Roles of gibberellins and abscisic acid in dormancy and germination of red bayberry (Myrica rubra) seeds

Division of Forest Biology, Taiwan Forestry Research Institute, Taipei 10066, Taiwan.
Tree Physiology (Impact Factor: 3.66). 09/2008; 28(9):1431-9. DOI: 10.1093/treephys/28.9.1431
Source: PubMed


Intact seeds from freshly harvested fruits of Myrica rubra (Sieb et Zucc.) were dormant and required 8 weeks of warm stratification followed by 12 weeks of cold stratification for germination. Exogenous application of gibberellic acid (GA(3)) to intact fresh seeds was effective in breaking dormancy, with > 70% of seeds germinating when treated with 5.2 mM GA(3) and incubated at a day/night temperature of 30/20 degrees C for 20 weeks. Removing the hard endocarp or endocarp plus seed coat of fresh seeds promoted germination, and addition of GA(3) to the embryo accelerated germination. The gibberellins GA(1) and GA(4) were more effective than GA(3) in promoting germination of seeds with the endocarp removed. Endogenous contents of GA(1), GA(3), GA(4), GA(7) and GA(20) were quantified by gas chromatography-mass spectrometry-selected ion monitoring in the endocarps, seed coats and embryos of fresh seeds treated with 5.2 mM GA(3). The content of GA(3) decreased in the endocarp during incubation, whereas GA(1) contents increased in the endocarp and seed coat. A high GA(1) content was detected in the endocarps and embryos of newly germinated seeds. We speculate that GA(3) was converted to GA(1) during incubation and that GA(1) is involved in seed germination. Endogenous abscisic acid (ABA) contents were measured in fresh seeds and in warm and cold stratified seeds. The ABA content in fresh seeds was distributed in the order endocarp > seed coat > embryo, with the content in the endocarp being about 132-fold higher than in the seed coat and embryo. Total ABA content of seeds subjected to warm or cold stratification, or both, was 8.7- to 14.0-fold lower than that of fresh seeds. Low contents of endogenous GA(1), GA(3), GA(7) and GA(20), but elevated contents of GA(4), were found in the seed coats and endocarps of warm plus cold stratified seeds and in the seed coats and embryos of newly germinated seeds. These observations, coupled with the finding that GA stimulated germination of dormant Myrica seeds, provide evidence that endogenous ABA inhibited release of dormancy and that endogenous gibberellins, especially GA(4) or GA(1), or both, are involved in germination.

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    • "Among soaking periods, GE (%) differed significantly between 8, 16 and 24 h (Table 3). It might also be due to initiation of embryo growth, as a result of which more growth hormone was synthesized by the growing embryo, which induced hydrolase synthesis (Chen et al. 2008). Between two temperatures , GE (%) was higher at 15 °C in comparison to 25 °C, but it was non-significant on GE. "

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    • "Fresh seeds and those cold-stratified for 4, 8 and 12 weeks as well as radicle-emerged seeds were used in the analyses; there were three replications of each sample (about 200 mg dry sample). The methods for extracting and quantifying ABA, GA 1 , GA 3 , GA 4 , GA 7 and GA 20 in the tissues have been described by Nakayama et al. (2001) and Chen et al. (2008). "
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    • "The enhancing effect of gibberellins in light conditions on germination at constant temperatures reflects the fact that sensitivity to gibberellins is controlled by temperature (Toh et al., 2008). The fact that gibberellins induced high germination (>90%) at constant temperatures of 20 • C or 25 • C suggests that gibberellins increased the growth embryo potential, reducing the constraint of the seed covers (Chen et al., 2008). Additionally, temperature fluctuations were replaced by gibberellins confirming that temperature is the main factor that breaks dormancy in nature (Baskin and Baskin, 2014). "
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