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Background: Climate-smart agriculture (CSA) addresses the challenge of meeting the growing demand for food, fibre and fuel, despite the changing climate and fewer opportunities for agricultural expansion on additional lands. CSA focuses on contributing to economic development, poverty reduction and food security; maintaining and enhancing the productivity and resilience of natural and agricultural ecosystem functions, thus building natural capital; and reducing trade-offs involved in meeting these goals. Current gaps in knowledge, work within CSA, and agendas for interdisciplinary research and science-based actions identified at the 2013 Global Science Conference on Climate-Smart Agriculture (Davis, CA, USA) are described here within three themes: (1) farm and food systems, (2) landscape and regional issues and (3) institutional and policy aspects. The first two themes comprise crop physiology and genetics, mitigation and adaptation for livestock and agriculture, barriers to adoption of CSA practices, climate risk management and energy and biofuels (theme 1); and modelling adaptation and uncertainty, achieving multifunctionality, food and fishery systems, forest biodiversity and ecosystem services, rural migration from climate change and metrics (theme 2). Theme 3 comprises designing research that bridges disciplines, integrating stakeholder input to directly link science, action and governance. Outcomes: In addition to interdisciplinary research among these themes, imperatives include developing (1) models that include adaptation and transformation at either the farm or landscape level; (2) capacity approaches to examine multifunctional solutions for agronomic, ecological and socioeconomic challenges; (3) scenarios that are validated by direct evidence and metrics to support behaviours that foster resilience and natural capital; (4) reductions in the risk that can present formidable barriers for farmers during adoption of new technology and practices; and (5) an understanding of how climate affects the rural labour force, land tenure and cultural integrity, and thus the stability of food production. Effective work in CSA will involve stakeholders, address governance issues, examine uncertainties, incorporate social benefits with technological change, and establish climate finance within a green development framework. Here, the socioecological approach is intended to reduce development controversies associated with CSA and to identify technologies, policies and approaches leading to sustainable food production and consumption patterns in a changing climate.

This study examined the relationship between performance anxiety and flow proneness. Ninety undergraduate music majors (52 females, 38 males) recruited from a major research university volunteered to participate. The data collection instrument consisted of two previously established inventories: the Performance Anxiety Inventory and the Music in Flow Inventory. As predicted, the data showed flow proneness to be significantly and negatively correlated with performance anxiety (r = -0.20, p = 0.034, one-tailed test). The data also supported a prediction that the ability to play/sing without destructive self-criticism would be negatively related to performance anxiety (r = -0.39, p < 0.001, one-tailed). The results suggest that both musical performance anxiety and a flow state of consciousness can exist simultaneously. It appears that creating performance conditions that foster flow may be a useful strategy for helping to alleviate the intensity of musical performance anxiety. [ABSTRACT FROM AUTHOR]

Examines root nitrate absorption in tomato plants under steady state conditions in the presence and absence of ammonia. High rate of nitrate absorption by plants grown under a low-salt regime; Gradual increase of proton efflux under ammonia exposure; Immediate decrease of net potassium ion absorption following first exposure to ammonia.

The behavior of many plant enzymes depends on the metals and other ligands to which they are bound. A previous study demonstrated that tobacco Rubisco binds almost equally to magnesium and manganese and rapidly exchanges one metal for the other. The present study characterizes the kinetics of Rubisco and the plastidial malic enzyme when bound to either metal. When Rubisco purified from five C 3 species was bound to magnesium rather than manganese, the specificity for CO 2 over O 2 , (S c/o ) increased by 25% and the ratio of the maximum velocities of carboxylation / oxygenation (V cmax /V omax ) increased by 39%. For the recombinant plastidial malic enzyme, the forward reaction (malate decarboxylation) was 30% slower and the reverse reaction (pyruvate carboxylation) was three times faster when bound to manganese rather than magnesium. Adding 6-phosphoglycerate and NADP + inhibited carboxylation and oxygenation when Rubisco was bound to magnesium and stimulated oxygenation when it was bound to manganese. Conditions that favored RuBP oxygenation stimulated Rubisco to convert as much as 15% of the total RuBP consumed into pyruvate. These results are consistent with a stromal biochemical pathway in which (1) Rubisco when associated with manganese converts a substantial amount of RuBP into pyruvate, (2) malic enzyme when associated with manganese carboxylates a substantial portion of this pyruvate into malate, and (3) chloroplasts export additional malate into the cytoplasm where it generates NADH for assimilating nitrate into amino acids. Thus, plants may regulate the activities of magnesium and manganese in leaves to balance organic carbon and organic nitrogen as atmospheric CO 2 fluctuates., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Programmed axon degeneration (AxD) is a key feature of many neurodegenerative diseases. In healthy axons, the axon survival factor NMNAT2 inhibits SARM1, the central executioner of AxD, preventing it from initiating the rapid local NAD+ depletion and metabolic catastrophe that precipitates axon destruction. Because these components of the AxD pathway act within neurons, it was also assumed that the timetable of AxD was set strictly by a cell-intrinsic mechanism independent of neuron-extrinsic processes later activated by axon fragmentation. However, using a rare human disease model of neuropathy caused by hypomorphic NMNAT2 mutations and chronic SARM1 activation (sarmopathy), we demonstrated that neuronal SARM1 can initiate macrophage-mediated axon elimination long before stressed-but-viable axons would otherwise succumb to cell-intrinsic metabolic failure. Investigating potential SARM1-dependent signals that mediate macrophage recognition and/or engulfment of stressed-but-viable axons, we found that chronic SARM1 activation triggers axonal blebbing and dysregulation of phosphatidylserine (PS), a potent phagocyte immunomodulatory molecule. Neuronal expression of the phosphatidylserine lipase ABDH12 suppresses nerve macrophage activation, preserves motor axon integrity, and rescues motor function in this chronic sarmopathy model. We conclude that PS dysregulation is an early SARM1-dependent axonal stress signal, and that blockade of phagocytic recognition and engulfment of stressed-but-viable axons could be an attractive therapeutic target for management of neurological disorders involving SARM1 activation.

