Abstract

The hydraulic resistance was measured on internodal cells of Chara corallina and Nitellopsis obtusa using the method of transcellular osmosis described by Kamiya and Tazawa in 1956. The transcellular hydraulic resistances of N. obtusa and C. corallina are 2.63 and 1.11 pm−1s Pa, resepectively. These values correspond to osmotic permeability coefficients (Pos) of 102.6 and 243.1 μm s−1, respectively. Cytochalasin A, B, and E (1–30 μg ml−1) increase the hydraulic resistance in a concentration-dependent manner. The order of effectiveness is: CE > CA = CB. CE increases the activation energy of water transport from 16.4 kJ mol−1 to 32.5 kJ mol−1 indicating that it increases the hydraulic resistance by eliminating a low resistance pathway. Cytochalasin B and E specifically increase the hydraulic resistance to endoosmosis; even when the driving force for transcellular osmosis is as low as 0.06 MPa. The effect of the cytochalasins is independent of their effect on cytoplasmic streaming since stopping streaming with N-ethyl maleimide or electrical stimulation has no effect on hydraulic conductivity. The possibility is discussed that a cortical actin cytoskeleton interacts with the plasma membrane in order to regulate the transport of water.

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