Basal Edge Research Articles

Tetraphenylphosphonium-trichloroplumbat(II), PPh4PbCl3 · CH3CN

Tetraphenylphosphonium Trichloroplumbate(II), PPh4PbCl3 · CH3CN PPh4PbCl3 · CH3CN was obtained by reaction of PbCl2 and PPh4Cl in acetonitrile. It was also formed along with (PPh4)2Se2Cl6 when PbSe was treated with chlorine in the presence of PPh4Cl. Its crystal structure was determined by X-ray diffraction (R = 0.029 for 4186 reflections). The triclinic crystals contain PbCl3– ions that are associated to polymer chains. Each Pb atom has distorted square pyramidal coordination; the pyramids share two opposite basal edges. The chloro bridges are rather asymmetrical.

Site-specific lead distribution in scales of lead-administered carp ( Cyprinus carpio) by non-destructive SR-XRF analysis

By utilizing non-destructive synchrotron radiation-excited X-ray fluorescence (SR-XRF), we observed the distribution of lead (Pb) in both ontogenic and regenerating scales of lead-administrated carp, Cyprinus carpio. The fish in the Pb-administered group were fed pellets containing 1 mg/g of Pb at a rate of 1.5% body weight per day for 30 days. In the ontogenic scales, Pb was highly accumulated near the basal edge of the scale and the accumulated amount decreased toward the focus of the scale. On the other hand, in the regenerating scales, high accumulation was observed near the basal edge and the accumulated amount remained high toward the focus. The present results of Pb accumulation correspond well with the region which is calcifying in the ontogenic and regenerating scales, and indicate that the distributions of Pb show when and how long Pb was administered.

Rho regulates association of both the ERM family and vinculin with the plasma membrane in MDCK cells.

Rho small G protein regulates various actin-dependent cell functions. As to the functioning sites of Rho, Rho regulates formation of stress fibers and focal adhesions in many types of cultured cells, whereas we have shown that the association sites of actin filaments with the plasma membrane controlled by the ERM (Ezrin, Radixin, Moesin) family are the functioning sites of Rho in MDCK cells stably expressing myc-RhoA. We have investigated here the effect of microinjection of Rho GDI, a negative regulator of Rho which inhibits activation of Rho, C3, an exoenzyme of Clostridium botulinum which ADP-ribosylates Rho and inhibits its functions, or guanosine 5'-(3-O-thio) triphosphate-bound active form of Rho on the intracellular localization of both the ERM family and vinculin, which is one of the structural proteins of focal adhesions, in wild type MDCK cells. The ERM family was preferentially localized at peripheral bundles of actin filaments which are localized at the outer edge of colonies of the cells, microvilli and low Ca2+-induced cortical bundles of actin filaments in wild type MDCK cells. Microinjection of Rho GDI or C3 inhibited the localization of the ERM family at both the peripheral bundles and the low Ca2+-induced cortical bundles. On the other hand, vinculin was localized at both focal adhesions and basal edges of the colonies of the cells, and microinjection of Rho GDI or C3 inhibited the localization of vinculin at both of these sites. These results indicate that activation of Rho is necessary for the association of both the ERM family and vinculin with the plasma membrane in wild type MDCK cells. Microinjection of the guanosine 5'-(3-O-thio) triphosphate-bound form of Rho induced an increase in the localization of vinculin at focal adhesions, but did not induce an increase in the localization of the ERM family at the plasma membrane, indicating that activation of Rho itself is sufficient only for the association of vinculin with the plasma membrane at focal adhesions.

Changes in the Distributions of Chemical Elements in Regenerating Scales of Carp, Cyprinus carpio, Studied by SRXRF Imaging

Two-dimensional distributions of calcium, phosphorus, strontium, and zinc in regenerating scales of carp, Cyprinus carpio, were observed over a period of 90 days by utilizing synchrotron radiation-excited X-ray fluorescence (SRXRF) imaging. On the 15th day, these elements were highly accumulated in the part that is exposed to the ambient water, and the accumulated amount decreased linearly toward the basal edge through the focal area of the scale. As the regeneration progressed, this characteristic pattern changed such that the amount of each element in the rim part, which was exposed to the ambient water, obviously increased, while the amount in the basal edge decreased. However, the relative amounts of phosphorus, strontium, and zinc with respect to calcium in the regenerating scale remained almost constant during the regeneration. In addition, it was found that the diameter of, and the number of ridges in, the regenerating scales increased rapidly during the first 15 days, and increased at a slower pace later on.

