Root apex physiological response to temporary changes in gravity conditions: an overview on oxygen and nitric oxide fluxes

Oxygen influx showed a gravity-regulated asymmetry in the transition zone (TZ) when root orientation varied from vertical to horizontal on ground. Nitric oxide was also monitored during ground gravistimulation, revealing a sudden burst in NO production only at root transition zone level. As NO is widely considered one of the first and most important signalling molecule in the stress-response pathway, this result focused on the role of this gaseous molecule in the graviperception. In order to confirm these results in real microgravity conditions, an experiment has been set up during an ESA parabolic flight campaign. Oxygen and nitric oxide concentration in the solution where roots of Zea mays were placed have been constantly monitored during normal, hyper- and microgravity conditions. An evident burst in oxygen and NO fluxes started just 2.0 ± 0.5 s after the imposition of microgravity conditions. No significant changes were noticed neither in normal nor in hypergravity conditions. Moreover, oxygen bursts were detected only in the apex zone The significance of these results on the nature of the graviperception will be discussed.