Analysis of Some Barley Chlorophyll Mutants and Their Response to Temperature Stress

Six barley chlorophyll (Chl) mutants, viridis, flavoviridis, chlorina, xanhta, lutea, and albina, differed in the contents of Chl (a+b) and carotenoids (Cars). In accordance with their Chl-deficient phenotype, the Chl a and b and Car contents of mutants decreased from viridis to albina, only xantha had the same or even higher concentration of Cars as the wild type plant. The albina mutant completely lacked and xantha had a significantly reduced photosynthetic activity. We found quantitative differences in protein contents between wild type and mutant plants, with the lowest concentration per fresh mass in the albina mutant. Chl fluorescence analysis revealed that heat-treated barley leaves of both the wild type and Chl mutants had a lower photosystem 2 efficiency than the untreated ones. With ³⁵S-methionine labelling and SDS-PAGE we found that six to nine de novo synthetized proteins appeared after heat shock (2 h, 42 °C) in the wild type and Chl mutants. In albina the expression of heat shock proteins (HSPs) was reduced to 50 % of that in the wild type. Hence mainly albina mutants, with a completely destroyed proteosynthetic apparatus of the chloroplasts, are able to synthesize a small set of HSPs. The albina mutant is a very useful tool for the study of different gene expression of chloroplast and nuclear DNA.     

Heat shock tolerance and antioxidant activity in moth bean seedlings treated with tetcyclacis

Moth bean (Vigna aconitifolia (Jacq.) Marechal cv. Jaadia) seeds were germinated in the presence of 0, 18, or 36 M solutions of the gibberellin biosynthesis inhibitor, tetcyclacis. After 72 h, seedlings were exposed to 22 or 48°C for 90 min. The 48°C temperature dramatically increased total electrolyte and sugar leakage from the seedlings, particularly in the controls. Tetcyclacis reduced electrolyte and sugar leakage at 48°C by 15–35% compared to the 48°C controls. High temperature increased malondialdehyde concentration in control seedlings but not in treated seedlings indicating that tetcyclacis inhibited high temperature-induced lipid peroxidation. Relative to the control, tetcyclacis tended to increase the total activities of catalase and peroxidase in the seedlings. In contrast, tetcyclacis tended to decrease ascorbic acid oxidase activity, particularly at 48°C. These results suggest that tetcyclacis conferred at least some heat shock tolerance to moth bean seedlings. This increased tolerance was correlated with increased activities of some antioxidant systems.     

Growth and macromolecular synthesis phenotypes of a heat-sensitive mutant strain, rip-1, of Neurospora crassa

Summary A heat-sensitive mutant of Neurospora crassa, strain 4M(t), was isolated using ultraviolet-light mutagenesis followed by the inositol-less death enrichment technique. The heat-sensitivity is the result of a single gene mutation which maps to the distal end of the right arm of linkage group II. The mutation defines the rip-1 gene locus. Both conidial germination and mycelial extension are inhibited in the mutant at 35°C and above (the nonpermissive temperature) but prolonged incubation at that temperature is not lethal to either cell type. Analysis of the lateral mycelial growth rates of wild type and of the rip-1 mutant at a variety of temperatures between 10 and 40°C indicated that the maximal growth rate occurs at 35°C in the wild type, and at 25°C in the rip-1 strain. The rip-1 mutant grows 239-times slower at 35°C than at 25°C, whereas the wild type grows 1.4-times faster. Temperature shift-up experiments showed that even 3 h at 20°C is not sufficient to allow germination at 37°C, thereby showing that the mutant cannot accumulate enough heat-sensitive product at the permissive temperature to contribute to germination at 37°C. The reciprocal temperature shift-down experiments showed that the molecular events at 37°C may be qualitatively useful for germination after shifting to 20°C. Studies of macromolecular synthesis showed that the biochemical defect in the heat-sensitive strain appears to affect RNA synthesis before protein synthesis, although there were differences in the relative effects depending on the age of the germinating conidia and the inhibition of the two processes was never complete. Messenger RNA synthesis is normal in the mutant at 37°C. Previous work has shown that the rip-1 mutant strain has a conditional defect in the accumulation of 25S rRNA and, hence, in 60S ribosomal subunit production (Loo et al. 1981). There are also indications from those studies that the 60S ribosomal subunit may be functionally impaired at the higher temperature. Thus, the growth and macromolecular synthesis phenotypes may result as a consequence of a conditional, ribosome function defect and leads to the hypothesis that the mutation in the rip-1 strain may be in a gene for a 60S ribosomal subunit component, perhaps a ribosomal protein.     

