The possible involvement of cytokinins in the pathogenicity of Helminthosporium maydis

Green islands/infection sites recorded higher cytokinin activity than surrounding tissue as well as non-inoculated tissue. This activity in infected areas increased with time of incubation while in tissue surrounding the green islands and non-inoculated tissue, cytokinin activity decreased with time of incubation. The culture filtrate extracts of H. maydis had cytokinin activity which increased with growth of the fungus. Cytokinin activity of thin-layer Chromatographic fractions from tissue and culture filtrate extracts revealed that a major portion of the activity was confined to Rf zone 0.6 to 0.8 which co-chromatographed with zeatin and zeatin riboside. Presence of zeatin and zeatin riboside in tissue and culture filtrates was confirmed by high performance liquid chromatography. Cytokinin substances, such as zeatin and zeatin riboside, increase at infection sites with growth of the pathogen suggesting they may be involved in the pathogenicity of H. maydis on maize.     

Calmodulin supports the force-generating function in desensitized muscle fibers

Externally added calmodulin (CaM) restored Ca2+ regulation for the tension development by skeletal muscle fibers of hamster and rabbit desensitized by the troponin C (TnC) extraction treatment. CaM produced this action by combining with the TnC-denuded sites in the fiber. However, the binding properties differed strikingly from TnC: unlike TnC, CaM binding required the continued presence of Ca2+ and the bound portion was completely released with EGTA in the physiological milieu. The maximal uptake was 1.7 g of CaM/kg of muscle in the present study. The apparent Ca2+ sensitivity for force development with 200 micrograms/ml CaM in the solution was lower than in the native fiber or in the TnC-loaded fiber. The apparent association constant for CaM binding to the TnC-denuded sites was found as 4.9 x 10(5) M-1, and the extrapolated maximum force (Fmax) with CaM was close to PO. The intrinsic CaM level in intact muscle was also measured and was 18.6 mg/kg, amounting to about 1% of the total TnC or the CaM uptake by TnC-denuded fibers. The intrinsic CaM was not dislodged by EDTA treatment, indicating tight binding and suggesting that it exists in a separate pool from the vacated TnC sites adsorbing externally added CaM. The stringent Ca+ dependence of the CaM adsorption to TnC sites in the regulatory complex in the fiber supports the view that the evolutionary replacement of residues in the amino terminus helix portion of the "EF-hand" motif of site IV may be critical for the functional specialization by TnC.     

Role of central histaminergic mechanism in behavioural depression (swimming despair) in mice

The role of the central histaminergic system in depression was studied by using swimming despair test in mice - a behavioural model of depression. In this test, immobility of mice reflects a state of depression. Intracerebral (ic) injection of histamine (50-200 micrograms) increased significantly the immobility. The H1-receptor blocker mepyramine (2.5-20 mg/kg ip) had no effect while H2-receptor blocker cimetidine (100-200 micrograms ic) caused a significant decrease in immobility. The histamine induced facilitation was blocked completely by cimetidine and antidepressant drugs-imipramine and desipramine, but remained unaffected in mice pretreated with mepyramine or atropine. The H2 agonist impromidine (20-40 micrograms ic) also enhanced significantly, the immobility which was blocked by cimetidine and antidepressant drugs. It has been concluded that central H2-receptors facilitate depression and antidepressant drugs block central H2-receptors.     

Down-regulation of alpha 2 adrenoceptors in ventrolateral medulla of spontaneously hypertensive rats.

The binding of [3H]idazoxan [correction of idaxazon] to imidazole sites and [3H]rauwolscine to alpha 2 adrenoceptors of neuronal membranes prepared from cerebral cortex and ventrolateral medulla of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [3H]idazoxan [correction of idaxazon] bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]idazoxan [correction of idaxazon] in ventrolateral medulla and cerebral cortex was found to be similar in SHR and WKY rats. [3H]Rauwolscine bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]rauwolscine in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [3H]rauwolscine binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due a decrease (32%) in the Bmax value in SHR rats as compared to WKY rats. The Kd values were similar in SHR and WKY rats. It is concluded that imidazole binding sites are not affected while, alpha 2 adrenergic binding sites are decreased in the ventrolateral medulla of SHR rats and may be contributing to the regulation of blood pressure.     

