Adjustment of osmotic pressure coupled with change of growth mode in Spirogyra
Katsuhisa Yoshida A C D , Ai Ohtani A , Tetsuro Mimura B and Teruo Shimmen AA Department of Life Science, Graduate School of Life Science, University of Hyogo, Kouto 3-2-1, Harima Science Park City, Hyogo 678-1297, Japan.
B Graduate School of Science, Kobe University, Rokkodai 1-1, Nada, Kobe 678-8501, Japan.
C Present address: Graduate School of Science, Kobe University, Rokkodai 1-1, Nada, Kobe 678-8501, Japan.
D Corresponding author. Email: yoshikatsu@silver.kobe-u.ac.jp
Functional Plant Biology 35(7) 580-584 https://doi.org/10.1071/FP08138
Submitted: 30 April 2008 Accepted: 1 July 2008 Published: 21 August 2008
Abstract
Spirogyra living in running water forms a rhizoid which anchors it to the substratum. Rhizoid differentiation can be induced in the laboratory by severing algal filaments. The terminal cell changes the growth mode from diffuse growth to tip growth, and finally differentiates to be a rhizoid. We found that the intracellular osmolarity of the rhizoid was significantly lower than that of other interjacent cells which did not form rhizoids. The decrease in the intracellular osmolarity began before the start of tip growth. TEA, a K+ channel blocker, inhibited the decrease in the intracellular osmolarity of the terminal cells; increase in the external K+ also inhibited this. It was suggested that K+ efflux through K+ channel is involved in the adjustment of osmotic pressure. When the adjustment of osmotic pressure was inhibited, tip growth did not start, inevitably, no rhizoid was formed. In Spirogyra sp. which was unable to form rhizoids, the terminal cell did not show the adjustment of osmotic pressure. Thus, this adjustment seems to be intimately coupled with the rhizoid differentiation. Possible roles of the adjustment of osmotic pressure in rhizoid differentiation are discussed.
Additional keywords: K+, rhizoid differentiation, tip growth, turgor pressure.
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