Investigating seed dormancy in cotton (Gossypium hirsutum L.): understanding the physiological changes in embryo during after-ripening and germination.

The dormancy of upland cottonseed can be broken during dry after-ripening, but the mechanism of its dormancy release remains unclear. Freshly harvested cottonseeds were subjected to after-ripening for 180 days. Cottonseeds at different days of after-ripening (DAR) were sampled for dynamic physiological determination and germination test. The intact seeds and isolated embryos were germinated contrastively for assessing the effects of seed coat on embryo germination. Contents of H2 O2 and phytohormones and the activities of antioxidases and glucose-6-phosphate dehydrogenase were measured during after-ripening and germination. The germination of intact seeds increased from 7% upon harvest to 96% at 30 DAR, while the embryo germination improved from an initial rate of 82% to 100% after 14 DAR. Based on T50 (the time when 50% of the seeds germinate) and germination index, the intact seed and isolated embryo needed 30 and 21 DAR to acquire relatively stable germination, respectively. The content of H2 O2 increased during after-ripening and continued to increase within the first few hours of imbibition, along with a decrease in ABA content. A noticeable increase was observed in GAs content during germination when ABA content decreased to a lower level. Coat removal treatment accelerated the embryo absorption of water, which further improved the accumulation of H2 O2 and altered the changes of peroxidase during germination. For cottonseed, the alleviation of coat-imposed dormancy needed 30 days of after-ripening, accompanied by a rapid dormancy release (within 21 DAR) in naked embryos. H2 O2 acted as a core link between the response to environmental changes and induction of other physiological changes for breaking seed dormancy. This article is protected by copyright. All rights reserved.