Supercooling in overwintering azalea flower buds: additional freezing parameters

Area of Science:

• Plant physiology
• Cryobiology
• Biophysics

Background:

• Floral primordia are susceptible to freezing injury.
• Understanding supercooling and freezing processes in plant tissues is crucial for crop survival.

Purpose of the Study:

• To investigate the biophysical mechanisms of freezing in supercooled azalea floral primordia.
• To determine the role of water status and ice formation in freezing injury.

Main Methods:

• Calorimetry to measure heat release during freezing.
• Pulsed nuclear magnetic resonance (NMR) spectroscopy to assess water dynamics.
• Low-temperature light microscopy to observe ice formation.

Main Results:

• Heat release during freezing aligned with predictions for supercooled pure water.
• Decreased spin-lattice and spin-spin relaxation times post-freezing indicated water redistribution and injury.
• No detectable ice formed until a significant freezing event; no resistance to ice growth was observed.

Conclusions:

• Azalea floral primordia exhibit freezing behavior similar to pure water.
• Freezing injury is associated with water redistribution, not immediate ice nucleation.
• A freezing barrier or thermodynamic equilibrium likely exists between primordia and surrounding bud tissues.