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Plant Cell Reports

, Volume 24, Issue 6, pp 357–365 | Cite as

Characterization of the altered anthranilate synthase in 5-methyltryptophan-resistant rice mutants

  • D. S. Kim
  • I. S. Lee
  • C. S. Jang
  • S.-Y. Kang
  • Y. W. SeoEmail author
Genetics and Genomics

Abstract

In an earlier investigation, homologous mutant lines resistant to growth inhibition by 5-methyltryptophan (5MT) were selected from a callus that had been irradiated with a 50-Gy gamma ray during embryo culture. In order to identify the 5MT-resistant mechanism, we have continued our investigations of these mutant lines and studied the anthranilate synthase activity of the M5 advanced lines by direct fluorometric detection of the anthranilate formed in both control plants and mutant lines grown on 500 μM 5MT. The anthranilate synthase activity of the mutant plants was 2.2- to 3-fold higher than that of the control. In a kinetic analysis with tryptophan, an anthranilate synthase of the mutant lines was insensitive to feedback inhibition. These lines showed an enhanced accumulation of storage proteins and amino acids. The increased rates of protein synthesis in the mutant lines, relative to that of the control seeds, were 17–28.5%. The amino acid contents were 2.4-fold (MRI-40-2) to 2.6-fold (MRI-110-6) higher in the MRI lines than in the control seeds, and 2.4-fold (MRII-12-5) to 3.5-fold (MRII-8-1) higher in the MRII lines than in the control seeds. Significant increases among the amino acids of the MR lines were observed for tryptophan, phenylalanine, and tyrosine, which had been biosynthesized through the shikimate pathway. The transcript levels of putative OASA2, which is one of the key-regulating enzyme subunits in the tryptophan biosynthesis pathway, were studied in the control and 5MT-resistant mutant lines subjected to inhibition by two tryptophan analogs (5MT and αMT) and to other abiotic stresses (ABA, NaCl, and cold). The putative OASA2 gene in the 5MT-resistant mutant lines was highly expressed in at a low 5MT concentration and at an early stage of the 5MT and αMT treatments. However, mRNA accumulation of the putative OASA2 gene in the mutant plants gradually decreased when the plants were subjected to abiotic stresses such as NaCl and cold. These results indicated that the 5MT resistance in the mutant lines is due to altered anthranilate synthase forms.

Keywords

Abiotic stress Anthranilate synthase Gamma-rays Rice 5-Methyltryptophan 

Abbreviations

ABA

Abscisic acid

ESTs

Expressed sequence tags

OASA2

Oryza sativa anthranilate synthase alpha 2

αMT

α-Methyltryptophan

5MT

5-Methyltryptophan

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • D. S. Kim
    • 1
  • I. S. Lee
    • 1
  • C. S. Jang
    • 2
  • S.-Y. Kang
    • 1
  • Y. W. Seo
    • 2
    Email author
  1. 1.Department of Radiation Plant Breeding and GeneticsKorea Atomic Energy Research InstituteDaejeonKorea
  2. 2.Division of Biotechnology and Genetic Engineering, College of Life & Environmental Sciences Korea UniversitySeoulKorea

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