Explanation of the epitaxial deposition of nylon 66 on carbon fibres and its extension to isotactic polypropylene

This work demonstrates epitaxial relationships between the crystal structure and growth faces of nylon 66 on high-modulus graphite fibres and explains observations in the literature. It also extends the concepts and applies them to the more complicated system of isotactic polypropylene (i-PP) on highly graphitic carbon fibre structures. The proposed arrangements are based upon matching a polymer's crystalline structure, along its growth face, to possible graphitic structure dimensions along carbon fibre surfaces. The matches involving substrates and overgrowths in both cases are nearly perfect, being within 5%, thus accommodating favourable low-energy positioning of the polymer's crystal structure. The relationship involving nylon 66 allows this polymer's chains to orient along fibre surfaces between graphite basal plane edges. This epitaxial relationship is consistent with the literature and is used to predict the orientation of crystalline i-PP chains when deposited on carbon fibres. To preserve a low-energy epitaxial relationship, the i-PP chains are suggested to be oriented some 78° across stepped graphite basal plane end surfaces and are most likely oriented at 78° to the fibre direction. Additional discussion, arising from complexities in the case of i-PP, concerns the relation between the number of possible polymer nucleation orientations and the nucleating ability of a given fibre surface.

Tetranuclear and Pentanuclear Vanadium(IV/V) Carboxylate Complexes: [V(4)O(8)(NO(3))(O(2)CR)(4)](2-) and [V(5)O(9)X(O(2)CR)(4)](2-) (X = Cl(-), Br(-)) Salts.

The syntheses and properties of tetra- and pentanuclear vanadium(IV,V) carboxylate complexes are reported. Reaction of (NBzEt(3))(2)[VOCl(4)] (1a) with NaO(2)CPh and atmospheric H(2)O/O(2) in MeCN leads to formation of (NBzEt(3))(2)[V(5)O(9)Cl(O(2)CPh)(4)] 4a; a similar reaction employing (NEt(4))(2)[VOCl(4)] (1b) gives (NEt(4))(2)[V(5)O(9)Cl(O(2)CPh)(4)] (4b). Complex 4a.MeCN crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -148 degrees C: a = 13.863(13) Å, b = 34.009(43) Å, c = 12.773(11) Å, and Z = 4. The reaction between (NEt(4))(2)[VOBr(4)] (2a) and NaO(2)CPh under similar conditions gives (NEt(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6a), and the use of (PPh(4))(2)[VOBr(4)] (2b) likewise gives (PPh(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6b). Complex 6b crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -139 degrees C: a = 18.638(3) Å, b = 23.557(4) Å, c = 12.731(2) Å, and Z = 4. The anions of 4a and 6b consist of a V(5) square pyramid with each vertical face bridged by a &mgr;(3)-O(2)(-) ion, the basal face bridged by a &mgr;(4)-X(-) (X = Cl, Br) ion, and a terminal, multiply-bonded O(2)(-) ion on each metal. The RCO(2)(-) groups bridge each basal edge to give C(4)(v)() virtual symmetry. The apical and basal metals are V(V) and V(IV), respectively (i.e., the anions are trapped-valence). The reaction of 1b with AgNO(3) and Na(tca) (tca = thiophene-2-carboxylate) in MeCN under anaerobic conditions gives (NEt(4))(2)[V(4)O(8)(NO(3))(tca)(4)] (7). Complex 7.H(2)O crystallizes in space group C2/c with the following unit cell dimensions at -170 degrees C: a = 23.606(4) Å, b = 15.211(3) Å, c = 23.999(5) Å, and Z = 4. The anion of 7 is similar to those of 4a and 6b except that the apical [VO] unit is absent, leaving a V(4) square unit, and the &mgr;(4)-X(-) ion is replaced with a &mgr;(4),eta(1)-NO(3)(-) ion. The four metal centers are now at the V(IV), 3V(V) oxidation level, but the structure indicates four equivalent V centers, suggesting an electronically delocalized system. Variable-temperature magnetic susceptibility data were collected on powdered samples of 4b, 6a, and 7 in the 2.00-300 K range in a 10 kG applied field. 4b and 6a both show a slow increase in effective magnetic moment (&mgr;(eff)) from approximately 3.6-3.7 &mgr;(B) at 320 K to approximately 4.5-4.6 &mgr;(B) at 11.0 K and then a slight decrease to approximately 4.2 &mgr;(B) at 2.00 K. The data were fit to the theoretical expression for a V(IV)(4) square with two exchange parameters J = J(cis)() and J' = J(trans)() (H = -2JS(i)()S(j)()): fitting of the data gave, in the format 4b/6a, J= +39.7/+46.4 cm(-)(1), J' = -11.1/-18.2 cm(-)(1) and g = 1.83/1.90, with the complexes possessing S(T) = 2 ground states. The latter were confirmed by magnetization vs field studies in the 2.00-30.0 K and 0.500-50.0 kG ranges: fitting of the data gave S(T) = 2 and D = 0.00 cm(-)(1) for both complexes, where D is the axial zero-field splitting parameter. Complex 7 shows a nearly temperature-independent &mgr;(eff) (1.6-2.0 &mgr;(B)) consistent with a single d electron per V(4) unit. The (1)H NMR spectra of 4b and 6a in CD(3)CN are consistent with retention of their pentanuclear structure on dissolution. The EPR spectrum of 7 in a toluene/MeCN (1:2) solution at approximately 25 degrees C yields an isotropic signal with a 29-line hyperfine pattern assignable to hyperfine interactions with four equivalent I = (7)/(2) (51)V nuclei.

