Barley aleurone cells contain two types of vacuoles. Characterization Of lytic organelles by use of fluorescent probes

Light microscopy was used to study the structure and function of vacuoles in living protoplasts of barley (Hordeum vulgare cv Himalaya) aleurone. Light microscopy showed that aleurone protoplasts contain two distinct types of vacuole: the protein storage vacuole and a lysosome-like organelle, which we have called the secondary vacuole. Fluorescence microscopy using pH-sensitive fluorescent probes and a fluorogenic substrate for cysteine proteases showed that both protein storage vacuoles and secondary vacuoles are acidic, lytic organelles. Ratio imaging showed that the pH of secondary vacuoles was lower in aleurone protoplasts incubated in gibberellic acid than in those incubated in abscisic acid. Uptake of fluorescent probes into intact, isolated protein storage vacuoles and secondary vacuoles required ATP and occurred via at least two types of vanadate-sensitive, ATP-dependent tonoplast transporters. One transporter catalyzed the accumulation of glutathione-conjugated probes, and another transported probes not conjugated to glutathione.     

Decreasing the Effective Thermal Conductivity in Glass Supported Thermoelectric Layers

As thermoelectric devices begin to make their way into commercial applications, the emphasis is put on decreasing the thermal conductivity. In this purely theoretical study, finite element analysis is used to determine the effect of a supporting material on the thermal conductivity of a thermoelectric module. The simulations illustrate the heat transfer along a sample, consisting from Cu, Cu₂O and PbTe thermoelectric layers on a 1 mm thick Pyrex glass substrate. The influence of two different types of heating, at a constant temperature and at a constant heat flux, is also investigated. It is revealed that the presence of a supporting material plays an important role on lowering the effective thermal conductivity of the layer-substrate ensemble. By using thinner thermoelectric layers the effective thermal conductivity is further reduced, almost down to the value of the glass substrate. As a result, the temperature gradient becomes steeper for a fixed heating temperature, which allows the production of devices with improved performance under certain conditions. Based on the simulation results, we also propose a model for a robust thin film thermoelectric device. With this suggestion, we invite the thermoelectric community to prove the applicability of the presented concept for practical purposes.     

Dexamethasone regulates the program of secretory glycoprotein synthesis in hepatoma tissue culture cells

The secretory glycoproteins synthesized by hepatoma tissue culture (HTC) cells were resolved by two-dimensional polyacrylamide gel electrophoresis of media from cells that were grown in the presence of [(3)H]fucose. These cells synthesize and secrete a complex set of fucose-containing glycoproteins. These secretory glycoproteins are distinct from those glycoproteins present in the plasma membrane of HTC cells. Incubation of HTC cells with dexamethasone has a pronounced effect on the quality and quantity (denoted here as the program) of secretory protein synthesis, as assayed by the short-term incorporation of labeled mannose, fucose, or methionine. The synthesis of two mannose- and fucose- containing glycoprotein series, one of 50,000 mol wt and a more heterogeneous series with mol wt of 35,000-50,000, is increased to a high level by the hormone; conversely, the synthesis of other secretory proteins, particularly one with mol wt of 70,000, is decreased or stopped completely. The synthesis of some major secretory proteins is not affected by the hormone. Dexamethasone has less of an effect on the composition of either total cell membrane glycoprotein or plasma membrane glycoprotein. But there is a decrease in the synthesis of a major membrane glycoprotein series with mol wt of 140,000. These effects of dexamethasone are relatively specific to HTC cells. Neither Reuber H-35 cells nor primary cultures of rat hepatocytes show the same response to the steroid. Two variant HTC cell lines, which were selected for their resistance to dexamethasone inhibition of extracellular plasminogen activator activity, respond only partially to the steroid-induced regulation of the secretory and membrane glycoproteins.     

Nitric oxide reduces seed dormancy in Arabidopsis

Dormancy is a property of many mature seeds, and experimentation over the past century has identified numerous chemical treatments that will reduce seed dormancy. Nitrogen-containing compounds including nitrate, nitrite, and cyanide break seed dormancy in a range of species. Experiments are described here that were carried out to further our understanding of the mechanism whereby these and other compounds, such as the nitric oxide (NO) donor sodium nitroprusside (SNP), bring about a reduction in seed dormancy of Arabidopsis thaliana. A simple method was devised for applying the products of SNP photolysis through the gas phase. Using this approach it was shown that SNP, as well as potassium ferricyanide (Fe(III)CN) and potassium ferrocyanide (Fe(II)CN), reduced dormancy of Arabidopsis seeds by generating cyanide (CN). The effects of potassium cyanide (KCN) on dormant seeds were tested and it was confirmed that cyanide vapours were sufficient to break Arabidopsis seed dormancy. Nitrate and nitrite also reduced Arabidopsis seed dormancy and resulted in substantial rates of germination. The effects of CN, nitrite, and nitrate on dormancy were prevented by the NO scavenger c-PTIO. It was confirmed that NO plays a role in reducing seed dormancy by using purified NO gas, and a model to explain how nitrogen-containing compounds may break dormancy in Arabidopsis is presented.     

