Effect Of Low Temperature Exposure Research Articles

Effects of low temperature exposure and acclimation on the behavioural responses of the green crab (Carcinus maenas) from Newfoundland, Canada.

Effects of low temperature exposure and acclimation on the behavioural responses of the green crab (Carcinus maenas) from Newfoundland, Canada.

Effects of low temperature on growth and metabolism of larval green sturgeon (Acipenser medirostris) across early ontogeny.

Southern Distinct Population Segment (sDPS) green sturgeon spawn solely in one stretch of the Sacramento River in California. Management of this spawning habitat is complicated by cold water temperature requirements for the conservation of winter-run Chinook salmon. This study assessed whether low incubation and rearing temperatures resulted in carryover effects across embryo to early juvenile life stages on scaling relationships in growth and metabolism in northern DPS green sturgeon used as a proxy for sDPS green sturgeon. Fish were incubated and reared at 11°C and 15°C, with a subset experiencing a reciprocal temperature transfer post-hatch, to assess recovery from cold incubation or to simulate a cold-water dam release which would chillrearing larvae. Growth and metabolic rate of embryos and larvae were measured to 118days post hatch. Reciprocal temperature transfers revealed a greater effect of low temperature exposure during larval rearing rather than during egg incubation. While 11°C eggs hatched at a smaller length, log-transformed length-weight relationships showed that these differences in developmental trajectory dissipated as individuals achieved juvenile morphology. However, considerable size-at-age differences persisted between rearing temperatures, with 15°C fish requiring 60days post-hatch to achieve 1g in mass, whereas 11°C fish required 120days to achieve 1g, resulting in fish of the same age at the completion of the experiment with a ca. 37-fold difference in weight. Consequently, our study suggests that cold rearing temperatures have far more consequential downstream effects than cold embryo incubation temperatures. Growth delays from 11°C rearing temperatures would greatly increase the period of vulnerability to predation in larval green sturgeon. The scaling relationship between log-transformed whole-body metabolism and mass exhibited a steeper slope and thus an increased oxygen requirement with size in 11°C reared fish, potentially indicating an energetically unsustainable situation. Understanding how cold temperatures affect green sturgeon ontogeny is necessary to refine our larval recruitment estimations for this threatened species.

Short Cold Storage as a Sustainable Postharvest Handling Method for Natural Enrichment in Antioxidants of Fresh and Dried Walnut Kernels—Cultivar Effect

Fresh (raw, non-dried) walnuts (kernel moisture > 17%) have unique sensory and nutritional attributes but a narrow time availability due to their rapid deterioration during storage. In the present study, the storage (1 °C, 90% RH) potential of fresh walnuts for 20 and 40 days was assessed in relation to cultivar (Chandler, Hartley, Ioli) and the form of exposure to storage (shelled or in-shell). The effect of low-temperature exposure (at 1 °C for 0, 10 and 20 days) before nut drying was also examined. Fresh walnuts from different cultivars showed diverse quality (size, color) and physiological (respiration, weight loss) traits. Using a very low storage temperature (1 °C) was feasible to store fresh walnuts marginally up to 40 days without losing the ‘fresh’ character. The form of in-shell storage compared with shelled ones helped to determine the retention of kernel moisture and had a mild protective role in the prevention of kernel browning. The storage of fresh walnuts at 1 °C resulted in increased total phenolics (TP, by 26% in average) and antioxidant capacity (by 46%, in average) of the kernels, supporting the improvement of nutritional value due to low temperatures. The dried kernels after this short cold storage showed increased TP levels by 35–40% in comparison with conventional dried ones. Therefore, the 10 d cold exposure could be proposed as a sustainable step for incorporation in the regular postharvest handling chain for the natural enrichment of fresh and dried kernels in antioxidants.

