The root cap is the covering of cells at the growing tip of a root, in front of its root apical meristem. Its central columella and surrounding lateral root cap have distinct positions and functions. The root cap participates in the response to gravity, while the bending growth response is expressed farther back in the root elongation zone.
A 1998 experiment mapped function more precisely than removing the entire tip. Elison B. Blancaflor and collaborators used laser ablation to eliminate selected cap cells, allowed recovery, then rotated Arabidopsis thaliana seedlings through90degrees. Removing inner central columella cells strongly reduced curvature without reducing axial growth in the same way. Damage to other tested cap regions had smaller effects.[ref]
This comparison matters because failure to bend could otherwise mean that the root simply stopped growing. Measuring both extension and curvature helps isolate a sensory or signaling defect from a general failure of growth. The observations support functional specialization within the cap, rather than treating every cap cell as an interchangeable gravity sensor.
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