147 research outputs found
Stylet Penetration Activities by Aphis craccivora (Homoptera: Aphididae) on Plants and Excised Plant Parts of Resistant and Susceptible Cultivars of Cowpea (Leguminosae)
Direct current electrical penetration graphs (DC-EPGs) were used to analyze the stylet penetration activities of cowpea aphid, Aphis craccivora Koch, on plants of aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cultivars of cowpea, Vigna unguiculata (L.) Walpers. Aphid stylet penetration on whole plants at seedling, flowering, and podding stages were studied in one experiment, and in another experiment excised leaves from seedling plants, excised flowers, and excised pods were tested. Electrical signals depicting the aphid stylet penetration activities on their host plants were amplified, recorded onto a paper chart recorder, and scored for specific waveform patterns. Compared with similar tissues of ICV-1, intact leaves and excised seedling foliage of ICV-12 plants caused severe disruption of aphid stylet penetration activities. This was manifested in frequent penetration attempts that were abruptly terminated or unsustained, and in shorter penetration times, signifying antixenosis resistance in ICV-12. There was reduced occurrence of E waveforms, which represent stylet activity in plant vascular tissues. Also, prior exposure of test aphids to plants of one cultivar did not significantly influence the expected stylet penetration activities on plants of the other cultivar. Overall, ICV-12 exhibited high levels of resistance against A. craccivor
The Reservoir Age Effect Varies With the Mobilization of Pre-Aged Organic Carbon in a High-Altitude Central Asian Catchment
Lake sediments provide excellent archives to study past environmental and hydrological
changes at high temporal resolution. However, their utility is often restricted by
chronological uncertainties due to the â reservoir age effect â (RAE), a phenomenon that
results in anomalously old radiocarbon ages of total organic carbon (TOC) samples that is
mainly attributed to the contribution of pre-aged carbon from aquatic organisms. Although
the RAE is a well-known problem especially in high altitude lakes, detailed studies analyzing
the temporal variations in the contribution of terrestrial and aquatic organic carbon (OC) on
the RAE are scarce. This is partially due to the complexity of isolating individual compounds
for subsequent compound-speci ïŹ c radiocarbon analysis (CSRA). We developed a rapid
method for isolating individual short-chain (C 16 and C 18 ) and long-chain ( > C 24 ) saturated
fatty acid methyl esters (FAMEs) by using high-pressure liquid chromatography (HPLC).
Our method introduces only minor contaminations (0.50 ± 0.22 ”g dead carbon on
average) and requires only few injections ( †10), therefore offering clear advantages
over traditional preparative gas chromatography (prep-GC). Here we show that
radiocarbon values ( Î 14C) of long-chain FAs, which originate from terrestrial higher
plant waxes, re ïŹ ect carbon from a substantially pre-aged OC reservoir, whereas the
Î 14C of short-chain FAs that originate from aquatic sources were generally less pre-aged.
14
C ages obtained from the long-chain FAs are in closer agreement with
14
C ages of the
corresponding bulk TOC fraction, indicating a high control of pre-aged terrestrial OC input
from the catchment on TOC-derived
14
C ages. Variations in the age offset between
terrestrial and aquatic biomarkers are related to changes in bulk sediment log(Ti/K) that
re ïŹ ect variations in detrital input from the catchment. Our results indicate that the
chronological offset between terrestrial and aquatic OC in this high-altitude catchment
is mainly driven by temporal variations in the mobilization of pre-aged OC from the
catchment. In conclusion, to obtain accurate and process-speci ïŹ c lake sediment
chronologies, attention must be given to the temporal dynamics of the RAE. Variations
in the apparent ages of aquatic and terrestrial contributions to the sediment and their mass
balance can substantially alter the reservoir age effect
A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin
Weproduced a composite depth scale and chronology for Site U1385 on the SWIberianMargin. Using log(Ca/Ti)measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopesof benthic foraminifera were correlated to a stacked d18O reference signal (LR04) to produce an oxygen isotopestratigraphy and age model.Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulationof these cycles provides a powerful tool for developing an orbitally-tuned agemodel.We tuned the U1385 recordby correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic d18O record of Site U1385,when placed on the tuned agemodel, generally agrees with other time scaleswithin their respective chronologicuncertainties.The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflectrelative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacialand interstadial climate states and decreases during glacial and stadial periods. Much of the variance in thelog(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereasthe residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti)variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can beused as a proxy for millennial-scale climate variability over the past 1.5 Ma.Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climatesover the past 1.5Ma, including glacial periods of the early Pleistocene (â41-kyrworldâ)when boundary conditionsdiffered significantly from those of the late Pleistocene (â100-kyr worldâ). Suborbital variability was suppressedduring interglacial stages and enhanced during glacial periods, especially when benthic d18O surpassed ~3.3â3.5â°. Each glacial inception was marked by appearance of strong millennial variability and each deglaciatio
Cucumber mosaic virus and its 2b RNA silencing suppressor modify plant-aphid interactions in tobacco
The cucumber mosaic virus (CMV) 2b protein not only inhibits anti-viral RNA silencing but also quenches
transcriptional responses of plant genes to jasmonic acid, a key signalling molecule in defence against
insects. This suggested that it might affect interactions between infected plants and aphids, insects that
transmit CMV. We found that infection of tobacco with a 2b gene deletion mutant (CMVD2b) induced
strong resistance to aphids (Myzus persicae) while CMV infection fostered aphid survival. Using electrical
penetration graph methodology we found that higher proportions of aphids showed sustained phloem
ingestion on CMV-infected plants than on CMVD2b-infected or mock-inoculated plants although this did
