Cold responses of Arabidopsis mutants impaired in freezing tolerance

Mutants of Arabidopsis thaliana L. (Heynh), characterized asdeficient in their freezing tolerance after cold acclimation,were surveyed for some of the normal responses to cold exposure.In foliar tissue, the coldinducibility of three proteins, thelevels of sucrose and glucose, the fatty acyl composition oflipids, and the accumulation of anthocyanin was examined. Fourmutations (sfr3, sfr4, sfr6, and sfr7) reduced or eliminatedthe accumulation of anthocyanin during cold acclimation. Onemutation (sfr4) prevented the normally cold-induced elevationof sucrose and glucose levels; both sfr4 and another mutation(sfr7) affected fatty acid composition after (and only after)cold acclimation. On the other hand mutations sfr1, sfr2 andsfr5 did not differ significantly from the wild type in anyof the parameters tested, suggesting that they have other, perhapshighly specific, effects on lowtemperature responses. Key words: Arabidopsis thaliana, cold acclimation, freezing tolerance, mutation     

Quantitative Analysis of Cold Hardening and Dehardening in Lolium

The change in cold hardiness of three Lolium multiflorum Lam.varieties was followed in plants exposed to hardening or dehardeningconditions at a range of temperatures. Hardening and dehardeningwere analysed as quantitative processes dependent upon temperatureand time. Their time courses changed exponentially to an asymptotewhich was logistically related to temperature. Both componentsof the model were fitted simultaneously. Parameters of biologicalinterest, such as the initial rates of hardening and dehardeningfor a given temperature and the percentage of the process completedin a given time, were derived and compared for varieties ofcontrasting hardiness. The analysis demonstrated the importanceof dehardening in determining hardiness. Similar results wereobtained when the model was applied to hardening and dehardeningdata for Lolium perenne L. The potential of this quantitative analysis for distinguishingbetween possible mechanisms of cold hardiness is discussed andfurther experiments required to characterise the kinetics ofhardening and dehardening more fully are identified. Lolium multiflorum, Lolium perenne, cold hardening, cold dehardening, processes, model, varieties     

Low Temperature Affects Pattern of Leaf Growth and Structure of Cell Walls in Winter Oilseed Rape (Brassica napus L., var. oleifera L.)

Three-week acclimation of winter oilseed rape (Brassica napusL. var. oleifera L.) plants in the cold (2 °C) resultedin a modified pattern of leaf cell enlargement, indicated bythe increased thickness of young leaf blades and modified dimensionsof mesophyll cells, as compared with non-acclimated tissuesgrown at 20/15 °C (day/night). The thickness of leaf cellwalls also increased markedly during cold acclimation but itdecreased in response to a transient freezing event (5 °Cfor 18 h followed by 6 or 24 h at 2 °C, in the dark). Cellwalls of the upper (adaxial) epidermis were most affected. Theirultrastructure was modified by cold and freezing treatmentsin different ways, as revealed by electron microscopy. Possiblereasons for the cold- and freezing-induced modifications inthe leaf and cell wall morphology and their role in plant acclimationto low temperature conditions are discussed. Copyright 1999Annals of Botany Company Acclimation, Brassica napus var. oleifera, cell wall ultrastructure, cold, freezing, leaf structure, winter oilseed rape.     

桔小实蝇自然种群蛹和越冬成虫的耐寒性

本文通过过冷却点和低温耐寒能力的测定,研究了我国桔小实蝇Boctrocera dorsalis (Hendel)不同季节种群和地理种群蛹的耐寒性规律。结果表明：桔小实蝇自然种群蛹的低温存活力有明显的季节规律,冬前种群的耐寒性显著强于夏季种群。如在0℃低温下暴露2天,夏季种群基本全部死亡,而冬前种群存活率仍为61.4%。2005-2006年不同月份桔小实蝇1日龄蛹过冷却点差异明显,以2月份均值最高,为-9.26℃,8月份最低,为-15.20℃;且2月份桔小实蝇蛹个体过冷却点值出现明显的分化现象,分别在-15℃左右和-6℃左右出现两个明显的聚集区。所研究的5个桔小实蝇地理区域种群没有出现明显的耐寒性分化。结合本文结果,文中还就桔小实蝇自然种群耐寒性影响因素进行了讨论。     

