Alterations in Protein Expression of Arabidopsis thaliana Cell Cultures During Hyper- and Simulated Micro-Gravity

Callus cell cultures of Arabidopsis thaliana exposed to hypergravity (8×g), 2D clinorotation and random positioning exhibit changes in gene expression (Martzivanou et al., Protoplasma 229:155–162, 2006). In a recent investigation we could show that after 2 h of exposure also the protein complement shows treatment-related changes which are indicative for reactive oxygen species being involved in the perception of/response to changes in the gravitational field. In the present study we have extended these investigations for a period of up to 16 h of exposure. We report on changes in abundance of 28 proteins which have been identified by nano HPLC-ESI-MS/MS, and which were altered in amount after 2 h of treatment. According to changes between 2 and 16 h we could distinguish four groups of proteins which either declined, increased from down-regulated to control levels, showed a transient decline or a transient increase. With regard to function, our data indicate stress relief or adaptation to a new gravitational steady state under prolonged exposure. The latter assumption is supported by the appearance of a new set of 19 proteins which is changed in abundance after 8 h of hypergravity. A comparative analysis of the different treatments showed some similarities in response between 8×g centrifugation and 2D clinorotation, while random positioning showed the least responses.