Senescence of attached leaves: Regulation by developing pods

Analysis of total nitrogen, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [ Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above-mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid-development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics.     

Effect of Light and Benzyladenine on Dark-Treated Growing Rice (Oryza sativa) Leaves II. Changes in Peroxidase Activity

Changes in peroxidase activity were studied in the attachedfirst leaf of dark-treated Oryza sativa L. cv. Bala seedlingsin response to benzyladenine and light treatments during laterperiods of leaf growth, prior to maturation. Darkness causeda mild decrease in peroxidase activity; but in illuminated leaves,the enzyme activity was stable at all times. There was a sharprise in peroxidase activity in dark-treated leaves upon lightor benzyladenine application, irrespective of the time of treatment.Benzyladenine treatment to illuminated leaves also caused arise in peroxidase activity. Exogenous hydrogen peroxide, glycolateand amizol resulted in a rise in peroxidase activity, whichwas further enhanced by benzyladenine treatment in both lightand dark incubated leaves. Proline maintained chlorophyll levels,whereas hydroxyproline caused chlorophyll degradation. Benzyladenineenhanced the proline effect and counteracted the hydroxyprolineeffect on chlorophyll. Both proline and hydroxyproline increasedperoxidase activity in the leaves of light and dark incubatedseedlings, and the enzyme activity further increased after benzyladeninetreatment. (Received December 7, 1984; Accepted May 8, 1985)     

Plasmodium gallinaceum: critical role for microtubules in the transformation of zygotes into Ookinetes

The role of microtubules and microfilaments in the transformation of spherical zygotes of Plasmodium gallinaceum (avian malaria parasite) into vermiform ookinetes has been studied by using specific drugs (taxol, colchicine, and cytochalasin-B). Both taxol and colchicine completely abolished the transformation of zygotes into ookinetes. The inhibitory effect was seen only if the drugs were added during the initial 6 hr of total time (20-24 hr) required for complete transformation; the addition of drugs after 6-8 hr of initiation of transformation had no effect. Electron microscopy revealed that microtubules were depolymerized by colchicine treatment, whereas in taxol-treated cells there was an extensive array of cytoplasmic and nuclear microtubules which appeared to be clumped in bundles. In contrast to the effects of taxol and colchicine, cytochalasin-B, which affects the microfilament system, had no effect on the transformation. Protein synthesis and expression of two ookinete-specific surface proteins were not affected in the drug-inhibited parasites. Zygotes treated with taxol for 4 hr at room temperature failed to develop into oocysts when they were subsequently fed to mosquitoes. These studies demonstrate a critical role for microtubules in the initial stages of transformation of zygotes into ookinetes.     

Synthesis and biological activity of 3 beta-fluorovitamin D3: comparison of the biological activity of 3 beta-fluorovitamin D3 and 3-deoxyvitamin D3

The alteration in the biologic activity of the vitamin D3 molecule resulting from the replacement of a hydrogen atom with a fluorine atom is a subject of fundamental interest. To investigate this problem we synthesized 3 beta-fluorovitamin D3 6 and its hydrogen analog, 3-deoxyvitamin D3 7, and tested the biologic activity of each by in vitro and in vivo methods. Contrary to previous reports which showed that 3 beta-fluorovitamin D3 was as active as vitamin D3 in vivo, we found that the fluoro-analog was less active than vitamin D3. With regard to stimulation of intestinal calcium transport and bone calcium mobilization in the D-deficient hypocalcemic rat, 3 beta-fluorovitamin D3 showed significantly greater biologic activity than its hydrogen analog, 3-deoxyvitamin D3. In the organ-cultured, embryonic chick duodenum, 3 beta-fluorovitamin D3 was approx 1/1000th as active as the native hormone, 1,25-dihydroxyvitamin D3, while 3-deoxyvitamin D3 was inactive even at microM concentrations, in the induction of the vitamin D-dependent, calcium-binding protein. With regard to in vitro activity in displacing radiolabeled 25-hydroxyvitamin D3 from vitamin D binding protein and radiolabelled 1,25-dihydroxyvitamin D3 from a chick intestinal cytosol receptor, 3 beta-fluorovitamin D3 and 3 beta-deoxyvitamin D3 both showed very poor binding efficiencies when compared with vitamin D3. Our results show that the substitution of a fluorine atom for a hydrogen atom at the C-3 position of the vitamin D3 molecule results in a fluorovitamin 6 with significantly more biological activity than its hydrogen analog, 3-deoxyvitamin D3 7.     

