Heat Stress Responses in Cultured Plant Cells : Heat Tolerance Induced by Heat Shock versus Elevated Growing Temperature

Using cultured pear (Pyrus communis cv Bartlett) cells, heat tolerance induced by heat shock was compared to that developed during growth at high temperature. After growth at 22°C, cells exposed to 38°C for 20 minutes (heat shock) showed maximum increased tolerance within 6 hours. Cells grown at 30°C developed maximum heat tolerance after 5 to 6 days; this maximum was well below that induced by heat shock. Heat shock-induced tolerance was fully retained at 22°C for 2 days and was only partly lost after 4 days. However, pear cells acclimated at 30°C lost all acquired heat tolerance 1 to 2 days after transfer to 22°C. In addition, cells which had been heat-acclimated by growth at 30°C showed an additional increase in heat tolerance in response to 39°C heat shock. The most striking difference between heat shock and high growth temperature effects on heat tolerance was revealed when tolerance was determined using viability tests based on different cell functions. Growth at 30°C produced a general hardening, i.e. increased heat tolerance was observed with all three viability tests. In contrast, significantly increased tolerance of heat-shocked cells was observed only with the culture regrowth test. The two types of treatment evoke different mechanisms of heat acclimation.     

Responses of the bed bug,Cimex lectularius,to temperature extremes and dehydration: levels of tolerance,rapid cold hardening and expression of heat shock proteins

This study of the bed bug, Cimex lectularius, examines tolerance of adult females to extremes in temperature and loss of body water. Although the supercooling point (SCP) of the bed bugs was approximately −20°C, all were killed by a direct 1 h exposure to −16°C. Thus, this species cannot tolerate freezing and is killed at temperatures well above its SCP. Neither cold acclimation at 4°C for 2 weeks nor dehydration (15% loss of water content) enhanced cold tolerance. However, bed bugs have the capacity for rapid cold hardening, i.e. a 1‐h exposure to 0°C improved their subsequent tolerance of −14 and −16°C. In response to heat stress, fewer than 20% of the bugs survived a 1‐h exposure to 46°C, and nearly all were killed at 48°C. Dehydration, heat acclimation at 30°C for 2 weeks and rapid heat hardening at 37°C for 1 h all failed to improve heat tolerance. Expression of the mRNAs encoding two heat shock proteins (Hsps), Hsp70 and Hsp90, was elevated in response to heat stress, cold stress and during dehydration and rehydration. The response of Hsp90 was more pronounced than that of Hsp70 during dehydration and rehydration. Our results define the tolerance limits for bed bugs to these commonly encountered stresses of temperature and low humidity and indicate a role for Hsps in responding to these stresses.     

Effects of acclimation on the thermal tolerance of the brown planthopper Nilaparvata lugens (Stål)

相似文献   

Effects of alternating exposure to cold and heat for 14 days on cold tolerance in winter

People are exposed to heat regularly due to their jobs or daily habits in cold winter, but few studies have reported whether parallel heat and cold exposure and diminish cold acclimation. This study was conducted to investigate the effects of alternating exposure to cold and heat on cold tolerance in eight young males. A daily acclimation program to cold and heat, which consisted of 2-h sitting at 10 °C air in the morning and 2-h running and rest at 30 °C air in the afternoon, was conducted for 14 consecutive days. Eight male subjects participated in a cold tolerance test (10 °C [ ± 0.3], 40%RH[ ± 3]) before (PRE) and after (POST) completing the alternating exposure program. During the cold tolerance test, subjects remained sitting upright on a chair for 60 min. Rectal temperature (T_re) was lower in POST than in PRE during the 60-min cold tolerance test (P = 0.027). During the cold tolerance test, systolic, diastolic, and mean arterial blood pressures in POST were lower than those in PRE (P = 0.006, P = 0.005, and P = 0.004). No significant differences in skin temperatures between PRE and POST were found for the cold tolerance test. There were no significant differences in energy expenditure during cold exposure between PRE and POST. Subjects felt less cold in POST than in PRE (P = 0.013) whereas there was no significant difference in overall thermal comfort between PRE and POST. These results suggest that cold adaptation can still occur in the presence of heat stress.     

