Flower choice in honeybees: Effects of food value and flower density

To test the effects of food value on the flower choice, individual honeybees (Apis mellifera) were offered a choice of 25 % sucrose solution (SS) and 1 of 6 different SSs, ranging from 5 % to 50 % SS, at either a low or a high flower density. Artificial flowers were filled with each SS. The honeybees showed a stronger preference for a concentrated SS to a diluted SS at a high than at a low flower density, and the degree of preference was positively correlated to the difference in the sucrose concentration between paired SSs. These foraging patterns were consistent with qualitative predictions from optimal foraging theory. Furthermore, it was found that experience in feeding on a concentrated SS lowered the foraging motivation for a diluted SS at the high flower density, but not at the low flower density. I discuss the effects of food density, food profitability and experience on the foraging behaviour of honeybees.     

Induction and Repair of Damage to DNA in Cucumber Cotyledons Irradiated with UV-B

Photoinduced lesions in DNA, namely, cyclobutane pyrimidinedimers (CPDs) and pyrimidine-(6-4)-pyrimidone photoproducts[(6-4)photoproducts], in cucumber cotyledons that had been irradiatedwith naturally occurring levels of UV-B (290–320 nm) werequantitated by enzyme-linked immunosorbent assays with monoclonalantibodies specific to each type of photolesion. Induction ofthese photolesions was dependent on temperature and their extentwas reduced by simultaneous irradiation with white light. Thedark repair of both types of photolesion was undetectable. Light-dependentremoval of (6-4)photoproducts was very slow, with 50% removalin 4 h. By contrast, 50% of initial CPDs were removed within15 min. Both photorepair processes were dependent on the intensityof white light and were sensitive to temperature. These resultsindicate that high photolyase activity is present in cucumbercotyledons and that repair activities in cucumber cotyledonsare different from those reported in Arabidopsis, in which (6-4)photoproductsare photorepaired more rapidly than CPDs. (Received October 13, 1995; Accepted December 28, 1995)     

A Novel Method for Generating Nested Deletions Using the in Vitro Bacteriophage T3 DNA Packaging System

To sequence a DNA segment inserted into a cosmid vector underthe directed sequencing strategy, we established a simple andrapid method for generating nested deletions which uses thein vitro packaging system of bacteriophage T3 DNA. The principleis based on the previous finding that this system can translocateany linear double-stranded DNA up to 40 kb into the phage capsidin a time-dependent manner and the encapsulated DNA becomesDNase-resistant. For this purpose, we constructed a cosmid vectorthat carries two different antibiotic selection markers at bothsides of the multiple cloning site, and after insertion of aDNA segment, the clone was linearized by -terminase at the cossite. After the packaging reaction in vitro followed by DNasetreatment, the encapsulated DNA was introduced into Escherichiacoli cells to give clones with unidirectional deletions by differentialantibiotic selection. Restriction and sequence analyses of deletionclones demonstrated that an ordered set of clones with nesteddeletions, ranging from less than 1 kb to 25 kb, was createdfrom either the end of the DNA segment. Thus, nested deletionclones that cover the entire region of a 40-kb cosmid insertcan be obtained by a single packaging reaction, and its restrictionmap can be simultaneously obtained.     

Computer determination of perfusion patterns in pulmonary capillary networks

Hanger, Christopher C., Robert G. Presson, Jr., Osamu Okada,Steven J. Janke, John J. Watkins, Wiltz W. Wagner, Jr., and Ronald L. Capen. Computer determination of perfusion patterns in pulmonarycapillary networks. J. Appl. Physiol.82(4): 1283-1289, 1997.Individual pulmonary capillaries are notsteadily perfused. By using in vivo microscopy, it can readily bedemonstrated that perfusion continually switches between capillarysegments and between portions of the network within a single alveolarwall. These changes in capillary perfusion occur even when upstream pressure and flow are constant. Flow switching between capillary segments in the absence of hemodynamic changes in large upstream vessels suggests that capillary perfusion patterns could be random. Tocalculate the probability that perfusion patterns could occur bychance, it is necessary to know the total number of possible perfusionpatterns in a given capillary network. We developed a computer programthat can determine every possible perfusion pattern for any givencapillary network, and from that information we can calculate whetherperfusion of individual segments in the network is random. With theresults of the computer program, we have obtained statistical evidencethat some capillary segments in a network are nonrandomly perfused.

