Abstract
Effects of octylguanidine (OG) were studied on the permeability of cells of the adaxial epidermis of Allium cepa bulb scales to water and methyl urea and on the protoplast surface. Interference of OG with the Ca2+ and Al3+ action on the cell surface was also investigated.
Permeability of the cell membrane for water and methyl urea increased nearly three times in presence of OG. The effect of OG on cell permeability depended on its direct contact with the protoplast surface.
The effect of OG on the interaction between the protoplast surface and the cell wall (wall attachment) was marked and rapid; OG (225 micromolar) decreased the time for protoplast detachment in hypertonic solutions from 420 to 120 seconds. The plasmolyzed protoplasts were immediately rounded off while the controls without OG remained heavily concave.
A considerable increase in protoplast detachment time and a decrease in rounding percentage were found when cells were plasmolyzed after pretreatment with AlCl3 (0.05 molar for 2 minutes). This effect was partially reversed by KCl which was further enhanced by addition of OG.
Penetration of OG into the mesoplasm was manifested only after 10 to 15 minutes. Vacuolization and swelling of the protoplasm, fragmentation of the protoplast, and aggregation of the spherosomes, however, were observed only 30 minutes after transfer. No evidence for penetration of OG into the vacuole was found.
The results support earlier suggestions that OG acts primarily on the protoplast surface by interacting with membrane proteins as well as with phospholipids. In several aspects, OG acts on the cell surface similarly to a surfactant.
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