In-vivo imaging of root growth in response to localized mechanical stress

Sammanfattning: By taking up nutrients and water, root growth has an important influence on plant growth and productivity. Thereby, root growth is influenced by its surrounding soil conditions, which vary spatially even on a small scale. Hence, different parts of the root system are exposed to different penetration resistances in the soil. As root cells are connected by their cell walls, information about growth conditions can be transferred throughout the root system, which is why roots can react to the soil conditions of their neighbouring roots. By doing in-vivo measurements in a hydroponic system, this study investigated the responses of unimpeded roots to local mechanical stress of their neighbouring roots. To do so, the primary or seminal roots were exposed to vertical or horizontal obstacles. Using a time-lapse imaging system under infra-red light in combination with particle image velocimetry the underlying processes of root growth, such as the growth direction, the growth rate, the cell elongation rate, and the growth zone length were quantified. In this study, the primary and seminal roots showed contrasting responses of root growth rate and root growth direction. While the primary roots did not response to a restriction in growth of the seminal roots, seminal roots reacted to the applied stress in the same way as the impeded roots, even if the stress did not occur in their environment. In the case, where the roots found a way to work around the anticipated stress, they compensated for the impaired root with an increase in growth rate. The fact, that the primary root did not show this response, might be due to their different functions in the root system. Furthermore, the relative root growth rate was stronger associated with the relative length of growth zone than with the relative elemental elongation rate. Nevertheless, the elemental elongation rate might be the driver for short-term adjustments. Keywords: kinematics analysis, time-lapse imaging, root growth rate, root curvature, soil heterogeneity, local mechanical stress