Water Permeability and Cold Hardiness of Cortex Cells in Cornus stolonifera Michx.—A Preliminary Report

When cooled at rapid rates to temperatures between -10 and -30°C, the incidence of intracellular ice formation was less in protoplasts enzymically isolated from cold acclimated leaves of rye (Secale cereale L. cv Puma) than that observed in protoplasts isolated from nonacclimated leaves. The extent of supercooling of the intracellular solution at any given temperature increased in both nonacclimated and acclimated protoplasts as the rate of cooling increased. There was no unique relationship between the extent of supercooling and the incidence of intracellular ice formation in either nonacclimated or acclimated protoplasts. In both nonacclimated and acclimated protoplasts, the extent of intracellular supercooling was snimlar under conditions that resulted in the greatest difference in the incidence of intracellular ice formation-cooling to -15 or -20°C at rates of 10 or 16'C/mitute. Further, the hydraulic conductivity determined during freeze-induced dehydration at -5°C was similar for both nonacclimated and acclimated protoplasts. A major distinction between nonacclimated and acclimated protoplasts was the temperature at which nucleation occurred. In nonacclimated protoplasts, nucleation occurred over a relatively narrow temperature range with a median nucleation temperature of -15°C, whereas in acclimated protoplasts, nucleation occurred over a broader temperature range with a median nucleation temperature of -42°C. We conclude that the decreased incidence of intracellular ice formation in acclimated protoplasts is attributable to an increase in the stability of the plasma membrane which precludes nucleation of the supercooled intracellular solution and is not attributable to an increase in hydraulic conductivity of the plasma membrane which purportedly precludes supercooling of the intracellular solution.It is commonly observed that the incidence of intracellular ice formation is a function of the cooling rate. As early as 1886, observed that rapid cooling resulted in intracellular ice formation whereas during slow cooling ice crystals were confined to extracellular spaces. Similar rates; and the higher the permeability to water, the lower the probability of intracellular ice formation. Further, because the deplasmolysis time of cells in cold hardy tissues was less than that for cells in nonhardy tissues, they inferred that water permeability increased following cold acclimation and that the incidence of intracellular ice formation would be less in acclimated tissues. In 1938, Siminovitch and Scarth (23) experimentally demonstrated that intracellular ice formation occurs less frequently in hardy tissues than nonhardy tissues when cooled at comparable rates. They too attributed this difference to the purported increase in water permeability of the plasma membrane following cold acclimation as proposed by Levitt and Scarth (10). Although this concept has been widely accepted and frequently cited, direct experimental verification of an increase in water permeability following cold acclimation has been...

mentioning

confidence: 99%

mentioning

confidence: 99%

Effect of Cold Acclimation on Intracellular Ice Formation in Isolated Protoplasts

Dowgert¹,

Steponkus²

1983

“…McKenzie et al (13) found that the diffusional water permeability of dogwood cortex cells increased during the photoperiodically controlled increase of cold hardiness (hardiness range from -3 to -12 C), but failed to change further as the cortex tissue cold hardiness increased to -65 C.…”

mentioning

confidence: 99%

“…The present study was designed to determine if membrane water permeability changes during cold acclimation (10,13) are associated with avoidance of intracellular ice formation at natural freezing rates. Attempts to correlate water permeability with frost hardiness (10,13,25) can at best only imply a relationship.…”

mentioning

confidence: 99%

Quantitative Study of the Importance of Water Permeability in Plant Cold Hardiness

