title: Effect of local heating and cooling on cambial activity and cell differentiation in the stem of Norway spruce (Picea abies).
abstract: BACKGROUND AND AIMS The effect of heating and cooling on cambial activity and cell differentiation in part of the stem of Norway spruce (Picea abies) was investigated.
  
  
  METHODS
  A heating experiment (23-25 degrees C) was carried out in spring, before normal reactivation of the cambium, and cooling (9-11 degrees C) at the height of cambial activity in summer. The cambium, xylem and phloem were investigated by means of light- and transmission electron microscopy and UV-microspectrophotometry in tissues sampled from living trees.
  
  
  RESULTS
  Localized heating for 10 d initiated cambial divisions on the phloem side and after 20 d also on the xylem side. In a control tree, regular cambial activity started after 30 d. In the heat-treated sample, up to 15 earlywood cells undergoing differentiation were found to be present. The response of the cambium to stem cooling was less pronounced, and no anatomical differences were detected between the control and cool-treated samples after 10 or 20 d. After 30 d, latewood started to form in the sample exposed to cooling. In addition, almost no radially expanding tracheids were observed and the cambium consisted of only five layers of cells. Low temperatures reduced cambial activity, as indicated by the decreased proportion of latewood. On the phloem side, no alterations were observed among cool-treated and non-treated samples.
  
  
  CONCLUSIONS
  Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.
authors.affiliation: University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, Rozna dolina, Cesta VIII/34, SI-1000 Ljubljana, Slovenia.
authors.forename: Jozica
authors.initials: J
authors.lastname: Gricar
authors.forename: Martin
authors.initials: M
authors.lastname: Zupancic
authors.forename: Katarina
authors.initials: K
authors.lastname: Cufar
authors.forename: Gerald
authors.initials: G
authors.lastname: Koch
authors.forename: Uwe
authors.initials: U
authors.lastname: Schmitt
authors.forename: Primoz
authors.initials: P
authors.lastname: Oven
mesh_terms: D002454:Cell Differentiation / Q000502:physiology*; D002473:Cell Wall / Q000648:ultrastructure; D002980:Climate; D003080:Cold Temperature; D006358:Hot Temperature; D046529:Microscopy, Electron, Transmission; D028222:Picea / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D018547:Plant Stems / Q000166:cytology / Q000502:physiology; D013056:Spectrophotometry, Ultraviolet