Differences in cold lability of pyruvate, Pi dikinase among C4 species

The cold lability of pyruvate, Pi dikinase in crude leaf extractswas studied in a number of C⁴ plants. The survey included C⁴monocots and dicots and species representingthe three C⁴ subgroups:NADP-malic enzyme, NAD-malic enzyme, and PEP-carboxykinase types. In some species (e.g., Digitaria sanguinalis, Sorghum bicolorand Echinochloa crus-galli), the enzyme was very sensitive tocold treatment (half life of about 8 min at 0?C and 10 to 15min at 10?C). In other species (Panicum miliaceum, Panicum maximumand Panicum texanum), the enzyme was very cold tolerant (retentionof 60 to 85% activity after 60 min at 0?C and 90% activity after60 min at 10?C). Among the plants examined, the most cold sensitivepyruvate,Pi dikinase was found among species of the NADP-malicenzyme subgroup. (Received March 9, 1979; )     

荒漠昆虫光滑鳖甲的耐寒性季节变化及其生理机制

光滑鳖甲Anatolica polita borealis生活于温差大的新疆荒漠环境, 为探讨其耐寒性及耐寒机制, 本研究测定了其3-9月份成虫在－10℃的耐寒性、过冷却点（SCP）、含水量、甘油含量和血淋巴热滞活性(thermal hysteresis activity, THA)以及冷驯化对增强光滑鳖甲成虫耐寒性的效果, 还测定了光滑鳖甲不同发育阶段幼虫的SCP。结果表明: 光滑鳖甲成虫的耐寒性和SCP具有明显的季节性变化, 3月初SCP为－12.5℃, 7月为－6℃, 9月底为－13.6℃。4℃冷驯化能够提高光滑鳖甲成虫在－10℃的存活率, 未驯化组在40 min的存活率为50%, 而驯化2 h的为70%, 驯化24 h的为90%。虫体含水量在夏季有显著降低, 3月、7月和9月结合水与自由水的比值分别为10.8∶1,2.6∶1和5.4∶1。成虫甘油含量与SCP的回归方程为y=－0.6204x－5.681, R²=0.7714。成虫血淋巴THA与过冷却点的回归方程为y=－5.26x－1.713, R²=0.9049。血淋巴THA比甘油浓度更能影响过冷却点降低的程度。随着幼虫的发育, 其SCP逐渐降低。结果提示, 光滑鳖甲通过提高结合水与自由水的比值、增加抗冻蛋白和甘油的含量使虫体保持较低的SCP, 因而具有较高的耐寒性。     

Endothelial modulation of neural sympathetic vascular tone in canine skeletal muscle

The effect of nitric oxide synthase (NOS)inhibition and endothelin-A(ET_A)-receptor blockade onneural sympathetic control of vascular tone in the gastrocnemius musclewas examined in anesthetized dogs under conditions of constant flow.Muscle perfusion pressure (MPP) was measured before and after NOSinhibition(N-nitro-L-argininemethyl ester; L-NAME) andET_A-receptor blockade [cyclo-(D-Trp-d-Asp-Pro-D-Val-Leu);BQ-123]. Zero and maximum sympathetic nerve activities wereachieved by sciatic nerve cold block and stimulation, respectively. Ingroup 1 (n = 6), MPP was measured1) before nerve cold block,2) during nerve cold block, and3) during nerve stimulation.Measurements under these conditions were repeated afterL-NAME and then BQ-123. The sameprotocol was followed in group 2 (n = 6) except that the order ofL-NAME and BQ-123 was reversed.MPP and muscle vascular resistance (MVR) increased afterL-NAME and then decreased tocontrol values after BQ-123. MVR decreased after BQ-123 alone and, withthe addition of L-NAME,increased to a level not different from that observed during thecontrol period. MVR fell during nerve cold block. This response was notaffected by administration ofL-NAME followed by BQ-123, butit was attenuated by administration of BQ-123 before L-NAME. The constrictor responseduring sympathetic nerve stimulation was enhanced byL-NAME; no further effect wasobserved with BQ-123, nor was the response affected when BQ-123 wasgiven first. These findings indicate that endothelin contributes to1) basal vascular tone in skeletalmuscle and 2) the increase inskeletal muscle vascular resistance after NOS inhibition. Finally,nitric oxide "buffers" the degree of constriction in skeletalmuscle vasculature during maximal sympathetic stimulation.

