Variation in leaf dark respiration among C3 and C4 grasses is associated with use of different substrates.

Measurements of respiratory properties have often been made at a single time point either during daytime using dark-adapted leaves or during night-time. The influence of the day-night cycle on respiratory metabolism has received less attention but is crucial to understand photosynthesis and photorespiration. Here, we examined how CO2- and O2-based rates of leaf dark respiration (Rdark) differed between midday (after 30-minute dark adaptation) and midnight in eight C3 and C4 grasses. We used these data to calculate the respiratory quotient (RQ; ratio of CO2 release to O2 uptake), and assessed relationships between Rdark and leaf metabolome. Rdark was higher at midday than midnight, especially in C4 species. The day-night difference in Rdark was more evident when expressed on a CO2 than O2 basis, with the RQ being higher at midday than midnight in all species, except in rice (Oryza sativa). Metabolomic analyses showed little correlation of Rdark or RQ with leaf carbohydrates (sucrose, glucose, fructose or starch) but strong multivariate relationships with other metabolites. The results suggest that rates of Rdark and differences in RQ were determined by several concurrent CO2-producing and O2-consuming metabolic pathways, not only the tricarboxylic acid cycle (organic acids utilisation), but also the pentose phosphate pathway, galactose metabolism, and secondary metabolism. As such, Rdark was time-, type- (C3/C4) and species-dependent, due to the use of different substrates.

Perception of butenolides by Bacillus subtilis via the α/ß hydrolase RsbQ.

The regulation of behavioral and developmental decisions by small molecules is common to all domains of life. In plants, strigolactones and karrikins are butenolide growth regulators that influence several aspects of plant growth and development, as well as interactions with symbiotic fungi.1,2,3 DWARF14 (D14) and KARRIKIN INSENSITIVE2 (KAI2) are homologous enzyme-receptors that perceive strigolactones and karrikins, respectively, and that require hydrolase activity to effect signal transduction.4,5,6,7 RsbQ, a homolog of D14 and KAI2 from the gram-positive bacterium Bacillus subtilis, regulates growth responses to nutritional stress via the alternative transcription factor SigmaB (σB).8,9 However, the molecular function of RsbQ is unknown. Here, we show that RsbQ perceives butenolide compounds that are bioactive in plants. RsbQ is thermally destabilized by the synthetic strigolactone GR24 and its desmethyl butenolide equivalent dGR24. We show that, like D14 and KAI2, RsbQ is a functional butenolide hydrolase that undergoes covalent modification of the catalytic histidine residue. Exogenous application of both GR24 and dGR24 inhibited the endogenous signaling function of RsbQ in vivo, with dGR24 being 10-fold more potent. Application of dGR24 to B. subtilis phenocopied loss-of-function rsbQ mutations and led to a significant downregulation of σB-regulated transcripts. We also discovered that exogenous butenolides promoted the transition from planktonic to biofilm growth. Our results suggest that butenolides may serve as inter-kingdom signaling compounds between plants and bacteria to help shape rhizosphere communities.

Causes of Low Milk Supply: The Roles of Estrogens, Progesterone, and Related External Factors.

Low milk supply (LMS) poses a significant challenge to exclusive and continued breastfeeding, affecting ∼10% to 15% of mothers. Milk production is intricately regulated by both endocrine and autocrine control mechanisms, with estrogens and progesterone playing pivotal roles in this process. In addition to endogenously produced hormones, external substances capable of interfering with normal hormonal actions, including phytoestrogens, mycoestrogens, synthetic estrogens, and hormonal contraceptives, can influence milk production. The effects of these extrinsic hormones on milk production may vary based on maternal body mass index. This comprehensive review examines the multifaceted causes of LMS, focusing on the involvement of estrogens, progesterone, and related external factors in milk production. Furthermore, it investigates the interplay between hormonal factors and obesity, aiming to elucidate the endocrine mechanisms underlying obesity-associated LMS. Insights from this review provide valuable perspectives for developing interventions to improve milk production and address the challenges associated with LMS.

Photosynthesis in newly developed leaves of heat-tolerant wheat acclimates to long-term nocturnal warming.

