Loss of chloroplast‐localized protein phosphatase 2Cs in Arabidopsis thaliana leads to enhancement of plant immunity and resistance to Xanthomonas campestris pv. campestris infection

Protein phosphatases (PPs) counteract kinases in reversible phosphorylation events during numerous signal transduction pathways in eukaryotes. PP2Cs, one of the four major classes of the serine/threonine‐specific PP family, are greatly expanded in plants. Thus, PP2Cs are thought to play a specific role in signal transduction pathways. Some rice PP2Cs classified in subgroup K are responsive to infection by the compatible Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight. In Arabidopsis thaliana, orthologous PP2C genes (AtPP2C62 and AtPP2C26) classified to subgroup K are also responsive to Xanthomonas campestris pv. campestris (Xcc, causal agent of black rot) infection. To elucidate the function of these subgroup K PP2Cs, atpp2c62‐ and atpp2c26‐deficient A. thaliana mutants were characterized. A double mutant plant which was inoculated with a compatible Xcc showed reduced lesion development, as well as the suppression of bacterial multiplication. AtPP2C62 and AtPP2C26 localized to the chloroplast. Furthermore, the photosynthesis‐related protein, chaperonin‐60, was indicated as the potential candidate for the dephosphorylated substrate catalysed by AtPP2C62 and AtPP2C26 using two‐dimensional isoelectric focusing sodium dodecylsulfate‐polyacrylamide gel electrophoresis (2D‐IDF‐SDS‐PAGE). Taken together, AtPP2C62 and AtPP2C26 are suggested to be involved in both photosynthesis and suppression of the plant immune system. These results imply the occurrence of crosstalk between photosynthesis and the plant defence system to control productivity under pathogen infection.     

Developmental gene expression of gastrin receptor in rat stomach

Gastrin, which is present in fetal plasma, may have important roles in the development of gastric mucosa, since it is not only a potent stimulator of gastric acid secretion but also a growth promoting factor. Gastrin regulates various cellular functions via its receptors on cell membrane. Therefore, in order to elucidate a role for gastrin in the development of gastrointestinal system during gestation, Northern blot analysis was performed. The results of the study suggested that gastrin receptor is mainly present on parietal cells. Furthermore, proton pump and gastrin receptor gene expressions in parietal cells were strongly stimulated by the administration of exogenous gastrin. In conclusion, gastrin may be involved in the developmental change of parietal cells through its receptors.     

Hyperpolarization-activated Cl current elicited by pituitary adenylate cyclase activating polypeptide in Xenopus oocytes

We examined the electrophysiological effect of pituitary adenylate cyclase activating polypeptide (PACAP) in isolated Xenopus laevis oocytes in vitro. In conventional two-electrode voltage clamp experiments, PACAP (1–10 μM) activated an inward rectifier current at membrane potentials more negative than −60 mV without causing any significant change in currents at potentials more positive than −60 mV both in the follicle-enclosed oocyte and in the defolliculated oocyte. This current reversed at −22.5 mV, close to the theoretical value of Cl⁻ equilibrium potential and the reversal potential of this current was shifted positively by reducing [Cl⁻]_o. This current was blocked by Cl⁻ channel blocker SITS and Ba²⁺. Furthermore, VIP and adenylate cyclase activator forskolin did not elicit the currents. In conclusion, PACAP elicited the hyperpolarization-activated Cl⁻ current in Xenopus laevis oocytes. This current may modulate the membrane potential of the oocyte, thereby affecting the oocyte physiology.     

Hyperventilation-induced airway injury and vascular leakage in dogs: effects of alpha 1-adrenergic agonists

Freed, Arthur N., Varsha Taskar, Brian Schofield, andChiharu Omori. Hyperventilation-induced airway injury and vascular leakage in dogs: effects of₁-adrenergic agonists.J. Appl. Physiol. 83(6):1884-1889, 1997.₁-Adrenergic agonistsinhibit hyperventilation-induced bronchoconstriction (HIB) in dogs. Wetested the hypothesis that -agonists inhibit HIB byreducing bronchovascular leakage and edema that theoretically couldcause airway obstruction. Peripheral airways were isolated by using abronchoscope; pretreated with either methoxamine (Mx), norepinephrine(NE), or saline aerosol; and then exposed to a 2,000 ml/min dry-airchallenge (DAC) for 2 min. Colloidal carbon was injected before DAC andused to quantify bronchovascular permeability. Mx-, NE-, andvehicle-treated airways were prepared for morphometric analysis within1 h after DAC. Light microscopy revealed that the 2-min DAC producedminimal bronchovascular leakage and little epithelial damage. However, pretreatment with either Mx or NE significantly enhanced dryair-induced bronchovascular hyperpermeability and mucosal injury. Theincreased damage associated with these₁-agonists implicates aprotective role for the bronchial circulation. The factthat ₁-agonists inhibit HIBsuggests that neither dry air-induced leakage nor injury directlycontributes to the development of airway obstruction. In addition,our data suggest that-agonists attenuate HIB in part byaugmenting hyperventilation-induced bronchovascular leakage and byreplacing airway water lost during a DAC.

