Molecular and Biophysical Dissection of Changes in Seed Dormancy and the Role of Chemical Stimulants
Metabolic rate, viscosity of the cytoplasm, and membrane fluidity play a role in seed dormancy.
An important objective of the MSB project is the safekeeping of living seeds. However, when seeds do not germinate they can either be dead or dormant. Overcoming dormancy and triggering growth can be achieved through the application of chemical stimulants, e.g. nitrate and gibberellic acid, that can affect the internal balance of hormones and the sensitivity of receptors. Results of this for the oilseed Vernonia galamensis have formed part of a PhD thesis and subsequent peer-reviewed publications (Nyamongo et al., 2009). In terms of chemical stimulants, one of the recent, exciting developments in germination ecology has been the identification of the active ingredient in smoke from the combustion of plant material. We tested this germination cue (a butenolide: 3-methyl-2H-furo[2,3-c]pyran-2-one) on 18 weed species from non-fire prone environments, comparing the relative effectiveness KNO3, GA3, smoke water and butenolide. Whilst none of the treatments were effective on all species, butenolide was effective on the widest range of species in terms of enhancing germination percentage, rate and seedling mass (Daws et al., 2007). The wide applicability of butenolide as a germination and seedling growth stimulant was further tested on parasitic weeds (Orobanche, Striga, Cistanche, Conopholis and Lathraea, indicating action similar to synthetic strigol analogues (Daws et al., 2008). Our data demonstrate that butenolide may have wide applicability as a germination and seedling growth stimulant, including the keystone species of European coastal heathlands, Calluna vulgaris (Måren et al., 2010). However, even species from non fire-prone habitats can respond to this stimulant (Light et al., 2009).
Nitrate too has been described as a germination cue in seeds of Sisymbrium officinale and Arabidopsis thaliana. Changes in seed dormancy coincide with changes in the sensitivity or responsiveness to light and nitrate. Nitrate was proposed to act as a cofactor in the binding of phytochrome to its putatively membrane-bound receptor, with a potential role for membrane fluidity in the accessibility of these receptors. Temperature physically changes the fluidity of membranes, and homeoviscous adaptation is the mechanism whereby unsaturated fatty acids aid in maintaining membranes in a fluid state necessary for biological functioning. Desaturases add to the buffering capacity in the maintenance of the membrane fluidity (Nishida and Murata, 1996), altering the fatty acid composition of the membrane. Putatively, this mechanism would function in seeds both to maintain the fluidity of the membrane, and to enable the breaking of dormancy. The objective of this project was to explain dormancy in terms of membrane fluidity and the molecular mechanism behind it, explaining the role of nitrate as a stimulant of germination. The purpose was to generate a better understanding of dormancy, which can be used to understand the behaviour of banked seeds. The project may lead to the development of a diagnostics test to assess dormancy in any accession of the MSB.
Project partners and collaborators
Kenyan Agricultural Research Institute, National Genebank of Kenya
University of KwaZulu-Natal
Key papers published since 2006
Daws, M.I., Davies, J., Pritchard, H.W., Brown, N.A.C., van Staden, J. (2007). Butenolide from plant-derived smoke enhances germination and seedling growth of arable weed species. Plant Growth Regulation 51: 73-82. (IF 1.63, times cited = 22)
Daws, M.I., Pritchard, H.W., van Staden, J. (2008). Butenolide from plant-derived smoke functions as a strigolactone analogue: Evidence from parasitic weed seed germination. South African Journal of Botany 74: 116-120. (IF 1.11, times cited = 8)
Light, M.E., Daws, M.I., van Staden, J. (2009). Minireview: Smoke-derived butenolide: towards understanding its biological effects. South African Journal of Botany 75: 1-7. (IF 1.11, times cited = 18)
Måren, I.E., Janovský, Z., Spindelböck, J.P., Daws, M.I., Kaland, P.E., Vandvik, V. (2010). Prescribed burning of northern heathlands: Calluna vulgaris germination cues and seed-bank dynamics. Plant Ecology 207: 245-256. (IF 1.88)
Nyamongo, D.O., Nyabundi, J., Daws, M.I. (2009). Germination and dormancy breaking requirements for Vernonia galamensis (Asteraceae). Seed Science and Technology 37: 1-9.(IF 0.61, times cited = 2)
Conferences and workshops
Workshop on Molecular Aspects of Seed Germination and Dormancy, Salamanca, 2007