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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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52 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Reply to: Is the debate over grana stacking formation finally solved?

In plants, the photosynthetic pigment–protein complexes catalysing energy conversion are harboured in the thylakoid membrane system of chloroplasts. Recent breakthroughs in electron tomography reveal the sophisticated architecture of this unique membrane system with stacked grana as a structural hallmark. Here, a long-standing question has been whether the combination of physicochemical forces alone can explain the strict stacking of grana with an intermembrane separation of 3–4 nm. In our 2017 Nature Plants paper, we argued that the balance between attractive van der Waals (vdW) forces (F vdW ) and repulsive electrostatic (F el ) and hydrostructural (F hydro ) forces could explain grana stacking, in contrast with previous reports. Our finding was challenged in the report by Gudarzi et al. This reply addresses this critique.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Impact of ion fluxes across thylakoid membranes on photosynthetic electron transport and photoprotection

In photosynthetic thylakoid membranes the proton motive force (pmf) not only drives ATP synthesis, in addition it is central to controlling and regulating energy conversion. As a consequence, dynamic fine-tuning of the two pmf components, electrical (Δψ) and chemical (ΔpH), is an essential element for adjusting photosynthetic light reactions to changing environmental conditions. Good evidence exists that the Δψ/ΔpH partitioning is controlled by thylakoid potassium and chloride ion transporters and channels. However, a detailed mechanistic understanding of how these thylakoid ion transporter/channels control pmf partitioning is lacking. In this work, we combined functional measurements on potassium and chloride ion transporter and channel loss-of-function mutants with extended mathematical simulations of photosynthetic light reactions in thylakoid membranes to obtain detailed kinetic insights into the complex interrelationship between membrane energization and ion fluxes across thylakoid membranes. The data reveal that potassium and chloride fluxes in the thylakoid lumen determined by the K + /H + antiporter KEA3 and the voltage-gated Cl – channel VCCN1/Best1 have distinct kinetic responses that lead to characteristic and light-intensity-dependent Δψ/ΔpH oscillations. These oscillations fine-tune photoprotective mechanisms and electron transport which are particularly important during the first minutes of illumination and under fluctuating light conditions. By employing the predictive power of the model, we unravelled the functional consequences of changes in KEA3 and VCCN1 abundance and regulatory/enzymatic parameters on membrane energization and photoprotection.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Plastocyanin is the long-range electron carrier between photosystem II and photosystem I in plants

In photosynthetic electron transport, large multiprotein complexes are connected by small diffusible electron carriers, the mobility of which is challenged by macromolecular crowding. For thylakoid membranes of higher plants, a long-standing question has been which of the two mobile electron carriers, plastoquinone or plastocyanin, mediates electron transport from stacked grana thylakoids where photosystem II (PSII) is localized to distant unstacked regions of the thylakoids that harbor PSI. Here, we confirm that plastocyanin is the long-range electron carrier by employing mutants with different grana diameters. Furthermore, our results explain why higher plants have a narrow range of grana diameters since a larger diffusion distance for plastocyanin would jeopardize the efficiency of electron transport. In the light of recent findings that the lumen of thylakoids, which forms the diffusion space of plastocyanin, undergoes dynamic swelling/shrinkage, this study demonstrates that plastocyanin diffusion is a crucial regulatory element of plant photosynthetic electron transport.

plastoquinone↗
DOE OSTI2025

What are grana in chloroplasts of vascular plants good for?

All plants and green algae contain stacked grana thylakoid membranes in their chloroplasts, underscoring an evolutionary pressure to maintain this unique structural feature. In addition, numerous studies have demonstrated that particular lateral and vertical dimensions of grana facilitate the function, regulation and repair of the photosynthetic machinery responsible for energy conversion. In this review, we present an updated overview of our understanding concerning the structure of grana thylakoids, the forces that contribute to their formation and their architectural dynamics. After establishing the structural foundation, we continue by reviewing the implications of grana formation on light harvesting, electron transport and protein maintenance in the thylakoid membranes of vascular plants. Regarding light harvesting, we discuss the implications of grana formation on energy spillover, macromolecular crowding, lateral versus vertical excitation energy transfer, and state transition. With respect to electron transport, we summarize recent findings regarding the functional connectivity of spatially separated photosystems facilitated by grana formation through small mobile electron carriers. We also explore how the dynamic responses of grana architecture regulate electron transport. Finally, we address how grana formation contributes to the organization of protein repair and biogenesis within thylakoid membranes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Azimuthal anisotropies of charged particles with high transverse momentum in Pb + Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV with the ATLAS detector