The physiological response of the sweet cherry leaf to non-freezing low temperatures

The effect of exposure of sweet cherry trees (Prunus avium L.) to non-freezing low temperature was investigated by measurements of chlorophyll fluorescence, gas exchange parameters and chlorophyll content in two experiments. In Experiment I, cultivars ‘Grace Star’ and ‘Schneiders’ were exposed to an average of 4.7 °C 21 and 27 days after full blooming (DAFB) and in Experiment II, cultivar ‘Grace Star’ to 2.2 °C 50 DAFB, for one, two or three consecutive nights. The aim of the present study was to evaluate the effect of low temperature exposure (LTE) on leaf physiology, recovery time and differences between cultivars in response to chilling stress. After the first, second and third LTE, a decrease in maximum and effective quantum yield of PS II (Fv/Fm and Fv′/Fm′), net photosynthesis (Pn), stomatal conductance (gs) and transpiration (E) was observed. Multiple LTE caused a greater physiological disturbance than single LTE. The recovery time after multiple LTE was prolonged. Trees with one and two LTE reached similar values to the controls within 24 and 48 h, respectively, while trees with three LTE did not reach within 48 h. The LTE in Experiment I showed no effect on Fv/Fm, while two LTE induced lower Pn, gs and E. After LTE, no differences between cultivars were found. The effect of chilling stress was more pronounced at lower temperatures and when the trees were chilled for several consecutive nights.

Effects of Low Temperature Exposure on Diapause, Development, and Reproductive Fitness of the Emerald Ash Borer (Coleoptera: Buprestidae): Implications for Voltinism and Laboratory Rearing.

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), native to Northeast Asia, is the most destructive invasive ash (Fraxinus spp.) pest in the United States. In the present study, we evaluated the effect of exposure of diapausing mature fourth instars (J-shaped larvae, JL) of EAB to cool temperatures, either 1.7 or 12.8°C for 1-9 mo, on their post-chill development including adult emergence, longevity, and lifetime fecundity under standard rearing conditions (26 ± 0.5°C, 16:8 h L:D). In addition, we determined the effect of different stages of the larvae chilled at 12.8°C for 3 mo on the subsequent post-chill development to EAB adults. Findings from the study revealed that a period (≥2 mo) of chill at 12.8°C is required for the termination of the EAB diapause. However, chill treatment of the larvae at the near zero temperature (1.7°C) does not result in the post-diapause larval development to adults, regardless of the chill time (1-9 mo). In addition, our results showed that chill treatment of immature young larvae (L1-L4 prior to JL) results in little production of EAB adults, indicating that EAB diapause predominantly as JL. Findings of this study may be useful to laboratory rearing of EAB from eggs through continuous generations and help us understand the pest's voltinism resulting from the diapause and post-diapause development under different climatic conditions.

Seed germination of a rare gypsum-associated species, Arctomecon californica (Papaveraceae), in the Mojave Desert

Persistence of rare species associated with unique soil habitats is uncertain with commonly accelerating threats such as habitat loss, fragmentation, and rapid environmental change and limited availability of critical life-history information, such as seed dormancy and germination. Exemplifying rare species of unique habitats in arid environments, Arctomecon californica Torr. & Frém. (Las Vegas bearpoppy) is endemic to gypsic- (calcium sulfate dihydrate) and calcic- (calcium carbonate) soil landscapes in the Mojave Desert of southern Nevada and northwestern Arizona, USA. We examined seed dormancy and germination of A. californica using integrated field and laboratory experiments assessing whether (i) field conditioning could enhance laboratory seed germination; (ii) sulfuric acid, as a potential constituent of gypsum soil water, could break dormancy; and (iii) different temperature regimes could affect germination. Our study demonstrates three findings pertaining to A. californica germination: the promotive effect of low temperature exposure, or more specifically single to multiple cold stratification (cold-wet) events; the potential initial enhancing role of sulfuric acid on the cold stratification process, which diminishes with prolonged cold stratification exposure; and the relative ineffectiveness of a one-season field conditioning treatment on A. californica germination, suggesting that longer cold stratification events, within season or over multiple seasons, are required to trigger germination. For land managers, the efficacy of cold stratification as a dormancy break has potential to inform A. californica conservation management within suitable habitat and support restoration applications such as in breaking dormancy before seeding and propagating plants.

