The effect of dormancy on the heat shock response in gladiolus cormels

Cormels of Gladiolus X gandavensis Van Houtte respond to heat shock by an induced synthesis of heat shock proteins. Synthesis of some of the non-heat shock proteins is concomitantly reduced. The ability of dormant cormels to synthesize heat shock proteins (hsps) and to repress the synthesis of non-hsps is greater than that of nondormant ones. A hsp of apparent molecular weight 68 kilodaltons is synthesized only in dormant cormels or in cormels that lost their dormancy after long storage at 25°C. The synthesis of hsps at 40°C, but not at 25°C, is promoted by abscisic acid in nondormant cormels. Methionine incorporation into hsps declines after a 4-hour incubation period at 40°C. Induction of hsps is stronger if exposure to extreme temperature is done gradually.     

Tissue specificity of the heat-shock response in maize

The tissue specificity of the heat-shock response in maize was investigated. The ability to synthesize heat shock proteins (hsp) at 40°C, as well as the intensity and duration of that synthesis, was analyzed in coleoptiles, scutella, green and etiolated leaves, suspension-cultured cells, germinating pollen grains, and primary root sections at different stages of development. One-dimensional sodium dodecyl sulfate gel electrophoresis of extracted proteins revealed that most of the tissues synthesized the typical set of 10 hsp, but that the exact characteristics of the response depended upon the tissue type. While elongating portions of the primary root exhibited a strong heat shock response, the more mature portions showed a reduced ability to synthesize hsp. Leaves, whether green or etiolated, excised or intact, constitutively synthesized a low level of hsp at 25°C, and high levels could be induced at 40°C. Suspension-cultures of Black Mexican sweet corn synthesized, besides the typical set of hsp, two additional polypeptides. In contrast to all the other tissues, germinating pollen grains could not be induced to synthesize the typical set of hsp but did synthesize two new polypeptides of 92 and 56 kD molecular weight.

The heat shock response was transient for most of the tissues which synthesized the standard set of hsp. Hsp synthesis was detected up to 2 to 3 hours, but not at 10 hours of continuous 40°C treatment. The exception was suspension cultured cells, in which hsp synthesis showed only a slight reduction after 10 hours at 40°C. Tissue-specific differences in the heat-shock response suggest that there are differences in the way a given tissue is able to adapt to high temperature.

We have confirmed the previous suggestion that maize hsp do not accumulate in substantial quantities. Using two-dimensional gel analysis, hsp could be detected by autoradiography but not by sensitive silver staining techniques.

     

Effect of temperature conditioning on chilling injury of cucumber cotyledons: possible role of abscisic Acid and heat shock proteins

Endogenous abscisic acid levels and induced heat shock proteins were measured in tissue exposed for 6 hours to temperatures that reduced their subsequent chilling sensitivity. One-centimeter discs excised from fully expanded cotyledons of 11-day-old seedlings of cucumber (Cucumis sativus L., cv Poinsett 76) were exposed to 12.5 or 37°C for 6 hours followed by 4 days at 2.5 or 12.5°C. Ion leakage, a qualitative indicator of chilling injury, increased after 2 to 3 day exposure to 2.5°C, but not to 12.5°C, a nonchilling temperature. Exposure to 37°C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.5°C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 or 37°C and held at the nonchilling temperature of 12.5°C. There was no relationship between abscisic acid content following exposure to 12.5 or 37°C and chilling tolerance. Five heat shock proteins, with apparent molecular mass of 25, 38, 50, 70, and 80 kilodaltons, were induced by exposure to 37 or 42°C for 6 hours, and their appearance coincided with increased chilling resistance. Heat shock treatments reduced the synthesis of three proteins with apparent molecular mass of 14, 17, and 43 kilodaltons. Induction of heat shock proteins could be a possible cause of reduced chilling injury in tissue exposed to 37 or 42°C.     

