Spatio‐temporal dynamics of expansion growth in roots: automatic quantification of diurnal course and temperature response by digital image sequence processing

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Abstract
A newly developed technique based on image sequence analysis allows automatic and precise quantification of the dynamics of the growth velocity of the root tip, the distribution of expansion growth rates along the entire growth zone and the oscillation frequencies of the root tip during growth without the need of artificial landmarks. These three major parameters characterizing expansion growth of primary roots can be analysed over several days with high spatial (20 μm) and temporal resolution (several minutes) as the camera follows the growing root by an image‐controlled root tracking device. In combination with a rhizotron set up for hydroponic plant cultivation the impact of rapid changes of environmental factors can be assessed. First applications of this new system proved the absence of diurnal variation of root growth in Zea mays under constant temperature conditions. The distribution profile of relative elemental growth rate (REGR) showed two maxima under constant and varying growth conditions. Lateral oscillatory movements of growing root tips were present even under constant environmental conditions. Dynamic changes in velocity‐ and REGR‐distribution within 1 h could be quantified after a step change in temperature from 21 °C to 26 °C. Most prominent growth responses were found in the zone of maximal root elongation.