Dr. Imogen Sparkes
Prof. Peter AshwinÂ
Organelles are membrane bound compartments in the cell which house the components for various biochemical reactions required to build and maintain cells. Several hundred organelles are present in plant epidermal cells, and they move in a seemingly random highly dynamic way. For example some organelles can move at speeds more than 8 times their diameter in a second, then stop, change direction and start moving again. There appears to be âsuper highwaysâ of fast movement in cytoplasmic streams, and more random motion outside of these streams similar to traffic on motorways versus side roads. The motion is controlled by molecular motors (myosins), but to what extent biophysical processes such as hydrodynamic flow exerted by the viscous cytoplasm, and potential tethering between organelles plays is not fully understood. Are tethers required to anchor organelles together (like a car and a trailer) or anchor them to sites in the cell? Could changing the viscosity in the cells cytoplasm provide a way of regulating organelle movement akin to moving through syrup versus water? A defect in key myosins affects the growth and development of the plant indicating that organelle movement has an important functional role. In addition, the seemingly random chaotic motion in non polarised tissues is affected upon pathogen ingress resulting in organelle clustering at the site of invasion. Currently, the functional role of organelle movement is poorly understood. Is movement required for delivery of metabolites / materials required for cell growth / maintenance / defence? Do organelles directly âcommunicateâ with one another through physical association? Do organelles migrate to âhot spotsâ within the cell where signals are relayed? How does movement relate to changes in environmental temperature? Is the seemingly chaotic movement actually more regulated than it first appears, and does it draw parallels with road networks allowing the organelles to âdrop offâ cargo to their target site which could then be shuttled to another destination in the cell in another organelle? To begin to answer these questions we first need to quantify the nature of organelle movement and association between organelles, and if movements between organelles are coordinated. The subsequent nature of these movements can then be assessed using mathematical modelling to determine if they are stochastic (random) or determined (regulated). In the long term, and probably beyond the scope of the project, changes in environmental conditions can then be related to the control growth conditions and potential functions for organelle movement tested.
This project will entail using Arabidopsis / tobacco plants producing fluorescent markers for several organelles. The movement of the organelles will be captured using live cell imaging (confocal and spinning disc microscopy). Subsequent analysis will be carried out using automated tracking algorithms and the results fed into a model to assess whether the movement is stochastic (random) or regulated / coordinated. Similar movement patterns between organelles will then be probed using optical tweezers to determine if there are biophysical associations between organelles, and tethering forces between the two structures determined. This will be carried out at the central laser facility at Harwell research complex. This project will therefore provide a comprehensive quantitative analysis of organelle movements in relation to one another, their cellular environment and the biophysical processes that could control their movement through tethering between organelles.
For details, please click theÂ Apply button below.
Closing date: Friday 10th January 2014.