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Plant Physiol, October 2001, Vol. 127, pp. 624-632
Long-Day Induction of Flowering in Lolium temulentum
Involves Sequential Increases in Specific Gibberellins at the Shoot
Apex1
Rod W.
King,*
Thomas
Moritz,
Lloyd T.
Evans,
Olavi
Junttila, and
Anthony J.
Herlt
Commonwealth Scientific and Industrial Research Organization
Plant Industry, G.P.O. Box 1600, Canberra, Australian Capitol Territory
2601, Australia (R.W.K., L.T.E.); Umea Plant Science Centre, Swedish
University of Agricultural Sciences, S-901 Umea, Sweden (T.M.);
Department of Plant Physiology and Microbiology, University of
Tromso, Tromso, Norway (O.J.); and Research School of Chemistry,
Australian National University, Canberra, Australian Capitol Territory
0020, Australia (A.J.H.)
One challenge for plant biology has been to identify floral stimuli
at the shoot apex. Using sensitive and specific gas chromatography-mass spectrometry techniques, we have followed changes in gibberellins (GAs)
at the shoot apex during long day (LD)-regulated induction of flowering
in the grass Lolium temulentum. Two separate roles of
GAs in flowering are indicated. First, within 8 h of an inductive LD, i.e. at the time of floral evocation, the GA5 content
of the shoot apex doubled to about 120 ng g 1 dry weight.
The concentration of applied GA5 required for floral induction of excised apices (R.W. King, C. Blundell, L.T. Evans [1993] Aust J Plant Physiol 20: 337-348) was similar to that in the shoot apex. Leaf-applied [2H4]
GA5 was transported intact from the leaf to the shoot apex, flowering being proportional to the amount of GA5 imported.
Thus, GA5 could be part of the LD stimulus for floral
evocation of L. temulentum or, alternatively, its
increase at the shoot apex could follow import of a primary floral
stimulus. Later, during inflorescence differentiation and especially
after exposure to additional LD, a second GA action was apparent. The
content of GA1 and GA4 in the apex increased
greatly, whereas GA5 decreased by up to 75%. GA4 applied during inflorescence differentiation strongly
promoted flowering and stem elongation, whereas it was ineffective for earlier floral evocation although it caused stem growth at all times of
application. Thus, we conclude that GA1 and GA4
are secondary, late-acting LD stimuli for inflorescence differentiation
in L. temulentum.
1
This work was supported by the Department of
Tourism and Industry, Australia (to R.W.K.) and by the Human Frontiers
Science Program (grant no. RG0303/1997-M to T.M.).
*
Corresponding author; e-mail r.king{at}pi.csiro.au; fax 61262465000.
© 2001 American Society of Plant Physiologists
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