Plant Glutamine Research Articles

The Role of Exogenous Glutamine as a Regulator of Gene Expression under Stress Conditions in Plants

Amino acids, which are necessary for the synthesis of proteins as well as some other nitrogenous components in organisms, are effective for the synthesis and in the activities of some enzymes and of gene expression. Stress tolerance is provided by different mechanisms, especially with the accumulation of some specific amino acids under stress conditions in plants. Although the role of some amino acids such as proline under stress conditions has been demonstrated by many studies, the mission of some other amino acids under stress conditions has not yet been fully elucidated. Like other amino acids in organisms, glutamine is involved in the synthesis of nitrogenous compounds such as amino acids and nucleotides. The functions of glutamine in plants, which are known to be involved in signal transmission in humans, yeast, and bacteria, are not yet fully known. For this reason, various studies conducted in recent years have focused on elucidating the role of glutamine in signal transduction pathways under stress conditions. It was revealed by transcriptome analyses that exogenous glutamine applications support growth and development in some plants by inducing the expression of several genes involved in metabolism, transport, signal transduction, and stress response. It was identified that these genes synthesize transcription factors that activate the genes involved in nitrogen metabolism or stress response. The induction of these transcription factor genes by glutamine supports the idea that it functions as a signaling molecule regulating gene expression in plants. In this review, research studies investigating the role of glutamine, especially under stress conditions, were examined, to create a resource for researchers of future studies on this topic.

Protection of Pepper Plants from Drought by Microbacterium sp. 3J1 by Modulation of the Plant's Glutamine and α-ketoglutarate Content: A Comparative Metabolomics Approach.

Drought tolerance of plants such as tomato or pepper can be improved by their inoculation with rhizobacteria such as Microbacterium sp. 3J1. This interaction depends on the production of trehalose by the microorganisms that in turn modulate the phyto-hormone profile of the plant. In this work we describe the characterization of metabolic changes during the interaction of pepper plants with Microbacterium sp. 3J1 and of the microorganism alone over a period of drought. Our main findings include the observation that the plant responds to the presence of the microorganism by changing the C and N metabolism based on its glutamine and α-ketoglutarate content, these changes contribute to major changes in the concentration of molecules involved in the balance of the osmotic pressure. These include sugars and amino-acids; the concentration of antioxidant molecules, of metabolites involved in the production of phytohormones like ethylene, and of substrates used for lignin production such as ferulic and sinapic acids. Most of the altered metabolites of the plant when inoculated with Microbacterium sp. 3J1 in response to drought coincided with the profile of altered metabolites in the microorganism alone when subjected to drought, pointing to a response by which the plant relies on the microbe for the production of such metabolites. To our knowledge this is the first comparative study of the microbe colonized-plant and microbe alone metabolomes under drought stress.

Bacterial Whole-Cell Biosensor for Glutamine with Applications for Quantifying and Visualizing Glutamine in Plants

A whole-cell biosensor for glutamine (GlnLux) was constructed by transforming an Escherichia coli glutamine (Gln) auxotroph with a constitutive lux reporter gene. Measurements of Gln in plant extracts using GlnLux correlated with quantification using high-performance liquid chromatography (Spearman's r = 0.95). GlnLux permitted charge-coupled-device (CCD) imaging of Gln from whole plant organs.

Nitrate Uptake and Reduction in Plants

Summary The nitrogen compounds nitrate and ammonium are the minerals plants need in high quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrate reduction resulting in ammonium which is fixed into the amino acids glutamine and glutamate in most plants. This article concentrates on nitrate uptake and nitrate reduction with respect to higher and lower plants. The physiology and the progress in molecular approaches of both processes are considered. For nitrate uptake the well established uptake systems are discussed and special attention is drawn on nitrate sensing and the distinct nitrate carriers with special consideration of the great number of carriers identified in Arabidopsis. Knowledge particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore further work should consider this topic more frequently. For nitrate reductase the focus is on the post translational modifications as regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metabolism and on the molecular approaches. Few remarks on how environmental conditions affect nitrate assimilation are also included. Further progress is needed to understand the transduction of positive and negative signals from the environment affecting the expression of genes coding for the nitrate assimilating pathway.