Kinetics of force redevelopment in isolated intact frog fibers in solutions of varied osmolarity.

Isolated intact frog muscle fibers, while shortening with the intrinsic maximal speed, were stretched back to the original length to measure the kinetics of force redevelopment. These kinetics give information on the attachment rate constant in the cross-bridge cycle in vivo, and a value of approximately 25.6 s-1 (0 degree C) is found in the present study. We find that these kinetics were slightly less sensitive to temperature than was the unloaded shortening speed. The effect of hyperosmolarity on force redevelopment was also measured in solutions with added sucrose or KCl. The rate constant was nearly halved with 120 mM sucrose, but there was practically no effect with isosmotic (60 mM) KCl. These results indicate that the rate constant of force redevelopment is insensitive to raised intracellular ionic strength. In sucrose, the fiber width was also compressed, and the attenuation of the rate constant of force redevelopment in this case is consequently attributed to the decrease in interfilament space. The order of magnitude of the rate constant found in this study suggests that tension transduction by a cross-bridge, during each turnover cycle, requires a series of elementary steps following the attachment.     

Histochemical localization of gamma glutamyl transpeptidase in the paranodal region of peripheral nerve

Gamma glutamyl transpeptidase (GGT), an amino acid transport enzyme, was investigated in normal and degenerated sciatic nerve of rat. The enzyme activity, which is considered to be a marker for cerebrovascular endothelium, was found to be absent in microvessels of normal and degenerated nerves. In the perineurium of normal nerve, GGT activity was faint, while in degenerated nerve, it increased. The most striking finding of this study was the observation of GGT activity at the paranode of each normal myelinated axon. It is interesting that after axotomy (8 weeks), no GGT activity was observed in the Schwann cells of degenerated nerve. Thus, Schwann cell plasmalemma contributed to GGT staining only when this cell was in contact with an axon mature enough to cause it to produce myelin. We conclude that, in peripheral nerve, transmembrane amino acid transport is apparently regional and associated with the paranodal region of myelinated nerve fibers.     

Effect of dose schedule of vitamin E and hydroxethylruticide on intestinal toxicity induced by adriamycin

CDF1 mice receiving Adriamycin, 12 mg/kg IP develop a toxic GI mucositis. The mean survival in CDF1 mice after Adriamycin injection was found to be 6.5 +/- 2.0 weeks and could be increased by alcohol or acetate Vitamin E pretreatment (with 2 g/kg qDx7d) to 22.06 +/- 12.3 weeks or by treatment with Venoruton after Adriamycin (qDx7 with 1.5 g/kg) to 23.7 +/- 12.7 weeks. Other schedules were ineffective or harmful. The ability of Venoruton to enhance survival when given after Adriamycin encouraged us to proceed to tumor bearing mice. The maximum survival with CDF1 mice bearing 5 X 10(6) L1210 cells was 1 +/- 0.2 week which could be increased to 2.17 +/- 0.8 weeks with optimal dose Adriamycin (10 mg/kg). Optimum survival with Venoruton and a single dose of Adriamycin was 2.45 +/- 0.91 weeks with Venoruton, 1.5 g, qd X 14, and 12 mg/kg Adriamycin. Treatment of L1210 bearing mice with Adriamycin, 10 mg/kg on days 1 and 8, yielded a survival of 2.23 +/- 0.7 weeks. An equitoxic regimen of Adriamycin, 11 mg/kg on days 1 and 9, plus Venoruton, 1.5 g, qd X 14, increased survival 30% to 3.08 +/- 2.9 weeks. Venoruton is a promising agent to increase the therapeutic index of Adriamycin.     

