https://phys.org/news/2018-07-root.html

The group of Reidunn Aalen at the University of Oslo, with postdoc and first author Chun-Lin Shi, discovered the signal and receptor that mediate communication at the root tip. They found that cells in the root cap secrete a small peptide, called IDL1. This peptide diffuses through the root tip. Cells at the root apical meristem, which divide to form a new root cap, have a receptor protein, called HSL2, which perceives the signal peptide IDL1. By this mechanism, the outer root cap cells that are shed and the inner cells that divide to replace them communicate.

Loss of root cap observed for first time