Effect of constant temperatures on germination, radial growth and virulence of Metarhizium anisopliae to three species of African tephritid fruit flies

The effect of temperatureon conidial germination, mycelial growth, andsusceptibility of adults of three tephritidfruit flies, Ceratitis capitata(Wiedemann), C. fasciventris (Bezzi) andC. cosyra (Walker) to six isolatesof Metarhizium anisopliae were studied inthe laboratory. There were significantdifferences among the isolates in the effect oftemperature on both germination and growth.Over 80% of conidia germinated at 20, 25 and30°C, while between 26 and 67% conidiagerminated at 35°C and less than 10% at15°C within 24 hours. Radial growth was slowat 15°C and 35°C with all of theisolates. The optimum temperature forgermination and mycelial growth was 25°C. Mortality caused by the six fungal isolatesagainst the three fruit fly species varied withtemperature, isolate, and fruit fly species.Fungal isolates were more effective at 25, 30and 35°C than at 20°C. The LT₉₀values decreased with increasing temperature upto the optimum temperature of 30°C. Therewere significant differences in susceptibilitybetween fly species to fungal infection at allthe temperatures tested.     

An experimental assessment of the temperature responses of two sympatric seagrasses,Amphibolis antarctica and Amphibolis griffithii,in relation to their biogeography

Walker, D. I. and Cambridge, M. L. 1994. An experimental assessment of the temperature responses of two sympatric seagrasses, Amphibolis antarctica and Amphibolis griffithii, in relation to their biogeography.Seedlings of the viviparous seagrasses, Amphibolis antarctica (Labill.) Sonder & Aschers. and Amphibolis griffithii (Black) den Hartog, were grown in seawater cultures at temperatures of 10–30 °C. This temperature range exceeded the range of temperatures occurring in habitats where Amphibolis grows.All seedlings of both species survived at 15 °C, and all A. antarctica at 10 and 20 °C. There was some mortality at 25 °C, but more in A. griffithii than in A. antarctica. All seedlings showed marked senescence at 30 °C within 2 weeks, and all seedlings of both species were dead at this temperature in 6 weeks. Leaf production rates were different at different temperatures for each species, but were high across the 15–25 °C temperature range for both species. Given the time of release of seedlings from parent plants (winter), these results are consistent with the observed distribution of adult plants, and so the more restricted range of A. griffithii can be explained partially by its' response to temperature in culture. These results do not explain the absence of both Amphibolis species from the east coast of Australia, which may be a consequence of habitat availability.     

Negative complementation among ad2 mutants of yeast

Summary Ad ₂ remedial mutants of Saccharomyces cerevisiae which showed conditional growth at 35°C or with 1 M KCl at 25° C or 35° C, were crossed with other remedial and non-remedial mutants in all pairwise combinations. 19 remedials (11 K ₂₅, 5 temp. and 3 K ₃₅) and 189 non-remedial mutants were used. The standard conditions used were incubation at 25° C in the absence of adenine.Among 1625 combinations there were 367 (22.6%) cases of negative complementation. In these cases the diploids were unable to grow under the same conditions which permitted a strong growth of the remedial haploid.No negative complementation was observed among K ₂₅×K ₂₅ combinations. When only one haploid partner was remedial the temp. ¢ non-remedial combinations showed a rate 2.5 times higher than that observed among K ₂₅ × non-remedial combinations. When the remedial haploid was a K ₃₅ the incidence was the same as that noted with temp. × non-remedial combinations. The high incidence observed in the latter temp. combinations was not subject to influence attributable to strain; the incidence being the same whether the remedial partner belonged to the a or to the mutant strains. The K ₂₅ × non-remedial combinations, on the other hand, showed such an influence.For an explanation of the mechanism involved in negative complementation it was postulated that, assuming non-random monomer aggregation, some mutant pairs would form only active heterologous multimers while others, due to the nature of their mutation, would form only inactive aggregates which entrap all the remedial monomers. It is thought that this postulate may have some application in explaning the complementation mechanism in general.Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Temperature/toxicity relationships of some pyrethroids onCenopalpus pulcher (Acari: Acaridae)

