The role of abscisic acid in the regulation of barley grain germination
1997
Wang, M. (Center for Phytotechnology RUL/TNO, Leiden (Netherlands). Department of Plant Molecular Biotechnology)
It was previously proposed that dormancy of barley grains is determined by at least three factors, (i) synthesis of the plant hormone abscisic acid (ABA), (ii) breakdown and/or removal of ABA, and (iii) sensitivity to ABA. In this paper some recent data on these three aspects are reviewed and additional evidence is provided to support this hypothesis. In different barley varieties isolated embryos showed an increased germination index as compared with intact grains. During germination the endogenous ABA in embryos of both intact dormant grains and isolated embryos from dormant grains was analyzed. A very high ABA level in the intact dormant grains was correlated with no germination of the grains. When isolated embryos were placed on filter paper or in water, the germination rate of embryos placed in water was much higher than the one of those on filter paper, which was negatively correlated with the ABA levels in the embryos. The inhibitory effect of filter paper vs. water on the germination rate of embryos might be due to a slower diffusion of endogenous ABA out of the embryos on paper. Removal of the husk caused also an enhancement of germination rate. Our results demonstrate that diffusion of endogenous ABA, in combination with our previously observed de novo ABA synthesis and ABA sensitivity, plays an important role in the control of germination
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