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Plant Physiol, April 2001, Vol. 125, pp. 2029-2039
Function and Dynamics of Auxin and Carbohydrates during
Earlywood/Latewood Transition in Scots
Pine1
Claes
Uggla,2
Elisabeth
Magel,
Thomas
Moritz, and
Björn
Sundberg*
Department of Forest Genetics and Plant Physiology, Swedish
University of Agricultural Sciences, 901 83 Umeå, Sweden (C.U., T.M.,
B.S.); and Physiologische Ökologie der Pflanzen,
Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle
1, 720 76 Tübingen, Germany (E.M.)
In temperate regions the annual pattern of wood development is
characterized by the formation of radially narrow and thick walled
latewood cells. This takes place at the later part of the growing
season when cambial cell division declines. To gain new insight into
the regulation of this process, micro-analytical techniques were used
to visualize the distribution of indole-3-acetic acid (IAA), soluble
carbohydrates, and activities of sucrose (Suc)-metabolizing enzymes
across the cambial region tissues in Scots pine (Pinus sylvestris). The total amount of IAA in the cambial region did not change with latewood initiation. But its radial distribution pattern was altered, resulting in an increased concentration in the
cambial meristem and its recent derivatives. Thus, initiation of
latewood formation and cessation of cambial cell division is not a
consequence of decreased IAA concentrations in dividing and expanding
cells. Rather, IAA most likely has a role in defining the altered
developmental pattern associated with latewood formation. Carbohydrates
and enzyme activities showed distinctive radial distribution patterns.
Suc peaked in the phloem and decreased sharply to low levels across the
cambial zone, whereas fructose and glucose reached their highest levels
in the maturing tracheids. Suc synthase was the dominating Suc cleaving
enzyme with a peak in the secondary wall-forming tracheids and in the
phloem. Soluble acid invertase peaked in dividing and expanding cells.
Suc-phosphate synthase had its highest activities in the phloem.
Activities of cell wall bound invertase were low. The absence of major
seasonal variations indicates that carbohydrate availability is not a
trigger for latewood initiation. However, steep concentration gradients of the sugars suggest a role for sugar signaling in vascular development.
1
This work was supported by the Swedish Council
for Forestry and Agricultural Sciences, by the Swedish Natural Sciences
Research Council, and by Deutschen Akademischen Austausch Dienst.
2
Present address: BioAgri AB/Plant Pathology and
Biocontrol Unit, Swedish University of Agricultural Sciences, P.O. Box
7035, SE-750 07 Uppsala, Sweden.
*
Corresponding author; e-mail bjorn.sundberg{at}genfys.slu.se; fax
46-90-7865901.
© 2001 American Society of Plant Physiologists
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