Enhancing rape pollen beetle parasitism within sown flower fields along a landscape complexity gradient

• 1 Sown flower habitats not only are employed in agri‐environment schemes in the European Union to enhance pollinators and birds, such as partridges, but also are hypothesized to contribute to the biological control of pests such as the rape pollen beetle Meligethes aeneus Fabr. by improving habitat and resource availability for its specialized parasitoids.
• 2 In the present study, we selected 20 sown flower fields that included one of the pollen beetles' host plants Sinapis alba L., each centred in a landscape of varying complexity, to test the influence of the surrounding landscape structure on parasitism rate and herbivory by M. aeneus. Additionally, plant cover of S. alba plants within the sown flower fields and numbers of S. alba flowers were also included in the analyses.
• 3 Landscapes with high proportions of semi‐natural habitats supported higher parasitism rates, and sown flower fields with dense S. alba plant cover hosted more parasitoids and suffered from less herbivory.
• 4 We conclude that sown flower fields are not only important for pollinators and birds, but also are long‐term undisturbed, unploughed, insecticide‐free habitats with rich food (nectar/pollen) and host resources for parasitoids, contributing to the build‐up and maintenance of large parasitoid populations, which are important biocontrol agents of rape pollen beetles.

     

Diffusion in gas exchange of insects

The air-filled tracheal system constitutes the organ for gas exchange in terrestrial insects-its finest branches, the tracheoles, contacting individual cells. In the pupal stage, in which the animal lacks significant ventilatory movement, diffusion in the gas phase of the tracheal system constitutes the only mechanism for gas transfer between the environment and the tissues, transport in the hemolymph being insignificant. We have attempted to identify the main sites of diffusional resistance in the tracheal gas system by measuring the evolution of inert gases of low solubility from the pupa of the giant silkworm moth (Hyalophora cecropia). The results are compatible wih a single model in which the resistance to diffusional gas transfer in the tracheal system is concentrated at its opening at the body surface (spiracle).     

Demonstration of a pH gradient in the gastric gland of the acid-secreting guinea pig mucosa

The gastric mucosa is covered by a continuous layer of mucus. Although important for understanding the mechanism of this protective function, only scarce information exists about the pH inside the gastric gland and its outlet. pH in the lumen of the gastric glands, in the outlet of gastric crypts, and in the adjacent cells was measured in the isolated acid-secreting mucosa of the guinea pig. Ultrafine double-barreled pH microelectrodes were advanced at high acceleration rates through the gastric mucus and the tissue to ensure precise intracellular and gland lumen pH measurements. A pH gradient was found to exist along the gastric gland, where the pH is 3.0 at parietal cells, i.e., in the deepest regions, and increases to 4.6 at the crypt outlet. Intracellular pH (pH(i)) of epithelial cells bordering a crypt outlet, and of neck cells bordering a gland, was acidic, averaging 6.0 and 6.5, respectively. pH(i) of deep cells bordering a gland was nearly neutral, averaging 7.1, and the secreting parietal cells were characterized by a slightly alkaline pH(i) of 7.5. This gland pH gradient is in general agreement with a model that we recently proposed for proton transport in the gastric mucus, in which protons secreted by the parietal cells are buffered to and transported with the simultaneously secreted mucus toward the gastric lumen, where they are liberated from the degraded mucus.     

Multiple phosphoinositide 3-kinase-dependent steps in activation of protein kinase B

The protein kinase B (PKB)/Akt family of serine kinases is rapidly activated following agonist-induced stimulation of phosphoinositide 3-kinase (PI3K). To probe the molecular events important for the activation process, we employed two distinct models of posttranslational inducible activation and membrane recruitment. PKB induction requires phosphorylation of two critical residues, threonine 308 in the activation loop and serine 473 near the carboxyl terminus. Membrane localization of PKB was found to be a primary determinant of serine 473 phosphorylation. PI3K activity was equally important for promoting phosphorylation of serine 473, but this was separable from membrane localization. PDK1 phosphorylation of threonine 308 was primarily dependent upon prior serine 473 phosphorylation and, to a lesser extent, localization to the plasma membrane. Mutation of serine 473 to alanine or aspartic acid modulated the degree of threonine 308 phosphorylation in both models, while a point mutation in the substrate-binding region of PDK1 (L155E) rendered PDK1 incapable of phosphorylating PKB. Together, these results suggest a mechanism in which 3' phosphoinositide lipid-dependent translocation of PKB to the plasma membrane promotes serine 473 phosphorylation, which is, in turn, necessary for PDK1-mediated phosphorylation of threonine 308 and, consequentially, full PKB activation.     

Gene inactivation in Arabidopsis thaliana is not accompanied by an accumulation of repeat-induced point mutations

Chromosomal integration of multicopy transgene inserts in higher plants is often followed by loss of expression. We have analysed whether this inactivation can trigger repeat-induced point mutations (RIP) as has been observed in Neurospora crassa. We have previously characterized transgenic lines of Arabidopsis thaliana containing the hygromycin phosphotransferase (hpt) gene either as a unique sequence in plants expressing the gene, or as multimeric, closely linked repeats in clones that were resistant to hygromycin directly after transformation but exhibited gene inactivation in the subsequent generation. At the sequence level, we have determined the mutation frequencies in the promoter and coding regions of active and inactive copies of transgene inserts after passage through three sexual generations. No RIP-like mutations were found in inactivated genes. Comparison of our data with those from Neurospora suggest that sequence divergence within plant repetitive DNA is either much slower than in Neurospora or is generated by a different mechanism.