Freeze avoidance: a dehydrating moss gathers no ice.

Area of Science:

• Plant Biology
• Cryobiology
• Ecology

Background:

• Mosses exhibit remarkable tolerance to freezing temperatures.
• Understanding the mechanisms behind plant freeze tolerance is crucial for ecological and agricultural applications.

Purpose of the Study:

• To investigate the structural and mechanical properties of Ceratodon purpureus in relation to freezing tolerance.
• To elucidate the cellular responses and biophysical mechanisms enabling survival at sub-zero temperatures.

Main Methods:

• Cryo-scanning electron microscopy (cryo-SEM) with energy-dispersive X-ray spectroscopy (EDX).
• Chlorophyll fluorescence measurements.
• Gas chromatography-mass spectrometry (GCMS).
• Differential scanning calorimetry (DSC).

Main Results:

• No intracellular ice accumulation was observed in Ceratodon purpureus during freezing.
• External ice induced cell-specific desiccation: hydroid cells cavitated, and parenchyma cells underwent cytorrhysis.
• Mosses acclimated to winter conditions showed no damage after thawing from -20 °C.
• Sugar concentrations were insufficient to explain the observed freeze tolerance.
• Internal ice nucleation occurred at approximately -12 °C in hydrated moss, but desiccated moss showed no freezing down to -20 °C.

Conclusions:

• Rapid dehydration is the primary mechanism for freeze tolerance in Ceratodon purpureus.
• This dehydration strategy effectively prevents damaging intracellular ice formation.
• The moss's ability to survive freezing is an elegantly simple solution to a significant environmental challenge.