PLANT PHYSIOLOGY , Vol 111, Issue 4 1127-1133, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Rapid Germination of a Barley Mutant Is Correlated with a Rapid Turnover of Abscisic Acid Outside the Embryo
K. Visser, APA. Vissers, M. I. Cagirgan, J. W. Kijne and M. Wang
Center for Phytotechnology, Leiden University/Netherlands Organization for Applied Research, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands (K.V., A.P.A.V., J.W.K., M.W.)
In our study of the role of abscisic acid (ABA) in controlling the
germination of barley grains, we tested a barley mutant line with a
gigantum appearance (Hordeum distichum cv Quantum) for an ABA-insensitive
phenotype by assaying germination in the presence of 10-4 M ABA. Dissected
embryos of the mutant germinated at least 10 h earlier than did those of
the wild type. The half-maximal concentrations of ABA inhibitory for
germination were determined to be 5 x 10-4 M for the mutant and 10-6 M for
the wild type. Expression of an ABA-induced Rab gene was studied to
determine ABA responsiveness. The ABA concentration required for a
half-maximal induction of Rab gene expression was 4 x 10-6 M in isolated
embryos of both the mutant and wild type. This result suggests that ABA
signal transduction pathways were not affected in the mutant. When isolated
embryos were allowed to imbibe in water, ABA was released from the mutant
and wild-type embryos at the same rate. However, the free ABA level in the
incubation medium of the mutant showed a much faster decrease than that of
the wild type, as demonstrated by two independent ABA assay methods
(high-performance liquid chromatography and enzyme-linked immunosorbent
assay). Our results suggest that turnover of ABA outside the embryo is a
determining factor in the germination of barley seeds.
