Albino inflorescence proliferation of Dendrocalamus latiflorus

Summary Inflorescence proliferation is a plant tissue culture technique that, can be used to obtain in vitro inflorescences year-round without the intervening development of vegetative organs. In this study, we used albino mutant inflorescences of Dendrocalamus latiflorus as the original explant material to investigate, the effect of plant growth regulators on long-term inflorescence proliferation. The albino inflorescences proliferated on solidified Murashige and Skoog (MS) basal medium supplemented with thidiazuron (TDZ), and the optimal concentration for successful long-term inflorescence proliferation was 0.45 μM TDZ. A combination of α-naphthaleneacetic acid (NAA) with 0.45 μM TDZ inhibited the inflorescence proliferation. Inflorescences cultured on a TDZ-free medium supplemented with 26.82 μM NAA rooted in 21 d, vegetative shoots formed by 42 d and, in one case, flowering occurred after 63 d. The auxins 2,4-dichlorophenoxyacetic acid (2,4-D, 4.52 μM) and pieloram (4.14 μM) induced shoot formation. The protocol described can be used to produce large numbers of mutant inflorescences within a relatively short period of time.     

Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin

doi:10.1111/j.1741‐2358.2009.00333.x
Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth.     

Evidence for the existence of three or more slow phases in the refolding of ribonuclease A and some characteristics of the phases

The slow refolding kinetics of RNase A have been analyzed, by using a nonlinear least-squares program for deconvoluting the kinetic phases and applying statistical tests for quality of fit. It is found that a minimum of three slow phases are required to fit the kinetic data properly, and this is true whether the method of detection is absorbance of fluorescence. Since the number of phases and the relaxation times for each phase are independent of the method of detection, it is concluded that the same three rate-limiting processes are seen by absorbance and fluorescence. These phases correspond to the XY, CT, and ct phases described in our earlier studies. The fact that fluorescence-detected kinetics are somewhat slower than absorbance-detected kinetics is a trivial effect due not to differences in relaxation times but to the fact that the amplitude of the CT phase is enhanced in fluorescence measurements, at the expense of the faster XY phase, because of intrinsic fluorescence changes associated with the isomerization of proline-93. By use of a new double-jump technique [Schmid, F.X., Grafl, R., Wrba, A., & Beintema, J.J. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 872], it is shown that proline-93 isomerizes as the rate-limiting step in only one of the three phases, the CT phase, and that this phase involves only 25-30% of the RNase molecules. There is still no indication as to the molecular events that occur in the large, ammonium sulfate dependent XY phase, which is the pathway for formation of the nativelike intermediate.     

Hydrolysis of dansyl-peptide substrates by leucine aminopeptidase: origin of dansyl fluorescence changes during hydrolysis

The origin of the fluorescence changes observed in stopped-flow experiments of the hydrolysis of three 5-(dimethylamino)naphthalene-1-sulfonyl-(dansyl) peptide substrates by porcine kidney cytosol leucine aminopeptidase has been investigated. The substrates used all have the potential to accept energy from aromatic residues of the enzyme via resonance energy transfer when they are bound as enzyme-substrate complexes, indicating that fluorescence changes due to the buildup and decay of such intermediates are possible. However, the fluorescence of these substrates differs from that of the products, and direct excitation of their dansyl groups during hydrolysis can also be responsible for the observed fluorescence changes due to changes in the concentrations of free substrate and product. The dansyl fluorescence changes observed with excitation wavelengths near 280 nm are not accompanied by quenching of the enzyme fluorescence, as would be expected if there were enzyme-to-substrate energy transfer. The magnitude of the maximal fluorescence change at a fixed concentration of substrate is also independent of the enzyme concentration. Furthermore, the excitation profile for the fluorescence changes shows that they arise from direct excitation of the dansyl group. Thus, there is no energy transfer in these reactions, and the fluorescence changes observed arise from direct excitation of the dansyl group and reflect the instantaneous concentration of substrate. This behavior contrasts sharply with that for the reaction of carboxypeptidase A with dansyl-Gly-Tyr, which has been studied as a positive control for an energy-transfer system.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nuclear envelope‐associated dynein drives prophase centrosome separation and enables Eg5‐independent bipolar spindle formation

The microtubule motor protein kinesin‐5 (Eg5) provides an outward force on centrosomes, which drives bipolar spindle assembly. Acute inhibition of Eg5 blocks centrosome separation and causes mitotic arrest in human cells, making Eg5 an attractive target for anti‐cancer therapy. Using in vitro directed evolution, we show that human cells treated with Eg5 inhibitors can rapidly acquire the ability to divide in the complete absence of Eg5 activity. We have used these Eg5‐independent cells to study alternative mechanisms of centrosome separation. We uncovered a pathway involving nuclear envelope (NE)‐associated dynein that drives centrosome separation in prophase. This NE‐dynein pathway is essential for bipolar spindle assembly in the absence of Eg5, but also functions in the presence of full Eg5 activity, where it pulls individual centrosomes along the NE and acts in concert with Eg5‐dependent outward pushing forces to coordinate prophase centrosome separation. Together, these results reveal how the forces are produced to drive prophase centrosome separation and identify a novel mechanism of resistance to kinesin‐5 inhibitors.