title: Physiological and molecular mechanisms mediating xylem Na+loading in barley in the context of salinity stress tolerance.
abstract: Time-dependent kinetics of xylem Na+loading was investigated using a large number of barley genotypes contrasting in their salinity tolerance. Salt-sensitive varieties were less efficient in controlling xylem Na+loading and showed a gradual increase in the xylem Na+content over the time. To understand underlying ionic and molecular mechanisms, net fluxes of Ca2+, K+and Na+were measured from the xylem parenchyma tissue in response to H2O2and ABA; both of them associated with salinity stress signalling. Our results indicate that NADPH oxidase-mediated apoplastic H2O2production acts upstream of the xylem Na+loading and is causally related to ROS-inducible Ca2+uptake systems in the root stelar tissue. It was also found that ABA regulates (directly or indirectly) the process of Na+retrieval from the xylem and the significant reduction of Na+and K+fluxes induced by bumetanide are indicative of a major role of chloride cation co-transporter (CCC) on xylem ion loading. Transcript levels of HvHKT1;5_like and HvSOS1_like genes in the root stele were observed to decrease after salt stress, while there was an increase in HvSKOR_like gene, indicating that these ion transporters are involved in primary Na+/K+movement into/out of xylem.
authors.affiliation: School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania, 7001, Australia.
authors.forename: Min
authors.initials: M
authors.lastname: Zhu
authors.affiliation: School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania, 7001, Australia.
authors.forename: Meixue
authors.initials: M
authors.lastname: Zhou
authors.affiliation: School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania, 7001, Australia.
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.affiliation: School of Land and Food, University of Tasmania, Private Bag 54, Hobart, Tasmania, 7001, Australia.
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D054712:Salinity; D012964:Sodium / Q000378:metabolism*; D013312:Stress, Physiological / Q000502:physiology*; D013890:Thiourea / Q000494:pharmacology; D052584:Xylem / Q000187:drug effects / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D000040:Abscisic Acid; D012964:Sodium; D006861:Hydrogen Peroxide; D013890:Thiourea; D011188:Potassium
keywords: ABA; CCC transporter; H2O2; NADPH oxidase; SKOR; SOS1; xylem sodium loading