Termite Prey Specialization in the Pitcher Plant Nepenthes albomarginata--Evidence from Stable Isotope Analysis

Old World pitcher plants (Nepenthes spp., Nepenthaceae) trapand digest invertebrate prey to derive nutrients, primarilynitrogen (N). In the majority of lowland Nepenthes species studiedto date, ants (Hymenoptera, Formicidae) are numerically thedominant prey taxon. Nepenthes albomarginata is unusual in showingan apparent bias towards the capture of termites (Isoptera).We tested the hypothesis that N. albomarginata derives N fromtermite capture, by comparison of foliar stable N isotope abundance(     

Actin acetylation in Drosophila tissue culture cells

In a permanent cell line derived from Drosophila embryos, cytoplasmic actin is produced as an unstable precursor, which is subsequently converted to a stable form. This conversion results in a reduction in isoelectric point, with no apparent change in molecular weight. The conversion involves an enzymatic acetylation, and results in an insensitivity to aminopeptidase digestion, suggesting N-terminal blockage. Both the acetylated and unacetylated actins can participate in the assembly of F-actin, but with different efficiencies.This work was supported by a grant from the NIH (GM 22866).     

A cross-continental test of the Enemy Release Hypothesis: leaf herbivory on Acer platanoides (L.) is three times lower in North America than in its native Europe

Acer platanoides (Norway maple) is a widespread native tree species in Europe. It has been introduced to North America where it has often established dense stands in both secondary woodlands and relatively undisturbed mature woodlands. In Europe A. platanoides is also extending its original range, but generally seems to exist at much lower densities. One explanation for the ‘aggressiveness’ of invasive plants such as A. platanoides is that they have left behind pests and diseases which limit their population densities in their native lands (the enemy release hypothesis or ERH). To assess the ERH for Norway maple, a large network of collaborators assessed leaf herbivory rates in populations throughout Europe and North America. We found significantly lower total leaf herbivory (1.6% ± 0.19, n = 21 vs. 7.4% ± 1.94, n = 34) and lower fungal damage (1.0% ± 0.35, n = 13 vs. 3.7% ± 0.85, n = 34) in North America than in Europe over a 2 year period, which is consistent with the predictions of the Enemy Release Hypothesis. Across years, the average total leaf herbivory was significantly correlated with average annual temperature of the site (P < 0.05), although this was mostly due to sites in Europe (P < 0.001), and not sites in North America (P > 0.05). Furthermore, only populations in Europe showed very high levels of herbivory (e.g., nine sites had total leaf herbivory ranging from 10.0 to 51.2% in at least 1 year) or leaf fungal damage (only one site in North America showed high levels of fungal damage in 1 year), suggesting the possibility of more frequent episodic outbreaks in the native range. Leaf herbivory and fungal damage are only two aspects of consumer pressure and we do not know whether the differences reported here are enough to actually elicit release from top-down population control, but such large scale biogeographic differences in herbivory contribute towards understanding exotic invasions. Jonathan M. Adams and Wei Fang—equally contributed as first authors. A list of the participating members of the Transatlantic Acer platanoides Invasion Network is given in the Appendix 3.     

The properties of cytochrome f and P700 in chloroplasts suspended in fluid media at sub-zero temperatures.

1. The properties of P700 and cytochrome f have been studied at sub-zero temperatures in chloroplasts suspended in a medium containing 50% (v/v) ethylene glycol. The dark reduction of these components after a period of illumination provided information about the rate-limiting step of photosynthetic electron transport under these conditions. 2. The oxidation of P700 on illumination in the presence of methyl viologen and its subsequent dark reduction can be observed at -35 degrees C. This cycle of reactions could be repeated many times. The rate of reduction was increased by NH4Cl and reduction was inhibited by 3(3,4-dichlorophenyl)-1,1-dimethylurea. 3. The oxidation and reduction of cytochrome f could also be observed under similar conditions. The activation energies for the reduction of cytochrome f and P700 are similar (about 75 kJ mol-1) and the reduction of cytochrome f is also inhibited by dichlorophenyldimethylurea and stimulated by NH4Cl. 4. The reduction of both cytochrome f and P700 seemed to follow first-order kinetics, but the t1/2 for the redcution of the cytochrome was at least three times that for the reduction of P700 at the same temperature. It was concluded that the results were only compatible with a model in which the main pathway of electrons from plastoquinone to P700 involved cytochrome f if the equilibrium constant between the cytochrome and P700 was very much less than that expected from their redox potentials.     

Chloroplast targeting of spectinomycin adenyltransferase provides a cell-autonomous marker for monitoring transposon excision in tomato and tobacco

Antibiotic resistance genes can act as either cell autonomous or non-cell autonomous genetic markers with which to monitor the excision of plant transposons. To convert spectinomycin resistance from a noncell autonomous resistance to cell autonomous resistance, a transit peptide for chloroplast localization from a petunia ribulose bisphosphate carboxylase (rbcS) gene was fused in-frame to the aadA gene, which confers spectinomycin and streptomycin resistance. Constructs were generated in which the expression of this chimeric gene was prevented by the presence, in the 5 untranslated leader, of the maize transposons Activator (Ac) or Dissociation (Ds). When progeny of tobacco or tomato plants transformed with these constructs were germinated on spectinomycin-containing medium, germinally revertant and somatically variegated individuals could be distinguished.     

Prospective guidance in a free-swimming cell

A systems theory of movement control in animals is presented in this article and applied to explaining the controlled behaviour of the single-celled Paramecium caudatum in an electric field. The theory-General Tau Theory-is founded on three basic principles: (i) all purposive movement entails prospectively controlling the closure of action-gaps (e.g. a distance gap when reaching, or an angle gap when steering); (ii) the sole informational variable required for controlling gaps is the relative rate of change of the gap (the time derivative of the gap size divided by the size), which can be directly sensed; and (iii) a coordinated movement is achieved by keeping the relative rates of change of gaps in a constant ratio. The theory is supported by studies of controlled movement in mammals, birds and insects. We now show for the first time that it is also supported by single-celled paramecia steering to the cathode in a bi-polar electric field. General Tau Theory is deployed to explain this guided steering by the cell. This article presents the first computational model of prospective perceptual control in a non-neural, single-celled system.