Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number

The optimal oviposition strategies of parasitoids, the host range, and the number of eggs laid per host which result in the maximum lifetime performance of reproduction, are investigated. To study the effects of parasitoid mortality and of limiting total number of eggs laid by a parasitoid, a standard criterion used in previous theories of optimal diet and optimal patch use, the maximization of the foraging rate, is no longer suitable. The model is solved analytically by using dynamic programming. The results are as follows: The host preference of solitary parasitoids depends on the mortality during handling times; i.e., the forager tends to avoid hosts with high risk of foraging mortality. If the total number of eggs produced by a parasitoid is limited, and if the mortality during handling is negligible, the host range is wider when a larger number of eggs remains in the parasitoid's body. In general, however, the mortality-cost of forager and the egg-cost interplay, because the loss of future reproduction by mortality increases with the number of available eggs. In an example with two host types, host range is widest with an intermediate number of eggs available in the body. The optimal number of eggs per host laid by a gregarious parasitoid is also affected by the differential mortality of the forager, and by the number of available eggs.     

Storage of Hg in the ileum of Blatella germanica: biochemical characterization of metallothionein

Cockroach ileum has a high capability to concentrate mercury compared with other tissues. Part of the mercury contained in the soluble phase of this organ is bound to metallothionein. It is suggested that mercury of the insoluble phase is stored in lysosomes under a polymerized metallothionein form.     

Expression of mosquitocidal crystal protein genes in non-insecticidal Bacillus thuringiensis subsp. israelensis

Bacillus thuringiensis NTB-1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis , it seemed to be non-insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non-insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG-14, highly toxic to mosquito larvae, were introduced into the isolate NTB-1. The expression of mosquitocidal crystal protein genes in NTB-1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry⁻ B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non-insecticidal crystal proteins was not observed.     

Changes in Membrane Fluidity and Protein Composition during Release of Cucumber Seeds from Dormancy by a Higher Temperature Shift

Dormancy of seeds of cucumber (Cucumis sativus L.) was inducedby imbibing in -1.8 MPa polyethylene glycol 6000 (PEG) solutionand pulsing with far red light for 15 min prior to washing anddrying. When re-imbibed with water at 20 °C, dormancy wasbroken by raising the temperature to 30 °C for 6 h. Thistreatment was also effective when -0.9 MPa PEG was present duringre-imbibition and high temperature. Seeds with broken dormancywere found to germinate in water over a smaller temperaturerange than seeds in which dormancy had not been induced. Whenthe duration of the temperature shift to 30 °C was varied,germination percentage increased from 7 to 60% after 6 h, butlonger exposures up to 12 h had no further promoting effect.The time course of germination after transfer to water following6 h at 30 °C in PEG showed piercing of the perisperm-endospermenvelope after 9–12 h and radicle protusion after 12–15h. If PEG was retained after high temperature treatment no visiblegermination was observed. Thus, to study membrane fluidity andthe protein content associated with germination, seeds weresampled 9 h after high temperature treatment. To study the germinablebut not germinating state, seed held in PEG for 9 h rather thanin water was used. Dormant seed was sampled before the hightemperature treatment. Membrane fluidity was assessed usingfluorescence polarization of membrane fractions treated withDPH (1,6-diphenyl-1,3,5-hexatriene) or its derivatives. Membraneproteins were compared using one-dimensional SDS-PAGE electrophoresis.Intracellular membrane fluidity was not increased in the transitionfrom the dormant to germinable state, but did increase in thetransition to germination. There were no detected changes inintracellular membrane proteins during either transition. Inplasma membrane fractions, fluidity increased during both transitions,while a marked increase in 21, 18 and 17 kD proteins was observedin the transition from germinable to germinating state. Thusmodification of plasma membrane fluidity rather than changesin protein profile is associated with the high temperature releaseof cucumber seeds from dormancy. Copyright 2000 Annals of BotanyCompany     

Unbalanced ribosome assembly in Saccharomyces cerevisiae expressing mutant 5 S rRNAs.

