The Plant Signaling ARC EMCS Experiment Payload was launched to the International Space Station (ISS) on STS 135, July 8, 2011. The experiment examined potential changes in intracellular signaling mechanisms in Arabidopsis thaliana as a function of exposure to micro-gravity. The Principal Investigator (PI) for the study is Dr. Imara Perera from North Carolina State University, Raleigh, North Carolina. The experiment was conducted successfully on the ISS and seedling samples were collected for analysis on the ground by the PI. In July 2012, a ground control experiment was performed in a growth chamber at Ames Research Center (ARC). The ground control experiment mimicked all of the conditions of the micro-gravity experiment (except of course micro-gravity), with particular interest in duplicating the slowly rising atmospheric CO2 levels seen in the ISS experiment chamber – the rising levels are due to known leakage of the ISS atmosphere into the experiment chamber. The ground control experiment was 100% successful, the seedling grew well, images of hydration and growth were obtained, and samples were collected and shipped to the PI for comparison to her in-flight samples. The data from the ARC ground control will be critical for interpreting the results from the micro-gravity samples.