Enhanced carbon dioxide leads to a modified diurnal rhythm of nitrate reductase activity in older plants, and a large stimulation of nitrate reductase activity and higher levels of amino acids in young tobacco plants

Higher rates of nitrate assimilation are required to support faster growth in enhanced carbon dioxide. To investigate how this is achieved, tobacco plants were grown on high nitrate and high light in ambient and enhanced (700 μmol mol–1) carbon dioxide. Surprisingly, enhanced carbon dioxide did not increase leaf nitrate reductase (NR) activity in the middle of the photoperiod. Possible reasons for this anomalous result were investigated. (a) Measurements of biomass, nitrate, amino acids and glutamine in plants fertilized once and twice daily with 12 mol m–3 nitrate showed that enhanced carbon dioxide did not lead to a nitrate limitation in these plants. (b) Enhanced carbon dioxide modified the diurnal regulation of NR activity in source leaves. The transcript for nia declined during the light period in a similar manner in ambient and enhanced carbon dioxide. The decline of the transcript correlated with a decrease of nitrate in the leaf, and was temporarily reversed after re‐irrigating with nitrate in the second part of the photoperiod. The decline of the transcript was not correlated with changes of sugars or glutamine. NR activity and protein decline in the second part of the photoperiod, and NR is inactivated in the dark in ambient carbon dioxide. The decline of NR activity was smaller and dark inactivation was partially reversed in enhanced carbon dioxide, indicating that post‐transcriptional or post‐translational regulation of NR has been modified. The increased activation and stability of NR in enhanced carbon dioxide was correlated with higher sugars and lower glutamine in the leaves. (c) Enhanced carbon dioxide led to increased levels of the minor amino acids in leaves. (d) Enhanced carbon dioxide led to a large decrease of glycine and a small decrease of serine in leaves of mature plants. The glycine:serine ratio decreased in source leaves of older plants and seedlings. The consequences of a lower rate of photorespiration for the levels of glutamine and the regulation of nitrogen metabolism are discussed. (e) Enhanced carbon dioxide also modified the diurnal regulation of NR in roots. The nia transcript increased after nitrate fertilization in the early and the second part of the photoperiod. The response of the transcript was not accentuated in enhanced carbon dioxide. NR activity declined slightly during the photoperiod in ambient carbon dioxide, whereas it increased 2‐fold in enhanced carbon dioxide. The increase of root NR activity in enhanced carbon dioxide was preceded by a transient increase of sugars, and was followed by a decline of sugars, a faster decrease of nitrate than in ambient carbon dioxide, and an increase of nitrite in the roots. (f) To interpret the physiological significance of these changes in nitrate metabolism, they were compared with the current growth rate of the plants. (g) In 4–5‐week‐old plants, the current rate of growth was similar in ambient and enhanced carbon dioxide (≈ 0·4 g–1 d–1). Enhanced carbon dioxide only led to small changes of NR activity, nitrate decreased, and overall amino acids were not significantly increased. (h) Young seedlings had a high growth rate (0·5 g–1 d–1) in ambient carbon dioxide, that was increased by another 20% in enhanced carbon dioxide. Enhanced carbon dioxide led to larger increases of NR activity and NR activation, a 2–3‐fold increase of glutamine, a 50% increase of glutamate, and a 2–3‐fold increase in minor amino acids. It also led to a higher nitrate level. It is argued that enhanced carbon dioxide leads to a very effective stimulation of nitrate uptake, nitrate assimilation and amino acid synthesis in seedlings. This will play an important role in allowing faster growth rates in enhanced carbon dioxide at this stage.

RÔLES OF GLUTAMINE IN GROWTH OF LACTOBACILLUS ARABINOSUS

A characteristic sigmoidal dose-response curve is usually obtained for n-glutamic acid in microbiological assays. When small amounts of n-glutamine are added to the basal medium, the response to glutamic acid is markedly enhanced at the lower concentrations (1). Archibald reviewed the known physiological r8les of glutamine in plants, animals, and microorganisms (‘2). In an addendum to the latter review, numerous references were given to reports showing growth-stimulating effects of glutamine on various strains of bacteria, fungi, and protozoa. Subsequently, important progress was made in the knowledge of the mechanism of glutamine synthesis (3, 4) and of the participation of glutamine in amide exchange reactions in bacteria (5,6) j plants (7)) and animals (8)) and in transamination in animal tissues (9). However, little is known of the importance of these reactions in growth processes. The purpose of the present investigation is to extend such knowledge by a study of the influence of glutamine on the utilization for growth of the optical isomers of glutamic acid and of a-ketoglutarate by Lactobacillus arabinosus 17-5.