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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ba20Cd4Hg99 by Materials Project

Ba20Hg99Cd4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are four inequivalent Ba sites. In the first Ba site, Ba is bonded in a 6-coordinate geometry to eighteen Hg atoms. There are a spread of Ba–Hg bond distances ranging from 3.76–3.85 Å. In the second Ba site, Ba is bonded in a 11-coordinate geometry to seventeen Hg atoms. There are a spread of Ba–Hg bond distances ranging from 3.54–4.07 Å. In the third Ba site, Ba is bonded in a 1-coordinate geometry to fifteen Hg atoms. There are a spread of Ba–Hg bond distances ranging from 3.43–3.70 Å. In the fourth Ba site, Ba is bonded in a 12-coordinate geometry to sixteen Hg atoms. There are a spread of Ba–Hg bond distances ranging from 3.76–3.97 Å. There are twelve inequivalent Hg sites. In the first Hg site, Hg is bonded in a 7-coordinate geometry to four Ba and four Hg atoms. There are a spread of Hg–Hg bond distances ranging from 2.97–3.09 Å. In the second Hg site, Hg is bonded to three equivalent Ba and nine Hg atoms to form distorted face-sharing HgBa3Hg9 cuboctahedra. There are a spread of Hg–Hg bond distances ranging from 3.18–3.33 Å. In the third Hg site, Hg is bonded in a tetrahedral geometry to four equivalent Ba atoms. In the fourth Hg site, Hg is bonded in a distorted body-centered cubic geometry to four Ba, three Hg, and one Cd atom. The Hg–Hg bond length is 3.02 Å. The Hg–Cd bond length is 3.23 Å. In the fifth Hg site, Hg is bonded in a distorted q6 geometry to three equivalent Ba and six Hg atoms. There are three shorter (3.15 Å) and three longer (3.20 Å) Hg–Hg bond lengths. In the sixth Hg site, Hg is bonded in a 7-coordinate geometry to three equivalent Ba, three equivalent Hg, and one Cd atom. All Hg–Hg bond lengths are 3.10 Å. The Hg–Cd bond length is 3.14 Å. In the seventh Hg site, Hg is bonded in a 10-coordinate geometry to four Ba and six Hg atoms. In the eighth Hg site, Hg is bonded in a 10-coordinate geometry to two Ba and eight Hg atoms. There are two shorter (3.18 Å) and two longer (3.36 Å) Hg–Hg bond lengths. In the ninth Hg site, Hg is bonded in a 1-coordinate geometry to three Ba, three Hg, and one Cd atom. The Hg–Cd bond length is 2.93 Å. In the tenth Hg site, Hg is bonded in a distorted trigonal planar geometry to three Ba atoms. In the eleventh Hg site, Hg is bonded in a 8-coordinate geometry to three Ba and five Hg atoms. There are one shorter (2.98 Å) and two longer (3.04 Å) Hg–Hg bond lengths. In the twelfth Hg site, Hg is bonded in a 1-coordinate geometry to three equivalent Ba, three equivalent Hg, and one Cd atom. The Hg–Cd bond length is 3.25 Å. Cd is bonded in a body-centered cubic geometry to eight Hg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li3(Mg2Si)4 by Materials Project

Li3(Mg2Si)4 crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Li is bonded in a body-centered cubic geometry to eight equivalent Mg atoms. All Li–Mg bond lengths are 2.86 Å. Mg is bonded in a 7-coordinate geometry to three equivalent Li and four Si atoms. There are three shorter (2.83 Å) and one longer (2.89 Å) Mg–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded in a body-centered cubic geometry to eight equivalent Mg atoms. In the second Si site, Si is bonded in a body-centered cubic geometry to eight equivalent Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U3As2Se by Materials Project

