The Association of Ascorbate and Ascorbate Oxidase in the Apoplast with IAA-Enhanced Elongation of Epicotyls from Vigna angularis

The level of (ascorbic acid (AA) plus dehydroascorbic acid (DHA))and the ratio of the level of AA to that of AA plus DHA in intercellularwashing fluid (IWF) of epicotyl segments from Vigna angularisdecreased from 2.8±0.3 to 1.2±0.5nmol (g fr wt)^–1and from 0.23±0.03 to 0.13±0.01, respectively,after incubation of the segments without IAA for 20 h at 27°C.However, these values changed to 5.3±1.7 nmol (g fr wt)^–1and 0.07±0.05 after incubation with 0.1 mM IAA. The activityof cell wall-bound ascorbate oxidase increased by about 20%and 70% after incubation without IAA and with IAA, respectively.However, the activity of cell wall-bound peroxidase was notaffected by incubation with or without IAA. The activities ofascorbate oxidase and peroxidase in IWF decreased by about 85and 75% after incubation without IAA. IAA did not affect thesedecreases to any great extent. A lignin-like compound was formedduring the incubation of epicotyl segments in the absence ofIAA. Formation of this compound was inhibited by IAA. The resultssuggest that one of the causes of the enhancement of elongationgrowth by IAA is the inhibition of peroxidase-dependent lignificationas a result of increases in levels of AA and DHA and in ascorbateoxidase activity. (Received August 16, 1993; Accepted December 6, 1993)     

The effects of deuterium oxide (2H2O) on the polymerization of tubulin in vitro

The initial rate and final extent of polymerization of both bovine brain tubulin and sea urchin egg tubulin were enhanced in the presence of ²H₂O. The yields were increased in association with the elevation of the ²H₂O concentration. ²H₂O also reduced the critical concentration for polymerization of brain tubulin. Thermodynamic analysis was attempted using the temperature dependence of the critical concentration for polymerization in the presence of ²H₂O. We obtained linear van 't Hoff plots and calculated thermodynamic parameters which were positive and were increased with the elevation of the ²H₂O concentration. The enhancement of the polymerization of tubulin by ²H₂O could, therefore, be the result of the strenghening of intra-and/or inter-molecular hydrophobic interactions of the tubulin molecules. We believe that the increase in lenghth and number of microtubules of the mitotic spindles in the dividing cells of the eukaryotes with ²H₂O may be caused by the direct involvement of ²H₂O in the polymerization of tubulin.     

Characterization of β-amylase and its deficiency in various rice cultivars

 β-Amylase deficiency in various cultivars of rice was examined at the molecular level. Using an antibody against β-amylase purified from germinating seeds of rice, we were able to demonstrate the expression and organization of the β-amylase gene in normal and deficient cultivars. Although β-amylase is a starch-hydrolyzing enzyme, as is α-amylase, the β-amylase protein/gene is expressed differently from the α-amylase protein/gene; i.e. (1) β-amylase is synthesized only in aleurone cells, (2) the enzyme production in the embryo-less half-seeds is not under hormonal control. We identified some cultivars of rice that are deficient for β-amylase activity. We present new evidence that synthesis is blocked at the level of mRNA synthesis in the deficient cultivars. The usefulness of β-amylase as a crop trait is also discussed. Received: 8 May 1998 / Accepted: 5 June 1998     

High performance liquid chromatography of nucleic acids and the related compounds on a fluorinated silica gel column.

Separations of nucleic acids and the related compounds were investigated by HPLC on a new fluorinated bonded silica gel column. Polyadenylate (Poly (A)) enzymatic partial hydrolysate sample and the mixture of various polynucleotide samples were sufficiently separated by the reversed-phase mode using a gradient elution with aqueous ammonium acetate/acetonitrile system. Mixed-mode separation on the fluorinated bonded phase coated with a tert-alkylammonium salt was also examined for the separation of the various polynucleotides including tRNAs.     

How to discriminate between vibration syndrome and local fatigue of motorcyclists

Motorcyclists who work in some offices sometimes complained of coldness, pain and numbness of upper limbs. We studied how to discriminate between vibration syndrome and local fatigue of the motorcyclists. Subjects are 42 motorcyclists of an office in Aichi prefecture. 25 of them held several letters in their left hand when they delivered the letters. They complained of coldness, pain and numbness in the left upper limbs more than in the right limbs (p less than 0.01). We think that it is the local fatigue rather than the disorder of vibration syndrome that causes such symptoms. So it is very important to recognize the existence of local fatigue in order to know how to discriminate between vibration syndrome and local fatigue of the motorcyclists.     

