Roles of gibberellins and abscisic acid in dormancy and germination of red bayberry (Myrica rubra) seeds
Shun-Ying Chen (1, 2), Shing-Rong Kuo (2) and Ching-Te Chien (3, 4)
1. Division of Forest Biology, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei 10066, Taiwan / 2. School of Forestry and Resource Conservation, National Taiwan University, 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan / 3. Division of Silviculture, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei 10066, Taiwan / 4. Corresponding author () / Received December 22, 2007; accepted April 7, 2008; published online July 1, 2008
Summary
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 (GA3) to intact fresh seeds was effective in breaking dormancy, with > 70% of seeds germinating when treated with 5.2 mM GA3 and incubated at a day/night temperature of 30/20 °C for 20 weeks. Removing the hard endocarp or endocarp plus seed coat
of fresh seeds promoted germination, and addition of GA3 to the embryo accelerated germination. The gibberellins GA1 and GA4 were more effective than GA3 in promoting germination of seeds with the endocarp removed. Endogenous contents of GA1, GA3, GA4, GA7 and GA20 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 GA3. The content of GA3 decreased in the endocarp during incubation, whereas GA1 contents increased in the endocarp and seed coat. A high GA1 content was detected in the endocarps and embryos of newly germinated seeds. We speculate that GA3 was converted to GA1 during incubation and that GA1 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 GA1, GA3, GA7 and GA20, but elevated contents of GA4, 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 GA4 or GA1, or both, are involved in germination.
