Abstract
Cytoplasmic streaming (CPS) is well known to assist the movement of nutrients, organelles and genetic material by transporting all of the cytoplasmic contents of a cell. CPS is generated by motility organelles that are driven by motor proteins near a membrane surface, where the CPS has been found to have a flat velocity profile in the flow field according to the sliding theory. There is a consistent mixing of contents inside the cell by CPS if the velocity gradient profile is flattened, which is not assisted by advection diffusion but is only supported by Brownian diffusion. Although the precise flow structure of the cytoplasm has an important role for cellular metabolism, the hydrodynamic mechanism of its convection has not been clarified. We conducted an experiment to visualise the flow of cytoplasm in Nitella cells by injecting tracer fluorescent nanoparticles and using a flow visualisation system in order to understand how the flow profile affects their metabolic system. We determined that the velocity field in the cytosol has an obvious velocity gradient, not a flattened gradient, which suggests that the gradient assists cytosolic mixing by Taylor–Aris dispersion more than by Brownian diffusion.
Highlights
Cytoplasmic streaming (CPS) was first discovered by Corti (1774) [1] as a mechanism of cytosis in the green algae Nitella and Chara following the development of a handmade optical microscope
Our result indicates that the velocity gradient in the cytosol clearly exists, former researchers believed that the cytosol in Nitella internodal cells has a flattened velocity distribution as originally reported by Kamiya (1956) [6]
We performed an experiment to confirm the inhibition of CPS and to measure the recovery time of CPS after needle stimulation
Summary
Cytoplasmic streaming (CPS) was first discovered by Corti (1774) [1] as a mechanism of cytosis in the green algae Nitella and Chara following the development of a handmade optical microscope. There are still many uncertainties about the mechanism of CPS, with respect to plant physiology and hydrodynamics. The motility of CPS has been hypothesised to be based on the sol-gel layer on the cell wall with slip motion, which is the ‘sliding theory’ of Kamiya and Kuroda (1956) [6]. They mentioned that the slip layer has a flattened velocity distribution, the PLOS ONE | DOI:10.1371/journal.pone.0144938. They mentioned that the slip layer has a flattened velocity distribution, the PLOS ONE | DOI:10.1371/journal.pone.0144938 December 22, 2015
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