title: Scanning ion-selective electrode technique and X-ray microanalysis provide direct evidence of contrasting Na+ transport ability from root to shoot in salt-sensitive cucumber and salt-tolerant pumpkin under NaCl stress.
abstract: Grafting onto salt-tolerant pumpkin rootstock can increase cucumber salt tolerance. Previous studies have suggested that this can be attributed to pumpkin roots with higher capacity to limit the transport of Na(+) to the shoot than cucumber roots. However, the mechanism remains unclear. This study investigated the transport of Na(+) in salt-tolerant pumpkin and salt-sensitive cucumber plants under high (200 mM) or moderate (90 mM) NaCl stress. Scanning ion-selective electrode technique showed that pumpkin roots exhibited a higher capacity to extrude Na(+), and a correspondingly increased H(+) influx under 200 or 90 mM NaCl stress. The 200 mM NaCl induced Na(+)/H(+) exchange in the root was inhibited by amiloride (a Na(+)/H(+) antiporter inhibitor) or vanadate [a plasma membrane (PM) H(+) -ATPase inhibitor], indicating that Na(+) exclusion in salt stressed pumpkin and cucumber roots was the result of an active Na(+)/H(+) antiporter across the PM, and the Na(+)/H(+) antiporter system in salt stressed pumpkin roots was sufficient to exclude Na(+) X-ray microanalysis showed higher Na(+) in the cortex, but lower Na(+) in the stele of pumpkin roots than that in cucumber roots under 90 mM NaCl stress, suggesting that the highly vacuolated root cortical cells of pumpkin roots could sequester more Na(+), limit the radial transport of Na(+) to the stele and thus restrict the transport of Na(+) to the shoot. These results provide direct evidence for pumpkin roots with higher capacity to limit the transport of Na(+) to the shoot than cucumber roots.
authors.affiliation: Key Laboratory of Horticultural Plant Biology, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, PR China.
authors.forename: Bo
authors.initials: B
authors.lastname: Lei
authors.forename: Yuan
authors.initials: Y
authors.lastname: Huang
authors.forename: Jingyu
authors.initials: J
authors.lastname: Sun
authors.forename: Junjun
authors.initials: J
authors.lastname: Xie
authors.forename: Mengliang
authors.initials: M
authors.lastname: Niu
authors.forename: Zhixiong
authors.initials: Z
authors.lastname: Liu
authors.forename: Molin
authors.initials: M
authors.lastname: Fan
authors.forename: Zhilong
authors.initials: Z
authors.lastname: Bie
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D018553:Cucumis sativus / Q000187:drug effects / Q000502:physiology*; D028464:Cucurbita / Q000187:drug effects / Q000502:physiology*; D004577:Electron Probe Microanalysis / Q000379:methods*; D017736:Ion-Selective Electrodes; D019441:Plant Epidermis / Q000187:drug effects / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D055049:Salt Tolerance; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013312:Stress, Physiological
chemical_list: D010940:Plant Proteins; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D012964:Sodium; D006180:Proton-Translocating ATPases; D011188:Potassium