Wheat and rice produce nutritious grains that provide 32% of the protein in the human diet globally. Here, we examine how genetic modifications to improve assimilation of the inorganic nitrogen forms ammonium and nitrate into protein influence grain yield of these crops. Successful breeding for modified nitrogen metabolism has focused on genes that coordinate nitrogen and carbon metabolism, including those that regulate tillering, heading date, and ammonium assimilation. Gaps in our current understanding include (1) species differences among candidate genes in nitrogen metabolism pathways, (2) the extent to which relative abundance of these nitrogen forms across natural soil environments shape crop responses, and (3) natural variation and genetic architecture of nitrogen-mediated yield improvement. Despite extensive research on the genetics of nitrogen metabolism since the rise of synthetic fertilizers, only a few projects targeting nitrogen pathways have resulted in development of cultivars with higher yields. To continue improving grain yield and quality, breeding strategies need to focus concurrently on both carbon and nitrogen assimilation and consider manipulating genes with smaller effects or that underlie regulatory networks as well as genes directly associated with nitrogen metabolism.

Premise: The agar-based culture of Arabidopsis seedlings is widely used for quantifying root traits. Shoot traits are generally overlooked in these studies, probably because the rosettes are often askew. A technique to assess the shoot surface area of seedlings grown inside agar culture dishes would facilitate simultaneous root and shoot phenotyping., Methods: We developed an image processing workflow in Python that estimates rosette area of Arabidopsis seedlings on agar culture dishes. We validated this method by comparing its output with other metrics of seedling growth. As part of a larger study on genetic variation in plant responses to nitrogen form and concentration, we measured the rosette areas from more than 2000 plate images., Results: The rosette area measured from plate images was strongly correlated with the rosette area measured from directly overhead and moderately correlated with seedling mass. Rosette area in the large image set was significantly influenced by genotype and nitrogen treatment. The broad-sense heritability of leaf area measured using this method was 0.28., Discussion: These results indicated that this approach for estimating rosette area produces accurate shoot phenotype data. It can be used with image sets for which other methods of leaf area quantification prove unsuitable., (© 2022 The Authors. Applications in Plant Sciences published by Wiley Periodicals LLC on behalf of Botanical Society of America.)

Axon loss contributes to many common neurodegenerative disorders. In healthy axons, the axon survival factor NMNAT2 inhibits SARM1, the central executioner of programmed axon degeneration. We identified 2 rare NMNAT2 missense variants in 2 brothers afflicted with a progressive neuropathy syndrome. The polymorphisms resulted in amino acid substitutions V98M and R232Q, which reduced NMNAT2 NAD+-synthetase activity. We generated a mouse model to mirror the human syndrome and found that Nmnat2V98M/R232Q compound-heterozygous CRISPR mice survived to adulthood but developed progressive motor dysfunction, peripheral axon loss, and macrophage infiltration. These disease phenotypes were all SARM1-dependent. Remarkably, macrophage depletion therapy blocked and reversed neuropathic phenotypes in Nmnat2V98M/R232Q mice, identifying a SARM1-dependent neuroimmune mechanism as a key driver of disease pathogenesis. These findings demonstrate that SARM1 induced inflammatory neuropathy and highlight the potential of immune therapy as a treatment for this rare syndrome and other neurodegenerative conditions associated with NMNAT2 loss and SARM1 activation.

Nitrogen is an essential element required for plant growth and productivity. Understanding the mechanisms and natural genetic variation underlying nitrogen use in plants will facilitate the engineering of plant nitrogen use to maximize crop productivity while minimizing environmental costs. To understand the scope of natural variation that may influence nitrogen use, we grew 1,135 Arabidopsis thaliana natural genotypes on two nitrogen sources, nitrate and ammonium, and measured both developmental and defense metabolite traits. By using different environments and focusing on multiple traits, we identified a wide array of different nitrogen responses. These responses are associated with numerous genes, most of which were not previously associated with nitrogen responses. Only a small portion of these genes appear to be shared between environments or traits, while most are predominantly specific to a developmental or defense trait under a specific nitrogen source. Finally, by using a large population, we were able to identify unique nitrogen responses, such as preferring ammonium or nitrate, which appear to be generated by combinations of loci rather than a few large-effect loci. This suggests that it may be possible to obtain novel phenotypes in complex nitrogen responses by manipulating sets of genes with small effects rather than solely focusing on large-effect single gene manipulations., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

TDP-43 mediates proper Stathmin-2 (STMN2) mRNA splicing, and STMN2 protein is reduced in the spinal cord of most patients with amyotrophic lateral sclerosis (ALS). To test the hypothesis that STMN2 loss contributes to ALS pathogenesis, we generated constitutive and conditional STMN2 knockout mice. Constitutive STMN2 loss results in early-onset sensory and motor neuropathy featuring impaired motor behavior and dramatic distal neuromuscular junction (NMJ) denervation of fast-fatigable motor units, which are selectively vulnerable in ALS, without axon or motoneuron degeneration. Selective excision of STMN2 in motoneurons leads to similar NMJ pathology. STMN2 knockout heterozygous mice, which better model the partial loss of STMN2 protein found in patients with ALS, display a slowly progressive, motor-selective neuropathy with functional deficits and NMJ denervation. Thus, our findings strongly support the hypothesis that STMN2 reduction owing to TDP-43 pathology contributes to ALS pathogenesis., Competing Interests: Declaration of interests A.D. and J.M. are co-founders, scientific advisory board members, and shareholders of Disarm Therapeutics, a wholly owned subsidiary of Eli Lilly. A.J.B. is a consultant to Disarm Therapeutics. The authors have no other competing conflicts or financial interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Premise: High-precision data acquisition (DAQ) is essential for developing new methods in the plant sciences. Commercial high-resolution DAQ systems are cost prohibitive, whereas the less expensive systems that are currently available lack the resolution and precision required for many physiological measurements., Methods and Results: We developed the software libraries, called piadcs, and hardware design for a DAQ system based on an ultra-high-resolution analog-to-digital converter and a Raspberry Pi computer. We tested the system precision with and without a thermocouple attached and found the precision with the sensor to be better than ±0.01°C and the maximum possible system resolution to be 0.4 ppm., Conclusions: The ultra-high-resolution DAQ system described here is inexpensive, flexible enough to be used with many different sensors, and can be built by researchers with rudimentary electronic and computer skills. This system is most applicable in the development of new measurement techniques and the improvement of existing methods., (© 2022 The Authors. Applications in Plant Sciences published by Wiley Periodicals LLC on behalf of Botanical Society of America.)

