title: Sequential depolarization of root cortical and stelar cells induced by an acute salt shock - implications for Na(+) and K(+) transport into xylem vessels.
abstract: Early events in NaCl-induced root ion and water transport were investigated in maize (Zea mays L) roots using a range of microelectrode and imaging techniques. Addition of 100 mm NaCl to the bath resulted in an exponential drop in root xylem pressure, rapid depolarization of trans-root potential and a transient drop in xylem K(+) activity (A(K+) ) within ∼1 min after stress onset. At this time, no detectable amounts of Na(+) were released into the xylem vessels. The observed drop in A(K+) was unexpected, given the fact that application of the physiologically relevant concentrations of Na(+) to isolated stele has caused rapid plasma membrane depolarization and a subsequent K(+) efflux from the stelar tissues. This controversy was explained by the difference in kinetics of NaCl-induced depolarization between cortical and stelar cells. As root cortical cells are first to be depolarized and lose K(+) to the environment, this is associated with some K(+) shift from the stelar symplast to the cortex, resulting in K(+) being transiently removed from the xylem. Once Na(+) is loaded into the xylem (between 1 and 5 min of root exposure to NaCl), stelar cells become more depolarized, and a gradual recovery in A(K+) occurs.
authors.affiliation: Plant Bioelectrics Group, Institute of Pulsed Power and Microwave Technology and Institute of Botany 1, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Lars H
authors.initials: LH
authors.lastname: Wegner
authors.forename: Giovanni
authors.initials: G
authors.lastname: Stefano
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.forename: Marika
authors.initials: M
authors.lastname: Rossi
authors.forename: Stefano
authors.initials: S
authors.lastname: Mancuso
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
mesh_terms: D001692:Biological Transport; D008839:Microelectrodes; D018517:Plant Roots / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D054712:Salinity; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological; D052584:Xylem / Q000378:metabolism*; D003313:Zea mays / Q000502:physiology
chemical_list: D012965:Sodium Chloride; D012964:Sodium; D011188:Potassium