Subboundaries in hcp4He crystals studied by SR X-ray topography

The internal structure of hcp4He crystals was studied by SR (synchrotron radiation) X-ray topography. Subboundaries in the crystals appeared as black or white bands in the X-ray topographs. In one of the hcp4He crystals, the subboundaries turned out to be flat planes perpendicular to the basal plane. They were small-angle tilt boundaries which consisted of basal edge dislocations. The dislocation spacing in one of the subboundaries was determined to be 800 nm and the total density of the boundary dislocations to be 2.6 × 105 cm−2. The subboundaries in another hcp4He crystal were curved and/or branching, indicating that the crystal was strained.

Initial stages of SiOx deposition on graphite

The reaction of tetraethoxysilane (TEOS) and the subsequent deposition of SiOx on the basal plane and edges of highly oriented pyrolytic graphite (HOPG) were studied. Interfacial bonding and surface morphologies resulting from different reaction conditions were probed using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), Rutherford backscattering spectroscopy (RBS), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS). The initial reaction of TEOS was found to occur at surface defects. STM images indicated that SiCx films do not grow layer-by-layer, confirming earlier indirect observations to that effect.

Cyclohexadiene and benzene derivatives of [Ru5C(CO)15

The reaction of [Ru5C(CO)15]1 with cyclohexa-1,3-diene and three equivalents of Me3NO yielded the new compound [Ru5C(CO)11(η4-C6H8)2]2 and also [Ru5C(CO)12(µ3-η2:η2:η2-C6H6)]3 and [Ru5C(CO)12(η6-C6H6)]4 in approximately equal yields. The molecular structure of 2 has been established by single-crystal X-ray diffraction. The two cyclohexadiene ligands are terminally bound on opposite basal ruthenium atoms of the square-pyramidal metal framework. Compound 2 may be converted to 3 by reaction with carbon monoxide. The isomeric pair [Ru5C(CO)10(µ3-η2:η2:η2-C6H6)(µ-η2:η2-C6H8)]5 and [Ru5C(CO)10(η6-C6H6)(µ-η2:η2-C6H8)]6 may be prepared from 3 and 4, respectively, upon reaction with cyclohexa-1,3-diene and two equivalents of Me3NO. Clusters 5 and 6 have also been studied by single-crystal X-ray diffraction. In both molecules the cyclohexadiene ligand bridges a basal edge of the square pyramid, while the benzene fragment is in face-capping and terminal bonding mode, respectively.

Synthesis and structural characterization of the alkaline earth aryloxide aggregates H2Ba8(.mu.5-O)2(OPh)14(HMPA)6 and H2Sr6Ba2(.mu.5-O)2(OPh)14(HMPA)6. A new structural type displaying metal ion site selectivity

The interest in the formation and chemistry of main group alkoxides and aryloxides has undergone a renaissance over the last few years. There are many reasons for this surge of interest in such compounds, many of which until recently were poorly characterized or not known at all. One such stimulus is the discovery of superconducting ceramics containing alkaline earth ions. The reaction of barium metal granules with phenol and hexamethylphosphoramide (HMPA) in toluene at 25[degrees]C yields a novel eight-metal atom aggregate. The reaction of Sr[sub 3](OPh)[sub 6](HMPA)[sub 5] with barium metal and phenol yields a structurally related species. The two aggregates have been characterized by IR and [sup 1]H, [sup 13]C, and [sup 31]P[l brace][sup 1]H[r brace] NMR spectroscopy and single-crystal X-ray studies and shown to consist to two square-based pyramidal M[sub 5]([mu][sub 5]-O) fragments sharing a common basal edge. The structure is completed by [mu][sub 3]- and [mu][sub 2]-phenoxide and terminal HMPA ligands. The selectivity for barium in the two polyhedral sites where the square-based pyramids are joined originates in the higher coordination number there. 20 refs., 2 figs., 3 tabs.

