The morphophysiological dormancy inAmborella trichopodaseeds is a pleisiomorphic trait in angiosperms

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.

Two disjunct Pleistocene populations and anisotropic postglacial expansion shaped the current genetic structure of the relict plant Amborella trichopoda

“…The age of first reproduction was a proxy of the generation time, probably underestimating actual generation time [ 45 ] which could be twice as large, displacing the lower bound of the expansion onset to the last stage of the glacial period. Likewise, seed dormancy [ 46 ] might affect the estimations. For Amborella , no fossil data and no reliable estimates of neutral substitution rate are currently available.…”

A Combination of Histological, Physiological, and Proteomic Approaches Shed Light on Seed Desiccation Tolerance of the Basal Angiosperm Amborella trichopoda

“…The fleshy part of the fruits was removed before sensu stricto seed isolation. For embryo isolation, surface-sterilized seeds were longitudinally cut in two with a razor blade [ 22 ]. A drop of sterile Milli-Q water was placed on the endospermic face on each half.…”

“…Indeed, the ratio (E:S) between the length of the embryo (E) and that of the seed (S) increases during evolution [ 17 ]. Seeds with a rudimentary embryo have morphological dormancy, which is considered the most primitive dormancy [ 20 , 21 , 22 ]. Consequently, such seeds can only germinate after continuation of the embryo development during seed imbibition after dispersal from the mother plant.…”

Prolonged embryogenesis in Austrobaileya scandens (Austrobaileyaceae): its ecological and evolutionary significance

“…It can range from c . 2 to 3 months in Schisandra (Grushvitzky, ; Nikolaeva et al ., ; Zhou & Wang, ; Chien et al ., ) to 3 months in Amborella (Fourcade et al ., ; Fogliani et al ., ), and 4 months in Illicium (Thien et al ., ; Olsen & Rutter, ). Seeds of Nymphaeales show a much more variable time to germination.…”