Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than similar to 200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population.

The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon. In this study, these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambient pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of

The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 +/- 0.2) x 10(6) km(3) of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.

Context. Imaged in the gap of a transition disk and found at a separation of about 195 mas (similar to 22 au) from its host star at a position angle of about 155 degrees, PDS 70 b is the most robustly detected young planet to date. This system is therefore a unique laboratory for characterizing the properties of young planetary systems at the stage of their formation.

We present L'-band Keck/NJRC2 imaging and H-band Subaru/A0188 HiCIA0 polarimetric observations of the CQ Tau disk with a new spiral arm. Apart from the spiral feature, our observations could not detect any companion candidates. We traced the spiral feature from the r2-scaled High-Contrast Coronographic Imager for Adaptive Optics (HiCIA0) polarimetric intensity image and the fitted result is used for forward modeling to reproduce the ADI-reduced NJRC2 image. We estimated the original surface brightness after throughput correction in the L' band to be-126 mJy arcsec-2 at most. We suggest that the grain temperature of the spiral may be heated up to-200 K in order to explain both of the H- and L'-band results. The H-band emission at the location of the spiral originates from the scattering from the disk surface while both scattering and thermal emission may contribute to the L'-band emission. If the central star is only the light source of scattered light, the spiral emission at the L' band should be thermal emission. If an inner disk also acts as the light source, the scattered light and the thermal emission may equally contribute to the L'-band spiral structure.

Previous work has established that the solar wind and micrometeoroids produce spectral changes on airless silicate bodies. However, the relative importance of these two weathering agents, the timescales over which they operate, and how their effects depend on composition have not yet been well determined. To help address these questions we make use of the fact that solar wind and micrometeoroid fluxes vary with latitude on the Moon. Previous work has shown that this latitudinally varying flux leads to systematic latitudinal variations in the spectral properties of lunar soils. Here we find that the way in which a lunar soil's spectral properties vary with latitude is a function of its iron content, when we consider soils with 14-22 wt% FeO. In particular, a 50% reduction in flux corresponds to a significant increase in reflectance for 14 wt% FeO soils, while the same flux reduction on 21 wt% FeO soils is smaller by a factor of similar to 5, suggesting that this brightening effect saturates for high FeO soils. We propose that lower iron soils may not approach saturation because grains are destroyed or refreshed before sufficient nano- and micro-phase iron can accumulate on their rims. We compare our results to the spectral variations observed across the Reiner Gamma swirl, which lies on a high-iron surface, and find it has anomalous brightness compared to our predictions. Swirls in Mare Marginis, which lie on a low iron surface, exhibit brightness differences that suggest reductions in solar wind flux between 20 and 40%. Our inferences suffer from the limited latitudinal extent of the maria and the convolution of micrometeoroid flux and solar wind flux changes with latitude. Superior constraints on how space weathering operates throughout the inner solar system would come from in situ measurements of the solar wind flux at lunar swirls.

Brassinosteroids (BRs) are known to be endogenous regulators of ethylene production, suggesting that some BR activity in plant growth and development is associated with ethylene. Here, we demonstrated that ethylene production in Arabidopsis thaliana roots is increased by BR signaling via the ethylene biosynthetic gene for ACC oxidase 1 (ACO1). Electrophoretic mobility shift and chromatin immune-precipitation assays showed that the BR transcription factor BES1 directly binds to two E-box sequences located in the intergenic region of ACO1. GUS expression using site mutations of the E-box sequences verified that ACO1 is normally expressed only when BES1 binds to the E-boxes in the putative promoter of ACO1, indicating that this binding is essential for ACO1 expression and the subsequent production of ethylene in A. thaliana roots. BR exogenously applied to A. thaliana roots enhanced the gravitropic response. Additionally, bes1-D exhibited a greater gravitropic response than did the wild-type specimens, proving that BR is a positive regulator of the gravitropic response in A. thaliana roots. The knock-down mutant aco1-1 showed a slightly lower gravitropic response than did the wild-type specimens, while bes1-D X aco1-1 exhibited a lower gravitropic response than did bes1-D. Therefore, ACO1 is a direct downstream target for BR transcription factor BES1, which controls ethylene production for gravitropism in A. thaliana roots.