not increase the rate of growth of individual aphids. This indicates that while CMV infection or certain viral
gene products might elicit aphid resistance, the 2b protein normally counteracts this during a wild-type
CMV infection. Our findings suggest that the 2b protein could indirectly affect aphid-mediated virus
transmission
Multi-basin depositional framework for moisture-balance reconstruction during the last 1300Â years at Lake Bogoria, central Kenya Rift Valley
Multi-proxy analysis of sediment cores from five key locations in hypersaline, alkaline Lake Bogoria (central Kenya Rift Valley) has allowed reconstruction of its history of depositional and hydrological change during the past 1300years. Analyses including organic matter and carbonate content, granulometry, mineralogical composition, charcoal counting and high-resolution scanning of magnetic susceptibility and elemental geochemistry resulted in a detailed sedimentological and compositional characterization of lacustrine deposits in the three lake basins and on the two sills separating them. Thesepalaeolimnological data were supplemented with information on present-day sedimentation conditions based on seasonal sampling of settling particles and on measurement of physicochemical profiles through the water column. A new age model based on Pb-210, Cs-137 and C-14 dating captures the sediment chronology of this hydrochemically complex and geothermally fed lake. An extensive set of chronological tie points between the equivalent high-resolution proxy time series of the five sediment sequences allowed transfer of radiometric dates between the basins, enabling interbasin comparison of sedimentation dynamics through time. The resulting reconstruction demonstrates considerable moisture-balance variability through time, reflecting regional hydroclimate dynamics over the past 1300years. Between ca 690 and 950AD, the central and southern basins of Lake Bogoria were reduced to shallow and separated brine pools. In the former, occasional near-complete desiccation triggered massive trona precipitation. Between ca 950 and 1100AD, slightly higher water levels allowed the build-up of high pCO(2) leading to precipitation of nahcolite still under strongly evaporative conditions. Lake Bogoria experienced a pronounced highstand between ca 1100 and 1350AD, only to recede again afterwards. For a substantial part of the time between ca 1350 and 1800AD, the northern basin was probably disconnected from the united central and southern basins. Throughout the last two centuries, lake level has been relatively high compared to the rest of the past millennium. Evidence for increased terrestrial sediment supply in recent decades, due to anthropogenic soil erosion in the wider Bogoria catchment, is a reason for concern about possible adverse impacts on the unique ecosystem of Lake Bogoria
A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin
We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meters composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked ÎŽ^18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model.
Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37^oN. The benthic ÎŽ^18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties.
The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma.
Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene (â41-kyr worldâ) when boundary conditions differed significantly from those of the late Pleistocene (â100-kyr worldâ). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic ÎŽ^18O surpassed ~ 3.3-3.5â°. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.This research was supported by the Natural Environmental Research Council Grant NE/K005804/1 to DH and LS and NE/J017922/1 to DH.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.gloplacha.2015.07.00
A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin
Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic Ύ18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties.
The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma.
Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene (â41-kyr worldâ) when boundary conditions differed significantly from those of the late Pleistocene (â100-kyr worldâ). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic ÎŽ18O surpassed ~ 3.3â3.5â°. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles
A Functional Genomics Approach Identifies Candidate Effectors from the Aphid Species Myzus persicae (Green Peach Aphid)
Aphids are amongst the most devastating sap-feeding insects of plants. Like most plant parasites, aphids require intimate associations with their host plants to gain access to nutrients. Aphid feeding induces responses such as clogging of phloem sieve elements and callose formation, which are suppressed by unknown molecules, probably proteins, in aphid saliva. Therefore, it is likely that aphids, like plant pathogens, deliver proteins (effectors) inside their hosts to modulate host cell processes, suppress plant defenses, and promote infestation. We exploited publicly available aphid salivary gland expressed sequence tags (ESTs) to apply a functional genomics approach for identification of candidate effectors from Myzus persicae (green peach aphid), based on common features of plant pathogen effectors. A total of 48 effector candidates were identified, cloned, and subjected to transient overexpression in Nicotiana benthamiana to assay for elicitation of a phenotype, suppression of the Pathogen-Associated Molecular Pattern (PAMP)âmediated oxidative burst, and effects on aphid reproductive performance. We identified one candidate effector, Mp10, which specifically induced chlorosis and local cell death in N. benthamiana and conferred avirulence to recombinant Potato virus X (PVX) expressing Mp10, PVX-Mp10, in N. tabacum, indicating that this protein may trigger plant defenses. The ubiquitin-ligase associated protein SGT1 was required for the Mp10-mediated chlorosis response in N. benthamiana. Mp10 also suppressed the oxidative burst induced by flg22, but not by chitin. Aphid fecundity assays revealed that in planta overexpression of Mp10 and Mp42 reduced aphid fecundity, whereas another effector candidate, MpC002, enhanced aphid fecundity. Thus, these results suggest that, although Mp10 suppresses flg22-triggered immunity, it triggers a defense response, resulting in an overall decrease in aphid performance in the fecundity assays. Overall, we identified aphid salivary proteins that share features with plant pathogen effectors and therefore may function as aphid effectors by perturbing host cellular processes
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