Electric-field-induced colour switching in colloidal quantum dot molecules at room temperature.

Colloidal semiconductor quantum dots are robust emitters implemented in numerous prototype and commercial optoelectronic devices. However, active fluorescence colour tuning, achieved so far by electric-field-induced Stark effect, has been limited to a small spectral range, and accompanied by intensity reduction due to the electron-hole charge separation effect. Utilizing quantum dot molecules that manifest two coupled emission centres, we present a unique electric-field-induced instantaneous colour-switching effect. Reversible emission colour switching without intensity loss is achieved on a single-particle level, as corroborated by correlated electron microscopy imaging. Simulations establish that this is due to the electron wavefunction toggling between the two centres, induced by the electric field, and affected by the coupling strength. Quantum dot molecules manifesting two coupled emission centres may be tailored to emit distinct colours, opening the path for sensitive field sensing and colour-switchable devices such as a novel pixel design for displays or an electric-field-induced colour-tunable single-photon source.

Physcomitrium patens response to elevated CO2 is flexible and determined by an interaction between sugar and nitrogen availability.

Mosses hold a unique position in plant evolution and are crucial for protecting natural, long-term carbon storage systems such as permafrost and bogs. Due to small stature, mosses grow close to the soil surface and are exposed to high levels of CO2 , produced by soil respiration. However, the impact of elevated CO2 (eCO2 ) levels on mosses remains underexplored. We determined the growth responses of the moss Physcomitrium patens to eCO2 in combination with different nitrogen levels and characterized the underlying physiological and metabolic changes. Three distinct growth characteristics, an early transition to caulonema, the development of longer, highly pigmented rhizoids, and increased biomass, define the phenotypic responses of P. patens to eCO2 . Elevated CO2 impacts growth by enhancing the level of a sugar signaling metabolite, T6P. The quantity and form of nitrogen source influences these metabolic and phenotypic changes. Under eCO2 , P. patens exhibits a diffused growth pattern in the presence of nitrate, but ammonium supplementation results in dense growth with tall gametophores, demonstrating high phenotypic plasticity under different environments. These results provide a framework for comparing the eCO2 responses of P. patens with other plant groups and provide crucial insights into moss growth that may benefit climate change models.

Isotopically nonstationary metabolic flux analysis of plants: recent progress and future opportunities.

Metabolic flux analysis (MFA) is a valuable tool for quantifying cellular phenotypes and to guide plant metabolic engineering. By introducing stable isotopic tracers and employing mathematical models, MFA can quantify the rates of metabolic reactions through biochemical pathways. Recent applications of isotopically nonstationary MFA (INST-MFA) to plants have elucidated nonintuitive metabolism in leaves under optimal and stress conditions, described coupled fluxes for fast-growing algae, and produced a synergistic multi-organ flux map that is a first in MFA for any biological system. These insights could not be elucidated through other approaches and show the potential of INST-MFA to correct an oversimplified understanding of plant metabolism.

Unveiling the Influence of Brightness Heterogeneity in Fluorescence Correlation Spectroscopy of Perovskite Nanocrystals.

Nanoparticles (NPs), including perovskite nanocrystals (PNCs) with single photon purity, present challenges in fluorescence correlation spectroscopy (FCS) studies due to their distinct photoluminescence (PL) behaviors. In particular, the zero-time correlation amplitude [g2(0)] and the associated diffusion timescale (τD) of their FCS curves show substantial dependency on pump intensity (IP). Optical saturation inadequately explains the origin of this FCS phenomenon in NPs, thus setting them apart from conventional dye molecules, which do not manifest such behavior. This observation is apparently attributed to either photo-brightening or optical trapping, both lead to increased NP occupancy (N) in the excitation volume, consequently reducing the g2(0) amplitude [since g2(0) α 1/N] at high IP. However, an advanced FCS study utilizing alternating laser excitation at two different intensities dismisses such possibilities. Further investigation into single-particle blinking behaviors as a function of IP reveals that the intensity dependence of g2(0) primarily arises from the brightness heterogeneity prevalent in almost all types of NPs. This report delves into the complexities of the photophysical properties of NPs and their adverse impacts on FCS studies.

