Conopy architecture of Larrea tridentata (DC.) Cov., a desert shrub: foliage orientation and direct beam radiation interception

Summary At sites in the United States, creosote bushes (Larrea tridentata (DC.) Cov.) orient foliage clusters predominantly toward the southeast. Foliage of bushes at the southernmost distribution extreme in Mexico shows no predominant orientation. Clusters at all sites are inclined between 33° and 71° from the horizontal. Inclinations are steeper in the drier and hotter Mojave Desert than in the Chihuahuan Desert. Individual leaflets, though not measured, appear more randomly oriented than foliage clusters. In several populations studied, branches were shorter in the southeastern sectors of the crown, reducing self-shading early in the morning. Measurements of direct beam radiation interception by detached branches, using digital image processing, indicated that foliage clusters oriented toward the southeast exhibited less self-shading during spring mornings than clusters oriented northeast. This effect was not apparent at the summer solstice. This type of canopy architecture may tend to minimize self-shading during the morning hours when conditions are more favorable for photosynthesis, resulting in an improved daily water use efficiency.     

Receptor occupancy by a bovine sialoglycopeptide inhibitor correlates with inhibition of protein synthesis

We have isolated from bovine cerebral cortex cells and purified to homogeneity an 18,000 dalton, pl 3.0 sialoglycopeptide that inhibits protein synthesis and DNA synthesis of nontransformed but not transformed cells without affecting uptake of radiolabeled precursors. In this paper, we examine the relationship between the binding of the sialoglycopeptide inhibitor to 3T3 cells and inhibition of protein synthesis. Binding of the sialoglycopeptide to 3T3 cells was rapid at 37 degrees C and reached a maximum at 30 min; the binding at 37 degrees C was shown to be saturable and specific. Scatchard analysis of the binding indicated that 3T3 cells contained about 2 X 10(4) receptors/cell with a dissociation constant of 1.0-1.5 nM. Several lines of evidence indicated that receptor occupancy on 3T3 cells correlated with the protein synthesis inhibitory activity of the sialoglycopeptide. A comparison of the kinetics of inhibitor binding with the kinetics of protein synthesis inhibition demonstrated that binding directly correlated with the inhibition of protein synthesis, concentration-dependent inhibition of protein synthesis directly correlated with concentration-dependent receptor occupancy, and a direct correlation was also observed between the kinetics of inhibitor dissociation from its specific cell surface receptor and the kinetics of recovery from protein synthesis inhibition.     

Seasonal Acclimation of Stem Photosynthesis in Woody Legume Species from the Mojave and Sonoran Deserts of California

Photosynthesis (Pn) was measured in stems of two desert legumes, Caesalpinia virgata at a low elevation site (118 m) in the Sonoran Desert and Senna armata at a higher elevation (950 m) in the Mojave Desert. The lower elevation site experienced higher spring and summer temperatures than the higher elevation site, but the air vapor pressure, irradiance, and rainfall patterns were similar. Mid-morning maximum stem Pn was highest in May for C. virgata (7.8 [mu]mol m-2 s-1) and in July for S. armata (5.8 [mu]mol m-2 s-1). The seasonal variation in maximum stem Pn was not associated with changes in bulk tissue water potential or chlorenchyma tissue nitrogen concentration. The main environmental regulators of seasonal stem Pn were temperature and leaf to air vapor pressure gradient. Light-response curves indicated no major differences in apparent quantum yield or light compensation point between the spring and summer, but light-saturated stem Pn at ambient temperature decreased for C. virgata between these seasons. The optimal temperature for stem Pn remained the same for both species between the spring and the summer. However, stem Pn of both species increased at all temperatures between the spring and summer. Potential stem Pn under optimal conditions and CO2-saturated stem Pn increased for both species between spring and summer. The increase in stem Pn potential allowed these species to maintain stem Pn during the summer even though stem Pn responses to temperature and vapor pressure did not acclimate to seasonal climatic conditions.     

Alkaloids of Zanthoxylum monophyllum and Z. punctatum

The known alkaloids N-methylcorydine and magnoflorine were major constituents of stems and branches of Zanthoxylum punctatum (Rutaceae). Berberine was the major alkaloid of Z. monophyllum, which also contained a new pyrano-2-quinolone alkaloid, zanthophylline, and its desmethyl analog. Zanthophylline has an —NCH₂OAc functional group which is readily hydrolyzed by dilute acid. Methyl vanillate and the furocoumarin columbianetin were also found in Z. monophyllum.     