We examined photosynthetic traits of pre-existing and newly developed flag leaves of four wheat genotypes grown in controlled-environment experiments. In newly developed leaves, acclimation of the maximum rate of net CO2 assimilation (An) to warm nights (i.e. increased An) was associated with increased capacity of Rubisco carboxylation and photosynthetic electron transport, with Rubisco activation state probably contributing to increased Rubisco activity. Metabolite profiling linked acclimation of An to greater accumulation of monosaccharides and saturated fatty acids in leaves; these changes suggest roles for osmotic adjustment of leaf turgor pressure and maintenance of cell membrane integrity. By contrast, where An decreased under warm nights, the decline was related to lower stomatal conductance and rates of photosynthetic electron transport. Decreases in An occurred despite higher basal PSII thermal stability in all genotypes exposed to warm nights: Tcrit of 45-46.5 °C in non-acclimated versus 43.8-45 °C in acclimated leaves. Pre-existing leaves showed no change in An-temperature response curves, except for an elite heat-tolerant genotype. These findings illustrate the impact of night-time warming on the ability of wheat plants to photosynthesize during the day, thereby contributing to explain the impact of global warming on crop productivity.

Enhancing crop yields through improvements in the efficiency of photosynthesis and respiration.

The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential ( Y p ) of crops is vital to address these challenges. In this review, we explore a component of Y p that has yet to be optimised - that being improvements in the efficiency with which light energy is converted into biomass ( ε c ) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production ( ε prod ) and efficiency of ATP use ( ε use ). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential for ε prod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improve ε use via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high-throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step-change in yield potential of globally important crops.

Distinct salinity-induced changes in wheat metabolic machinery in different root tissue types.

The impact of salinity on wheat plants is often studied by analysis of shoot responses, even though the main mechanism of tolerance is shoot Na+ exclusion. Wheat roots directly experience rising NaCl concentrations and show more physiological responses in root tips than in mature roots and altered responses with time; but the molecular reason for these differential responses is unclear. We have found that there is a distinct difference between the proteome responses of wheat root tip and mature root tissues to salinity. Translation and protein synthesis related proteins showed a significant decrease in abundance, most of the glycolytic enzymes and selected TCA cycle enzymes and ATP synthase subunits were significantly decreased in abundance under salt stress in root tips only. The root tip response in wheat indicates the protein synthesis capacity and energy production were impaired under salt stress which correlated with the anatomical response of root growth decrease and its respiratory rate. Wheat root responses are direct and rapid effects of the soil salinity in this species, therefore shoot responses such as reduction in shoot growth and photosynthetic capacity need to be considered in light of these effects on root metabolism. SIGNIFICANCE: Salinity is a critical environmental factor limiting crop production throughout the world. Wheat (Triticum aestivum) is the most significant cereal crop for human nutrition and both its growth and yield is negatively impacted by salinity. Salinity stress is known to impose osmotic stress in plants during the initial phase of exposure and ion toxicity in the later stages of development. Roots are the first plant organ to perceive the salt. However, intensive breading approaches to develop salt tolerant crops have mainly focussed on exclusion of salt from above ground tissues, and only achieved limited success to date. Wheat roots physiologically respond to salinity by overall reduction in the length of seminal roots. The stunting of the wheat root system is considered to be a result of higher sensitivity of root tips to salinity. However, the metabolic changes that underpin selective root tip sensitivity is largely unknown. Here, we carried out non-targeted profiling of mature root versus root tip proteomes under control and salt stress conditions. We found distinct changes in abundance of proteins involved in carbon and energy metabolism and protein metabolism in mature roots and root tips in response to salt stress. We further investigated the impact of these changes on metabolic machinery in the wheat root proteome using a targeted MS approach. We found evidence that protein synthesis and energy production machinery becomes limiting in root tips, while the same processes in mature root remains less affected by salt stress. Our proteomic data explain the impairment of root growth and physiological characteristics as well as improve the understanding of wheat root responses under salinity which is an essential first step for further investigation of molecular traits underpinning root characteristics to improve salt tolerance of wheat.

Assessment of Mitochondrial Protein Composition and Purity by Mass Spectroscopy.

While the routine mitochondrial extraction and isolation protocols have not fundamentally changed since the introduction of density gradients, the approaches we use to examine the proteome have. The initial characterisation of mitochondrial proteomes was carried out using two-dimensional gel electrophoresis in 2001 and gel spot mass spectrometry have now largely been superseded as the throughput and sensitivity of commercial mass spectrometers increases. Whist many of these early studies established the components of the mitochondrial proteome, as gels were replaced by gel free approaches the numbers of confirmed components rapidly increased. In this chapter we present gel-based approaches for the separation and concentration of mitochondrial proteins for their characterization by mass spectrometry. We also describe two gel-free approaches which can be used to quantity the degree of contamination arising during the isolation of mitochondria. These approaches are equally suitable for studies comparing one treatment to another.