Interaction of heat and salt shock in cultured tobacco cells

Cultured tobacco cells (Nicotiana tabacum L. var Wisconsin-38) developed tolerance to otherwise nonpermissive 54°C treatment when heat-shocked at 38°C (2 h) but not at 42°C. Heat-shocked cells (38°C) exhibited little normal growth when the 54°C stress came immediately after heat shock and normal growth when 54°C stress was administered 8 hours after heat shock. Heat shock extended the length of time that the cells tolerated 54°C. Tobacco cells developed tolerance to otherwise lethal 2% NaCl treatment when salt-shocked (1.2% NaCl for 3 hours). The time course for salt tolerance development was similar to that of thermotolerance. Heat-shocked cells (38°C) developed tolerance of nonpermissive salt stress 8 hours after heat shock. Alternatively, cells heat-shocked at 42°C exhibited immediate tolerance to lethal salt stress followed by a decline over 8 hours. Radioactive methionine incorporation studies demonstrated synthesis of heat shock proteins at 38°C. The apparent molecular weights range from 15 to 115 kilodaltons with a protein complex in the 15 to 20 kilodalton range. Synthesis of heat shock proteins appeared to persist at 42°C but with large decreases in incorporation into selected heat shock protein. During salt shock, the synthesis of normal control proteins was reduced and a group of salt shock proteins appeared 3 to 6 h after shock. Similarities between the physiology and salt shock proteins/heat shock proteins suggest that both forms of stress may share common elements.     

Accumulation of heat shock proteins in field-grown cotton

Cotton (Gossypium hirsutum L.) plants grown under field water deficits exhibited an 80 to 85% reduction in leaf area index, plant height, and dry matter accumulation compared with irrigated controls. Midday photosynthetic rates of dryland plants decreased 2-fold, and canopy temperatures increased to 40°C at 80 days after planting compared with canopy temperatures of 30°C for irrigated plants. Leaves from dryland plants which had exhibited canopy temperatures of 40°C for several weeks accumulated stainable levels of polypeptides with apparent molecular weights of 100, 94, 89, 75, 60, 58, 37, and 21 kilodaltons. These polypeptides did not accumulate in leaves from irrigated plants.

Addition of [³⁵S]methionine to leaves of growth chamber-grown cotton plants and subsequent incubation at 40°C for 3 hours radiolabeled polypeptides with molecular weights similar to those that accumulate in dryland cotton leaves. These data suggest that the proteins which accumulate in water-stressed cotton leaves at elevated temperatures (40°C) are heat shock proteins and that these proteins can accumulate to substantial levels in field-stressed plants.

     

Heat Shock Proteins and Their mRNAs in Dry and Early Imbibing Embryos of Wheat

Two-dimensional gels of in vitro translation products of mRNAs isolated from quiescent wheat (Triticum aestivum) embryos demonstrate the presence of mRNAs encoding heat shock proteins (hsps). There were no detectable differences in the mRNAs found in mature embryos from field grown, from 25°C growth chamber cultivated, or from plants given 38°C heat stresses at different stages of seed development. The mRNAs encoding several developmentally dependent (dd) hsps were among those found in the dry embryos. Stained two-dimensional gels of proteins extracted from 25°C growth chamber cultivated wheat embryos demonstrated the presence of hsps, including dd hsps. A study of the relationship of preexisting hsp mRNAs and the heat shock response during early imbibition was undertaken. Heat shocks (42°C, 90 minutes) were administered following 1.5, 16, and 24 hours of 25°C imbibition. While the mRNAs encoding the low molecular weight hsps decayed rapidly upon imbibition, the mRNAs for dd hsps persisted longer and were still detectable following 16 hours of imbibition. After 1.5 hours of imbibition, the mRNAs for the dd hsps did not accumulate in response to heat shock, even though the synthesis of the proteins was enhanced. Thus, an applied heat shock appeared to lead to the preferential translation of preexisting dd hsp mRNAs. The mRNAs for the other hsps, except hsp 70, were newly transcribed at all of the imbibition times examined. The behavior of the hsp 70 group of proteins during early imbibition was examined by RNA gel blot analysis. The mRNAs for the hsp 70 group were detectable at moderate levels in the quiescent embryo. The relative level of hsp 70 mRNA increased after the onset of imbibition at 25°C and remained high through 25.5 hours of prior imbibition. The maximal levels of these mRNAs at 25°C was reached at 17.5 hours of imbibition. Heat shock caused modest additional accumulation of hsp70 mRNA at later imbibition times.     

