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Two experiments were conducted in a naturally lit research greenhouse to validate our modified strategy for delivering nutrients to sub-irrigated chrysanthemum plants. A split-plot design was used with four blocks arranged randomly, three nutrient rates as the main plot, and two contrasting cultivars as the subplot. The entire nutrient supply was removed at bud break and markedly reduced during vegetative growth, compared to common commercial fertilizer formulations, without adversely affecting tissue nutrient levels and plant/inflorescence quality, indicating that the plants were functioning in the low nutrient sufficiency zone. Specific nutrients (Nt) were more likely to exhibit improved uptake efficiency (shoot Nt content/Nt supply) than improved utilization efficiency (inflorescence DM/shoot Nt content) with decreasing nutrient supply. Thus, the common practice of delivering superfluous nutrient levels to greenhouse-grown chrysanthemum has little scientific merit in terms of nutrient accumulation and plant longevity. Applying a low‐input nutrient delivery strategy to the cultivation of indoor-grown, potted ornamental plants would improve the overall sustainability of the Canadian floricultural industry. [ABSTRACT FROM AUTHOR]

Abstract: We discuss the origin of 4-aminobutyrate (GABA) from glutamate and polyamines, and its subsequent catabolism to succinic semialdehyde and either succinate or 4-hydroxybutyrate. Promiscuous activities of GABA transaminase, glyoxylate/succinic [...]

Abstract: 4-Aminobutyrate (GABA) is a nonproteinogenic amino acid that functions in stress tolerance and signaling. Here, we report that salinity stress and elevated GABA levels coincided with the induction of [...]

The ubiquitous nonprotein amino acid known as [gamma]-aminobutyrate (GABA) has been proposed as a mechanism whereby environmental and developmental cues are translocated in phloem. Information about the composition of translocation fluids from various species that bleed spontaneously reveals that GABA is always present in xylem at minor levels, but sometimes absent in phloem. In species that do not bleed spontaneously, GABA is also absent or present at minor levels in aphid stylet exudate. By contrast, GABA in ethylene-diaminetetraacetate-facilitated phloem exudates is relatively abundant compared to other amino acids or the concentration of total amino acids present in xylem. Evidence indicates that xylemborne GABA is primarily retrieved and metabolized by mature leaves, and tissue pools of GABA reflect in situ biosynthesis. Recovery of significant GABA from phloem might be an artifact of wounding and the use of ethylene-diaminetetraacetate. Scarce data from aphid stylectomy experiments indicates that GABA is a wound signal. However, the composition of phloem sap collected by this method is not uniform, shedding doubt on some results in the scientific literature. Elevated GABA levels in the host plant are known to influence the success of biotic interactions; however, these outcomes could be attributed to the impact of wounding at local sites, rather than delivery of GABA via phloem. Further research is required to provide unambiguous support for long-distance [gamma]-aminobutyrate signaling in phloem. Key words: [gamma]-aminobutyrate, phloem, signaling, translocation, biotic interactions. On a propose que l'acide amine nonproteique ubiquiste connu sous le nom de y-aminobutyrate (AAGB) constitue un mecanisme par lequel des signaux environnementaux et developpementaux se deplacent vers le phloeme. L'information au sujet de la composition des fluides de deplacement, chez diverses especes perdant spontanement de la seve, revele une presence constante l'AAGB a faibles teneurs dans le xyleme, mais quelques fois son absence dans le phloeme. Chez les especes ne perdant pas de seve spontanement, l'AAGB on note egalement l'absence ou la presence en faible quantite dans les exsudats obtenus a partir de stylets de pucerons. Au contraire, l'AAGB dans le tetraacetate d'ethylene diamine (TEDA) facilite l'exsudation du phloeme en quantite relativement abondante, comparativement a d'autres acides amines ou a la teneur totale des acides amines presents dans le xyleme. Tout indique que l'AAGB provenant du xyleme est surtout tire et metabolise par les feuilles matures et que les reserves histologiques en AAGB refletent la biosynthese in situ. La recuperation de quantites significatives d'AAGB a partir du phloeme pourrait representer un artefact provenant de blessures et de l'utilisation du TEDA. Les rares donnees provenant d' experiences de stylectomie de pucerons indiquent que l'AAGB constitue un signal de blessure. Cependant, la composition de la seve du phloeme recoltee avec cette methode n' etant pas uniforme, ceci seme un doute sur certains resultats provenant de la litterature scientifique. On sait que la presence de fortes teneurs en AAGB dans la plante hote influence le succes des interactions biotiques; cependant, on pourrait attribuer ces observations a l'impact d'une blessure sur des sites localises, plutot qu'a un deversement d'AAGB via le phloeme. On doit conduire d'autres recherches pour obtenir une preuve sans ambigiiite supportant une signalisation a longue distance par la [gamma]-aminobutyrate dans le phloeme. Mots-cles : [gamma]-aminobutyrate, phloeme, signalisation, translocation, interactions. [Traduit par la Redaction], In vascular plants, long-distance translocation from roots to regions of transpiration in the shoot occurs through xylem, whereas translocation from photosynthetically active leaves to sites where photosynthate is consumed either [...]

