Differential effects of oxygen on N2 fixation and C2H2 reduction by Anabaena cylindrica

Both nitrogen fixation and acetylene reduction by intact cellsof Anabaena cylindrica were inhibited by oxygen, but nitrogenfixation was invariably less sensitive than acetylene reduction.The C₂H₂/N₂ ratio ranged from 6 to 8 in the absence of oxygen,and it decreased with increase in partial pressure of oxygento 2 at a pO₂ of 0.3 atm. (Received June 5, 1979; )     

Effects of the protein phosphatase inhibitors okadaic acid and calyculin A on insulin release from rat pancreatic islets.

The role of protein phosphatases in the regulation of insulin release from rat pancreatic islets was studied with protein phosphatase inhibitors, okadaic acid and calyculin A. Okadaic acid inhibited glucose- and glyceraldehyde-induced insulin release dose-dependently and also inhibited the potentiation of glucose-induced release either by adding forskolin, an activator of adenylate cyclase or by increasing K+ concentration to 25 mM. At a non-stimulatory concentration of 3 mM glucose, a high concentration (2 microM) of okadaic acid inhibited insulin release induced by high K+ or 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, but a low concentration (1 microM) of okadaic acid did not significantly inhibit TPA-induced insulin release. Calyculin A also inhibited glucose-induced insulin release, and the effect was greater than that of okadaic acid. The data suggest that protein phosphatases may play an important role in the regulation of insulin release.     

Role of brain histamine H1- and H2-receptors in neostigmine-induced hyperglycemia in rats.

We previously reported that when neostigmine, an inhibitor of acetylcholine esterase, was injected into the third cerebral ventricle, the concentration of hepatic venous plasma glucose was increased via central muscarinic receptors in anesthetized rats. To determine whether brain histamine receptors are involved in cholinergic system transmission with regard to central nervous system (CNS)-mediated glucoregulation, we examined the effects of the H1 receptor antagonist pyrilamine and the H2 receptor antagonist ranitidine on neostigmine-induced hyperglycemia in anesthetized rats. The injection of pyrilamine (5 x 10(-9)-5 x 10(-7) mol) into the third cerebral ventricle suppressed hyperglycemia induced by intraventricular injection of neostigmine (1 x 10(-9) mol) in a dose-dependent manner. Injection of ranitidine (5 x 10(-9)-5 x 10(-7) mol) into the third cerebral ventricle did not suppress the hyperglycemia induced by neostigmine, but enhanced it in a dose-dependent manner. These findings suggest that neostigmine-induced CNS-mediated hyperglycemia is transmitted by not only brain cholinergic muscarinic receptors but also in part by histamine H1 receptors.     

Roles of Inorganic Nitrogen in Gametophytic Growth and in Initiation and Development of Sporophytic Shoots of Equisetum arvense

The formation of sporophytic shoots, which is induced by treatmentwith benzylaminopurine of gametophyte tissue of Equisetum arvense,can be divided into initiation and developmental phases. Thenitrogen in MS medium was suitable for two phases as well as gametophytic growth, buta reduction in the concentration of available nitrogen was neededfor the development of shoots. ions alone were effective for gametophytic growth and the initiationof sporophytic shoots, but both and ions was required for the developmental phase. (Received February 18, 1992; Accepted April 14, 1992)     

Parturition in a free-ranging Japanese monkey (Macaca fuscata)

Parturition behavior of a multiparous female and her interactions with group members throughout the birth process were recorded for a free-ranging Japanese monkey (Macaca fuscata). The female showed evidence of 18 contractions during the 35 min prior to delivery, with a mean duration and a mean intercontraction interval of 30 sec and 96 sec, respectively. These values were similar to those in individually caged Japanese monkeys. Some adult females remained in proximity to the female who was giving birth during the prepartum phase, and her 2-year-old daughter watched the delivery of the infant. Even during the prepartum phase the female moved in order to keep up with the group which traveled from the feeding site to a sleeping site in the forest.     

Influence of livestock grazing on vegetation in a saline area in Northeast Thailand

The influence of grazing by water buffalo (Bubalas bufalis) and cattle (Bos taurus) was estimated for vegetation inside and outside cages in a saline area at Khon Kaen, Northeast Thailand. The home range of water buffalo and cattle shifted in response to the period of rice cultivation: during the rice-growing season these animals grazed on roadsides and abandoned places such as the study area; after rice harvest they grazed mainly rice stubble on the paddy. The vegetation in the study area was divided into three types: 1) dominated by the annual grassesChloris barbata andIschaemum rugosum; vegetational cover and plant height in the cage increase due to the increase of these grasses; 2) thorny shrub patch ofMaytenus mekongensis; other species in this patch almost died a year after experimental elimination of this shrub; this salt-tolerant shrub not only protected the co-existing species from grazing, but also suppressed salt accumulation; 3) almost pure stand ofPanicum repens; livestock preferred this perennial grass over others. Electrical conductivity (EC) of surface soil did not increase under the vegetation protected from grazing. Litter and other organic matter in the soil suppressed the upward movement of brine. Grazing led to an increase of bare ground where NaCl accumulated, and modified the heterogeneity of vegetation, which was reflected in the degree of salt accumulation.