Stressor interactions in freshwater habitats: Effects of cold water exposure and food limitation on early‐life growth and upper thermal tolerance in white sturgeon, Acipenser transmontanus

Abstract Limited food availability and altered thermal regimes (e.g. cold water releases from dams) are two common stressors threatening the persistence of fishes inhabiting anthropogenically disturbed freshwater systems. Yet, the combined effects of these stressors remain poorly characterised. To remedy this, we examined the isolated and combined effects of low temperature exposure and food restriction on specific growth rate (SGR, % body mass/day) and upper thermal tolerance (critical thermal maxima, CTMax) in larval white sturgeon (Acipenser transmontanus [Acipenseridae], 32 days post‐hatch, body mass: 0.25 ± 0.03 g, mean ± standard deviation). A 2 × 2 factorial design was implemented with fish exposed to one of two ecologically‐relevant acclimation temperatures (cold exposure: 11°C or a control temperature: 18°C) and one of two food restriction treatments designed to emulate observed declines in food availability (100% or 40% optimal feed rate) for 6 weeks (N: 3 replicate tanks/treatment, 50 fish/tank). Specific growth rate was affected by both low temperature exposure and food restriction in isolation; low temperature exposure reduced SGR by 56.5% and food restriction reduced SGR by 30.6%. Simultaneous exposure to low temperature and food restriction resulted in a greater but less than additive reduction in SGR (80.6%), indicating that the stressors interacted antagonistically. Critical thermal maxima were c. 2°C higher in 18°C‐acclimated fish (CTMax = 30.7 ± 0.4°C, mean ± standard error) compared to 11°C‐acclimated fish (CTMax = 28.6 ± 0.2°C, mean ± standard error); however, CTMax was independent of food restriction in both 11°C‐ and 18°C‐acclimated fish. These data highlight the unpredictability of stressor interactions and may guide holistic conservation strategies, which target co‐occurring stressors in freshwater habitats.

Time Course Studies on Impact of Low Temperature Exposure on the Levels of Protein and Enzymes in Fifth Instar Larvae of Eri Silkworm, Philosamia ricini (Lepidoptera: satuniidae)

Lactate dehydrogenase (LDH; EC 1.1.1.27) and malate dehydrogenase (MDH; EC 1.1.1.37) are the enzymes involved in energy metabolism of Eri silkworm, Philosamia ricini. However, no previous study has been reported about effect of low temperature exposure on their levels in different tissues of Eri silkworm. The present study was aimed to the time-course effects of low temperature (~10°C) exposure of 5th instar P. ricini on the levels of protein and energy metabolism enzymes of three major tissues (haemolymph, silk gland and fat body). The Eri silkworm larvae, reared on fresh leaves of castor-oil-plant (Ricinus communis), were divided into 4 groups: a control group reared at 25 ± 2°C along with three experimental groups reared at 10 ± 1°C containing 50 larvae in each, for varying durations (2, 4 and 7 days). The cell free extract was prepared by centrifuging the tissue homogenate at 9000 g and used for biochemical estimations (total protein content, lactate dehydrogenase and malate dehydrogenase activities). For isozyme analysis, another set of homogenates (20% w/v) was prepared in buffer (0.2 M Tris HCl, pH 7.0) containing 0.2 M sucrose and 10 mM EDTA, and analyzed by native-PAGE followed by activity staining. The activities of lactate dehydrogenase and malate dehydrogenase showed significant decrease in haemolymph, whereas in fat bodies both enzymes showed increased activity. In silk gland, Lactate dehydrogenase activity decreased uniformly, whereas malate dehydrogenase activity increased at all exposure durations. The isozyme analysis revealed significant perturbations in their expression profiles. The low temperature exposure resulted into accumulation of protein content in haemolymph and depletion in silk gland and fat body tissues. Fat bodies emerged as the main energy producing organ under this condition. Lactate dehydrogenase and malate dehydrogenase displayed presence of only one isozyme in all the tissues tested. The isozyme behaviour of lactate dehydrogenase and malate dehydrogenase towards low temperature varied in different tissues. These results suggested that alterations in expression and functions of these enzymes might be associated to the acclimation of larvae at low temperature.

