AOBPreview published online on May 7, 2008
Annals of Botany, doi:10.1093/aob/mcn069
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Carry-over of Differential Salt Tolerance in Plants Grown from Dimorphic Seeds of Suaeda splendens
1 Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080–Sevilla, Spain
2 Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
* For correspondence. E-mail susana{at}us.es
Received: 28 November 2007 Returned for revision: 20 March 2008 Accepted: 10 April 2008
Background and Aims: Halophytic species often show seed dimorphism, where seed morphs produced by a single individual may differ in germination characteristics. Particular morphs are adapted to different windows of opportunity for germination in the seasonally fluctuating and heterogeneous salt-marsh environment. The possibility that plants derived from the two morphs may also differ physiologically has not been investigated previously.
Methods: Experiments were designed to investigate the germination characteristics of black and brown seed morphs of Suaeda splendens, an annual, C4 shrub of non-tidal, saline steppes. The resulting seedlings were transferred to hydroponic culture to investigate their growth and photosynthetic (PSII photochemistry and gas exchange) responses to salinity.
Key Results: Black seeds germinated at low salinity but were particularly sensitive to increasing salt concentrations, and strongly inhibited by light. Brown seeds were unaffected by light, able to germinate at higher salinities and generally germinated more rapidly. Ungerminated black seeds maintained viability for longer than brown ones, particularly at high salinity. Seedlings derived from both seed morphs grew well at high salinity (400 mol m–3 NaCl). However, seedlings derived from brown seeds performed poorly at low salinity, as reflected in relative growth rate, numbers of branches produced, Fv/Fm and net rate of CO2 assimilation.
Conclusions: The seeds most likely to germinate at high salinity in the Mediterranean summer (brown ones) retain a requirement for higher salinity as seedlings that might be of adaptive value. On the other hand, black seeds, which are likely to delay germination until lower salinity prevails, produce seedlings that are less sensitive to salinity. It is not clear why performance at low salinity, later in the life cycle, might have been sacrificed by the brown seeds, to achieve higher fitness at the germination stage under high salinity. Analyses of adaptive syndromes associated with seed dimorphism may need to take account of differences over the entire life cycle, rather than just at the germination stage.
Key words: Chlorophyll fluorescence, germination, growth rate, halophyte, photosynthesis, photosystem II, salt tolerance, seed dimorphism, seed viability, Suaeda splendens