Cluster chemistry: LXXXIII. Reactions of Ru 5(μ 5-C 2PPh 2)(μ-PPh 2)(CO) 13 with olefins: Products formed by addition of an alkene to the C 2 fragment. X-ray structures of Ru 5(μ 4-PPh){μ14-C 2(CHCHR)CHCH 2R}(μ-PPh 2)-(CO) 12 (R = H, Me) and RU 5(μ 4-PPh) (μ -PPh 2) (μ-CO)(CO) 10-{μ 5-C 5H 3Me-1-(CHCH 2)-3}

Addition of two molecules of ethene to the C 2PPh 2 unit of Ru 5S(μ 5-C 2PPh 2)(μ-PPh 2)(CO) 13 ( 1) produced two isomers of Ru 5(μ 4-PPh)(μ 4-C 2(CHCH 2)CHMe) (μ-PPh 2XCO) 12 ( 4a, 4b). The metal core consists of a wing-tip-bridged butterfly, one Ru 4 face of which is capped by carbon atom of a hydrocarbon ligand formed by addition of two molecules of ethene to one carbon of a C 2 unit derived from the C 2PPh 2 ligand. The other Ru 4 face is capped by a μ 4-PPh group. The isomers differ in the relative locations of the μ-PPh 2 and CO groups. Reactions with propene and but-l-ene yielded the analogous complexes Ru 5(μ 4-PPh)(μ 4-C 2(CHCHR)CHCH 2R)(μ-PPh 2)(CO) 12 [R = Me ( 5a, 5b), Et ( 6a, 6b)] l. Reaction of 4a with further ethene produced Ru 5(μ 4-PPh)(μz-PPh 2)(μ-CO) (CO) 10 {η 5-C 5H 3Me-1-(CHCH 2)-3} ( 8), in which a square pyramidal Ru 5 core is capped on the square face by a μ 4-PPh ligand. One basal edge is bridged by the μ-PPh 2 group and one of the other basal Ru atoms carries the disubstituted cyclopentadienyl ligand, which has been formed by combination of the third ethene molecule with the μ 4-C 2(CHCH 2)CHMe ligand of 4. Complexes 4a, 5b and 8 were characterised by single-crystal X-ray studies.

Differentiation of isolated murine embryonic palatal epithelium in culture: exogenous transforming growth factor alpha modulates matrix biosynthesis in defined experimental conditions

A novel culture technique, which supports the growth and differentiation of mouse embryonic palatal epithelial cells in the absence of either an extracellular matrix substratum or feeder layers, has been developed. Using this technique we have investigated the effects of exogenous transforming growth factor alpha (TGF alpha) and serum on extracellular matrix biosynthesis by primary cultures of mouse embryonic epithelial sheets under defined experimental conditions. In all culture treatments (chemically defined medium with and without TGF alpha or serum) the palatal epithelial sheets differentiated into three regionally distinct cell phenotypes after 36 h. Nasal and oral cells differentiated into pseudostratified, ciliated columnar, and stratified squamous keratinizing epithelium, respectively. In addition, basal medial edge epithelial (MEE) cells at the oral/nasal regional interface assumed an elongated cobblestoned phenotype. In serum-free medium, collagen types IV and V, laminin, fibronectin, and heparan sulphate proteoglycan were detected immunocytochemically throughout the entire epithelial sheet. Tenascin and collagen IX were present almost exclusively in MEE cells. Types I, II, and III collagen were completely absent. Addition of TGF alpha or serum universally increased the intensity of staining, most notably that for tenascin and collagen IX in MEE cells. These results indicate that mouse embryonic palatal epithelial sheets can be maintained under defined culture conditions during which they exhibit patterns of differentiation similar to those observed in vivo. TGF alpha, known to localize to the MEE in vivo, can modulate palatal extracellular matrix biosynthesis, particularly by the MEE, suggesting a regulatory role for this factor. The culture system is suitable for further investigating the effects of exogenous factors on mouse embryonic palatal epithelial cell bioactivity and differentiation.

