The significance of the leaf epidermis in the taxonomy of the Combretaceae

The epidermal anatomy, with special reference to the glandular trichomes, is surveyed in the Asian species of the genus Combretum. Emphasis is laid on the value of such characters in reviewing the sectional classification of the genus. It is concluded that sections Quadrangulares, Squamosae, Tetragonocarpus and Flagrocarpeae should be amalgamated to form an enlarged section Tetragonocarpus. It is also likely that sections Quisqualoides, Ovalifoliae and Dasystachyeae , and sections Decandra'e and Kaloëdron , should be amalgamated.     

Induction of the blue form of bacteriohodopsin by low concentrations of sodium dodecyl sulfate

The effects produced on bacteriorhodopsin by low concentrations of several detergents have been studied by absorption and fourth-derivative spectrophotometry. Sodium dodecyl sulfate induces the appearance of the blue form of bacteriorhodopsin (λ_max = 600 nm) at pH values up to 7.0 in a reversible manner. The apparent pK of the purple-to-blue transition raised with increasing concentration of SDS. Of the other detergents tested, only sodium dodecyl-N-sarcosinate showed a slight red-shift of the absorption band to 580 nm, whereas sodium taurocholate, Triton X-100 and cetyltrimethylammonium bromide did not favour the appearance of the blue form. The effect of SDS was found to be consistent with a localized conformational change that moves away the counter-ion of the protonated Schiff base.     

Antagonistic and synergistic interactions between aluminum and manganese on growth of Vigna unguiculata at low ionic strength

Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm⁻¹). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required.     

Habitat characteristics contributing to local occupancy and habitat use in rock pool <Emphasis Type="Italic">Daphnia</Emphasis> metapopulations

The effects of invasive macrophytes, water level fluctuations and predation on freshwater unionids Pyganodon grandis and Utterbackia imbecillis were studied in three small impoundments in Northeastern Texas in 2003–2005. Mussel density was sampled with quadrats. Mortality, associated with the water level fluctuations and predation, was estimated by collecting dead shells on the shore at about two month intervals. In two ponds, horizontal distribution of unionids was limited by dense beds of invasive and noxious macrophytes (mainly Eurasian watermilfoil Myriophyllum spicatum and American lotus Nelumbo lutea): mussel densities were significantly lower in these macrophyte beds (P < 0.001). In the third pond with the lowest density of macrophytes (stonewort Chara sp.), unionids were distributed more evenly, and the average unionid biomass was the highest among all ponds studied. Vertical distribution of unionids in all ponds was likely limited by low oxygen at depth >2 m. The total amount of shells found on the shore per year varied from 0.1% to 28% of the total population in the pond and was negatively correlated with water level (r = −0.72 to −0.81, P < 0.005). Mammalian predators consumed up to 19% of the total unionid population and predation was facilitated by water level fluctuations. Handling editor: K. Martens     

Instability of serum 17 beta-hydroxysteroid dehydrogenases of placental origin

The stabilization by glycerol of the serum estradiol 17 beta dehydrogenase has been investigated here in terms of time and temperature. The protected enzyme is stable for a month at least at --20 degrees C. Its activity reaches a maximum at 60 degrees C. In another connection, effect of reduced glutathione, of N. acetyl-cysteine and of various mineral ions on the enzymic conversion has been studied.     

Esters of trehalose from Corynebacterium diphtheriae: A modified purification procedure and studies on the structure of their constituent hydroxylated fatty acids

The purification procedure of 6,6′-diesters of trehalose from Corynebacterium diphtheriae was modified and the isolated substance was analysed by mass spectrometry as its permethylated derivative. The fatty acid moiety released from the glycolipid after alkaline hydrolysis was studied by mass spectral analysis of the O-methylated and O-acetylated methyl ester derivatives. By argentation thin-layer chromatography, three species of O-acetylated methyl esters were recognized, corresponding to saturated, mono-unsaturated and di-unsaturated α-branched-β-hydroxylated fatty acids. The double bond was located by ozonolysis of the O-acetylated methyl ester derivatives, by gas chromatography of the reaction product and mass spectrometry of the effluent from the gas chromatograph. The main components of each species of α-branched-β-hydroxylated fatty acids found in the gly colipid fraction of C. diphtheriae were 2-tetradecyl-3-hydroxyoctadecanoic acid (C₃₂H₆₄O₃, corynomycolic acid), 2-tetradecyl-3-hydroxy-11-octadecenoic acid (C₃₂H₆₂O₃, corynomycolenic acid), 2-tetradec-7′-enyl-3-hydroxy octadecanoic acid (C₃₂H₆₂O₃) and 2-tetradec-7′-enyl-3-hydroxy-11-octadecenoic acid (C₃₂H₆₀O₃, corynomycoldienic acid). The glycolipid fraction from C. diphtheriae is obviously a complex mixture of 6,6′-diesters of trehalose.     

Changes in Calcium Reserves in Breeding Lesser Snow Geese (Chen caerulescens caerulescens)

Calcium and fat reserves of the femur medullary bone were examined in sexually mature lesser snow geese (Chen caerulescens caerulescens) collected during the 1974–1975 season. In females, femur calcium and fat levels increased by 80 and 30%, respectively, during the spring migration, much of the increase taking place while the birds staged in southwestern Manitoba and North Dakota prior to their departure for the breeding area. In males. femur calcium levels showed no seasonal change but femur fat increased in a manner similar to that found in the females, although the increase was not as great (17%). In the females, femur fat content fell by 40% during egg-laying whereas in males a decrease in femur lipid was not evident until incubation was well underway. Femur calcium levels in females declined during egg production and early incubation, showing a 56% decrease over spring migratory levels, indicating that dietary calcium intake was limited during the nesting period. However, the low femur calcium levels in birds collected during the spring were not significantly different from those of wintering birds, suggesting that no calcium deficiencies were apparent. Plasma calcium levels in males remained relatively constant throughout the year, although there was some elevation in May. Plasma calcium levels in the females increased almost threefold during egg laying and returned to pre-laying levels during incubation. Medullary bone was evident only in reproducing females and appeared during spring migration, concomitant with increased femur weight, fat and calcium content. Medullary bone degradation commenced during the first week of incubation and no medullary bone was in evidence by molt. Calcium reserves of medullary bone accounted for only 17.2% of the calcium required for eggshell production, suggesting that. at least during the laying period, the female must depend on some exogenous source, perhaps from grit or brackish water.