Addressing Research Bottlenecks to Crop Productivity.

Asymmetry of investment in crop research leads to knowledge gaps and lost opportunities to accelerate genetic gain through identifying new sources and combinations of traits and alleles. On the basis of consultation with scientists from most major seed companies, we identified several research areas with three common features: (i) relatively underrepresented in the literature; (ii) high probability of boosting productivity in a wide range of crops and environments; and (iii) could be researched in 'precompetitive' space, leveraging previous knowledge, and thereby improving models that guide crop breeding and management decisions. Areas identified included research into hormones, recombination, respiration, roots, and source-sink, which, along with new opportunities in phenomics, genomics, and bioinformatics, make it more feasible to explore crop genetic resources and improve breeding strategies.

Can Alternative Metabolic Pathways and Shunts Overcome Salinity Induced Inhibition of Central Carbon Metabolism in Crops?

The annual cost of lost crop production from exposure to salinity has major impacts on food security in all parts of the world. Salinity stress disturbs energy metabolism and knowledge of the impacts on critical processes controlling plant energy production is key to successfully breeding salt tolerant crops. To date, little progress has been achieved using classic breeding approaches to develop salt tolerance. The hope of some salinity researchers is that through a better understanding of the metabolic responses and adaptation to salinity exposure, new breeding targets can be suggested to help develop salt tolerant crops. Plants sense and react to salinity through a complex system of sensors, receptor systems, transporters, signal transducers, and gene expression regulators in order to control the uptake of salts and to induce tolerant metabolism that jointly leads to changes in growth rate and biomass production. During this response, there must be a balance between supply of energy from mitochondria and chloroplasts and energy demands for water and ion transport, growth, and osmotic adjustment. The photosynthetic response to salinity has been thoroughly researched and generally we see a sharp drop in photosynthesis after exposure to salinity. However, less attention has been given to the effect of salt stress on plant mitochondrial respiration and the metabolic processes that influence respiratory rate. A further complication is the wide range of respiratory responses that have been observed in different plant species, which have included major and minor increases, decreases, and no change in respiratory rate after salt exposure. In this review, we begin by considering physiological and biochemical impacts of salinity on major crop plants. We then summarize and consider recent advances that have characterized changes in abundance of metabolites that are involved in respiratory pathways and their alternative routes and shunts in terms of energy metabolism in crop plants. We will consider the diverse molecular responses of cellular plant metabolism during salinity exposure and suggest how these metabolic responses might aid in salinity tolerance. Finally, we will consider how this commonality and diversity should influence how future research of the salinity responses of crops plants should proceed.

Diel- and temperature-driven variation of leaf dark respiration rates and metabolite levels in rice.

Leaf respiration in the dark (Rdark ) is often measured at a single time during the day, with hot-acclimation lowering Rdark at a common measuring temperature. However, it is unclear whether the diel cycle influences the extent of thermal acclimation of Rdark , or how temperature and time of day interact to influence respiratory metabolites. To examine these issues, we grew rice under 25°C : 20°C, 30°C : 25°C and 40°C : 35°C day : night cycles, measuring Rdark and changes in metabolites at five time points spanning a single 24-h period. Rdark differed among the treatments and with time of day. However, there was no significant interaction between time and growth temperature, indicating that the diel cycle does not alter thermal acclimation of Rdark . Amino acids were highly responsive to the diel cycle and growth temperature, and many were negatively correlated with carbohydrates and with organic acids of the tricarboxylic acid (TCA) cycle. Organic TCA intermediates were significantly altered by the diel cycle irrespective of growth temperature, which we attributed to light-dependent regulatory control of TCA enzyme activities. Collectively, our study shows that environmental disruption of the balance between respiratory substrate supply and demand is corrected for by shifts in TCA-dependent metabolites.

Protein corona formation moderates the release kinetics of ion channel antagonists from transferrin-functionalized polymeric nanoparticles.

