Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008
In this paper, we discuss the occurrence of liebermannite (
- NSF-PAR ID:
- 10045983
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Meteoritics & Planetary Science
- Volume:
- 53
- Issue:
- 1
- ISSN:
- 1086-9379
- Page Range / eLocation ID:
- p. 50-61
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract TC 3). However, correlating properties of the meteorite with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70–80% are ureilites (achondrites) and 20–30% are various types of chondrites. Asteroid 2008TC 3was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008TC 3. AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (<10 μm to 3 mm) of olivine, pyroxenes, plagioclase, graphite, and metal‐sulfide, as well as chondrules (~130–600 μm) and chondrule fragments. The C1 material consists of fine‐grained phyllosilicates (serpentine and saponite) and amorphous material, magnetite, breunnerite, dolomite, fayalitic olivine (Fo 28‐42), an unidentified Ca‐rich silicate phase, Fe,Ni sulfides, and minor Ca‐phosphate and ilmenite. It has similarities toCI 1 but shows evidence of heterogeneous thermal metamorphism. Its bulk oxygen isotope composition (δ18O = 13.53‰, δ17O = 8.93‰) is unlike that of any known chondrite, but similar to compositions of severalCC ‐like clasts in typical polymict ureilites. Its Cr isotope composition is unlike that of any known meteorite. The enclosed clasts and chondrules do not belong to the C1 lithology. The olivine (Fo 75‐88), pyroxenes (pigeonite of Wo ~10 and orthopyroxene of Wo ~4.6), plagioclase, graphite, and some metal‐sulfide are ureilitic, based on mineral compositions, textures, and oxygen isotope compositions, and represent at least six distinct ureilitic lithologies. The chondrules are probably derived from type 3OC and/orCC , based on mineral and oxygen isotope compositions. Some of the metal‐sulfide clasts are derived fromEC . AhS 91A and AhS 671 are plausible representatives of the bulk of the asteroid that was lost. Reflectance spectra of AhS 91A are dark (reflectance ~0.04–0.05) and relatively featureless inVNIR , and have an ~2.7 μm absorption band due toOH −in phyllosilicates. Spectral modeling, using mixtures of laboratoryVNIR reflectance spectra of AhS stones to fit the F‐type spectrum of the asteroid, suggests that 2008TC 3consisted mainly of ureilitic and AhS 91A‐like materials, with as much as 40–70% of the latter, and <10% ofOC ,EC , and other meteorite types. The bulk density of AhS 91A (2.35 ± 0.05 g cm−3) is lower than bulk densities of other AhS stones, and closer to estimates for the asteroid (~1.7–2.2 g cm−3). Its porosity (36%) is near the low end of estimates for the asteroid (33–50%), suggesting significant macroporosity. The textures of AhS 91A and AhS 671 (finely comminuted clasts of disparate materials intimately mixed) support formation of 2008TC 3in a regolith environment. AhS 91A and AhS 671 could represent a volume of regolith formed when aCC ‐like body impacted into already well‐gardened ureilitic + impactor‐derived debris. AhS 91A bulk samples do not show a solar wind component, so they represent subsurface layers. AhS 91A has a lower cosmic ray exposure (CRE ) age (~5–9 Ma) than previously studied AhS stones (11–22 Ma). The spread inCRE ages argues for irradiation in a regolith environment. AhS 91A and AhS 671 show that ureilitic asteroids could have detectable ~2.7 μm absorption bands. -
Summary Traditionally, leaves were thought to be supplied with
CO 2for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem‐transportedCO 2that is assimilated, vs simply lost to transpiration.Cut leaves of
Populus deltoides andBrassica napus were placed in eitherKC l or one of three [NaH13CO 3] solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem‐transportedCO 2exiting the leaf across light andCO 2response curves in real‐time using a tunable diode laser absorption spectroscope.The rates of assimilation and efflux of xylem‐transported
CO 2increased with increasing xylem [13CO 2*] and transpiration. Under saturating irradiance, rates of assimilation using xylem‐transportedCO 2accounted forc. 2.5% of the total assimilation in both species in the highest [13CO 2*].The majority of xylem‐transported
CO 2is assimilated, and efflux is small compared to respiration. Assimilation of xylem‐transportedCO 2comprises a small portion of total photosynthesis, but may be more important whenCO 2is limiting. -
Summary We investigated the molecular basis and physiological implications of anion transport during pollen tube (
PT ) growth inArabidopsis thaliana (Col‐0).Patch‐clamp whole‐cell configuration analysis of pollen grain protoplasts revealed three subpopulations of anionic currents differentially regulated by cytoplasmic calcium ([Ca2+]cyt). We investigated the pollen‐expressed proteins
