Abstract
Structural requirements for florigenic activity among gibberellins (GAs) and GA derivatives, including several new ones, applied once to leaves of Lolium temulentum, were examined. The compounds were applied to plants kept either in non-inductive short days (SD) or exposed to one inductive long day (LD). Inflorescence initiation and stem-elongation responses were assessed three weeks later. Among the GAs used, the range in effective dose for inflorescence initiation was more than 1000-fold, but substantially less for stem elongation. Some GAs promoted both stem elongation and inflorescence initiation, some promoted one without the other, and some affected neither. The structural features enhancing florigenic activity were often different from those enhancing stem elongation. Except in the case of 2,2-dimethyl GA4, a double bond in the A ring at either C-1,2 or C-2,3 was essential for high florigenic activity, though not for stem elongation. A free carboxy group was needed for both. Inflorescence initiation in Lolium was enhanced by hydroxylation at C-12, −13 and −15, whereas hydroxylation at C-3 reduced the effect on inflorescence initiation but increased that on stem elongation. A 12β-hydroxyl was more effective than the α epimer for inflorescence initiation whereas the reverse was true for stem elongation. Although such differential effectiveness of GAs for inflorescence initiation and for stem elongation could reflect differences in uptake, transport or metabolism, we suggest that it is indicative of specific structural requirements for inflorescence initiation.
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Abbreviations
- GA:
-
gibberellin
- LD:
-
long day(s)
- SD:
-
short day(s)
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We are grateful to Professor N. Murofushi for supplying the sample of GA32 and to Dr. C.L. Willis and Dr. A.M. Fowles for the samples of 2α-methyl GA4 and 1β-methyl GA4; to Bruce Twitchin, Canberra, and M. Noma, Calgary, for the synthesis of various GAs; to Cheryl Blundell and Inara Licis for expert technical assistance; and to Drs. P. Chandler, J.V. Jacobsen and Professor J. MacMillan for their comments on the manuscript.
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Evans, L.T., King, R.W., Chu, A. et al. Gibberellin structure and florigenic activity in Lolium temulentum, a long-day plant. Planta 182, 97–106 (1990). https://doi.org/10.1007/BF00239990
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DOI: https://doi.org/10.1007/BF00239990