The plant haploid generation is specified late in higher plant development, and post-meiotic haploid plant cells divide mitotically to produce a haploid gametophyte, in which a subset of cells differentiates into the gametes. The immediate mother of the angiosperm seed is the female gametophyte, also called the embryo sac. In most flowering plants the embryo sac is comprised of two kinds of gametes (egg and central cell) and two kinds of subsidiary cells (antipodals and synergids) all of which descend from a single haploid spore produced by meiosis. The embryo sac develops within a specialized organ of the flower called the ovule, which supports and controls many steps in the development of both the embryo sac and the seed. Double fertilization of the central cell and egg cell by the two sperm cells of a pollen grain produce the endosperm and embryo of the seed, respectively. The endosperm and embryo develop under the influence of their precursor gametes and the surrounding tissues of the ovule and the gametophyte. The final size and pattern of the angiosperm seed then is the result of complex interactions across multiple tissues of three different generations (maternal sporophyte, maternal gametophyte, and the fertilization products) and three different ploidies (haploid gametophyte, diploid parental sporophyte and embryo, and triploid endosperm).

A central problem in speciation is the origin and mechanisms of reproductive barriers that block gene flow between sympatric populations. Wind-pollinated plant species that flower in synchrony with one another rely on post-pollination interactions to maintain reproductive isolation. In some locations in Mexico, sympatric populations of domesticated maize and annual teosinte grow in intimate associate and flower synchronously, but rarely produce hybrids. This trait is typically conferred by a single haplotype, Teosinte crossing barrierl-s. Here, we show that the Teosinte crossing barrierl-s haplotype contains a pistil-expressed, potential speciation gene, encoding a pectin methylesterase homolog. The modification of the pollen tube cell wall by the pistil, then, is likely a key mechanism for pollen rejection in Zea and may represent a general mechanism for reproductive isolation in grasses.

A central challenge in global change research is the projection of the future behavior of a system based upon past observations. Tree-ring data have been used increasingly over the last decade to project tree growth and forest ecosystem vulnerability under future climate conditions. But how can the response of tree growth to past climate variation predict the future, when the future does not look like the past? Space-for-time substitution (SFTS) is one way to overcome the problem of extrapolation: the response at a given location in a warmer future is assumed to follow the response at a warmer location today. Here we evaluated an SFTS approach to projecting future growth of Douglas-fir (Pseudotsuga menziesii), a species that occupies an exceptionally large environmental space in North America. We fit a hierarchical mixed-effects model to capture ring-width variability in response to spatial and temporal variation in climate. We found opposing gradients for productivity and climate sensitivity with highest growth rates and weakest response to interannual climate variation in the mesic coastal part of Douglas-fir's range; narrower rings and stronger climate sensitivity occurred across the semi-arid interior. Ring-width response to spatial versus temporal temperature variation was opposite in sign, suggesting that spatial variation in productivity, caused by local adaptation and other slow processes, cannot be used to anticipate changes in productivity caused by rapid climate change. We thus substituted only climate sensitivities when projecting future tree growth. Growth declines were projected across much of Douglas-fir's distribution, with largest relative decreases in the semiarid U.S. Interior West and smallest in the mesic Pacific Northwest. We further highlight the strengths of mixed-effects modeling for reviving a conceptual cornerstone of dendroecology, Cook's 1987 aggregate growth model, and the great potential to use tree-ring networks and results as a calibration target for next-generation vegetation models.

Gametophytic cross-incompatibility systems in corn have been the subject of genetic studies for more than a century. They have tremendous economic potential as a genetic mechanism for controlling fertilization without controlling pollination. Three major genetically distinct and functionally equivalent cross-incompatibility systems exist inZea mays:Ga1,Tcb1, andGa2. All three confer reproductive isolation between maize or teosinte varieties with different haplotypes at any one locus. These loci confer genetically separable functions to the silk and pollen: a female function that allows the silk to block fertilization by non-self-type pollen and a male function that overcomes the block of the female function from the same locus. Identification of some of these genes has shed light on the reproductive isolation they confer. The identification of both male and female factors as pectin methylesterases reveals the importance of pectin methylesterase activity in controlling the decision between pollen acceptance versus rejection, possibly by regulating the degree of methylesterification of the pollen tube cell wall. The appropriate level and spatial distribution of pectin methylesterification is critical for pollen tube growth and is affected by both pectin methylesterases and pectin methylesterase inhibitors. We present a molecular model that explains how cross-incompatibility systems may function that can be tested inZeaand uncharacterized cross-incompatibility systems. Molecular characterization of these loci in conjunction with further refinement of the underlying molecular and cellular mechanisms will allow researchers to bring new and powerful tools to bear on understanding reproductive isolation inZea maysand related species.

We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution (R similar to 11,000) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of <[Fe/H]> = -2.62 +/- 0.11 dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of -143.5 +/- 1.2 km s(-1) and a velocity dispersion of sigma(rv) = 2.5(-0.8)(+1.3) km s(-1), which results in a dynamical mass of M(1/2()r(h)) = 8(-4)(+12) 2 x 10(5) M-circle dot and a mass-to-light ratio of M/L-V = 440(-250)(+650) M-circle dot/L-circle dot. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L> 80 M-circle dot/L-circle dot). However, we do not resolve a metallicity dispersion (sigma([Fe/H]) < 0.44 dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass-metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central densities ( rho(1/2) similar to 3.5(-2 1)(+5.7) x 10(7) M-circle dot kpc(-3))of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies.

