Biophysical boundaries for dormancy release in sunflower achenes

Area of Science:

• Plant Physiology
• Seed Science
• Biophysics

Background:

• Dormancy release (DR) in orthodox seeds is poorly understood, particularly its dependence on moisture content (MC) and storage temperature (ST°).
• Understanding these factors is crucial for seed longevity and germination success.

Purpose of the Study:

• To investigate the effects of combined MC and ST° on DR dynamics in sunflower achenes.
• To characterize embryo sensitivity to abscisic acid (ABA), oxygen uptake, and ageing indicators under varying conditions.
• To correlate water status, including sorption isotherms and glass transition temperature (Tg), with DR.

Main Methods:

• Sunflower achenes were subjected to a range of MC and ST°.
• DR was assessed by testing germination at 10°C and 25°C.
• Embryo ABA sensitivity, oxygen uptake, and ageing were monitored.
• Water status was determined using sorption isotherms and Tg measurements.

Main Results:

• Small variations in MC and ST° significantly impacted achene dormancy and embryo ABA responsiveness.
• Three distinct regions (glassy, rubbery, fluid) were identified in a 'temperature by humidity' phase diagram, influencing DR.
• Full DR occurred only in the rubbery state (above Tg).
• Optimal ST° for full DR decreased from +30°C to -18°C as MC increased from 0.045 to 0.10 gH2O.gDW-1.
• In the glassy and fluid states, DR was incomplete and required warm ST°, which accelerated ageing.

Conclusions:

• Seed moisture content and storage temperature are critical determinants of dormancy release in sunflower achenes.
• The physical state of the seed (glassy, rubbery, fluid), defined by Tg, dictates the extent of dormancy release.
• Optimal conditions for full dormancy release are found in the rubbery state, while glassy and fluid states lead to incomplete release and accelerated ageing.