Crystal chemistry of Ba-rich trioctahedral micas-\M

Ten single-crystal X-ray structure refinements of igneous and metamorphic Ba-bearing micas were determined to define the exchange vectors required to compensate for the excess in positive layer charge caused by [XII] Ba 2+ for [XII] K + substitution. The determined exchange vector is BaAlK −1 Si −1 . The micas have a Ba 2+ content in the range 0.01-1.09 apfu (atoms per formula unit) with octahedra mostly populated by Mg 2+ (2.21 ≤ Mg 2+ ≤ 3.07 apfu) and Fe 2+ (0.13 ≤ Fe 2+ ≤ 1.53 apfu). All samples are 1M polytype and the structure were refined in space group C2/m (0.020 ≤ R ≤ 0.034). lncreasing the substitution of [IV] Al 3+ for [IV] Si 4+ distorts the tetrahedra by progressively increasing the dimensions of the basal edges. This increase in the lateral dimensions of the tetrahedral sheet allows for a greater rotation angle α (5.9 ≤ α ≤ 11.5). Octahedral sheet crystal chemical features (ordering pattern, size and distortion of both M(1) and M(2) sites) are similar to those reported for micas in the phlogopite-annite join. The most notable variation involves the length of M(1) unshared edges, which decreases in samples with the highest [XII] Ba 2+ content

Synthesis and structural characterization of the phosphido cluster [Ir4H(CO)10(µ-PPh2)] and its facile carbonyl substitution reactions with a series of phosphines and phosphites

The tetranuclear cluster [Ir4H(CO)10(µ-PPh2)]1 is formed from [Ir4(CO)11(PPh2)]2 by deprotonation, which yields [Ir4(CO)10(µ-PPh2)]–3, followed by protonation of the anion. It has been fully characterized by an X-ray analysis, and exhibits a tetrahedral arrangement of metal atoms with the three basal edges bridged by a phosphido, a hydrido and a carbonyl ligand. Both 1 and 3 undergo facile carbonyl substitution reactions with phosphites and phosphines L [PPh3, PPhMe2, P(OPh)3 or P(C6H4X-4)3(X = F, Cl, Me, 4-Ome or 2-OMe)] to give [Ir4H(CO)9L(µ-PPh2)]4a–4h and [Ir4(CO)9L(µ-PPh2)]–5a–5h respectively, the latter being converted into the corresponding hydride derivatives by protonation. Further substitution of a CO in 4a–4h affords [Ir4H(CO)8L2(µ-PPh2)]6a–6h. An X-Ray analysis of [Ir4H(CO)9(PPh3)(µ-PPh2)]4a shows that carbonyl substitution has occurred at a basal Ir atom which is not bridged by the phosphido ligand.

Neoplastic invasion in experimental carcinoma of the colon: abnormal differentiation and release of mucus

Carcinomas of the colon were induced in F344 rats with dimethylhydrazine (20 mg/kg for 12 weeks). The invasive edges of the lesions were examined with the electron microscope. As in human colorectal cancer, the invasive edges show neoplastic cells with abnormal differentiation of apical cytoplasmic rootlets and processes at the basal or invasive edge of the cell, 'apical reversal'. Mucous carcinoma cells release material into the interstitial connective tissue matrix. The features may contribute to the complex phenomenon of neoplastic invasion.

Alveolar Epithelial Cell Keratin Expression during Lung Development

Defining the expression and organization of keratins has provided insight into epithelial cell differentiation during tissue development and remodeling. We have used monoclonal antibodies to examine keratin distribution in lung epithelial cells in the rat from the preglandular phase of gestation to the adult. Of particular interest were the distributions of keratin No. 18 and keratin No. 19, since previous results have suggested these keratins may be important in alveolar epithelial cell transitions occurring in adult remodeling lung and in cultured type II cells. The epithelial tubes at 15 days of gestation do not react with 24A3 monoclonal antibody to keratin No. 18, nor is this antigen apparent by gel or immunoblot analysis. Staining is apparent at day 16, however, showing a light punctate pattern at the basal edge of the cells, and becomes prominent by day 17, with intensity greatest in the larger airway tubes. The intensity and number of cells in the parenchyma staining with 24A3 peaks at postnatal days 5 to 10, when proliferation and cytodifferentiation of type I and type II cells is most active. In the adult, staining of type II cells is present mainly at the cell periphery, and occasional reactive attenuated type I-like cells can be observed. Keratin No. 19 immunoreactivity is not present in the primitive epithelial tube until 19 days' gestation but predominantly stains type II pneumocytes in the adult rat lung throughout the entire cell. AE3 antibody to basic keratins stains similarly to keratin No. 19. We conclude that keratin No. 18 is expressed at high levels in type II cells during development in periods of intense proliferation and alveolarization. This correlates with our previous observations on keratin expression following bleomycin lung injury.

