Abstract
Seed dormancy status regulates the response of seeds to environmental cues that can trigger germination. Anigozanthos flavidus (Haemodoraceae) produces seeds with morphophysiological dormancy (MPD) that are known to germinate in response to smoke, but embryo growth dynamics and germination traits in response to temperatures and after-ripening have not been well characterized. Seeds of A. flavidus, after-ripened for 28 months at 15 °C/15 % relative humidity, were incubated on water agar, water agar containing 1 μM karrikinolide (KAR1) or 50 μM glyceronitrile at 5, 10, 15, 20, 25, 20/10 and 25/15 °C for 28 days. After incubation at 5, 10 and 25 °C for 28 days, seeds were transferred to 15 °C for another 28 days. Embryo growth dynamics were tested at 5, 10, 15 and 25 °C. Results demonstrated that fresh seeds of A. flavidus had MPD and the physiological dormancy (PD) component could be broken by either glyceronitrile or dry after-ripening. After-ripened seeds germinated to ≥80 % at 15–20 °C while no additional benefit of germination was observed in the presence of the KAR1 or glyceronitrile. Embryo length significantly increased at 10 °C, and only slightly increased at 5 °C, while growth did not occur at 25 °C. When un-germinated seeds were moved from 5–10 °C to 15 °C for a further 28 days, germination increased from 0 to >80 % in significantly less time indicating that cold stratification may play a key role in the germination process during winter and early spring in A. flavidus. The lower germination (<50 %) of seeds moved from 25 to 15 °C was produced by the induction of secondary dormancy. Induction of secondary dormancy in seeds exposed to warm stratification, a first report for Anigozanthos species, suggests that cycling of PD may be an important mechanism of controlling germination timing in the field.
Highlights
Seed germination is the initial and most crucial stage in the life cycle of most flowering plants
We examined the germination traits of A. flavidus seeds aiming to determine whether the (i) incubation temperatures and warm and/or cold stratification will influence the seed germination potential by affecting the elongation of embryos; (ii) seed sensitivity to the smoke-derived products glyceronitrile and/or KAR1 is dictated by dormancy status
Warm stratification breaks dormancy in many species with morphophysiological dormancy (MPD) (Baskin and Baskin 2004), we found the opposite in seeds of A. flavidus, whereby seeds exposed to extended periods of warm (25 °C), moist conditions lost the ability to germinate and appeared to enter into secondary dormancy; a first report for the Anigozanthos genus
Summary
Seed germination is the initial and most crucial stage in the life cycle of most flowering plants. Seeds of the majority of plant species are dormant at maturity (Baskin and Baskin 2014). Dormancy is an adaptive trait that helps regulate the timing of seed germination ensuring that the chances of seedling survival are greatest. Seeds respond to a host of environmental factors. Ma et al – Seed germination of Anigozanthos flavidus to control germination timing including fluctuation in moisture availability, temperature, light, and cues provided by naturally occurring chemicals such as nitrates, and compounds present in smoke (Baker et al 2005a; Downes et al 2014; Abu et al 2016; Villa-Reyes and Barrera 2016; Cox et al 2017). Seeds with non-deep PD, the least stringent form of PD control, commonly cycle between dormant and non-dormant states in the soil seed bank in response to seasonal changes in environmental conditions (Baskin and Baskin 2004; Chauhan et al 2006; Long et al 2011)
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