     

Reproductive behaviour of the white-tailed zygaenid moth,Elcysma westwoodii (Lepidoptera,Zygaenidae). II. Female mating strategy

Male white-tailed zygaenid moths.Elcysma westwoodii, often gather to a female to mate her. One of the factors that seems to cause male gathering is the females' tendency to refuse males. Field observations indicated that there was a relationship between the courtship duration, the copulation duration and egg fertilization: short courtship was followed by long copulation and oviposition of fertile eggs in the same day, while long courtship was followed by short copulation and failure of oviposition. This phenomenon may be the result of differences in male activity. More “fertile” males can reach copulation more quickly and continue it longer than males by limiting receptivity. This “passive female choice” seems to function in high male density. Long copulation usually continued until the female began oviposition.     

Seroepidemiological Survey of Lymphocytic Choriomeningitis Virus in Wild House Mice in China with Particular Reference to Their Subspecies

Serum samples from 337 wild house mice (Mus musculus) from 35 sites in China, collected in 1992 and 1993, were examined for antibodies against lymphocytic choriomeningitis virus (LCMV). Ten samples from eight sites were found to contain such antibodies. Six of the eight positive sites were located in the territory of M. m. gansuensis. One of the other two sites was located in the territory of M. m. castaneus in southern China and the other site was in a habitat of M. m. castaneus which had invaded into the western end of the territory of M. m. homourus. It seems likely that LCMV is distributed in the territories of M. m. gansuensis and M. m. castaneus in China. This is the first report of detection of these antibodies in wild house mice in China and specifically in the territories of M. m. gansuensis and M. m. castaneus.     

Seasonal Variations in the Presence of Antibodies against Coxiella burnetii in Dairy Cattle in Hokkaido,Japan

The prevalence and seasonal variations of infection by Coxiella burnetii in cattle were investigated seroepidemiologically on a farm in Hokkaido, Japan, by an immunofluorescent antibody test. A total of 364 serum samples from 28 cows were collected from August 1993 to October 1995 in two barns on the farm. It was found that the number of antibody-positive cows and their antibody titers were significantly elevated in winter and decreased in summer. In addition, antibodies were detectable in seroconverted cows for about five months.     

2,4-D-Sustained Photomixotrophic Growth of a Chlorophyllous Cell Suspension Culture of Nicotiana tabacum

A chlorophyllous, photomixotrophic cell suspension culture oftobacco (Nicotiana tabacum L.) was established using mediumcontaining 30 g/liter of sucrose and 1.5 µM 2,4-D. The2,4-D-sustained photomixotrophic line was able to show rapidregreening in the light after bleaching in the dark and characterizedwith a much slower and longer growth cycle than a heterotrophicline derived from the same original callus (cell doubling timeof 100 h vs. 40 h and duration of logarithmic phase of 17 daysvs. 7 days). The photomixotrophic line took up sucrose morerapidly than the heterotrophic line and accumulated starch duringthe early logarithmic phase when it showed a maximum photosyntheticcapacity on a chlorophyll basis (6.3µmol O₂/min/mg Chl).Chlorophyll content and photosynthetic capacity on a per cellbasis and on a cell fresh weight basis, on the other hand, decreasedduring this phase and reincreased later to reach maximum levels(310 µg Chl/g fr wt; 1.4 µmol O₂/min/g fr wt) whenthe line exhibited the highest activities of dark respiration(1.0 µmol; O₂/min/g fr wt) and cell division (mitoticindex of 3.0%). These characteristics of the photomixotrophicline were lost if it was grown in the dark to become non-chlorophyllous.Although net O₂ evolution could not be detected in the photomixotrophicline throughout the growth cycle when assayed under suboptimumlight intensity, reaccumulation of starch and a marked increasein cell fresh weight upon addition of minerals, vitamins and2,4-D without sucrose at the late logarithmic phase indicatedthe development of photosynthetic activity under the cultureconditions. ¹The investigations reported were included in the thesis submittedto the Graduate School, Faculty of Agriculture, Kobe University,in partial fulfillment of the requirement for M. Agr. degree. (Received May 30, 1988; Accepted October 5, 1988)