Academic Staff - Professor Robyn Overall

Areas of Interest

I am interested in the structure and function of plasmodesmata, the channels responsible for intercellular transport of ions, metabolites, signals and viruses in plants. Despite their fundamental importance in plant development physiology and health, little is known of the details of the mode of transport through these channels and the mechanisms used to regulate their permeablity. In order to identify the macromolecular architecture of plasmodesmata we are using both direct isolation of plasmodesmatal proteins and immuno-gold cytochemistry with antibodies to known proteins. The details of their structure are being probed using high resolution scanning electron microscopy and freeze-substitution. The function of plasmodesmata is monitored using either electrophysiological techniques or microinjection of fluorescently labelled dyes.

The shape of plant cells and tissues is orchestrated by the precise alignment of inelastic cellulose microfibrils in the cell wall, which is in turn oriented by the microtubules in the cortex of plant cells. However, it is not known what controls the orientation of these cortical microtubules. We are attempting to answer this question, in particular assessing a possible role for electrical and mechanical fields.

Plants generate steady electrical fields around themselves which can be measured with a vibrating probe. We are assessing the hypothesis that these fields play a central role in the development and maintenance of polarity and co-ordination in growth of plant tissues by studying the effects of small applied electric fields on the orientation of cell expansion and polar auxin transport.
Studying the electric field induced re-orientations of cortical microtubules have led us to be interested in the detailed mechanism of this reorientation. We have been studying the details of microtubule dynamics in living plant cells following microinjection of fluorescently labelled tubulin. We are also attempting to identify the component which perceives the electric field and transduces the orienting signal to the microtubules.

My laboratory is well equipped with a Zeiss confocal scanning laser microscope, microinjection apparatus and electrophysiological set-ups.

Research Output

Selected Publications

• Holdaway-Clarke,T.L., Walker, N.A. & Overall, R.L. (1996). Measurement of the electrical resistance of plasmodesmata and membranes of corn suspension-culture cells. Planta 199: 537-544.
• Overall, R.L. & Blackman, L.M. (1996). A model of the macromolecular structure of plasmodesmata. Trends in Plant Science 1 (9): 307-311.
• Blackman, L.M. & Overall, RL. (1995). Electric fields affect the orientation of microtubules and cell expansion in pea callus. Protoplasma, 189: 256-266.