Validation of a primary production model of the desert shrub Larrea tridentata using soil-moisture augmentation experiments

Summary In previous papers we have described and verified a primary production model of the desert shrub Larrea tridentata. Here we address the validation phase of the evaluation of this model. Two versions of the model which differ in the priority scheme used for allocating carbon to reproductive or vegetative organs were compared on the basis of their usefulness and reliability over a range of soil-moisture conditions. Over an entire growing season when soil-moisture conditions were near normal both versions of the model were adequate predictors of total above-ground vegetative growth and one was an adequate predictor of reproductive growth as well. A more detailed analysis revealed that the versions varied in the range of soil-moisture conditions over which they were adequate and that neither was adequate when soil-moisture had remained high for extended periods. The validation process has revealed some likely areas for model improvement to increase adequacy.     

Polypeptide molecular weights of the (Na+,K+)-ATPase from porcine kidney medulla

The molecular weights of the polypeptide chains from (Na+,K+)-ATPase of porcine kidney medulla have been determined by analytical sedimentation equilibrium. The alpha-subunit molecular weight is 93 900, and the beta subunit is a glycoprotein with a polypeptide molecular weight of 32 300 (41 400 including protein and carbohydrate). Amino acid and carbohydrate compositions are presented together with related properties (i.e., partial specific volumes, extinction coefficients, and hydrophobic/hydrophilic amino acid content).     

Thermoregulatory behavior of juvenile cromileptes altivelis (serranidae), a tropical marine fish

Ten juvenile Cromileptes altivelis were tested individually for 3-day periods in electronic shuttleboxes to measure their thermoregulatory behavior. The fish voluntarily occupied a 21–27°C span, out of a potentially available 0–50°C range. The mean final thermal preferendum was 24.5°C for all individuals. The thermoregulatory performance of this species is similar to that of cool temperate freshwater fishes.     

Molecular weight of (Na+,K+)ATPase from shark rectal gland.

The (Na+,k+)ATPase from the rectal gland of Carcharhinus obscurus has been solubilized in Lubrol WX as an active complex containing 379,900 g of protein and 61 mol of phospholipid. This detergent-lipid-protein complex contains two catalytic subunits of molecular weight 106,400 and four glycopeptide subunits of protein molecular weight 36,600. The latter subunit has a total molecular weight of 51,700 when the carbohydrate is included. Attempts to dissociate this active enzyme complex to smaller size by increasing the detergent concentration led to inactivation. Thus, the smallest active particle in the presence of Lubrol WX contains the two polypeptide subunits in a mole ratio of 2:4 under conditions where the micellar form of detergent is present at a 70:1 molar ratio. This large excess of Lubrol WX eliminates any possibility of artificial togetherness as the result of statistical considerations.     

Effect of temperature on locomotor activity in the goldfish (Carassius auratus) and the bluegill (Lepomis macrochirus): Presence of an ‘activity well’ in the region of the final preferendum

Goldfish (Carassius auratus) and bluegill sunfish (Lepomis macrochirus) were placed in aquaria where their locomotor activity was monitored by photocells, and tested at various acclimation temperatures over a range encompassing their final thermal preferenda. Activity was pooled over 24-hour periods to eliminate any circadian rhythm effects. Both species exhibited an activity well of reduced locomotor activity in the region of the final preferendum. Goldfish, tested either singly or in groups of 2–5 individuals, exhibited a social-interaction effect which became more pronounced at higher temperatures. These results are discussed in relation to a thermokinetic interpretation of thermo-regulatory behavior in fishes, and to the correspondence between thermal preferenda and thermal optima.     

Thermoregulatory behavior of the bluespotted sunfish,Enneacanthus Gloriousus

Twenty bluespotted sunfish, Enneacanthus gloriosus, were individually tested for thermoregulatory behavior in an electronic shuttlebox. The first fishes of this genus to be tested for thermoregulatory behavior, these individuals were captured near the northern limit of their zoogeographic range, in northeastern Pennsylvania. The mean final preferendum from pooled data of all 20 fish was 28.5°C; there were no significant differences between day and night.     

Biologically related iron-sulfur clusters as reaction centers. Reduction of acetylene to ethylene in systems based on [Fe4S4(SR)4]3-

The possibility that clusters containing the Fe4S4 core unit found in a wide variety of proteins can effect reductive transformations of Fe-S enzyme substrates has been investigated using the reduced synthetic clusters [Fe4S4(SPh)4]3- and acetylene, an alternate nitrogenase substrate. The system [Fe4S4(SPh)4]3-/acetic acid/acetic anhydride in N-methylpyrollidinone at approximately 25 degrees was found to reduce acetylene homogeneously to ethylene, and in the presence of a deuterium source to afford as the principal stereochemical product cis-1,2-C2H2D2. No appreciable reduction was found using the oxidized cluster [Fe4S4(SPh)4]2-. The system is not catalytic and departs from the strict stoichiometry of the reaction, 2[Fe4S4(SPh)4]3- + C2H2 + 2H+ leads to 2 [Fe4S4(SPh)4]2- + C2H4, primarily because of a competing cluster oxidation reaction which could not be eliminated. Based on this reaction ca. 60% conversion of acetylene to ethylene was achieved. A reaction sequence based on absorption and 1H nmr spectral observations and product stereo-chemistry is suggested. The results demonstrate that biologically related, reduced Fe4S4 clusters can effect reduction of at least one Fe-S enzyme substrate, and raise the general possibility of substrate transformation with such clusters as reaction sites in biological systems.     

In vitro adhesion of tufted oral streptococci toBacterionema matruchotii

The adhesive interaction between the ectosymbionts of the corn cob configuration (CCC), a naturally occurring bacterial consortium in human dental plaque, was studied. In vitro association was produced in mixed cultures consisting ofBacterionema matruchotii and streptococci resemblingStreptococcus sanguis previously isolated from human CCC. Phase-contrast, selective immunofluorescence, and scanning electron microscopy showed that in this aggregative system, a tuftlike polar structure typical of the coccal epibiont mediated binding to the core filament. This aggregative model provides evidence that a specialized structure on the cell surface of epiphytic organisms may participate in interbacterial adherence.