Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2004
Publication Date: 7/15/2004
Citation: Gusta, L.V., Wisniewski, M.E., Nesbitt, N.T., Gusta, M.L. 2004. The effect of water, sugars, and proteins on the pattern of ice nucleation and propagation in acclimated and non-acclimated canola (brassica napus) leaves. Plant Physiology. July 2004, Vol. 135, pp. 1642-1653. Interpretive Summary: Every year, freeze damage to crops results in millions of dollars of losses. In some cases, adequate frost protection measures or the ability to rapidly acclimate plants could alleviate these devastating financial hardships. In order to develop novel and effective new methods of frost protection, a better understanding of the factors that induce plants to freeze at specific temperatures is necessary. We have utilized high-resolution infrared thermography to visualize the freezing process in plants. The use of this technology has significantly enhanced our knowledge of ice nucleation and propagation in plants. The current study utilized infrared thermography to study the effect of water status, sugars, and proteins on the pattern of freezing in canola (Brassica napus) leaves. We also developed a novel method to examine the effect of sugars and proteins in the cell walls on the freezing process. Results demonstrated that the temperature of ice nucleation and the rate of ice propagation is strongly dependent on the water status of the leaves (which in turn depends on water availability and sugar content). Simple sugars had a dramatic effect on the freezing rate compared to proteins which had only a minor effect. Cell solutes were also able to depress the nucleation temperature of leaves, i.e. the temperature at which ice was initiated. These results, along with numerous other studies on ice nucleation and propagation, are being used to develop a comprehensive knowledge of how plants freeze. This information will, in turn, be utilized to develop novel methods of frost protection.
Technical Abstract: Infrared video thermography was used to observe ice nucleation temperatures, patterns of ice formation, and freezing rates in non-acclimated and cold acclimated leaves of a spring (cv. Quest) and a winter (cv. Express) canola (Brassica napus). In this study, distinctly different freezing patterns are revealed. When freezing was initiated by INA+ bacteria, ice growth rapidly spread throughout the non-acclimated leaves. In contrast, acclimated leaves initiated freezing in a horseshoe pattern at the tip edge with ice growth slowing progressing across the leaf. However when re-frozen, fully acclimated leaves either previously killed by a slow freeze (2°C h-1) or by direct submersion in liquid nitrogen froze in a similar pattern to non-acclimated leaves. A novel technique was developed to determine both the effects of sugars and proteins on the rate of freezing, as well as the effects of ice nucleation temperature for leaf cell extracts. Cell sap extracts from non-acclimated leaves froze three-fold faster than extracts from acclimated leaves. The rate of freezing in leaves is strongly dependent upon the osmotic potential of the leaves. Non-acclimated leaves containing high water content did not supercool as low as acclimated leaves. In addition, wetted leaves did not supercool to temperatures as low as non-wetted leaves. Simple sugars had a dramatic effect on the freezing rate compared to proteins. Cell solutes appear to depress the nucleation temperature of leaves.