Journal Article

Control of longitudinal and cambial growth by gibberellins and indole-3-acetic acid in current-year shoots of <i>Pinus sylvestris</i>

Q. Wang, C. H. A. Little and P. C. Odén

in Tree Physiology

Volume 17, issue 11, pages 715-721
Published in print November 1997 | ISSN: 0829-318X
Published online November 1997 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/17.11.715
Control of longitudinal and cambial growth by gibberellins and indole-3-acetic acid in current-year shoots of Pinus sylvestris

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We investigated the involvement of gibberellins (GAs) and indole-3-acetic acid (IAA) in the control of longitudinal and cambial growth in current-year shoots of Pinus sylvestris L. Elongating terminal shoots, located at the apex of previous-year (1-year-old) branches in the uppermost whorl on the main stem, were variously decapitated (apical 5 to 10 mm removed), defoliated (all developing needle fascicles removed) and treated with endogenous GA4/7 or IAA, or both. Shoot length and the radial widths of xylem and phloem were measured, and the concentrations of GA1, GA3, GA4, GA9 and IAA in the stem were determined by combined gas chromatography–mass spectrometry with deuterated GAs and [13C6]-IAA as internal standards. Decapitation decreased the production of xylem and phloem and the IAA concentration, but did not alter either longitudinal growth or the concentrations of GAs. Defoliation markedly inhibited shoot elongation, as well as cambial growth, and reduced the concentrations of GA1, GA3, GA4, GA9 and IAA. Application of GA4/7 to defoliated shoots promoted longitudinal growth and phloem production, without affecting xylem production or IAA concentration. Application of GA4/7 and IAA together to decapitated + defoliated shoots increased shoot elongation, xylem and phloem production and IAA concentration, whereas applying either substance alone had a smaller effect or none at all. We conclude that, for elongating current-year shoots of Pinus sylvestris, (1) both the shoot apex and the developing needle fascicles are major sources of the IAA present in the stem, whereas stem GAs originate primarily in the needle fascicles, (2) GAs and IAA are required for both shoot elongation and cambial growth, and (3) GAs act directly in the control of shoot growth, rather than indirectly through affecting the IAA concentration.

Keywords: decapitation; defoliation; phloem; Scots pine; shoot elongation; vascular cambium; xylem

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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