Ubiquitin Pool Modulation and Protein Degradation in Wheat Roots during High Temperature Stress

Ubiquitin, a key component in an ATP-dependent proteolytic pathway, participates in the response of various eucaryotic organisms to high temperature stress. Our objective was to determine if ubiquitin serves a similar capacity for metabolizing altered proteins in higher plants during stress. Degradation of total proteins was measured, and ubiquitin pools (free versus conjugated) were extracted with an improved protocol from wheat (Triticum aestivum L. cv Len) roots treated at 22, 27, 32, 37, and 42°C for 1 hour and assayed by western blots and radioimmunoassays. Heat-shock protein synthesis was detected by in vivo labeling and autoradiography. Mean half-life of total root proteins decreased from 51 hours at 22°C to 23 hours at 40°C. Ubiquitin pools were extracted better and proteolysis was slowed more by the improved protocol than by a conventional procedure for plant proteins. Amounts of high molecular mass conjugates were elevated and levels of low molecular mass conjugates and free ubiquitin were depressed when roots were treated at 37 or 42°C than at lower temperatures; the same high temperatures also induced synthesis of heat-shock proteins. We concluded that high temperatures increase breakdown of root proteins, which are degraded via the ubiquitin proteolytic pathway. A conjugate with an apparent molecular mass of 23 kilodaltons was tentatively identified as an ubiquitinated histone.     

Protein Synthesis in Bromegrass (Bromus inermis Leyss) Cultured Cells during the Induction of Frost Tolerance by Abscisic Acid or Low Temperature

Bromus inermis Leyss cell cultures treated with 75 micromolar abscisic acid (ABA) at both 23 and 3°C developed more freezing resistance than cells cultured at 3°C. Protein synthesis in cells induced to become freezing tolerant by ABA and low temperature was monitored by [¹⁴C]leucine incorporation. Protein synthesis continued at 3°C, but net cell growth was stopped. Most of the major proteins detected at 23°C were synthesized at 3°C. However, some proteins were synthesized only at low temperatures, whereas others were inhibited. ABA showed similar effects on protein synthesis at both 23 and 3°C. Comparative electrophoretic analysis of [¹⁴C]leucine labeled protein detected the synthesis of 19, 21 and 47 kilodalton proteins in less than 8 hours after exposure to exogenous ABA. Proteins in the 20 kilodalton range were also synthesized at 3°C. In addition, a 31 kilodalton protein band showed increased expression in freezing resistant ABA treated cultures after 36 hours growth at both 3 and 23°C. Quantitative analysis of [¹⁴C]leucine labeled polypeptides in two-dimensional gels confirmed the increased expression of the 31 kilodalton protein. Two-dimensional analysis also resolved a 72 kilodalton protein enriched in ABA treated cultures and identified three proteins (24.5, 47, and 48 kilodaltons) induced by low temperature growth.     

Corn mitochondrial protein synthesis in response to heat shock

Corn (Zea mays L., W23(N), OH43(N), and reciprocal single cross hybrid) seedling mitochondria respond to a 10°C temperature shift (27-37°C) by incorporating a greater amount of [³⁵S]methionine into acid-insoluble material than mitochondria incubated at the original growing temperature (27°C). This increase is in part manifested in the enhanced synthesis of a 52 kilodaltons protein. At both temperatures mitochondria of two inbreds and their reciprocal hybrids synthesize normal (N) cytoplasm proteins sensitive to chloramphenicol and insensitive to cyclohexamide treatment. The 52 kilodaltons protein is found in the supernatants of pelleted (15,000g, 5 min) mitochondria after heat shock. The role of this protein in the heat shock response is discussed in light of the implication of mitochondria as the primary cellular target to temperature stress.     

Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Decoated pepper (Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds. The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C.

The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons.

Application of gibberellic acid₄₊₇ (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high O₂ concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid₄₊₇, but only at 25°C. At 15°C, high O₂ concentrations slowed germination and endosperm strength decline.

