AOBPreview originally published online on March 3, 2009
Annals of Botany 2009 103(7):1145-1157; doi:10.1093/aob/mcp050
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Anatomical features that facilitate radial flow across growth rings and from xylem to cambium in Cryptomeria japonica
1 Institute of Wood Technology, Akita Prefectural University, Kaieisaka 11-1, Noshiro-shi 016-0876, Japan
2 Tama Forest Science Garden, FFPRI, Todori 1833-81, Hachioji, Tokyo 193-0843, Japan
3 Forestry and Forest Products Research Institute, Tsukuba Science City, 305-8687 Japan
4 Royal Museum for Central Africa, B-3080 Tervuren, Belgium
* For correspondence. Present address: Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA. E-mail peter.kitin{at}oregonstate.edu
Received: 12 June 2008 Returned for revision: 18 July 2008 Accepted: 16 January 2009 Published electronically: 3 March 2009
Background and Aims: Although the lateral movement of water and gas in tree stems is an important issue for understanding tree physiology, as well as for the development of wood preservation technologies, little is known about the vascular pathways for radial flow. The aim of the current study was to understand the occurrence and the structure of anatomical features of sugi (Cryptomeria japonica) wood including the tracheid networks, and area fractions of intertracheary pits, tangential walls of ray cells and radial intercellular spaces that may be related to the radial permeability (conductivity) of the xylem.
Methods: Wood structure was investigated by light microscopy and scanning electron microscopy of traditional wood anatomical preparations and by a new method of exposed tangential faces of growth-ring boundaries.
Key Results: Radial wall pitting and radial grain in earlywood and tangential wall pitting in latewood provide a direct connection between subsequent tangential layers of tracheids. Bordered pit pairs occur frequently between earlywood and latewood tracheids on both sides of a growth-ring boundary. In the tangential face of the xylem at the interface with the cambium, the area fraction of intertracheary pit membranes is similar to that of rays (2·8 % and 2·9 %, respectively). The intercellular spaces of rays are continuous across growth-ring boundaries. In the samples, the mean cross-sectional area of individual radial intercellular spaces was 1·2 µm2 and their total volume was 0·06 % of that of the xylem and 2·07 % of the volume of rays.
Conclusions: A tracheid network can provide lateral apoplastic transport of substances in the secondary xylem of sugi. The intertracheid pits in growth-ring boundaries can be considered an important pathway, distinct from that of the rays, for transport of water across growth rings and from xylem to cambium.
Key words: Cryptomeria japonica, bordered pit, intercellular spaces, lateral transport, tracheid network, water conduction, xylem permeability
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