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Development and Growth Regulation

Distribution of Endogenous Indole-3-Acetic Acid and Compression Wood Formation in Reoriented Branches of Douglas-Fir ¹

Department of Forestry and Wildlife Management, University of Massachusetts, Amherst, Massachusetts 01003, Department of Forest Science, Oregon State University, Corvallis, Oregon 97331

Five-year-old segments of intact 7-year-old branches of Douglas-fir (Pseudotsuga meziesii [Mirb.] Franco) were reoriented to determine the relation between indole-3-acetic acid (IAA) and the formation of compression wood. Eight branches per treatment were either left at their original angle (mean of 69°, the control), or bent proximal to the segment to reorient it up or down 30°. Differentiating xylem tissue from the upper and lower sides of each segment was collected and extracted separately for IAA analysis by in-line fluorescence detection of free IAA and IAA methyl ester after sequential C₁₆ reversed-phase high performance liquid chromatography. The IAA methyl ester was confirmed by gas chromatography-mass spectroscopy. Compression wood formed on the upper side of branches reoriented up and on the lower side of controls or branches reoriented down. IAA was present in all samples. The difference in IAA concentration between upper and lower sides was either not correlated, or negatively correlated in segments reoriented down, with both the occurrence of compression wood and the rate of new tracheid production. Mean concentrations for whole branch segments were not affected by the treatments, regardless of whether IAA concentrations were expressed on a surface area, weight, or cell basis.

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