Physical Dormancy Release in Medicago truncatula Seeds Is Related to Environmental Variations

Abstract

Seed dormancy and timing of its release is an important developmental transition determining the survival of individuals, populations, and species in variable environments. Medicago truncatula was used as a model to study physical seed dormancy at the ecological and genetics level. The effect of alternating temperatures, as one of the causes releasing physical seed dormancy, was tested in 178 M. truncatula accessions over three years. Several coefficients of dormancy release were related to environmental variables. Dormancy varied greatly (4–100%) across accessions as well as year of experiment. We observed overall higher physical dormancy release under more alternating temperatures (35/15 °C) in comparison with less alternating ones (25/15 °C). Accessions from more arid climates released dormancy under higher experimental temperature alternations more than accessions originating from less arid environments. The plasticity of physical dormancy can probably distribute the germination through the year and act as a bet-hedging strategy in arid environments. On the other hand, a slight increase in physical dormancy was observed in accessions from environments with higher among-season temperature variation. Genome-wide association analysis identified 136 candidate genes related to secondary metabolite synthesis, hormone regulation, and modification of the cell wall. The activity of these genes might mediate seed coat permeability and, ultimately, imbibition and germination.

Seed Dormancy: Molecular Control of Its Induction and Alleviation

“…Temperature and soil moisture oscillations are the major players under natural conditions. Renzi et al [ 33 ] present a study on temperature-related physical dormancy release in seeds of Medicago truncatula. These seeds exhibit both physical and physiological dormancy, the latter being non-deep.…”

Release of Medicago truncatula Gaertn. and Pisum sativum subsp. elatius (M. Bieb.) Asch. et Graebn. Seed Dormancy Tested in Soil Conditions

“…Corresponding to the study by Renzi et al [33], a set of 112 M. truncatula accessions originated from INRA Montpellier (http://www1.montpellier.inra.fr) and from the University of Minnesota, USA (http://www.medicagohapmap.org). Forty-six wild pea (Pisum sativum subsp.…”

“…To obtain sufficient seed stock for the experiments and to minimize environmentally induced maternal effects, obtained seeds were planted and cultivated in glasshouse conditions at the Department of Botany, Palacký University, Olomouc, Czechia from September to May (2017, 2018, and 2019) in either 3 litre (barrel medic) or 5 litre (wild pea) pots with sand peat substrate (1:9) mixture (Florcom Profi, BB Com Ltd., Letovice, Czechia), watered daily and fertilized weekly (Kristalon Plod a Květ, Agro Ltd.,Říkov, Czechia). Supplementary light (Sylvania Grolux 600 W, Hortilux Schreder, Holland) was provided to extend the photoperiod to 14 h. The mature pods were collected, packed in paper bags, dried at room temperature (22-24 • C), 30% air humidity and seeds were manually cleaned [30,31,33]. After that, the randomly selected seeds of each accession were packed into permeable nylon bags within 2 to 3 weeks from the harvest and prepared for soil burial experiments.…”

“…elatius [30] and M. truncatula [33] seeds to temperature alternations, tested in water-saturated conditions in the laboratory. Barrel medic seed dormancy release plasticity correlated with increased aridity of the environment of origin, suggesting that plastic responses provide seeds with a bet-hedging capacity [33]. In wild pea, dormant genotypes are found in the environment with smaller temperature variation, seasonality and milder winter.…”

Seed Dormancy Breaking and Germination in Bituminaria basaltica and B. bituminosa (Fabaceae)

“…For this reason, seed dormancy and germination patterns in legume species have been long since investigated, mainly in wild annual taxa (e.g., Lotus , Trifolium , Medicago, and Scorpiurus ) [ 9 , 10 , 11 , 12 ]. Annual legumes have an elevated capacity of self-reseeding, but also low levels of germinability [ 13 ], a trait that was found to be linked to a strong PY mechanism, preventing seeds from achieving rapid germination, optimal emergence and uniform seedling establishment [ 6 , 8 , 14 ]. From an anatomical perspective, PY is due to the oxygen- and water-impermeability of the seed coat, which has phenolics- and suberin-impregnated layers of palisade cells (outer macrosclereids) [ 6 , 7 , 15 ].…”