Bruno Fogliani1,2, Gildas Gâteblé3, Matthieu Villegente2, Isabelle Fabre3, Nicolas Klein1,2, Nicolas Anger3, Carol C Baskin4,5, Charlie P Scutt6. 1. Institut Agronomique néo-Calédonien (IAC), BP 73 Port Laguerre, 98890 Païta, New Caledonia. 2. Laboratoire Insulaire du Vivant et de l'Environnement (LIVE)-EA 4243, University of New Caledonia (UNC), BP R4, 98851 Noumea, New Caledonia. 3. Institut Agronomique néo-Calédonien (IAC), BP 73 Port Laguerre, 98890?Païta, New Caledonia. 4. Department of Biology, University of Kentucky, Lexington, KY 40506, USA. 5. Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546, USA. 6. Reproduction et Développement des Plantes (RDP; UMR5667, CNRS-INRA-Université de Lyon), Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France.
Abstract
Background and Aims: Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda , the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade. Methods: Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms. Key Results: Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth. Conclusions: Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.
Background and Aims: Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda , the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade. Methods: Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms. Key Results: Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth. Conclusions: Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.
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