Journal of Experimental Botany, Vol. 54, No. 384, pp. 1013-1022,
March 1, 2003
© 2003 Oxford University Press
Changes in phosphorylation of 50 and 53 kDa soluble proteins in graviresponding oat (Avena sativa) shoots
Received 12 April 2002; Accepted 6 November 2002
1 Center for Cell Signaling Research, Ewha Woman’s University, Seoul 120-750, Korea
2 Department of Biology, Yonsei University, Seoul 120-749, Korea
3 Department of Life Science, Chung-Ang University, Seoul 156-756, Korea
4 Department of Biological Science, Ewha Woman’s University, Seoul 120-750, Korea
5 Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, MI 48109-1048, USA
6 To whom correspondence should be addressed: Fax: +1 734 647 0884. E-mail: pbk{at}umich.edu
Abbreviations: CHI, cycloheximide; OA, okadaic acid; STA, staurosporine.
The present work indicates that phosphorylation of a 50 kDa soluble protein is involved in the gravitropic response in graviresponsive pulvini of oat (Avena sativa) stems. This 50 kDa protein shows a differential pattern of phosphorylation between lower and upper halves of pulvini both in vivo and in vitro. The differential phosphorylation of this protein is detected only when stem segments are gravistimulated for short and long time periods. The differential phosphorylation of the 50 kDa protein occurs as early as 5 min after the initiation of gravistimulation. This corresponds closely to the presentation time of 5.2 min. This differential phosphorylation pattern was changed by treatments with cycloheximide, implying that a newly-synthesized protein is involved in the differential phosphorylation during the gravitropic response. An autophosphorylation experiment shows that the 50 kDa protein has kinase activity. The phosphorylation patterns of a 53 kDa protein were similar to those of the 50 kDa protein, but were only expressed in vitro. These findings indicate that the differential phosphorylation of the 50 (and 53 kDa) soluble proteins in graviresponding oat shoots may be an important component of the gravity signal transduction pathway.
Key words: Avena sativa, gravitropism, protein phosphoryl ation, pulvini.