Organic matter processing by chironomid larvae (Diptera: Chironomidae)

In laboratory experiments, we used fluorescent dye markers to investigate processing of organic matter by larvae of Psectrocladius limbatellus (Holm.) (Diptera: Chironomidae). 59% of the organic matter used was incorporated into tubes, 39% was present in faecal pellets (both after 24 h), and 2% was found in the larval gut at the end of experiments. Ingested matter passed through the gut rapidly, resulting in the gut being emptied more than 20 times each day. Further 24-h experiments using dye-marked faecal pellets showed that 6% of pellets produced were re-ingested and 12% were incorporated into tubes. There was no preference for conditioned faecal pellets as food over those that had recently been egested and tubes also provided a food reserve on which larvae feed. Chironomid larvae recycle organic matter resulting in its mineralization and their ‘engineering’ has a dramatic effect on the substratum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crystalline Cellulose in Hydrated Primary Cell Walls of Three Monocotyledons and One Dicotyledon

The molecular ordering of cellulose, including its crystallinity,in the unlignified primary cell walls of three monocotyledons(Italian ryegrass, pineapple, and onion) and one dicotyledon(cabbage) was characterized by solid-state ¹³C NMR spectroscopy.These species were chosen because their primary cell walls havedifferent non-cellulosic polysaccharides and this may affectthe molecular ordering of cellulose. Values of the proton rotating-framerelaxation [T_1p(H)] and spin-spin relaxation [T₂(H)] time constantsshowed that the cellulose in the cell walls of all four specieswas in a crystalline rather than an amorphous state. Furthermore,a resolution enhancement procedure showed that the triclinic(I) and the monoclinic (I_rß) crystal forms of cellulosewere present in similar proportions in these cell walls. However,the calculated cross-sectional dimensions of the cellulose crystallitesvaried among the cell walls (in the range 2–3 nm): thelargest were in the Italian ryegrass, the smallest were in theonion and cabbage, and those of intermediate size were in thepineapple. The crystallite dimensions may thus be affected bythe non-cellulosic polysaccha-ride compositions of the cellwalls. ⁴Present address: Food Science Postgraduate Programme, Departmentof Chemistry, The University of Auckland, Private Bag 92019,Auckland, New Zealand.     

Impact of elevated CO2 on the metabolic diversity of microbial communities in N-limited grass swards

The impact of elevated atmospheric CO2 on qualitative and qua ntitative changes in rhizosphere carbon flow will have important consequences fo r nutrient cycling and storage in soil, through the effect on the activity, biom ass size and composition of soil microbial communities. We hypothesized that mic robial communities from the rhizosphere of Danthonia richardsonii, a n ative C3 Australian grass, growing at ambient and twice ambient CO2 a nd varying rates of low N application (20, 60, 180 kg N ha-1) will be different as a consequence of qualitative and quantitative change in rhizosphere carbon flow. We used the Biolog^TM system to construct sole carbon source utilisation profiles of these communities from the rhizosphere of D. richardsonii. Biolog^TM GN and MT plates, the latter to which more ecologically relevant root exudate carbon sources were added, were used to characterise the communities. Microbial communities from the rhizosphere of D. richardsonii grown for four years at twice ambient CO2 had significantly greater utilisation of all carbon sources except those with a low C:N ratio (neutral and acidic amino acids, amides, N-heterocycles, long chain aliphatic acids) than communities from plants grown at ambient CO2. This indicates a change in microbial community composition suggesting that under elevated CO2 compounds with a higher C:N ratio were exuded. Enumeration of microorganisms, using plate counts, indicated that there was a preferential stimulation of fungal growth at elevated CO2 and confirmed that bacterial metabolic activity (C utilisation rates), not population size (counts), were stimulated by additional C flow at elevated CO2. Nitrogen was an additional rate-limiting factor for microbial growth in soil and had a significant impact on the microbial response to elevated CO2. Microbial populations were higher in the rhizosphere of plants receiving the highest N application, but the communities receiving the lowest N application were most active. These results have important implications for carbon turnover and storage in soils where changes in soil microbial community structure and stimulation of the activity of microorganisms which prefer to grow on rhizodeposits may lead to a decrease in the composition of organic matter and result in an accumulation of soil carbon.     

DNA methylation levels and ethylene production in senescent,suspension-cultured pear fruit cells: Implications for epigenetic control?

Auxin‐deprived, senescent, suspension‐cultured pear ( Pyrus communis cv. Passe Crassane) fruit cells that can be stimulated to produce ethylene were employed in the search for a possible interdependence between DNA methylation levels and ethylene production. Neither short‐term stimulation of ethylene production by CuCl₂, nor longer‐term stimulation by auxin, nor the inhibition of ethylene biosynthesis had a significant effect on the cellular level of DNA methylation. However, short‐term exposure to S‐adenosylhomocysteine enhanced cellular ethylene production and long‐term exposure to azacytidine resulted in the reduction of both DNA methylation levels and stress‐induced ethylene production. These and other correlative findings, or lack thereof, are discussed in the context of ethylene physiology, DNA methylation/demethylation, and epigenetic control.     