Cold stress affects H+-ATPase and phospholipase D activity in Arabidopsis

Low temperature is an environmental stress that greatly influences plant performance and distribution. Plants exposed to cold stress exhibit modifications of plasma membrane physical properties that can affect their functionality. Here it is reported the effect of low temperature exposure of Arabidopsis plants on the activity of phospholipase D and H+-ATPase, the master enzyme located at the plasma membrane. The H+-ATPase activity was differently affected, depending on the length of cold stress imposed. In particular, an exposure to 4 °C for 6 h determined the strong inhibition of the H+-ATPase activity, that correlates with a reduced association with the regulatory 14-3-3 proteins. A longer exposure first caused the full recovery of the enzymatic activity followed by a significant activation, in accordance with both the increased association with 14-3-3 proteins and induction of H+-ATPase gene transcription. Different time lengths of cold stress treatment were also shown to strongly stimulate the phospholipase D activity and affect the phosphatidic acid levels of the plasma membranes.Our results suggest a functional correlation between the activity of phospholipase D and H+-ATPase mediated by phosphatidic acid release during the cold stress response.

Moderately lower temperatures greatly extend the lifespan of Brachionus manjavacas (Rotifera): Thermodynamics or gene regulation?

Environmental temperature greatly affects lifespan in a wide variety of animals, but the exact mechanisms underlying this effect are still largely unknown. A moderate temperature decrease from 22°C to 16°C extends the lifespan of the monogonont rotifer Brachionus manjavacas by up to 163%. Thermodynamic effects on metabolism contribute to this increase in longevity, but are not the only cause. When rotifers are exposed to 16°C for four days and then transfered to 22°C, they survive until day 13 at nearly identical rates as rotifers maintained at 16°C continuously. This persistence of the higher survival for nine days after transfer to 22°C suggests that low temperature exposure alters the expression of genes that affect the rate of aging. The relative persistence of the gene regulation effect suggests that it may play an even larger role in slowing aging than the thermodynamic effects. The life extending effects of these short-term low temperature treatments are largest when the exposure happens early in the life cycle, demonstrating the importance of early development. There is no advantage to lowering the temperature below 16°C to 11° or 5°C. Rotifers exposed to 16°C also displayed increased resistance to heat, starvation, oxidative and osmotic stress. Reproductive rates at 16°C were lower than those at 22°C, but because they reproduce longer, there is no significant change in the lifetime fecundity of females. To investigate which genes contribute to these effects, the expression of specific temperature sensing genes was knocked down using RNAi. Of 12 genes tested, RNAi knockdown of four eliminated the survival enhancing effects of the four-day cold treatment: TRP7, forkhead box C, Y-box factor, and ribosomal protein S6. This demonstrates that active gene regulation is an important factor in temperature mediated life extension, and that these particular genes play an integral role in these pathways. As a thermoresponsive sensor, TRP7 may be responsible for triggering the signaling cascade contributing to temperature mediated life extension. The TRP genes may also provide especially promising candidates for targeted gene manipulations or pharmacological interventions capable of mimicking the effects of low temperature exposure. These results support recent theories of aging that claim rate of aging is determined by an actively regulated genetic mechanism rather than an accumulation of molecular damage.

