Diurnal Changes in Asparaginase Activity in Pea Leaves: I. THE REQUIREMENT FOR LIGHT FOR INCREASED ACTIVITY

During the growth of leaves of Pisum sativum L., levels of asparaginase(E.C. 3.5.1.1 [EC] ) showed a diurnal variation during a 3 d periodof leaf expansion, increasing in the light and decreasing inthe dark period; the greatest diurnal variation being foundin half-expanded leaves. Asparaginase activity in half-expandedleaves reached a maximum after 4 h exposure to light and thisactivity was maintained over the rest of the light period. Changesin asparaginase activity were not influenced by diurnal temperaturechanges. The increase in asparaginase activity during the lightperiod was directly proportional to the photon flux densityover the range 0–285 µmol m^-2 s^-1 PAR. The increaseof asparaginase activity during illumination of detached leaveswas inhibited by the photosynthetic electron transport inhibitors3-(3', 4'-dichlorophenyl)-1, 1-dimethylurea (DCMU) and atrazine.These observations indicate that the increase in asparaginaseactivity in half-expanded leaves is dependent upon non-cyclicelectron transport. Key words: Pisum sativum, asparaginase, photosynthetic electron transport     

Biomass: Is it a useful tool in paleocommunity reconstruction?

In general, more of the biomass of the community is preserved than is its numerical abundance. Thus, the paleontologist, on the average, works with more of the community when biomass is used. Community characteristics such as taxon dominance and habitat proportions are at least as accurately derived from biomass as numerical abundance. The use of biomass is clearly more appropriate in describing energy flow and trophic proportions. Whenever possible, biomass should be used as a complement to numerical abundance in future paleoecologic reconstructions.     

MUSCARINIC ACETYLCHOLINE RECEPTOR SUBTYPE mRNAs IN THE HUMAN AND RAT VESTIBULAR PERIPHERY

The expression of the five muscarinic acetylcholine receptor (mAChR) subtypes (m1–m5) in the vestibular end-organs and in the primary afferent vestibular ganglia of the human and rat was studied using RT-PCR from the two tissue populations from both species. In the human, although all five mAChR subtypes were expressed in brain, only the m1, m2, and m5 mAChR subtypes were amplified from both the vestibular ganglia and the vestibular end-organs, while in the rat, all five mAChR subtypes were expressed. These data suggest that the efferent cholinergic axo-dendritic and axo-somatic synapses have a muscarinic component and that there are pharmacologic implications for patients with vestibular dysfunction.     

Sensitive detection of mycoplasmalike organisms in field-collected and in vitro propagated plants of Brassica, Hydrangea and Chrysanthemum by polymerase chain reaction

A polymerase chain reaction (PCR) protocol, previously designed for amplification of a DNA fragment from aster yellows mycoplasmalike organism (MLO), was employed to investigate the detection of MLO DNA in field-collected and in vitro micropropagated plants. PCR with template DNA extracted from symptomatic, naturally-infected samples of Brassica, Chrysanthemum and Hydrangea, each yielded a DNA band corresponding to 1.0 Kbp. However, no DNA product was observed when either infected Ranunculus (with phyllody disease) or Gladiolus with (symptoms of ‘germs fins’) was used as source of template nucleic acid for PCR; further experiments indicated absence of target DNA in the case of Ranunculus and the presence of substances in Gladiolus which inhibited the PCR. The MLO-specific DNA was detected by PCR using less than 95 pg of total nucleic acid (equivalent to total nucleic acid from 1.9, ug tissue) in the case of field-collected Hydrangea and less than 11.4 pg of nucleic acid (equivalent to total nucleic acid from 19 ng of tissue) in the case of field-collected Brassica. The findings illustrate highly sensitive detection of MLOs in both field-grown and in vitro micropropagated infected plants.     

Temperature cues phenological synchrony in ant‐mediated seed dispersal

Species‐specific climate responses within ecological communities may disrupt the synchrony of co‐evolved mutualisms that are based on the shared timing of seasonal events, such as seed dispersal by ants (myrmecochory). The spring phenology of plants and ants coincides with marked changes in temperature, light and moisture. We investigate how these environmental drivers influence both seed release by early and late spring woodland herb species, and initiation of spring foraging by seed‐dispersing ants. We pair experimental herbaceous transplants with artificial ant bait stations across north‐ and south‐facing slopes at two contrasting geographic locations. This use of space enables robust identification of plant fruiting and ant foraging cues, and the use of transplants permits us to assess plasticity in plant phenology. We find that warming temperatures act as the primary phenological cue for plant fruiting and ant foraging. Moreover, the plasticity in plant response across locations, despite transplants being from the same source, suggests a high degree of portability in the seed‐dispersing mutualism. However, we also find evidence for potential climate‐driven facilitative failure that may lead to phenological asynchrony. Specifically, at the location where the early flowering species (Hepatica nobilis) is decreasing in abundance and distribution, we find far fewer seed‐dispersing ants foraging during its fruit set than during that of the later flowering Hexastylis arifolia. Notably, the key seed disperser, Aphaenogaster rudis, fails to emerge during early fruit set at this location. At the second location, A. picea forages equally during early and late seed release. These results indicate that climate‐driven changes might shift species‐specific interactions in a plant–ant mutualism resulting in winners and losers within the myrmecochorous plant guild.     

