Root Growth Dynamics

Plants can change their growth and morphology as a part of their strategies to survive under fluctuating environments. In contrast to animals where organ movement can be driven by musculoskeletal systems with a nervous control, alteration of plant growth dynamics relies solely on the division and elongation behaviors of constituting cell units. Intuitively, such a distributed processing system requires highly coordinated cell-cell communication to achieve desired movement of the organs as a whole. What cellular dynamics and genetic networks enable plant organ movement, and how are they coordinated?

To address these question, we are studying the growth dynamics of the Arabidopsis thaliana roots. While the Arabidopsis root tip has been used extensively as a distinguished model system to study mechanisms of tissue patterning and stem cell maintenance in plant development, there has been a critical obstacle to use it for long-term growth dynamic analyses, due to an intrinsic nature of root growth behavior that immediately displaces the root tip from a microscopic observation field. 

To circumvent this problem and to further extend the use of Arabidopsis roots in plant developmental biology, we established a horizontal-axis motion-tracking confocal microscope system.

This microscope system allows time-lapse imaging of the tips of growing roots along the gravity vector for a few days. It can capture not only cell division and cell elongation behaviors at a high spatiotemporal resolution, but also gene and protein expression, as well as organelle behaviors, in the tip of growing root. By combining this microscopic technique with genetic tools and resources available for the Arabidopsis roots, we are currently addressing fundamental questions of plant growth in multiple scales.

An eye-catching example of the utilization of this microscope system is visualization of periodic cell detachment and associated expression dynamics of the cell wall-degrading enzymes. Although the root cap is known to play essential roles in directing root growth and plant-rhizosphere interaction, their molecular mechanisms are mostly unknown. We are studying how periodical turnover of the root cap is regulated and the process is linked to organ-level movement of the roots.