15n NMR Spectroscopic Study of Ammonium Ion Assimilation by Spirodela Oligorrhiza—lemnaceae—as Affected by Light and Carbon Supply in Green and Extoliated Plants

Abstract

This article is dedicated to the memory of my father, Professor Shaul Paul Monselise, a decade after his departure.ABSTRACT Nitrogen assimilation and amino acid production in Spirodela oligorrhiza plants exposed to 30 mM 15 NHFI was studied using 15 N NMR spectroscopy. Green and etiolated plants were studied under different light regimes and in the presence of added carbon, either as sucrose or as a-ketoglutarate. Etiolated plants are capable of ammonium assimilation and, as in green plants, this occurs via the glutamine synthetase/glutamine oxoglutarate amine transferase (GS/GOGAT) and the aspartate aminotransferase/asparagine synthetase pathways. The major assimilation products in both etiolated and green plants were glutamine and asparagine. Thus our results confirm that N-amides are key detoxification products when plants are exposed to external ammonium ion, and act as storage reservoirs or sinks for assimilated ammonium. In plants grown under continuous light, ammonium ion was taken up and assimilated to completion. L-methionine DL-sulfoximine, a GS inhibitor, inhibited ammonium ion assimilation but not its uptake. Addition of azaserine, a GOGA T inhibitor, resulted in the disappearance of a-amino signals, and 15 N incorporation into the glutamine amide-N position only. This is evidence for the operation of the GS/GOGAT pathway, as opposed to the glutamate dehydrogenase (GDH) pathway, in both green and etiolated plants. Even in the dark and under various stress conditions, no sign of ammonium ion assimilation via the GDH pathway could be detected.The amount of amino acid metabolites strongly depended on the light regime and the extent of external carbon supply. Supply of a-ketoglutarate to the etiolated plants increased ammonium ion uptake and assimilation. Ornithine and arginine were also formed, consistent with the operation of the ornithine cycle.

Ultraviolet radiation induces stress in etiolated Landoltia punctata, as evidenced by the presence of alanine, a universal stress signal: a 15N NMR study

“…The 15 N-NMR chemical shift assignments were based on published data and compared with those of authentic samples of amino acids. Chemical shifts are reported relative to 15 NH þ 4 at 0 ppm (Monselise & Kost 1998;Monselise et al 2003Monselise et al , 2011. In 15 N-NMR spectroscopy the various nitrogen compounds present in the plants are completely transparent to the method, which probes only 15 N-labelled material in the plant tissue.…”

Bioassay for assessing cell stress in the vicinity of radio-frequency irradiating antennas

“…Etiolated plants (grown in continuous darkness for 5 months) (Fig. 2) were grown under sterile conditions in 250 ml Erlenmeyer flasks (Kimax, Lawrence, Kansas, USA) containing 100 ml Hutner's growth medium 36 containing 0.5% sucrose at 24 AE 2 C. 37 Ammonium ion assimilation was studied by introducing 30 ml of sterilized Hutner's growth medium into a 100 ml Erlenmeyer flask, followed by filter-sterilized (Sartorius, Goettingen, FRG; membrane filter 0.45 mm) 15 N-labelled NH 4…”

Biosensor-Mediated In Situ Imaging Defines the Availability Period of Assimilatory Glutamine in Maize Seedling Leaves Following Nitrogen Fertilization

“…For example, glutamate, asparagine, and aspartate are important downstream products of assimilatory Gln [7], and their quantification may provide a layer of data with which to annotate GlnLux images. Additionally, genetic mutants or chemical inhibitors [14,15] that block Gln conversion, or N 15 labeling experiments [9] would provide confirmation that reduction of GlnLux output over time is the result of Gln conversion to downstream molecules. The exact timing of Gln disappearance may also be characterized with analytical chemistry methods [9], or an alternative GlnLux methodology which analyzes plant extracts for more quantitative results [11].…”

“…For example, glutamate, asparagine, and aspartate are important downstream products of assimilatory Gln [7], and their quantification may provide a layer of data with which to annotate GlnLux images. Additionally, genetic mutants or chemical inhibitors [14,15] that block Gln . Three different seedling leaves were harvested and imaged using GlnLux agar (B).…”