Interacting signal transduction chains in gravity-stimulated maize roots

Gravitropism in roots involves at least three signal transduction chains. The first signal transduction chain is sub-cellular and operates within the gravity-perceiving cells in the root apex. The output of this perception system feeds into a second intercellular signal transduction chain (widely considered to involve auxin movement) that links events in the apical regions with the third signal transduction chain that controls cell expansion in the elongating cells. The present study probes the disputed role of ethylene in gravitropism by seeking to identify which parts of the gravitropism cascade are influenced by ethylene action. The results suggest that another signal transduction chain, initiated by mechanical impedance to the root apex, interacts with the early stages of the gravitropism cascade and the effects of ethylene on gravitropism could be mediated by the mechanical impedance sensing and response systems.