Mechanisms for tolerance of very high tissue phosphorus concentrations in Ptilotus polystachyus

Study of plants with unusual phosphorus (P) physiology may assist development of more P‐efficient crops. Ptilotus polystachyus grows well at high P supply, when shoot P concentrations ( [P] ) may exceed 40 mg P g^?1 dry matter (DM). We explored the P physiology of P. polystachyus seedlings grown in nutrient solution with 0–5 mM P. In addition, young leaves and roots of soil‐grown plants were used for cryo‐scanning electron microscopy and X‐ray microanalysis. No P‐toxicity symptoms were observed, even at 5 mM P in solution. Shoot DM was similar at 0.1 and 1.0 mM P in solution, but was ～14% lower at 2 and 5 mM P. At 1 mM P, [P] was 36, 18, 14 and 11 mg P g^?1 DM in mature leaves, young leaves, stems and roots, respectively. Leaf potassium, calcium and magnesium concentrations increased with increasing P supply. Leaf epidermal and palisade mesophyll cells had similar [P]. The root epidermis and most cortical cells had senesced, even in young roots. We conclude that preferential accumulation of P in mature leaves, accumulation of balancing cations and uniform distribution of P across leaf cell types allow P. polystachyus to tolerate very high leaf [P].     

USING ATOMIC FORCE MICROSCOPY TO INVESTIGATE PATCH-CLAMPED NUCLEAR MEMBRANE

Nuclear patch clamp is an emerging research field that aims to disclose the electrical phenomena underlying macromolecular transport across the nuclear envelope (NE), its properties as an ion barrier and its function as an intracellular calcium store. The authors combined the patch clamp technique with atomic force microscopy (AFM) to investigate the structure—function relationship of NE. In principle, patch clamp currents, recorded from the NE can indicate the activity of the nuclear pore complexes (NPCs) and/or of ion channels in the two biomembranes that compose the NE. However, the role of the NPCs is still unclear because the observed NE current in patch clamp experiments is lower than expected from the known density of the NPCs. Therefore, AFM was applied to link patch clamp currents to structure. The membrane patch was excised from the nuclear envelope and, after electrical evaluation, transferred from the patch pipette to a substrate. We could identify the native nuclear membrane patches with AFM at a lateral and a vertical resolution of 3nm and 0.1nm, respectively. It was shown that complete NE together with NPCs can be excised from the nucleus after their functional identification in patch clamp experiments. However, we also show that membranes of the endoplasmic reticulum can contaminate the tip of the patch pipette during nuclear patch clamp experiments. This possibility must be considered carefully in nuclear patch clamp experiments.     

Inhibitors acting on Nucleic Acid Synthesis in an Oncogenic RNA Virus

IN infection with an oncogenic RNA virus, synthesis of viral RNA seems to be catalysed by an RNA dependent DNA polymerase in the host cell^1–4. Several specific inhibitors of viral DNA polymerases have been found^5–7 and Spiegelman⁸ has shown that the activity of viral enzymes depends strongly on the chemical composition of the template. We report here first a new highly specific poison of the Rauscher murine leukaemia virus (RMLV) DNA polymerases; second, several inactivators of the RNA and DNA template involved in the RMLV enzyme systems; and third, the action of actinomycin D on viral DNA polymerases and on host DNA/RNA polymerase. The results are discussed with respect to the influence of actinomycin D on virus multiplication.     

A root trait accounting for the extreme phosphorus sensitivity of Hakea prostrata (Proteaceae)

Proteaceae are adapted to acquire P from nutrient‐impoverished soils; many function at very low leaf P levels, but are killed by P fertilization. Phosphorus toxicity develops at a remarkably low external P concentration. Previous studies have described P toxicity in Proteaceae, but the physiological basis for it remained unclear. The aim of the present study was to elucidate the physiological basis of P toxicity in Hakea prostrata R. Br. (Proteaceae). Triticum aestivum L. (Gramineae), Medicago truncatula Gaertn., Lupinus albus L. (both Fabaceae) and Hakea prostrata R.Br. were grown in solution at a range of P concentrations (0–1000 mmol P m^?3), and determined net P‐uptake rates at 5 (all species) and 50 mmol P m^?3 (H. prostrata only). With the exception of H. prostrata, net P‐uptake rates were fastest for plants grown without added P. Down‐regulation occurred for T. aestivum, M. truncatula and L. albus when the P concentration during growth was increased from 0 to 0.8 mmol P m^?3, whereas in H. prostrata rates decreased only for plants grown at 10 mmol P m^?3 or more. The leaf [P] at which P toxicity occurred in H. prostrata exceeded 10 mg g^?1 dry matter, similar to that for crop species. The low capacity to reduce P uptake in response to increased supply offers a physiological explanation for the extreme sensitivity to P supply in H. prostrata, and possibly other Proteaceae.     

Seasonal changes on two different spatial scales： response of aquatic invertebrates to water body and microhabitat

Knowledge about the spatial and temporal scales of both habitat use and the functional significance of different adaptations is essential for an understanding of the population dynamics of invertebrate assemblages. This fundamental knowledge is not only interesting from an academic point of view, but is sorely lacking and needed in the field of restoration ecology. Many species are threatened due to degradation. Knowing what environmental conditions are needed dtLring the life cycle of these species is important in the design of restoration measures which aim to lift existing bottlenecks for threatened species. To assess the relative importance of water type and microhabitat in structuring the invertebrate assemblage during different seasons, invertebrates were sampled in three water bodies differing in trophic level and acidity. Different parts within a water body （microhabitats） were sampled separately and each water body was sampled in all four seasons. Results show that water body is an important factor structuring the invertebrate assemblage early in the season, whereas microhabitat became more important later in the season. Structural complexity of microhabitats was related to the type of locomotion employed by invertebrates. Seasonal differences could be related to population dynamics （reproduction, mortality）. Moreover, fluctuations in resource availability were expected to differ between the water bodies, with highest fluctuations in the eutrophic water body and with fluctuations becoming less predictable later in the season. This was confirmed by the data： species synchronization to pulses in food availability was strongest in the eutrophic water body. Moreover, synchronization was strongest in summer, while in autumn waters were invaded by dispersive species. Based on these results a synthesis is presented on the functioning of the different waters during the different seasons.     

Control of methyl farnesoate synthesis in the mandibular organ of the crayfish Procambarus clarkii: Evidence for peptide neurohormones with dual functions

Summary

Red pigment-concentrating hormone stimulates the mandibular organ of Procambarus clarkii to synthesize methyl famesoate. The mandibular organs of male crayfish were more active than those of females. Hormonal stimulation can be mimicked by calcium ionophore A23187 and the activity of the gland can be reduced by replacing calcium in the media with lanthanum. Mandibular organ synthetic activity is inhibited by pigment-dispersing hormone.