JXB Advance Access published online on January 6, 2009
Journal of Experimental Botany, doi:10.1093/jxb/ern324
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Changes in the effective gravitational field strength affect the state of phosphorylation of stress-related proteins in callus cultures of Arabidopsis thaliana
arko Barjaktarovi
1
1University of Tübingen, Botany Institute, Physiological Ecology of Plants, Auf der Morgenstelle 1, D-72076 Tübingen, Germany
2University of Tübingen, Interfaculty Institute for Cell Biology, Proteom Centrum Tübingen, Auf der Morgenstelle 15, D-72076 Tübingen, Germany
* To whom correspondence should be addressed: ruediger.hampp{at}uni-tuebingen.de
In a recent study it was shown that callus cell cultures of Arabidopsis thaliana respond to changes in gravitational field strengths by changes in protein expression. Using ESI-MS/MS for proteins with differential abundance after separation by 2D-PAGE, 28 spots which changed reproducibly and significantly in amount (P <0.05) after 2 h of hypergravity (18 up-regulated, 10 down-regulated) could be identified. The corresponding proteins were largely involved in stress responses, including the detoxification of reactive oxygen species (ROS). In the present study, these investigations are extended to phosphorylated proteins. For this purpose, callus cell cultures of Arabidopsis thaliana were exposed to hypergravity (8 g) and simulated weightlessness (random positioning; RP) for up to 30 min, a period of time which yielded the most reliable data. The first changes, however, were visible as early as 10 min after the start of treatment. In comparison to 1 g controls, exposure to hypergravity resulted in 18 protein spots, and random positioning in 25, respectively, with increased/decreased signal intensity by at least 2-fold (P <0.05). Only one spot (alanine aminotransferase) responded the same way under both treatments. After 30 min of RP, four spots appeared, which could not be detected in control samples. Among the protein spots altered in phosphorylation, it was possible to identify 24 from those responding to random positioning and 12 which responded to 8 g. These 12 proteins (8 g) are partly (5 out of 12) the same as those changed in expression after exposure to 2 h of hypergravity. The respective proteins are involved in scavenging and detoxification of ROS (32%), primary metabolism (20.5%), general signalling (14.7%), protein translation and proteolysis (14.7%), and ion homeostasis (8.8%). Together with our recent data on protein expression, it is assumed that changes in gravitational fields induce the production of ROS. Our data further indicate that responses toward RP are more by post-translational protein modulation (most changes in the degree of phosphorylation occur under RP-treatment) than by protein expression (hypergravity).
Key words: Arabidopsis thaliana, cell cultures, hypergravity, phosphoproteomics, ROS detoxification, simulated microgravity
Received 14 October 2008; Revised 18 November 2008 Accepted 19 November 2008