Diaminopimelic Acid Synthesis in Cultures of an Escherichia coli Double Auxotroph: Effects of Cultural Conditions

The metabolic response to L-lysine of Escherichia coli ATCC 13002, a lysine-histidine double auxotroph, has been examined in a synthetic medium containing sucrose. In shaken cultures largest amounts of extracellular DAP were produced with an initial lysine concentration of 7·5 mg/1 and in static cultures of 2·5 mg/1. Considerably smaller amounts of DAP accumulated under stationary conditions. In cultures shaken for 20 and 43 h there was an overall decrease in the yields of DAP, expressed in terms of cell biomass and of sucrose consumed, as the initial concentration of lysine was increased from 0·75 mg/1 in steps up to 25 mg/1. The regulatory effect of lysine on DAP production was also observed when lysine was supplied to cultures at a constant rate employing diffusion capsules.     

Summer water relations of the desert phreatophyte Prosopis glandulosa in the Sonoran Desert of southern California

Summary Two shoot populations of the rhizomatous, patchforming herb Solidago canadensis were studied throughout a developmental cycle in two abandoned pasture sites in southern Ontario. The shoot cohorts that emerged in spring dominated the two populations; subsequent recruitment was very low. Shoot mortality was highest in June and was concentrated in the smallest size classes. Both populations showed a pronounced bimodal size structure for most of the growth cycle. Relative growth rate of shoots declined as the growing season progressed and tended to be lowest in the smallest size classes. Inflorescence production depended on shoot size. The calculated relationship between log mean weight and log density of shoots was not constant during the growth cycle and the calculated maximum biomass values do not transgress the ultimate thinning line suggested from previously published data.Address for proofs and present address: Department of Geography, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX. England     

Ontogenetic changes in spot configuration (numbers,circularity, size and asymmetry) and lateral line in Neurergus microspilotus (Caudata: Salamandridae)

Coloration in three of four species of the genus Neurergus including N. microspilotus is characterized by the presence of yellow spots on a dark skin, but there is no available information about changes in spot configuration, speed of development and degree of association between melanophore‐free region and the lateral line. In this study, spot numbers, spot circularity, spot size and spot asymmetry were studied during larval to adult growth in N. microspilotus during July 2012 to June 2015. The mean numbers of spots increased during the late larval stage till postmetamorphic period from 13.33 ± 3.77 to 22.53 ± 4.09 and reached 42.62 ± 4.06 in adults. At the same time, the extent of spots gradually decreased in size from 5.80 ± 1.00 to 3.57 ± 0.97 mm² and reached 3.55 ± 1.42 mm² in adults, but the spot circularity increased from 0.48 ± 0.23 to 0.78 ± 0.49 and reached 0.80 ± 0.15 in adults. In adults, the numbers, circularity, size and asymmetry of spots remain stable with little but non‐significant changes during the study period. Histological study shows that formation of a melanophore‐free region correlates with the development of the lateral line receptors. This study demonstrates that the effects of lateral line on chromatophores persist through middle larval stages but diminish as metamorphosis completes.     

Effects of manipulation of water and nitrogen regime on the water relations of the desert shrub Larrea tridentata

Summary Water and nitrogen regimes of Larrea tridentata shrubs growing in the field were manipulated during an annual cycle. Patterns of leaf water status, leaf water relations characteristics, and stomatal behavior were followed concurrently. Large variations in leaf water status in both irrigated and nonirrigated individuals were observed. Predawn and midday leaf water potentials of nonirrigated shrubs were lowest except when measurements had been preceded by significant rainfall. Despite the large seasonal variation in leaf water status, reasonably constant, high levels of turgor were maintained. Pressure-volume curve analysis suggested that changes in the bulk leaf osmotic potential at full turgor were small and that nearly all of the turgor adjustment was due to tissue elastic adjustment. The increase in tissue elasticity with increasing water deficit manifested itself as a decrease in the relative water content at zero turgor and as a decrease in the tissue bulk elastic modulus. Because of large hydration-induced displacement in the osmotic potential and relative water content at zero turgor, it was necessary to use shoots in their natural state of hydration for pressure-volume curve determinations. Large diurnal and seasonal differences in maximum stomatal conductance were observed, but could not easily be attributed to variations in leaf water potential or leaf water relations characteristics such as the turgor loss point. The single factor which seemed to account for most of the diurnal and seasonal differences in maximum stomatal conductance between individual shrubs was an index of soil/root/ shoot hydraulic resistance. Daily maximum stomatal conductance was found to decrease with increasing soil/root/ shoot hydraulic resistance. This pattern was most consistent if the hydraulic resistance calculation was based on an estimate of total canopy transpiration rather than the more commonly used transpiration per unit leaf area. The reasons for this are discussed. It is suggested that while stomatal aperture necessarily represents a major physical resistance controlling transpiration, plant hydraulic resistance may represent the functional resistance through its effects on stomatal aperture.