Background: In response to injury, neurons activate a program of organized axon self-destruction initiated by the NAD + hydrolase, SARM1. In healthy neurons SARM1 is autoinhibited, but single amino acid changes can abolish autoinhibition leading to constitutively active SARM1 enzymes that promote degeneration when expressed in cultured neurons., Methods: To investigate whether naturally occurring human variants might disrupt SARM1 autoinhibition and potentially contribute to risk for neurodegenerative disease, we assayed the enzymatic activity of all 42 rare SARM1 alleles identified among 8507 amyotrophic lateral sclerosis (ALS) patients and 9671 controls. We then intrathecally injected mice with virus expressing SARM1 constructs to test the capacity of an ALS-associated constitutively active SARM1 variant to promote neurodegeneration in vivo., Results: Twelve out of 42 SARM1 missense variants or small in-frame deletions assayed exhibit constitutive NADase activity, including more than half of those that are unique to the ALS patients or that occur in multiple patients. There is a > 5-fold enrichment of constitutively active variants among patients compared to controls. Expression of constitutively active ALS-associated SARM1 alleles in cultured dorsal root ganglion (DRG) neurons is pro-degenerative and cytotoxic. Intrathecal injection of an AAV expressing the common SARM1 reference allele is innocuous to mice, but a construct harboring SARM1 V184G , the constitutively active variant found most frequently among the ALS patients, causes axon loss, motor dysfunction, and sustained neuroinflammation., Conclusions: These results implicate rare hypermorphic SARM1 alleles as candidate genetic risk factors for ALS and other neurodegenerative conditions., (© 2022. The Author(s).)

Public understanding about complex issues such as climate change relies heavily on online resources. Yet the role that online instruction should assume in post-secondary science education remains contentious despite its near ubiquity during the COVID-19 pandemic. The objective here was to compare the performance of 1790 undergraduates taking either an online or face-to-face version of an introductory course on climate change. Both versions were taught by a single instructor, thus, minimizing instructor bias. Women, seniors, English language learners, and humanities majors disproportionately chose to enroll in the online version because of its ease of scheduling and accessibility. After correcting for performance-gaps among different demographic groups, the COVID-19 pandemic had no significant effect on online student performance and students in the online version scored 2% lower (on a scale of 0-100) than those in the face-to-face version, a penalty that may be a reasonable tradeoff for the ease of scheduling and accessibility that these students desire., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2022.)

The extent to which rising atmospheric CO2 concentration has already influenced food production and quality is uncertain. Here, we analyzed annual field trials of autumn-planted common wheat in California from 1985 to 2019, a period during which the global atmospheric CO2 concentration increased 19%. Even after accounting for other major factors (cultivar, location, degree-days, soil temperature, total water applied, nitrogen fertilization, and pathogen infestation), wheat grain yield and protein yield declined 13% over this period, but grain protein content did not change. These results suggest that exposure to gradual CO2 enrichment over the past 35 years has adversely affected wheat grain and protein yield, but not grain protein content., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

SARM1 is an inducible TIR-domain NAD + hydrolase that mediates pathological axon degeneration. SARM1 is activated by an increased ratio of NMN to NAD + , which competes for binding to an allosteric activating site. When NMN binds, the TIR domain is released from autoinhibition, activating its NAD + hydrolase activity. The discovery of this allosteric activating site led us to hypothesize that other NAD + -related metabolites might activate SARM1. Here, we show the nicotinamide analog 3-acetylpyridine (3-AP), first identified as a neurotoxin in the 1940s, is converted to 3-APMN, which activates SARM1 and induces SARM1-dependent NAD + depletion, axon degeneration, and neuronal death. In mice, systemic treatment with 3-AP causes rapid SARM1-dependent death, while local application to the peripheral nerve induces SARM1-dependent axon degeneration. We identify 2-aminopyridine as another SARM1-dependent neurotoxin. These findings identify SARM1 as a candidate mediator of environmental neurotoxicity and suggest that SARM1 agonists could be developed into selective agents for neurolytic therapy., Competing Interests: Declaration of interests A.J.B. and Y.S. have consulted for Disarm Therapeutics. A.D. and J.M. are co-founders, scientific advisory board members, and shareholders of Disarm Therapeutics, a wholly owned subsidiary of Eli Lilly & Company., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

We have proposed that rising atmospheric CO 2 concentrations inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein in shoots of C 3 plants, a phenomenon that will strongly influence primary productivity and food security under the environmental conditions anticipated during the next few decades. Although hundreds of studies support this proposal, several publications in 2018 and 2019 purport to present counterevidence. The following study evaluates these publications as well as presents new data that elevated CO 2 enhances root nitrate assimilation in wheat and Arabidopsis while it inhibits shoot nitrate assimilation., (© 2019 Scandinavian Plant Physiology Society.)

Plethysmograph measurement of respiratory phenotypes provides a highly sensitive means to study nicotine response in experimental model animals. We measured average respiratory frequency, tidal volume, minute volume and inspiratory time in C3H/HeJ and C57BL/6J mice subcutaneously administered 0.35 and 0.70 mg/kg nicotine. Both mouse strains showed significantly altered respiratory and locomotion phenotypes relative to saline-injected controls when administered the higher dose, but only C57BL/6J responded to the lower nicotine dose. Respiratory and locomotion phenotypes rarely differed significantly by sex. To investigate whether the strain-specific differences in nicotine sensitivity were related to differences in clearance, we followed up by measuring nicotine clearance in C3H/HeJ and C57BL/6J mice (0.35 mg/kg subcutaneous) and found sex differences in both strains, but no difference between strains.

Two indole compounds, indole-3-carbinol (I3C) and its acid condensation product, 3,3'-diindolymethane (DIM), have been shown to suppress the expression of flavin-containing monooxygenases (FMO) and to induce some hepatic cytochrome P450s (CYPs) in rats. In liver microsomes prepared from rats fed I3C or DIM, FMO-mediated nicotine N-oxygenation was decreased, whereas CYP-mediated nicotine metabolism to nicotine iminium and subsequently to cotinine was unchanged. Therefore, it was hypothesized that in mice DIM would also suppress nicotine N-oxygenation without affecting CYP-mediated nicotine metabolism. Liver microsomes were produced from male and female C57BL/6 J and CD1 mice fed 2500 parts per million (ppm) DIM for 14 days. In liver microsomes from DIM-fed mice, FMO-mediated nicotine N-oxygenation did not differ from the controls, but CYP-mediated nicotine metabolism was significantly increased, with results varying by sex and strain. To confirm the effects of DIM in vivo, control and DIM-fed CD1 male mice were injected subcutaneously with nicotine, and the plasma concentrations of nicotine, cotinine and nicotine-N-oxide were measured over 30 minutes. The DIM-fed mice showed greater cotinine concentrations compared with the controls 10 minutes following injection. It is concluded that the effects of DIM on nicotine metabolism in vitro and in vivo differ between mice and rats and between mouse strains, and that DIM is an effective inducer of CYP-mediated nicotine metabolism in commonly studied mouse strains., (© 2019 John Wiley & Sons, Ltd.)