Quantitative reverse transcription PCR (qRT-PCR) analysis and ProACO2::GUS expression showed that ACO2 was highly expressed in the shoots of Arabidopsis seedlings under light conditions. Exogenously applied aminocyclopropane-1-carboxylic acid (ACC) enhanced the expression of ACO2, whereas Co2+ ions suppressed its expression. In comparison with wild-type seedlings, the ACO2 knockdown mutant aco2-1 produced less ethylene, which resulted in the inhibited growth of Arabidopsis seedlings. Exogenously applied brassinolide reduced the expression of ACO2. ACO2 expression was increased in det2, a brassinosteroid (BR)-deficient mutant; however, it was decreased in bes1-D, a brassinosteroid insensitive 1-EMS-suppressor 1 (BES1)-dominant mutant. In the putative promoter region of ACO2, 11 E-box sequences for BES1 binding but not BR regulatory element sequences for brassinazole-resistant 1 (BZR1) binding were found. Chromatin immunoprecipitation assay showed that BES1 could directly bind to the E-boxes located in the putative promoter region of ACO4. Less ethylene was produced in bes1-D seedlings compared with wild-type seedlings, suggesting that the direct binding of BES1 to the ACO2 promoter may negatively regulate ACO2 expression to control the endogenous level of ethylene in Arabidopsis seedlings.

The increased level of endogenous abscisic acid (ABA) in brassinosteroid (BR)-deficient mutants, such as det2 and cyp85a1 x cyp85a2, suggests that ABA synthesis is inhibited by endogenous BRs in Arabidopsis thaliana. Expression of the ABA biosynthesis gene ABA-deficient 2 (ABA2) was negatively regulated by exogenously applied BR but up-regulated by the application of brassinazole and in det2 and cyp85a1 x cyp85a2. In addition, ABA2 expression decreased in bzr1-1D, showing that ABA biosynthesis is inhibited by BR signaling via BZR1, intermediated by ABA2, in Arabidopsis. Four cis-element sequences (E-boxes 1-4) in the putative promoter region of ABA2 were identified as BZR1 binding sites. The electrophoretic mobility shift assay and chromatin immune precipitation analysis demonstrated that BZR1 directly binds to overlapped E-boxes (E-box 3/4) in the promoter region of ABA2. The level of endogenous ABA was decreased in bzr1-1D compared to wild-type, indicating that binding of BZR1 to the ABA2 promoter inhibits ABA synthesis in Arabidopsis. Compared to wild-type, aba2-1 exhibited severely reduced growth and development. The abnormalities in aba2-1 were rescued by the application of ABA, suggesting that ABA2 expression and ABA synthesis are necessary for the normal growth and development of A. thaliana. Finally, bzr1-KO x aba2-1 exhibited inhibitory growth of primary roots compared to bzr1-KO, verifying that ABA2 is a downstream target of BZR1 in the plant. Taken together, the level of endogenous ABA is down-regulated by BR signaling via BZR1, controlling the growth of A. thaliana.

Brachypodium distachyon is a monocotyledonous model plant that contains castasterone (CS) but no brassinolide (BL) as the end product of brassinosteroids (BR) biosynthesis, indicating dysfunction of BL synthase, which catalyzes the conversion of CS to BL. To increase BR activity, Arabidopsis cytochrome P450 85A2 (AtCYP85A2) encoding BR 6-oxidase/BL synthase was introduced into B. distachyon with the seed-specific promoters pBSU1, pAt5g10120, and pAt5g54000. RT-PCR analysis and GUS activity revealed that AtCYP85A2 was only expressed in the seeds of the transgenic plants pBSU1-AtCYP85A2::Bd21-3, pAt5g10120-AtCYP85A2::Bd21-3, and pAt5g54000-AtCYP85A2::Bd21-3. The crude enzyme prepared from the seeds of these three transgenic plants catalyzed the conversion of 6-deoxoCS to CS. The transgenic plants showed greater specific enzyme activity than the wild-type plant for the conversion of 6-deoxoCS to CS, indicating enhanced BR 6-oxidase activity in the transgenic plants. The enzyme solution also catalyzed the conversion of CS into BL. Additionally, BL was identified from the seeds of transgenic plants, verifying that seed-specific AtCYP85A2 encodes a functional BL synthase to increase BR activity in the seeds of transgenic Brachypodium. In comparison with wild-type Brachypodium, the transgenic plants showed better growth and development during the vegetative growing stage. The flowers of the transgenic plants were remarkably larger, resulting in increments in the number, size, and height of seeds. The total starch, protein, and lipid contents in transgenic plants were higher than those in wild-type plants, indicating that seed-specific expression of AtCYP85A2 improves both grain yield and quality in B. distachyon.