Metabolic flux analysis of the non-transitory starch tradeoff for lipid production in mature tobacco leaves.

The metabolic plasticity of tobacco leaves has been demonstrated via the generation of transgenic plants that can accumulate over 30% dry weight as triacylglycerols. In investigating the changes in carbon partitioning in these high lipid-producing (HLP) leaves, foliar lipids accumulated stepwise over development. Interestingly, non-transient starch was observed to accumulate with plant age in WT but not HLP leaves, with a drop in foliar starch concurrent with an increase in lipid content. The metabolic carbon tradeoff between starch and lipid was studied using 13CO2-labeling experiments and isotopically nonstationary metabolic flux analysis, not previously applied to the mature leaves of a crop. Fatty acid synthesis was investigated through assessment of acyl-acyl carrier proteins using a recently derived quantification method that was extended to accommodate isotopic labeling. Analysis of labeling patterns and flux modeling indicated the continued production of unlabeled starch, sucrose cycling, and a significant contribution of NADP-malic enzyme to plastidic pyruvate production for the production of lipids in HLP leaves, with the latter verified by enzyme activity assays. The results suggest an inherent capacity for a developmentally regulated carbon sink in tobacco leaves and may in part explain the uniquely successful leaf lipid engineering efforts in this crop.

Coupled Colloidal Quantum Dot Molecules.

ConspectusElectronic coupling and hence hybridization of atoms serves as the basis for the rich properties for the endless library of naturally occurring molecules. Colloidal quantum dots (CQDs) manifesting quantum strong confinement possess atomic-like characteristics with s and p electronic levels, which popularized the notion of CQDs as artificial atoms. Continuing this analogy, when two atoms are close enough to form a molecule so that their orbitals start overlapping, the orbitals energies start to split into bonding and antibonding states made out of hybridized orbitals. The same concept is also applicable for two fused core-shell nanocrystals in close proximity. Their band edge states, which dictate the emitted photon energy, start to hybridize, changing their electronic and optical properties. Thus, an exciting direction of "artificial molecules" emerges, leading to a multitude of possibilities for creating a library of new hybrid nanostructures with novel optoelectronic properties with relevance toward diverse applications including quantum technologies.The controlled separation and the barrier height between two adjacent quantum dots are key variables for dictating the magnitude of the coupling energy of the confined wave functions. In the past, coupled double quantum dot architectures prepared by molecular beam epitaxy revealed a coupling energy of few millielectron volts, which limits the applications to mostly cryogenic operation. The realization of artificial quantum molecules with sufficient coupling energy detectable at room temperature calls for the use of colloidal semiconductor nanocrystal building blocks. Moreover, the tunable surface chemistry widely opens the predesigned attachment strategies as well as the solution processing ability of the prepared artificial molecules, making the colloidal nanocrystals as an ideal candidate for this purpose. Despite several approaches that demonstrated enabling of the coupled structures, a general and reproducible method applicable to a broad range of colloidal quantum materials is needed for systematic tailoring of the coupling strength based on a dictated barrierThis Account addresses the development of nanocrystal chemistry to create coupled colloidal quantum dot molecules and to study the controlled electronic coupling and their emergent properties. The simplest nanocrystal molecule, a homodimer formed from two core/shell nanocrystal monomers, in analogy to homonuclear diatomic molecules, serves as a model system. The shell material of the two CQDs is structurally fused, resulting in a continuous crystal. This lowers the potential energy barrier, enabling the hybridization of the electronic wave functions. The direct manifestation of the hybridization reflects on the band edge transition shifting toward lower energy and is clearly resolved at room temperature. The hybridization energy within the single homodimer molecule is strongly correlated with the extent of structural continuity, the delocalization of the exciton wave function, and the barrier thickness as calculated numerically. The hybridization impacts the emitted photon statistics manifesting faster radiative decay rate, photon bunching effect, and modified Auger recombination pathway compared to the monomer artificial atoms. Future perspectives for the nanocrystals chemistry paradigm are also highlighted.

An efficient LC-MS method for isomer separation and detection of sugars, phosphorylated sugars, and organic acids.

