Diurnal variations in the kinetics of delayed luminescence from Scenedesmus obtusiusculus after exposure to various light and CO2 regimes

Delayed luminescence was measured from samples of a synchronously growing cell culture of the unicellular green alga, Scenedesmus obtusiusculus Chod., every second hour during the 24 h cell cycle under a 15/9 h lighi/dark regime. Both high (air + 2.5% CO₂) and low (0.03% CO₂) CO₂ conditions were used. Under high CO₂ conditions, while light excitation induces formation of a late (maximum reached after 10–60 s) transient peak in delayed luminescence in cells sampled after 10–16 h in the cell cycle. During most of the cell cycle low CO₂ conditions stimulate a late transient peak formation. Excitation with 700 nm light, but not with 680 nm light, induces a late transient peak in delayed luminescence under high CO₂ conditions. The transient peak is more or less pronounced depending on the cell stage. The variations might be due to a changing capacity for light-induced state I/stale II transitions during the cell cycle. It is assumed that the formation of a late transient peak in delayed luminescence is due to ATP hydrolyzation and is thus favoured by a high ATP/NADPH ratio. Hydrolyzation of ATP affects the transthylakoidal ΔpH, which regulates the reverse electron flow to the plastoquinone-pool and Q_A/Q_B, thus affecting the decay kinetics of the delayed luminescence.     

Niche differentiation with respect to light utilization among coexisting dwarf shrubs in a subarctic woodland

Summary Canopy structure, shoot design, and photosynthetic light recruitment were used to compare four coexisting dwarf shrub species with respect to light utilization. All four species showed different shoot designs which probably result in different light interception properties. Leaves of Vaccinium uliginosum showed the highest levels of photosynthetic light saturation but in situ the shoots of this species reached their maximum photosynthetic rate at the lowest photon flux densities. No consistent differences with respect to photosynthetic light responses were found between deciduous and evergreen species. At sites dominated by one of the deciduous species (Vaccinium uliginosum or V. myrtillus), the two evergreen species studied (V. vitis-idaea and Empetrum hermaphroditum) occurred in the understory, i.e., with their leaf distribution slightly below that of the deciduous species. Sites dominated by one of the evergreen species showed less vertical differentiation in leaf distribution between species.     

Ecological aspects of swidden cultivation among the Andoke and Witoto Indians of the Colombian Amazon

The investigation of crop and soil-crop conditions among Andoke and Witoto cultivators in southeast Colombia is used as a basis for assessing Geertz' (1963) model of swidden cultivation. In this respect, the extent to which maniocdominated swiddens in the study area simulate the structure and composition of the forest climax community is questioned. As Geertz (1963) indicates, an initial nutrient boost for crop cultivation results from the preliminary burning of forest debris, but weed competition, rather than progressive loss of soil fertility, is reported to be the primary cause of abandoning manioc cultivation after 2–3 years. While the Andoke and Witoto crop system remains adaptive at the individual field level, particularly in its constituent species, its fundamental adaptation is considered to be its integration into the broader field and fallow system that juxtaposes crop production with extended periods of forest regeneration.     

MHC nonrestricted cytotoxic T cell clones with selective specificity from patients with transitional cell carcinoma (TCC) of the urinary bladder

Summary Lymphocytes from patients with transitional cell carcinoma (TCC) of the urinary bladder are more cytotoxic to bladder tumor cells than to a variety of control cells. This disease-related cytotoxicity has previously been shown to involve several mechanisms and different types of effector cells. To analyze further the nature of the effector cells operative in this system, peripheral blood lymphocytes from eight TCC patients were stimulated in vitro with TCC extract and cultured in the presence of interleukin 2 and allogeneic feeder cells. When tested for cytotoxicity in vitro on a target cell panel including both adherent and nonadherent cell lines, the lymphocytes killed a broad spectrum of targets in a major histocompatibility complex (MHC)-unrestricted fashion. When cloned by limiting dilution, clones were obtained which displayed a more restricted pattern of target cell killing. Some of the clones were highly but not exclusively selective for TCC-derived target cells. Phenotypically, these cells resembled mature T cells of CTL-type (CD8⁺/CD4^–). They also expressed the CD3/5 T cell antigen receptor complex but target cell killing was not MHC-restricted. The results of various inhibition experiments suggested that the CD3/TCR complex was involved in the cytotoxicity exhibited by these effector cells. However, its precise role in target cell recognition and the identification of the tumor cell structures recognised by the effector cells require further studies.     

Electroporation and conjugal plasmid transfer to members of the genus Aquaspirillum

Electroporation methods and conjugal matings were used to transfer several plasmid vectors to Aquaspirillum dispar and Aquaspirillum itersonii. The incompatibility P class plasmid RP4 was conjugally transferred from Escherichia coli HB101 to these spirilla, and the transconjugants subsequently donated the molecule to plasmid-free E. coli and A. dispar strains via conjugal matings. High-voltage electrotransformation was used to transfer plasmids pUCD2, pSa151 and RP4 to A. dispar and A. itersonii, at efficiencies as high as 3×10⁴ transformants per μg plasmid DNA. RP4 DNA isolated from spirillum hosts, but not RP4 from E. coli cells was successfully transferred to A. dispar and A. itersonii by electrotransformation, suggesting that modification and/or restriction activity may be present in these Aquaspirillum species.     

Transient electrical birefringence characterization of heavy meromyosin

Heavy meromyosin (HMM) and myosin subfragment 1 (S1) were prepared from myosin by using low concentrations of alpha-chymotrypsin. The light chain distribution in HMM was identical with that of myosin, within experimental error, when analyzed on 12% polyacrylamide gels after electrophoresis. Specific birefringences and birefringence decay times were measured by transient electrical birefringence in 5 mM KCl, 5 mM tris(hydroxymethyl)aminomethane (pH 7), and 1 mM MgCl2 at 4 degrees C under gentle conditions that reduced the CaATPase activity by less than 10%. For solutions of HMM, by use of electric field pulses shorter than 0.5 microseconds, the birefringence decay signal from the S1 portions of HMM could be resolved and the rotational motions of the S1 moieties observed directly. The rotation relaxation time, adjusted to 20 degrees C, was 0.34 microseconds; this is in quantitative agreement with previous hydrodynamic results obtained by using covalently attached probes. The assignment of the fast decay time obtained with HMM to the S1 portions was confirmed by birefringence decay measurements on free S1, for which the relaxation time was 0.13 microseconds, corrected to 20 degrees C. The specific birefringences for S1 and HMM, respectively, were 0.37 X 10(-6) and 12.8 X 10(-6) (cm/statvolt)2. Thus, for much longer electric field pulses, the signal from HMM is due almost entirely to its subfragment 2 (S2) portion, and its rotational dynamics can also be monitored directly by using electrical birefringence. The decay of the signal from the S2 portion could be adequately fit without evoking bending of the S2 portion of HMM other than at its junction with S1.