Relationships between post-treatment temperature and toxicity of four synthetic pyrethroids, bioallethrin,d-phenothrin, fenvalerate and cypermethrin, to the fruit-tree false spider mite,Cenopalpus pulcher (Canestrini and Fanzago) were determined in the laboratory. Pyrethroids were evaluated by the slide-dip technique at three post-treatment temperatures, 15, 25 and 35°C.Bioallethrin,d-phenothrin and fenvalerate exhibited positive temperature coefficients againstC. pulcher at all temperature ranges tested. On the other hand, cypermethrin displayed a neutral temperature coefficient at 25–35°C and negative temperature coefficients at 15–25°C and 15–35°C temperature ranges.     

Effect of LAB 173 711, an ABA analogue,on low-temperature resistance of mung bean seedlings

The effect of LAB 173 711, a synthetic analogue of abscisic acid, has been evaluated on chilling-sensitive mung bean (Vigna radiata L. cv. Local V.) seedlings. Electrical conductivity was used for assessing the degree of chilling injury. Exposure of 8-day-old mung bean seedlings to 4°C for 35 h resulted in a 50% electrolyte leakage and induced irreversible chilling injury. The seedlings gained the best protection against chilling injury by pretreatment with LAB 173 711 (5 × 10^–4 M) for 3 days. The protection effect could be sustained for 4 days. The LAB 173 711 pretreatment at 28°C did not cause a significant difference in the electrolyte leakage over the ambient temperature (28°C) control. Application of LAB 173 711 at 28°C reduced visible injury and the treated seedlings had higher ethylene production and respiration rate over the untreated control. LAB 173 711 helped maintain the integrity of the cell membrane and thus reduced the leakage of soluble sugar and amino acids. These combined effects led to a higher chilling tolerance in the mung bean seedlings.     

Effect of aVirido-Xantha mutation in barley on the content of individual plastid pigments

Summary A virido-xantha (vx) barley mutant with reduced chlorophyll content when grown at 15°C was investigated to determine quantitative and qualitative changes in the plastid pigments. Both chlorophyll and the capacity to produce protochlorophyllide from exogeneously supplied δ-aminolevulinic acid are reduced in the mutant. The total carotenoid content is also reduced in the mutant, but individual carotenoids are not reduced coordinately. Antheraxanthin actually accumulates in the mutant, and zeaxanthin was found in significant amounts in mutant seedlings but could not be detected in normal barley seedlings. Included in the methods is a procedure for the preliminary identification of zeaxanthin employing spectrophotometric analysis of fractions eluted from a sucrose column. The presence of recessive suppressors of thevx mutant results in increased contents of the chlorophyll pigments accompanied by a partial reversal of the changes in carotenoid indicated above. The changes in chlorophyll and carotenoid contents are also partially reversed when mutant seedlings are grown at 21°C. Research supported under contract AT(11-1)-332 with the United States Atomic Energy Commission.     

Do Polyamines Participate in the Long-Distance Translocation of Stress Signals in Plants?

Accumulation and ethylene-dependent translocation of free polyamines was studied in various organs, the phloem and xylem exudates of common ice plants (Mesembryanthemum crystallinum L.). Under normal conditions (23–25°C), spermidine predominated among polyamines. Cadaverine was found in old leaves, stems, and, in large quantities, in roots. The heat shock treatment (HS; 47°C, 2 h) of intact plant shoots induced intense evolution of ethylene from leaves but reduced the leaf content of polyamines. Under these conditions, the concentration of polyamines in roots, particularly of cadaverine, increased many times. The HS treatment of roots (40°C, 2 h) induced translocation of cadaverine to stems and putrescine to leaves. An enhanced polyamine content after HS treatment was also found in the xylem and phloem exudates. The exposure of detached leaves to ethylene led to a reduction in their putrescine and spermidine and accumulation of cadaverine, which implies the ethylene-dependent formation of cadaverine and a possible relation between the HS-induced translocation of this diamine to roots and the transient ethylene evolution by leaves. To validate this hypothesis, we compared the ethylene evolution rate and interorgan partitioning of cadaverine and other polyamines for two lines of Arabidopsis thaliana: the wild type (Col-0) and ein4 mutant with impaired ethylene reception. In plants grown in light at 20–21°C, the rate of ethylene evolution by rosetted leaves was higher in the mutant than in the wild type. The content of putrescine and spermidine was reduced in mutant leaves, whereas cadaverine concentration increased almost threefold compared with the wild type. In roots, cadaverine was found only in the wild type and not in the mutant line. Our data indicate the ethylene-dependent formation of cadaverine in leaves and possible involvement of cadaverine and ethylene in the long-distance translocation of stress (HS) signal in plants.     