The Nitric Oxide-Cyclic GMP Pathway Plays an Essential Role in Both Promoting Cell Survival of Cerebellar Granule Cells in Culture and Protecting the Cells Against Ethanol Neurotoxicity

Abstract: NMDA has two beneficial effects on primary neuronal cultures of cerebellar granule cells (CGCs) established from 10-day-old rat pups. First, NMDA is neurotrophic and will enhance survival of CGCs in culture in the absence of ethanol. Second, ethanol exposure will induce cell death in CGC cultures, and NMDA can lessen this ethanol-induced cell loss, i.e., NMDA is neuroprotective. Because NMDA can stimulate production of nitric oxide (NO), which can in turn enhance synthesis of cyclic GMP, this study tested the hypothesis that the NO-cyclic GMP pathway is essential for NMDA-mediated neurotrophism and neuroprotection. Inhibiting the synthesis of NO with N ^G-nitro- l -arginine methyl ester eliminated both the NMDA-mediated neurotrophic and neuroprotective effects. Similarly, inhibiting production of cyclic GMP with the agent LY83583 also abolished these effects. The NO generator 2,2'-(hydroxynitrosohydrazono)bisethanamine produced neurotrophic and neuroprotective effects that were similar to those induced by NMDA. Also, 8-bromo-cyclic GMP produced neurotrophic and neuroprotective effects that were quite similar to the effects produced by NMDA. In conclusion, NMDA enhances survival of cerebellar granule cells and protects the cells against ethanol-induced cell death by a mechanism(s) that involves the NO-cyclic GMP pathway.     

Iron-rich particles in embryos of seeds from the family Pinaceae

Summary Iron-rich particles, previously reported in seeds of members of the genus Pinus, were found in radicle-hypocotyl tissues of dry embryos from eight other genera in the family Pinaceae. Thus, these Fe-rich particles are of common occurrence in seeds of this conifer family. These particles were most difficult to locate inPseudolarix amabilis, which has green embryos. Energy-dispersive X-ray analysis was used to determine the elements present in conifer Fe-rich particles and phytoferritin deposits in pea embryo axes. Ferich particles from all species studied contained mainly Fe and P but also contained considerable K and Mg. Abietoideae group I (genera Cedrus andAbies) had lower Fe P ratios compared to all the other combined subfamilies within the Pinaceae. Pea phytoferritin deposits contained markedly lower amounts of P relative to Fe based on peakto-background ratios and quantitative values calculated by using a ferric phosphate standard. We also found, for the first time, that pea phytoferritin contained considerable K. A strong similarity was found between the energy-dispersive X-ray analysis spectra from Ferich particles and portions of a laboratory-synthesized Fe, K, Mg phytate salt. Phytate is a common mineral-nutrient storage compound in seeds. The possibility of these Fe-rich particles being phytoferritin cannot be ruled out, but if they are phytoferritin, they have lower Fe P ratios than almost all other ferritins reported to date.Abbreviations EDX energy-dispersive X-ray     

A description of Mallomonas marsupialis nov. sp. (Synurophyceae), a new chrysophyte from Australia, with comments on the endemicity of Australian freshwater algae

Mallomonas marsupialis is described and illustrated by TEM and SEM micrographs, being found in Australia on sub-tropical Fraser Island and in cool-temperate Tasmania. Its taxonomic location within the genus Mallomonas (sect. Mallomonopsis, ser. Marsupiales) is discussed, together with its inclusion in a suite of unusual endemic algae which have been described from Australian sites largely protected from human interference.     

Evidence that humidity influences snake activity patterns: a field study of the Malayan pit viper Calloselasma rhodostoma

Multivariate statistical methods were used to elucidate which environmental factors influence the activity patterns of free-living Malayan pit vipers, Calloselasma rhodostoma. Fourteen adult snakes were implanted with miniature radiotransmitters and located a total of 887 times in 5 months. The pit vipers usually remained coiled on the ground for several consecutive days before moving at night to a new site. Partial correlation tests revealed that the frequency and distance of movements to new sites by tagged snakes were highly positively correlated with ambient relative humidity, but not with rainfall, ambient temperature or the lunar cycle. This finding was corroborated by the frequency with which active non-tagged C. rhodostoma were encountered at night, In each site, the proportion of the snakes' bodies exposed to view was positively correlated with ambient humidity, and the snakes retreated to areas with deeper undergrowth when ambient humidity was low. Overt thermoregulatory behaviour was not observed, and implanted thermosensitive transmitters revealed that the snakes were passive thermoconformers.
These findings seem lo contradict much of the current literature which shows temperature to be the dominant abiotic factor affecting reptilian activity, but most herpetologists have considered only temperate forms. Ambient temperature in our tropical study site was warm and relatively constant throughout the year (mean daily range = 24- 33°C), so the pit vipers could passively maintain body temperature within a fairly narrow range, with a daytime mean of 29.4°C. Ambient relative humidity, on the other hand, was very variable, and confining exposure and activity to periods of high ambient humidity may be necessary to avoid dehydration