EFFECT OF LATERALLY APPLIED GIBBERELLIN A(4 7) ON CAMBIAL GROWTH AND THE LEVEL OF INDOLE-3-ACETIC-ACID IN PINUS-SYLVESTRIS SHOOTS/

Gibberellin A(4/7) (GA(4/7)) was applied in lanolin or ethanol around the circumference at the midpoint of the previous-year terminal of dor mant Pinus sylvestris seedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cam bial growth was measured as the radial widths of xylem and phloem, and the level of indole-3-acetic acid (IAA) was determined by combined ga s chromatography-mass spectrometry using [C-13(6)](IAA) as the interna l standard. In intact seedlings, both 1 mg GA(4/7) g(-1) lanolin and 5 0 mg GA(4/7) I-1 ethanol increased phloem production and the cambial r egion IAA level in the current-year terminal, without significantly al tering its longitudinal growth. In the previous-year terminal, 1 mg GA (4/7) g(-1) lanolin promoted phloem production at the application poin t and increased the cambial region IAA level above this point, whereas 50 mg GA(4/7) l(-1) ethanol stimulated the production of both xylem a nd phloem at the treatment site and elevated the cambial region IAA le vel beneath it. Laterally applied GA(4/7) at 50 mg l(-1) ethanol stimu lated 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 cambia l growth in debudded terminals treated apically with 1 mg IAA g(-1) la nolin and laterally with 50 mg GA(4/7) l(-1) ethanol was not associate d with an elevated IAA content in the cambial region. The results indi cate that exogenous GA(4/7) can promote xylem and phloem production pr ovided an IAA source is present, and that it or a metabolic product ac ts directly, rather than indirectly by stimulating longitudinal growth and/or raising the cambial region IAA level.