U3As2Se is Heusler-like structured and crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded in a body-centered cubic geometry to six equivalent As and two equivalent Se atoms. All U–As bond lengths are 3.05 Å. Both U–Se bond lengths are 3.06 Å. In the second U site, U is bonded in a body-centered cubic geometry to five equivalent As and three equivalent Se atoms. There are a spread of U–As bond distances ranging from 3.03–3.06 Å. All U–Se bond lengths are 3.05 Å. As is bonded in a body-centered cubic geometry to eight U atoms. Se is bonded in a body-centered cubic geometry to eight U atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc2BeB2Ir5 by Materials Project

BeSc2Ir5B2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Be is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Be–Ir bond lengths are 2.53 Å. Sc is bonded in a 1-coordinate geometry to ten Ir and three equivalent B atoms. There are a spread of Sc–Ir bond distances ranging from 2.76–2.93 Å. There are one shorter (2.58 Å) and two longer (2.87 Å) Sc–B bond lengths. There are two inequivalent Ir sites. In the first Ir site, Ir is bonded in a 8-coordinate geometry to two equivalent Be, four equivalent Sc, and two equivalent B atoms. Both Ir–B bond lengths are 2.20 Å. In the second Ir site, Ir is bonded in a distorted body-centered cubic geometry to four equivalent Sc and four equivalent B atoms. All Ir–B bond lengths are 2.25 Å. B is bonded in a 7-coordinate geometry to three equivalent Sc and six Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn4Fe8Si3Ge by Materials Project

Mn4Fe8GeSi3 is Tungsten-derived structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a distorted body-centered cubic geometry to eight Fe and six Si atoms. There are a spread of Mn–Fe bond distances ranging from 2.38–2.44 Å. There are three shorter (2.80 Å) and three longer (2.81 Å) Mn–Si bond lengths. In the second Mn site, Mn is bonded in a distorted body-centered cubic geometry to eight Fe, three equivalent Ge, and three equivalent Si atoms. There are a spread of Mn–Fe bond distances ranging from 2.42–2.49 Å. All Mn–Ge bond lengths are 2.81 Å. All Mn–Si bond lengths are 2.81 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe is bonded in a body-centered cubic geometry to four Mn and four Si atoms. All Fe–Si bond lengths are 2.43 Å. In the second Fe site, Fe is bonded in a body-centered cubic geometry to four equivalent Mn and four Si atoms. All Fe–Si bond lengths are 2.43 Å. In the third Fe site, Fe is bonded in a body-centered cubic geometry to four equivalent Mn, three equivalent Ge, and one Si atom. There are three shorter (2.42 Å) and one longer (2.49 Å) Fe–Mn bond lengths. All Fe–Ge bond lengths are 2.45 Å. The Fe–Si bond length is 2.40 Å. In the fourth Fe site, Fe is bonded in a body-centered cubic geometry to four Mn, one Ge, and three equivalent Si atoms. The Fe–Ge bond length is 2.50 Å. All Fe–Si bond lengths are 2.42 Å. In the fifth Fe site, Fe is bonded in a body-centered cubic geometry to four equivalent Mn and four Si atoms. All Fe–Si bond lengths are 2.43 Å. In the sixth Fe site, Fe is bonded in a body-centered cubic geometry to four equivalent Mn, three equivalent Ge, and one Si atom. All Fe–Ge bond lengths are 2.45 Å. The Fe–Si bond length is 2.40 Å. In the seventh Fe site, Fe is bonded in a body-centered cubic geometry to four equivalent Mn, three equivalent Ge, and one Si atom. All Fe–Ge bond lengths are 2.45 Å. The Fe–Si bond length is 2.40 Å. Ge is bonded in a distorted body-centered cubic geometry to six equivalent Mn and eight Fe atoms. There are two inequivalent Si sites. In the first Si site, Si is bonded in a distorted body-centered cubic geometry to six Mn and eight Fe atoms. In the second Si site, Si is bonded in a distorted body-centered cubic geometry to six equivalent Mn and eight Fe atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe3Co3Si2 by Materials Project