γ-Aminobutyrate (GABA) is a ubiquitous nonprotein amino acid that accumulates in plants in response to abiotic and biotic stresses. In a companion paper, we discussed the origin of GABA from glutamate and subsequent catabolism to succinic semialdehyde and either succinate or γ-hydroxybutyrate (GHB), and the characteristics of genes and proteins responsible for GABA permease, glutamate decarboxylase, GABA transaminase, succinic semialdehyde dehydrogenase, and succinic semialdehyde reductase activities. In this paper, we explore gene expression and transcript-metabolite relationships during the response to abiotic stress, and describe phenotypes of genetic mutants and relationships of GABA metabolism to other plant functions. Evidence indicates that both gene-dependent and -independent processes are involved in the response of the GABA pathway to abiotic stresses. Study of stress-specific responses and their interplay with the C/N network and various signalling pathways would be more informative if circadian rhythms and light-dark transitions upon imposition of the stress were always taken into account, and relevant genes and metabolites simultaneously profiled in wild-type plants or genetic mutants. Key words: abiotic stress, metabolomics, mutants, signaling, transcriptomics, translatomics. Le γ-Aminobutyrate (GABA) est un acide amine non proteinique ubiquiste s'accumulant dans les plantes en reaction a des stress abiotiques et biotiques. Dans une publication antecedente apparentee, les auteurs ont discute de l'origine du GABA a partir du glutamate et son catabolisme subsequent en semi-aldehyde succinique et en succinate ou γ- hydroxybutyrate (GHB), ainsi que des caracteristiques genes et proteines responsables des activites GABA permease, glutamate decarboxylase, GABA transaminase, deshydrogenase semi-aldehyde succinique et reductase semi-aldehyde succinique. Ici, les auteurs explorent l'expression des genes et les relations transcript-metabolite au cours de la reaction a un stress abiotique et ils decrivent les phenotypes des mutants genetiques ainsi que les relations du metabolisme du GABA avec d'autres fonctions de la plante. La preuve indique que des processus dependants aussi bien qu'independants des genes sont impliques dans la reaction du sentier GABA aux stress abiotiques. Les etudes de reactions specifiques au stress et leurs interactions avec le reseau C/N ainsi que divers sentiers de signalisation fourniraient de meilleures informations si les rythmes circadiens et les transitions lumiere-noirceur au moment d'appliquer le stress etaient prises en compte, et que les genes et les metabolites impliques etaient simultanement profiles chez les plantes de type sauvage et les mutant genetiques. Mots-cles : stress abiotique, metabolomique, mutants, signalisation, transcriptomique, translatomique. [Traduit par la Redaction], Introduction Numerous studies have demonstrated that γ-aminobutyrate (GABA) accumulates in plants upon exposure to abiotic and biotic stresses (Shelp et al. 1999, 2009; Kinnersley and Turano 2000) so that GABA [...]