Ambient temperature: a factor affecting performance and physiological response of broiler chickens

An experiment was conducted to elucidate the influence of four constant ambient temperatures (20°, 25°, 30° and 35°C) on the performance and physiological reactions of male commercial broiler chicks from 3 to 7 weeks of age. A 12 h light-dark cycle was operated, while relative humidity and air circulation were not controlled. Exposure of broiler chickens to the 20°, 25°, 30° and 35°C treatments showed highly significant (P<0.0001) depression in growth rate, food intake and efficiency of food utilization, and a significant increase in water consumption for the 30° and 35°C groups. Mortality was, however, not affected by the temperature treatments. Changes in physiological status, such as increased rectal temperatures, decreased concentration of red blood cells, haemoglobin, haematocrit, and total plasma protein were observed in birds housed in the higher temperature (30° and 35°C) environments. Moreover, in these broiler chickens, there was an increased blood glucose concentration and a decreased thyroid gland weight. These results indicate that continuous exposure of broiler chickens to high ambient temperatures markedly affects their performance and physiological response.     

Temperature-conditional nuclear mutation of Chlamydomonas reinhardtii decreases the CO2/O2 specificity of chloroplast ribulosebisphosphate carboxylase/oxygenase

The Chlamydomonas reinhardtii (Dangeard) temperature-conditional mutant 68-11AR is phenotypically indistinguishable from the wild type at the permissive temperature (25°C), but has greatly reduced photosynthetic ability and requires acetate for growth at the restrictive temperature (35°C). The mutant strain is deficient in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) holoenzyme when grown at 35°C. This decrease in the level of enzyme appears to be due to degradation of assembled holoenzyme rather than to a reduction in the synthesis of enzyme subunits. When grown at 25°C, the mutant has a substantial amount of Rubisco. Enzyme purified from 25°C-grown mutant cells was found to have a 16% decrease in the CO₂/O₂ specificity factor when compared to the wild-type enzyme. This alteration was accompanied by changes in the kinetic constants for both carboxylation and oxygenation. Although the Rubisco active site is located on the chloroplast-encoded large subunit, genetic analysis showed that the 68-11AR strain arose from a nucleargene mutation. The two nuclear genes that encode the Rubisco small subunits (rbcS1 and rbcS2) were cloned from mutant 68-11AR and completely sequenced, but no mutation was found. Analysis of restriction-fragment length polymorphisms also failed to detect linkage between mutant and rbcS gene loci. These results indicate that nuclear genes can influence Rubisco catalysis without necessarily encoding polypeptides that reside within the holoenzyme.Abbreviations and Symbols K _c Michaelis constant for CO₂ - K _o Michaelis constant for O₂ - mt mating type - pf paralyzed flagella - RFLP restriction-fragment length polymorphism - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose 1,5-bisphosphate - V _c V _max for carboxylation - V _o V _max for oxygenation - CO₂/O₂ specificity factor C. G. gratefully acknowledges fellowship support from the Consejo Superior de Investigaciones Cientificas (Spain). This work was supported by National Science Foundation grant MCB-9005547, and is published as Paper No. 10481, Journal Series, Nebraska Agricultural Research Division.     

Influence of salinity and temperature on the germination of Kochia scoparia

Kochia scoparia is one of the most common annual halophytes foundin the Great Basin. Seeds were collected from a population growing in asalt playa at Faust, Utah and were germinated at 5 temperature regimes(12 h night/12 h day, 5–15 ^°C, 10–20 ^°C, 15–25 ^°C,20–30 ^°C and 25–35 ^°C) and 6 salinities (0, 200, 400,600, 800 and 1000 mM NaCl) to determine optimal conditions forgermination and recovery of germination from saline conditions after beingtransferred to distilled water. Maximum germination occurred in distilledwater, and an increase in NaCl concentration progressively inhibited seedgermination. Few seeds germinated at 1000 mM NaCl. A temperatureregime of 25 ^°C night and 35 ^°C day yielded maximumgermination. Cooler temperature 5–15 ^°C significantly inhibited seedgermination. Rate of germination decreased with increase in salinity.Germination rate was highest at 25–35 ^°C and lowest at5–15 ^°C. Seeds were transferred from salt solutions to distilled waterafter 20 days and those from high salinities recovered quickly at warmertemperature regimes. Final recovery germination percentages in high salttreatments were high, indicating that exposure to high concentration ofNaCl did not inhibit germination permanently.     

