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 GA(4/7) or IAA, or both. Shoot length and the radial widths of xylem and phloem were measured, and the concentrations of GA(1), GA(3), GA(4), GA(9) and IAA in the stem were determined by combined gas chromatography-mass spectrometry with deuterated GAs and [(13)C(6)]-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 GA(1), GA(3), GA(4), GA(9) and IAA. Application of GA(4/7) to defoliated shoots promoted longitudinal growth and phloem production, without affecting xylem production or IAA concentration. Application of GA(4/7) 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.

Gibberellin A4/7 (GA4/7) was applied twice weekly to 2‐year‐old Pinus sylvestris (L.) seedlings in each of two years, starting close to budbreak and ending after shoot elongation, but before cambial activity ceased. In 1988, the GA4/7 was injected into the 1987 terminal shoot (0, 0.2 or 2 mg seedling−1 application−1), while in 1990 it was applied as a soil drench (0, 10 or 50 mg seedling−1 application−1). In the 1988 experiment, GA4/7 treatment promoted diameter growth, and tended to increase both longitudinal growth and the indole‐3‐acetic acid (IAA) level in the 1988 terminal. In the 1990 experiment, GA4/7 treatment increased tracheid production, longitudinal growth, and the cambial region IAA concentration in the 1990 terminal, but did not affect its pith diameter, needle number, needle dry weight, or needle IAA level. Tracheid production in the previous‐year's terminal was also promoted in both experiments. The 50 mg GA4/7 soil drench markedly elevated the concentrations of GA4, GA7 and GA9 in the needles and cambial region of the 1990 terminal, while the 10 mg treatment raised the GA4 level in the cambial region, providing evidence that GA4 and GA7 applied to the roots reaches the shoot system. The results support the hypothesis that the exogenous GA4/7‐induced stimulation of tracheid production in the terminal shoot of intact plants is mediated through an increase in the IAA level in the cambial region. However, per se activity of GA4, GA7 or their metabolites cannot be ruled out.

No abstract

The application of gibberellin A4/7 (GA4/7) to the stem of previous‐year (1‐year‐old) terminal shoots of Scots pine (Pinus sylvestris) seedlings has been observed to stimulate cambial growth locally, as well as at a distance in the distal current‐year terminal shoot, but the distribution and metabolic fate of the applied GA4/7, as well as the pathway of endogenous GA biosynthesis in this species, has not been investigated. As a first step, we analysed for endogenous GAs and monitored the transport and metabolism of labelled GAs 4, 9 and 20. Endogenous GAs from the elongating current‐year terminal shoot of 2‐year‐old seedlings were purified by column chromatography and high‐performance liquid chromatography and analysed by combined gas chromatography‐mass spectrometry (GC‐MS). GAs 1, 3, 4, 9, 12 and 20 were identified in the stem, and GAs 1, 3 and 4 in the needles, by full‐scan mass spectrometry (GAs 1, 3, 4, 9 and 12) or selected‐ion monitoring (GA20) and Kovats retention index. Tritiated and deuterated GA4, GA9 or GA20 were applied around the circumference at the midpoint of the previous‐year terminal shoot, and metabolites were extracted from the elongating current‐year terminal shoot, the application point, and the 1‐year‐old needles and the cambial region above and below the application point. After purification, detection by liquid scintillation spectrometry and analysis by GC‐MS, it was evident that, for each applied GA, unmetabolised [2H2]GA and [3H]radioactivity were present in every seedling part analysed. Most of the radioactivity was retained at the application point when [3H]GA9 and [3H]GA20 were applied, whereas the largest percentage of radioactivity derived from [3H]GA4 was recovered in the current‐year terminal shoot. It was also found that [2H2]GA9 was converted to [2H2]GA20 and to both [2H2]GA4 and [2H2]GA1, [2H2]GA4 was metabolised to [2H2]GA1, and [2H2]GA20 was converted to [2H2]GA29. The data indicate that for Pinus sylvestris shoots (1) GAs applied laterally to the outside of the vascular system of previous‐year shoots not only are absorbed and translocated extensively throughout the previous‐year and current‐year shoots, but also are readily metabolised, (2) the GA metabolic pathways found are closely related to the endogenous GAs identified, and (3) GA9 metabolism follows two distinctly different routes: in one, GA9 is converted to GA1 through GA4, and in the other it is converted to GA20, which is then metabolised to GA29. The results suggest that the late 13‐hydroxylation pathway is an important route for GA biosynthesis in shoots of Pinus sylvestris, and that the stimulation of cambial growth in Scots pine by exogenous GA4/7 may be due to its conversion to GA1, rather than to it being active per se.

Gibberellin A4/7 (GA4/7) was applied in lanolin or ethanol around the circumference at the midpoint of the previous‐year terminal of dormant Pinus sylvestris seedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cambial growth was measured as the radial widths of xylem and phloem, and the level of indole‐3‐acetic acid (IAA) was determined by combined gas chromatography‐mass spectrometry using [136](IAA) as the internal standard. In intact seedlings, both 1 mg GA4/7 g−1 lanolin and 50 mg GA4/7 I−1 ethanol increased phloem production and the cambial region IAA level in the current‐year terminal, without significantly altering its longitudinal growth. In the previous‐year terminal, 1 mg GA4/7 g−1 lanolin promoted phloem production at the application point and increased the cambial region IAA level above this point, whereas 50 mg GA4/7 I−1 ethanol stimulated the production of both xylem and phloem at the treatment site and elevated the cambial region IAA level beneath it. Laterally applied GA4/7 at 50 mg I−1 ethanol stimulated xylem and phloem production in debudded previous‐year terminals treated at the apical cut surface with 1 mg IAA g−1 lanolin, but not in those treated with plain lanolin. However, the promotion of cambial growth in debudded terminals treated apically with 1 mg IAA g−1 lanolin and laterally with 50 mg GA4/7 I−1 ethanol was not associated with an elevated IAA content in the cambial region. The results indicate that exogenous GA4/7 can promote xylem and phloem production provided an IAA source is present, and that it or a metabolic product acts directly, rather than indirectly by stimulating longitudinal growth and/or raising the cambial region IAA level.