57] Methods to study the freezing process in plants

Abstract

Publisher Summary This chapter discusses various methods to study plant tissue water in relation to freezing and injury. Changes during freezing are the transformation of liquid water to ice and is reflected in the freeze-induced dehydration of cells during extracellular freezing. Cell water relations are investigated in the chapter, with the emphasis on the freeze-induced dehydration and the cellular changes during plant tissue freezing using nuclear magnetic resonance (NMR) methods. The freezing behaviors, including supercooling and ice nucleation characteristics, have a significant effect on plant survival and are extensively studied in many plant species. NMR methods have a wide application in the study of water in various kinds of aqueous solutions and biological tissues, including living systems. The NMR signal intensity is proportional to the amount of water in a sample. In a partially frozen tissue, both liquid water and ice contribute to the NMR signal. The rate of ice formation during the extracellular freezing represents the rate of water migration across the plasma membrane. Therefore, the rate of freezing and thawing of cellular water is obtained by following the liquid water signal as a function of time. The return of a perturbed nuclear spin system to its equilibrium is characterized by various relaxation processes. Spin lattice or longitudinal ( T 1 ) and spin–spin or transverse ( T 2 ) relaxations are discussed in the chapter.