No abstract

In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 µm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 µm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20-50 µm from the tip. The Sperms are found no closer than 90 µm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid.

An experimental study and computer simulation of collimated sputtering of titanium (Ti) thin films onto submicrometer trenches is presented. The effect of square grid collimators with aspect ratios varying from 0.5 to 2 has been studied. Simulation of collimated sputtering involves the combination of the simulation of sputter distributions vapor transport model and the simulation by ballistic deposition film growth model. This combination is able to simulate the effect of collimation on the spatial and angular distributions of deposited atoms, and is able to predict the film coverage, deposition rate change, and microstructure of the deposited films. Both experimental and simulation results show that bottom coverage in trenches of aspect ratio 1.2 can be significantly improved from 50% to more than 80% using collimation. However, a penalty is paid by a corresponding decrease in deposition rate down to 15% of the uncollimated value. Additionally, the microstructure (grain size and orientation) is altered by collimation. The good agreement between the simulation and experimental results indicates that the model will be very useful for predicting and optimizing the properties of films deposited by collimated sputtering over topographical features.

1. The patch-clamp technique was used to characterize chloride channels from the apical membranes of bovine tracheal epithelial cells. Application of GTPyS or NaF to excised patches revealed the existence of a novel type of Cl-channel regulated by G-proteins in a membrane-delimited manner. 2. The channel had a linear current-voltage relationship, with a conductance of 100-120 pS.Its open probability was independent of voltage.3. The channel was highly anion selective (permeability ratio, PNa/Pcl = 0-06 + 004) and had the halide permeability sequence: 1> Br-> Cl-> F-, corresponding to the Eisenman I sequence. This suggested that neither ionic size nor diffusion rate determined ion permeation through the channel. 4. The mole fraction behaviour was studied using fluoride and chloride ions. Mixtures of ions produced currents that would be expected from the linear combination of the two ions acting independently, indicating relatively simple permeation through the pore and compatible with a single ion binding site. 5. The channel was inhibited by the stilbene disulphonates SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) and DNDS (4,4'-dinitrostilbene-2,2'-sulphonic acid). SITS introduced voltage dependence to channel gating and indicated the possible involvement of lysine residues in the channel permeation pathway. 6. NaF was unable to activate Cl-channels in the presence of the aluminum chelator, deferoxamine mesylate. This indicates that A13+ ions play an important role in chloride channel activation by fluoride. NaF activation was not dependent on the presence of calcium ions. 7. The channel was insensitive to alkaline phosphatase and to the specific inhibitors of protein phosphatase types I and 2A, okadaic acid and calyculin A. 8. The channels could be activated by GTPyS or by NaF in the presence of the phospholipase A2 inhibitor quinacrine, indicating that this enzyme is not involved in channel regulation.