     

Long-lived and short-lived heat-shock proteins in tobacco mesophyll protoplasts

We have studied modifications in the pattern of proteins synthesized by tobacco (Nicotiana tabacum var Maryland) mesophyll protoplasts when they are transferred from 25°C to 40°C. The synthesis of one group of proteins is practically unaffected by the heat shock. On the other hand, the synthesis of most other 25°C proteins is greatly reduced, while specific heat-shock proteins appear: 17 stable, neutral, major proteins, which are synthesized throughout the culture period at the higher temperature and which correspond to those observed in other organisms, and two basic proteins with a short lifetime and which are synthesized only during the first 2 hours of heat shock. We suggest that these latter proteins are regulatory peptides which intervene in the inhibition of 25°C syntheses.     

Partial Purification and Characterization of Two Hydrogenases from the Extreme Thermophile Methanococcus jannaschii

F₄₂₀-nonreactive and F₄₂₀-reactive hydrogenases have been partially purified from Methanococcus jannaschii, an extremely thermophilic methanogen isolated from a submarine hydrothermal vent. The molecular weights of both hydrogenases were determined by native gradient electrophoresis in 5 to 27% polyacrylamide gels. The F₄₂₀-nonreactive hydrogenase produced one major band (475 kilodaltons), whereas the F₄₂₀-reactive hydrogenase produced two major bands (990 and 115 kilodaltons). The F₄₂₀-nonreactive hydrogenase consisted of two subunits (43 and 31 kilodaltons), and the F₄₂₀-reactive hydrogenase contained three subunits (48, 32, and 25 kilodaltons). Each hydrogenase was active at very high temperatures. Methyl viologen-reducing activity of the F₄₂₀-nonreactive hydrogenase was maximal at 80°C but was still detectable at 103°C. The maximum activities of F₄₂₀-reactive hydrogenase for F₄₂₀ and methyl viologen were measured at 80 and 90°C, respectively. Low but measureable activity toward methyl viologen was repeatedly observed at 103°C. Moreover, the half-life of the F₄₂₀-nonreactive hydrogenase at 70°C was over 9 h, and that of the F₄₂₀-reactive enzyme was over 3 h.     

Characterization of the heat shock response in cultured sugarcane cells : I. Physiology of the heat shock response and heat shock protein synthesis

Effect of heat shock on the growth of cultured sugarcane cells (Saccharum officinarum L.) was measured. Heat shock (HS) treatment at 36 to 38°C (2 hours) induced the development of maximum thermotolerance to otherwise nonpermissive heat stress at 54°C (7 minutes). Optimum thermotolerance was observed 8 hours after heat shock. Development of thermotolerance was initiated by treatments as short as 30 minutes at 36°C. Temperatures below 36°C or above 40°C failed to induce maximum thermotolerance. In vivo labeling revealed that HS at 32 to 34°C induced several high molecular mass heat shock proteins (HSPs). A complex of 18 kilodalton HSPs required at least 36°C treatment for induction. The majority of the HSPs began to accumulate within 10 minutes, whereas the synthesis of low molecular mass peptides in the 18 kilodalton range became evident 30 minutes after initiation of HS. HS above 38°C resulted in progressively decreased HSP synthesis with inhibition first observed for HSPs larger than 50 kilodaltons. Analysis of two-dimensional gels revealed a complex pattern of label incorporation including the synthesis of four major HSPs in the 18 kilodalton range and continued synthesis of constitutive proteins during HS.     

Interaction of Fusarium oxysporum f. sp. ciceri and Meloidogyne javanica on Cicer arietinum

Interaction of Meloidogyne javanica and Fusarium oxysporum f. sp. ciceri was studied on Fusarium wilt-susceptible (JG 62 and K 850) and resistant (JG 74 and Avrodhi) chickpea cultivars. In greenhouse experiments, inoculation of M. javanica juveniles prior to F. oxysporum f. sp. ciceri caused greater wilt incidence in susceptible cultivars and induced vascular discoloration in roots of resistant cultivars. Nematode reproduction was greatest (P = 0.05) at 25 °C. Number of galls and percentage of root area galled increased when the temperature was increased from 15 °C to 25 °C. Wilt incidence was greater at 20 °C than at 25 °C. Chlorosis of leaves and vascular discoloration of plants did not occur at 15 °C. The nematode enhanced the wilt incidence in wilt-susceptible cultivars only at 25 °C. Interaction between the two pathogens on shoot and root weights was significant only at 20 °C, and F. o. ciceri suppressed the nematode density at this temperature. Wilt incidence was greater in clayey (48% clay) than in loamy sand (85% sand) soils. The nematode caused greater plant damage on loamy sand than on clayey soil. Fusarium wilt resistance in Avrodhi and JG 74 was stable in the presence of M. javanica across temperatures and soil types.     

