Occurrence of phosphorylated castasterone in Arabidopsis thaliana and Lycopersicum esculentum. Issue 1 (29th July 2014)

• Record Type: Journal Article
• Authors: Kim, Min Kyun; Jang, Mun‐Seok; Youn, Ji‐Hyun; Son, Seung‐Hyun; Lee, Ji Eun; Kim, Tae‐Wuk; Kim, Seong‐Ki
• Is Part Of: Physiologia plantarum. Volume 153:Issue 1(2015:Jan.)
• Page Start: 58
• Page End: 67
• Publication Date: 2014-07-29
• Subjects: Plant physiology -- Periodicals; 571.2
• DOI: 10.1111/ppl.12242
• Languages: English
• ISSNs: 0031-9317

Abstract

<abstract abstract-type="main" id="ppl12242-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p id="ppl12242-para-0001">An in vitro enzyme assay using radioisotope‐labeled <sup>3</sup>H‐castasterone (<sup>3</sup>H‐CS) or <sup>32</sup>P‐ATP showed that CS can be phosphorylated by ATP in <italic>Arabidopsis</italic> and tomato plants. Gas chromatography‐mass spectrometry (GC‐MS) analysis using non‐isotope‐labeled CS and ATP revealed that the phosphorylation of CS occurs at the side chain, most likely at the C‐23 hydroxyl. The polar fractions than free brassinosteroids (BRs) obtained from extracts of <italic>Arabidopsis</italic> and tomato showed almost no BRs activity in a rice lamina inclination bioassay. However, the fractions showed increased bioactivity after treatment with wheat germ acidic phosphatase (WGAP). Additionally, CS was identified from the hydrolysate by WGAP using GC‐MS analysis in both plants. In contrast, the polar fractions obtained from BR‐deficient mutants, <italic>Arabidopsis cyp85a2</italic> and tomato <italic>d<sup>x</sup></italic>, did not show an increase in biological activity with WGAP treatment, and no free BRs, including CS, were detected in the hydrolysate. This suggests that CS phosphate is a naturally occurring biologically inactive conjugate that is generated when CS is normally synthesized in <italic>Arabidopsis</italic> and tomato plants. Taken together, these results suggest that phosphorylation of CS is an important conjugation process for the maintenance of the homeostatic level of an active BR and thus the regulation of the growth and development of plants.</p> </abstract>