A broad range of biochemicals, from proteins to nucleic acids, function properly only when associated with a metal, usually a divalent cation. Not any divalent metal will do: these metals differ in their ionic radius, dissociation in water, ionization potential, and number of unpaired electrons in their outer shells, and so substituting one metal for another often changes substrate positioning, redox reactivities, and physiological performance, and thus may serve as a regulatory mechanism. For instance, exchanging manganese for magnesium in several chloroplast enzymes maintains plant carbon-nitrogen balance under rising atmospheric CO 2 concentrations. Here, we review this and a few other cases where association of proteins or nucleic acids with different metals control metabolism., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Common variation in the CYP2B6 gene, encoding the cytochrome P450 2B6 enzyme, is associated with substrate-specific altered clearance of multiple drugs. CYP2B6 is a minor contributor to hepatic nicotine metabolism, but the enzyme has been proposed as relevant to nicotine-related behaviors because of reported CYP2B6 mRNA expression in human brain tissue. Therefore, we hypothesized that CYP2B6 variants would be associated with altered nicotine oxidation, and that nicotine metabolism by CYP2B6 would be detected in human brain microsomes. We generated recombinant enzymes in insect cells corresponding to nine common CYP2B6 haplotypes and demonstrate genetically determined differences in nicotine oxidation to nicotine iminium ion and nornicotine for both (S) and (R)-nicotine. Notably, the CYP2B6.6 and CYP2B6.9 variants demonstrated lower intrinsic clearance relative to the reference enzyme, CYP2B6.1. In the presence of human brain microsomes, along with nicotine- N -oxidation, we also detect nicotine oxidation to nicotine iminium ion. However, unlike N -oxidation, this activity is NADPH independent, does not follow Michaelis-Menten kinetics, and is not inhibited by NADP or carbon monoxide. Furthermore, metabolism of common CYP2B6 probe substrates, methadone and ketamine, is not detected in the presence of brain microsomes. We conclude that CYP2B6 metabolizes nicotine stereoselectively and common CYP2B6 variants differ in nicotine metabolism activity, but did not find evidence of CYP2B6 activity in human brain.

Most plants, contrary to popular belief, do not waste over 30% of their photosynthate in a futile cycle called photorespiration. Rather, the photorespiratory pathway generates additional malate in the chloroplast that empowers many energy-intensive chemical reactions, such as those involved in nitrate assimilation. Thus, the balance between carbon fixation and photorespiration determines the plant carbon-nitrogen balance and protein concentrations. Plant protein concentrations, in turn, depend not only on the relative concentrations of carbon dioxide and oxygen in the chloroplast but also on the relative activities of magnesium and manganese, which are metals that associate with several key enzymes in the photorespiratory pathway and alter their function. Understanding the regulation of these processes is critical for sustaining food quality under rising CO 2 atmospheres.

A common haplotype of the flavin-containing monooxygenase gene FMO3 is associated with aberrant mRNA splicing, a twofold reduction in in vivo nicotine N-oxidation and reduced nicotine dependence. Tobacco remains the largest cause of preventable mortality worldwide. CYP2A6, the primary hepatic nicotine metabolism gene, is robustly associated with cigarette consumption but other enzymes contribute to nicotine metabolism. We determined the effects of common variants in FMO3 on plasma levels of nicotine-N-oxide in 170 European Americans administered deuterated nicotine. The polymorphism rs2266780 (E308G) was associated with N-oxidation of both orally administered and ad libitum smoked nicotine (P⩽3.3 × 10 -5 controlling for CYP2A6 genotype). In vitro, the FMO3 G308 variant was not associated with reduced activity, but rs2266780 was strongly associated with aberrant FMO3 mRNA splicing in both liver and brain (P⩽6.5 × 10 -9 ). Surprisingly, in treatment-seeking European American smokers (n=1558) this allele was associated with reduced nicotine dependence, specifically with a longer time to first cigarette (P=9.0 × 10 -4 ), but not with reduced cigarette consumption. As N-oxidation accounts for only a small percentage of hepatic nicotine metabolism we hypothesized that FMO3 genotype affects nicotine metabolism in the brain (unlike CYP2A6, FMO3 is expressed in human brain) or that nicotine-N-oxide itself has pharmacological activity. We demonstrate for the first time nicotine N-oxidation in human brain, mediated by FMO3 and FMO1, and show that nicotine-N-oxide modulates human α4β2 nicotinic receptor activity in vitro. These results indicate possible mechanisms for associations between FMO3 genotype and smoking behaviors, and suggest nicotine N-oxidation as a novel target to enhance smoking cessation.

Rubisco, the enzyme that constitutes as much as half of the protein in a leaf, initiates either the photorespiratory pathway that supplies reductant for the assimilation of nitrate into amino acids or the C3 carbon fixation pathway that generates carbohydrates. The relative rates of these two pathways depend both on the relative extent to which O 2 and CO 2 occupies the active site of Rubisco and on whether manganese or magnesium is bound to the enzyme. This study quantified the activities of manganese and magnesium in isolated tobacco chloroplasts and the thermodynamics of binding of these metals to Rubisco purified from tobacco or a bacterium. In tobacco chloroplasts, manganese was less active than magnesium, but Rubisco purified from tobacco had a higher affinity for manganese. The activity of each metal in the chloroplast was similar in magnitude to the affinity of tobacco Rubisco for each. This indicates that, in tobacco chloroplasts, Rubisco associates almost equally with both metals and rapidly exchanges one metal for the other. Binding of magnesium was similar in Rubisco from tobacco and a bacterium, whereas binding of manganese differed greatly between the Rubisco from these species. Moreover, the ratio of leaf manganese to magnesium in C3 plants increased as atmospheric CO 2 increased. These results suggest that Rubisco has evolved to improve the energy transfers between photorespiration and nitrate assimilation and that plants regulate manganese and magnesium activities in the chloroplast to mitigate detrimental changes in their nitrogen/carbon balance as atmospheric CO 2 varies., (© 2017 Scandinavian Plant Physiology Society.)

