The radial distribution and metabolism of IAA-¹⁴C in Pinus echinata stems in relation to wood formation

Abstract

NIX, L. E., and T. J. WODZICKI. 1974. The radial distribution and metabolism of in Pirlro eclrir~ata stems in relation to wood formation. Can. J. Bot. 52: 1349-1355. Radial distribution of auxin in differentiating xylem tissues was studied in decapitated 8-to 14-year-old Pitzrw echir7ata stems to wlich indoleacetic acid (IAA-1°C) in lanolin paste was applied during early and late growing season. Small segments of the treated stems were sectioned tangentially with a sliding microtome, the serial sections were collected, and the radioactivity of each section was measured. The results indicate that JAA is radially distributed in the differentiating tissues along a steep gradient from the cambial region to the differentiating xylem and that this distribution varies during the growing season in relation to the seasonal transition t o latewood formation in intact trees.Forty-five to 60y0 of the radioactivity recovered in methanolic extracts of the differentiating xylem after a 2-day labeling period was in the form of IAA. After 7 days 10-15~o of the radioactivity recovered was in the form of IAA. The radioactivity recovered separated into ether and aqueous fractions when the methanol extract was reduced, acidified, and partitioned with ether. Chromatography of aliquots of both fractions in several solvent systems revealed no individually significant metabolite of IAA. The aqueous fraction derivatives accumulated in the tissue, and later in the season the metabolism of IAA and the accumulation of the aqueous fraction apparently decreased. In experiments where excised differentiating xylem was incubated with a liquld medium containing IAA-"C, the conversion of radioactivity to the aqueous fraction was twofold greater in early season than in late season. The significance of the results is discussed with possible relation to the control of the seasonal transition to latewood formation in conifers.

Auxin as a positional signal in pattern formation in plants.

“…This conclusion is supported by the finding of Nix and Wodzicki (25), that radiolabeled IAA, which had been apically fed to decapitated Pinus echinata internodes, and which had been transported in a polar manner, was distributed in a gradient across the cambial region identical to that of endogenous IAA in this study. It has been suggested that the polar IAA transport pathway involves both symplast and apoplast (23).…”

7. The role of plant growth regulators in forest tree cambial growth

“…with 'H-IAA indicated that IAA transport was localized in the cambial zone, differentiating derivatives, and phloem parenchyma during cambial activity, but occurred in the cambial zone and phloem parenchyma during cambial dormancy (89,90) . Similarly, Nix and Wodzicki (130) found that the cambial zone and differentiating derivatives, particularly on the xylem side, contained most of the radioactivity recovered 2 days after '"C-IAA was applied apically to growing Pinus echinata Mill . stems .…”

Distribution of Indole-3-Acetic Acid and the Occurrence of Its Alkali-Labile Conjugates in the Extraxylary Region of Pinus sylvestris Stems

“…However, this notion cannot be tested until it becomes possible to localize the measurement of IAA to an individual cell or tissue at all times of the year. A high concentration of IAA in the cambium might be expected as there is evidence that this tissue is the major site of polar IAA transport (10,14). The cambium may also be a site of IAA synthesis (13), but this possibility remains to be verified.…”