by primary selection using antibody and complement, followed by limiting dilution cloning and secondary selection using immunofluorescence or antibody and complement. The geometric mean frequency of in vivo mutant lymphocytes was 3.08 X 10(-5) for the HLA-A2 allele and 4.68 X 10(-6) for the HLA-A3 allele. Mutagenesis by X-radiation or mitomycin produced a dose-related increase in mutant frequency. HLA-B phenotyping and Southern Analysis of the HLA-A gene suggested that mutation was frequently due to gene deletion, which was often substantial.     

Sink Metabolism in Tomato Fruit : II. Phloem Unloading and Sugar Uptake

Analysis of [³H]-(fructosyl)-sucrose translocation in tomato (Lycopersicon esculentum Mill.) indicates that phloem unloading in the fruit occurs, at least in part, to the apoplast followed by extracellular hydrolysis. Apoplastic sucrose, glucose, and fructose concentrations were estimated as 1 to 7, 12 to 49, and 8 to 63 millimolar, respectively in the tomato fruit pericarp tissue. Hexose concentrations were at least four-fold greater than sucrose at all developmental stages. Short-term uptake of [¹⁴C]sucrose, -glucose, and -fructose in tomato pericarp disks showed first order kinetics over the physiologically relevant concentration range. The uptake rate of [¹⁴C]-(glucosyl)-1′-fluorosucrose was identical to the rate of [¹⁴C]sucrose uptake, suggesting sucrose may be taken up directly without prior extracellular hydrolysis. Short-term uptake of all three sugars was insensitive to 10 micromolar carbonyl cyanide m-chlorophenylhydrazone and to 10 micromolar p-chloromercuribenzene sulfonic acid. However, long-term accumulation of glucose was sensitive to carbonyl cyanide m-chlorophenylhydrazone. Together these results suggest that although sucrose is at least partially hydrolyzed in the apoplast, sucrose may enter the metabolic carbohydrate pool directly. In addition, sugar uptake across the plasma membrane does not appear to be energy dependent, suggesting that sugar accumulation in the tomato fruit is driven by subsequent intracellular metabolism and/or active uptake at the tonoplast.     

Gravitropism in Higher Plant Shoots : V. Changing Sensitivity to Auxin

An alternative to the Cholodny-Went, auxin-transport hypothesis of gravitropic stem bending was proposed as early as 1958, suggesting that gravistimulation induces changes in sensitivity to auxin, accounting for differential growth and bending. To test the sensitivity hypothesis, we immersed marked, decapitated sunflower (Helianthus annuus L.) hypocotyl sections in buffered auxin solutions over a wide concentration range (0, 10⁻⁸ to 10⁻² molar IAA), photographed them at half-hour intervals, analyzed the negatives with a digitizer/computer, and evaluated surface-length changes in terms of Michaelis-Menten enzyme kinetics. Bending decreases with increasing auxin concentration; above about 10⁻⁴ molar IAA the hypocotyls bend down; increasing auxin inhibits elongation growth of lower surfaces (which is high at zero or relatively low auxin levels) but promotes upper-surface growth (which is low at low auxin levels). Thus, lower surfaces have a greater K_m sensitivity to applied auxin than upper surfaces. At optimum auxin levels (maximum growth), growth of bottom surfaces exceeds that of top surfaces, so bottom tissues have a greater V_max sensitivity. V_max sensitivity of vertical controls is slightly lower than it is for either horizontal surface; K_m sensitivity is intermediate. Clearly, gravistimulation leads to significant changes in tissue sensitivity to applied auxin. Perhaps these changes are also important in normal gravitropism.     

Ultrastructure of the calcium release channel of sarcoplasmic reticulum

This study is concerned with the characterization of the morphology of the calcium release channel of sarcoplasmic reticulum (SR) from fast-twitch skeletal muscle, which is involved in excitation-contraction coupling. We have previously purified the ryanodine receptor and found it to be equivalent to the feet structures, which are involved, in situ, in the junctional association of transverse tubules with terminal cisternae of SR. The receptor is an oligomer of a single high molecular weight polypeptide and when incorporated into phospholipid bilayers, has channel conductance which is characteristic of calcium release in terminal cisternae of SR. The purified channel can be observed by electron microscopy using different methods of sample preparation, with complementary views being observed by negative staining, double staining, thin section and rotary shadowing electron microscopy. Three views can be observed and interpreted: (a) a square face which, in situ, is junctionally associated with the transverse tubule or junctional face membrane; (b) a rectangle equivalent to the side view; and (c) a diamond shape equivalent to the side view, of which the base portion appears to be equivalent to the transmembrane segment. Negative staining reveals detailed substructure of the channel. A computer averaged view of the receptor displays fourfold symmetry and ultrastructural detail. The dense central mass is divided into four domains with a 2-nm hole in the center, and is enclosed within an outer frame which has a pinwheel appearance. Double staining shows substructure of the square face in the form of parallel linear arrays (six/face). The features of the isolated receptor can be correlated with the structure observed in terminal cisternae vesicles. Sections tangential to the junctional face membrane reveal that the feet structures (23-nm squares) overlap so as to enclose smaller square spaces of approximately 14 nm/side. We suggest that this is equivalent to the transverse tubule face and that the terminal cisternae face is smaller (approximately 17 nm/face) and has larger alternating spaces as a consequence of the tapered sides of the foot structures. Image reconstruction analysis appears to be feasible and should provide the three-dimensional structure of the channel.