Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/1/2002
Publication Date: 11/1/2002
Citation: WISNIEWSKI, M.E., FULLER, M., GLENN, D.M., GUSTA, L., DUMAN, J., GRIFFITH, M. EXTRINSIC ICE NUCLEATION IN PLANTS: WHAT ARE THE FACTORS INVOLVED AND CAN THEY BE MANIPULATED. In: Plant Cold Hardiness: Gene Regulation and Genetic Engineering. eds. P.H. Li and E.T. Palva, Kluwer Academic, New York, November 2002, pgs. 211-222. Interpretive Summary:
Technical Abstract: The factors that determine when and to what extent a plant will freeze are complex. In herbaceous plants, it appears that extrinsic nucleating agents play a key role in initiating ice formation. Ice-nucleating-active bacteria and moisture are two major extrinsic agents, however, their influence on the freezing process can be moderated by the presence of natural or applied hydrophobic barriers. Evidence suggests that ice crystals formed on the surface of plants must physically grow into the interior of the plant in order to initiate freezing of the plant. This can occur through stomates, or cracks in the cuticle. Thick cuticles, as found on many evergreen plants, and the application of synthetic, hydrophobic materials appear to serve as effective barriers and can inhibit the effect of extrinsic ice nucleating agents by preventing moisture from collecting on the surface of the plant and/or inhibiting the growth of ice crystals into the interior of the plant. In this regard, the application of hydrophobic barriers may provide a new approach to frost protection. Woody plants appear to possess native, intrinsic nucleating agents that are just as active as many extrinsic ice nucleating agents. The exact identification of the intrinsic nucleating agents in woody plants, however, is unknown. Despite the presence of internal nucleating agents that are active at warm temperatures, barriers exist in woody plants that inhibit growth of ice from older stems into primary, lateral appendages. This is important because many of tissues in woody plants that are frost sensitive are flowers and primary, elongating, shoot tissues that arise from buds attached to older stems. The barriers that prevent ice propagation into the lateral appendages are most effective when ice forms in the main stem tissues at warm temperatures (-1.0 to -2.5 °C). Cold acclimation appears to influence the freezing response of plants. Evidence suggests that native antifreeze proteins can affect the freezing process in plants and also that plants transformed to express insect antifreeze proteins will supercool to a greater extent than wild-type plants.