Interaction of Gravity with Cell Metabolism

Plants orient their organs, explore, and adapt to their environment mainly by sensing light and the direction of gravity. Some theories exist about gravity sensing including as a starting point the presence of dense sedimentable particles in specialized gravity-sensing cell types or protoplast-pressure phenomena inducing a cascade of biophysical and biochemical events that finally transform the directional information into gravioriented growth. However, apart from the directional information, plant cells show various more general gravity effects like changes in membrane-located processes and changes in gene expression, protein expression, and protein modulation as well as metabolic consequences in response to altered gravity conditions. In the following, mainly based on data from callus cultures of A. thaliana, we summarize the present knowledge in the field of gravity-affected cell metabolism, especially related to Ca2+ and hydrogen peroxide signaling.