Cytoplasmic streaming, also called protoplasmic streaming and cyclosis, is the directed flow of cytosol (the liquid component of the cytoplasm) and organelles around large fungal and plant cells through the mediation of actin. This movement aids in the delivery of organelles, nutrients, metabolites, genetic information, and other materials to all parts of the cell. Cytoplasmic streaming occurs along actin filaments in the cytoskeleton of the cell.
Cytoplasmic streaming was first discovered in the 1830s. The scientific breakthrough assisted scientists in developing an understanding of the different roles of cells and how they function as the basic operating systems of life.
This process occurs through the operation of motor proteins called myosins. These proteins use energy of adenosine triphosphate (ATP) to act as a molecular motor, which slides along actin filaments. This works in a manner that tows the organelles and other cytoplasmic contents in the same direction. Myosin proteins consist of two conjoined proteins. If one protein remains attached to the substrate, the substance acted upon by the protein, such as a microfilament, has the ability to move organelles through the cytoplasm.
The green alga genus Chara and other genera in the Division Charophyta, such as Coleochaete, are thought to be the closest relatives of land plants. These haploid organisms contain some of the largest plant cells on earth, a single cell of which can reach up to 10 cm in length. The large size of these cells demands an efficient means to distribute resources, which is enabled via cytoplasmic streaming.
Cytoplasmic streaming is strongly dependent upon intracellular pH and temperature. It has been observed that the effect of temperature on cytoplasmic streaming created linear variance and dependence at different high temperatures in comparison to low temperatures. This process is complicated, with temperature alterations in the system increasing its efficiency, with other factors such as the transport of ions across the membrane being simultaneously affected. This is due to cells homeostasis depending upon active transport which may be affected at some critical temperatures.
In plant cells, chloroplasts may be moved around with the stream, possibly to a position of optimum light absorption for photosynthesis. The rate of motion is usually affected by light exposure, temperature, and pH levels.
In reference to pH, because actin and myosin are both proteins, strong dependence on pH is expected. The optimal pH at which cytoplasmic streaming is highest, is achieved at neutral pH and decreases at both low and high pH.
The flow of cytoplasm may be stopped by:
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- Lodish 2000, Section 18.5: Actin and Myosin in Nonmuscle Cells