Altering flux through the sucrose biosynthesis pathway in transgenic Arabidopsis thaliana modifies photosynthetic acclimation at low temperatures and the development of freezing tolerance

To test the hypothesis that the up‐regulation of sucrose biosynthesis during cold acclimation is essential for the development of freezing tolerance, the acclimation responses of wild‐type (WT) Arabidopsis thaliana (Heynh.) were compared with transgenic plants over‐expressing sucrose phosphate synthase (over‐sps) or with antisense repression of either cytosolic fructose‐1,6‐bisphosphatase (antifbp) or sucrose phosphate synthase (antisps). Plants were grown at 23 °C and then shifted to 5 °C. The leaves shifted to 5 °C for 10 d and the new leaves that developed at 5 °C were compared with control leaves on plants at 23 °C. Plants over‐expressing sucrose phosphate synthase showed improved photosynthesis and increased flux of fixed carbon into sucrose when shifted to 5 °C, whereas both antisense lines showed reduced flux into soluble sugars relative to WT. The improved photosynthetic performance by the over‐sps plants shifted to 5 °C was associated with an increase in freezing tolerance relative to WT (?9.1 and ?7.2 °C, respectively). In contrast, both antisense lines showed impaired development of freezing tolerance (? 5.2 and ?5.8 °C for antifbp and antisps, respectively) when shifted to 5 °C. In the new leaves developed at 5 °C the recovery of photosynthesis as typically seen in WT was strongly inhibited in both antisense lines and this inhibition was associated with a further failure of both antisense lines to cold acclimate. Thus, functional sucrose biosynthesis at low temperature in the over‐sps plants reduced the inhibition of photosynthesis, maintained the mobilization of carbohydrates from source leaves to sinks and increased the rate at which freezing tolerance developed. Modification of sucrose metabolism therefore represents an additional approach that will have benefits both for the development of freezing tolerance and over‐wintering, and for the supply of exportable carbohydrate to support growth at low temperatures.     

The role of the photosynthetic apparatus in cold acclimation of <Emphasis Type="Italic">Lolium multiflorum</Emphasis>. Characteristics of novel genotypes low-sensitive to PSII over-reduction

During cold acclimation by higher plants, temperature perception via changes in redox state of Photosystem II (PSII) and subsequent acclimation of the photosynthetic apparatus to cold is very important for achieving freezing tolerance. These properties were studied in two groups (A and B) of the same backcross 3 (BC₃) progeny derived from a triploid hybrid of Festuca pratensis (2×) × Lolium multiflorum (4×) backcrossed three times onto diploid L. multiflorum cultivars. Leaves of Group A plants formed at 20°C at medium-low light were unable to acclimate their photosynthetic apparatus to cold. Compared to Group B, the Group A plants were also more frost sensitive. This acclimation ability correlated with the freezing tolerance of the plants. However, leaves of the same Group A plants developed at 20°C, but under higher-light conditions had increased ability to acclimate their photosynthetic apparatus to cold. It was concluded that Group A plants may have impaired PSII temperature perception, and this then resulted in their poor capability to cold acclimate.     

Plant Cold Acclimation: The Role of Abscisic Acid

The freezing tolerance or cold acclimation of plants is enhanced over a period of time by temperatures below 10°C and by a short photoperiod in certain species of trees and grasses. During this process, freezing tolerance increases 2–8°C in spring annuals, 10–30°C in winter annuals, and 20–200°C in tree species. Gene upregulation and downregulation have been demonstrated to be involved in response to environmental cues such as low temperature. Evidence suggests ABA can substitute for the low temperature stimulus, provided there is also an adequate supply of sugars. Evidence also suggests there may be ABA-dependent and ABA-independent pathways involved in the acclimation process. This review summarizes the role of ABA in cold acclimation from both a historical and recent perspective. It is concluded that it is highly unlikely that ABA regulates all the genes associated with cold acclimation; however, it definitely regulates many of the genes associated with an increase in freezing tolerance.     

Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.     

Cold acclimation in warmer extended autumns impairs freezing tolerance of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense)

The effect of variable autumn temperatures in combination with decreasing irradiance and daylength on photosynthesis, growth cessation and freezing tolerance was investigated in northern‐ and southern‐adapted populations of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense) intended for use in regions at northern high latitudes. Plants were subjected to three different acclimation temperatures; 12, 6 and 9/3°C (day/night) for 4 weeks, followed by 1 week of cold acclimation at 2°C under natural light conditions. This experimental setup was repeated at three different periods during autumn with decreasing sums of irradiance and daylengths. Photoacclimation, leaf elongation and freezing tolerance were studied. The results showed that plants cold acclimated during the period with lowest irradiance and shortest day had lowest freezing tolerance, lowest photosynthetic activity, longest leaves and least biomass production. Higher acclimation temperature (12°C) resulted in lower freezing tolerance, lower photosynthetic activity, faster leaf elongation rate and higher biomass compared with the other temperatures. Photochemical mechanisms were predominant in photoacclimation. The northern‐adapted populations had a better freezing tolerance than the southern‐adapted except when grown during the late autumn period and at the highest temperature; then there were no differences between the populations. Our results indicate that the projected climate change in the north may reduce freezing tolerance in grasses as acclimation will take place at higher temperatures and shorter daylengths with lower irradiance.     

Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing-tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing-tolerant Solanum commersonii (LT₅₀=-4.6°C) and -sensitive S. tuberosum (LT₅₀=-3.0°C). The distribution of non-acclimated freezing tolerance (NA-freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA-freezing tolerance. When a population of 25 genotypes was tested both for NA-freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA-freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA-freezing sensitive genotypes (2022) (LT₅₀=-3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA-freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA-freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA-freezing tolerance and AC (R =-0.05) in the S1 population points to independent genetic control of NA-freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold-acclimated plants compared to non-acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing-tolerant genotype.     

Modification of the intracellular sugar content alters the incidence of freeze-induced membrane lesions of protoplasts isolated from Arabidopsis thaliana leaves

Sugar content and freezing tolerance of protoplasts of Arabidopsis thaliana leaves were manipulated by incubating seedlings in a sucrose solution before protoplast isolation. Incubation in a 400 mM sucrose solution at 2 °C in the dark increased their freezing tolerance equivalent to that achieved after a conventional cold acclimation at 2 °C. The increased freezing tolerance was due to a decrease in the incidence of freeze‐induced lesions: expansion‐induced lysis (EIL) between ?2 and ?4 °C and loss of osmotic responsiveness (LOR) between ?5 and ?12 °C. The concentration of sucrose in the incubation medium required to minimize the incidence of the lesions was substantially different: 10–35 mM for EIL and 30–400 mM for LOR. Incubation in the sucrose solution at 23 °C decreased LOR only at ?5 and ?6 °C but less than that incubated at 2 °C, and there was no effect on EIL. Incubation in sorbitol solutions at 2 °C also decreased LOR at ?5 and ?6 °C but much less than in the sucrose solution. These results suggest that low concentrations of sucrose act as a metabolic substrate for the low‐temperature‐induced alterations required for the amelioration of EIL and, at higher concentrations, sucrose has a direct cryoprotective effect to minimize LOR.     

