title: Enhanced salt resistance in apple plants overexpressing a Malus vacuolar Na+/H+ antiporter gene is associated with differences in stomatal behavior and photosynthesis.
abstract: High salinity is a major abiotic factor that limits crop production. The dwarfing apple rootstock M.26 is sensitive to such stress. To obtain an apple that is adaptable to saline soils, we transformed this rootstock with a vacuolar Na(+)/H(+) antiporter, MdNHX1. Differences in salt tolerance between transgenic and wild-type (WT) rootstocks were examined under field conditions. We also compared differences when 'Naganofuji No. 2' apple was grafted onto these transgenic or WT rootstocks. Plants on the transgenic rootstocks grew well during 60 d of mild stress (100 mM NaCl) while the WT exhibited chlorosis, inhibited growth and even death. Compared with the untreated control, the stomatal density was greater in both non-grafted and grafted WT plants exposed to 200 mM NaCl. In contrast, that density was significantly decreased in leaves from grafted transgenic plants. At 200 mM NaCl, net photosynthesis, stomatal conductance, intercellular CO2 concentration, and chlorophyll contents were markedly reduced in the WT, whereas the declines in those values were only minor in similarly stressed transgenic plants. Therefore, we conclude that overexpressing plants utilize a better protective mechanism for retaining higher photosynthetic capacity. Furthermore, this contrast in tolerance and adaptability to stress is linked to differences in stomatal behavior and photosynthetic rates.
authors.affiliation: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Wei
authors.forename: Dong
authors.initials: D
authors.lastname: Liang
authors.forename: Shasha
authors.initials: S
authors.lastname: Zhou
authors.forename: Yonghong
authors.initials: Y
authors.lastname: Li
authors.forename: Changhai
authors.initials: C
authors.lastname: Liu
authors.forename: Fengwang
authors.initials: F
authors.lastname: Ma
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D015870:Gene Expression; D017343:Genes, Plant; D027845:Malus / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D010788:Photosynthesis / Q000235:genetics*; D018515:Plant Leaves / Q000033:anatomy & histology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D054046:Plant Stomata; D030821:Plants, Genetically Modified; D054712:Salinity; D055049:Salt Tolerance / Q000235:genetics*; D012492:Salts; D012965:Sodium Chloride / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics; D014170:Transformation, Genetic; D014617:Vacuoles / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D012492:Salts; D017923:Sodium-Hydrogen Exchangers; D002734:Chlorophyll; D002245:Carbon Dioxide; D012965:Sodium Chloride
keywords: Apple; C(i); Chl; G(s); MdNHX1; NHX1; Na(+)/H(+) antiporter; P(n); Photosynthesis; REL; Salt; Stomatal response; T(r); TTC; chlorophyll; intercellular CO(2) concentration; net photosynthetic rate; relative electrolyte leakage; stomatal conductance; transpiration rate; triphenyl tetrazolium chloride; vacuolar Na(+)/H(+) transporter