     

A general characteristic of tumor mitochondria: Leakage of endogenous Mg2+ on incubation with uncoupler and resultant reduction of uncoupler-stimulated ATPase activity

Previous studies showed that stimulation of mouse mitochondrial ATPase activity of tumor cells, fetal liver, and adult brain by the uncoupler 2,4-dinitrophenol was markedly suppressed during incubation of the mitochondria with the uncoupler (J.-I. Hayashi et al., 1980, Biochem. Biophys. Res. Commun.92, 261–267). The present work showed the reason for this suppression. More than half the endogenous Mg²⁺ leaked from mitochondria of all tumor cells tested, and of fetal liver and adult brain during incubation with the uncoupler, while only about 30% of the endogenous Mg²⁺ leaked from mitochondria of other normal tissues. The effect of the uncoupler on Mg²⁺ leakage from liver mitochondria changed from the fetal to the adult type within about 30 min after birth. In hypotonic medium, normal liver mitochondria also lost more than half their total Mg²⁺ and concomitantly stimulation of their ATPase activity by uncoupler was considerably reduced. Exogenously added Mg²⁺ could reverse this reduced effect of the uncoupler on ATPase activity of mitochondria from normal tissues and tumor cells. These results show that the endogenous Mg²⁺ content of mitochondria directly affects the stimulation by uncoupler of ATPase activity of mitochondria from both normal tissues and tumor cells. Thus, mitochondria of all tumor cells tested, and of fetal liver and adult brain are leaky to Mg²⁺ during incubation with uncoupler and as a result of the leakage, the stimulatory effect of the uncoupler on their ATPase activity is greatly reduced.     

Dammarane saponins of leaves of Panax pseudo-ginseng subsp. himalaicus

From dried leaves of Panax pseudo-ginseng subsp. himalaicus collected in Eastern Himalaya, new dammarane saponins, named pseudo-ginsenosides-F₁₁ and -F₈ were isolated along with the known Ginseng-root saponins, ginsenosides-Rb₃, Rd and -Re. Pseudo-ginsenoside-F₈ was proved to be a mono-acetyl-ginsenoside-Rb₃ and the location of its acetyl group was established mainly by ¹³C NMR spectroscopy. Pseudo-ginsenoside-F₁₁, was identified as the 6-O-α-rhamnopyransyl(1 → 2)-β-glucopyranoside of 3β,6α,12β,25-tetrahydoxy-(20S,24R)-epoxy-dammarane. The C-24 configuration of ocotillone and its related triterpenes was confirmed to be 24R excluding the recent comment by Lavie et al.     

Prostaglandin D2, a potential antineoplastic agent

Cytotoxic actions of various prostaglandins were examined on L1210 mouse leukemia and several human leukemia cell lines, and prostaglandin D₂ (PGD₂) was found most active. PGD₂ exerted a dose dependent inhibition of L1210 cell growth over 3.6 μ$\text{M}$. At 14.3 μ$\text{M}$ growth was completely inhibited, and the number of viable cells remarkably decreased during culture. Microscopically the remaining cells showed degenerative changes with many vacuoles in their cytoplasm. The IC₅₀ value of PGD₂ on L1210 cell growth was calculated to be 6.9 μ$\text{M}$ (2.4 μg/ml), and at this concentration the DNA synthesis in 24 hr cultured cells was also decreased to a half of the level in the control cells. Such growth inhibition by PGD₂ was also found at similar concentrations with several human leukemia cell lines such as NALL-1, RPMI-8226, RPMI-8402, and Sk-Ly-16. Among other prostaglandins tested, PGA₂ showed a comparable, and PGE₂ a less but significant growth inhibitory activity, while PGB₂, PGF_2α and PGI₂ had no such effects on cell proliferation at 14.3 μ$\text{M}$ concentration. These results suggest a potential antineoplastic activity of PGD₂.     

Serotonin in neuroblastoma × glioma NG108-15 hybrid cells

Mouse neuroblastoma × rat glioma NG108-15 hybrid cells contain a considerable amount of serotonin, and possess small but significant tryptophan hydroxylase activity. The results suggest that NG108-15 hybrid cells are serotonergic, in addition to the known cholinergic property.     

Role of prostaglandin endoperoxides in the serum thiobarbituric acid reaction

In the presence of heme and reduced glutathione, prostaglandin (PG) endoperoxides underwent rapid conversion to malondialdehyde and 12l-hydroxy-5,8,10-heptadecatrienoic acid. In addition, PG endoperoxides as well as lipid peroxides produced malondialdehyde to yield a red pigment during the thiobarbituric acid reaction with different efficiencies. The relative rates of the reaction were: 1,1,3,3-tetraethoxypropane, 100; PGG₂, 55; PGH₂, 32; and 15-hydroperoxyarachidonic acid, 6. The thiobarbituric acid reactive materials in rabbit serum decreased by 25–60%, after intravenous administration of aspirin (a cyclo-oxygenase inhibitor) and with a concomitant decline of serum PG levels. These results, taken together, suggested that serum thiobarbituric acid values, considered to be an indicator of lipid peroxide levels, were to a significant extent due to PG endoperoxides and their derivatives.