γ-Aminobutyrate (GABA) is a ubiquitous four-C, nonprotein, amino acid that has been linked to stress, signaling, and storage in plants. In this paper, we discuss analytical, enzyme-linked, and colorimetric methods for analyzing GABA and related metabolites, and review tracer evidence for the derivation of GABA from glutamate and its subsequent catabolism to succinic semialdehyde and either succinate or γ-hydroxybutyrate. Also, we describe biochemical, complementation, bioinformatic, recombinant, and modelling strategies for identifying genes and investigating properties of the encoded proteins responsible for transport and metabolism of GABA. For Arabidopsis, evidence supports the involvement of a plasma membrane GABA transporter, a mitochondrial GABA permease, a cytosolic [Ca.sup.2+]/calmodulin- and pH-regulated cytosolic glutamate decarboxylase, a pyruvate- and glyoxylate-regulated mitochondrial GABA transaminase, a redox-regulated mitochondrial succinic semialdehyde dehydrogenase, and redox-regulated glyoxylate/succinic semialdehyde reductases located in both cytosol and plastid, respectively. This simple biochemical model does not account for species and tissue differences in the isoform complement of GABA pathway enzymes or transcriptional control of the pathway. In a companion review, we provide a more integrated view of GABA metabolism and function. Key words: γ-aminobutyrate, γ-hydroxybutyrate, gene isolation, metabolism, proteins, protein structure- function, transport. L'aminobutyrate (GABA) est un acide amine non proteique ubiquiste a quatre carbones, souvent relie au stress, a la signalisation et a la reserve des plantes. Les auteurs discutent les liens enzymatiques et les methodes colorimetriques pour l' analyse du GABA et metabolites relies, et les preuves par tracage concernant la derivation du GABA a partir du glutamate ainsi que son catabolisme subsequent en semialdehyde succinique ou encore en γ-hydroxybutyrate. Il decrivent de plus les strategies biochimiques, de complementarisation, de bio-informatique, de recombinant et de modelisation pour identifier les genes et etudier les proprietes des proteines encodees responsables pour le transport et le metabolisme du GABA. Chez l'Arabidopsis, la preuve supporte l'implication d'un transporteur du GABA dans la membrane plasmique, d'une permease mitochondriale du GABA, d'une [Ca.sup.2+]/calmoduline cytosolique, d'une decarboxylase glutamique cytosolique regulee par le pH, d'une transaminase mitochondriale regulee par le pyruvate et le glyoxalate, une deshydrogenase succinique semialdehyde regulee par la redox, des reductases glyoxylate/succinique semialdehydes regulees par la redox localisees dans le cytosol et les plastes, respectivement. Ce modele biochimique simple ne tient pas compte des differences histologiques et specifiques dans la forme complementaire les sentiers enzymatiques du GABA, ou du controle transcriptionnel du sentier. Dans une revue complementaire, les auteurs presentent un regard plus integre du metabolisme et de la fonction du GABA. Mots-cles: γ-aminobutyrate, γ-hydroxybutyrate, isolement de genes, metabolisme, proteines, structure- fonction des proteines, transport. [Traduit par la Redaction], Introduction γ-Aminobutyrate (GABA) is a ubiquitous four-C, nonprotein, amino acid found in prokaryotes and eukaryotes (Satya Narayan and Nair 1990; Shelp et al. 1999). GABA was first identified in potato [...]