Fe3Co3Si2 is Tungsten-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to four Fe and four Si atoms. There are one shorter (2.42 Å) and three longer (2.43 Å) Fe–Fe bond lengths. All Fe–Si bond lengths are 2.43 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to one Fe, seven Co, and six Si atoms. There are three shorter (2.42 Å) and four longer (2.43 Å) Fe–Co bond lengths. There are three shorter (2.81 Å) and three longer (2.82 Å) Fe–Si bond lengths. In the third Fe site, Fe is bonded in a 8-coordinate geometry to three equivalent Fe, five Co, and six Si atoms. All Fe–Co bond lengths are 2.44 Å. There are three shorter (2.80 Å) and three longer (2.81 Å) Fe–Si bond lengths. There are three inequivalent Co sites. In the first Co site, Co is bonded in a distorted body-centered cubic geometry to four Fe and four Si atoms. There are one shorter (2.43 Å) and three longer (2.44 Å) Co–Si bond lengths. In the second Co site, Co is bonded in a distorted body-centered cubic geometry to four Fe and four Si atoms. There are three shorter (2.42 Å) and one longer (2.44 Å) Co–Si bond lengths. In the third Co site, Co is bonded in a body-centered cubic geometry to four Fe and four Si atoms. There are three shorter (2.43 Å) and one longer (2.44 Å) Co–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded in a distorted body-centered cubic geometry to nine Fe and five Co atoms. In the second Si site, Si is bonded in a distorted body-centered cubic geometry to seven Fe and seven Co atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb2CdPd3 by Materials Project

Yb2Pd3Cd is Heusler-like structured and crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are three inequivalent Yb sites. In the first Yb site, Yb is bonded in a body-centered cubic geometry to eight Pd atoms. There are two shorter (2.89 Å) and six longer (2.93 Å) Yb–Pd bond lengths. In the second Yb site, Yb is bonded in a distorted body-centered cubic geometry to eight Pd atoms. There are a spread of Yb–Pd bond distances ranging from 2.83–3.09 Å. In the third Yb site, Yb is bonded in a body-centered cubic geometry to eight Pd atoms. There are two shorter (2.95 Å) and six longer (2.96 Å) Yb–Pd bond lengths. There are four inequivalent Pd sites. In the first Pd site, Pd is bonded in a body-centered cubic geometry to four Yb and four equivalent Cd atoms. There are one shorter (2.86 Å) and three longer (2.96 Å) Pd–Cd bond lengths. In the second Pd site, Pd is bonded in a body-centered cubic geometry to seven Yb and one Cd atom. The Pd–Cd bond length is 2.90 Å. In the third Pd site, Pd is bonded in a body-centered cubic geometry to five Yb and three equivalent Cd atoms. All Pd–Cd bond lengths are 2.94 Å. In the fourth Pd site, Pd is bonded in a body-centered cubic geometry to seven Yb and one Cd atom. The Pd–Cd bond length is 2.90 Å. Cd is bonded in a distorted body-centered cubic geometry to eight Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbOF by Materials Project

TbOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Tb3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Tb–O bond lengths are 2.29 Å. There are three shorter (2.46 Å) and one longer (2.48 Å) Tb–F bond lengths. O2- is bonded to four equivalent Tb3+ atoms to form distorted OTb4 tetrahedra that share corners with six equivalent OTb4 tetrahedra, corners with ten equivalent FTb4 tetrahedra, edges with three equivalent OTb4 tetrahedra, and edges with three equivalent FTb4 tetrahedra. F1- is bonded to four equivalent Tb3+ atoms to form distorted FTb4 tetrahedra that share corners with six equivalent FTb4 tetrahedra, corners with ten equivalent OTb4 tetrahedra, edges with three equivalent OTb4 tetrahedra, and edges with three equivalent FTb4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NdOF by Materials Project

NdOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Nd3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Nd–O bond lengths are 2.38 Å. There are three shorter (2.55 Å) and one longer (2.56 Å) Nd–F bond lengths. O2- is bonded to four equivalent Nd3+ atoms to form distorted ONd4 tetrahedra that share corners with six equivalent ONd4 tetrahedra, corners with ten equivalent FNd4 tetrahedra, edges with three equivalent ONd4 tetrahedra, and edges with three equivalent FNd4 tetrahedra. F1- is bonded to four equivalent Nd3+ atoms to form distorted FNd4 tetrahedra that share corners with six equivalent FNd4 tetrahedra, corners with ten equivalent ONd4 tetrahedra, edges with three equivalent ONd4 tetrahedra, and edges with three equivalent FNd4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PrOF by Materials Project

PrOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Pr3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Pr–O bond lengths are 2.40 Å. There are three shorter (2.56 Å) and one longer (2.60 Å) Pr–F bond lengths. O2- is bonded to four equivalent Pr3+ atoms to form distorted OPr4 tetrahedra that share corners with six equivalent OPr4 tetrahedra, corners with ten equivalent FPr4 tetrahedra, edges with three equivalent OPr4 tetrahedra, and edges with three equivalent FPr4 tetrahedra. F1- is bonded to four equivalent Pr3+ atoms to form distorted FPr4 tetrahedra that share corners with six equivalent FPr4 tetrahedra, corners with ten equivalent OPr4 tetrahedra, edges with three equivalent OPr4 tetrahedra, and edges with three equivalent FPr4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SmOF by Materials Project

SmOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Sm3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Sm–O bond lengths are 2.34 Å. There are three shorter (2.51 Å) and one longer (2.53 Å) Sm–F bond lengths. O2- is bonded to four equivalent Sm3+ atoms to form distorted OSm4 tetrahedra that share corners with six equivalent OSm4 tetrahedra, corners with ten equivalent FSm4 tetrahedra, edges with three equivalent OSm4 tetrahedra, and edges with three equivalent FSm4 tetrahedra. F1- is bonded to four equivalent Sm3+ atoms to form distorted FSm4 tetrahedra that share corners with six equivalent FSm4 tetrahedra, corners with ten equivalent OSm4 tetrahedra, edges with three equivalent OSm4 tetrahedra, and edges with three equivalent FSm4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoOF by Materials Project

HoOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ho3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Ho–O bond lengths are 2.26 Å. There are three shorter (2.44 Å) and one longer (2.45 Å) Ho–F bond lengths. O2- is bonded to four equivalent Ho3+ atoms to form distorted OHo4 tetrahedra that share corners with six equivalent OHo4 tetrahedra, corners with ten equivalent FHo4 tetrahedra, edges with three equivalent OHo4 tetrahedra, and edges with three equivalent FHo4 tetrahedra. F1- is bonded to four equivalent Ho3+ atoms to form distorted FHo4 tetrahedra that share corners with six equivalent FHo4 tetrahedra, corners with ten equivalent OHo4 tetrahedra, edges with three equivalent OHo4 tetrahedra, and edges with three equivalent FHo4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ErOF by Materials Project

ErOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Er3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All Er–O bond lengths are 2.26 Å. There are three shorter (2.43 Å) and one longer (2.46 Å) Er–F bond lengths. O2- is bonded to four equivalent Er3+ atoms to form distorted OEr4 tetrahedra that share corners with six equivalent OEr4 tetrahedra, corners with ten equivalent FEr4 tetrahedra, edges with three equivalent OEr4 tetrahedra, and edges with three equivalent FEr4 tetrahedra. F1- is bonded to four equivalent Er3+ atoms to form distorted FEr4 tetrahedra that share corners with six equivalent FEr4 tetrahedra, corners with ten equivalent OEr4 tetrahedra, edges with three equivalent OEr4 tetrahedra, and edges with three equivalent FEr4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Error Analysis on Numerical Integration Algorithms in a Hypoelasticity Framework

