Abstract
The aim of this study was to investigate the role of ASN3-encoded asparagine synthetase (AS, EC 6.3.5.4) during vegetative growth, seed development and germination of Arabidopsis thaliana. Phenotypic analysis of knockout (asn3-1) and knockdown (asn3-2) T-DNA insertion mutants for the ASN3 gene (At5g10240) demonstrated wild-type contents of asparagine synthetase protein, chlorophyll and ammonium in green leaves at 35 days after sowing. In situ hybridization localized ASN3 mRNA to phloem companion cells of vasculature. Young siliques of the asn3-1 knockout line showed a decrease in asparagine but an increase in glutamate. The seeds of asn3-1 and asn3-2 displayed a wild-type nitrogen status expressed as total nitrogen content, indicating that the repression of ASN3 expression had only a limited effect on mature seeds. An analysis of amino acid labeling of seeds imbibed with (15N) ammonium for 24 h revealed that asn3-1 seeds contained 20% less total asparagine while 15N-labeled asparagine ((2-15N)asparagine, (4-15N)asparagine and (2,4-15N)asparagine) increased by 12% compared to wild-type seeds. The data indicate a fine regulation of asparagine synthesis and hydrolysis in Arabidopsis seeds.
Highlights
Higher plants take up inorganic nitrogen by absorbing nitrate and ammonium from the soil.Nitrate is reduced to ammonium by the combined action of nitrate reductase (NAD(P)H-NR, EC 1.7.1.1; EC 1.7.1.2; EC 1.7.1.3) and ferredoxin (Fd)-nitrite reductase (Fd-NiR, EC 1.7.1.4) while ammonium is produced by photorespiration and the breakdown of nitrogenous compounds
ASN3 mRNA levels were measured by qPCR relative to Actin 2 (At3g18780) and expressed as the mean SE of three biological replicates
We assessed the physiological role of ASN3-encoded asparagine synthetase in nitrogen metabolism at three developmental stages including vegetative growth, seed maturation and seed germination
Summary
Nitrate is reduced to ammonium by the combined action of nitrate reductase (NAD(P)H-NR, EC 1.7.1.1; EC 1.7.1.2; EC 1.7.1.3) and ferredoxin (Fd)-nitrite reductase (Fd-NiR, EC 1.7.1.4) while ammonium is produced by photorespiration and the breakdown of nitrogenous compounds. It is assimilated into glutamine and glutamate by glutamine synthetase (GS, EC 6.3.1.3) and glutamate synthase (GOGAT, EC 1.4.7.1 and EC 1.4.1.14) [1]. Asparagine, glutamine, aspartate and glutamate are important nitrogen carriers transported in the phloem; asparagine is a major nitrogen transporter since it contains more nitrogen per carbon (2N:4C) compared to glutamine (2N:5C), aspartate (1N:4C) and glutamate (1N:5C) [2,3].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