Core formation may modify the stable isotopic signatures for both the mantles and cores of differentiated planetary bodies. We performed high P-T experiments with a piston-cylinder apparatus at 1 GPa and 1873-2073 K to determine the Cr isotopic fractionation factor during metal-silicate segregation. Experimental results consistently indicate that the metal phase is isotopically heavier than the coexisting silicate phase, with Delta Cr-53(metal-sliicate) up to 0.3 parts per thousand at the investigated experimental conditions. Oxygen fugacity, silicate composition, and S content in the metal phase do not have significant effects on the Cr isotopic fractionation factor. By contrast, increasing Ni content in the metal increases the Cr-53(metal-sliicate) value, implying that the Ni content of the core could influence planetary isotopic signatures. We conclude that heavier Cr isotopes enter the core preferentially during planetary core formation. The delta Cr-53 value of the terrestrial mantle could be lowered by up to similar to 0.02 parts per thousand by core formation, despite that this is within current analytical uncertainty of chondritic Cr isotopic composition. For smaller bodies such as the Moon, Mars, and Vesta, the lower core formation temperatures could potentially generate a resolvable coremantle Cr isotopic fractionation. However, the Moon's small core size would limit the change in the Cr isotopic composition of the lunar mantle compared to chondritic. For Vesta and Mars, core formation could lower the delta Cr-53 values of their mantles by similar to 0.01-0.02 parts per thousand, which is trivial relative to the analytical uncertainty. On the other hand, core formation could increase the delta Cr-53 values of the cores of the parent bodies of iron meteorites by up to similar to 0.2 parts per thousand at 1873 K. Therefore, the significantly heavy Cr isotopic composition (up to 2.85 parts per thousand) of iron meteorites cannot be explained by equilibrium fractionation between the core and the mantle of the parent bodies of iron meteorites. (C) 2022 Elsevier B.V. All rights reserved.

The iron-silicon phase diagram has been established at the conditions of Mercury's core. The resulting phase diagram is remarkably complex, and presents an array of new mechanisms which may power Mercury's inner dynamo.

Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558-562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen. (C) 2020Author(s).

Globally, soils store two to three times as much carbon as currently resides in the atmosphere, and it is critical to understand how soil greenhouse gas (GHG) emissions and uptake will respond to ongoing climate change. In particular, the soil-to-atmosphere CO(2)flux, commonly though imprecisely termed soil respiration (R-S), is one of the largest carbon fluxes in the Earth system. An increasing number of high-frequencyR(S)measurements (typically, from an automated system with hourly sampling) have been made over the last two decades; an increasing number of methane measurements are being made with such systems as well. Such high frequency data are an invaluable resource for understanding GHG fluxes, but lack a central database or repository. Here we describe the lightweight, open-source COSORE (COntinuous SOil REspiration) database and software, that focuses on automated, continuous and long-term GHG flux datasets, and is intended to serve as a community resource for earth sciences, climate change syntheses and model evaluation. Contributed datasets are mapped to a single, consistent standard, with metadata on contributors, geographic location, measurement conditions and ancillary data. The design emphasizes the importance of reproducibility, scientific transparency and open access to data. While being oriented towards continuously measuredR(S), the database design accommodates other soil-atmosphere measurements (e.g. ecosystem respiration, chamber-measured net ecosystem exchange, methane fluxes) as well as experimental treatments (heterotrophic only, etc.). We give brief examples of the types of analyses possible using this new community resource and describe its accompanying R software package.

The influence of atmosphere pollution on human health is receiving more and more concerns as strengthened anthropogenic activity had brought excessive pollutant into the atmosphere. To date, the quantitative estimation about the contribution of atmosphere on the accumulation of heavy metal in the edible cereal parts induced by anthropogenic forcing is scarce. Taking the Yangtze River Delta area, China as an example, this study estimates quantitatively the influence of atmosphere on the concentration of heavy metal in the aboveground wheat tissues induced by anthropogenic industrial activity at the regional scale. The results show that the aboveground wheat tissues in the southern Yangtze River Delta area accumulated much more heavy metals than that in the northern area, although there is no significant difference in the geological and climate conditions, soil types, agricultural manages, wheat cultivar and soil heavy metals concentrations (even heavy metals concentrations in wheat mot) between the southern area and northern area. The mean concentrations of Pb, Zn, Cu and Cd in wheat grain in southern area have exceeded the thresholds of contamination levels. The present study suggests that the influence of atmosphere on the accumulation of Hg, Cd, Pb, Zn, Cu, Ni and Cr in the aboveground wheat tissues is greatly significant when high amounts of pollutant are measured in the atmosphere. Based on translocation coefficient of the element, it is estimated that atmospheric pollution induced by anthropogenic forcing might lead to the concentration of heavy metals in wheat straw and grain increase by approximately 100% and 354% (Hg), 64% and 293% (Pb), 122% and 160% (Cr), 50% and 38% (Cd) and 14% and 41% (Cu), respectively.