Improved Functional Expression of Human Cardiac Kv1.5 Channels and Trafficking-Defective Mutants by Low Temperature Treatment

We herein investigated the effect of low temperature exposure on the expression, degradation, localization and activity of human Kv1.5 (hKv1.5). In hKv1.5-expressing CHO cells, the currents were significantly increased when cultured at a reduced temperature (28°C) compared to those observed at 37°C. Western blot analysis indicated that the protein levels (both immature and mature proteins) of hKv1.5 were significantly elevated under the hypothermic condition. Treatment with a proteasome inhibitor, MG132, significantly increased the immature, but not the mature, hKv1.5 protein at 37°C, however, there were no changes in either the immature or mature hKv1.5 proteins at low temperature following MG132 exposure. These observations suggest that the enhancement of the mature hKv1.5 protein at reduced temperature may not result from the inhibition of proteolysis. Moreover, the hKv1.5 fluorescence signal in the cells increased significantly on the cell surface at 28°C versus those cultured at 37°C. Importantly, the low temperature treatment markedly shifted the subcellular distribution of the mature hKv1.5, which showed considerable overlap with the trans-Golgi component. Experiments using tunicamycin, an inhibitor of N-glycosylation, indicated that the N-glycosylation of hKv1.5 is more effective at 28°C than at 37°C. Finally, the hypothermic treatment also rescued the protein expression and currents of trafficking-defective hKv1.5 mutants. These results indicate that low temperature exposure stabilizes the protein in the cellular organelles or on the plasma membrane, and modulates its maturation and trafficking, thus enhancing the currents of hKv1.5 and its trafficking defect mutants.

False codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae) larvae are chill‐susceptible

Abstract This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7°C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is −11.5 ± 0.3°C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from −15.6°C to −17.4°C after larvae were fasted for 24 h. Twenty‐four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to −17.2°C and −18.2°C respectively. Inoculative freezing (by water contact) raised SCP from −15.6°C to −6.8°C which could have important implications for post‐harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life‐stage, at least over the short time‐scales investigated here. In conclusion, larvae of T. leucotreta are chill‐susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post‐harvest sterilization efficacy.

Effect of low temperature exposure on impact characteristics of epoxy bonded high strength steels

In the development of vehicle structures, the proper selection of adhesives to bond the steels is important for safety of operation. In this study, toughened epoxy was tested for the ability to bond steels developed for low temperature use. Lap shear bonded DP600 and DP780 steel joints were prepared and tested in open air at ambient temperature and inside an environmental chamber at −40°C respectively using a split Hopkinson tensile bar machine. The impact properties of bulk adhesive at −40°C were also measured. It was found that the exposure of joints to a −40°C environment had little influence on impact strength and energy absorption. Scanning electron microscopy of fracture surfaces indicates differences in fracture paths and interfacial regions for the −40°C exposed specimens. Changes in the interphase region caused by low temperature exposure may contribute to an increased susceptibility of the adhesive joint to bond degradation.

Time–mortality relationships of larvae and adults of grain beetles exposed to extreme cold

Mortality effects of low temperature exposure to −16 °C were investigated on larvae and adults of the grain beetles Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) and Trogoderma granarium (Everts) (Coleoptera: Dermestidae), in the laboratory. The main effects and interactions of exposure time (0.2, 0.5, 1, 2, 4, 8, 12, 24 and 48 h), developmental stage (larva and adult) and individual’s age (young and old) were examined. After 4 h of exposure 100% mortality has been achieved in most of the treatments. The only exceptions were that of old larvae of T. granarium and O. surinamensis, and adults of T. granarium which needed 48, 8, and 24 h, respectively. T. granarium was the most cold-hardy species irrespective of developmental stage, and age, followed in decreasing order by O. surinamensis and T. confusum. Younger adults were generally more susceptible to cold in the cases of O. surinamensis and T. confusum. On the contrary, older adults of T. granarium suffered higher mortality than younger ones. Larvae of T. granarium were generally more cold-tolerant than adults but the opposite pattern was observed in O. surinamensis and T. confusum. Main effects of exposure time, developmental stage and individual’s age on mortality proved to be significant for all species, with the exception of T. granarium where the effect of developmental stage proved to be insignificant. Lethal time values were estimated via probit analysis. Values of LT 50 ranged between 0.7 and 1.0 h for T. confusum, 0.7–1.9 h for O. surinamensis and 1.2–3.4 h for T. granarium. Our results are discussed with findings from relevant studies and the possibility of including extreme cooling to IPM programs against stored product pests is investigated.