Critical for predicting the future of primary productivity is a better understanding of plant responses to rising atmospheric carbon dioxide (CO2) concentration. This review considers recent results on the role of the inorganic nitrogen (N) forms nitrate (NO3-) and ammonium (NH4+) in determining the responses of wheat and Arabidopsis to elevated atmospheric CO2 concentration. Here, we identify four key issues: (i) the possibility that different plant species respond similarly to elevated CO2 if one accounts for the N form that they are using; (ii) the major influence that plant-soil N interactions have on plant responses to elevated CO2; (iii) the observation that elevated CO2 may favor the uptake of one N form over others; and (iv) the finding that plants receiving NH4+ nutrition respond more positively to elevated CO2 than those receiving NO3- nutrition because elevated CO2 inhibits the assimilation of NO3- in shoots of C3 plants. We conclude that the form and amount of N available to plants from the rhizosphere and plant preferences for the different N forms are essential for predicting plant responses to elevated CO2., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

QTL stm9 controlling rapid-onset water stress tolerance in S. habrochaites was high-resolution mapped to a chromosome 9 region that contains genes associated with abiotic stress tolerances. Wild tomato (Solanum habrochaites) exhibits tolerance to abiotic stresses, including drought and chilling. Root chilling (6 °C) induces rapid-onset water stress by impeding water movement from roots to shoots. S. habrochaites responds to such changes by closing stomata and maintaining shoot turgor, while cultivated tomato (S. lycopersicum) fails to close stomata and wilts. This response (shoot turgor maintenance under root chilling) is controlled by a major QTL (designated stm9) on chromosome 9, which was previously fine-mapped to a 2.7-cM region. Recombinant sub-near-isogenic lines for chromosome 9 were marker-selected, phenotyped for shoot turgor maintenance under root chilling in two sets of replicated experiments (Fall and Spring), and the data were used to high-resolution map QTL stm9 to a 0.32-cM region. QTL mapping revealed a single QTL that was coincident for both the Spring and Fall datasets, suggesting that the gene or genes contributing to shoot turgor maintenance under root chilling reside within the marker interval H9-T1673. In the S. lycopersicum reference genome sequence, this chromosome 9 region is gene-rich and contains representatives of gene families that have been associated with abiotic stress tolerance.

One of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients.

Many studies of plant nitrogen relations assess only the total amount of the element available from the soil and the total amount of the element within the plant. Nitrogen, however, is a constituent of diverse compounds that participate in some of the most energy-intensive reactions in the biosphere. The following characterizes some of these reactions, especially those that involve ammonium and nitrate, and highlights the importance of distinguishing both among the nitrogen sources available to plants and among the nitrogen forms within plants when considering plant responses to rising atmospheric CO2 concentrations., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A major contributor to the global carbon cycle is plant respiration. Elevated atmospheric CO2 concentrations may either accelerate or decelerate plant respiration for reasons that have been uncertain. We recently established that elevated CO2 during the daytime decreases plant mitochondrial respiration in the light and protein concentration because CO2 slows the daytime conversion of nitrate (NO3 (-)) into protein. This derives in part from the inhibitory effect of CO2 on photorespiration and the dependence of shoot NO3 (-) assimilation on photorespiration. Elevated CO2 also inhibits the translocation of nitrite into the chloroplast, a response that influences shoot NO3 (-) assimilation during both day and night. Here, we exposed Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum) plants to daytime or nighttime elevated CO2 and supplied them with NO3 (-) or ammonium as a sole nitrogen (N) source. Six independent measures (plant biomass, shoot NO3 (-), shoot organic N, (15)N isotope fractionation, (15)NO3 (-) assimilation, and the ratio of shoot CO2 evolution to O2 consumption) indicated that elevated CO2 at night slowed NO3 (-) assimilation and thus decreased dark respiration in the plants reliant on NO3 (-). These results provide a straightforward explanation for the diverse responses of plants to elevated CO2 at night and suggest that soil N source will have an increasing influence on the capacity of plants to mitigate human greenhouse gas emissions., (© 2015 American Society of Plant Biologists. All Rights Reserved.)

The objective of this study was to determine if low stomatal conductance (g) increases growth, nitrate (NO3 (-)) assimilation, and nitrogen (N) utilization at elevated CO2 concentration. Four Arabidopsis (Arabidopsis thaliana) near isogenic lines (NILs) differing in g were grown at ambient and elevated CO2 concentration under low and high NO3 (-) supply as the sole source of N. Although g varied by 32% among NILs at elevated CO2, leaf intercellular CO2 concentration varied by only 4% and genotype had no effect on shoot NO3 (-) concentration in any treatment. Low-g NILs showed the greatest CO2 growth increase under N limitation but had the lowest CO2 growth enhancement under N-sufficient conditions. NILs with the highest and lowest g had similar rates of shoot NO3 (-) assimilation following N deprivation at elevated CO2 concentration. After 5 d of N deprivation, the lowest g NIL had 27% lower maximum carboxylation rate and 23% lower photosynthetic electron transport compared with the highest g NIL. These results suggest that increased growth of low-g NILs under N limitation most likely resulted from more conservative N investment in photosynthetic biochemistry rather than from low g., (© 2015 American Society of Plant Biologists. All Rights Reserved.)

C3 carbon fixation has a bad reputation, primarily because it is associated with photorespiration, a biochemical pathway thought to waste a substantial amount of the carbohydrate produced in a plant. This review presents evidence collected over nearly a century that (1) Rubisco when associated with Mn(2+) generates additional reductant during photorespiration, (2) this reductant participates in the assimilation of nitrate into protein, and (3) this nitrate assimilation facilitates the use of a nitrogen source that other organisms tend to avoid. This phenomenon explains the continued dominance of C3 plants during the past 23 million years of low CO2 atmospheres as well as the decline in plant protein concentrations as atmospheric CO2 rises.

