Dynamics of leaf and root growth

Abstract

Growing tissues dominate sink activity during the vegetative phase of many plant species. Growth is characterised by its spatio-temporal dynamics. Thus, in order to understand sink-source interactions, growth processes have to be quantified in space and time. New techniques based on image sequence analysis have been developed during the last years that allow for the first time to map expansion growth in time and space scales relevant for mechanistic control on the biochemical and molecular level. Growth mapping is done via motion analysis by the optical flow-based structure tensor algorithm. Image heaps are virtually constructed from digital image sequences of leaves and roots taken in the near-IR. Orientation analysis in local neighbourhoods of these 3D-matices (x, y, t) give a large number of velocity vectors on the growing tissues. Calculating the divergence of these velocities results in high-density maps of growth rates. Dicot leaf expansion was mapped with much higher resolution than in classical analysis. We report on experiments that combine growth mapping with analysis on the cellular, biochemical and molecular parameters and that study the interaction between source function, light conditions and growth activity including local treatments in growing tissues. Expansion gradients were measured diurnally and used to quantify deposition rates. Other physiological parameters like transpiration and water content were also mapped by image sequence analysis. Root expansion mapping allows to follow the variation of growth distribution during dynamic to changes environmental conditions like temperature, nutrients and light. Such non-invasive techniques will open new approaches to study dynamics of sink-source interactions in the future.