Ultradian Oscillation of Growth Reveals Regulatory Mechanism in the Straightening Movement of Wheat Coleoptile

Plants regulate their shape and movements in accordance with their surrounding environment. This regulation occurs by a curving movement driven by differential growth. Recent studies has unraveled part of the mechanisms leading to differential growth though lateral polar auxin transport. However the real interplay between elongation, curvature variation, and accordingly the regulation process of growth distribution has not been really investigated so far. This issue is addressed in this study through gravitropic experiments on wheat coleoptiles, using a recently published kinematic approach, KimoRod. Here we show that median elongation is not affected by gravitropic perturbation. However kinematics studies reveal temporal oscillation of the median elongation rate. These oscillations propagate from the apex to the base during the movement with a characteristic velocity that is similar to auxin propagation in coleoptiles. The curvature variation exhibits a similar spatiotemporal pattern to the median elongation which reveals a nontrivial link between this two parameters and potential effect on perception and biomechanics of the tissue.