Rationale: The CHRNA5-CHRNA3-CHRNB4 locus is associated with self-reported smoking behavior and also harbors the strongest genetic associations with chronic obstructive pulmonary disease (COPD) and lung cancer. Because the associations with lung disease remain after adjustment for self-reported smoking behaviors, it has been asserted that CHRNA5-CHRNA3-CHRNB4 variants increase COPD and lung cancer susceptibility independently of their effects on smoking., Objectives: To compare the genetic associations of exhaled carbon monoxide (CO), a biomarker of current cigarette exposure, with self-reported smoking behaviors., Methods: A total of 1,521 European American and 247 African American current smokers recruited into smoking cessation studies were assessed for CO at intake before smoking cessation. DNA samples were genotyped using the Illumina Omni2.5 microarray. Genetic associations with CO and smoking behaviors (cigarettes smoked per day, Fagerstrom test for nicotine dependence) were studied., Measurements and Main Results: Variants in the CHRNA5-CHRNA3-CHRNB4 locus, including rs16969968, a nonsynonymous variant in CHRNA5, are genomewide association study-significantly associated with CO (β = 2.66; 95% confidence interval [CI], 1.74-3.58; P = 1.65 × 10(-8)), and this association remains strong after adjusting for smoking behavior (β = 2.18; 95% CI, 1.32-3.04; P = 7.47 × 10(-7)). The correlation between CO and cigarettes per day is statistically significantly lower (z = 3.43; P = 6.07 × 10(-4)) in African Americans (r = 0.14; 95% CI, 0.02-0.26; P = 0.003) than in European-Americans (r = 0.36; 95% CI, 0.31-0.40; P = 0.0001)., Conclusions: Exhaled CO, a biomarker that is simple to measure, captures aspects of cigarette smoke exposure in current smokers beyond the number of cigarettes smoked per day. Behavioral measures of smoking are therefore insufficient indices of cigarette smoke exposure, suggesting that genetic associations with COPD or lung cancer that persist after adjusting for self-reported smoking behavior may still reflect genetic effects on smoking exposure.

Premise of the Study: Measurement of leaf areas from digital photographs has traditionally required significant user input unless backgrounds are carefully masked. Easy Leaf Area was developed to batch process hundreds of Arabidopsis rosette images in minutes, removing background artifacts and saving results to a spreadsheet-ready CSV file. •, Methods and Results: Easy Leaf Area uses the color ratios of each pixel to distinguish leaves and calibration areas from their background and compares leaf pixel counts to a red calibration area to eliminate the need for camera distance calculations or manual ruler scale measurement that other software methods typically require. Leaf areas estimated by this software from images taken with a camera phone were more accurate than ImageJ estimates from flatbed scanner images. •, Conclusions: Easy Leaf Area provides an easy-to-use method for rapid measurement of leaf area and nondestructive estimation of canopy area from digital images.

Stable (15)N isotopes have been used to examine movement of nitrogen (N) through various pools of the global N cycle. A central reaction in the cycle involves the reduction of nitrate (NO(-) 3) to nitrite (NO(-) 2) catalyzed by nitrate reductase (NR). Discrimination against (15)N by NR is a major determinant of isotopic differences among N pools. Here, we measured in vitro (15)N discrimination by several NRs purified from plants, fungi, and a bacterium to determine the intrinsic (15)N discrimination by the enzyme and to evaluate the validity of measurements made using (15)N-enriched NO(-) 3. Observed NR isotope discrimination ranged from 22 to 32‰ (kinetic isotope effects of 1.022-1.032) among the different isozymes at natural abundance (15)N (0.37%). As the fractional (15)N content of substrate NO(-) 3 increased from natural abundance, the product (15)N fraction deviated significantly from that expected based on substrate enrichment and (15)N discrimination measured at natural abundance. Additionally, isotopic discrimination by denitrifying bacteria used to reduce NO(-) 3 and NO(-) 2 in some protocols became a greater source of error as (15)N enrichment increased. We briefly discuss potential causes of the experimental artifacts with enriched (15)N and recommend against the use of highly enriched (15)N tracers to study N discrimination in plants or soils.

Dietary deficiencies of zinc and iron are a substantial global public health problem. An estimated two billion people suffer these deficiencies, causing a loss of 63 million life-years annually. Most of these people depend on C3 grains and legumes as their primary dietary source of zinc and iron. Here we report that C3 grains and legumes have lower concentrations of zinc and iron when grown under field conditions at the elevated atmospheric CO2 concentration predicted for the middle of this century. C3 crops other than legumes also have lower concentrations of protein, whereas C4 crops seem to be less affected. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partly address these new challenges to global health.

Genome-wide significant associations with cigarettes per day (CPD) and risk for lung cancer and chronic obstructive pulmonary disease (COPD) were previously reported in a region of 19q13, including CYP2A6 (nicotine metabolism enzyme) and EGLN2 (hypoxia response). The associated single nucleotide polymorphisms (SNPs) were assumed to be proxies for functional variation in CYP2A6. Here, we demonstrate that when CYP2A6 and EGLN2 genotypes are analyzed together, the key EGLN2 variant, rs3733829, is not associated with nicotine metabolism independent of CYP2A6, but is nevertheless independently associated with CPD, and with breath carbon monoxide (CO), a phenotype associated with cigarette consumption and relevant to hypoxia. SNPs in EGLN2 are also associated with nicotine dependence and with smoking efficiency (CO/CPD). These results indicate a previously unappreciated novel mechanism behind genome-wide significant associations with cigarette consumption and disease risk unrelated to nicotine metabolism.

Background and Aims: Evidence suggests that both the nicotinic receptor α5 subunit (CHRNA5) and Cytochrome P450 2A6 (CYP2A6) genotypes influence smoking cessation success and response to pharmacotherapy. We examine the effect of CYP2A6 genotype on smoking cessation success and response to cessation pharmacotherapy, and combine these effects with those of CHRNA5 genotypes., Design: Placebo-controlled randomized smoking cessation trial., Setting: Ambulatory care facility in Wisconsin, USA., Participants: Smokers (n = 709) of European ancestry were randomized to placebo, bupropion, nicotine replacement therapy or combined bupropion and nicotine replacement therapy., Measurements: Survival analysis was used to model time to relapse using nicotine metabolism derived from CYP2A6 genotype-based estimates. Slow metabolism is defined as the lowest quartile of estimated metabolic function., Findings: CYP2A6-defined nicotine metabolic function moderated the effect of smoking cessation pharmacotherapy on smoking relapse over 90 days [hazard ratio (HR) = 2.81, 95% confidence interval (CI) = 1.32-5.99, P = 0.0075], with pharmacotherapy significantly slowing relapse in fast (HR = 0.39, 95% CI = 0.28-0.55, P = 1.97 × 10(-8)), but not slow metabolizers (HR = 1.09, 95% CI = 0.55-2.17, P = 0.80). Further, only the effect of nicotine replacement, and not bupropion, varies with CYP2A6-defined metabolic function. The effect of nicotine replacement on continuous abstinence is moderated by the combined genetic risks from CYP2A6 and CHRNA5 (Wald = 7.44, d.f. = 1, P = 0.0064)., Conclusions: Nicotine replacement therapy is effective among individuals with fast, but not slow, CYP2A6-defined nicotine metabolism. The effect of bupropion on relapse likelihood is unlikely to be affected by nicotine metabolism as estimated from CYP2A6 genotype. The variation in treatment responses among smokers with genes may guide future personalized smoking cessation interventions., (© 2013 Society for the Study of Addiction.)

