Thermospermine is Required for Stem Elongation in Arabidopsis thaliana

Jun Ichi Kakehi, Yoshitaka Kuwashiro, Masaru Niitsu, Taku Takahashi

Research output: Contribution to journalArticlepeer-review

133 Citations (Scopus)


Loss-of-function mutants of the ACAULIS5 (ACL5) gene in Arabidopsis thaliana have severe defects in stem elongation. ACL5 was previously reported as encoding a spermine synthase. A more recent study, however, showed that the bacterial expressed recombinant ACL5 protein catalyzes the conversion of spermidine to thermospermine, a structural isomer of spermine, rather than to spermine. In the present study, we found that thermospermine was detected in wild-type seedlings but was not detectable in the acl5-1 mutant. We further examined the effect of exogenous application of these isomers on the growth of acl5-1. Daily application of 0.1 mM thermospermine onto the shoot apex partially rescued the dwarf phenotype of acl5-1, while that of spermine had no effects on the morphology of the mutant. The acl5-1 transcript level in acl5-1 seedlings, which is much higher than the ACL5 transcript level in wild-type seedlings, was reduced by exogenous thermospermine. Thus we conclude that thermospermine is indeed produced through the action of ACL5 and required for stem elongation in Arabidopsis.

Original languageEnglish
Pages (from-to)1342-1349
Number of pages8
JournalPlant and Cell Physiology
Issue number9
Publication statusPublished - Sept 2008


  • Acaulis5
  • Arabidopsis thaliana
  • Polyamine
  • Spermine
  • Stem elongation
  • Thermospermine

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology


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