Effect of the venom of the gregarious parasitoid Apanteles glomeratus on its hemocytic encapsulation by the host, Pieris

When eggs from the lateral oviduct of the gregarious parasitoid Apanteles glomeratus were injected with calyx fluid and venom apparatus material into host larvae, Pieris rapae crucivora, most of the eggs were not encapsulated. Apanteles eggs deposited by the parasitoid from which the venom apparatus was removed were usually encapsulated by the host. These results indicate that the parasitoid venom apparatus material is an important factor in suppressing the encapsulation of 1- or 2-day-old eggs in the host. In order to clearly demonstrate that the venom suppresses egg encapsulation but not the encapsulation of other foreign objects, DEAE-Sephadex A-50 ion-exchange particles stained with 0.001% (w/v) Congo Red solution were injected into hosts together with venom apparatus material. The Sephadex particles were encapsulated by host hemocytes. The results suggest that the venom does not inhibit the encapsulation ability of the host.     

Developmental mutants showing abnormal organ differentiation in rice embryos

Summary Zygotes of rice (Oryza sativa L. cv Taichung 65) were treated with 1.0 mM solution of the chemical mutagen N-methyl-N-nitrosourea. Out of 1420 M₂ lines, 28 single-locus recessive mutants on embryogenesis were identified. Among them, we analyzed 11 mutants in the present study, which differentiated the shoot (plumule) and/or root (radicle) with abnormality. Of the 11 mutants, two showed no shoot differentiation with normal root. On the other hand, we could not detect any mutant which exhibited a normal shoot without a root. This suggests that shoot and root are genetically controlled by different loci and that the alleles associated with shoot formation mutate more frequently than do those of the root. Five mutants showed aberrant morphology of shoot when both the shoot and root developed. One of them, odm 5 (organ differententiation mutant 5) was germinable, but produced many fine and twisted leaves. This mutant was, however, lethal at the early post-germination stage under the usual cultural conditions. In another mutant (odm 4), shoot differentiation seemed to be initiated at an arbitrary position, resulting in a very abnormal morphology of the shoot when the position fronted the endosperm. The other two mutants showed abnormal morphology of both the shoot and root. One (odm 11) of the remaining two mutants showed a wide variation of abnormalities including no organ differentiation, either shoot or root differentiation and the development of both shoot and root with abnormalities. The last one (odm 16) was unique. It had an embryo with normal shoot and root but the embryo size was only one-third to one-half of normal embryos in length. Of course, the shoot and root are also small but viable. Therefore, odm 16 is considered to be a mutant in the size regulation of the embryo. Although an allelism test has not yet been done, most of these mutants are probably non-allelic, as the phenotypic abnormality differs largely with each one. In rice, the shoot and root highly differentiate in contrast to dicotyledonous embryo. Accordingly, these developmental mutants are very useful materials for investigating the regulatory mechanism of gene expression in organ differentiation.     

Kinetic study of the effects of solvation on the dimerization process of alpha-chymotrypsin

The dimeric association process of alpha-chymotrypsin has been studied with the aid of a stopped-flow spectrophotometer at various temperatures and pH values. From the temperature dependences of the forward reaction rate constant (kf) and the equilibrium dimerization constant (KD), the reaction system observed here is concluded to be entropy-driven. The increase in entropy can be attributed to the release of water molecules from both the active site and the surface part of the protein molecule during the course of dimerization. From the pH dependences of the reaction rate constants and the equilibrium constant, the reaction is concluded to depend strongly on the dissociations of the site between the carboxyl group of the aspartic acid and imidazolyl group of the histidine residues (in the higher pH region), and the site between the imidazolyl group of the histidine and the carboxyl group of the tyrosine residue (in the lower pH region), respectively.     

Kinetic study of a hollow-fiber enzyme reactor

Enzymes, such as urease and uricase, were entrapped in three kinds of hollow fibers. The apparent Michaelis–Menten constants K_m(app) obtained for these enzyme reactors were always larger than K_m of free enzyme because of the permeation resistance of substrate across the hollow-fiber membrane. K_m(app) increased with increasing degree of permeation resistance across the membrane by the increase in enzyme concentration. The half-life of the entrapped urease in the continuous reaction system was 60–80% of that of free enzyme. Activation energies of hollow-fiber enzyme reactors were always smaller than that of the free enzyme, because the activation energy of permeation was smaller than that of the enzyme reaction.     

