A Secondary Alcohol Dehydrogenase from Tetrahymena furgasoni1

ABSTRACT. Dehydrogenase activity with hydroxysteroids has been observed in Tetrahymena furgasoni (formerly T. pyriformis strain W), and the enzyme responsible has been isolated from this organism. The purified dehydrogenase is active with a variety of steroid alcohols at apparent K_m values ranging from 0.2 to 4.0 mM. The C-3 hydroxyl of ring A of the steroid nucleus is the preferred position of oxidation. However, a variety of other secondary alcohols are also substrates, with apparent K_m values for 2-butanol, 2-pentanol, and cyclohexanol of 880, 1000. and 150 mM, respectively. With both steroidal and nonsteroidal alcohols. NAD is the preferred co-substrate, although low activity with NADP is observed. Evidence is presented that the activity with secondary alcohols, whether steroidal or not, is the property of a single protein species.     

Diagnostic Genetic Marker That Differentiates Eastern Fox Squirrels From Eastern Gray Squirrels

Abstract The Delmarva fox squirrel (Sciurus niger cinereus) has been listed as endangered by the United States Department of Interior since 1967. A high-priority task for the recovery of this taxon is to determine its current geographic distribution. Toward this end, we have identified a microsatellite locus that unambiguously differentiates Delmarva fox squirrels from eastern gray squirrels (S. carolinensis), which frequently co-occur with Delmarva fox squirrels. Analysis of this marker in noninvasively collected hair samples will allow unequivocal identification of localities occupied by Delmarva fox squirrels with a minimum investment of funds, time, and effort because handling individuals will be unnecessary. This protocol will expedite site review in connection with the Endangered Species Act consultation process.     

Nitrogen fixation in a desert stream ecosystem

Few measurements of nitrogen fixation exist for streams. Desertstreams are warm, well lighted, and often supportabundant cyanobacterial populations; thus N₂ fixationmay be significant in these N-poor ecosystems. N₂fixation was measured in situ by acetylene reductionfor two patch types (Anabaena mat and anepilithic assemblage). Patch-specific rates were highcompared with published values (maximum 775 µgN₂ [83 µmol C₂H₄]mg chl a ^-1 h^-1or 51 mg N₂ [5.4 mmol C₂H₄] m_-2 h_-1).Daytime fixation was higher than nighttimefixation, and temperature, light and inorganic Nconcentration explained 52% of variance in hourlyrates over all dates. Diel input-output budgets wereconstructed on five dates when cyanobacteria werepresent in the stream. Diel N₂ fixation rates weremeasured for comparison with reach-scale diel nitrogenretention, to assess the importance of this vector to Neconomy of the stream. Fixation accounted for up to85% of net N flux to the benthos, but its importancevaried seasonally. Finally, we applied biomass-specificfixation rates to 1992 and 1993 biomass data to obtainseasonal and annual N₂ fixation estimates.Cyanobacteria were absent or rare during winter andspring, thus most of the annual N₂ fixation occurredduring summer and autumn. Annual rates of nitrogenfixation for 1992 and 1993 (8.0 g/m₂ and 12.5g/m₂) were very high compared to other streams,and moderately high compared to other ecosystems.Like other phenomena in this disturbance-proneecosystem, nitrogen fixation is strongly influenced bythe number and temporal distribution of flood events.     

The Effect of Specific Sterols on Cell Size and Fatty Acid Composition of Tetrahymena pyriformis W

The size and fatty acid composition of Tetrahymena pyriformis W cells were influenced by the provision of a nutritional supplement of ergosterol, cholesterol, or tetrahymanol, but not of 20-isocholesterol. Ergosterol and cholesterol addition led to a reduction in cellular volume, an increase in glycerophospholipid saturated fatty acid content, and an increase in palmitoleic acid and its metabolic products when compared to unsupplemented controls. Tetrahymanol supplementation resulted in an increase in cellular volume, a decrease in saturated fatty acid content, and a reduction in palmitoleic acid and derivatives. 20-Isocholesterol was accumulated by the cells; however, this compound had no effect on any of the parameters followed in this investigation and had only a small depressant effect on tetrahymanol biosynthesis. Ergosterol and cholesterol had the same impact on the ciliates, even though the ergosterol-supplemented cells contained approximately three times as much free sterol as did cholesterol-grown cells. The amount of the free cholesterol and metabolic products in supplemented cultures was similar to the amount of tetrahymanol present in control cultures. This observation suggests that the cells recognize qualitative differences among the various polycyclic alcohols rather than responding to the amount of sterol present. Increased cellular levels of tetrahymanol led to a response unlike that of the true sterols, which again suggests that the high degree of specificity depends on the structure of the added polycyclic alcohol. The changes in fatty acid composition may be required to maintain proper interaction of the polar lipids and the polycyclic alcohols to give an appropriate degree of membrane fluidity.     

Alternative modes of leaf dissection in monocotyledons

Although a majority of monocotyledons have simple leaves, pinnately or palmately dissected blades are found in four orders, the Alismatales, Pandanales, Dioscoreales and Arecales. Independent evolutionary origins of leaf dissection are indicated by phylogenetic analyses and are reflected in the diversity of mechanisms employed during leaf development. The mechanism of blastozone fractionation through localized enhancement and suppression of growth of the free margin of the leaf primordium occurs in the Araceae and Dioscoreaceae. By contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through intercalary growth in a submarginal position and, second, the initially simple leaf blade is dissected through an abscission-like process of leaflet separation. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. In this mode, discrete patches of cells undergo programmed cell death during lamina development, resulting in formation of open perforations. When perforations are positioned near the leaf margin, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. Whereas blastozone fractionation defines the early primary morphogenesis phase of leaf development, the other two modes occur later, during the secondary morphogenesis/histogenesis phase. Evolution of these mechanisms presumably has involved recruitment of other developmental programmes into the development of dissected leaves.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 25–44.     

Experimental investigations of diel vertical movements by lotic mayflies over substrate surfaces

SUMMARY. 1. The vertical distribution within the substrate of three lotic mayflies (Rhithrogena sp., Paraleptophlebia sp. and Baetis tricaudalus Dodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.
2. Rhithrogena sp. and B. tricaudatus exhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although >64% of B. tricaudalus occupied the upper surfaces throughout the 24 h period. In contrast, Parakplophlebia sp. larvae did not change their vertical distribution over the 24 h period.
3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.
4. The movement of Rhiihrogena sp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.
5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.