Interacting signal transduction chains in gravity‐stimulated maize roots

Abstract

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.

The ‘root-brain’ hypothesis of Charles and Francis Darwin

“…The root cap is essential for these crawling movements. 22,[85][86][87] All this is in accordance with data and concepts of the Darwins' 'Root-Brain' hypothesis. 16,17,19 On page 196 of their book, they note that the way the root movements are coordinated is admirably perfect.…”

“…The two zones can bend independently of each other, but they are obviously coordinated and ethylene is essential for this motoric coordination. 22,[84][85][86][87] The result is that intact growing root apices can, under appropriate circumstances, perform crawling-like searching movements 22,86 which closely resemble the type of behavior of a lower animal. The root cap is essential for these crawling movements.…”

Photophobic behavior of maize roots

“…3,4,20,23 Crawling behavior of maize roots was discovered only few years ago. 26 This unique root behavior supports the Darwinian view of roots, 20,21 documenting that plant roots display rich repertoire of behavior. In fact, we predict that this complexity is just the 'tip of iceberg' 27,28 as far as root behavior is concerned.…”

Plant roots: autopoietic and cognitive constructions

“…Whether such micro-movements are spontaneous -i.e., outcomes of random events -or induced by sensitivity to some property of the soil, is not known. Mutation, such as the agt mutation in maize roots (Abeysekara and McCully 1993), as well as those factors which regulate root-looping (Hahn et al 2006), can amplify these small growth deviations. In these cases, the growth elements of the cells appear to have become more sensitive to, or the roots have become more cognisant of, perturbations external to its boundary.…”