CYCLOSIS · The biophysics of cytoplasmic streaming in Chara corallina

Cytoplasmic streaming (CS) is the name given to the continuous flow of cytoplasm observed in many eukaryotic cells, and is especially evident in freshwater algae like C. corallina, which display a remarkably steady and fast helical flow of cytoplasm along their centimeter-long internodal cells. Such flow is generated by a constant shearing force present at the endoplasm-ectoplasm interface, generated by a well characterized mechanism. The plant probably pays a steep energetic price to mantain CS, but it is not clear what it receives in exchange. Several hypotheses have been proposed, but progress is hindered by lack of experimental evidence. The project is aimed at critically advancing our understanding of the biological implications of CS, through a systematic series of experiments, both in vivo and in vitro. These experiments are based on the implementation of modern multidisciplinary techniques like confocal microscopy, microrheology, optical tweezing, PIV, and soft lithography, never used in this context before. These will guarantee unprecedented levels of accuracy and control. The first objective is to investigate what determines the flow profile and its speed, through the experimental characterization of CS and cytoplasm's rheology. The second is studying the flow's response to external stimuli, which should be connected to the plant's ability to react to environmental changes. The third is to investigate the transport properties of CS, since strong advection can qualitatively impact important quantities like the rate of nutrient intake. The project will contribute to develop a new area of biophysics, focused on problems that are more specifically biological. It is an exciting opportunity for the European scientific community to build a new and more integrated collaboration between physicists and biologists. It will be an excellent training for my future career, and a great introduction to doing research in Europe, where I wish to continue to work.