Mutant 5 S rRNA genes were expressed in Saccharomyces cerevisiae to further define the function of the ribosomal 5 S RNA. RNA synthesis and utilization were assayed using previously constructed markers which have been shown to be functionally neutral and easily detected by gel electrophoresis. Most mutations were found not to affect the growth rate because they were poorly expressed or could be accommodated effectively in the ribosomal structure. Two of the mutants, Y5A99U56U57 and Y5U90i5 adversely affected cell growth as well as protein synthesis in vitro. Polyribosome profiles in both of these mutants were substantially shorter, and an analysis of the ribosomal subunit composition revealed a significant imbalance with a 25-35% excess in 40 S subunits. Kinetic analyses of RNA labeling indicated very low cellular levels of mutant RNA either because it was poorly expressed (Y5U90i5) or rapidly degraded before being incorporated into mature 60 subunits (Y5A99U56U57). The results suggest that the 5 S RNA is required for the assembly of stable ribosomal 60 S subunits and raise the possibility that this RNA or, more likely, its corresponding ribonucleoprotein complex is critical for subunit assembly or even RNA processing.     

Ultrastructural study of enzymes in reactive astrocytes: Clarification of astrocytic activity

Summary Enzymes in reactive astrocytes of the corebral cortex were examined at the ultrastructural level in an attempt to resolve some conflicting aspects of astrocytic activity. Correlations between morphological and enzyme changes after injury established that the apparent increase in oxidative enzyme activity was exclusively mitochondrial and not an artefactual reaction product resulting from anoxic cellular damage. Pronounced glucose-6-phosphatase activity within cisternae of an increased amount of the granular endoplasnie reticulum was related to increased glycogen. Further evidence from acid phosphatase activity indieated that astrocytes played a minimal role in phagocytosis.     

Burrowing dynamics and energy cost of transport in the soft-bodied marine invertebrates Polyphysia crassa and Priapulus caudatus

The dynamics and mechanical forces generated during burrowing in Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were investigated. Both animals live in soft marine muds and burrow by utilizing a direct peristaltic wave alternating with a high internal pressure event which thrusts the anterior part of the body into the substratum. Forces generated during the various phases of a typical burrowing cycle were measured in animals moving beneath the natural substratum at 5±3 °C using electronic transducers and recorder. During 'head' advance Polyphysia generated 0.027 N, and during 'tail' advance 0.020 N, with peak internal pressures averaging 0.95 kPa (= 0.095 N/cm²). Force by Priapulus during head advance and tail advance was 0.081 N and 0.121 N, respectively, with peak internal pressures averaging 2.47 kPa (= 0.247 N/cm²). Polyphysia moves more slowly (0.24 cm/min) than does Priapulus (0.76 cm/min) and expends more energy on mass moved per unit distance. These force measurements during a burrowing cycle were used in place of respirometry as a basis for computation of net cost of transport (NCT) for each animal. NCT for Polyphysia was 635 J kg^-1 m^-1 and for Priapulus was 314Jkg^-1m^-l. Cost of transport for all burrowing animals thus far investigated is high compared to swimming, running and flying. For soft-bodied invertebrates that live an entirely buried existence this high cost must be interpreted in the broader context of the adaptive value of infaunal life, especially protection against predation, and not as simply a means of moving about.     

Insecticides and soil microorganisms. III. Fate of 14C-labelled Dipterex as affected by two nodule-forming rhizobium spp. and roots of their respective leguminous host plants.

Chromatographic analysis led to the identification of monomethyl- and dimethyl-phosphates as metabolites resulting from the enzymatic degradation of 14C-labelled Dipterex in the buffer solutions and root tissues of broad bean and clover plants, as well as in the culture media of rhizobium leguminosarum and Rhizobium trifolii. The formation of 14CO2 from rhizobial cultures containing radioactive Dipterex suggests that some of the liberated methanol groups (during breakdown of Dipterex) are oxidatively degraded by the two Rhizobium spp.