     

PEP Carboxylases from Two C4 Species of Panicum with Markedly Different Susceptibilities to Cold Inactivation

Phosphoenolpyruvate carboxylase (PEPC) (EC 4.1.1.31 [EC] ) assayedin extracts of Panicum maximum Jacq. loses up to 50% of itsactivity after incubation for 60 minutes at 0C while the enzymefrom P. miliaceum L. is completely stable under these conditions.Following dilution at room temperature the enzyme from P. maximumis labile, while that from P. miliaceum is stable. The P. maximumenzyme can be largely stabilized against dilution and againstcold-inactivation by D₂O which stabilizes hydrophobic bondsand the compatible solutes proline, betaine and trimethylamine-N-oxide.Mineral ions, previously demonstrated to be protective againstcold inactivation of pyruvate, P_i dikinase from maize, provideno protection of P. maximum PEPC against either cold or dilution.The chaotropic ion SCN^- causes partial inactivation of the enzymefrom P. miliaceum in the cold. The possible interrelationshipbetween inactivation by dilution and inactivation by cold isdiscussed. The enzyme from both species, when assayed withoutpreincubation at low temperature, exhibits similar, slightlycurvilinear Arrhenius plots; and no differences were found betweenthe two species in the temperature dependence of photosynthesis. ¹Present address: Botany Dept., University of California, DavisCA 95616 U.S.A.     

Are antarctic zooplankton metabolically more cold-adapted than arctic zooplankton? An intra-generic comparison of oxygen consumption rates

Because of the greater age of the antarctic ecosystem in relationto the arctic ecosystem, an elevated metabolic rate and moreobligate stenothermy of antarctic zooplankton compared withtheir arctic counterparts are predicted from the concept ofmetabolic cold adaptation. When oxygen consumption rates werestandardized to 1 mg body nitrogen and 0°C and comparedbetween the species belonging to the same genus, the antarcticrates were greater than arctic rates in Clione (pteropods) andCalanus (copepods), while the reverse was true in Parathemisto(amphipods), Thysanoessa (euphausiids) and Sagitta (chaetognaths).No significant differences were seen in Limacina (pteropods)and Metridia (copepods). These inconsistent results do not supportthe hypothesis of metabolic cold adaptation in the zooplanktonof polar seas.     

Changes in Sugar Content during Cold Acclimation and Deacclimation of Cabbage Seedlings

The relationship between freezing tolerance and sugar contentin cabbage seedlings was investigated. Seedlings exposed tonon-freezing low temperature (5 °C) acquired freezing tolerancedown to -6 °C. The degree of freezing tolerance increasedwith duration of exposure to low temperature (up to 10 d). Sucrose,glucose, fructose and myo -inositol were detected as solublesugars in cabbage leaves, and all soluble sugars, except formyo -inositol, and starch increased gradually during cold acclimationsuch that their levels were positively correlated with the degreeof freezing tolerance. The induced freezing tolerance was attributednot to ontogenetic changes but to cold acclimation. However,the induced freezing tolerance was lost after only 1 d of deacclimationat control temperatures, and this change was associated witha large reduction in sugar content. These results reveal that the sugar content of cabbage leavesis positively correlated with freezing tolerance. Brassica oleracea L.; cabbage; cold acclimation; deacclimation; freezing tolerance; sugars     

Early Developments in RNA, Protein, and Sugar Levels during Cold Stress in Winter Rye (Secale cereale) Leaves

Changes in freezing tolerance of winter rye (Secale cerealeL. cv. Voima) were determined for leaf tissues during a 1-weekcold stress, which was performed by transferring the 7-d-oldseedlings from a greenhouse (25°C, long day) to 3°Cand short day conditions. The development of cold hardeningwas shown by using an ion leakage test and by determining theamounts of carbohydrates, soluble proteins and RNA. The firstevidence of the development of freezing resistance was foundafter 1 d at low temperature, i.e. an LT₅₀ value increased from-5 to -7°C. Plants cold treated for 7 d reached an LT₅₀value of -9°C. This increase in freezing tolerance was foundto be associated with the increased levels of soluble carbohydrates,total RNA and soluble proteins. These metabolic changes indicatethe association with adjustment of growth and cell metabolismto low temperatures at the beginning of cold acclimation ofwinter rye.Copyright 1994, 1999 Academic Press Secale cereale L., winter rye, cold stress, proteins, RNA, sugars     