Deleterious Effects of Low Temperature Exposure on Learning Expression in a Parasitoid

In this paper, we review the learning capacities of insect parasitoids. We present data on the learning capacity of the parasitoid wasp, Anaphes victus (Hymenoptera: Mymaridae), in the host (egg) discrimination process. In addition, we examine the effect of low temperature exposure on the wasp’s learning. Our results showed that A. victu s females learned rapidly to recognize their own chemical cues that they left on the host eggs, and retained this learning from patch to patch. Conspecific chemical cues left on the eggs took more time to be learned, but two learning trials induced a prolonged memory for the cues. Our results also showed that the use of learned, conspecific chemical cues was more affected by cold exposure than was the use of learned personal cues.

Low temperature effects on ubiquinone content, respiration rates and lipid peroxidation levels of etiolated seedlings of two differentially chilling‐sensitive species

Ubiquinone functions primarily in the electron transport chain of the mitochondria of plants and animals. Secondary roles in plant tissue, such as antioxidant activity, have also been proposed. The effect of low temperature exposure on etiolated seedling embryonic axes of two differentially chilling‐sensitive species, mung bean (Vigna radiata L.) (chilling‐sensitive) and pea (Pisum sativum L. cv. Lincoln) (chilling‐tolerant) with respect to respiration rate, lipid peroxidation and ubiquinone content was examined. Whole seedlings (embryonic axis and cotyledon) of both species were exposed to control temperatures (20°C) (6 days) or an acclimatory low temperature treatment of 10°C (3 days) followed by exposure at 5°C (3 days). Measurements were initiated 3 days after seedlings had reached 50% germination (D0). Prior to measurements the cotyledons were removed and only the embryonic axis was used in these experiments. Ubiquinol (UQH2), ubiquinone (UQ) and total ubiquinone (UQtot) content decreased in mung bean in response to the temperature treatment and UQH2 and UQtot remained stable in the more chilling‐tolerant pea. The reduction of the total Q‐pool was approximately 85–92%, suggesting a high degree of saturation of the respiration pathways. Respiration declined and the RQ ratio increased in both species in response to low temperature. Cytochrome c oxidase (COX) (EC 1.9.3.1) activity was higher in pea than in mung bean but decreased during low temperature exposure in both species. Considering that levels of MDA (lipid peroxidation) did not increase in either species in response to chilling, decreased levels of UQH2 and UQ observed in chilling‐sensitive mung bean may indicate that these compounds were damaged prior to other membrane lipids during low temperature treatment and rendered undetectable.

