Effect of Ions on the Orientation of Cortical Microtubules in Spirogyra Cells

Abstract

Effects of ions on the orientation of cortical microlubules (MTs) in Spirogyra cells were studied. After depolymerizalion with amiprophos-methyl (APM), MTs were allowed to reorganize in NaCI solutions of various concentrations. As the concentration of NaCI increased, the frequency of cells that had oblique MTs increased. When cells in NaCI solution were transferred into artificial pond water (APW) and incubated for 6 h, all the MTs changed to become transverse to the longitudinal axis of the cell. KC1 and MgCl 2 also had effects on the orientation of MTs. However, NH4CI, CaCl;, CoCI2, and Co(NO3)2 did not show any effect. These results suggest that Na + , K + , and Mg 2+ have effects on MT orientation and that NHtf, Ca !+ , Co 2+ , Cl~, and NOf have little effect. When MTs were reorganized in either NaCI or KCI solutions, all the oblique MTs were organized into an S-helix. In contrast, some of the oblique MTs were found as a Z-helix in the cells incubated in MgCl2 or mannitol solutions. These results suggest that effects of Na + and K + on the orientation of MTs are not the same as those of Mg 2+ and mannitol. These results provide the first evidence that ions are involved in the orientation of MTs in algae.