Cold Acclimation, Freezing Resistance and Protein Synthesis in Alfalfa (Medicago sativaL. cv. Saranac)

Mohapatra, S. S., Poole, R. J. and Dhindsa, R. S. 1987. Coldacclimation, freezing resistance and protein synthesis in alfalfa(Medicago sativa L. cv. Saranac).—J. exp. Bot. 38: 1697–1703. Changes in freezing resistance (percent survival at —10°C), pattern of protein synthesis and translatable mRNApopulation during cold acclimation of alfalfa (Medicago sativaL. cv. Saranac) have been examined. Two days of cold acclimationat 4 °C increased freezing resistance from about 6% to 40%,protein content by 200% and total RNA content by 100%. Acclimationfor longer periods did not cause further increases in freezingresistance, protein content or RNA content. Examination of proteinchanges by sodium dodecyl sulphate-polyacrylamide gel electrophoresis(SDS-PAGE) coupled with protein staining, and by fluorographyof in vivo labelled proteins separated by SDS-PAGE, showed thatseveral proteins are increasingly or newly synthesized duringcold acclimation. Analysis of in vitro translation productsby SDS-PAGE and fluorography shows changes in the populationof translatable mRNAs. It is concluded that in this varietyof alfalfa cold acclimation for only 2 d is sufficient to confermaximum freezing resistance, and that changes in proteins duringcold acclimation are regulated most probably at the transcnptionallevel. Key words: Freezing resistance, protein synthesis, cold acclimation, SDS-PAGE, Medicago sativa L.     

Beneficial Effects of Moist Chilling on the Seeds of Black Spruce (Picea mariana [Mill.] B.S.P.)

Moist chilling (cold stratification) is well-known as a simpleand effective means of overcoming physiological seed dormancyand enhancing germination of many temperate tree and shrub species.However, the apparent activation of intracellular repair mechanismsin non-dormant black spruce (Picea mariana) seeds followingmoist chilling, has not previously been reported. The presentcontribution records the beneficial effects of moist chillingafter accelerated ageing (40°C/98% relative humidity) for3–10 d of black spruce seeds. This treatment was maximallyeffective after 7 d of accelerated ageing, increasing germinationfrom 43 to 61%. Ultrastructural examination of embryo cellsindicated that intracellular activation occurred during moistchilling even when seeds had not been subjected to acceleratedageing, and that the increasing levels of damage accumulatingover the 3–7 d period of ageing were substantially reversedduring subsequent moist chilling. The results of cold stratificationof non-dormant seeds are discussed in terms of the value ofthis practice in nursery seedling production from seeds thatare of less than the highest quality.Copyright 2000 Annals ofBotany Company Accelerated ageing, black spruce, cold stratification, embryonic axes, germination, moist chilling, Picea mariana, repair mechanisms, ultrastructure     

Alterations in Detergent-Resistant Plasma Membrane Microdomains in Arabidopsis thaliana During Cold Acclimation

Microdomains in the plasma membrane (PM) have been proposedto be involved in many important cellular events in plant cells.To understand the role of PM microdomains in plant cold acclimation,we isolated the microdomains as detergent-resistant plasma membranefractions (DRMs) from Arabidopsis seedlings and compared lipidand protein compositions before and after cold acclimation.The DRM was enriched in sterols and glucocerebrosides, and theproportion of free sterols in the DRM increased after cold acclimation.The protein-to-lipid ratio in the DRM was greater than thatin the total PM fraction. The protein amount recovered in DRMsdecreased gradually during cold acclimation. Cold acclimationfurther resulted in quantitative changes in DRM protein profiles.Subsequent mass spectrometry and Western blot analyses revealedthat P-type H⁺-ATPases, aquaporins and endocytosis-related proteinsincreased and, conversely, tubulins, actins and V-type H⁺-ATPasesubunits decreased in DRMs during cold acclimation. Functionalcategorization of cold-responsive proteins in DRMs suggeststhat plant PM microdomains function as platforms of membranetransport, membrane trafficking and cytoskeleton interaction.These comprehensive changes in microdomains may be associatedwith cold acclimation of Arabidopsis.     

