Freezing of Nonwoody Plant Tissue

Abstract

MATERIALS AND METHODSCylinders measuring 5 mm in diameter were punched from fresh fruits or vegetables with a cork borer, trimmed to a length of 20 mm, and used without washing. Temperature at the center was measured with a thermistor mounted in a 24-gauge hypodermic needle and recorded as described previously (4). Tissues studied included primarily the parenchyma of cucumber (Cucumis sativus), peach (Prunus persica) and cantaloupe (Cucumis melo cantalupensis). Other tissues studied are listed in Table I. Specimens were frozen by immersion in octafluorocyclobutane (Freon C-318,' b.p. -5.8 C).In order to observe the effect of degree of sample hydration upon the shape of the freezing curve, weighed cylinders cut longitudinally from cucumber fruits were held for 3 hr at constant relative humidity over saturated salt solutions (NaCl, 76% RH5; Mg(NO4),, 54% RH; KCO,CH,, 25% RH) or over distilled water at room temperature. In some experiments, this treatment was followed by rehydration in water for 2 hr prior to freezing.Tests for determining degree of cell rupture by loss of pigments or electrolytes, and degrees of softening by increased compressibility were described previously (3). RESULTSTypical freezing curves for cylindrical sections of cucumber are shown in Figure 1. Initiation of freezing was followed by the first freezing region (FR-1) or plateau. After a temperature drop, there was usually a second freezing region (FR-2) of reduced slope, although not necessarily a plateau, with a great number of temperature spikes and a shape characteristic of the tissue. The variability in intensity of these spikes in freezing curves of a number of other edible tissues is presented in Table I. Figure 2 shows some of the variations possible in these freezing curves (Fig. 2A)

Field and controlled environment measurements show strong seasonal acclimation in photosynthesis and respiration potential in boreal Scots pine

“…The response of photosynthetic rate to subzero temperature also calls for improvement to frequently used exponential-like temperature response models to address low-temperature inhibition, for instance, by including an additional term (Collatz et al, 1992 , Equation 7). The steep drop in photosynthetic rate below 0°C and the diminishing CO 2 exchange signal, including respiration, at about −5°C could be linked with extracellular freezing in the shoots, which takes place few degrees below zero (Brown et al, 1974 ; Lintunen et al, 2014 ). Freezing results in the decrease in leaf water potential which inhibits cell metabolism and may cause embolism in water-conducting tissues.…”

Freezing of Nonwoody Plant Tissues

“…In the course of this work, small temperature spikes were observed in some of the freezing curves between -2 and -4 C. Details of their occurrence and significance are reported in two other publications (2,3).…”

Sudden Collapse of Vacuoles in Saintpaulia sp. Palisade Cells Induced by a Rapid Temperature Decrease

“…This damage is referred to as temperature injury, and can be mediated by effects on membrane fluidity, causing lethal damage to cells [17]–[19]. Likewise, the growth of extracellular ice crystals under freezing conditions results in cell injury [20], [21].…”