Community recommendations on terminology and procedures used in flooding and low oxygen stress research

Apart from playing a key role in important biochemical reactions, molecular oxygen (O2) and its by-products also have crucial signaling roles in shaping plant developmental programs and environmental responses. Even under normal conditions, sharp O2 gradients can occur within the plant when cellular O2 demand exceeds supply, especially in dense organs such as tubers, seeds and fruits. Spatial and temporal variations in O2 concentrations are important cues for plants to modulate development (van Dongen & Licausi, 2015; Considine et al., 2016). Environmental conditions can also expand the low O2 regions within the plant. For example, excessive rainfall can lead to partial or complete plant submergence resulting in O2 deficiency in the root or the entire plant (Voesenek & Bailey-Serres, 2015). Climate change-associated increases in precipitation events have made flooding a major abiotic stress threatening crop production and food sustainability. This increased flooding and associated crop losses highlight the urgency of understanding plant flooding responses and tolerance mechanisms. Timely manifestation of physiological and morphological changes triggering developmental adjustments or flooding survival strategies requires accurate sensing of O2 levels. Despite progress in understanding how plants sense and respond to changes in intracellular O2 concentrations (van Dongen & Licausi, 2015), several questions remain unanswered due to a lack of high resolution tools to accurately and noninvasively monitor (sub)cellular O2 concentrations. In the absence of such tools, it is therefore critical for researchers in the field to be aware of how experimental conditions can influence plant O2 levels, and thus on the importance of accurately reporting specific experimental details. This also requires a consensus on the definition of frequently used terms. At the 15th New Phytologist Workshop on Flooding stress (Voesenek et al., 2016), community members discussed and agreed on unified nomenclature and standard norms for low O2 and flooding stress research. This consensus on terminology and experimental guidelines is presented here. We expect that these norms will facilitate more effective interpretation, comparison and reproducibility of research in this field. We also highlight the current challenges in noninvasively monitoring and measuring O2 concentrations in plant cells, outlining the technologies currently available, their strengths and drawbacks, and their suitability for use in flooding and low O2 research

Increased ratio of electron transport to net assimilation rate supports elevated isoprenoid emission rate in eucalypts under drought

Plants undergoing heat and low-CO₂ stresses emit large amounts of volatile isoprenoids compared with those in stress-free conditions. One hypothesis posits that the balance between reducing power availability and its use in carbon assimilation determines constitutive isoprenoid emission rates in plants and potentially even their maximum emission capacity under brief periods of stress. To test this, we used abiotic stresses to manipulate the availability of reducing power. Specifically, we examined the effects of mild to severe drought on photosynthetic electron transport rate (ETR) and net carbon assimilation rate (NAR) and the relationship between estimated energy pools and constitutive volatile isoprenoid emission rates in two species of eucalypts: Eucalyptus occidentalis (drought tolerant) and Eucalyptus camaldulensis (drought sensitive). Isoprenoid emission rates were insensitive to mild drought, and the rates increased when the decline in NAR reached a certain species-specific threshold. ETR was sustained under drought and the ETR-NAR ratio increased, driving constitutive isoprenoid emission until severe drought caused carbon limitation of the methylerythritol phosphate pathway. The estimated residual reducing power unused for carbon assimilation, based on the energetic status model, significantly correlated with constitutive isoprenoid emission rates across gradients of drought (r² > 0.8) and photorespiratory stress (r² > 0.9). Carbon availability could critically limit emission rates under severe drought and photorespiratory stresses. Under most instances of moderate abiotic stress levels, increased isoprenoid emission rates compete with photorespiration for the residual reducing power not invested in carbon assimilation. A similar mechanism also explains the individual positive effects of low-CO₂, heat, and drought stresses on isoprenoid emission.14 page(s

Bioprocessing of grains

A method of treating a crop kernel prior to milling to improve millability, which includes the step of exposing the crop kernel to one or more plant hormones is provided. Typically, the crop kernel is a cereal such as wheat. The plant hormone is selected from the group consisting of auxins, gibberellins and abscisic acid. The method further includes the step of exposing the crop kernel to an enzyme. Typically the enzyme is a plant cell-wall degrading enzyme such as xylanase, lipase and cellulase. Also provided are methods of production of flour, food products and compositions. A particular application of this method is the optimisation of milling performance for the production of high quality flour

Mechanisms of growth and patterns of gene expression in oxygen-deprived rice coleoptiles

