Plant and Cell Physiology, 1995, Vol. 36, No. 7 1205-1211
© 1995
Effects of Gibberellins on Seed Germination of Phytochrome-Deficient Mutants of Arabidopsis thaliana
1 Laboratory for Plant Hormone Function, Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN) Wako-shi, Saitama, 351-01 Japan
2 Laboratory for Photoperception and Signal Transduction, Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN) Wako-shi, Saitama, 351-01 Japan
Experiments were carried out to explore the involvement of gibberellins (GAs) in the light-induced germination of Arabidopsis thaliana (L.) Heynh, using wild type (WT) and phytochrome-deficient mutants (phyA, phyB and phyAphyB deficient in phytochrome A, B and A plus B, respectively). Seed germination of WT and phytochrome-deficient mutants was inhibited by uniconazole (an inhibitor of an early step in biosynthesis of GA, the oxidation of ent-kaurene) and prohexadione (an inhibitor of late steps, namely, 2rß- and 3rß-hydroxylation). This inhibition was overcome by simultaneous application of 10-5 M GA4. The relative activity of GAs for promoting germination of uniconazole-treated seeds was GA4>GA1=GA9>GA20. The wild type and the phyA and phyB mutants had an increased response to a red light pulse in the presence of GA1, GA4, GA9, GA20 and GA24 but there were no significant differences in activity of each GA between the mutants. Therefore, neither phytochrome A nor hytochrome B appears to regulate GA biosynthesis from GA12 to GA4 during seed germination, since the conversion of GA12 to GA9 is regulated by one enzyme (GA 20-oxidase). However, GA responsiveness appears to be regulated by phytochromes other than phytochromes A and B, since the phyAphyB double mutant retains the photoreversible increased response to GAs after a red light pulse.
(Received February 13, 1995; Accepted July 11, 1995)
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