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (III). Growth kinetics of the basal face of zinc single crystals and its edge under diffusion conditions

AbstractThe growth kinetics of the basal face and its edge of zinc single crystals grown from zinc vapours in the presence of argon at pressures 5 – 250 Torr has been investigated simultaneously. The alterations of the crystal size R and the length of the basal edge a with time t have been measured at constant temperature and supersaturation. It is shown that the R2(t) and a2(t) dependences change their initial shape into linear at one and the same moment. It is established that the transition from a kinetic to a diffusion regime can be determined both by the kinetic critical size Rk and by the kinetic critical size ak. It is found also that in the kinetic regime the lateral growth rate of the basal edge is higher than the normal growth rate of the {0001} face. During the growth in a diffusion regime the R2(t) and a2(t) curves of a given single crystal become parallel, due to the isotropic character of the transport processes of the material. The rate determining role of the diffusion in the parent phase on the growth of the basal face and its edge is demonstrated.

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (I). Growth kinetics of the basal face of zinc single crystals under diffusion conditions

The growth kinetics of the basal face and its edge of zinc single crystals grown from zinc vapours in the presence of argon at pressures 5 – 250 Torr has been investigated simultaneously. The alterations of the crystal size R and the length of the basal edge a with time t have been measured at constant temperature and supersaturation. It is shown that the R2(t) and a2(t) dependences change their initial shape into linear at one and the same moment. It is established that the transition from a kinetic to a diffusion regime can be determined both by the kinetic critical size Rk and by the kinetic critical size ak. It is found also that in the kinetic regime the lateral growth rate of the basal edge is higher than the normal growth rate of the {0001} face. During the growth in a diffusion regime the R2(t) and a2(t) curves of a given single crystal become parallel, due to the isotropic character of the transport processes of the material. The rate determining role of the diffusion in the parent phase on the growth of the basal face and its edge is demonstrated.

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (II). Growth kinetics of the edge of the basal face of zinc single crystals under diffusion conditions

The growth kinetics of the edge of the basal face of zinc single crystals grown from a vapour phase under diffusion controlled conditions has been investigated. The growth of the basal edge with time at constant temperature and supersaturation and argon pressures between 5 and 250 Torr or in vacuum 1 × 10−6 Torr has been plotted. It is established that the length a of the edge of the {0001} face is changed with time t according to a linear and a parabolic dependence. The kinetic critical size ak is determined by the intersection point between the two parts of a2(t) curves. It is shown that the results from the kinetic investigations of the basal face edge are in qualitative agreement with the basic relationships characterizing the growth kinetics of crystals in a kinetic and a diffusion regime Experimental facts are presented (e.g. the parallel running a2(t) curves, etc.) which confirm the diffusion character of the observed transition of the basal edge of zinc single crystals from a kinetic regime to a diffusion growth mode.

Polar Transport of 1-Naphthaleneacetic Acid Determines the Distribution of Flower Buds on Explants of Tobacco

Upon addition of 1-naphthaleneacetic acid (1-NAA) and benzylaminopurine, flower buds developed on explants from flower stalks of Nicotiana tabacum L. cv Samsun cultured in vitro. At low concentrations of 1-NAA, buds emerged mainly at the basal edge, whereas at high concentrations they developed on the remaining surface. The optimum concentrations for the two groups of buds were 0.45 micromolar and 2.2 micromolar, respectively, and the shapes of the concentration versus response curves were similar. The level of benzylaminopurine in the medium affected neither the shape nor the optimum concentration of these curves. The distribution of the buds over the explants was shown to be caused by polar auxin transport, leading to accumulation at the basal side. First, in the presence of the inhibitors 2,3,5-triiodobenzoic acid and 1-naphthylphthalamic acid, both groups of buds had the same optimum concentration of 1 micromolar 1-NAA. Second, after 6 hours of culture applied 1-NAA had accumulated in the basal part of the explant. In the presence of 1-naphthylphthalamic acid, no transport or accumulation of applied 1-NAA occurred.