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Ionic processes underlying the decrease in osmotic potential of Chara L‐cell fragments in dilute electrolyte solutions
Author(s) -
Kiyosawa Keitaro
Publication year - 1996
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1996.tb00495.x
Subject(s) - chara , electrolyte , counterion , chemistry , turgor pressure , osmotic pressure , potassium , cell permeability , ionic bonding , ion , membrane , permeability (electromagnetism) , chromatography , sodium , cell membrane , membrane permeability , biophysics , biochemistry , botany , organic chemistry , biology , electrode
Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L‐cell fragments) were prepared. The L‐cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , NO − 3 . and SO 2− 4 . in the external electrolyte solutions in which L‐cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 m M KCL + 0.1 m M CaCl 2 solution, Chara L‐cell fragments absorbed K + and Cl − to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K + On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca 2+ , SO 2− 4 and NO − 3 showed much less permeability than K + and Cl − for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L‐cells is limited by the permeability of the least permeable ion.