Coupled ultradian growth and curvature oscillations during gravitropic movement in disturbed wheat coleoptiles

Abstract

To grow straight and upright, plants need to regulate actively their posture. Gravitropic movement, which occurs when plants modify their growth and curvature to orient their aerial organ against the force of gravity, is a major feature of this postural control. A recent model has shown that graviception and proprioception are sufficient to account for the gravitropic movement and subsequent organ posture demonstrated by a range of species. However, some plants, including wheat coleoptiles, exhibit a stronger regulation of posture than predicted by the model. Here, we performed an extensive kinematics study on wheat coleoptiles during a gravitropic perturbation (tilting) experiment in order to better understand this unexpectedly strong regulation. Close temporal observations of the data revealed that both perturbed and unperturbed coleoptiles showed oscillatory pulses of elongation and curvature variation that propagated from the apex to the base of their aerial organs. In perturbed coleoptiles, we discovered a non-trivial coupling between the oscillatory dynamics of curvature and elongation. The relationship between those oscillations and the postural control of the organ remains unclear, but indicates the presence of a mechanism that is capable of affecting the relationship between elongation rate, differential growth, and curvature.

A digital sensor to measure real-time leaf movements and detect abiotic stress in plants

“…Later in their development, maize plants no longer exhibit these frequent bursts, but show larger, more gradual and low-frequent movements ( Figure 8 ). It is very likely to assume that these movements are the result of meticulous and time-specific organization of graviception, autotropism ( Hamant and Moulia, 2016 ), and ultimately posture control ( Bastien et al, 2014 , 2018 ; Moulia et al, 2019 ). Interestingly, our sensor analysis of maize seedling stem orientation suggests that stem motion is related to the outgrowth of leaves into a certain direction, although our time-lapse images indicate that there is a phase difference between mass distribution and actual leaf position.…”

Spatiotemporal growth pattern during plant nutation implies fast dynamics for cell wall mechanics and chemistry: a multiscale study in Averrhoa carambola

“…On the contrary when the growth potential or signal globally starts to decline, near the end of the growth zone, then any variation in the growth potential or signal is directly translated into a variation of actual growth. The same interpretation could apply to the straightening of wheat coleoptiles (46): as the coleoptile bends towards the vertical, the differential growth potential or signal is at its maximum, and no oscillation is observed. On the contrary, when the coleoptile approaches a vertical posture, the potential or signal is lower, and nutation of the tip becomes visible again.…”

Plants sum and subtract stimuli over different timescales

“…Observed oscillations in the gravitropic reorientation of wheat coleoptiles have been conjectured to speed up the regulation of posture control ( 14 , 49 , 50 ). The half period of observed oscillations was found to be h ( 49 , 50 ), consistent with the delay time of maximal subtraction, and anything occurring further than a full oscillation period ( h) is forgotten ( Fig. 4 G ).…”