A measurement is presented of elliptic (𝑣 2 ) and triangular (𝑣 3 ) azimuthal anisotropy coefficients for charged particles produced in Pb + Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV using a dataset corresponding to an integrated luminosity of 0.44nb −1 collected with the ATLAS detector at the LHC in 2018. The values of 𝑣 2 and 𝑣 3 are measured for charged particles over a wide range of transverse momentum (𝑝 T ), 1–400 GeV, and Pb + Pb collision centrality, 0–60%, using the scalar-product and multiparticle cumulant methods. These methods are sensitive to event-by-event fluctuations and nonflow effects in the measurements of azimuthal anisotropies. Positive values of 𝑣 2 are observed up to a 𝑝 T of approximately 100 GeV from both methods across all centrality intervals. Positive values of 𝑣 3 are observed up to approximately 25 GeV using both methods, though the application of the three-subevent technique to the multiparticle cumulant method leads to significant changes at the highest 𝑝 T . At high 𝑝 T (𝑝 T ⪆ 10 GeV), charged particles are dominantly from jet fragmentation. These jets, and hence the measurements presented here, are sensitive to the path-length dependence of parton energy loss in the quark-gluon plasma produced in Pb + Pb collisions.

Collective flow↗
DOE OSTI2025

Search for decays of the Higgs boson into scalar particles decaying into four or six 𝑏 quarks using 𝑝⁢𝑝 collisions at $\sqrt{𝑠}$ = 13 TeV with the ATLAS detector

A search for exotic decays of the Higgs boson 𝐻 into new scalar or pseudoscalar particles that subsequently decay into 𝑏-quarks is presented. The search considers 𝑍⁢𝐻 production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, 𝐻 → 2⁢𝑎 → 4⁢𝑏, second to a pair of scalars with different masses (𝑚 𝑎⁢1 < 𝑚 𝑎⁢2 ), either directly, 𝐻 → 𝑎 1 ⁢𝑎 2 → 4⁢𝑏, or via a longer decay chain, 𝐻 → 𝑎 1 ⁢𝑎 2 → 3⁢𝑎 1 → 6⁢𝑏. The analysis uses proton-proton collision data at $\sqrt{𝑠}$ = 13 TeV collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb −1 . No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into 4⁢𝑏 or 6⁢𝑏, between 4% and 25% for 𝜎⁡(𝑍⁢𝐻)/𝜎 SM ⁡(𝑍⁢𝐻) × ℬ⁡(𝐻→ 2⁢𝑎→ 4⁢𝑏), between 24% and 38% for 𝜎⁡(𝑍⁢𝐻)/𝜎 SM ⁡(𝑍⁢𝐻) × ℬ⁡(𝐻 → 𝑎 1 ⁢𝑎 2 → 4⁢𝑏), and between 10% and 20% for 𝜎⁡(𝑍⁢𝐻)/𝜎 SM ⁡(𝑍⁢𝐻) × ℬ⁡(𝐻→𝑎 1⁢ 𝑎 2 → 3⁢𝑎 1 → 6⁢𝑏), depending on the masses of the scalar particles.

extensions of Higgs sector↗
DOE OSTI2026

How state transitions balance photosynthetic electron transport in plants – a quantitative study

