A model for extracellular freezing based on observations on Equisetum hyemale

Area of Science:

• Plant Physiology
• Cryobiology
• Biophysics

Background:

• Frost hardiness in plants is crucial for survival, requiring mechanisms to prevent lethal intracellular ice formation.
• Extracellular ice formation, alongside supercooling and dehydration, is a key strategy for managing ice development in plant tissues.
• Ice accumulates in intercellular spaces, often at specific sites, driving water movement within plant tissues.

Purpose of the Study:

• To theoretically investigate the physico-chemical processes governing water movement towards sites of extracellular ice formation.
• To understand the physical mechanisms of extracellular ice formation in frost-hardy plants, using Equisetum hyemale as a model.
• To elucidate how subzero temperatures trigger osmotic-mechanic responses in plant cells.

Main Methods:

• Theoretical modeling of water movement based on physico-chemical principles.
• Analysis of observations from the frost-hardy horsetail, Equisetum hyemale.
• Focus on the cellular osmotic-mechanic system's response to falling and subzero temperatures.

Main Results:

• Falling temperatures induce water outflow from plant cells.
• Cells with stiffer walls exhibit less water loss compared to those with softer walls.
• Increased water loss from cells correlates with a less negative turgor loss point.

Conclusions:

• Cellular water movement during freezing is a passive consequence of the osmotic system's structure, not active cellular processes.
• Subzero temperatures can initiate directed water flow due to inherent cellular properties.
• This mechanism of directed water flow is likely common in frost-hardy species employing extracellular ice formation.