Biphasic and differential expression of cytosolic glutamine synthetase genes of radish during seed germination and senescence of cotyledons.
Three structurally distinct cDNA clones for cytosolic glutamine synthetase (GS1) were isolated from libraries prepared from senescing radish cotyledons. Northern blot analysis showed that transcripts from two of the three genes encoding GS1, Gln1;1 and Gln1;3, accumulated in the cotyledons during both dark-induced and natural senescence. Transcripts from the last gene, Gln1;2, remained at a low level during both processes. Transcripts from all three Gln1 genes accumulated in cotyledons of germinating seeds. We infer from these findings that GS1 enzymes function in both germination and senescence to convert ammonium to glutamine to remobilize nitrogen from source to sink organs. We have also examined the pattern of expression of these genes in different tissues. All three genes are expressed in roots. A large amount of transcripts from Gln1;1 accumulated in hypocotyls. Whereas none were transcribed in flowers. During dark-induced senescence of cotyledons, application of inorganic nitrogen delayed chlorophyll degradation. Inorganic nitrogen enhanced the accumulation of Gln1;1 transcripts, but decreased those of Gln1;3. In contrast, application of glutamine promoted yellowing of cotyledons during the dark treatment, and slightly increased the amounts of transcripts from Gln1;3 but decreased those of Gln1;1. Transcription of the three Gln1 genes appears, therefore, to be differentially regulated in radish cotyledons during senescence and germination.
Graduate Division of Biochemical Regulation, School of Agricultural Sciences, Nagoya University, Japan.
A
A
Watanabe
K
K
Hamada
H
H
Yokoi
A
A
Watanabe
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000494:pharmacology; D001483:Base Sequence; D002451:Cell Compartmentation; D016922:Cellular Senescence; D018548:Cotyledon / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D003583:Cytokinins / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D018076:DNA, Complementary / Q000235:genetics; D003624:Darkness; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D005974:Glutamate-Ammonia Ligase / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014675:Vegetables / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development
D000596:Amino Acids; D003583:Cytokinins; D018076:DNA, Complementary; D005974:Glutamate-Ammonia Ligase