title: Characterization of a rice variety with high hydraulic conductance and identification of the chromosome region responsible using chromosome segment substitution lines.
abstract: OBJECTIVE
  The rate of photosynthesis in paddy rice often decreases at noon on sunny days because of water stress, even under submerged conditions. Maintenance of higher rates of photosynthesis during the day might improve both yield and dry matter production in paddy rice. A high-yielding indica variety, 'Habataki', maintains a high rate of leaf photosynthesis during the daytime because of the higher hydraulic conductance from roots to leaves than in the standard japonica variety 'Sasanishiki'. This research was conducted to characterize the trait responsible for the higher hydraulic conductance in 'Habataki' and identified a chromosome region for the high hydraulic conductance.
  
  
  METHODS
  Hydraulic conductance to passive water transport and to osmotic water transport was determined for plants under intense transpiration and for plants without transpiration, respectively. The varietal difference in hydraulic conductance was examined with respect to root surface area and hydraulic conductivity (hydraulic conductance per root surface area, L(p)). To identify the chromosome region responsible for higher hydraulic conductance, chromosome segment substitution lines (CSSLs) derived from a cross between 'Sasanishiki' and 'Habataki' were used.
  
  
  RESULTS
  The significantly higher hydraulic conductance resulted from the larger root surface area not from L(p) in 'Habataki'. A chromosome region associated with the elevated hydraulic conductance was detected between RM3916 and RM2431 on the long arm of chromosome 4. The CSSL, in which this region was substituted with the 'Habataki' chromosome segment in the 'Sasanishiki' background, had a larger root mass than 'Sasanishiki'.
  
  
  CONCLUSIONS
  The trait for increasing plant hydraulic conductance and, therefore, maintaining the higher rate of leaf photosynthesis under the conditions of intense transpiration in 'Habataki' was identified, and it was estimated that there is at least one chromosome region for the trait located on chromosome 4.
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Adachi
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Tsuru
authors.forename: Motohiko
authors.initials: M
authors.lastname: Kondo
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Arai-Sanoh
authors.forename: Tsuyu
authors.initials: T
authors.lastname: Ando
authors.forename: Taiichiro
authors.initials: T
authors.lastname: Ookawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yano
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hirasawa
mesh_terms: D001692:Biological Transport / Q000235:genetics / Q000502:physiology*; D032461:Chromosomes, Plant / Q000235:genetics*; D012275:Oryza / Q000235:genetics* / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D040641:Quantitative Trait Loci / Q000235:genetics; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water
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