Fractal property of eye movements in schizophrenia

 On the basis of a temporal model of animal behavior we conducted temporal analysis of eye movements in schizophrenic subjects (n=10) and normal controls (n=10). We found a fractal property in schizophrenic subjects, the fixation time of eye movement during reading ambiguous and difficult sentences showing a clear inverse power law distribution. An exponential distribution of a nonfractal nature was found in normal controls. Received: 21 July 1995/Accepted in revised form: 30 April 1996     

Mechanisms of modulation of neuronal nicotinic receptors by substance P and OAG

Substance P is known to modulate neuronal nicotinicacetylcholine receptors (nAChRs) in the sympathetic nervous system.There are two conflicting proposals for the mechanism of this effect, an indirect action mediated by protein kinase C (PKC) and a direct interaction with receptor subunits. We studied the mechanisms of thiseffect in PC-12 cells. Substance P enhanced the decay of thenicotine-induced whole cell current. This effect was fast in its onsetand was not antagonized by guanosine5'-O-(2-thiodiphosphate), a G protein blocker, orstaurosporine, a nonselective PKC blocker. Staurosporine failed toreverse the inhibition by 1-oleoyl-2-acetyl-sn-glycerol (OAG), a synthetic diacylglycerol analog known to activate PKC. Theinhibitory effects of the peptide and OAG were preserved in excisedpatches, but substance P applied to the extra patch membrane wasineffective in the cell-attached patch configuration. We conclude thatsubstance P modulates neuronal nAChRs most likely by direct interactions with the receptors but independently from activation ofPKC or G proteins and that PKC does not participate in modulation by OAG.

     

Inhibiting Effect of Auxin on Glucosamine Incorporation into Cell Walls of Rice Coleoptiles

Auxin induced growth and decreased the hexosamine content ofthe cell walls of rice coleoptile sections. Indole-3-aceticacid (IAA) at 10^–5 M inhibited the incorporation of ¹⁴C-glucosamineinto the cell walls. IAA did not affect the ¹⁴C-incorporationinto the cytoplasm, while inhibitors of glycoprotein synthesis,unicamycin and monensin, suppressed the incorporation into boththe cytoplasm and the cell walls. The radioactivity due to labeledglucosamine in the cell walls increased during the chase, butthis increase was inhibited by IAA. Among the cell wall fractions,the increase in radioactivity and its inhibition by IAA wereconspicuous in the hemicellulose I fraction. The inhibitoryeffect of IAA on glucosamine incorporation into the cell wallswas observed even in the presence of 0.15 M mannitol solutionwhich completely suppressed the IAA-induced growth. These resultssuggest that auxin induces growth at least partly by inhibitingthe transport of asparagine-linked glycoproteins from the cytoplasmto the cell walls. ¹ Present address: Department of Biology, Faculty of Science,Osaka City University, Sumiyoshi-ku, Osaka 558, Japan (Received July 23, 1986; Accepted December 22, 1986)     

Effect of Osmotic Stress on Turgor Pressure in Mung Bean Root Cells

Turgor pressure in cells of the elongating region of intactmung bean roots was directly measured by using the pressure-probetechnique. After the external osmotic pressure had been increasedfrom 0 MPa to 0.5 MPa, turgor pressure rapidly decreased byabout 0.5 MPa from 0.65 MPa to 0.14 MPa and root elongationstopped. Subsequent turgor regulation was clearly confirmed,which followed the osmotic adjustment to maintain a constantdifference in the osmotic pressure between root-cell sap andthe external medium ( II). It took at least 6 h for turgor pressureto recover to an adjusted constant level of about 0.5 MPa dueto turgor regulation, but rootelongation resumed within onlyan hour after the osmotic treatment. Therefore, the resumptionof root elongation under osmotic stress could not have beendirectly connected with turgor regulation. Furthermore, sincethe amounts of decrease in turgor pressure just after applicationsof various degrees of osmotic stress could be interpreted inrelation to those in II, hydraulic conductivity between theinside and the outside of root cells must be large enough toattain water potential equilibrium rapidly in response to osmoticstress. We conclude that turgor pressure in the cells of theelongating region of mung bean roots is determined mainly by II because of water potential equilibrium. (Received January 27, 1987; Accepted May 21, 1987)     

Further evidence from sectioned material in support of the existence of a linear terminal complex in cellulose synthesis

Summary Transmembrane linear terminal complexes considered to be involved in the synthesis of cellulose microfibrils have been described in the plasma membrane ofBoergesenia forbesii. Evidence for the existence of these structures has been obtained almost exlusively using the freeze etching technique. In the present study an attempt has been made to complete these studies using conventional fixation, staining, and sectioning procedures. In developing cells ofBoergesenia forbesii, strongly stained structures traversing the plasma membrane and averaging 598.9 nm ± 171.3 nm in length, 28.7 nm ± 4.2 nm in width, and 35.2 nm ± 6.6 nm in depth have been demonstrated. These structures are considered to be linear terminal complexes. At their distal (cell wall) surface, they appear to be closely associated with cellulose microfibrils. At the proximal (cytoplasmic) surface, they are associated with microtubules and polysomes. A model of the possible interrelation of the terminal complexes and microtubules leading to the generation of cell wall microfibrils is proposed.