Coleoptiles of rice (Oryza sativa) seedlings grown under water commonly elongate by up to 1 mm h⁻¹ to reach the atmosphere. We initially analysed this highly specialized phenomenon by measuring epidermal cell lengths along the coleoptile axis to determine elongation rates. This revealed a cohort of cells in the basal zone that elongated rapidly following emergence from the embryo, reaching 200 μm within 12 h. After filming coleoptiles in vivo for a day, kinematic analysis was applied. Eight time-sliced ‘segments’ were defined by their emergence from the embryo at four-hourly intervals, revealing a mathematically simple growth model. Each segment entering the coleoptile from the embryo elongated at a constant velocity, resulting in accelerating growth for the entire organ. Consistent with the epidermal cell lengths, relative rates of elongation (mm mm⁻¹ h⁻¹) were tenfold greater in the small, newly emerged basal segments than the older distal tip segments. This steep axial gradient defined two contrasting growth zones (bases versus tips) in which we measured ATP production and protein, RNA and DNA content, and analysed the global transcriptome under steady-state normoxia, hypoxia (3% O₂) and anoxia. Determination of the transcriptome revealed tip-specific induction of genes encoding TCP [Teosinte Branched1 (Tb1) of maize, Cycloidea (Cyc), and Proliferating Cell Factor (Pcf)] transcription factors, RNA helicases, ribosomal proteins and proteins involved in protein folding, whilst expression of F–box domain-containing proteins in the ubiquitin E3–SCF complex (Skp, Cullin, F-box containing complex) was induced specifically in bases under low oxygen conditions. We ascribed the sustained elongation under hypoxia to hypoxia-specific responses such as controlled suppression of photosystem components and induction of RNA binding/splicing functions, indicating preferential allocation of energy to cell extension.16 page(s

Community recommendations on terminology and procedures used in flooding and low oxygen stress research

Apart from playing a key role in important biochemical reactions, molecular oxygen (O2) and its by-products also have crucial signaling roles in shaping plant developmental programs and environmental responses. Even under normal conditions, sharp O2 gradients can occur within the plant when cellular O2 demand exceeds supply, especially in dense organs such as tubers, seeds and fruits. Spatial and temporal variations in O2 concentrations are important cues for plants to modulate development (van Dongen & Licausi, 2015; Considine et al., 2016). Environmental conditions can also expand the low O2 regions within the plant. For example, excessive rainfall can lead to partial or complete plant submergence resulting in O2 deficiency in the root or the entire plant (Voesenek & Bailey-Serres, 2015). Climate change-associated increases in precipitation events have made flooding a major abiotic stress threatening crop production and food sustainability. This increased flooding and associated crop losses highlight the urgency of understanding plant flooding responses and tolerance mechanisms. Timely manifestation of physiological and morphological changes triggering developmental adjustments or flooding survival strategies requires accurate sensing of O2 levels. Despite progress in understanding how plants sense and respond to changes in intracellular O2 concentrations (van Dongen & Licausi, 2015), several questions remain unanswered due to a lack of high resolution tools to accurately and noninvasively monitor (sub)cellular O2 concentrations. In the absence of such tools, it is therefore critical for researchers in the field to be aware of how experimental conditions can influence plant O2 levels, and thus on the importance of accurately reporting specific experimental details. This also requires a consensus on the definition of frequently used terms. At the 15th New Phytologist Workshop on Flooding stress (Voesenek et al., 2016), community members discussed and agreed on unified nomenclature and standard norms for low O2 and flooding stress research. This consensus on terminology and experimental guidelines is presented here. We expect that these norms will facilitate more effective interpretation, comparison and reproducibility of research in this field. We also highlight the current challenges in noninvasively monitoring and measuring O2 concentrations in plant cells, outlining the technologies currently available, their strengths and drawbacks, and their suitability for use in flooding and low O2 research

Nocturnal stomatal conductance responses to rising [CO₂], temperature and drought