Effects of temperature on acaricidal and insecticidal activities of the benzoylureas flucycloxuron and diflubenzuron

Effects of temperature on the activity of flucycloxuron on larval stages of Panonychus ulmi (Koch), based on LC₅₀ values, were highly significant (P < 0.001) with temperature coefficients of-1.7 in both the ranges of 15° to 25°C and 20° to 30°C. The slopes of probit regression lines at 15° and 20°C were significantly steeper than those at 25° and 30°C. As a consequence the temperature coefficients based on LC₉₀ values were-4.4 and-2.2, for the 2 temperature ranges. The ovicidal activity of flucycloxuron on P. ulmi was low and was only statistically detectable at 20°C (LC₉₀ of 84 mg a.i./l). In studies with larvae of Aedes aegypti (Linnaeus), Leptinotarsa decemlineata (Say), Plutella xylostella (Linnaeus), Spodeptera exigua (Hübner) and Spodoptera littoralis (Boisduval) probit regression lines were parallel over temperature. The activity of flucycloxuron on these five insect species was not affected by temperature. Based on LC₅₀ values, diflubenzuron showed positive temperature coefficients on P. xylostella of + 2.1 at 15° to 25°C and + 2.5 at 20° to 30°C. For S. littoralis the temperature coefficient was positive (+ 2.4) at 15° to 25°C but negative (-1.9) at the 20° to 30°C range. Temperature coefficients of diflubenzuron were neutral for A. aegypti, L. decemlineata and S. exigua. In the design and analysis of these studies special allowance was made for date effects and variation in natural mortality over temperature.     

Effect of temperature on growth of juvenile Oreochromis mossambicus and Sarotherodon melanotheron

Synopsis Survival and competitive ability of juvenile fish is often dependent on their growth rate. Temperature is the physical component of their environment which most affects growth rate. To determine the effect of temperature on the growth rate of two exotic warm water species we measured growth of Oreochromis mossambicus and Sarotherodon melanotheron at 25, 30 and 35°C. There was a significant interaction of species and temperature on growth. The growth rate of O. mossambicus was faster than that of S. melanotheron at 25 and 30°C but slower at 35°C. Weight gain of S. melanotheron was significantly greater at 30°C than at 25°C. Weight gain of O. mossambicus at 25 and 30°C was significantly greater than at 35°C. Temperature had no effect on the weight-length relationship of either species.Scientific Series No. 1546-AEL from UM-CEES, Appalachian Environmental Laboratory     

Growth and hyoscyamine production of ‘hairy root’ cultures of Datura stramonium in a modified stirred tank reactor

Summary The growth and hyoscyamine production of transformed roots of Datura stramonium have been examined in a modified 14-1 stirred tank reactor in both batch and continuous fermentations on media containing half or full strength Gamborg's B5 salts and at three different temperatures. Under a range of conditions, roots grown on half strength B5 salts with 3% w/v sucrose had a higher dry matter content (up to 8.3% w/w) and a higher hyoscyamine content (up to 0.52 mg·g^–1 wet weight) than roots grown on full strength B5 salts with the same level of sucrose (up to 4.6% w/w dry matter and up to 0.33 mg hyoscyamine g^–1 wet weight). Growth at 30°C was initially faster than at either 25°C or 35°C and by day 12, the drained weight of roots in the fermentor at 30°C was about fourfold greater than at 25°C and twice that at 35°C. The ultimate hyoscyamine levels attained (approximately 0.5 mg·g^–1 wet weight) were similar at both 25°C and 30°C but some 40% lower at 35°C. Final packing densities of 70% w/v were achieved for roots after 37 days growth at 25°C and the highest production rate of 8.2 mg hyoscyamine l^–1 per day was obtained for roots grown at 30°C. In continuous fermentation at 25°C, the release of hyoscyamine into the culture medium was low (less than 0.5% w/w of the total) but was up to sevenfold higher in fermentors operated at 30°C or 35°C. Offprint requests to: M. G. Hilton     

The influence of root-zone temperature on growth of Betula pendula Roth.