Stout¹,

Steponkus²,

Cotts³

1977

The rate of ice formation was meaored for Hedera helir L. cv. Thorndale (English ivy) bark exposed to -10 C. The cooling rate of bark exposed to -10 C was 31 C per minute. The water effiux rate required for ice formation to occur extraceularly was calculated from the rate of ice formation and the average cell diameter. (to KNO3, urea, and H2O) paralleled seasonal changes in frost hardiness (10). The hypothesis provided an explanation for the observation that lethal intracellular ice formation occurred in nonacclimated plant tissue at a slower freezing rate than in cold-acclimated plant tissue (20).Other experiments have failed to detect a correlation between cold hardiness and membrane water permeability. Sukumaran and Weiser (25) found no difference between the water permeability of cold-acclimated and nonacclimated potato leaf cells. McKenzie et al. (13) found that the diffusional water permeability of dogwood cortex cells increased during the photoperiodically controlled increase of cold hardiness (hardiness range from -3 to -12 C), but failed to change further as the cortex tissue cold hardiness increased to -65 C.It seems well established that "fast" freezing rate injury is caused by intracellular ice formation (9,12,20). The magnitude of a fast freezing rate depends upon the particular cell type (12). For example, intracellular ice formation in red blood cells does not occur until the freezing rate exceeds 5,000 C/min (12). In contrast, red beet roots have to be frozen at rates less than 0.2 C/ hr to prevent cell injury due to intracellular ice formation (4). The cause of intracellular ice nucleation under fast freezing conditions may be limited water efflux through the cell membranes as originally proposed by Scarth (18); however, there are other potential causes of intracellular ice nucleation. For example, intracellular ice nucleation may be due to surface effects related to the proximity of solid substances, presence of cryophylactic agents, cell geometry, increased concentration of intracellular solutes, the presence of intracellular nucleation sites, or physiochemical properties of the plasmalemma prior to freezing (2).The present study was designed to determine if membrane water permeability changes during cold acclimation (10, 13) are associated with avoidance of intracellular ice formation at natural freezing rates. Attempts to correlate water permeability with frost hardiness (10,13,25) can at best only imply a relationship. In this study the resistance of the barrier to water movement from inside the cell to sites of extracellular ice formation was estimated. The resistance of this barrier to water movement would be a function of membrane resistance and extracellular resistance. The importance of membrane resistance in controlling water movement was then evaluated by comparing the known membrane resistance (24)

“…These observations may be related to the loss of NADH-induced contraction of mitochondria from drought-stressed corn seedlings (4), since many similarities exist between changes which occur during cold and drought stress. Recent electron microscopy studies (9) (10,16) demonstrated increased permeability of the plasmalemma during hardening, and this has generally been attributed to increased flexibility of the membrane. However, the greater initial swelling rate of mitochondria from 24 C grown seedlings, observed in the present study, suggests that these membranes may in fact be more permeable than those in mitochondria obtained from 2 C grown seedlings.…”

Section: Methodsmentioning

confidence: 99%

Swelling and Contraction of Mitochondria from Cold-hardened and Nonhardened Wheat and Rye Seedlings

Pomeroy

1976

A comparison of mitochondria isolated from 2 and 24 C grown winter wheat (Triticum aestivum L.) and winter rye (Secak cereak L.) seedlings revealed no correlation between changes in swelling and contraction characteristics and extent of cold hardiness. The swelling response changed markedly due to growth at low temperature, but the change was similar for the four cultivars examined. The swelling response was also observed to change rapidly during aging of isolated mitochondria, either at 2 or 24 C. Spontaneously swollen mitochondria, isolated from 24 C grown seedlings, contracted abruptly upon addition of certain oxidizable substrates, but this response was lost when seedlings were transferred from 24 to 2 C. Studies on the effect of various substrates and respiratory inhibitors on the swelling and contraction responses indicate that inhibitors which reduce or stop electron flow through the electron transport chain also inhibit substrate induced mitochondrial contraction.Although the swelling and contraction characteristics of isolated plant mitochondria have been thoroughly investigated, the mechanisms involved in these processes are not completely understood. Numerous studies (3,13,18,22) have demonstrated a passive, energy-independent swelling of plant mitochondria in the presence of isomolar salt solutions, or isomolar solutions of monosaccharide sugars. The existence of an energy-dependent (active) swelling component in plant mitochondria has also been demonstrated (2,5,19,21). Addition of certain oxidizable substrates to swollen mitochondria results in an immediate rapid contraction of the mitochondria while the addition of ATP initiates contraction of swollen corn mitochondria (18), but not swollen castor bean endosperm mitochondria (20). Earlier studies on the effect of specific inhibitors of electron transport and oxidative phosphorylation on swelling and contraction (18,20) postulated that high energy intermediates are associated with the active swelling and contraction observed in plant mitochondria. More recent investigations of energized swelling and contraction have led to interpretation of these phenomena in chemiosmotic terms, suggesting that the energy required is derived from changes in the electrochemical proton gradient (2).Recent studies (11,15) in our laboratories on the mechanism of cold hardening in plants have been directed to investigations of structural and functional properties of wheat and rye mitochondria in relation to growth at low temperature. These studies have revealed a marked increase in the level of fatty acid unsaturation during growth at low temperature, but no differences were observed among cultivars of contrasting cold hardiness. The functional properties of mitochondria from cold hardy cultivars were similar to those from less hardy cultivars. Electron spin resonance studies identified three possible temperature-dependent structural transitions in the mitochondrial membranes, and the shift in one of these appeared to be quantitatively greater in the cold hardy ...