Transition state structures are central to the rates and outcomes of chemical reactions, but their fleeting existence often leaves their properties to be inferred rather than observed. By treating polybutadiene with a difluorocarbene source, we embedded gem-difluorocyclopropanes (gDFCs) along the polymer backbone. We report that mechanochemical activation of the polymer under tension opens the gDFCs and traps a 1,3-diradical that is formally a transition state in their stress-free electrocyclic isomerization. The trapped diradical lives long enough that we can observe its noncanonical participation in bimolecular addition reactions. Furthermore, the application of a transient tensile force induces a net isomerization of the trans-gDFC into its less-stable cis isomer, leading to the counterintuitive result that the gDFC contracts in response to a transient force of extension.

SummaryDinoflagellates of the genus Symbiodinium express broad diversity in both genetic identity (phylogeny) and photosynthetic function to presumably optimize ecological success across extreme light environments; however, whether differences in the primary photobiological characteristics that govern photosynthetic optimization are ultimately a function of phylogeny is entirely unresolved.We applied a novel fast repetition rate fluorometry approach to screen genetically distinct Symbiodinium types (n = 18) spanning five clades (A-D, F) for potential phylogenetic trends in factors modulating light absorption (effective cross-section, reaction center content) and utilization (photochemical vs dynamic nonphotochemical quenching;The variability of PSII light absorption was independent of phylogenetic designation, but closely correlated with cell size across types, whereas PSII light utilization intriguingly followed one of three characteristic patterns: (1) Our functional trait-based approach shows, for the first time, how Symbiodinium photosynthetic function is governed by the interplay between phylogenetically dependent and independent traits, and is potentially a means to reconcile complex biogeographic patterns of Symbiodinium phylogenetic diversity in nature.

In bacteria, the tubulin homolog FtsZ assembles a cytokinetic ring, termed the Z-ring, and plays a key role in the machinery that constricts to divide the cells. Many archaea encode two FtsZ proteins from distinct families, FtsZ1 and FtsZ2, of previously unclear functions. Here we show that Haloferax volcanii cannot divide properly without either or both FtsZ proteins, but DNA replication continues, and cells proliferate in alternative ways, such as blebbing and fragmentation, via remarkable envelope plasticity. FtsZ1 and FtsZ2 co-localise to form the dynamic division ring. However, FtsZ1 can assemble rings independently of FtsZ2, and stabilises FtsZ2 in the ring, whereas FtsZ2 functions primarily in the constriction mechanism. FtsZ1 also influenced cell shape suggesting it forms a hub-like platform at midcell for the assembly of shape-related systems too. Both FtsZ1 and FtsZ2 are widespread in archaea with a single S-layer envelope, but archaea with a pseudomurein wall and division septum only have FtsZ1. FtsZ1 is therefore likely to provide a fundamental recruitment role in diverse archaea, and FtsZ2 is required for constriction of a flexible S-layer envelope, where an internal constriction force might dominate the division mechanism, in contrast to the single-FtsZ bacteria and archaea that divide primarily by wall ingrowth.

A method for constructing diabatic potential energy matrices by interpolation of ab initio quantum chemistry data is described and tested. This approach is applicable to any number of interacting electronic states, and relies on a formalism and a computational procedure that are more general than those presented previously for the case of two electronic states. The method is tested against an analytic model for three interacting electronic states of NH(3) (+).

A method is presented for constructing diabatic potential energy matrices from ab initio quantum chemistry data. The method is similar to that reported previously for single adiabatic potential energy surfaces, but correctly accounts for the nuclear permutation symmetry of diabatic potential energy matrices and other complications that arise from the derivative coupling of electronic states. The method is tested by comparison with an analytic model for the two lowest energy states of H(3).

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How the functional traits (FTs) of phytoplankton change with temperature is important for understanding the impacts of ocean warming on phytoplankton mediated biogeochemical fluxes. This study quantifies the thermal performance curves (TPCs) of FTs in the cosmopolitan model diatom, Thalassiosira pseudonana, to advance understanding of trade-offs between physiological (photoacclimation, carbon fixation, nitrate, phosphate, and silicate uptake) and morphological traits (cell volume and frustule silicification). We show that each FT has substantial phenotypic plasticity and exhibits a unique TPC, varying in both shape and thermal optimum, and diverging from the growth response. The TPC for growth was symmetric with a thermal optimum (T opt ) of 18 • C. In comparison, the TPC for primary productivity was warm-skewed with a T opt around 21 • C, whereas frustule silicification decreased linearly with increasing temperature. Together, this suggests that the optimal temperature for overall fitness is a balance of trade-offs in the underlying functional traits. Moreover, these results demonstrate that growth is not necessarily an accurate estimate of overall biogeochemical performance and that temperature change will likely influence elemental fluxes such as carbon and silicon. Finally, we show that temperature-driven changes in individual traits e.g., photoacclimation, can mimic responses experienced under other environmental stressors (high light) and so a multi-trait assessment is essential for accurate interpretation of the cellular impact of warming. This study also reveals that multi-trait analysis, in the context of TPCs, provides insight into the cellular physiology regulating the whole cell response and has the potential to provide better estimates of how diatom-mediated biogeochemical fluxes are likely to be impacted in the context of ocean warming. Analyzing the response of multiple traits more comprehensively over other environmental gradients may therefore provide a useful framework to advance understanding of how taxon-specific functional traits will respond to multifaceted ocean change.

Corals are acclimatized to populate dynamic habitats that neighbour coral reefs. Habitats such as seagrass beds exhibit broad diel changes in temperature and pH that routinely expose corals to conditions predicted for reefs over the next 50-100 years. However, whether such acclimatization effectively enhances physiological tolerance to, and hence provides refuge against, future climate scenarios remains unknown. Also, whether corals living in low-variance habitats can tolerate present-day high-variance conditions remains untested. We experimentally examined how pH and temperature predicted for the year 2100 affects the growth and physiology of two dominant Caribbean corals (Acropora palmata and Porites astreoides) native to habitats with intrinsically low (outer-reef terrace, LV) and/or high (neighbouring seagrass, HV) environmental variance. Under present-day temperature and pH, growth and metabolic rates (calcification, respiration and photosynthesis) were unchanged for HV versus LV populations. Superimposing future climate scenarios onto the HV and LV conditions did not result in any enhanced tolerance to colonies native to HV. Calcification rates were always lower for elevated temperature and/or reduced pH. Together, these results suggest that seagrass habitats may not serve as refugia against climate change if the magnitude of future temperature and pH changes is equivalent to neighbouring reef habitats.