title: Conditioning of Roots with Hypoxia Increases Aluminum and Acid Stress Tolerance by Mitigating Activation of K+ Efflux Channels by ROS in Barley: Insights into Cross-Tolerance Mechanisms.
abstract: Aluminum (Al) is prevalent in soils, but Al toxicity is manifested only under acid conditions. It causes severe damages to the root system. Short-term waterlogging stress can occur simultaneously with Al toxicity in areas with high rainfall or an inappropriate irrigation pattern. Barley (Hordeum vulgare L.) is one of the most Al-sensitive small-grained cereals. In this work, we have investigated effects of short-term treatments with hypoxia and phenolic acid (two major constraints in waterlogged soils) on root sensitivity to low-pH and Al stresses. We showed that hypoxia-primed roots maintained higher cell viability when exposed to low-pH/Al stress, in both elongation and mature root zones, and possessed superior ability to retain K(+) in response to low-pH/Al stresses. These priming effects were not related to higher H(+)-ATPase activity and better membrane potential maintenance, and could not be explained by the increased expression levels of HvHAK1, which mediates high-affinity K(+) uptake in roots. Instead, hypoxia-conditioned roots were significantly less sensitive to H2O2 treatment, indicated by the 10-fold reduction in the magnitude of K(+) efflux changes. This suggested that roots pre-treated with hypoxia desensitized reactive oxygen species (ROS)-inducible K(+) efflux channels in root epidermis, most probably via enhanced antioxidative capacity. A possible role for Ca(2+) in stress-induced ROS signaling pathways is also discussed. Overall, our results report, for the first time, the phenomenon of cross-protection between hypoxia and low-pH/Al stresses, and causally link it to the cell's ability to maintain cytosolic K(+) homeostasis.
authors.affiliation: School of Land and Food, University of Tasmania, Hobart TAS 7001, Australia.
authors.forename: Yanling
authors.initials: Y
authors.lastname: Ma
authors.affiliation: School of Land and Food, University of Tasmania, Hobart TAS 7001, Australia.
authors.forename: Min
authors.initials: M
authors.lastname: Zhu
authors.affiliation: School of Land and Food, University of Tasmania, Hobart TAS 7001, Australia.
authors.forename: Lana
authors.initials: L
authors.lastname: Shabala
authors.affiliation: School of Land and Food, University of Tasmania, Hobart TAS 7001, Australia.
authors.forename: Meixue
authors.initials: M
authors.lastname: Zhou
authors.affiliation: School of Land and Food, University of Tasmania, Hobart TAS 7001, Australia Sergey.Shabala@utas.edu.au.
authors.forename: Sergey
authors.initials: S
authors.lastname: Shabala
mesh_terms: D000535:Aluminum / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis; D001467:Hordeum / Q000187:drug effects / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008564:Membrane Potentials / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012987:Soil / Q000737:chemistry; D013312:Stress, Physiological
chemical_list: D015221:Potassium Channels; D017382:Reactive Oxygen Species; D012987:Soil; D006861:Hydrogen Peroxide; D000535:Aluminum; D010100:Oxygen
keywords: Aluminum toxicity; Calcium; Cross-tolerance; Hypoxia; Potassium; Reactive oxygen species