Short-day and Low-temperature Induction in Lolium

The requirements for floral induction of several outbreedingpopulations of Lolium perenne, L. multiflorum, and L. rigidumhave been studied. Floral induction can be brought about byeither low temperature (0–30° C.) or short day (8hr.) independently, but short day is ineffective at low temperatures. The exact inductive requirement varies with the population.The summerannual Westerwolds ryegrass needs neither cold norshort day, the winter-annual Wimmera ryegrass shows a quantitativeresponse, while the perennial varieties from north-west Europehave an obligatory requirement for either cold or short daybefore floral induction. This relation between the annual orperennial habit and the inductive requirement was confirmedin a number of Mediterranean collections of L. perenne and L.rigidum. Considerable genetic variation in inductive requirement couldbe detected within each outbreeding population, and rapid responseto selection proved possible in Wimmera, Irish, and Kent ryegrass.     

COMPETITION BETWEEN TWO LAND GASTROPODS ALONG ALTITUDINAL GRADIENTS IN SOUTH-EASTERN FRANCE: NEONTOLOGICAL AND PALAEONTOLOGICAL EVIDENCE

In south-eastern France, Trochoidea geyeri (Soós) todaycharacterizes open upland environments from about 1000 m abovesea level. At lower altitude it is replaced by Candidula unifasciata(Poiret)—another member of the Helicellinae—whilethe other members of the community remain almost the same. Duringthe cold stages of the Quaternary, T. geyeri was also an importantelement of lowland gastropod communities in Provence, whileit was always replaced by C. unifasciata during the interglacialstages. Thus, T. geyeri seems to be a valuable cold indicatorspecies for palaeoclimatic reconstructions. Some anomalies in this pattern, however, show that each of thesespecies can live in bioclimatic conditions which characterizethe area of the other. This suggests a competitive dominancephenomenon from a threshold situated around 1000 m on the altitudinalgradient. The influence of competitive interaction is demonstratedusing similar altitudinal gradients in which T. geyeri is missingbecause of historical factors: in such cases, C. unifasciataoccupies the entire gradient, up to 2250 m. Quaternary climaticchanges produced altitudinal shifts of the contact zone betweenT. geyeri and C. unifasciata, and, correlatively, repeated isolationsof T. geyeri populations. (Received 26 December 1992; accepted 4 February 1993)     

A Comparative Study of the Cold-Sensitivity of Pyruvate,Pi Dikinase in Flaveria Species

Pyruvate,P_i dikinase (PPDK) was isolated and purified from theleaf tissue of a number of Flaveria species and the cold labilityof the purified enzymes studied. The PPDK from F. brownii (aC₃/C₄ intermediate species) showed a high level of stabilitycompared to other Flaveria species. (Received September 7, 1989; Accepted November 22, 1989)     

Analysis of the Effect of Cold Stratification on the Germination Response to Light and Alternating Temperatures using Selected Seed Populations of Ranunculus sceleratus L.

From a single population of achenes (seeds) of Ranunculus sceleratusL. sub-populations were selected on the basis of the sensitivityof individuals to an increasing number of daily light/temperatureshift cycles. Each cycle comprised a 4 h pulse of red lightfollowed by a 4 h temperature shift from 16 to 31 ?C. Selectionfor low dormancy (NND and ND) and high dormancy (D and DD) populationsresulted in a > 5-fold difference in the number of cyclesrequired for 50% germination. Despite a shift in the mean levelof dormancy the distributions of sensitivity (slopes of dose-responsecurves) were similar in all four selected populations. Differentialeffects of cold stratification on the germination response tolight and alternating temperatures were related to the depthof primary dormancy. The proportion of individuals that respondedpositively to the dormancy breaking effects of cold stratificationfollowed the trend DD < D < ND < NND. In high dormancypopulations (D and DD) the rate and uniformity of germinationof some individuals was reduced by cold stratification, indicatinga dormancy inducing effect. Over the range 2 to 11 ?C the effectivenessof dormancy release or dormancy induction was inversely relatedto temperature. The effects of cold stratification on the expressionof dormancy in R. sceleratus are discussed in relation to areproductive strategy involving winter and summer annual behaviour. Key words: Cold stratification, selection, dormancy, light, alternating temperatures, germination