A biological clock activated by oscillating signals, known as root clock, has been linked to lateral root (LR) formation and is essential for regular LR spacing along the primary root. However, it remains unclear how this internal mechanism is influenced by environmental factors known to affect the LR pattern. Here, we report that excessive cadmium (Cd) inhibits LR formation by disrupting the lateral root cap (LRC)-programmed cell death (PCD)-regulated root clock. Cd restricts the frequency of the oscillating signal rather than its amplitude. This could be attributed to the inhibition on meristematic activity by Cd, which resulted in decreased LRC cell number and LRC-PCD frequency. Genetic evidence further showed that LRC cell number is positively correlated with root resistance to Cd. Our study reveals root cap dynamics as a novel mechanism mediating root responses to Cd, providing insight into the signalling pathways of the root clock responding to environmental cues.
Keywords: cadmium; lateral root; primary root; programmed cell death; root cap; root clock.
© 2019 John Wiley & Sons Ltd.