Overcoming Dormancy of Mayapple Rhizome Segments with Low Temperature Exposure

American mayapple (Podophyllum peltatum L.) is a rhizomatous, herbaceous perennial found in wooded areas of eastern North America and is a source of the pharmaceutical compound podophyllotoxin. This research was conducted to determine the optimum duration of low temperature exposure in overcoming dormancy of fall-harvested rhizome segments for subsequent use as propagules in greenhouse plantings. Two types of rhizome segments were harvested from the wild and used in this study: two-node rhizome segments consisting of a terminal node and its adjacent one-year-old node and one-node rhizome segments consisting of a single node, other than a terminal node, of unknown age or rhizome position. For growth cycle I, rhizome segments were exposed to low temperature (≈4 °C) for 30, 45, 60, 75, or 90 days, planted in pots, and grown in a greenhouse set at 21 °C. Shoot emergence, shoots per pot, and plant height were recorded. Leaves were removed from plants when senescence first became evident, and leaf area was recorded. For growth cycle II, rhizome segments remained undisturbed in the original pots and were exposed to low temperatures (≈4 °C) for 90 days. Pots were again placed in the greenhouse and shoot emergence, shoots per pot, plant height, and leaf area were recorded. Increasing duration of low temperature exposure of rhizome segments up to 75 days appeared to increase percent emergence and plant height and decrease days to emergence, though changes in greenhouse conditions over the study period may have also influenced shoot emergence and plant growth. Two-node rhizome segments exhibited higher percent shoot emergence, shoot longevity, leaf area, and plant height than single-node segments during each growth cycle. Two-node rhizome segments also exhibited fewer days to emergence during growth cycle I. Rhizome segments produced no more than a single shoot in growth cycle I, whereas more than one shoot was produced in growth cycle II. Most of the effects of low temperature exposure during growth cycle I persisted throughout growth cycle II. These results indicate that dormancy of mayapple rhizomes can be overcome with low temperature exposure and shoots can be induced to grow at any time of year.

Effect of short term cold stress on rice seedlings

A method was developed for exposing riceseedlings to low temperatures for shortperiods. These seedlings were from 70F9 inbred lines derived originallyfrom a hybrid of a salt tolerant cultivar,which provided a source of resistance toabiotic stress, and a non salt tolerantcultivar as the other parent. Seedlingswere grown hydroponically in a warm growthroom then placed in the air above afreezing bath for 6 hours at –0.2 °C,–1.0 °C or –2.0 °C beforereturning them to the growth room for a7–10 day period. Seedling survival in theinbred lines of rice was compared afterexposure to these temperature treatments toidentify the presence of low temperaturetolerance. An average survival of 93%occurred 7days after exposures to –0.2, and–1.0 °C and a survival of 35% afteran exposure of –2.0 °C. The non-salttolerant parent cultivar was killed byexposure to –2.0 °C but the salttolerant parent survived. The effect of lowtemperature exposure was examined in moredetail in lines selected for lowtemperature tolerance and susceptibility.Alterations to the total leaf proteinprofile, including fragmentation ofRubisco, were observed in these lines butno obvious difference was detected betweensusceptible and tolerant individuals.

An Analysis of Cell Freezing and Dehydration

A quantitative picture of the effect of low-temperature exposure on the survival of living cells is presented through discussion of solutions to a differential equation relating the volume of intracellular water to the temperature, the cooling rate, and various cell parameters. It is found that for a given cell, a single parameter which depends on the cooling rate governs the behavior of the cell when it is exposed to low temperatures. The analysis develops relationships between solutions to the differential equation and the phenomena affecting cell survival, namely, intracellular freezing and cell dehydration. Theoretical predictions are found to agree well with existing experimental observations.

The Effect of Low Temperatures on the Motility of Diphyllobothrium Latum Plerocercoids

The effect of low temperature exposure on the motility of Diphyl-lobothrium latum plerocercoids was studied, with the particular aim of finding the exposure that immobilizes all the larvae in fish freezing. Both isolated larvae immersed in normal horse serum and larvae enclosed in pieces of muscle tissue of the size of 1 cm3 were tested. The pieces of tissue containing a larva were placed in the middle of a plastic beaker filled with densely packed minced fish flesh. In the central part of this phantom, where the plerocercoids were situated, the temperature decline was considered to take place in the same way as in the interior of a whole fish. A total of 200 isolated larvae were tested, and a temperature of −14° G was found to have a fully immobilizing effect on them. The number of plerocercoids frozen enclosed in muscular tissue was 453, and −10° G was found to immobilize them. The observed difference seems to be mainly due to the cryoprotective properties of serum.