Assessing central carbon metabolism in plants can be challenging due to the dynamic range in pool sizes, with low levels of important phosphorylated sugars relative to more abundant sugars and organic acids. Here, we report a sensitive liquid chromatography-mass spectrometry method for analysing central metabolites on a hybrid column, where both anion-exchange and hydrophilic interaction chromatography (HILIC) ligands are embedded in the stationary phase. The liquid chromatography method was developed for enhanced selectivity of 27 central metabolites in a single run with sensitivity at femtomole levels observed for most phosphorylated sugars. The method resolved phosphorylated hexose, pentose, and triose isomers that are otherwise challenging. Compared with a standard HILIC approach, these metabolites had improved peak areas using our approach due to ion enhancement or low ion suppression in the biological sample matrix. The approach was applied to investigate metabolism in high lipid-producing tobacco leaves that exhibited increased levels of acetyl-CoA, a precursor for oil biosynthesis. The application of the method to isotopologue detection and quantification was considered through evaluating 13C-labeled seeds from Camelina sativa. The method provides a means to analyse intermediates more comprehensively in central metabolism of plant tissues.

Luminescent Anisotropic Wurtzite InP Nanocrystals.

Indium phosphide (InP) nanocrystals are emerging as an alternative to heavy metal containing nanocrystals for optoelectronic applications but lag behind in terms of synthetic control. Herein, luminescent wurtzite InP nanocrystals with narrow size distribution were synthesized via a cation exchange reaction from hexagonal Cu3P nanocrystals. A comprehensive surface treatment with NOBF4 was performed, which removes excess copper while generating stoichiometric In/P nanocrystals with fluoride surface passivation. The attained InP nanocrystals manifest a highly resolved absorption spectrum with a narrow emission line of 80 meV, and photoluminescence quantum yield of up to 40%. Optical anisotropy measurements on ensemble and single particle bases show the occurrence of polarized transitions directly mirroring the anisotropic wurtzite lattice, as also manifested from modeling of the quantum confined electronic levels. This shows a green synthesis path for achieving wurtzite InP nanocrystals with desired optoelectronic properties including color purity and light polarization with potential for diverse optoelectronic applications.

Neck Barrier Engineering in Quantum Dot Dimer Molecules via Intraparticle Ripening.

Coupled colloidal quantum dot (CQD) dimers represent a new class of artificial molecules composed of fused core/shell semiconductor nanocrystals. The electronic coupling and wave function hybridization are enabled by the formation of an epitaxial connection with a coherent lattice between the shells of the two neighboring quantum dots where the shell material and its dimensions dictate the quantum barrier characteristics for the charge carriers. Herein we introduce a colloidal approach to control the neck formation at the interface between the two CQDs in such artificial molecular constructs. This allows the tailoring of the neck barrier in prelinked homodimers formed via fusion of multifaceted wurtzite CdSe/CdS CQDs. The effects of reaction time, temperature, and excess ligands are studied. The neck filling process follows an intraparticle ripening mechanism at relatively mild reaction conditions while avoiding interparticle ripening. The degree of surface ligand passivation plays a key role in activating the surface atom diffusion to the neck region. The degree of neck filling strongly depends also on the initial relative orientation of the two CQDs, where homonymous plane attachment allows for facile neck growth, unlike the case of heteronymous plane attachment. Upon neck filling, the observed red-shift of the absorption and fluorescence measured both for ensemble and single dimers is assigned to enhanced hybridization of the confined wave function in CQD dimer molecules, as supported by quantum calculations. The fine-tuning of the particle interface introduced herein provides therefore a powerful tool to further control the extent of hybridization and coupling in CQD molecules.

ZnSe/ZnS Core/Shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth.

Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and biotagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission line width. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on-off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.

Semiconductor Bow-Tie Nanoantenna from Coupled Colloidal Quantum Dot Molecules.