In plants, the process of state transition regulates the allocation of sunlight energy between Photosystem II (PSII) and PSI. However, the implications of state transitions for harmonizing electron transport rates between photosystems, and a full quantitative picture of this process, remain underexplored. We integrated quantitative biology (biochemical and biophysical approaches) with in vivo spectroscopy on wild-type Arabidopsis and protein phosphorylation mutants. This combination facilitated monitoring of Chl redistribution and its functional implications for light harvesting and electron transport. Our findings demonstrate the reallocation of 12% of highly phosphorylated ‘extra’ light-harvesting complex II under state 2 from stacked to unstacked thylakoids. This reduces the number of Chls per PSII from 216 to 182, while increasing the number in PSI from 187 to 223. Such Chl redistribution compensates for differences in photosystem stoichiometry and photochemical quantum efficiencies, thereby precisely synchronizing electron transport rates in both photosystems. Mutant analyses corroborate that this regulatory mechanism involves reversible phosphorylation. We inferred that state transitions optimize linear electron transport, leaving no additional capacity for cyclic electron transport. Furthermore, the results suggest that the controversies about long-range migration of LHCII from stacked to unstacked thylakoid domains arise from differences in phosphorylation levels.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Unraveling design principles of protein landscapes in photosynthetic membranes in plant chloroplasts

The supramolecular organization of proteins within photosynthetic membranes is crucial for energy conversion in plants. Here, we introduce an analytical and computational pipeline that integrates high-resolution cryo–scanning electron microscopy, biochemical quantification, advanced Monte Carlo computer simulations, and statistical methods to elucidate the elusive protein landscapes of grana membranes in intact Arabidopsis leaves. Our integrated analysis challenges the prevailing view that particles on the exoplasmic fracture faces in freeze-fracture samples represent photosystem II exclusively. Instead, these particles also include cytochrome b 6 f complexes. Furthermore, our steric clash analysis demonstrates that stacked membranes contain a mixture of larger PSII supercomplexes (C 2 S 2 M 2 and C 2 S 2 ) in addition to a smaller complex (C 2 ). This suggests that in vivo PSII supercomplexes exist in an equilibrium distribution of differing sizes. Furthermore, we discovered that, although size exclusion effects govern the global protein arrangement, local packing exhibits orientational order indicative of lateral attractive protein-protein interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Risk Factors and Trends for HPV-Associated Subsequent Malignant Neoplasms among Adolescent and Young Adult Cancer Survivors

Subsequent malignant neoplasms (SMN; new cancers that arise after an original diagnosis) contribute to premature mortality among adolescent and young adult (AYA) cancer survivors. Because of the high population prevalence of human papillomavirus (HPV) infection, we identify demographic and clinical risk factors for HPV-associated SMNs (HPV-SMN) among AYA cancer survivors in the SEER-9 registries diagnosed from 1976 to 2015. Outcomes included any HPV-SMN, oropharyngeal-SMN, and cervical-SMN. Follow-up started 2 months after their original diagnosis. Standardized incidence ratios (SIR) compared risk between AYA survivors and general population. Age-period-cohort (APC) models examined trends over time. Fine and Gray's models identified therapy effects controlling for cancer and demographic confounders. Of 374,408 survivors, 1,369 had an HPV-SMN, occurring on average 5 years after first cancer. Compared with the general population, AYA survivors had 70% increased risk for any HPV-SMN [95% confidence interval (CI), 1.61–1.79] and 117% for oropharyngeal-SMN (95% CI, 2.00–2.35); cervical-SMN risk was generally lower in survivors (SIR, 0.85; 95% CI, 0.76–0.95), but Hispanic AYA survivors had a 8.4 significant increase in cervical-SMN (SIR, 1.46; 95% CI, 1.01–2.06). AYAs first diagnosed with Kaposi sarcoma, leukemia, Hodgkin, and non-Hodgkin lymphoma had increased HPV-SMN risks compared with the general population. Oropharyngeal-SMN incidence declined over time in APC models. Chemotherapy and radiation were associated with any HPV-SMN among survivors with first HPV-related cancers, but not associated among survivors whose first cancers were not HPV-related. HPV-SMN in AYA survivors are driven by oropharyngeal cancers despite temporal declines in oropharyngeal-SMN. Hispanic survivors are at risk for cervical-SMN relative to the general population. Encouraging HPV vaccination and cervical and oral cancer screenings may reduce HPV-SMN burden among AYA survivors.

60 APPLIED LIFE SCIENCES↗