Succinate semialdehyde (SSA) is a mitochondrially generated intermediate in the metabolism of γ-aminobutyrate (GABA), which accumulates in response to a variety of biotic and abiotic stresses. SSA can be reduced to γ- hydroxybutyrate (GHB) in plants exposed to various abiotic stress conditions. Recent evidence indicates that distinct cytosolic and plastidial glyoxylate reductase isoforms from Arabidopsis thaliana (L.) Heynh (GLYR1 and GLYR2, respectively) catalyze the in vitro conversion of SSA to GHB, as well as glyoxylate to glycolate, via NADPH-dependent reactions. In the present study, recombinant Arabidopsis GLYR1 was demonstrated to catalyze the NADPH-dependent reduction of both glyoxylate and SSA simultaneously to glycolate and GHB, respectively. Six-hour time-course experiments with intact vegetative wild-type Arabidopisis plants subjected to submergence demonstrated that GHB accumulates in rosette leaves, and this is accompanied by increasing levels of GABA and alanine, NADH/[NAD.sup.+] and NADPH/[NADP.sup.+] ratios, and GLYR1 and GLYR2 transcript abundance. The use of GLYR (glyr1 or glyr2 knockout) and NAD kinase1 (NADK1 suppression or overexpression) mutants demonstrated that under submergence the production of GHB is mediated via both GLYR isoforms, the loss of either GLYR1 or GLYR2 activity influences redox status and the levels of GABA and alanine, and the manipulation of NADP(H) availability, specifically in the cytosol, influences the production of GHB. These results suggest that biochemical mechanisms are more important than transcriptional mechanisms in the regulation of GLYR activity and SSA detoxification in plants during the onset of submergence-induced oxygen deficiency. Key words: abiotic stress, γ-aminobutyrate, γ-hydroxybutyrate, NAD kinase, pyridine nucleotide, succinate semialdehyde, transgenic plants. La succinate semialdehyde (SSA) est un intermediaire genere dans les mitochondries lors du metabolisme des γ-aminobutyrate (GABA), s'accumulat en reaction a une variete de stress biotiques et abiotiques. La SSA peut etre reduite en γ-hydroxybutyrate (GHB) chez les plantes exposees a diverses conditions de stress abiotique. Des donnees recentes indiquent que les differentes isoformes cytosoliques et plastidiques de la glyoxylate reductase d'Arabidopsis thaliana (L.) Heynh (GLYR1 et GLYR2, respectivement) catalysent la conversion in vitro de la SSA en GHB, ainsi que le glyoxylate en glycolate, par le biais de reactions NADPH dependantes. La presente etude demontre que le recombinant Arabidopsis GLYR1 catalyse simultanement la reduction dependante du NADPH de la glyoxylate et de la SSA en glycolate et GHB respectivement. Des experiences d'une duree de six heures ont demontre que des plants d'Arabidopsis intacts de type sauvage soumis a l'immersion accumulent le GHB dans les feuilles en rosette et ceci est accompagne d'une augmentation des niveaux de GABA et d'alanine, du ratio NADH/[NAD.sup.+] et NADPH/[NADP.sup.+], une abondance des transcrits de GLYR1 et GLYR2. L'utilisation de mutants GLYR (glyr1 ou glyr2 inactive) et NAD kinase1 (NADK1 supprime ou surexprime) a demontre que sous immersion, la production de GHB est regulee par les deux isoformes GLYR, la perte d'activite soit de GLYR1 ou de GLYR2 influence le statut redox et les niveaux de GABA et d'alanine, et la modification de la disponibilite de NADP(H) specifiquement dans le cytosol influence la production de GHB. Ces resultats suggerent que les mecanismes biochimiques sont plus importants que les mecanismes transcriptionnels dans la regulation de l'activite GLYR et de la detoxification de SSA chez les plantes des l'apparition d'une carence en oxygene induite par l'immersion. Mots-cles : stress abiotique, γ-aminobutyrate, γ-hydroxybutyrate, NAD kinase, nucleotide pyrimidique, succinate semialdehyde, plantes transgeniques. [Traduit par la Redaction], Introduction The aldehyde chemical grouping (i.e., H-C=O) is found in many molecules involved in cellular functions. These molecules, known as aldehydes, can accumulate in plants and become toxic because of [...]

