AOBPreview published online on November 4, 2009
Annals of Botany, doi:10.1093/aob/mcp268
The role of the persistent fruit wall in seed water regulation in Raphanus raphanistrum (Brassicaceae)
1 Department of Resource Management and Geography, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Victoria 3121, Australia
2 Department of Agriculture and Food Systems, The University of Melbourne, Dookie Campus, Dookie College, Victoria 3647, Australia
3 Faculty of Agriculture, Shahrekord University, PO Box 115, Shahrekord, Iran
* For correspondence, E-mail rcousens{at}unimelb.edu.au
Received: 22 July 2009 Returned for revision: 7 September 2009 Accepted: 21 September 2009
Background and Aims: Dry fruits remain around the seeds at dispersal in a number of species, especially the Brassicaceae. Explanations for this vary, but usually involve mechanisms of innate dormancy. We speculate that, instead, a persistent fruit may give additional protection through control of dehydration, to species growing in arid or Mediterranean environments where water is sporadic.
Methods: X-rays and weight measurements were used to determine the extent to which Raphanus raphanistrum seeds within mature fruits imbibe water, and germination tests determined the roles of the fruit and seed coat in seed dormancy. Rates of water uptake and desiccation, and seedling emergence were compared with and without the fruit. Finally, germinability of seeds extracted from fruits was determined after various periods of moist conditions followed by a range of dry conditions.
Key Results: Most seeds rapidly take up water within the fruit, but they do not fully imbibe when compared with naked seeds. The seed coat is more important than the dry fruit wall in maintaining seed dormancy. The presence of a dry fruit slows emergence from the soil by up to 6–8 weeks. The fruit slows the rate of desiccation of the seed to a limited extent. The presence of the fruit for a few days during imbibition somehow primes more seeds to germinate than if the fruit is absent; longer moist periods within the pod appear to induce dormancy.
Conclusions: The fruit certainly modifies the seed environment as external conditions change between wet and dry, but not to a great extent. The major role seems to be: (a) the physical restriction of imbibition and germination; and (b) the release and then re-imposition of dormancy within the seed. The ecological significance of the results requires more research under field conditions.
Key words: Wild radish, Raphanus raphanistrum, imbibition, desiccation, dry fruit wall, germination, dormancy, X-ray
Present address: Australian Pesticides and Veterinary Medicines Authority, PO Box 6182, Kingston, ACT 2604, Australia