Chronopharmacology of roflumilast: a comparative pharmacokinetic study of morning versus evening administration in healthy adults

The human circadian system is known to affect the pharmacokinetics and pharmacodynamics of several classes of respiratory disease medications. The current study involving 16 healthy adults investigated if the time-of-day of dosing of roflumilast, a novel phosphodiesterase-4 inhibitor, affects its pharmacokinetics. The rate of drug absorption (t(max): 1.50 versus 2.00 h) and peak concentration at t(max) (C(max): 3.79 versus 3.06 μg/L) was slightly greater with morning than evening administration, but without clinical significance. The extent of drug absorption (AUC) and drug elimination (t(1/2)) did not differ between the two dosing times. The pharmacokinetics of the active main metabolite, roflumilast N-oxide, also was not affected by the time of drug administration. Finally, the safety and tolerability of roflumilast did not differ between the two different times of administration.     

Stomatal and Nonstomatal Components to Inhibition of Photosynthesis in Leaves of Capsicum annuum during Progressive Exposure to NaCl Salinity

Young bell pepper (Capsicum annuum L.) plants grown in nutrient solution were gradually acclimated to 50, 100, or 150 moles per cubic meter NaCl, and photosynthetic rates of individual attached leaves were measured on several occasions during the salinization period at external CO₂ concentrations ranging from approximately 70 to 1900 micromoles per mole air. Net CO₂ assimilation (A) was plotted against computed leaf internal CO₂ concentration (C_i), and the initial slope of this A-C_i curve was used as a measure of photosynthetic ability. During the 10 to 14 days after salinization began, leaves from plants exposed to 50 moles per cubic meter NaCl showed little change in photosynthetic ability, whereas those treated to 100 or 150 moles per cubic meter NaCl had up to 85% inhibition, with increase in CO₂ compensation point. Leaves appeared healthy, and leaf chlorophyll content showed only a 14% reduction at the highest salinity levels. Partial stomatal closure occurred with salinization, but reductions in photosynthesis were primarily nonstomatal in origin. Photosynthetic ability was inversely related to the concentration of either Na⁺ or Cl⁻ in the leaf laminas sampled at the end of the experimental period. However, the concentration of Cl⁻ expressed on a tissue water basis was greater, exceeding 300 moles per cubic meter, and Cl⁻ was more closely associated (R² = 0.926) with the inhibition of photosynthetic ability. Leaf turgor was not reduced by salinization and leaf osmotic potential decreased to a slightly greater extent than the osmotic potential decreases of the nutrient solutions. Concentration of accumulated Na⁺ and Cl⁻ (on a tissue water basis) accounted quantitatively for maintenance of leaf osmotic balance, assuming that these ions were sequestered in the vacuoles.     

Hormonally regulated programmed cell death in barley aleurone cells

Cell death was studied in barley (cv Himalaya) aleurone cells treated with abscisic acid and gibberellin. Aleurone protoplasts incubated in abscisic acid remained viable in culture for at least 3 weeks, but exposure to gibberellin initiated a series of events that resulted in death. Between 4 and 8 days after incubation in gibberellin, >70% of all protoplasts died. Death, which occurred after cells became highly vacuolated, was manifest by an abrupt loss of plasma membrane integrity followed by rapid shrinkage of the cell corpse. Hydrolysis of DNA began before death and occurred as protoplasts ceased production of alpha-amylase. DNA degradation did not result in the accumulation of discrete low molecular weight fragments. DNA degradation and cell death were prevented by LY83583, an inhibitor of gibberellin signaling in barley aleurone. We conclude that cell death in aleurone cells is hormonally regulated and is the final step of a developmental program that promotes successful seedling establishment.     

Gibberellin signaling

Recent findings provide insights into the gibberellin signaling system in plants. Genes for gibberellin biosynthetic enzymes have been cloned, and an emerging theme is that gibberellin biosynthesis is negatively regulated by gibberellin responses. Mutants defective in gibberellin signaling have been analyzed, and an important finding is that gibberellin represses growth inhibition. The list of intracellular gibberellin signal-transduction elements has been expanded to include G-proteins and protein kinases.