AFPs - A bit of ecology, physiology, and biochemistry



My deer watch on a chilly Friday
morning

On Friday morning, I was freezing to death standing on my deer watch.  The sun hadn’t come up yet, and wind was blowing right in my face.  The freshly fallen snow was soaking my boots and pants, and sent extra chills up my spine.  These freezing temperatures, howling wind, and inches of snow surely meant death to all of the once vibrant and colourful herbs.  But beneath the accumulating snow, there were a few green survivors trying to hold on.  How were they not frozen when I – dressed in layers of long underwear, jackets, and gloves – clearly was?



In most herbaceous plants, ice crystals begin to form within the liquid-filled intercellular spaces of cells when winter comes.  These crystals continue to expand, bursting and killing the cell, and eventually the whole herbaceous plant.  However, some plants – along with animals and insects – produce antifreeze proteins (AFPs) in their bodies to adapt to cold environments.  Reduced day length and cold trigger production of AFPs in many plants to make them freeze tolerant (capable of tolerating some cold) or freeze avoidant (avoiding freezing altogether). 

AFPs bind to specific faces on ice crystals as they begin to form, preventing further crystal growth.  In areas where freeze-thaw cycles are common, AFPs can also hinder recrystallization within the cell by supressing cellular melting temperatures; previously formed ice-crystals will not melt with warming temperatures, avoiding re-freezing into larger, dangerous crystals from a following cold snap.



The leaves have fallen, but the grass is still green!

This class of proteins was first discovered in fish that were capable of surviving in chilly oceanic waters much colder than the freezing temperature of their blood.  Further studies have found a large diversity of proteins and molecules that act similarly in a wide variety of organisms; more than 23 species angiosperms – including ones eaten by humans – contain AFPs.  It is thought that AFPs (and similar molecules) evolved approximately one to two million years ago in the Northern hemisphere and ten to thirty million years ago in Antarctica in response to glaciation.

Since AFPs work so well in plants, their use has even been investigated in humans; the proteins could provide therapy for hypothermia, improve crysosurgery, and help preserve transplant or transfusion tissues.  Maybe eventually, AFPs could also be used as a treatment for cold tolerance.  If so, I would definitely get an injection so I could sit still on my deer watch next time – all my pacing to warm up likely eliminated any chance I had of having a deer coming out to me!

Sources:

http://www.sciencedaily.com/releases/2010/03/100301151923.htm

http://en.wikipedia.org/wiki/Antifreeze_protein

http://www.ncbi.nlm.nih.gov/pubmed/15358271