Characterization of the Heat Shock Response in Lactococcus lactis subsp. lactis

The heat shock response in Lactococcus lactis subsp. lactis was characterized with respect to synthesis of a unique set of proteins induced by thermal stress. A shift in temperature from 30 to 42°C was sufficient to arrest the growth of L. lactis subsp. lactis, but growth resumed after a shift back to 30°C. Heat shock at 50°C reduced the viable cell population by 10³; however, pretreatment of the cells at 42°C made them more thermoresistant to exposure at 50°C. The enhanced synthesis of approximately 13 proteins was observed in cells labeled with ³⁵S upon heat shock at 42°C. Of these heat shock-induced proteins, two appeared to be homologs of GroEL and DnaK, based on their molecular weights and reactivity with antiserum against the corresponding Escherichia coli proteins. Therefore, we conclude that L. lactis subsp. lactis displays a heat shock response similar to that observed in other mesophilic bacteria.     

Identification of Proteins Correlated with Increased Freezing Tolerance in Bromegrass (Bromus inermis Leyss. cv Manchar) Cell Cultures

Cellular and extracellular protein profiles from Bromus inermis Leyss. cv Manchar cell suspension cultures cold hardened by low temperature and abscisic acid (ABA) treatment were analyzed by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. Cellular proteins (25, 165, 190, and 200 kilodaltons) increased by low temperature growth and cellular proteins (20, 25, 28, 30, 32, 37, 40, 45, 200 kilodaltons) increased by exogenous ABA treatment were identified. Low temperature treatment inhibited the synthesis of a 22 kilodalton protein and ABA treatment resulted in the synthesis of two extracellular proteins (17 and 21 kilodaltons). Low temperature and ABA-induced hardening conditions increased or induced a 25 and a 200 kilodalton protein. The 25 and a 30 kilodalton protein previously shown to be enriched by ABA-induced hardening conditions at both 3 and 23°C temperatures co-fractionated with the crude membrane fraction (30,000g sediment). The 200 kilodalton protein was detected in the 30,000g supernatant. Two-dimensional analysis of the crude membrane fraction resolved the 30 kilodalton protein band into a major polypeptide with an apparent isoelectric point of 6.85.     

Acquisition of Thermotolerance in Soybean Seedlings : Synthesis and Accumulation of Heat Shock Proteins and their Cellular Localization

When soybean Glycine max var Wayne seedlings are shifted from a normal growth temperature of 28°C up to 40°C (heat shock or HS), there is a dramatic change in protein synthesis. A new set of proteins known as heat shock proteins (HSPs) is produced and normal protein synthesis is greatly reduced. A brief 10-minute exposure to 45°C followed by incubation at 28°C also results in the synthesis of HSPs. Prolonged incubation (e.g. 1-2 hours) at 45°C results in greatly impaired protein synthesis and seedling death. However, a pretreatment at 40°C or a brief (10-minute) pulse treatment at 45°C followed by a 28°C incubation provide protection (thermal tolerance) to a subsequent exposure at 45°C. Maximum thermoprotection is achieved by a 2-hour 40°C pretreatment or after 2 hours at 28°C with a prior 10-minute 45°C exposure. Arsenite treatment (50 micromolar for 3 hours) also induces the synthesis of HSP-like proteins, and also provides thermoprotection to a 45°C HS; thus, there is a strong positive correlation between the accumulation of HSPs and the acquisition of thermal tolerance under a range of conditions.

