Annals of Botany

Salt stimulates Suaeda seeds

The requirement for cold to break seed dormancy is common in species that inhabit cool temperate regions. However, low temperature is not the only environmental feature encountered by seeds. This is clearly exemplified by the salt-marsh plant Suaeda maritima, as discussed by Wetson et al. (Universities of Sussex, UK and Catania, Italy, pp. 1319–1327). In a typical winter dormancy period of 20 weeks the seeds certainly do experience low temperatures but they are also exposed to varying levels of salinity and hypoxia. The question here is, how do these other factors affect dormancy? From a very extensive study we can focus on only a selection of the results. Seeds pre-treated dry at 4 °C and then set to germinate on filter paper soaked in 50 % artificial sea-water (ASW) exhibited a minimum temperature for germination of 15 °C. All subsequent germination experiments were carried out under a day/night temperature regime of 15/5 °C, equivalent to conditions during the germination season in the plant’s local habitat. Pre-treatment conditions were then compared. The previously used conditions, dry/4 °C, led to approx. 45 % germination; seeds pre-treated dry at 17 °C did not germinate. Low temperature is thus important. However, dry exposure to -18 °C for 20 weeks killed the seeds, although a 2-week exposure to this temperature late in the dormancy period led to some seeds germinating. Salinity also had a major effect: pre-treatment at 4 °C in ASW caused nearly 100 % germination whereas hydration with distilled H2O at 4 °C did not break dormancy. Further, seeds stored dry for 12 weeks at 4 or 17 °C and then transferred to ASW at the same temperatures for 2 weeks exhibited 40–50 % germination; thus a relatively short-term exposure to damp saline conditions is enough for at a least partial dormancy breakage even at 17 °C. The salt effect was mediated osmotically rather than via specific ions; polyethylene glycol at equivalent osmotic potentials having the same effects as ASW.