Top-down fabricated nanoantenna architectures of both metallic and dielectric materials show powerful functionalities for Raman and fluorescence enhancement with relevance to single molecule sensing while inducing directionality of chromophore emission with implications for single photon sources. We synthesize the smallest bow-tie nanoantenna by selective tip-to-tip fusion of two tetrahedral colloidal quantum dots (CQDs) forming a dimer. While the tetrahedral monomers emit non-polarized light, the bow-tie architecture manifests nanoantenna functionality of enhanced emission polarization along the bow-tie axis, as predicted theoretically and revealed by single-particle spectroscopy. Theory also predicts the formation of an electric-field hotspot at the bow-tie epicenter. This is utilized for selective light-induced photocatalytic metal growth at that location, unlike growth on the free tips in dark conditions, thus demonstrating bow-tie dimer functionality as a photochemical reaction center.

Electronic coupling in colloidal quantum dot molecules; the case of CdSe/CdS core/shell homodimers.

Coupled colloidal quantum dot molecules composed of two fused CdSe/CdS core/shell sphere monomers were recently presented. Upon fusion, the potential energy landscape changes into two quantum dots separated by a pretuned potential barrier with energetics dictated by the conduction and valence band offsets of the core/shell semiconductors and the width controlled by the shell thickness and the fusion reaction conditions. In close proximity of the two nanocrystals, orbital hybridization occurs, forming bonding and antibonding states in analogy to the hydrogen molecule. In this study, we examine theoretically the electronic and optical signatures of such a quantum dot dimer compared to its monomer core/shell building-blocks. We examine the effects of different core sizes, barrier widths, different band offsets, and neck sizes at the interface of the fused facets on the system wave-functions and energetics. Due to the higher effective mass of the hole and the large valence band offset, the hole still essentially resides in either of the cores, breaking the symmetry of the potential for the electron as well. We found that the dimer signature is well expressed in a red shift of the band gap both in absorption and emission, in slower radiative lifetimes and in an absorption cross section which is significantly enhanced relative to the monomers at energies above the shell absorption onset, while remains essentially at the same level near the band-edge. This study provides essential guidance to predesign of coupled quantum dot molecules with specific attributes which can be utilized for various new opto-electronic applications.

Spectroscopic and Calorimetric Studies of Molecular Recognitions in a Dendrimer-Surfactant Complex.

Molecular recognitions, causing supramolecular complex formation between a hyperbranched polymer molecule (polyamidoamine (PAMAM) dendrimer generation 3) with oppositely charged surfactant sodium dodecyl sulfate (SDS) in aqueous solution, were studied by using various spectroscopic techniques and calorimetric titration of heat change measurements. Spectroscopic measurements were performed using dynamic Stokes shift (DSS), rotational anisotropy decay, and translational diffusion of a fluorescent probe molecule coumarin 153 (C153) noncovalently attached to the dendrimer-surfactant complex. All these studies unanimously confirm that the critical aggregation concentration (CAC) of SDS falls to ∼0.8 mM (from its critical micelle concentration (CMC) ∼ 8 mM) in the presence of ∼0.2 mM dendrimer. Further studies of isothermal titration calorimetry (ITC) measurement show that the CAC of SDS in the presence of dendrimer remains invariant to the dendrimer concentration. Complexation reaction between SDS and dendrimer is highly exothermic in nature. A maximum heat release (ΔH∼ -6.6 kJ/mol of SDS binding) was observed at a SDS-to-dendrimer mole ratio of ∼3-5; where up to 3 to 5 SDS molecules were encapsulated by one dendrimer molecule to form dendrimer-SDS encapsulation complex. When negatively charged SDS was replaced with a positively charged surfactant dodecyl-trimethylammonium-bromide (DTAB), we found that the DTAB hardly interacted with positively charged dendrimer due to the charge-charge repulsions.

A deeper insight into an intriguing acetonitrile-water binary mixture: synergistic effect, dynamic Stokes shift, fluorescence correlation spectroscopy, and NMR studies.