Transferrin (Tf)-functionalized p(HEMA-ran-GMA) nanoparticles were designed to incorporate and release a water-soluble combination of three ion channel antagonists, namely zonampanel monohydrate (YM872), oxidized adenosine triphosphate (oxATP) and lomerizine hydrochloride (LOM) identified as a promising therapy for secondary degeneration that follows neurotrauma. Coupled with a mean hydrodynamic size of 285 nm and near-neutral surface charge of -5.98 mV, the hydrophilic nature of the functionalized polymeric nanoparticles was pivotal in effectively encapsulating the highly water soluble YM872 and oxATP, as well as lipophilic LOM dissolved in water-based medium, by a back-filling method. Maximum loading efficiencies of 11.8 ± 1.05% (w/w), 13.9 ± 1.50% (w/w) and 22.7 ± 4.00% (w/w) LOM, YM872 and oxATP respectively were reported. To obtain an estimate of drug exposure in vivo, drug release kinetics assessment by HPLC was conducted in representative physiological milieu containing 55% (v/v) human serum at 37 °C. In comparison to serum-free conditions, it was demonstrated that the inevitable adsorption of serum proteins on the Tf-functionalized nanoparticle surface as a protein corona impeded the rate of release of LOM and YM872 at both pH 5 and 7.4 over a period of 1 hour. While the release of oxATP from the nanoparticles was detectable for up to 30 minutes under serum-free conditions at pH 7.4, the presence of serum proteins and a slightly acidic environment impaired the detection of the drug, possibly due to its molecular instability. Nevertheless, under representative physiological conditions, all three drugs were released in combination from Tf-functionalized p(HEMA-ran-GMA) nanoparticles and detected for up to 20 minutes. Taken together, the study provided enhanced insight into potential physiological outcomes in the presence of serum proteins, and suggests that p(HEMA-ran-GMA)-based therapeutic nanoparticles may be promising drug delivery vehicles for CNS therapy.

Energy costs of salt tolerance in crop plants.

Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H+ -ATPase also is a critical component. One proposed leak, that of Na+ influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na+ and Cl- concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components.

Wheat mitochondrial respiration shifts from the tricarboxylic acid cycle to the GABA shunt under salt stress.

Mitochondrial respiration and tricarboxylic acid (TCA) cycle activity are required during salt stress in plants to provide ATP and reductants for adaptive processes such as ion exclusion, compatible solute synthesis and reactive oxygen species (ROS) detoxification. However, there is a poor mechanistic understanding of how salinity affects mitochondrial metabolism, particularly respiratory substrate source. To determine the mechanism of respiratory changes under salt stress in wheat leaves, we conducted an integrated analysis of metabolite content, respiratory rate and targeted protein abundance measurements. Also, we investigated the direct effect of salt on mitochondrial enzyme activities. Salt-treated wheat leaves exhibit higher respiration rate and extensive metabolite changes. The activity of the TCA cycle enzymes pyruvate dehydrogenase complex and the 2-oxoglutarate dehydrogenase complex were shown to be directly salt-sensitive. Multiple lines of evidence showed that the γ-aminobutyric acid (GABA) shunt was activated under salt treatment. During salt exposure, key metabolic enzymes required for the cyclic operation of the TCA cycle are physiochemically inhibited by salt. This inhibition is overcome by increased GABA shunt activity, which provides an alternative carbon source for mitochondria that bypasses salt-sensitive enzymes, to facilitate the increased respiration of wheat leaves.

Elucidating the Inability of Functionalized Nanoparticles to Cross the Blood-Brain Barrier and Target Specific Cells in Vivo.

The adsorption of serum proteins on the surface of nanoparticles (NPs) delivered into a biological environment has been known to alter NP surface properties and consequently their targeting efficiency. In this paper, we use random copolymer (p(HEMA- ran-GMA))-based NPs synthesized using 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA). We show that serum proteins bind to the NP and that functionalization with antibodies and peptides designed to facilitate NP passage across the blood-brain barrier (BBB) to bind specific cell types is ineffective. In particular, we use systematic in vitro and in vivo analyses to demonstrate that p(HEMA- ran-GMA) NPs functionalized with HIV-1 trans-activating transcriptor peptide (known to cross the BBB) and α neural/glial antigen 2 (NG2) (known for targeting oligodendrocyte precursor cells (OPCs)), individually and in combination, do not specifically target OPCs and are unable to cross the BBB, likely due to the serum protein binding to the NPs.

An Ancient Peptide Family Buried within Vicilin Precursors.