Production of high-lutein maize grain is of particular interest as a value-added feed source to produce high-lutein eggs. In this paper, it is demonstrated that heterosis for total carotenoid concentration and for the ratio of lutein to zeaxanthin (L:Z ratio), or profile type, exists infrequently in yellow dent crosses. However, yellow dent inbred maize lines A619 and CG102, both possessing high-lutein profiles, produce [F.sub.1] seed with a classic overdominant expression of lutein levels (i.e., 49 µg/g dry weight (DW) above the high-parent value). Reciprocal crosses of A619 and CG102 with one another and with two high-zeaxanthin (i.e., low lutein), high-carotenoid lines both suggest that the A6i9 and CGi02 high-lutein phenotypes are achieved by different and complementary genotypes. The contribution of CG102 to the heterotic response was examined using a QTL-based approach that involved phenotyping the mapping population in a testcross to A619. Significant QTL were found at loci known to be involved in the carotenoid pathway but also at loci proximate to, but separate from, known carotenoid pathway steps. Exploiting an overdominant heterotic response for lutein and total carotenoids should be given strong consideration as a viable method of producing high-carotenoid hybrid maize lines. Key words: maize, heterosis, QTL, carotenoid, lutein, zeaxanthin. La production de mais a forte teneur en luteine presente de l'interet comme ingredient de moulee a valeur ajoutee pour la production d'oeufs riches en luteine. Dans ce travail, les auteurs montrent qu'il existe rarement de l'heterosis pour la concentration en carotenoides totaux et pour le ratio luteine : zeaxanthine (ratio L:Z), aussi connu sous le nom de profil, au sein de croisements entre mais dentes jaunes. Cependant, les lignees fixees de type dente jaune A6i9 et CGi02, tous deux ayant un profil a forte teneur en luteine, produisent des [F.sub.1] presentant une expression surdominante en matiere de luteine (49 µg/g au dessus du parent superieur sur une base de poids sec). Des croisements reciproques entre A619 et CG102 de meme qu'avec deux lignees riches en carotenoides de type zeaxanthine (et donc faibles en luteine) ont suggere que les phenotypes luteine-riche de A6i9 et CGi02 etaient le produit de genotypes differents et complementaires. La contribution de CGi02 a la reponse heterotique a ete examinee en employant une approche de cartographie QTL, soit en realisant une caracterisation phenotypique d'une population de cartographie derivee d'un croisement test avec A619. Des QTL significatifs ont ete trouves a des locus connus comme etant impliques dans le sentier de synthese des carotenoides, mais egalement a des locus a proximite mais distincts de genes dans ce sentier. Il serait ainsi utile d'exploiter cette reponse heterotique surdominante pour la teneur en luteine et en carotenoides totaux pour developper des hybrides de mais a forte teneur en carotenoides. Mots-cles : mais, heterosis, QTL, carotenoide, luteine, zeaxanthine. [Traduit par la Redaction], Introduction Maize (Zea mays L.) grain is a source of several healthrelated carotenoids, of which lutein and zeaxanthin are the most abundant (Buckner et al. 1996). These two carotenoids are [...]

We tested the hypothesis that γ-aminobutyrate transaminase (GABA-T) regulates the supply of succinate semialdehyde for succinate semialdehyde dehydrogenase or NADPH-dependent glyoxylate/succinate semialdehyde reductase 1 (GLYR1) during stress. Constitutive overexpression (OX) lines of GABA-T were generated in Arabidopsis via the floral-dip method for Agrobacterium-mediated transformation. Polymerase chain reaction enabled selection of four transgenic lines with higher GABA-T transcript levels than the wild-type (WT), but assay of cell-free leaf extracts revealed that only OX1 had elevated GABA-T activity. Brief cold treatments (4°C exposure for 20 min or 1 h in the dark) increased leaf GABA concentrations in both the WT and OX1, but the concentrations in OX1 were consistently lower. These findings confirm that GABA-T limits the catabolism of GABA when its production is stimulated by stress, and suggest a bioengineering strategy for improving the availability of succinate semialdehyde for the Krebs cycle or GLYR1, a potential redox-modulating reaction during stress. Key words: abiotic stress, γ-aminobutyrate, γ-aminobutyrate transaminase, γ-hydroxybutyrate, succinate semialdehyde reductase, transgenic plants. Les auteurs ont verifie l'hypothese selon laquelle la γ-aminobutyrate transaminase (GABA-T) regule la disponibilite de succinate semialdehyde pour la succinate semialdehyde deshydrogenase ou la glyoxylate dependante du NADPH/ succinate semialdehyde reductase 1 (GLYR1) durant un stress. Des ligneees a surexpression constitutive (OX) de GABA-T ont ete generees chez Arabidopsis via une transformation realisee par Agrobacterium selon la meethode de l'immersion florale. La reaction de polymerase en chaine a permis la selection de quatre lignees transgeeniques avec des niveaux de transcription GABA-T plus eleves que les lignees sauvages, mais l'analyse d'extraits foliaires sans cellule a revele que seul OX1 avait une activite GABA-T eeleveee. De brefs traitements au froid (une exposition a 4°C pendant 20 min ou 1 h dans le noir) augmentaient la concentration de GABA dans les feuilles autant pour les lignees sauvages que pour OX1, mais les concentrations chez OX1 etaient systematiquement plus faibles. Ces observations confirment que la GABA-T limite le catabolisme de GABA lorsque sa production est stimuleee par un stress, et suggerent une strategie de genie geneetique pour ameliorer la disponibilite de succinate semialdehyde pour le cycle de Krebs, ou de GLYR1, un modulateur potentiel du processus redox pendant un stress. Mots-cles: stress abiotique, γ-aminobutyrate, γ-aminobutyrate transaminase, γ-hydroxybutyrate, succinate semialdehyde reductase, plantes transgeeniques. [Traduit par la Redaction], Introduction As a consequence of being sessile, plants must rapidly undergo metabolic adaptations to survive stress conditions. Metabolic changes during stress are often associated with alterations in redox homeostasis (i.e., [...]

