18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades

The Aschelminthes is a collection of at least eight animal phyla, historically grouped together because the absence of a true body cavity was perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes. At least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.      

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO₂ concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO₂ concentrationduring growth was increased from 160 to 990 mm³ dm^–3.Photosynthetic rates of canopies grown at 330 and 660 mm³ CO₂dm^–3 were similar when measured at the same CO₂ concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO₂ concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm³ CO₂ dm^–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm³ CO₂ dm^–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO₂ concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO₂ aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO₂ limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO₂ concentration, soybean, canopy photosynthesis     

Nucleotide analogue inhibitors of purine nucleoside phosphorylase

The diphosphate of the antiherpetic agent acyclovir [9-[(2-hydroxyethoxy)methyl]guanine] has been shown to inhibit purine nucleoside phosphorylase with unique potency (Tuttle, J. V., and Krenitsky, T. A. (1984) J. Biol. Chem. 259, 4065-4069). A major factor contributing to the superior inhibition by this diphosphate over the corresponding mono- and triphosphates is revealed here. Homologues of acyclovir mono- and diphosphate that extend the ethoxy moiety by one to four methylene groups were synthesized. These homologues were evaluated for their ability to inhibit human purine nucleoside phosphorylase. Within the diphosphate series, the Ki values increased progressively with increasing chain length. With the monophosphates, the Ki values reached a minimum with the homologue containing a pentoxy moiety. A plot of chain length versus Ki values for both mono- and diphosphates showed that both series had similar optimal distances between the aminal carbon and the terminal oxygen anion. Monophosphates with optimal positioning were somewhat less potent than diphosphates with similar positioning. Nevertheless, it was clear that a major factor in determining potency of inhibition was the distance of the terminal phosphate from the guanine moiety.     

Potential habitat dependence in deposition rate of presumptive annual lines in shells of the bivalve Protothaca staminea

Although repeating depositional features in shells of bivalve molluscs continue to be used in ecology and paleoecology to age individual specimens and thereby provide a potentially powerful tool for geochronological reconstruction of past events, few studies actually test the basic assumptions of growth line analysis: (1) that line deposition is truly periodic and (2) that the length of the period is one year. Recapture of marked individuals of the bivalve Protothaca staminea after 12 or 24 months in field plots in two habitats of Mugu Lagoon (California, U.S.A.) suggests a habitat-specific pattern of deposition of the major growth lines previously assumed to be annual. External (surface) and internal (cross-sectional) growth lines were in excellent agreement on any given specimen and showed that each specimen from a muddy-sand environment deposited a single annual line over 12 months, whereas all but one specimen from a clean-sand environment deposited several more major growth lines than predicted from the numbers of years of additional growth. Although more frequent handling or natural disturbance in the higher-energy, clean-sand habitat may explain these differences, the results demand caution in extrapolating tests of annual periodicity in growth line deposition across species or even across habitats for a single species.     

Distribution and oxidation of malondialdehyde in mice

The in vivo metabolism of malondialdehyde (MDA) by male and female Swiss mice was investigated. Distribution of an i.p. dose of MDA is rapid and uniform throughout the body. Conversion of 14C-labeled MDA to CO2 is complete 4 hours after an i.p. dose of 5 mumol to 200 mumol with no signs of short term toxicity. The yields of CO2 from [1-14C]-beta-alanine, [3-14C]-beta-alanine, [1-14C]-sodium acetate, and [2-14C]-sodium acetate were also determined. Comparison of the yields of CO2 from this series of compounds suggests the intermediacy of malonic semialdehyde in the metabolism of MDA. High doses (600 mumol) of beta-alanine or acetate given prior to 14C-MDA reduced the yield of 14CO2. Ethanol and disulfiram were both inhibitors of MDA metabolism, indicating the involvement of aldehyde dehydrogenase in the oxidation of MDA. These data demonstrate the ability of animal tissues to rapidly remove exogenously administered MDA. They also have implications with respect to the possible pathological consequences of in vivo MDA generation.     

Temperature Effects on Rice at Elevated CO2 Concentration

The continuing increase in atmospheric carbon dioxide concentration([CO₂]) and projections of possible future increases in globalairtemperatures have stimulated interest in the effects of theseclimate variables on agriculturally important food crops. Thisstudywas conducted to determine the effects of [CO₂] and temperatureon rice (Oryza sativa L., cv. IR–30). Rice plants weregrownseason-long in outdoor, naturally sunlit, controlled-environment,plant growth chambers in temperature regimes ranging from 25/18/21°Cto 37/30/34°C (daytime dry bulb air temperature/night-timedry bulb air temperature/paddy water temperature)and [CO₂] of660 µmol CO₂ mol1 air. An ambient chamber was maintainedat a [CO₂] of 330 µmol mol^–1 and temperature regimesof 28/21/25°C. Carbon dioxide enrichment at 28/21/25°Cincreased both biomass accumulation and tillering and increasedgrain yield by 60%. In the 660 µmol mol^–1 [CO₂]treatment, grain yield decreased from 10.4 to 1.0 Mg ha^–1with increasing temperature from 28/21/25°C to the 37/30/34°Ctemperature treatment. Across this temperature range, the numberof panicles plant^–1 nearly doubled while the number ofseeds panicle^–1 declined sharply. These results indicatethat while future increases in atmospheric [CO₂] are likelyto be beneficial to rice growth and yield, potentially largenegative effects on rice yield are possible if air temperaturesalso rise. Key words: Oryza sativa, CO₂, temperature, growth, yield     

A Fossil Myxomycete Plasmodium from Eocene-Oligocene Amber of the Dominican Republic

ABSTRACT The first known fossil slime mold with part of the plasmodium preserved, from Eocene-Oligocene amber of the northern Dominican Republic, is described here. We assign it to the myxomycetes on the basis of its cytoplasmic structure. The paleoecological and evolutionary importance of this fossil is briefly discussed.