During 40°C HS, some HSPs become localized and stably associated with purified organelle fractions (e.g. nuclei, mitochondria, and ribosomes) while others do not. A chase at 28°C results in the gradual loss over a 4-hour period of the HSPs from the organelle fractions, but the HSPs remain selectively localized during a 40°C chase period. If the seedlings are subjected to a second HS after a 28°C chase, the HSPs rapidly (complete within 15 minute) relocalize in the organelle fractions. The relative amount of the HSPs which relocalize during a second HS increases with higher temperatures from 40°C to 45°C. Proteins induced by arsenite treatment are not selectively localized with organelle fractions at 28°C but become organelle-associated during a subsequent HS at 40°C.

     

Induction of freezing tolerance in spinach is associated with the synthesis of cold acclimation induced proteins

Spinach (Spinacia oleracea L. cv Bloomsdale) seedlings cultured in vitro were used to study changes in protein synthesis during cold acclimation. Seedlings grown for 3 weeks postsowing on an inorganic-nutrient-agar medium were able to increase their freezing tolerance when grown at 5°C. During cold acclimation at 5°C and deacclimation at 25°C, the kinetics of freezing tolerance induction and loss were similar to that of soil-grown plants. Freezing tolerance increased after 1 day of cold acclimation and reached a maximum within 7 days. Upon deacclimation at 25°C, freezing tolerance declined within 1 day and was largely lost by the 7th day. Leaf proteins of intact plants grown at 5 and 25°C were in vivo radiolabeled, without wounding or injury, to high specific activities with [³⁵S]methionine. Leaf proteins were radiolabeled at 0, 1, 2, 3, 4, 7, and 14 days of cold acclimation and at 1, 3, and 7 days of deacclimation. Up to 500 labeled proteins were separated by two-dimensional gel electrophoresis and visualized by fluorography. A rapid and stable change in the protein synthesis pattern was observed when seedlings were transferred to the low temperature environment. Cold-acclimated leaves contained 22 polypeptides not found in nonacclimated leaves. Exposure to 5°C induced the synthesis of three high molecular weight cold acclimation proteins (CAPs) (M_r of about 160,000, 117,000, and 85,000) and greatly increased the synthesis of a fourth high molecular weight protein (M_r 79,000). These proteins were synthesized during day 1 and throughout the 14 day exposure to 5°C. During deacclimation, the synthesis of CAPs 160, 117, and 85 was greatly reduced by the first day of exposure to 25°C. However, CAP 79 was synthesized throughout the 7 day deacclimation treatment. Thus, the induction at low temperature and termination at warm temperature of the synthesis of CAPs 160, 117, and 85 was highly correlated with the induction and loss of freezing tolerance. Cold acclimation did not result in a general posttranslational modification of leaf proteins. Most of the observed changes in the two-dimensional gel patterns could be attributed to the de novo synthesis of proteins induced by low temperature. In spinach leaf tissue, heat shock altered the pattern of protein synthesis and induced the synthesis of several heat shock proteins (HSPs). One polypeptide synthesized in cold-acclimated leaves had a molecular weight and net charge (M_r 79,000, pI 4.8) similar to that of a HSP (M_r 83,000, pI 4.8). However, heat shock did not increase the freezing tolerance, and cold acclimation did not increase heat tolerance over that of nonacclimated plants, but heat-shocked leaf tissue was more tolerant to high temperatures than nonacclimated or cold-acclimated leaf tissue. When protein extracts from heat-shocked and cold-acclimated leaves were mixed and separated in the same two-dimensional gel, the CAP and HSP were shown to be two separate polypeptides with slightly different isoelectric points and molecular weights.     

Concomitant changes in high temperature tolerance and heat-shock proteins in desert succulents

Raising the day/night air temperatures from 30°C/20°C to 50°C/40°C increases the high temperature tolerated by Agave deserti, Carnegiea gigantea, and Ferocactus acanthodes by 6°C to 8°C; the increase is about half completed in 3 days and fully completed in 10 days. A 25 to 27 kilodalton protein concomitantly accumulates for all three desert succulents upon transfer to 50°C/40°C, while accumulation of other heat “heat-shock” proteins is species specific. Some of the induced proteins are more abundant at 3 days, while others (including the 25-27 kilodalton protein) remain after completion of high temperature acclimation.