We have examined shoot and root growth and the concentration of carbohydrates in seedlings of a northern (67°N) and a southern (61°N) ecotype of Betula pendula Roth. cultivated at root-zone temperatures of 2, 6, 12 and 17°C. Three hydroponic experiments were conducted in controlled environments. We used three different pretreatments before seedlings were subjected to the experimental temperature treatments. Actively growing seedlings that were acclimated to the hydroponic solution for 3 weeks at a root temperature of 17°C, continued to grow at all the experimental temperatures, with an expected increase in growth from 2 to 17°C. However, if we started with ecodormant cold stored plants or used seedlings grown actively in perlite, no growth was observed at 2°C and only minor growth was found at 6°C. The highest root temperature always produced the best growth. The concentration of nonstructural carbohydrates was higher in seedlings grown at 2°C than at 17°C, and this is probably due to extensive incorporation of carbohydrates into cell walls and other structural elements at 17°C. We found no evidence for differences between the two ecotypes in root growth, in timing of bud burst, but shoot growth terminated in the northern ecotype in the first experiment because the natural photoperiod was below the critical value. Our study highlights the importance of post-transplantation stress (planting check) related to root growth, and that root threshold temperatures may change according to the way plants are pretreated.     

Ecdysterone responsive functions in the mutantl(1)su(f) ts67g ofDrosophila melanogaster

Summary Transferring the temperature sensitive mutantl(1)su(f) ^ts67g from 25° C to 30° C before or early in the third larval instar blocks the increase in the ecdysterone titer that normally occurs at the end of the larval period. Feeding exogenous ecdysterone to these hormone-deficient larvae results in the formation of pseudopupae. The mutant was used to study ecdysterone-inducible functions in late larval salivary glands by preparing three animal samples with different hormone titers: the titer was low in one sample because of an earlier temperature shift, high in a second sample because the larvae were subsequently transferred to ecdysterone-supplemented food, and also high in a third sample that was kept at 25°C, providing a control for normal development. The effect of the different hormone conditions was studied by³⁵S-methionine labeling of the salivary gland proteins during the larval to prepupal transition and the prepupal period. The results indicate that synthesis of several of the proteins normally appearing during the transition and prepupal period is induced by exogenous ecdysterone.     

Germination of Tagetes minuta L. II. Role of gibberellins

The effect of the application of gibberellins to Tagetes minuta L. achenes (seeds) was determined at both 25°C, the optimal germination temperature, and 35°C, at which temperature the achenes are thermoinhibited. Both GA₃ and GA₄₊₇ accelerated germination at 25°C. Seed germination at 25°C was inhibited by paclobutrazol, but on subsequent application of GA₄₊₇ rapid germination was induced. Following application of GA₃ or GA₄₊₇ to thermoinhibited seeds, a significantly higher final germination percentage was observed than in the distilled water control. However, endogenous gibberellin levels in germinating and thermoinhibited seeds did not differ significantly.     

Effect of Low Temperature on the Protein Metabolism of Wheat Leaves

The effect of low temperature on the protein metabolism of wheat primary leaves was examined. In seedlings transferred from 25 to 5 °C, total soluble protein accumulation, in vivo protein synthesis and breakdown, in vitro protein breakdown, and SDS-PAGE profiles of proteinases in gelatine-containing gels were analysed. Leaf protein content increased within a 7-d period (70 % over the initial value) in plants exposed to 5 °C. The fast protein accumulation observed on days 0 – 2 was mainly attributed to a decreased breakdown. In further days, parallelly to a slowdown in the rate of protein accumulation, the leaf proteolytic activity increased. The incubation temperature also had an influence on the proteolytic activity: Q ₁₀ values for the 15 – 5 °C range were 80 – 200 % higher than those observed for the 25 – 15 °C range. On the other hand, the in vivo protein synthesis capacity, at either 25 or 55 °C, was not significantly modified in cold-treated plants. In addition to the enhanced activities of two serine-proteinases (previously found in control plants by SDS-PAGE analysis), cold-treated plants displayed a new proteinase, which had not been detected so far.