•The response of nocturnal stomatal conductance (gs,n) to rising atmospheric CO₂ concentration ([CO₂]) is currently unknown, and may differ from responses of daytime stomatal conductance (gs,d). Because night-time water fluxes can have a significant impact on landscape water budgets, an understanding of the effects of [CO₂] and temperature on gs,n is crucial for predicting water fluxes under future climates. •Here, we examined the effects of [CO₂] (280, 400 and 640 μmol mol⁻¹), temperature (ambient and ambient + 4°C) and drought on gs,n, and gs,d in Eucalyptus sideroxylon saplings. •gs,n was substantially higher than zero, averaging 34% of gs,d. Before the onset of drought, gs,n increased by 85% when [CO₂] increased from 280 to 640 μmol mol⁻¹, averaged across both temperature treatments. gs,n declined with drought, but an increase in [CO₂] slowed this decline. Consequently, the soil water potential at which gs,n was zero (Ψ0) was significantly more negative in elevated [CO₂] and temperature treatments. gs,d showed inconsistent responses to [CO₂] and temperature. •gs,n may be higher in future climates, potentially increasing nocturnal water loss and susceptibility to drought, but cannot be predicted easily from gs,d. Therefore, predictive models using stomatal conductance must account for both gs,n and gs,d when estimating ecosystem water fluxes.10 page(s

Synthesis and Pharmacological Characterization of C4_β‑Amide-Substituted 2‑Aminobicyclo[3.1.0]­hexane-2,6-dicarboxylates. Identification of (1<i>S,</i>2<i>S,</i>4<i>S,</i>5<i>R,</i>6<i>S</i>)‑2-Amino-4-[(3-methoxybenzoyl)­amino]­bicyclo[3.1.0]­hexane-2,6-dicarboxylic Acid (LY2794193), a Highly Potent and Selective mGlu₃ Receptor Agonist

Multiple therapeutic opportunities have been suggested for compounds capable of selective activation of metabotropic glutamate 3 (mGlu₃) receptors, but small molecule tools are lacking. As part of our ongoing efforts to identify potent, selective, and systemically bioavailable agonists for mGlu₂ and mGlu₃ receptor subtypes, a series of C4_β-N-linked variants of (1<i>S</i>,2<i>S</i>,5<i>R</i>,6<i>S</i>)-2-amino-bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid <b>1</b> (LY354740) were prepared and evaluated for both mGlu₂ and mGlu₃ receptor binding affinity and functional cellular responses. From this investigation we identified (1<i>S</i>,2<i>S</i>,4<i>S</i>,5<i>R</i>,6<i>S</i>)-2-amino-4-[(3-methoxybenzoyl)­amino]­bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid <b>8p</b> (LY2794193), a molecule that demonstrates remarkable mGlu₃ receptor selectivity. Crystallization of <b>8p</b> with the amino terminal domain of hmGlu₃ revealed critical binding interactions for this ligand with residues adjacent to the glutamate binding site, while pharmacokinetic assessment of <b>8p</b> combined with its effect in an mGlu₂ receptor-dependent behavioral model provides estimates for doses of this compound that would be expected to selectively engage and activate central mGlu₃ receptors in vivo

Synthesis and Pharmacological Characterization of C4_β‑Amide-Substituted 2‑Aminobicyclo[3.1.0]­hexane-2,6-dicarboxylates. Identification of (1<i>S,</i>2<i>S,</i>4<i>S,</i>5<i>R,</i>6<i>S</i>)‑2-Amino-4-[(3-methoxybenzoyl)­amino]­bicyclo[3.1.0]­hexane-2,6-dicarboxylic Acid (LY2794193), a Highly Potent and Selective mGlu₃ Receptor Agonist

Multiple therapeutic opportunities have been suggested for compounds capable of selective activation of metabotropic glutamate 3 (mGlu₃) receptors, but small molecule tools are lacking. As part of our ongoing efforts to identify potent, selective, and systemically bioavailable agonists for mGlu₂ and mGlu₃ receptor subtypes, a series of C4_β-N-linked variants of (1<i>S</i>,2<i>S</i>,5<i>R</i>,6<i>S</i>)-2-amino-bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid <b>1</b> (LY354740) were prepared and evaluated for both mGlu₂ and mGlu₃ receptor binding affinity and functional cellular responses. From this investigation we identified (1<i>S</i>,2<i>S</i>,4<i>S</i>,5<i>R</i>,6<i>S</i>)-2-amino-4-[(3-methoxybenzoyl)­amino]­bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid <b>8p</b> (LY2794193), a molecule that demonstrates remarkable mGlu₃ receptor selectivity. Crystallization of <b>8p</b> with the amino terminal domain of hmGlu₃ revealed critical binding interactions for this ligand with residues adjacent to the glutamate binding site, while pharmacokinetic assessment of <b>8p</b> combined with its effect in an mGlu₂ receptor-dependent behavioral model provides estimates for doses of this compound that would be expected to selectively engage and activate central mGlu₃ receptors in vivo