At SLAH 3,At ALMT 12,At TMEM 16 andAt CCC as the putative anion transporters responsible for these currents.At CCC ‐GFP was observed at the shank andAt SLAH 3‐GFP at the tip and shank of thePT plasma membrane. Both are likely to carry the majority of anion current at negative potentials, as extracellular anionic fluxes measured at the tip ofPT s with an anion vibrating probe were significantly lower inslah3 −/− andccc −/− mutants, but unaffected inalmt12 −/− andtmem16 −/− . We further characterised the effect ofpH andGABA by patch clamp. Strong regulation by extracellularpH was observed in the wild‐type, but not intmem16 −/− . Our results are compatible withAt TMEM 16 functioning as an anion/H+cotransporter and therefore, as a putativepH sensor.GABA presence: (1) inhibited the overall currents, an effect that is abrogated in thealmt12 −/− and (2) reduced the current inAt ALMT 12 transfectedCOS ‐7 cells, strongly suggesting the direct interaction ofGABA withAt ALMT12.Our data show that
At SLAH 3 andAt CCC activity is sufficient to explain the major component of extracellular anion fluxes, and unveils a possible regulatory system linkingPT growth modulation bypH ,GABA , and [Ca2+]cytthrough anionic transporters. -
Abstract Plant development requires communication on many levels, including between cells and between organelles within a cell. For example, mitochondria and plastids have been proposed to be sensors of environmental stress and to coordinate their responses. Here we present evidence for communication between mitochondria and chloroplasts during leaf and root development, based on genetic and physical interactions between three
M echanosensitive channel ofS mall conductance‐L ike (MSL ) proteins fromArabidopsis thaliana .MSL proteins areArabidopsis homologs of the bacterialM echanos ensitivec hannel ofS mall conductance (MscS), which relieves cellular osmotic pressure to protect against lysis during hypoosmotic shock.MSL 1 localizes to the inner mitochondrial membrane, whileMSL 2 andMSL 3 localize to the inner plastid membrane and are required to maintain plastid osmotic homeostasis during normal growth and development. In this study, we characterized the phenotypic effect of a genetic lesion in , both in wild type and inMSL 1msl2 msl3 mutant backgrounds.msl1 single mutants appear wild type for all phenotypes examined. The characteristic leaf rumpling inmsl2 msl3 double mutants was exacerbated in themsl1 msl2 msl3 triple mutant. However, the introduction of themsl1 lesion into themsl2 msl3 mutant background suppressed othermsl2 msl3 mutant phenotypes, including ectopic callus formation, accumulation of superoxide and hydrogen peroxide in the shoot apical meristem, decreased root length, and reduced number of lateral roots. All these phenotypes could be recovered by molecular complementation with a transgene containing a wild type version of . In yeast‐based interaction studies,MSL 1MSL 1 interacted with itself, but not withMSL 2 orMSL 3. These results establish that the abnormalities observed inmsl2 msl3 double mutants is partially dependent on the presence of functionalMSL 1 and suggest a possible role for communication between plastid and mitochondria in seedling development. -
Summary Autotrophic respiration is a major driver of the global C cycle and may contribute a positive climate warming feedback through increased atmospheric concentrations of
CO 2. The extent of this feedback depends on plants' ability to acclimate respiration to maintain a constant carbon use efficiency (CUE ).We quantified respiratory partitioning of gross primary production (GPP) and
CUE of field‐grown trees in a long‐term warming experiment (+3°C). We delivered a13C–CO 2pulse to whole tree crowns and chased that pulse in the respiration of leaves, whole crowns, roots, and soil. We also measured the isotopic composition of soil microbial biomass and the respiration rates of leaves and whole crowns.We documented homeostatic respiratory acclimation of foliar and whole‐crown respiration rates; the trees adjusted to experimental warming such that leaf‐level respiration rates were not increased. Experimental warming had no detectable impact on respiratory partitioning or mean residence times. Of the13C label acquired by the trees, aboveground respiration consumed 10%, belowground respiration consumed 40%, and the remaining 50% was retained.
Experimental warming of +3°C did not alter respiratory partitioning at the scale of entire trees, suggesting that complete acclimation of respiration to warming is likely to dampen a positive climate warming feedback.