Effect of inorganic cations and metabolic inhibitors on putrescine transport in roots of intact maize seedlings

The specificity and regulation of putrescine transport was investigated in roots of intact maize (Zea mays L.) seedlings. In concentration-dependent transport studies, the kinetics for putrescine uptake could be resolved into a single saturable component that was noncompetitively inhibited by increasing concentrations of Ca²⁺ (50 micromolar to 5 millimolar). Similarly, other polyvalent cations, including Mg²⁺ (1.8 millimolar) and La³⁺ (200 micromolar), almost completely abolished the saturable component for putrescine uptake. This suggests that putrescine does not share a common transport system with other divalent or polyvalent inorganic cations. Further characterization of the putrescine transport system indicated that 0.3 millimolar N-ethyl-maleimide had no effect on putrescine uptake, and 2 millimolar p-chloromercuribenzene sulfonic acid only partially inhibited transport of the diamine (39% inhibition). Metabolic inhibitors, including carbonylcyanide-m-chlorphenylhydrazone (20 micromolar) and KCN (0.5 millimolar), also partially inhibited the saturable component for putrescine uptake (V_max reduced 48-60%). Increasing the time of exposure to carbonylcyanide-m-chlorphenylhydrazone from 30 minutes to 2 hours did not significantly increase the inhibition of putrescine uptake. Electrophysiological evidence indicates that the inhibitory effect on putrescine uptake by these inhibitors is correlated to a depolarization of the membrane potential, suggesting that the driving force for putrescine uptake is the transmembrane electrical potential across the plasmalemma.     

Flightlessness in insects

The evolution of wings is heralded as the most important event in the diversification of insects, yet flight-wing loss has occurred in nearly all pterygote insect orders. Flight loss is especially prevalent among taxa inhabiting historically stable habitats. Recent studies of wing-polymorphic species have revealed numerous selective trade-offs in the reproductive potentials of winged versus flightless forms. A diverse set of environmental factors, both biotic and abiotic, trigger flight loss in alary polyphenic taxa, presumably by influencing juvenile hormone titers. Phylogenetic comparisons promise to elucidate much about the historical contexts and consequences of flight loss.     

Kinetics of carrot somatic embryo development in suspension culture

Somatic embryos in liquid culture can serve as a mass cloning system in a plant propagation program. A quantitative formulation of embryo development obtained from cell suspension cultures is used to develop a segregated kinetic model. The model is based on standard classification schemes as previously developed by plant physiologists. Dependent variables include carbohydrate concentrations (sucrose, fructose, and glucose) and biomass apportioned among the inoculum (free single cells, cell clusters), normal developmental stages, and aberrant cell and embryo types. Good agreement between the model and experimental results is indicated and allows for a rigorous approach to media optimization and reactor scaleup for embryo formation.     

Defective Histone Transition during Spermiogenesis in Heterozygous SEGREGATION DISTORTER Males of DROSOPHILA MELANOGASTER

Males of Drosophila melanogaster that are heterozygous for the segregation distorter (SD) chromosome produce a gross excess of SD-bearing offspring because most of the non-SD-bearing sperm are dysfunctional. These dysfunctional sperm exhibit abnormalities in chromatin condensation and compaction during spermiogenesis. Use of the fluorescent dye sulfoflavine, which is specific for basic proteins, has now revealed that the dysfunctional sperm are also defective in the normal transition from somatic to spermatid-specific histones.     

Cell division cycles and circadian clocks : phase-response curves for light perturbations in synchronous cultures of euglena

The cell division rhythm in Euglena gracilis Klebs (Z strain) freeruns with a circadian period (30.2 ± 1.8 hours for 156 monitored oscillations) in aerated, magnetically stirred, 8-liter, axenic batch cultures grown photoautotrophically at 25°C in LD: 3,3, (7,500 lux, cool-white fluorescent) 6-hour light cycles from the moment of inoculation. Cell number was measured at 2-hour intervals with an automatic fraction collector and Coulter Electronic Particle Counter. At different circadian times throughout the 30-hour division cycle, 3-hour light perturbations were imposed on free-running cell populations by giving light during one of the intervals when dark would have fallen in the LD: 3,3 regimen. Using the onset of division as the phase reference point, the net steady-state phase advance or delay (±Δ) of the rhythm was determined after transients, if any, had subsided (usually in one or two days) relative to an unperturbed control culture. Both +Δ and −Δ were found, with maximum values of approximately ±11 to 12 hours being obtained at circadian time (CT) 20 to 22 (the `breakpoint'); little, if any phase shift occurred if the light signal was given between CT 6 and CT 12. The phase-resetting curve obtained by plotting new phase (′) versus old phase () was of the type 0 (`strong') variety. Light perturbations, no matter when imposed, engendered new phases which mapped to a relatively restricted portion (CT 6 to CT 13) of the circadian cycle.