There is considerable confusion about N use efficiency (NUE) in the plant literature. We would like to propose the simple and ubiquitous definitions described by Good et al. (2004) as a starting point for studies of NUE. Based on this terminology, there is evidence from breeding programs for variation in both uptake efficiency (UpE) and utilization efficiency (NUE). Molecular physiology studies typically address mechanisms for improving NUE, but often do not calculate NUE or even acquire appropriate data for calculating NUE. Herein, we report in detail on recent studies involving molecular approaches for improving NUE, and calculate changes in NUE where possible. The evidence suggests that there is potential for improving usage index and UpE in dicots and UpE and UtE in monocots by overexpressing enzymes for N assimilation, specifically glutamine synthetase 1, glutamate synthase, and alanine aminotransferase. If decreased fertilizer-N input and improved NUE are truly goals of the plant biology community, researchers are encouraged to (i) consider the use of both wild type and azygous controls, (ii) compare general NUE (on the basis of grain or biomass yield per unit of applied N) of overexpression mutants and controls at both limiting and non-limiting N levels, (iii) select an appropriate type of specific NUE for assessing the physiological mechanisms involved (uptake versus internal utilization), and (iv) confirm promising results under field conditions. Key words: bioengineering, dicot, glutamine synthetase, monocot, nitrogen use efficiency, overexpression mutants. Il existe beaucoup de confusion a propos de l'efficacite de l'utilisation de l'azote (NUE) dans la litterature sur les plantes. Comme point de depart pour l'etude de la NUE, les auteurs proposent les definitions simples et ubiquistes decrites par Good et al. (2004). Sur la base de cette terminologie, on trouve des donnees provenant de programmes d'amelioration genetique montrant une variation de l'efficacite; de l'absorption (UpE) et l'efficacite; de l'utilisation (UtE). Les etudes en physiologie moleculaire s'interessent typiquement aux mecanismes pouvant ameliorer la NUE, mais souvent ne calculent pas la NUE ou meme n'obtiennent pas les donnees appropriees pour calculer la NUE. Les auteurs font etats d'etudes recentes impliquant des approches moleculaires pour ameliorer la NUE, et calculent les changements de la NUE oil c'est possible. Les donnees suggerent la possibilite d'ameliorer l'utilisation d'index et de l'UpE chez les dicotyles et UpE ainsi que UtE chez les moncotyles, en surexprimant les enzymes de l'assimilationde N, specifiquement la 1-glutamine synthetase, la glutamate synthase et l'alanine aminotransferase. Si la diminution de l'apport en fertilisant azote; et l'ameelioration de la NUE constituent de veritables enjeux de la communaute des biologistes des plantes, on doit encourager les chercheurs a (i) considerer l'utilisation a la fois des temoins de type sauvage et azygotes, (ii) comparer la NUE generale (sur la base du rendement en biomasse de grains par unite d'azote apportee) de la surexpression des mutants et des temoins en presence d'apport en azote limitant et non limitant, (iii) selectionner un type appropriee de NUE specifique pour evaluer les mecanismes physiologiques impliques (absorption vs utilisation), et (iv) confirmer les resultats prometteurs sous des conditions de terrain. Mots-cles: bioingenierie, dicotyle, glutamine synthetase, monocotyle, efficacite; de l'utilisation de l'azote, surexpression de mutants. [Traduit par la Redaction], Introduction Nitrogen application is necessary to maintain high crop yields, but it comes at a high cost to both the farmer and the environment (Frink et al. 1999; Glass 2003). [...]