This report determines local truncation errors for common stress integration algorithms used in explicit finite element codes with hypoelastic material models. The hypoelastic integration algorithms in question utilize an operator splitting procedure in a rotation neutralized configuration, where the stress response is determined from de- coupling the total deformation into rotational and strain dependent components. This document analyzes the error in evolving the stress given a one-step time increment Δt and compares the errors associated with both the rotational and strain components of the operator splitting method. A slight modification to a traditional algorithm is proposed and studied, where the rate of deformation is appropriately rotated from the midstep configuration at t n+1/2 to the end step configuration at t n+1 before the constitutive evaluation. The proposed modification either completely eliminates the error associated with the rotation rate or is of the same order of magnitude as the original algorithm for the three test cases considered in this report. These cases consist of an unaxial stretch with a constant true strain rate with a rigid body rotation, an uniaxial stretch with a constant engineering strain rate with a rigid body rotation, and a simple shear deformation. All three cases are compared to a closed form solution, and in almost every test case the alternative algorithm yields the most accurate one-step local truncation error.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Nickel-rich, volatile depleted iron meteorites: Relationships and formation processes

Ungrouped iron meteorites Tishomingo, Willow Grove, and Chinga, and group IVB iron meteorites, are Ni-rich. Similarities include enrichments of 10–100 × CI for some refractory siderophile elements, and equivalent depletions in more volatile siderophile elements. Superimposed on the overall enrichment/depletion trend, certain siderophile elements (P, W, Fe, Mo) are depleted relative to elements of similar volatility. All three ungrouped irons derive from parent bodies formed in the early Solar System. Willow Grove and Chinga are characterized by cosmic ray exposure corrected 182 W/ 184 W consistent with metal-silicate segregation on their parent bodies within 1–3 Myr of Solar System formation, within the age range determined for segregation of magmatic iron meteorite parent bodies, including group IVB irons. Tishomingo is characterized by a younger model age 4–5 Myr subsequent to Solar System formation, reflecting either late stage melting resulting from 26 Al decay, or an impact resetting. The discovery of stishovite in Tishomingo, indicating exposure to a minimum shock pressure of 8–9 GPa, is consistent with the latter. Stishovite in Tishomingo and chromite included in troilite-daubréelite in IVB irons allows oxygen isotopic composition comparison between these meteorites. Different mass independent oxygen isotopic compositions of IVB irons and Tishomingo indicate genetically distinct parent bodies. By contrast, mass independent Mo isotopic compositions overlap within analytical uncertainties, indicating a similar, carbonaceous chondrite (CC) type genetic heritage. Molybdenum and 183 W isotopic data for Chinga and Willow Grove indicate derivation from CC type parent bodies. Willow Grove shares Mo and 183 W isotopic compositions with the Ni-rich South Byron Trio (SBT) grouplet and the Milton pallasite. These Ni-rich meteorites likely formed in the same general nebular environment as other CC planetesimals, likely the outer Solar System. Highly siderophile element (HSE) abundances of Willow Grove and Tishomingo are similar to some IVB meteorites, consistent with formation by moderate degrees of fractional crystallization from initial metallic melts with low S and P, and modestly fractionated HSE. The comparable HSE abundances of Tishomingo and Willow Grove to some IVB irons, yet substantially higher Ni concentrations, indicate formation on parent bodies with lower bulk HSE abundances or HSE concentration in proportionally smaller volumes of metal. HSE abundances in Chinga are considerably lower than in IVB irons, highly fractionated, and processes responsible for these remain elusive. For IVB irons and these ungrouped irons, high temperature condensation likely dominated the enrichment and depletion of the refractory and volatile siderophile elements, respectively. Parent body degassing may have also played a role. Relative depletion of volatile siderophile elements is not, however, a universal feature of high-Ni meteorites. The SBT and Milton pallasite are Ni-rich, but less depleted in the more volatile siderophile elements. Nickel enrichment was likely driven by oxidation of Fe metal during parent body accretion or core segregation. Oxidation of the Tishomingo and Willow Grove parent bodies may have occurred at ~ IW + 1, indicated by relative Mo and W depletions due to metal/water reaction during differentiation. Late-stage reduction, indicated by the presence of Cr-bearing sulfides in Tishomingo and IVB irons, may have resulted from exhaustion of the oxidant.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Temperature-Controlled Reversible Formation and Phase Transformation of 3D Nanocrystal Superlattices Through In Situ Small-Angle X-ray Scattering