Comparison of somatostatin-28 and somatostatin-14 clearance by the perfused rat liver

The hepatic clearances of somatostatin (SS)-28 and SS-14 by the perfused rat liver were compared, using a recirculating, plasma-free, erythrocyte-containing perfusion system. The disappearance rate constant, half time, clearance, and hepatic extraction ratio when 1.2 nM SS-28 was added to the perfusate were 0.0221 +/- 0.0051 min-1, 36.6 +/- 7.6 min, 0.34 +/- 0.08 mL/min, and 17.2 +/- 3.9%, respectively. The corresponding values obtained when SS-14 was added to the perfusate were 0.0405 +/- 0.0022 min-1, 17.3 +/- 1.0 min, 0.71 +/- 0.05 mL/min, and 35.4 +/- 2.6%, respectively. The differences between the SS-28 and SS-14 indices were all statistically significant. In addition, the perfusates with SS-28 added were eluted on Sephadex G-25 fine columns and somatostatinlike immunoreactivity (SLI) was determined. No SS-14 was found in perfusate containing SS-28 at both 5 and 30 min after the beginning of the perfusion. To investigate whether or not the liver plays an important role in the clearance of SS-28 or the conversion of SS-14 in vivo, the plasma disappearance of 2 micrograms SS-28 was compared in the whole rat and the functionally hepatectomized model. The half time of plasma SS-28 was 1.43 +/- 0.12 min in the whole rat, significantly shorter than the 2.20 +/- 0.14 min in the hepatectomized model. Gel filtration of plasma extract samples at 0.5 min after the SS-28 injection showed two major peaks of SLI: a first peak corresponding to SS-28 and a second peak coeluted in the position of SS-14 in both the whole rat and the hepatectomized model. At 4 min after the SS-28 injection, the first peak disappeared and only a small second peak was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Accelerated shoot overgrowth of rice mutant <Emphasis Type="Italic">ao-1</Emphasis> is epistatic to gibberellin-sensitive and -insensitive dwarf mutants

 A shoot overgrowth mutant of rice (Oryza sativa L.), accelerated internode overgrowth-1 (ao-1), is marked by accelerated longitudinal elongation of aerial parts and overgrowth of internodes at the vegetative stage. The physiological properties of ao-1 were similar to those of wild plants treated with a saturating level of exogenous gibberellins (GAs), except for the internode-overgrowth phenotype, which was not mimicked by GA-treated wild plants. The ao-1 mutant was less sensitive to a GA biosynthesis inhibitor, Uniconazole-P, than the wild type. Dwarf alleles of three loci, including two GA-sensitive and one GA-insensitive mutation, were introduced to produce double-mutants with ao-1, but the overgrowth phenotype was not suppressed in double-homozygous mutants. These results suggest that the overgrowth phenotype of ao-1 is caused by abolition of GA signaling rather than by GA overproduction. It is likely that a part of the shoot regulation system of ao-1 is saturated with the GA signal. As a possible model consistent with the results, we propose that AO-1 protein acts as a negative regulator in GA signal transduction. Received: August 14, 2001 / Accepted: February 8, 2002     

Diversity and Complexity of Ceramide Signalling in Apoptosis

Sphingolipid ceramide has emerged as a lipid messenger of cell functions including differentiation and apoptosis. Diverse kinds of stresses (ultraviolet, irradiation, heat shock and hypoxia) and biological factors (TNF-, IFN-γ and Fas antibody) require ceramide generation to execute apoptosis. The review summarises the diversity and complexity of up- and downstream of ceramide signalling in apoptosis and clinical implications of ceramide-induced apoptosis.     

Resistance of Apanteles eggs to the haemocytic encapsulation by their habitual host, Pieris

The calyx fluid in the lateral oviduct of a gregarious parasitoid, Apanteles glomeratus contained ellipsoid particles of ca. 130 × 200 nm. These calyx fluid particles did not appear to be embedded in a fibrous outer layer on the surface of eggs in the lateral oviduct. They were not observed on the surfaces of the eggs 3 to 4 hr after being deposited into the host haemocoele. Oviposition experiments indicated that the occurrence of haemocytic defence reactions of the late 2nd instar larvae of the Pieris rapae crucivora against 1 st instar larvae of the parasitoid increased with a decreasing number of the parasitoid eggs introduced into a host, and that more than 5 to 9 parasitoid eggs were needed for suppressing the ability of the host to encapsulate its parasitoid larvae immediately after hatching. When eggs with calyx fluid obtained from egg reservoir were injected into the host, they were found to be encapsulated 1 to 2 days after the injection. They could not start their embryonic development. When calyx fluid-free 3-hr-old eggs were injected in a number of more than 5 eggs into a 5th instar larva of Pieris, 58% of 31 eggs injected had normally hatched without evoking encapsulation reactions by the host. Both electron microscopic observations of parasitoid eggs in the host haemocoele and the experimental results suggested that calyx fluid or calyx fluid particles of the parasitoid might not be involved in the encapsulation-inhibiting activity of the parasitoid eggs. Rather it was anticipated that a substance (or substances) might be secreted by the parasitoid eggs into the haemocoele of the host, which suppressed defence reactions of the host.