Do pollen beetles need pollen? The effect of pollen on oviposition,survival, and development of a flower‐feeding herbivore

Abstract.  1. Pollen is considered to be an important dietary component for many species of flower-feeding herbivores. Its influence on oviposition site selection by the pollen beetle Meligethes aeneus , and on the development of its larvae was investigated.
2. The effects of pollen presence and absence on adult, egg, and larval incidence in the field, and on larval development in the laboratory were compared through the use of Synergy, a composite hybrid oilseed rape Brassica napus variety comprising male-fertile (with pollen) and male-sterile (without pollen) plants.
3. In the field, adult females were more abundant on male-fertile plants during flowering, and a greater proportion of male-fertile than male-sterile buds were accepted for oviposition. These data indicate a possible role of pollen in oviposition site selection by female pollen beetles.
4. The numbers of first instar larvae on the two plant lines did not differ; however, more second instars were found on male-fertile than on male-sterile flowers. This suggests a greater larval survival on male-fertile plants, possibly due to the more readily available food resources and better nutrition afforded by the presence of pollen.
5. Laboratory experiments confirmed that a diet which included pollen improved survival to adulthood and resulted in heavier pupae and adults; however, pollen was not obligatory for larval survival and development.
6. The pollen beetle, previously thought to be an obligate pollen feeder, is therefore more generalist in its requirements for development. These findings may relate to the nutritional and behavioural ecology of other flower-feeding herbivores.     

Behavior ofPseudomonas fluorescens within the hydrodynamic boundary layers of surface microenvironments

Phase, darkfield, and computer-enhanced microscopy were used to observe the surface microenvironment of flow cells during bacterial colonization. Microbial behavior was consistent with the assumptions used previously to derive surface colonization kinetics and to calculate surface growth and attachment rates from cell number and distribution. Surface microcolonies consisted of closely packed cells. Each colony contained 2ⁿ cells, where n is the number of cell divisions following attachment. Initially, cells were freely motile while attached, performing circular looping movements within the plane of the solid-liquid interface. Subsequently, cells attached apically, maintained a fixed position on the surface, and rotated. This type of attachment was reversible and did not necessarily lead to the formation of microcolonies. Cells became irreversibly attached by progressing from apical to longitudinal attachment. Longitudinally attached cells increased in length, then divided, separated, moved apart laterally, and slid next to one another. This resulted in tight cell packing and permitted simultaneous growth and adherence. After approximately 4 generations, individual cells emigrated from developing microcolonies to recolonize the surface at new locations. Surface colonization byPseudomonas fluorescens can thus be subdivided into the following sequential colonization phases: motile attachment phase, reversible attachment phase, irreversible attachment phase, growth phase, and recolonization phase.     

Detection of lipid hydroperoxides and hydrogen peroxide at picomole levels by an HPLC and isoluminol chemiluminescence assay

An isoluminol assay is utilized for the detection of hydrogen peroxide and lipid hydroperoxides in biological samples. The combination of this assay as a post-column detection for HPLC avoids interference of antioxidants and enables characterization of hydroperoxides at picomole levels. Two useful HPLC conditions for the separation of hydrogen peroxide, lipid hydroperoxides, antioxidants, and unoxidized lipids are described.     

An alkyl hydroperoxide reductase induced by oxidative stress in Salmonella typhimurium and Escherichia coli: genetic characterization and cloning of ahp

The ahp genes encoding the two proteins (F52a and C22) that make up an alkyl hydroperoxide reductase were mapped and cloned from Salmonella typhimurium and Escherichia coli. Two classes of oxidant-resistant ahp mutants which overexpress the two proteins were isolated. ahp-1 was isolated in a wild-type background and is dependent on oxyR, a positive regulator of defenses against oxidative stress. ahp-2 was isolated in an oxyR deletion background and is oxyR independent. Transposons linked to ahp-1 and ahp-2 or inserted in ahp mapped the genes to 13 min on the S. typhimurium chromosome, 59% linked to ent. Deletions of ahp obtained in both S. typhimurium and E. coli resulted in hypersensitivity to killing by cumene hydroperoxide (an alkyl hydroperoxide) and elimination of the proteins F52a and C22 from two-dimensional gels and immunoblots. ahp clones isolated from both S. typhimurium and E. coli complemented the cumene hydroperoxide sensitivity of the ahp deletion strains and restored expression of the F52a and C22 proteins. A cis-acting element required for oxyR-dependent, rpoH-independent heat shock induction of the F52a protein was present at the S. typhimurium but not the E. coli ahp locus.     

Alterations in levels of 5'-adenyl dinucleotides following DNA damage in normal human fibroblasts and fibroblasts derived from patients with xeroderma pigmentosum

Levels of 5'-adenyl dinucleotides, measured as diadenosine-5',5'-P1,P4-tetraphosphate (Ap4A), were found to accumulate in cultured human fibroblasts following treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), the radiomimetic drug bleomycin, and nitroquinoline-1-oxide (NQO) or UV-irradiation in the presence of cytosine arabinofuranoside (araC). In contrast, cells derived from patients with xeroderma pigmentosum complementation group A (XP-A) did not demonstrate an increase in DNA-strand breaks following UV irradiation or NQO in the presence of araC nor an increase in Ap4A levels. Ap4A accumulation did occur in XP-A cells following treatment with MNNG. Cells derived from patients characterized as XP variants, which are incision repair-proficient, accumulated 5'-dinucleotides following bleomycin, MNNG and UV or NQO in the presence of araC. Taken together, these data suggest that Ap4A accumulates as a response to DNA-strand breaks.     

Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake

Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. - Physiol. Plant. 72: 565–571.
Soybean [ Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non-VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28-day period by rewatering at soil water potentials of -1.0, -0.3 or -0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non-VAM plants. Phosphorus fertilization was applied to produce VAM and non-VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non-VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non-VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non-stressed plants. Growth enhancement of VAM plants relative to P-fertilized non-VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non-VAM plants suggests lower permanent wilting potentials for the former.     

Role of the intercistronic region in post-transcriptional control of gene expression in the histidine transport operon of Salmonella typhimurium: involvement of REP sequences

The high-affinity histidine permease of Salmonella typhimurium is encoded by a four-gene operon containing a large intercistronic region located between the first gene (hisJ) and the three distal genes (hisQ, hisM, hisP). The level of expression of hisJ is 30-fold greater than that of hisP. In order to investigate the role of the intercistronic region in intra-operonic control of gene expression, we have isolated MudII-mediated lacZ gene fusions to hisQ, hisM and hisP. We have used these fusions to isolate and analyse mutants that have altered levels of expression of the hisQ gene, the first gene downstream from the intercistronic region. The results indicate that intra-operonic regulation is due to a combination of factors including efficiency of translational initiation, mRNA degradation, and retroregulation of hisJ expression. They also suggest that the REP (Repetitive Extragenic Palindromic) sequences, which are located in the hisJ-hisQ intercistronic region, may interfere with translation of the hisQ gene and affect upstream messenger RNA stability by protecting it from 3' to 5' nuclease degradation (in agreement with data presented by Newbury et al., 1987).     

ATP-dependent bacterial transporters and cystic fibrosis: analogy between channels and transporters.

The traffic ATPases superfamily includes known transporters, both prokaryotic and eukaryotic, including the medically important proteins, P-glycoprotein, and the cystic fibrosis gene product (CFTR), which is known to be a Cl- channel. The structure and mechanism of action of the best-studied members of the superfamily, the periplasmic permeases, are described and related to that of CFTR and eukaryotic traffic ATPases in general. The contention is put forward that the distinction between the architecture and mechanisms of action of channels and transporters is blurred.     

Light-induced increases in cGMP metabolic flux correspond with electrical responses of photoreceptors

The metabolism of photoreceptor cGMP and the relationship of its light-sensitive regulation to rhodopsin photoisomerization and to the photoreceptor electrical response was examined in isolated, intact rabbit retinas. The dynamics of cGMP metabolism were assessed by measuring the rate of 18O incorporation from 18O-water into the alpha-phosphoryls of the guanine nucleotides. The photoreceptor electrical response was determined by measuring the aspartate-isolated mass receptor potential. Basal cGMP flux in dark-adapted retinas was 33 pmol cGMP X mg protein-1 X s-1 which translates into a metabolic rate in the rod outer segment (ROS) of 1.7 mM/min in ATP equivalents. Photic stimulation increased this flux as much as 4.5-fold. With continuous illumination, increasing intensity caused increments in cGMP metabolic flux to a maximum of 4.5-fold, with corresponding increases in the electrical response over the same 3-log unit intensity range. Tight coupling between activation of guanylate cyclase and phosphodiesterase was indicated by either no changes in cGMP steady state concentrations or relatively small fluctuations represented by increases of 50% at lower light intensities and a 12% decrease at one of the highest intensities. A stoichiometry of about 10,000 molecules of cGMP generated and hydrolyzed per photon absorbed was calculated for the lowest light intensity when the increment in cGMP metabolic flux per photon was maximal. Flashing light caused an increase in flux in proportion to frequency up to 1 Hz and a nearly proportional increase in the voltage time integral of the electrical response up to 0.5 Hz. This indicates that the temporal resolution, or "on"/"off" rate, of the cGMP metabolic response was as fast or faster than the temporal resolution of the electrical response. The concentration of cGMP remained relatively stable in spite of the marked acceleration of cGMP flux that occurred over the 32-fold range of frequencies tested. Taken together these results show that the light-accelerated rate of cGMP synthesis tightly coupled to hydrolysis becomes a primary energy-utilizing system in the photoreceptor and represents a response that fulfills certain of the fundamental criteria required of a metabolic event playing an essential role in phototransduction.     

Complete analysis of tRNA-modified nucleosides by high-performance liquid chromatography: the 29 modified nucleosides of Salmonella typhimurium and Escherichia coli tRNA

A high-performance liquid chromatography (HPLC) method has been developed to quantify the major and modified nucleoside composition of total, unfractionated transfer RNA. The method is rapid and sensitive and offers a high degree of chromatographic resolution suitable for quantifying both stable and unstable modified nucleosides. It is nondestructive and allows the recovery of nucleosides for further characterization. We apply the method in the analysis of the 29 modified nucleosides in tRNA from Salmonella typhimurium (and Escherichia coli) and show it to be useful in examining changes in the modified nucleoside content of tRNA. Such changes may be important in regulation.