New proteins can evolve by duplication and divergence or de novo, from previously noncoding DNA. A recently observed mechanism is for peptides to evolve within a "host" protein and emerge by proteolytic processing. The first examples of such interstitial peptides were ones hosted by precursors for seed storage albumin. Interstitial peptides have also been observed in precursors for seed vicilins, but current evidence for vicilin-buried peptides (VBPs) is limited to seeds of the broadleaf plants pumpkin and macadamia. Here, an extensive sequence analysis of vicilin precursors suggested that peptides buried within the N-terminal region of preprovicilins are widespread and truly ancient. Gene sequences indicative of interstitial peptides were found in species from Amborellales to eudicots and include important grass and legume crop species. We show the first protein evidence for a monocot VBP in date palm seeds as well as protein evidence from other crops including the common tomato, sesame and pumpkin relatives, cucumber, and the sponge loofah ( Luffa aegyptiaca). Their excision was consistent with asparaginyl endopeptidase-mediated maturation, and sequences were confirmed by tandem mass spectrometry. Our findings suggest that the family is large and ancient and that based on the NMR solution structures for loofah Luffin P1 and tomato VBP-8, VBPs adopt a helical hairpin fold stapled by two internal disulfide bonds. The first VBPs characterized were a protease inhibitor, antimicrobials, and a ribosome inactivator. The age and evolutionary retention of this peptide family suggest its members play important roles in plant biology.

Cold sensitivity of mitochondrial ATP synthase restricts oxidative phosphorylation in Arabidopsis thaliana.

The combined action of the electron transport chain (ETC) and ATP synthase is essential in determining energy efficiency in plants, and so is important for cellular biosynthesis, growth and development. Owing to the sessile nature of plants, mitochondria must operate over a wide temperature range in the environment, necessitating a broad temperature tolerance of their biochemical reactions. We investigated the temperature response of mitochondrial respiratory processes in isolated mitochondria and intact plants of Arabidopsis thaliana and considered the effect of instantaneous responses to temperature and acclimation responses to low temperatures. We show that at 4°C the plant mitochondrial ATP synthase is differentially inhibited compared with other elements of the respiratory pathway, leading to decreased ADP : oxygen ratios and a limitation to the rate of ATP synthesis. This effect persists in vivo and cannot be overcome by cold-temperature acclimation of plants. This mechanism adds a new element to the respiratory acclimation model and provides a direct means of temperature perception by plant mitochondria. This also provides an alternative explanation for non-phosphorylating ETC bypass mechanisms, like the alternative oxidase to maintain respiratory rates, albeit at lower ATP synthesis efficiency, in response to the sensitivity of ATP synthase to the prevailing temperature.

Editorial for Special Issue "Plant Mitochondria".

The primary function of mitochondria is respiration, where catabolism of substrates is coupled to adenosine triphosphate (ATP) synthesis via oxidative phosphorylation (OxPhos). [...].

A family of small, cyclic peptides buried in preproalbumin since the Eocene epoch.

Orbitides are cyclic ribosomally-synthesized and post-translationally modified peptides (RiPPs) from plants; they consist of standard amino acids arranged in an unbroken chain of peptide bonds. These cyclic peptides are stable and range in size and topologies making them potential scaffolds for peptide drugs; some display valuable biological activities. Recently two orbitides whose sequences were buried in those of seed storage albumin precursors were said to represent the first observable step in the evolution of larger and hydrophilic bicyclic peptides. Here, guided by transcriptome data, we investigated peptide extracts of 40 species specifically for the more hydrophobic orbitides and confirmed 44 peptides by tandem mass spectrometry, as well as obtaining solution structures for four of them by NMR. Acquiring transcriptomes from the phylogenetically important Corymboideae family confirmed the precursor genes for the peptides (called PawS1-Like or PawL1) are confined to the Asteroideae, a subfamily of the huge plant family Asteraceae. To be confined to the Asteroideae indicates these peptides arose during the Eocene epoch around 45 Mya. Unlike other orbitides, all PawL-derived Peptides contain an Asp residue, needed for processing by asparaginyl endopeptidase. This study has revealed what is likely to be a very large new family of orbitides, uniquely buried alongside albumin and processed by asparaginyl endopeptidase.

The Protein Corona of PEGylated PGMA-Based Nanoparticles is Preferentially Enriched with Specific Serum Proteins of Varied Biological Function.

The composition of the protein corona formed on poly(ethylene glycol)-functionalized (PEGylated) poly(glycidyl methacrylate) (PGMA) nanoparticles (NPs) was qualitatively and quantitatively compared to the protein corona on non-PEGylated PGMA NPs. Despite the reputation of PEGylated NPs for stealth functionality, we demonstrate the preferential enrichment of specific serum proteins of varied biological function in the protein corona on PEGylated NPs when compared to non-PEGylated NPs. Additionally, we suggest that the base material of polymeric NPs plays a role in the preferential enrichment of select serum proteins to the hard corona.