title: Chill-induced decrease in capacity of RuBP carboxylation and associated H2O2 accumulation in cucumber leaves are alleviated by grafting onto figleaf gourd.
abstract: OBJECTIVE
  Chilling results in a significant decrease in Rubisco content and increased generation of reactive oxygen species (ROS) in cucumber (Cucumis sativus), a chilling-sensitive species. The role of roots in the regulation of the tolerance is unknown. Here, cucumber plants grafted onto figleaf gourd (Cucurbita ficifolia), a chilling-tolerant species were used to study the role of roots in the regulation of shoot functioning and the associated root-to-shoot communication.
  
  
  METHODS
  Gas exchange and chlorophyll fluorescence were measured using an infrared gas analyser combined with a pulse amplitude fluorimeter during chilling at 14 degrees C or 7 degrees C and subsequent recovery. At the same time, Rubisco content and activity and ROS generation were spectrophotometrically assayed. Abscisic acid and cytokinin concentrations in xylem sap were also determined by enzyme-linked immunosorbent assay.
  
  
  CONCLUSIONS
  Grafted plants showed a significantly higher light-saturated rate of CO(2) assimilation (A(sat)) than own-rooted plants when roots were gradually cooled, but no differences were detected when shoots were cooled. Chill at 7 degrees C irreversibly reduced A(sat), and significantly decreased maximum carboxylation activity, Rubisco content and initial Rubisco activity. However, grafted plants showed weaker inhibition, together with decreased electron flux in the water-water cycle. Higher activity of antioxidant enzymes with less ROS production was found in grafted plants. In addition, ABA concentration increased by 48.4-fold whilst cytokinin concentration decreased by 91.5% in the xylem sap of own-rooted plants after exposure to a 7 degrees C chill. In comparison, ABA and cytokinin concentrations increased by 10.5-fold and 36.9%, respectively, for the grafted plants. Improved plant growth was also observed in grafted plants after the chill. These results suggest that some signals coming from chilling-resistant roots (i.e. ABA and cytokinins) protect leaf photosynthesis in shoots of chilling-sensitive plants.
authors.affiliation: Department of Horticulture, Huajiachi Campus, Zhejiang University, Kaixuan Road 268, Hangzhou, PR China 310029.
authors.forename: Yanhong
authors.initials: Y
authors.lastname: Zhou
authors.forename: Lifeng
authors.initials: L
authors.lastname: Huang
authors.forename: Yili
authors.initials: Y
authors.lastname: Zhang
authors.forename: Kai
authors.initials: K
authors.lastname: Shi
authors.forename: Jingquan
authors.initials: J
authors.lastname: Yu
authors.forename: Salvador
authors.initials: S
authors.lastname: Nogués
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003080:Cold Temperature; D018553:Cucumis sativus / Q000378:metabolism*; D028464:Cucurbita / Q000502:physiology*; D003583:Cytokinins / Q000378:metabolism; D005453:Fluorescence; D006861:Hydrogen Peroxide / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
chemical_list: D003583:Cytokinins; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; D012273:Ribulose-Bisphosphate Carboxylase