Articles
WINTER RYE ANTIFREEZE PROTEINS ARE NOT CRYPROTECTIVE, RATHER THEY MODIFY THE GROWTH OF ICE IN PLANTA
Article number
618_2
Pages
31 – 37
Language
English
Abstract
Antifreeze proteins (AFPs) bind to the surface of ice and modify its growth.
In overwintering plants, AFPs accumulate in the apoplast where ice forms during freezing, suggesting that their major function is to modify the growth of ice.
However, AFPs in other overwintering organisms are reported to play a cryoprotective role through interactions with proteins and membranes.
To better understand the role of AFPs, we examined their ability to protect the activity of rabbit lactate dehydrogenase (LDH) and volume of spinach thylakoids subjected to freeze-thaw cycles.
Winter rye AFPs were added to solutions of LDH, which were then frozen and thawed and LDH was assayed for activity.
In these experiments, LDH activity was higher in the presence of rye AFPs, but the protection was no greater than observed in the presence of bovine serum albumin.
Thus, the cryoprotection of LDH was due to the nonspecific effects achieved by increasing the protein concentration of the solution.
Spinach thylakoids frozen and thawed in the presence of rye AFPs lost the ability to stack in the presence of Mg2+, whereas thylakoids frozen in aqueous solution retained the ability to stack.
In this case, the presence of rye AFPs during freezing and thawing was injurious.
We then examined the freezing process in rye leaves by infrared thermography.
After nucleating with ice on the leaf surface, nonacclimated rye leaves froze continuously.
In contrast, cold-acclimated rye leaves that had accumulated AFPs froze at a lower temperature and the freezing process occurred in two distinct exothermic steps.
We conclude that the rye AFPs do not play a cryoprotective role in the plant, rather they influence the freezing process in the tissues by interacting with ice.
In overwintering plants, AFPs accumulate in the apoplast where ice forms during freezing, suggesting that their major function is to modify the growth of ice.
However, AFPs in other overwintering organisms are reported to play a cryoprotective role through interactions with proteins and membranes.
To better understand the role of AFPs, we examined their ability to protect the activity of rabbit lactate dehydrogenase (LDH) and volume of spinach thylakoids subjected to freeze-thaw cycles.
Winter rye AFPs were added to solutions of LDH, which were then frozen and thawed and LDH was assayed for activity.
In these experiments, LDH activity was higher in the presence of rye AFPs, but the protection was no greater than observed in the presence of bovine serum albumin.
Thus, the cryoprotection of LDH was due to the nonspecific effects achieved by increasing the protein concentration of the solution.
Spinach thylakoids frozen and thawed in the presence of rye AFPs lost the ability to stack in the presence of Mg2+, whereas thylakoids frozen in aqueous solution retained the ability to stack.
In this case, the presence of rye AFPs during freezing and thawing was injurious.
We then examined the freezing process in rye leaves by infrared thermography.
After nucleating with ice on the leaf surface, nonacclimated rye leaves froze continuously.
In contrast, cold-acclimated rye leaves that had accumulated AFPs froze at a lower temperature and the freezing process occurred in two distinct exothermic steps.
We conclude that the rye AFPs do not play a cryoprotective role in the plant, rather they influence the freezing process in the tissues by interacting with ice.
Authors
M. Griffith, C. Lumb, S.B. Wiseman, R.W. Johnson, M. Wisniewski, M.C. Loewen
Keywords
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