Background: To develop a predictive genetic model of nicotine metabolism. UDP-glucuronosyltransferase-2B10 (UGT2B10) is the primary catalyst of nicotine glucuronidation., Materials and Methods: The conversion of deuterated (D2)-nicotine to D2-nicotine-glucuronide, D2-cotinine, D2-cotinine-glucuronide, and D2-trans-3'-hydroxycotinine were quantified in 188 European Americans, and the contribution of UGT2B10 genotype to variability in first-pass nicotine glucuronidation assessed, following a procedure previously applied to nicotine C-oxidation. The proportion of total nicotine converted to nicotine-glucuronide [D2-nicotine-glucuronide/(D2-nicotine+D2-nicotine-glucuronide+D2-cotinine+D2-cotinine-glucuronide+D2-trans-3'-hydroxycotinine)] was the primary phenotype., Results: The variant, rs61750900T (D67Y) (minor allele frequency=10%), is confirmed to abolish nicotine glucuronidation activity. Another variant, rs112561475G (N397D) (minor allele frequency=2%), is significantly associated with enhanced glucuronidation. rs112561475G is the ancestral allele of a well-conserved amino acid, indicating that the majority of human UGT2B10 alleles are derived hypomorphic alleles., Conclusion: CYP2A6 and UGT2B10 genotype explain 53% of the variance in oral nicotine glucuronidation in this sample. CYP2A6 and UGT2B10 genetic variants are also significantly associated with undeuterated (D0) nicotine glucuronidation in individuals smoking ad libitum. We find no evidence for further common variation markedly influencing hepatic UGT2B10 expression in European Americans.

The Cytochrome P450 2B6 (CYP2B6) enzyme makes a small contribution to hepatic nicotine metabolism relative to CYP2A6, but CYP2B6 is the primary enzyme responsible for metabolism of the smoking cessation drug bupropion. Using CYP2A6 genotype as a covariate, we find that a non-coding polymorphism in CYP2B6 previously associated with smoking cessation (rs8109525) is also significantly associated with nicotine metabolism. The association is independent of the well-studied non-synonymous variants rs3211371, rs3745274, and rs2279343 (CYP2B6*5 and *6). Expression studies demonstrate that rs8109525 is also associated with differences in CYP2B6 mRNA expression in liver biopsy samples. Splicing assays demonstrate that specific splice forms of CYP2B6 are associated with haplotypes defined by variants including rs3745274 and rs8109525. These results indicate differences in mRNA expression and splicing as potential molecular mechanisms by which non-coding variation in CYP2B6 may affect enzymatic activity leading to differences in metabolism and smoking cessation.

Premise of the Study: Cultivated tomato, Solanum lycopersicum, suffers chilling induced wilting because water movement through its roots decreases with declining soil temperatures. Certain wild tomato species exhibit resistance to chilling-induced wilting, but the extent of this chilling tolerance in wild tomatoes is not known. •, Methods: We measured shoot wilting during root chilling in wild Solanum accessions from habitats differing in elevation, temperature, and precipitation. We also measured shoot wilting during root chilling in introgression lines (ILs) with chromosome 9 segments collinear to the shoot turgor maintenance QTL stm9 region from chilling-tolerant S. habrochaites, chilling and drought-tolerant S. lycopersicoides, or drought-tolerant S. pennellii. •, Key Results: Wild tomato species, which experience chilling temperatures (<10°C) in their native habitat, maintain shoot turgor under root chilling. Among accessions of S. lycopersicum var. cerasiforme, a typically chilling sensitive species, shoot turgor maintenance during root chilling was correlated with the precipitation of the native habitat. By contrast, S. pennellii, a species that is typically drought adapted, did not maintain turgor under root chilling. Grafted plants with roots containing S. habrochaites and S. lycopersicoides introgressions improved shoot turgor maintenance under root chilling. •, Conclusions: Resistance to chilling-induced water stress is an important adaptation to chilling temperatures in wild tomatoes. There is some overlap in adaptation to drought and chilling stress in some tomato species. Root-based resistance to chilling-induced water stress in wild tomatoes may involve orthologous gene(s).

Terrestrial higher plants are composed of roots and shoots, distinct organs that conduct complementary functions in dissimilar environments. For example, roots are responsible for acquiring water and nutrients such as inorganic nitrogen from the soil, yet shoots consume the majority of these resources. The success of such a relationship depends on excellent root-shoot communications. Increased net photosynthesis and decreased shoot nitrogen and water use at elevated CO2 fundamentally alter these source-sink relations. Lower than predicted productivity gains at elevated CO2 under nitrogen or water stress may indicate shoot-root signaling lacks plasticity to respond to rising atmospheric CO2 concentrations. The following presents recent research results on shoot-root nitrogen and water signaling, emphasizing the influence that rising atmospheric carbon dioxide levels are having on these source-sink interactions.

A synonymous variant in the first exon of CYP2A6, rs1137115 (51G>A), defines the common reference allele CYP2A6*1A, and is associated with lower mRNA expression and slower in-vivo nicotine metabolism. Another common allele, CYP2A6*14, differs from CYP2A6*1A by a single variant, rs28399435 (86G>A, S29N). However, CYP2A6*14 shows in-vivo activity comparable with that of full-function alleles, and significantly higher than CYP2A6*1A. rs1137115A is predicted to create an exonic splicing suppressor site overlapping an exonic splicing enhancer (ESE) site in the first exon of CYP2A6, whereas rs28399435A is predicted to strengthen another adjacent ESE, potentially compensating for rs1137115A. Using an allelic expression assay to assess cDNAs produced from rs1137115 heterozygous liver biopsy samples, lower expression of the CYP2A6*1A allele is confirmed while CYP2A6*14 expression is found to be indistinguishable from that of rs1137115G alleles. Quantitative PCR assays to determine the relative abundance of spliced and unspliced or partially spliced CYP2A6 mRNAs in liver biopsy samples show that *1A/*1A homozygotes have a significantly lower ratio, due to both a reduction in spliced forms and an increase in unspliced or partially spliced CYP2A6. These results show the importance of common genetic variants that effect exonic splicing suppressor and ESEs to explain human variation regarding clinically-relevant phenotypes.