For decades, the spontaneous organization of nanocrystals into superlattices has captivated the scientific community. However, achieving direct control over the formation of the superlattice and its phase transformations has proven to be a grand challenge, often resulting in the generation of multiple symmetries under the same experimental conditions. Here, we achieve direct control over the formation of the superlattice and its phase transformations by modulating the thermal energy of a nanocrystal dispersion without relying on solvent evaporation. In this study, we follow the temperature-dependent dynamics of the self-assembly process using synchrotron-based small-angle X-ray scattering. When cooled below –24.5 °C, lead sulfide nanocrystals form micrometer-sized three-dimensional phase-pure body-centered cubic superlattices. When cooled below –35.1 °C, these superlattices undergo a collective diffusionless phase transformation that yields denser body-centered tetragonal phases. These structural changes can be reversed by increasing the temperature of the dispersion and may lead to the direct modulation of the optical properties of these artificial solids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Let it rip: The mechanics of self-bisection in asexual planarians determines their population reproductive strategies

Asexual freshwater planarians reproduce by transverse bisection (binary fission) into two pieces. This process produces a head and a tail, which fully regenerate within 1-2 weeks. How planarians split into two offspring - using only their musculature and substrate traction – is a challenging biomechanics problem. We found that three different species, Dugesia japonica, Girardia tigrina and Schmidtea mediterranea, have evolved three different mechanical solutions to self-bisect. Using time lapse imaging of the fission process, we quantitatively characterize the main steps of division in the three species and extract the distinct and shared key features. Across the three species, planarians actively alter their body shape, regulate substrate traction, and use their muscles to generate tensile stresses large enough to overcome the ultimate tensile strength of the tissue. Moreover, we show that how each planarian species divides dictates how resources are split among its offspring. This ultimately determines offspring survival and reproductive success. Furthermore, heterospecific differences in the mechanics of self-bisection of individual worms explain the observed differences in the population reproductive strategies of different planarian species.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Aspartate Residues in a Forisome-Forming SEO Protein Are Critical for Protein Body Assembly and Ca 2+ Responsiveness

Forisomes are protein bodies known exclusively from sieve elements of legumes. Forisomes contribute to the regulation of phloem transport due to their unique Ca 2+ -controlled, reversible swelling. The assembly of forisomes from sieve element occlusion (SEO) protein monomers in developing sieve elements and the mechanism(s) of Ca 2+ -dependent forisome contractility are poorly understood because the amino acid sequences of SEO proteins lack conventional protein–protein interaction and Ca 2+ -binding motifs. Here we selected amino acids potentially responsible for forisome-specific functions by analyzing SEO protein sequences in comparison to those of the widely distributed SEO-related (SEOR), or SEOR proteins. SEOR proteins resemble SEO proteins closely but lack any Ca 2+ responsiveness. We exchanged identified candidate residues by directed mutagenesis of the Medicago truncatula SEO1 gene, expressed the mutated genes in yeast ( Saccharomyces cerevisiae ) and studied the structural and functional phenotypes of the forisome-like bodies that formed in the transgenic cells. We identified three aspartate residues critical for Ca 2+ responsiveness and two more that were required for forisome-like bodies to assemble. The phenotypes observed further suggested that Ca 2+ -controlled and pH-inducible swelling effects in forisome-like bodies proceeded by different yet interacting mechanisms. Finally, we observed a previously unknown surface striation in native forisomes and in recombinant forisome-like bodies that could serve as an indicator of successful forisome assembly. To conclude, this study defines a promising path to the elucidation of the so-far elusive molecular mechanisms of forisome assembly and Ca 2+ -dependent contractility.

59 BASIC BIOLOGICAL SCIENCES↗