Determination of Unfrozen Water in Winter Cereals at Subfreezing Temperatures

Abstract

The freezing of water in acclimated and nonacclimated cereals was studied using pulsed nuclear magnetic resonance spectroscopy. The quantity of unfreezable water per unit dry matter was not strongly dependent on the degree of cold acclimation. In contrast, the fraction of water frozen which was tolerated by nonacclimated winter cereals and by an acclimated spring wheat (Triticum aestivum L.) was less than in acclimated hardy cereals. The freezing curves had the following form: LT = LoATm/T + K LT and Lo are liquid water per unit dry matter at T and 0 C, respectively. ATm is the melting point depression and K is the liquid water which does not freeze.Horticultural Science, University of Mininesota, St. Paul, 1939 used the cryoscopic and plasmolytic methods to determine the freezing point lowerings of the cell sap, then assumed ideal freezing behavior. Ideal freezing behavior described here implies the absence of eutectics, the formation of pure ice during freezing, and the concentration of ideal solute in the liquid phase. Then the freezing curve predicted by plotting the liquid water against temperature is a hyperbola. Johansson (4) made extensive use of calorimetric methods to study the freezing process. He also assumed the hyperbolic form for the freezing curve and restricted his measurements of liquid water to two temperatures, -2.65 and -9C.Nuclear magnetic resonance has frequently been used to determine the liquid water content of partially frozen samples (1, 2, 6-8, 11). In this study, pulsed NMR' spectroscopy is used to study the freezing process in crown tissue from a spring wheat, two winter wheats, and a hardy fall rye. The relationship of the freezing process to the killing temperature and the mathematical form of the freezing curve are described. Determinations of ice formation in the plant generally involve cryoscopic, plasmolytic, or calorimetric methods. Levitt (9) in MATERIALS AND METHODS Seeds of three cultivars of wheat (Triticum aestivum L.), namely Manitou spring wheat, Cappelle-Desprez and Kharkov winter wheat, and Frontier fall rye (Secale cereale L.) were germinated at 15 C in a soil-sand-peat mixture (2:1:1). At the three leaf stage, plants were cold acclimated by the following temperature (light-period temperature/dark-period temperature) and photoperiod regimes: 10/8 C, 16 hr for the first 7 days, 8/5 C, 16 hr for the next 7 days, 5/3 C, 14 hr for the next 7 days, and 5/1 to 0 C, 12 hr for the following 21 days. The last 7 days of hardening included a frost of -2 to -3 C for 4 hr during the dark period. This cold hardening regime acclimates crowns of Manitou to -5.5 + 0.5 C, Cappelle-Desprez to -11 1 C, Kharkov to -18 ± 1 C, and Frontier to -24 t 1 C. Hardiness was determined by slowly cooling crowns at -2 C/hr. Ten crowns were used per test temperature spaced at 2 C intervals. After 3 weeks of 20 C, 24-hr photoperiod the crowns were rated for viability by regrowth of roots and leaves. One series of Kharkov plants was hardened for 14 days as described above for the first 14 d...

Cell-Wall Changes and Cell Tension in Response to Cold Acclimation and Exogenous Abscisic Acid in Leaves and Cell Cultures

“…Pressure potential was obtained by subtracting cell osmotic pressure during intracellular freezing from that during extracellular freezing at a given temperature. The osmolality of expressed cell sap was estimated using an osmometer (Wescor, Logan, UT) or by using NMR methods to determine the melting point depression in intracellularly frozen samples (Gusta et al, 1975).…”

Freezing Characteristics of Rigid Plant Tissues (Development of Cell Tension during Extracellular Freezing)

“…The amount of nonfreezable water was estimated by using L, versus 1 / T plots for thawing (Gusta et al, 1975).…”

“…The sap was expressed using a manual leaf press. For grape pith and xylem, osmolality was determined using NMR methods by direct measurement of the melting point depression during thawing of the sample that had been cooled to -196°C (Gusta et al, 1975).…”

“…The freezing behavior of water in plant tissues has been studied extensively (Burke et al, 1975;Gusta et al, 1975). The amount of unfrozen water in plant tissues during freezing has been experimentally determined in various plant tissues and has been calculated based on osmotic considerations of cell sap (Gusta et al, 1975;Rajashekar and Burke, 1982).…”

“…The amount of unfrozen water in plant tissues during freezing has been experimentally determined in various plant tissues and has been calculated based on osmotic considerations of cell sap (Gusta et al, 1975;Rajashekar and Burke, 1982). Ice generally forms in the extracellular spaces in plant tissues under conditions of slow cooling.…”