An insight study reveals the strong synergistic solvation behaviours from reporter dye molecules within the acetonitrile (ACN)-water (WT) binary mixture. Synergism of a binary mixture refers to some unique changes of the physical and thermodynamic properties of the solvent mixture, originating from the interactions among its cosolvents, which are absent within the pure cosolvents. Synergistic solvation of a binary mixture is likely to be fundamental for greater stabilization of an excited state solute dipole; at least to some extent greater as compared to one stabilized by any of its cosolvents alone. A dynamic Stokes shift due to the solvation of an excited dipole in the ACN-WT binary mixture is found to be highly relevant to the ground state physical properties of the solute molecule (polarity, hydrophilicity, acidity, etc.). Largely different solvation times in the ACN-WT mixture are observed from different dye molecules with widely varying polarities. However, earlier study shows that dye molecules, irrespective of their varying polarities, exhibit very similar solvation times within a pure solvent (J. Phys. Chem. B, 2014, 118, 7577-7785). On further study with fluorescence correlation spectroscopy (FCS) we observed that, unlike the translational diffusion coefficient (Dt) of a dye molecule within a pure solvent, which remains the same irrespective of the location of the dye molecule inside the solvent, a broad distribution among the Dt values of a dye molecule is obtained from different locations within the ACN-WT binary mixture. Lastly our 1H NMR study in the ACN-WT binary mixture shows the existence of strong hydrogen bond interactions among the cosolvents in the ACN-WT mixture.

The study of electron transfer reactions in a dendrimeric assembly: proper utilization of dendrimer fluorescence.

The PAMAM dendrimer with a cage like structure acts as an excellent electron donor in the presence of an electron deficient molecule. Electron transfer (ET) causes significant quenching of dendrimer fluorescence. Trapping of quencher molecules within the dendrimer cage helps ET to take place through an expeditious route. Utilization of intrinsic fluorescence and sensing applications of dendrimers have been established here.

Study of Microheterogeneity in Acetonitrile-Water Binary Mixtures by using Polarity-Resolved Solvation Dynamics.

The solvation dynamics of three coumarin dyes with widely varying polarities were studied in acetonitrile-water (ACN-H2O) mixtures across the entire composition range. At low ACN concentrations [ACN mole fractions (X(ACN))≤0.1], the solvation dynamics are fast (<40 ps), indicating a nearly homogeneous environment. This fast region is followed by a sudden retardation of the average solvation time (230-1120 ps) at higher ACN concentrations (X(ACN)≈0.2), thus indicating the onset of nonideality within the mixture that continues until X(ACN)≈0.8. This nonideality regime (X(ACN)≈0.2-0.8) comprises of multiple dye-dependent anomalous regions. At very high ACN concentrations (X(ACN)≈0.8-1), the ACN-H2O mixtures regain homogeneity, with faster solvation times. The source of the inherent nonideality of the ACN-H2O mixtures is a subject of debate. However, a careful examination of the widths of time-resolved emission spectra shows that the origin of the slow dynamics may be due to the diffusion of polar solvent molecules into the first solvation shell of the excited coumarin dipole.

Probe dependent anomalies in the solvation dynamics of coumarin dyes in dimethyl sulfoxide-glycerol binary solvent: confirming the local environments are different for coumarin dyes.

The solvation dynamics of coumarin dyes in dimethyl sulfoxide (DMSO)-glycerol (GLY) binary mixtures were studied across the GLY concentrations. Three coumarin dyes with widely different hydrophobicities were used for probing the entire polarity regions of this solvent mixture. Multiple anomalous concentration regions with significantly slow solvation times were detected from all three coumarin dyes. However, their precise positions were found to be probe molecule dependent. The solvation dynamics of the moderately hydrophobic dye coumarin 480 (C480) maintain a plateau region with a similar solvation time (∼550 ps) with the increase in GLY concentration until X(GLY) (the mole fraction of glycerol) reaches 0.5. This plateau region is followed by a sudden slowdown (to ∼975 ps) on the addition of more GLY to the DMSO-GLY mixture, and then this slow region persists from X(GLY)∼ 0.55 to 0.65 (peak at 0.6). On further addition of GLY (X(GLY) > 0.7), the solvation dynamics again become slower to ∼828 ps (at X(GLY)∼ 0.8) from ∼612 ps (at X(GLY)∼ 0.7). For very high GLY-content samples (X(GLY) > 0.85), the solvation times remain similar on further changes of the GLY concentrations. In contrast to C480, the most hydrophobic dye coumarin 153 (C153) shows a linear increase of solvation time in the DMSO-GLY mixture, from 102 ps (at X(GLY)∼ 0.1) to 946 ps (at X(GLY)∼ 0.9) with increase in GLY concentration, except for the concentration region, X(GLY)∼ 0.45-0.55 (peak at 0.5), where a substantial slowdown of the solvation time is observed. The highly hydrophilic probe coumarin 343 (C343) demonstrates multiple concentration regions (X(GLY)∼ 0.05-0.10, 0.25-0.35 and 0.55-0.65) where the solvation dynamics are significantly retarded. The presence of probe dependent anomalies in the DMSO-GLY mixture is a clear indication of there being different locations of probe molecules within this solvent mixture. We assume that the slowing-down of the solvation time could be a reflection of several aspects, including the inherit inhomogeneity, intriguing structural transformations in the DMSO-GLY mixture, percolation among DMSO molecules and network structure formation, where DMSO:GLY complexes contribute to the dynamical features.