Synthesis and biologic activity of 3 beta-thiovitamin D3

We synthesized 3 beta-thiovitamin D3 from 7-dehydrocholesterol and tested its biological activity and protein binding properties. The thiovitamin was found to be a weak vitamin D agonist at high doses in vivo. It was poorly bound by both vitamin D-binding protein as well as by the intestinal cytosol receptor for 1,25-dihydroxyvitamin D. It did not increase the synthesis of calcium binding protein in the chick embryonic duodenum and did not block the activity of 1,25-dihydroxyvitamin D3 in this system. We conclude that 3 beta-thiovitamin D3 is a weak vitamin D agonist in vivo with no agonist activity or antagonist activity to 1,25-dihydroxyvitamin D3 in the chick embryonic duodenum.     

A method for the controlled cleavage of disulfide bonds in proteins in the absence of denaturants

A simple method was developed for the controlled cleavage of protein disulfide bonds and the simultaneous blockage of the free sulfhydryl groups in the absence of a denaturant. The disulfide bonds of bovine serum albumin were cleaved unsymmetrically at pH 7.0 using 0.1 M sulfite in 0.1 M phosphate buffer and the free sulfhydryl groups formed were sulfonated in an oxidation-reduction cycle using molecular oxygen and 400 microM cupric sulfate as a catalyst. The reaction was affected by cupric ion concentration, sulfite concentration, reaction pH and temperature. The standardized method was successfully used to cleave the disulfide bonds of other proteins pepsin, trypsin, and chymotrypsin. The method is reliable and can be used for achieving progressive cleavage of disulfide bonds in proteins without employing a denaturant.     

Isolation and characterization of plasma membrane fromAcanthamoeba culbertsoni

A rapid method for preparation of plasma membrane fromAcanthamoeba culbertsoni involving toluene treatment followed by lithium bromide extraction is described. In the plasma membrane preparation, 5′-nucleotidase, Na⁺ + K⁺ -ATPase, Mg²⁺ -ATPase and glucose-6-phosphatase activities were enriched. The membrane preparation was free from nucleic acid, cytochrome P-450 and cytochrome b5. Amino acid (¹⁴C-Ieucine) was not incorporated in the plasma membrane in 2 min. Succinic dehydrogenase was not detectable in the plasma membrane preparation. The molar ratio of cholesterol and phospholipids was 0.95 which is characteristics for plasma membranes. Under electronmicroscopy the preparation was homogenous without any other component of the cell. Plasma membrane proteins and glycoproteins were separated on acrylamide gel electrophoresis     

Molecular epidemiology of plasmid patterns in Shigella dysenteriae type I obtained from an outbreak in West Bengal (India)

Abstract Multiple antibiotic-resistant Shigella dysenteriae type 1 isolates from a recent epidemic in West Bengal (India) showed identical plasmid patterns. All isolates were resistant to ampicillin (Am), chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm) and trimethoprim (Tp) and contained 6 plasmids, ranging from 2.5–120 kb. The Am resistance determinant was located on the 120 kb plasmid. This plasmid was unstable when the S. dysenteriae strains were grown above 37°C. The Bangladesh strains of S. dysenteriae type 1 showed identical plasmid patterns, except that many isolates were Am-sensitive and lacked the 120 kb plasmid. In strains from both Bangladesh and West Bengal, predominantly group-B plasmids conferred resistance to Cm and Tc. Comparisons of Eco R1 fragments generated from the total plasmid DNA content of each strain support the view that the plasmids present in the S. dysenteriae type 1 strains isolated from all recent epidemics in India and Bangladesh were identical.