Immunologic-mediated Protection of Trypanosoma congolense-Infected Mice by Polyribonucleotides

SYNOPSIS. When the synthetic polyribonucleotides polyinosinic acid-polycytidylic acid (poly I poly C) and polyadenylic acid-polyuridylic acid (poly A poly U) were tested against mice infected with varying numbers of Trypanosoma congolense the results varied with the method of passage of trypanosomes in mice. Thus, when 100 flagellates were passaged every 7th day and experiments were initiated with these trypanosomes from mice on the 7th day of their infection, the protective effects of poly I poly C and poly A poly U apparently varied independently of each other as assayed by the mean parasitemias and cumulative mortalities of infected mice. Poly I poly C-resistant and poly I poly C-susceptible variants (“R” and “S”, respectively) were isolated and maintained in mice by passage of 10⁶ trypanosomes every 4th day. Mice infected with these variants responded consistently to poly I poly C and poly A poly U injections in that mice infected with the “R” variant showed no response to either polyribonucleotide but those infected with the “S” variant consistently had a decrease in mean parasitemias and cumulative mortality when treated with poly I poly C, but not with poly A poly U. Using mice infected with the “S” variant, the protective effect of poly I poly C was dose-dependent and best protection was afforded when 1st injections of poly I poly C were given around the time of infection of the mice. The protective effects of the synthetic polyribonucleotides used in these experiments are probably due to their immunologic enhancing capacities and not to interferon. To support this, injections of Newcastle disease virus, a strong inducer of interferon in mice, did not protect against T. congolense in mice. It was not possible to determine whether serum from poly I poly C-treated mice had a greater neutralizing effect upon trypanosomes in vitro than serum from saline-treated mice since any effect of antibody was masked by a naturally occurring inhibitor in normal mouse serum which was reduced during infection. The protective effects of poly I poly C in T. congolense-infected mice were reversed by treatment with cyclophosphamide. This strong immunosuppressant, however, could not reverse the protective effects of poly I poly C against mice infected with Semliki Forest virus, strongly suggesting that the protective mechanisms stimulated by poly I poly C in these 2 infections were different. The response of mice infected with the “R” and “S” variants of T. congolense to synthetic polyribonucleotides is discussed in relation to antigenic variation of trypanosomes.     

The evolution of avian migration

The study of avian migration has reached sophisticated levels in many areas, including ecology, behaviour, and physiology. Traditional discussions of the evolution of migration, however, have been compromised for several reasons. Previous ideas concerning the ancestral home of migrant species, southern or northern, and whether a partially migratory stage always precedes a fully migratory stage, were not expressed as testable hypotheses. Plotting migratory behaviour on phylogenetic trees has become commonplace and allows tests of traditional hypotheses. Some of these studies are reviewed, lending some support for almost all of the previous ideas. Although phylogenetic mapping helps to frame questions about the evolution of migration in a testable framework, there are two serious issues. First, experimental and observational studies reveal that the expression of migratory behaviour can change rapidly within a lineage, which can violate assumptions of character mapping. In addition, a species distribution model is used to show that current conditions for obligate migratory populations of the chipping sparrow were much restricted at the Last Glacial Maximum, and that the species might have been considered a partial migrant at that time. The expression of migratory behaviour in an extant species might be an artefact of the current inter‐glacial period. Only if the rate of gains and losses of migratory behaviour can be incorporated into a phylogenetic mapping exercise will the actual evolutionary pattern of migration be revealed. For example, reconstruction of the ancestral area and the evolutionary history of migratory categories in a clade of New World warblers depended on the assumptions of character state transitions. A second concern is that the trait ‘migratory’ is too broad for evolutionary analysis and that, if possible, the expression of hyperphagia, Zugunruhe, and navigation could be mapped individually. Loss or suppression of any of these components can lead to sedentary populations, revealing how migratory behaviour can appear and disappear rapidly. A report of low levels of Zugunruhe in a sedentary bird, Saxicola torquata, is reconstructed as derived in a clade of otherwise migratory populations, suggesting that the loss of migration was a result of suppression (but not elimination) of Zugunruhe. When researchers mention the independent origin of migration in a clade, they are most likely referring to the gain or loss of the expression of the ancestral migratory programme, not the de novo evolution of migration per se. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 237–250.     

Factors affecting aphid acquisition and transmission of soybean mosaic virus

Myzus persicae transmitted soybean mosaic virus (SMV) most efficiently following 30 or 60 s acquisition probes on infected plants. There were no differences in susceptibility to SMV infection of soybean plants 1 to 12 wk old, but symptoms were more severe in plants inoculated when young than when old. Soybeans inoculated between developmental stages R3 and R6 only showed yellowish-brown blotching on one or more leaves. There were no observable differences in the time of appearance or type of symptoms shown by soybean seedlings inoculated either by sap or by aphids; infected plants became acquisition hosts for aphids 5–6 days after inoculation. There was no change in the efficiency with which M. persicae transmitted SMV from source plants up to 18 wk after inoculation. M. persicae transmitted SMV from leaves of field-grown soybeans when plants were inoculated at developmental stages V6, R2, and R3 and tested as sources 57–74 days after inoculation but not from plants inoculated at R5 and tested as sources 14 to 32 days after inoculation. M. persicae acquired SMV from soybean buds, flowers, green bean pods, and unifoliolate, trifoliolate, and senescent leaves. Middle-aged and deformed leaves were better sources of the virus than buds, unfolding and old symptomless leaves. The results are being incorporated into a computer model of SMV epidemiology.