Background: Flavin-containing monooxygenases (FMO) catalyze the metabolism of nucleophilic heteroatom-containing drugs and xenobiotics, including nicotine. Rare mutations in FMO3 are responsible for defective N-oxidation of dietary trimethylamine leading to trimethylaminuria, and common genetic variation in FMO3 has been linked to interindividual variability in metabolic function that may be substrate specific., Methods: A genetic model of CYP2A6 function is used as a covariate to reveal functional polymorphism in FMO3 that indirectly influences the ratio of deuterated nicotine metabolized to cotinine following oral administration. The association is tested between FMO3 haplotype and cigarette consumption in a set of nicotine-dependent smokers., Results: FMO3 haplotype, based on all common coding variants in Europeans, significantly predicts nicotine metabolism and accounts for ∼2% of variance in the apparent percent of nicotine metabolized to cotinine. The metabolic ratio is not associated with FMO2 haplotype or an FMO1 expression quantitative trait locus. Cross-validation demonstrates calculated FMO3 haplotype parameters to be robust and significantly improve the predictive nicotine metabolism model over CYP2A6 genotype alone. Functional classes of FMO3 haplotypes, as determined by their influence on nicotine metabolism to cotinine, are also significantly associated with cigarettes per day in nicotine-dependent European Americans (n=1025, P=0.04), and significantly interact (P=0.016) with CYP2A6 genotype to predict cigarettes per day., Conclusion: These findings suggest that common polymorphisms in FMO3 influence nicotine clearance and that these genetic variants in turn influence cigarette consumption.

This study demonstrates a novel approach to test associations between highly heterogeneous genetic loci and complex phenotypes. Previous investigations of the relationship between Cytochrome P450 2A6 (CYP2A6) genotype and smoking phenotypes made comparisons by dividing subjects into broad categories based on assumptions that simplify the range of function of different CYP2A6 alleles, their numerous possible diplotype combinations and non-additive allele effects. A predictive model that translates CYP2A6 diplotype into a single continuous variable was previously derived from an in vivo metabolism experiment in 189 European Americans. Here, we apply this model to assess associations between genotype, inferred nicotine metabolism and smoking behaviors in larger samples without direct nicotine metabolism measurements. CYP2A6 genotype is not associated with nicotine dependence, as defined by the Fagerström Test of Nicotine Dependence, demonstrating that cigarettes smoked per day (CPD) and nicotine dependence have distinct genetic correlates. The predicted metric is significantly associated with CPD among African Americans and European American dependent smokers. Individual slow metabolizing genotypes are associated with lower CPD, but the predicted metric is the best predictor of CPD. Furthermore, optimizing the predictive model by including additional CYP2A6 alleles improves the fit of the model in an independent data set and provides a novel method of predicting the functional impact of alleles without direct metabolism measurements. Lastly, comprehensive genotyping and in vivo metabolism data are used to demonstrate that genome-wide significant associations between CPD and single nucleotide polymorphisms are the result of synthetic associations.

This study measured total osmolarity and concentrations of NH(4)(+), NO(3)(-), K(+), soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH(4)(+) and NO(3)(-) in xylem sap for plants receiving NH(4)(+) or NO(3)(-) as a sole N-source, NH(4)(+) plus NO(3)(-), or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH(4)(+) indicated that growing cells imported NH(4)(+) from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH(4)(+) absorbed. Net root NO(3)(-) influx under Ca(NO(3))(2) nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced. The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3). These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

The CO2 concentration in Earth's atmosphere may double during this century. Plant responses to such an increase depend strongly on their nitrogen status, but the reasons have been uncertain. Here, we assessed shoot nitrate assimilation into amino acids via the shift in shoot CO2 and O2 fluxes when plants received nitrate instead of ammonium as a nitrogen source (deltaAQ). Shoot nitrate assimilation became negligible with increasing CO2 in a taxonomically diverse group of eight C3 plant species, was relatively insensitive to CO2 in three C4 species, and showed an intermediate sensitivity in two C3-C4 intermediate species. We then examined the influence of CO2 level and ammonium vs. nitrate nutrition on growth, assessed in terms of changes in fresh mass, of several C3 species and a Crassulacean acid metabolism (CAM) species. Elevated CO2 (720 micromol CO2/mol of all gases present) stimulated growth or had no effect in the five C3 species tested when they received ammonium as a nitrogen source but inhibited growth or had no effect if they received nitrate. Under nitrate, two C3 species grew faster at sub-ambient (approximately 310 micromol/mol) than elevated CO2. A CAM species grew faster at ambient than elevated or sub-ambient CO2 under either ammonium or nitrate nutrition. This study establishes that CO2 enrichment inhibits shoot nitrate assimilation in a wide variety of C3 plants and that this phenomenon can have a profound effect on their growth. This indicates that shoot nitrate assimilation provides an important contribution to the nitrate assimilation of an entire C3 plant. Thus, rising CO2 and its effects on shoot nitrate assimilation may influence the distribution of C3 plant species.

Precise targeting of retinal projections is required for the normal development of topographic maps in the mammalian primary visual system. During development, retinal axons project to and occupy topographically appropriate positions in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC). Phr1 retinal mutant mice, which display mislocalization of the ipsilateral retinogeniculate projection independent of activity and ephrin-A signaling, were found to have a more global disruption of topographic specificity of retinofugal inputs. The retinocollicular projection lacks local refinement of terminal zones and multiple ectopic termination zones originate from the dorsal-nasal (DN) retinal quadrant. Similarly, in the dLGN, the inputs originating from the contralateral DN retina are poorly refined in the Phr1 mutant. These results show that Phr1 is an essential regulator of retinal ganglion cell projection during both dLGN and SC topographic map development., (Copyright © Cambridge University Press, 2010)

The concentration of carbon dioxide in Earth's atmosphere may double by the end of the 21st century. The response of higher plants to a carbon dioxide doubling often includes a decline in their nitrogen status, but the reasons for this decline have been uncertain. We used five independent methods with wheat and Arabidopsis to show that atmospheric carbon dioxide enrichment inhibited the assimilation of nitrate into organic nitrogen compounds. This inhibition may be largely responsible for carbon dioxide acclimation, the decrease in photosynthesis and growth of plants conducting C(3) carbon fixation after long exposures (days to years) to carbon dioxide enrichment. These results suggest that the relative availability of soil ammonium and nitrate to most plants will become increasingly important in determining their productivity as well as their quality as food.