Biophysical boundaries for dormancy release in sunflower achenes

Reactions leading to dormancy release (DR) in “dry”, orthodox seeds are still poorly understood, as well as their dependence on moisture content and temperature. Sunflower achenes were used to explore the effects of MC combined with a wide range of storage temperatures (ST°) on DR dynamics, tested at 10 and 25°C. Embryo sensitivity to abscisic acid, oxygen uptake and ageing indicators were followed and complemented with predicted viability loss dynamics. Water status was addressed with sorption isotherms and the glass transition temperature (Tg). Small variations in MC and ST° had profound effects on achene dormancy and embryo responsiveness to ABA. Using a ‘temperature by humidity’ coordinate system we mapped three regions allowing DR within the glassy, rubbery and fluid states. Full DR (allowing germination at 10 and 25°C) occurred only in the rubbery state (above Tg), and optimal ST° for full DR dropped from +30 to -18°C with MC increasing from 0.045 to 0.10 gH2O.gDW-1. Differently, under both glassy and fluid states, DR was incomplete (allowing germination at 25°C but not at 10°C) and required warm ST° which also promoted ageing.