The nature of protein differentiation in the growing pea root

Abstract Sections of the growing root of pea (Pisum sativum) have been microdissected into stele, cortex and epidermis. Using labelled amino acids, two dimensional separations employing non-equilibrium pH gel electrophoresis (NEPHGE) and isoelectric focusing (IEF), and silver staining, the complexity of protein differences between the cortex and the stele has been assessed. Analyses commenced as cells in these two tissues appear in the meristem (0.7—1 mm from the tip) and continued up to 30 mm from the tip as they subsequently mature. From the earliest stages at which the cortex and stele can be distinguished and dissected apart the protein patterns differ substantially. However these tissue differences, involving over one third of the detected protein species, are almost all quantitative. Very few qualitative (i.e. tissue specific) proteins were detected. Many proteins also show quantitative stage-specific variation, detected using successively older root segments. In vitro translation studies involving isolated mRNA showed only a very limited stage-specific variation in translated proteins. This supports the notion that translational controls may contribute significantly to the development of these two tissue types.     

Nitrogen Fixation by Subterranean Clover at Varying Stages of Nodule Dehydration: I. CARBOHYDRATE STATUS AND SHORT-TERM RECOVERY OF NODULATED ROOT RESPIRATION

The nodule water potential (_nod) of subterranean clover (Trifoliumsubterraneum L.) cv. Seaton Park incubated in a flow-throughgas-exchange system was induced to decline independently ofleaf water potential (₁) by passing a continuous dry airstreamover the nodulated roots of intact well-watered plants. Reducedtranspiration by plants whose nodules had become dehydratedwas hypothesized to be related to the decline in nitrogen fixation.Whole-plant and nodule soluble carbohydrates increased as _noddeclined. Throughout an 8 d period of continual nodule dehydration,the gaseous diffusion resistance of nodules increased and theoptimum pO₂ for nitrogenase activity declined from 52 to 28kPa. Following rehydration of the nodulated roots between days4 and 5 and between days 7 and 8, nodulated root respirationincreased to or above pre-stress levels whereas nitrogenaseactivity did not recover. Re-establishment of initial ratesof nodulated root respiration was due to the stimulation ofgrowth and maintenance respiration, not to the respiration coupledto nitrogenase activity. Although no recovery of nitrogenaseactivity occurred, the elapsed time from the introduction ofacetylene into the gas stream flowing past the nodules untilmeasurement of the acetylene-induced decline in nitrogenaseactivity, decreased substantially. This was characteristic ofan increase in the permeability of the nodules to gaseous diffusionupon rehydration. However, calculated values of nodule diffusionresistance after the 24 h periods of rehydration did not indicateany recovery of gaseous diffusion resistance based on measurementsof the respiration coupled to nitrogenase activity. Hence, useof a diffusion analogue (i.e. Fick's Law) in conjunction withnodule respiratory CO₂ efflux was unable to predict changesin permeability of the variable barrier of legume nodules followingnodule dehydration and recovery. Key words: Subterranean clover, gaseous diffusion, respiration, carbohydrates, drought     

Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study

Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of free‐air‐CO₂‐enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18‐year‐old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO₂ availability. Averaged over all 6 years of the study, CO₂ enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO₂ enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO₂‐enrichment on fine root proliferation tended to shift from shallow (0–15 cm) to deeper soil depths (15–30) with increasing duration of the study. Diameters of fine roots were initially increased by CO₂‐enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m^?2 yr^?1 in CO₂‐enriched plots and 130 g dw m^?2 yr^?1 in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m^?2 yr^?1 in CO₂‐enriched plots. A lack of consistent CO₂× year effects suggest that the positive effects of CO₂ enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO₂ fumigation). Although CO₂‐enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south‐eastern pine forests.     

Geometric morphometric analysis of shell shape variation in Conus (Gastropoda: Conidae)

Geometric morphometric techniques allow for the direct quantification and analysis of variation in biological shape and have been used in studies in systematic biology. However, these techniques have not been used for species discrimination in the gastropod genus Conus, a major taxon of significant tropical reef predators recognized for their peptide‐based toxins. Here, we used landmark digitization and analysis to show that five species commonly studied for their conotoxins –Conus consors, Conus miles, Conus stercusmuscarum, Conus striatus, and Conus textile – can be effectively distinguished from each other by their shape, as manifested in the results of a principal components analysis (PCA) and the generated thin‐plate splines. Two piscivorous species, C. stercusmuscarum and C. striatus, show clear overlaps in the PCA plot, although each taxon clusters within itself, as does each of the others. The loadings on the first two principal components show that the forms of the shells' aperture and spire are particularly important for discrimination. Phylogenetic analysis using neighbour‐joining methods shows that group separations are comparable with published phylogenetic schemes based on molecular data and feeding mode (i.e. piscivory, vermivory, molluscivory). The results of this study establish the utility of geometric morphometric methods in capturing the interspecific differences in shell form in the genus Conus. This may lead to the utilization of these methods on other gastropod taxa and the creation of species‐recognition programs based on shell shape. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 296–310.     

Genetic variation in Irish pygmy shrews Sorex minutus (Soricomorpha: Soricidae): implications for colonization history

The status of the pygmy shrew ( Sorex minutus L.) as a native or an introduced species in Ireland has been subject to much debate. To examine this and other aspects of the colonization history of the Irish pygmy shrew, genetic variation was determined in 247 pygmy shrews collected throughout Ireland, using mitochondrial control region sequences and five polymorphic microsatellite loci. Genetic diversity was low for both types of marker. The median-joining network for control region sequences was star-like, suggesting that the colonization of Ireland involved a small number of founders and rapid population expansion thereafter; this was supported by other statistics. Molecular dating with both mitochondrial DNA and microsatellite data is consistent with a human introduction. This would have been several thousand years ago; a recent colonization within historical times can be ruled out. This is the first detailed population genetic study of the pygmy shrew anywhere in its range.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 918–927.     

Long‐term ammonium nutrition of Arabidopsis increases the extrachloroplastic NAD(P)H/NAD(P)+ ratio and mitochondrial reactive oxygen species level in leaves but does not impair photosynthetic capacity

Ammonium nutrition has been suggested to be associated with alterations in the oxidation‐reduction state of leaf cells. Herein, we show that ammonium nutrition in Arabidopsis thaliana increases leaf NAD(P)H/NAD(P)⁺ ratio, reactive oxygen species content and accumulation of biomolecules oxidized by free radicals. We used the method of rapid fractionation of protoplasts to analyse which cellular compartments were over‐reduced under ammonium supply and revealed that observed changes in NAD(P)H/NAD(P)⁺ ratio involved only the extrachloroplastic fraction. We also showed that ammonium nutrition changes mitochondrial electron transport chain activity, increasing mitochondrial reactive oxygen species production. Our results indicate that the functional impairment associated with ammonium nutrition is mainly associated with redox reactions outside the chloroplast.     

Species segregation during predator evasion in cyprinid fish shoals

SUMMARY. 1. When a predator attacks a mixed-species group, individual prey arc faced with a conflict between retaining the advantages of large group size and the disadvantages of remaining among aliens. Experiments were designed to show how this conflict is resolved in fish shoals.
2. Simulated attacks with a model predator were made upon mixed and single species shoals of three cyprinid species under semi-natural conditions in a fluvarium.
3. Measurements of elective group size, neighbour identity and distance, and encounters within and between species revealed behaviour which sorted fish into species at the onset of predator attack.
4. A control experiment demonstrated the same effect for fish of matched size.
5. The value to the individual of segregative behaviour in response to predator threat is discussed.