title: Electrical signalling and cytokinins mediate effects of light and root cutting on ion uptake in intact plants.
abstract: Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1-2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from -18 to -12 nmol m(-2) s(-1)) and K+ uptake (approximately 2 nmol m(-2) s(-1)) reverted to efflux (approximately -3 nmol m(-2) s(-1)). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a approximately 3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 mm NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (-50 nmol m(-2) s(-1)). Kinetin (2-4 microM), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.
authors.affiliation: School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia.
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
authors.forename: Jiayin
authors.initials: J
authors.lastname: Pang
authors.forename: Meixue
authors.initials: M
authors.lastname: Zhou
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Cuin
authors.forename: Peter
authors.initials: P
authors.lastname: Nick
authors.forename: Lars H
authors.initials: LH
authors.lastname: Wegner
mesh_terms: D003583:Cytokinins / Q000494:pharmacology*; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007701:Kinetin / Q000494:pharmacology; D008027:Light; D008564:Membrane Potentials; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D052584:Xylem / Q000187:drug effects / Q000378:metabolism; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism
chemical_list: D003583:Cytokinins; D012965:Sodium Chloride; D007701:Kinetin; D011188:Potassium