The function of intercellular spaces along the ray parenchyma in sapwood, intermediate wood, and heartwood of Cryptomeria japonica (Cupressaceae).
OBJECTIVE
Intercellular spaces along ray parenchyma (ISRP) are common in many conifer xylems, but their function is uncertain because the in-situ structural network among ISRP, ray parenchyma, and tracheids has not been evaluated. Analysis of water distribution in ISRP from sapwood to heartwood is needed to elucidate the function of ISRP in sapwood, intermediate wood, and heartwood.


METHODS
We used cryo-scanning electron microscopy, x-ray photography, and water content measurement in xylem to analyze the presence of liquids in ISRP, ray parenchyma, and tracheids from sapwood to heartwood in Cryptomeria japonica (Cupressaceae).


RESULTS
In sapwood, almost all ISRP were empty. "Cingulate-cavitated regions", which lose water along the tangential direction within one annual ring, formed in the earlywood tracheids, and their frequency increased toward the inner annual rings, whereas ray parenchyma cells were alive and not involved in the partial cavitation. In intermediate wood, almost all ISRP and earlywood tracheids and many of the ray cells were empty, and only some latewood tracheids retained liquid in their lumina. The ISRP were connected with tracheids via gas-filled ray parenchyma cells.


CONCLUSIONS
The ISRP work as a pathway of gas for aspiration of ray parenchyma cells in sapwood. On the other hand, the occurrence of a gas network between ISRP, ray parenchyma, and tracheids facilitates cavitation of tracheids, resulting in the generation of low-moisture, intermediate wood.
Forestry Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Ikaba 430, Yamasaki, Shiso, Hyogo 671-2515, Japan. satoshi_nagai@pref.hyogo.lg.jp
Satoshi
S
Nagai
Yasuhiro
Y
Utsumi
D020285:Cryoelectron Microscopy; D032485:Cryptomeria / Q000166:cytology* / Q000648:ultrastructure; D005110:Extracellular Space / Q000378:metabolism*; D014867:Water; D014934:Wood / Q000166:cytology* / Q000648:ultrastructure; D052584:Xylem / Q000033:anatomy & histology / Q000166:cytology / Q000648:ultrastructure
D014867:Water