Parallel study of thermal resistance and permeability barrier stability of Enterococcus faecalis as affected by salt composition,growth temperature and pre-incubation temperature

In this study Enterococcus faecalis cells were grown to stationary phase in various conditions resulting in strong but similar variations in both cellular thermoresistance and permeability barrier stability (the temperature T_m that induced rapid dissipation of the ion concentration gradient during constant heating). Cells grown at 17–22°C were heat sensitive and barrier labile whilst cells grown at 10–13°C and 42–47°C were heat resistant and barrier stable. The thermal resistance and barrier stability in heat-sensitive cells, compared to the same parameters in heat-resistant cells, remained low after an additional culture at 43–47°C, indicating a persistent effect of culture at 17–22°C. In cells grown at 10–13°C, these parameters were as low as they were in the heat-sensitive cells, provided the growth media contained an ammonium salt (1%) which thus abolished the cold acclimation. Both parameters were reduced in cells growth at increased salinity (1–3% Na and K salts) and the reduction was more pronounced during growth at 17–22°C. Moreover, cells pre-cultured at 21°C with increased salinity (3% NaCl) displayed strong phenotypic effect during subsequent culturing which reflected in a 6°C decrease in both the optimal temperature and maximal temperature of growth. Compared to other bacterial strains, only a part of the change in membrane stability could be related to the variations in fatty acid composition. The index of unsaturation changed in accordance with the barrier stability and survival of cells. These findings support the conclusion that stability of permeability barrier as affected by the growth temperature, presence of ammonium and cultural conditions of progenitor cells was involved in thermal sensitivity and temperature-acclimation of E. faecalis.     

Low temperature effects on growth and actin cytoskeleton organisation in suspension cells of winter oilseed rape

Rhodamine-phalloidin staining of winter oilseed rape suspension cells revealed that the structure of actin cytoskeleton changes with the phase of cell growth. In small, 4-day-old cells, entering the exponential phase of growth, a dense and uniformly distributed cortical microfilament networks was seen. In six-day-old vacuolated cells, which reached the stationary phase of growth, the actin cytoskeleton was composed of thicker microfilament cables in irregular arrangements. In cells acclimated in cold for 7 days a dense, uniformly distributed and cortical microfilament network was still seen. The fine microfilament network was sensitive to extracellular freezing since the structures underwent depolymerization at −3 °C (in the presence of extracellular ice), both in non-acclimated and cold-acclimated cells. The thicker transvacuolar cables in cells of the stationary growth phase resisted freezing to −7 °C. Acclimation of suspensions at 2 °C resulted in slowing down growth of cells and in the increased freezing tolerance of cells as indicated by a decrease of LT₅₀ from −11 °C to −17.5^o or to −25 °C when determined 7 or 20 days after the beginning of the cold treatment, respectively. Freezing tolerance of non-acclimated cells decreased from −11 °C to −8 °C during subculture, showing a transient increase to −17 °C on the day 6. Results indicate that the arrangement of actin microfilaments and their sensitivity to freezing-induced depolymerization depends on the phase of cell growth rather than on cell acclimation status. Possible mechanisms involved in the freezing-induced depolymerization of actin microfilaments are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cold acclimation induces freezing tolerance via antioxidative enzymes, proline metabolism and gene expression changes in two chrysanthemum species

Cold acclimation is necessary for chrysanthemum to achieve its genetically determined maximum freezing tolerance, but the underlying physiological and molecular mechanisms are unclear. The aim of this study was to discover whether changes in antioxidative enzymes, proline metabolism and frost-related gene expression induced by cold acclimation are related to freezing tolerance. Our results showed that the semi-lethal temperature (LT₅₀) decreased from ?7.3 to ?23.5 °C in Chrysanthemum dichrum and ?2.1 to ?7.1 °C in Chrysanthemum makinoi, respectively, after cold acclimation for 21 days. The activities of SOD, CAT and APX showed a rapid and transient increase in the two chrysanthemum species after 1 day of cold acclimation, followed by a gradual increase during the subsequent days and then stabilization. qRT-PCR analysis showed that the expression levels of some isozyme genes (Mn SOD, CAT and APX) were upregulated, which was consistent with the SOD, CAT and APX activities, while others remained relatively constant (Fe SOD and Cu/Zn SOD). P5CS and PDH expression were increased under cold acclimation and the level of P5CS presented similar trends as proline content, indicating proline accumulation was via P5CS and PDH cooperation. Cold acclimation also promoted DREB, COR413 and CSD gene expression. The activities of three enzymes and gene expression were higher in C. dichrum than in C. makinoi after cold acclimation. Our data suggested that cold-inducible freezing-tolerance could be attributed to higher activity of antioxidant enzymes, and increased proline content and frost-related gene expression during different periods.     