These data provide the first detailed phase-response curve for a circadian mitotic clock. The findings, therefore, not only further support the hypothesis that a circadian oscillator (perhaps exhibiting limit cycle behavior) can modulate cell division in eukaryotic cells, but also provide a useful basis for the dissection of the nature and extent of the coupling between cell division and circadian cycles.

     

Evidence for Sulfhydryl Involvement in Regulation of Phytoalexin Accumulation in Trifolium repens Callus Tissue Cultures

White clover (Trifolium repens L.) callus tissue cultures accumulated the phytoalexin medicarpin after treatment with sulfhydryl reagents. After 24-hour exposures to sulfhydryl reagents, maximum obtainable levels of medicarpin, determined by high performance liquid chromatography analysis, were found with 50 millimolar N-ethyl maleimide, 25 millimolar HgCl₂, 2 millimolar p-chloromercuribenzoic acid, and 0.5 millimolar iodoacetamide. Increased medicarpin levels were also observed in callus treated with p-chloromercuribenzene sulfonic acid, but the highest concentration tested (11.8 millimolar) did not produce the maximum response. After sulfhydryl treatment, medicarpin levels were unchanged for 4 to 6 hours, but steadily increased thereafter with maximum accumulation occurring by 48 to 50 hours for p-chloromercuribenzoic acid, p-chloromercuribenzene sulfonic acid, and HgCl₂ treated callus. Medicarpin levels did not increase in iodoacetamide-treated callus until 8 hours after sulfhydryl exposure, and medicarpin levels were still increasing linearly after 50 hours. Three other metabolic inhibitors, KCN, NaF, and Na₃AsO₄, did not exhibit elicitor activity, indicating cell death was not a factor in the response. Pretreatment of callus with 20 millimolar dithiothreitol followed by 40 millimolar N-ethyl maleimide did not produce the phytoalexin response. Preincubation with dithiothreitol also prevented elicitor activity of HgCl₂ and p-chloromercuribenzene sulfonic acid. These results suggested that dithiothreitol pretreatment somehow prevented sulfhydryl groups within the cell from reacting with the test compounds. These experiments established that the integrity of sulfhydryl groups is important in regulating phytoalexin accumulation in callus cells.     

Arterial imaging with computerized fluoroscopy

Computerized fluoroscopy (CF) allows visualization of any segment of the arterial vascular system with intravenous injection of small volumes of standard iodinated contrast media. Because it avoids the risk of arterial puncture and the need for hospitalization, this technique is safer and more economical than standard arteriography. Because of these advantages, CF is likely to expand the role of arteriography in the clinical management of vascular disease. Computerized arteriographic imaging requires an intravenous power injection of 40 to 60 cc of iodinated contrast media. Immediately after injection, six to ten fluoroscopic images (1/15 sec duration) are obtained at 1.5-sec intervals. The first image serves as a mask from which subsequent images are serially subtracted by means of a digital video image processor. The sequence of different images is contrast enhanced and stored on a video disk. Video images are converted to hard copy arteriography with a standard multiformat camera. Technical failures (<5%) may result from patient motion, inadequate peripheral venous access, or extravasation of contrast media. Nearly 600 computerized intravenous arteriograms have been performed in 240 patients with peripheral vascular disease. Qualitative com-parisons with standard arteriograms suggest a close correlation between these two imaging techniques. Computerized fluoroscopy allows the identification of atheromatous plaque ulceration, stenoses, occlusions, and aneurysms. This method has been used to visualize the aortic arch and its branches, the cervical and intracranial vessels, the abdominal aorta, and arteries of the extremities. Computerized fluoroscopy has great potential as a method for safe, simple diagnostic screening and assessment of the postoperative patient.