SIMPEL: using stable isotopes to elucidate dynamics of context specific metabolism.

The capacity to leverage high resolution mass spectrometry (HRMS) with transient isotope labeling experiments is an untapped opportunity to derive insights on context-specific metabolism, that is difficult to assess quantitatively. Tools are needed to comprehensively mine isotopologue information in an automated, high-throughput way without errors. We describe a tool, Stable Isotope-assisted Metabolomics for Pathway Elucidation (SIMPEL), to simplify analysis and interpretation of isotope-enriched HRMS datasets. The efficacy of SIMPEL is demonstrated through examples of central carbon and lipid metabolism. In the first description, a dual-isotope labeling experiment is paired with SIMPEL and isotopically nonstationary metabolic flux analysis (INST-MFA) to resolve fluxes in central metabolism that would be otherwise challenging to quantify. In the second example, SIMPEL was paired with HRMS-based lipidomics data to describe lipid metabolism based on a single labeling experiment. Available as an R package, SIMPEL extends metabolomics analyses to include isotopologue signatures necessary to quantify metabolic flux.

Complete Mapping of Interacting Charging States in Single Coupled Colloidal Quantum Dot Molecules.

Colloidal quantum dots (CQDs), major building blocks in modern optoelectronic devices, have so far been synthesized with only one emission center where the exciton resides. Recent development of coupled colloidal quantum dots molecules (CQDM), where two core-shell CQDs are fused to form two emission centers in close proximity, allows exploration of how charge carriers in one CQD affect the charge carriers in the other CQD. Cryogenic single particle spectroscopy reveals that while CQD monomers manifest a simple emission spectrum comprising a main emission peak with well-defined phonon sidebands, CQDMs exhibit a complex spectrum with multiple peaks that are not all spaced according to the known phonon frequencies. Based on complementary emission polarization and time-resolved analysis, this is assigned to fluorescence of the two coupled emission centers. Moreover, the complex peak structure shows correlated spectral diffusion indicative of the coupling between the two emission centers. Utilizing Schrödinger-Poisson self-consistent calculations, we directly map the spectral behavior, alternating between neutral and charged states of the CQDM. Spectral shifts related to electrostatic interaction between a charged emission center and the second emission center are thus fully mapped. Furthermore, effects of moving surface charges are identified, whereby the emission center proximal to the charge shows larger shifts. Instances where the two emission centers are negatively charged simultaneously are also identified. Such detailed mapping of charging states is enabled by the coupling within the CQDM and its anisotropic structure. This understanding of the coupling interactions is progress toward quantum technology and sensing applications based on CQDMs.

Metabolic synergy in Camelina reproductive tissues for seed development.

Photosynthesis in fruits is well documented, but its contribution to seed development and yield remains largely unquantified. In oilseeds, the pods are green and elevated with direct access to sunlight. With 13C labeling in planta and through an intact pod labeling system, a unique multi-tissue comprehensive flux model mechanistically described how pods assimilate up to one-half (33 to 45%) of seed carbon by proximal photosynthesis in Camelina sativa. By capturing integrated tissue metabolism, the studies reveal the contribution of plant architecture beyond leaves, to enable seed filling and maximize the number of viable seeds. The latent capacity of the pod wall in the absence of leaves contributes approximately 79% of seed biomass, supporting greater seed sink capacity and higher theoretical yields that suggest an opportunity for crop productivity gains.