Mechano-perception in Chara cells: the influence of salinity and calcium on touch-activated receptor potentials, action potentials and ion transport

• Published in: Plant, cell and environment cell and environment, 2008-11, Vol.31 (11), p.1575-1591
• Main Authors: SHEPHERD, VIRGINIA A, BEILBY, MARY J, AL KHAZAALY, SABAH A.S, SHIMMEN, TERUO
• Format: Article
• Language: English
• Subjects: Action Potentials; Biological and medical sciences; Calcium - metabolism; Cell Survival; Chara; Chara - metabolism; excitation; Fundamental and applied biological sciences. Psychology; Ion Transport; Mechanotransduction, Cellular; Models, Biological; Patch-Clamp Techniques; Physical Stimulation; plant mechano‐perception; Potassium - metabolism; Potassium Channels - metabolism; proton pump; Proton Pumps - metabolism; salt stress
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2008.01866.x

This paper investigates the impact of increased salinity on touch-induced receptor and action potentials of Chara internodal cells. We resolved underlying changes in ion transport by current/voltage analysis. In a saline medium with a low Ca²⁺ ion concentration [(Ca²⁺)ext], the cell background conductance significantly increased and proton pump currents declined to negligible levels, depolarizing the membrane potential difference (PD) to the excitation threshold [action potential (AP)threshold]. The onset of spontaneous repetitive action potentials further depolarized the PD, activating K⁺ outward rectifying (KOR) channels. K⁺ efflux was then sustained and irrevocable, and cells were desensitized to touch. However, when [Ca²⁺]ext was high, the background conductance increased to a lesser extent and proton pump currents were stimulated, establishing a PD narrowly negative to APthreshold. Cells did not spontaneously fire, but became hypersensitive to touch. Even slight touch stimulus induced an action potential and further repetitive firing. The duration of each excitation was extended when [Ca²⁺]ext was low. Cell viability was prolonged in the absence of touch stimulus. Chara cells eventually depolarize and die in the saline media, but touch-stimulated and spontaneous excitation accelerates the process in a Ca²⁺-dependent manner. Our results have broad implications for understanding the interactions between mechano-perception and salinity stress in plants.