Implication of Triticum searsii as the B-genome donor to wheat using DNA hybridizations

In vitro DNA:DNA hybridizations and hydroxyapatite thermal chromatography were employed to help identify the species ancestral to the B genome of the polyploid wheats. We hybridized 3H-Triticum aestivum DNA to the unlabeled DNAs of T. urartu, T. speltoides, T. sharonensis, T. bicorne, T. longissimum, and T. searsii, 3H-Labeled DNA of T. urartu was hybridized with the DNA of a synthetic tetraploid. AADD. The heteroduplex thermal stabilities indicated that T. searsii was most closely related to T. aestivum (ABD) and that the genome of T. urartu was more closely related to the A genome than the B genome. The degree of reassociation which may have occurred between the six diploid species and the D genome of T. aestivum was evaluated by hybridizing 3H-T. tauschii DNA with the DNAs of the diploids. The results indicated that T. urartu had the least sequence homology to T. tauschii, the D-genome donor lending additional support to the conclusion that T. urartu is related to the A genome. Thus, it is highly probable that T. searsii is the B-genome donor to the polyploid wheats or a major chromosome donor if the B genome is, in fact, polyphyletic in origin.     

Food web manipulation in Lake Zwemlust: Positive and negative effects during the first two years

The hypertrophic Lake Zwemlust, a small water body used as a swimming pool, was characterized by algal blooms in summer, reducing the Secchi disk transparency to less than 0.3 m. Since in The Netherlands a Secchi disk transparency of 1 m is obligatory for swimming waters, corrective measures were called for to improve the light climate of the lake. In March, 1987, as an experiment, the lake was drained by pumping out the water to facilitate fish elimination. Planktivorous and benthivorous fish species, which were predominant, were removed by seine- and electro-fishing. After the lake had refilled by seepage it was restocked by a new simple fish community comprising pike (Esox lucius) and rudd (Scardinius erythrophthalmus) only. Stacks of willow twigs (Salix) and macrophytes (roots ofNuphar lutea and seedlings ofChara globularis) were introduced into the lake as spawning grounds and refuges for the pike against cannibalism and as shelter for the zooplankton. The effects of this food web manipulation on the light climate, phytoplankton, zooplankton, fish, macrophytes, macrofauna and on the nutrient concentrations were monitored during 1987 and 1988. In summer 1987, despite of high nutrient concentrations, the phytoplankton density was low, due to control by zooplankton, causing a Secchi disk transparency of 2.5 m, the maximum depth. Chlorophyll-a concentrations were low (<5 g Chl.l^–1), blooms of cyanobacteria did not occur and a shift from rotifers to cladocerans took place. In 1988, however, also some negative effects were noticed. Macrophytes and filamentous green algae reached a much higher biomass (50–60% cover of the lake bottom) than in 1987; some species, growing through the entire water column, interfered with the lake's recreational use. Associated with the macro-vegetation and possibly with the absence of larger cyprinids, the diet of which also comprises snails, a large scale development of the snail population, among themLymnaea peregra var.ovata took place. This species is known to act as an intermediate host of the bird-parasitizing trematodeTrichobilharzia ocellata, the cercariae of which cause an itching sensation at the spot of penetration of the human skin, accompanied by rash (schistosome dermatitis or swimmers' itch); in July, 1988, about 40% of the bathers complained about this itching. A positive effect of the macrophytes and filamentous green algae was the high uptake of nitrogen, resulting in a low nitrogen concentration in the lake and growth limitation of the phytoplankton population by nitrogen in the summer of 1988. In 1988 the cladocerans were abundant in April only; and unlike in 1987, in the summer of 1988 there was a shift from cladocerans to rotifers. Therefore, only in early spring (April) zooplankton grazing controlled phytoplankton growth and in summer nitrogen limitation was the major controlling factor, keeping chlorophyll-a concentrations low.