ROOTFLOW · Dynamic cell coordination in the plant root

Dynamic cell coordination in the plant root

The fellow spent the year conducting research in the Centre for Plant Integrative Plant Biology, housed in the Department of Plant and Crop Science at the University of Nottingham (UK). His project focused on the stable division of the growing region of the plant root into zones, namely the meristem where cells divide and the elongation zone where cells elongate rapidly. This zonation is stable even though the boundary moves over cells as they change from being members of the meristem to members of the elongation zone. The overall objective of the project was to uncover mechanisms orchestrating this orderly change of cell fate, mechanisms that are largely unknown. The fellow took the approach of high-resolution imaging, using the popular model plant species, Arabidopsis thaliana. The project proposal invoked collaboration with image processing expertise in the Computer Science Department at the University of Nottingham to develop software to track individual cells. However, this proved impossible owing to unexpected staffing problems. Nevertheless, the fellow took advantage of extant software. Using this, and optimizing conditions for growth and imaging, he discovered that the position where cells begin elongating rapidly oscillates towards and away from the root tip. The period is about 90 minutes and the amplitude is about 50 micrometres. The fellow has entered into a collaboration with a mathematician at the University of Nottingham to analyse the oscillation with statistical rigor. The oscillation implies the existence of a negative feedback loop that is used to control the transition of cells from the meristem to the zone of rapid elongation. Insofar as the root shifts the position of the boundary between meristem and elongation zone in acclimatizing responses to stimuli, both biotic and abiotic, this finding is likely to be relevant for anyone attempting to optimize root behaviour for humankind. In the absence of the anticipated cell tracking software, the fellow pursued two other promising lines of research, taking advantage of expertise at CPIB. He developed an experimental platform for studying rapid elongation in plant stems. The challenge here is that stems grow most rapidly in darkness; therefore, the fellow worked in the absolute absence of visible light. This was facilitated by using a device that converts infrared to visible light (a night-vision ‘scope). The growth zone of a seedling stem is cut into short (~3 mm) segments, floated on a treatment solution and imaged under infrared light at defined times. Changes in segment length and width (i.e., growth) are then recovered from the images. Preliminary measurements were done manually but s software tool is under development that make the measurements algorithmically, increasing the precision and throughput of the platform. The fellow intends to continue developing this platform at his home institution, where he will collaborate with both molecular biologists and biomechanics experts to answer long unresolved questions about how a stem grows. The other line of research concerns the structure of the cell wall of rapidly elongating root cells. In work at his home institute, the fellow has developed methods for imaging the cell wall, methods that reveal the component macromolecular components (cellulose, pectin, hemicellulose). However, the structures are complex and difficult to analyse quantitatively. In collaboration with a PhD student in the Department of Computer Science, the fellow developed an analytical tool to quantify attributes of the texture of the images. Currently, the fellow is testing this routine on sample images and if successful will publish it. A tool of this kind will able to help analyse fibrous structures of all kinds and scales, from fabrics to the extracellular matrix of animal tissue. Finally, an article appeared in Nature during the fellow’s tenure that contained claims concerning root growth that were wholly unsupported by the paper’s data and contrary to received wisdom in the literature. The fellow ran a few experiments and published a critical paper describing these shortcomings.

Data: CORDIS, © European Union