Root Hair Growth in Arabidopsis Thaliana Is Directed by Calcium and an Endogenous Polarity

The 1997 study explored how calcium (Ca²⁺) gradients influence the growth direction of root hairs in Arabidopsis thaliana. Researchers found that artificially creating an asymmetrical Ca²⁺ influx at the root hair tip could temporarily redirect growth towards the higher Ca²⁺ concentration, but the root hair would revert to its original direction within 15 minutes. This suggests that while Ca²⁺ gradients can localize growth at the tip, they are not the primary determinant of growth direction. The study also observed that root hairs maintain a fixed growth angle of approximately 90 degrees from the root surface, which is likely regulated by unknown factors to optimize soil exploration. The study involved various sample sizes, including 40 root hairs for the Ca²⁺ elevation response and 19 root hairs for the touch stimulus response. The findings indicate that other factors from the root continuously reset the growth direction away from the root surface, and the role of electrical fields and voltage-gated Ca²⁺ channels in growth direction remains unclear. The research was supported by grants from the USDA/DOE/NSF and NSF.