Poster: Hormones

Abs # 598: Gibberellins and iaa in wood formation of populus tremula x tremuloides

Presenter:	Björklund, Simon , simon.bjorklund@genfys.slu.se
Authors	Björklund, Simon  (A)   Moritz, Thomas  (A)   Sundberg, Björn  (A)
Affiliations:	(A): Umeå Plant Science Centre

Apically applied auxin to decapitated woody shoots is polarly transported and maintains and stimulates cambial growth and wood formation. It is also well known that addition of GA:s to the auxin source results in further stimulation of secondary xylem production, well below the hormone source. The mechanism of this synergistic effect is surprising as GA:s is not considered to be transported by an active process similar to IAA. To shed some light on this phenomenon we measured a time course of the resulting internal concentrations of IAA and GA (by GC-MS) after apical application of IAA and GA₄, alone and in combination, to decapitated shoots of aspen (Populus tremula x tremuloides L.). A basipetal transport of GA in the stem was demonstrated after application of radio labelled GA. More interestingly we found that addition of GA to the auxin source increased the resulting internal concentration of IAA. Experiments using ¹³C₆ IAA showed that this increase resulted from IAA originating in the apical source, rather than from de novo synthesis in the stem. Our result indicates that GA stimulates the uptake/polar transport of IAA in the poplar shoot. To further investigate the mechanisms behind the synergy between IAA and GA we are now studying global gene expression in these stem tissues with defined hormone balances using our poplar microarray