Heat Tolerance of Cold Acclimated Puma Winter Rye Seedlings and the Effect of a Heat Shock on Freezing Tolerance

An increase in tolerance to one form of abiotic stress oftenresults in an increase in tolerance to another stress. The heattolerance of Puma rye (Secale cereale) was determined for seedlingseither not cold hardened or hardened under either controlledenvironmental or natural conditions. The heat tolerance wasdetermined either as a function of time at 42°C or the abilityto tolerate a maximum temperature. The seedlings were eithernot heat preconditioned or heat preconditioned before the heatstress. In all cases cold hardened seedlings were more heattolerant than non or partially cold hardened seedlings. Heatpreconditioning had no effect on the heat tolerance of naturallycold hardened seedlings. In contrast, seedlings cold hardenedin a controlled environment chamber, then heat preconditioned,were more heat tolerant than non preconditioned seedlings. Aheat shock of 36°C for 2 h increased the freezing toleranceof non hardened seedlings from –2.5°C to –4.5°C.Analysis of heat shock protein 70 (HSP70) gene expression indicatedthat the HSP70 gene was not induced by cold acclimation andtherefore not directly involved in the increased thermo toleranceobserved. A number of heat stable proteins, simple sugars andlong chain carbohydrate polymers accumulated during the coldacclimation process and may have a role in increasing heat toleranceas well as freezing tolerance. These data suggest cold hardeningincreases heat tolerance, however, a heat shock to non acclimatedseedlings only marginally increased the freezing tolerance ofPuma rye seedlings. ³Present address: Agriculture and Agri-Food Canada, 107 SciencePlace, Saskatoon SK S7N 0X2, Canada.     

Cold-Induced Alterations in Plasma Membrane Proteins That are Specifically Related to the Development of Freezing Tolerance in Cold-Hardy Winter Wheat

The objective of this study was to identify plasma membraneproteins that are specifically induced by cold acclimation inwheat (Triticum aestivum L.). Two cultivars with a marked differencein the genetic ability to cold-acclimate, namely, spring wheat(cv. Chinese Spring) and winter wheat (cv. Norstar), were usedas the experimental material. After four weeks of growth ina cold chamber, the freezing tolerance in the shoots of winterwheat increased to –18°C, whereas it increased onlyto –8°C in the shoots of spring wheat. In the caseof roots from both cultivars, freezing tolerance increased onlyslightly after the growth in the cold environment. Cold acclimationinduced remarkable changes in the electrophoretic patterns ofplasma membrane proteins which depended on both the cultivarand the tissue examined. Levels of polypeptides with molecularmasses from 22 to 31 kDa decreased in both the root and shootplasma membranes from both cultivars. Among these polypeptides,levels of those of 28 and 26 kDa decreased abruptly after oneweek of cold acclimation. By contrast, levels of polypeptidesof 89, 83, 52, 23, 18 and 17 kDa increased specifically in theshoots of winter wheat. The increases in the levels of the 23-,18- and 17-kDa polypeptides were proportional to the developmentof freezing tolerance. Freeze-fracture electron microscopy ofplasma membranes from shoot cells revealed that the number ofintramembrane particles on the fracture faces decreased markedlyin winter wheat after cold acclimation, but to a lesser extentin spring wheat. These results suggest that the plasma membranesmight undergo molecular reorganization during cold acclimation. ¹Contribution no. 3709 from the Institute of Low TemperatureScience, Hokkaido University.