Alterations in Protein Synthesis in vivo in Chilling Sensitive Mung Bean Hypocotyls Caused by Chilling Stress

The effects of chilling on protein synthesis in vivo in etiolatedhypocotyls of Vigna radiata L. were investigated. After exposureof the tissues to 0?C for various periods of time, proteinswere labeled with [³⁵S]-methionine at 26?C. The total amountof ³⁵S incorporated into soluble and membrane proteins was reversiblyreduced by chilling for 24 h, during which time the tissuessuffered no injury. Further prolonged chilling produced an irreversibledecline both in the incorporation of radioactivity and in cellviability as assessed by the extent of leakage of electrolyte.The ³⁵S-labeled proteins in the soluble and the total membranefractions were analyzed quantitatively. Chilling of etiolatedhypocotyls for one or two days induced the syntheses of twosoluble proteins (82 and 74 kDa) and one membrane protein (80kDa). Moreover, three heat-shock proteins (HSPs) that were inducedby heat stress (41 ?C, 4h) had the same electrophoretic mobilitiesas those of the proteins induced directly or indirectly by thechilling treatment. ¹Contribution No. 3170 from the Institute of Low TemperatureScience. (Received April 22, 1988; Accepted September 30, 1988)     

Studies on chilling injury in plant cells II. Ultrastructural changes in cells rewarmed at 26?C after chilling treatment

Both the restoration and deterioration of ultrastructures wereobserved during therewarming of cultured cells of Cornus stoloniferain which chilling at 0?C had caused an apparent change in themorphology of the organelles. Complete restoration of the ultrastructures,moderately altered by the 12-hr chilling, took place within12 hr of wanning at 26?C. Even in cells chilled for 24 hr, severelyaltered ultrastructures were partially or completely repairedin more than fifty percent of the treated cells. Some cellschilled for 24 hr, however, displayed further deteriorationof their ultrastructures during rewarming. Restoration of therough endoplasmic reticulum and the development of polysomesin recovering cells were characteristic of the early stage ofrewarming. Rupture of the tonoplast was sometimes observed duringrewarming of cells chilled for 24 hr. A possible role for therough endoplasmic reticulum and for the integrity of the tonoplastin cell recovery during the chill-warm sequence is discussed. ¹Contribution No. 2026 from the Institute of Low TemperatureScience, Hokkaido University. ²This work was supported in part by Grant 248004 from the Ministryof Education. (Received November 6, 1978; )     

Polyamine Titre in Relation to Chill-Sensitivity in Phaseolus sp.

Guye, M G., Vigh, L. and Wilson, J. M. 1986. Polyamine titrein relation to chill-sensitivity in Phaseolus sp.—J. exp.Bot. 37: 1036–1043. Endogenous levels of the polyamines putrescine, spermidine andspermine were quantified in the primary leaves of five cultivarsof bean (Phaseolus sp.) differing in their ‘wilting response’to a chilling exposure of 5 ?C for 24 h. Levels of polyamines prior to chilling treatment did not appearto be correlated with chill-tolerance as levels in the non-chilledcontrols were highest in cultivars of medium chill-sensitivity.Plants grown under a vapour saturation deficit (VSD) of 8?4gm^–3 day/6?1 g m^–3 night exhibited a mild hardeningas compared to plants grown under a VSD of 5?7 gm^–3 day/4?1gm^–3 night, as the former showed less wilting on chilling.Hardening at high VSD had the effect of slightly lowering theputrescine content of non-chilled tissue but total polyaminecontent remained unchanged. However, on chilling, the largestrelative increase in polyamine levels, in particular that ofputrescine, occurred in hardened plants. There was also a significantrelative increase in putrescine titre in response to chillingin non-hardened genotypes of high chill-tolerance, whereas morechill-sensitive genotypes remained unchanged or slightly declinedin putrescine content on chilling. Relative changes in putrescine content rather than absolutelevels appears to be correlated with chill-tolerance. Theseresults are discussed in view of present knowledge on the adaptivesignificance of stress-induced changes in polyamines, especiallywith regard to membrane stability Key words: Chilling, polyamines, Phaseolus sp.     

Phospholipid, Sterol Composition and Ethylene Production in Relation to Choline-Induced Chill-Tolerance in Mung Bean (Vigna radiata L. Wilcz.) During a Chill-Warm Cycle

Mung bean (Vigna radiata L. Wilcz. cv. Berken) seedlings wereraised hydroponically in 0, 5 and 15 mol m^–3 choline.Fourteen-day-old plants were chilled at 5°C (under lightconditions) for 24 h and then returned to warm conditions fora further 24 h. Primary leaf lamina tissue was used for thedetermination of phospholipid, mole ratio of sterol to phospholipid(ST/PL), sterol composition, and ethylene-forming enzyme (EFE)activity for the various choline-temperature treatments employed.Chilling caused an irreversible loss of lipid in the absence,of choline. Differential loss of lipid resulted in an increasein ST/PL and a decline in the mole ratio of sitosterol to stigmasterol(S/S). There was no recovery of EFE activity following chillingin the absence of choline. Choline (5 and 15 mol m^–3)enhanced phospholipid and sterol levels prior to chilling andmaintained lipid levels throughout the chill-warm cycle, withoutany significant change in ST/PL. At 5.0 mol m^–3 choline,the chilling-induced decline in S/S was reduced, while at 15mol m^–3 S/S increased following chilling. Choline treatment,though reducing EFE activity prior to chilling, allowed recoveryof EFE activity following transfer of plants from chilling towarm conditions. Key words: Chill sensitivity, choline, phospholipid, sterol ethylene forming enzyme, Vigna radiata     

ABA Levels and Effects in Chilled and Hardened Phaseolus vulgaris

Leaf abscisic acid (ABA) levels of chilled P. vulgaris weremeasured after 18 h chilling at 5°C, at a saturation deficitof 1.24 g m^–3 (SD), and after chilling in a water-saturatedatmosphere. Changes were also followed during a chill hardeningperiod of 4 d at 12°C, 2.1 g m^–3 SD. It was foundthat hardening resulted in an almost 5. fold increase in ABAlevels after 3 d at 12°C, and this decreased to approximatelycontrol levels on the fourth day. Subsequent chilling of hardenedplants produced no change in ABA levels from that of controlplants (22° C). In contrast, non-hardened plants chilledat 1.24 g m^–3 SD had ABA levels almost 3 times the levelof control plants. However, chilling in a water-saturated atmosphereresulted in a decrease in ABA levels. In addition, the response of leaf diffusion resistance (LDR)to exogenous ABA fed via the transpiration stream was measuredat 5 ° C and 22° C in hardened and non-hardened plants.Use of tritium-labelled ABA was made to calculate the stomatalsensitivity to ABA. It was found that exogenous ABA caused anincreased in LDR at 22°C in both hardened and non-hardenedplants. However, the sensitivity of the hardened plants to ABAwas greater in terms of rate of closure and amount of ABA requiredto close the stomata. At 5°C, however, ABA caused stomatalopening and the maintainance of open stomata in non-hardenedplants. In hardened plants, ABA caused stomatal closure at 5°C.These results are discussed in relation to the locking-openresponse of chilled P. vulgaris stomata. Key words: Chilling, Stomata, ABA, Phaseolus vulgaris     

Chilling injury in cotton (Gossypium hirsutum L.) : Effects of antimicrotubular drugs

When exposed to 4°C for more than three days, intact cotton(Gossypium hirsutum L.) seedlings and isolated cotyledonarydiscs suffered chilling injury as shown by the leakage of electrolytesfrom the tissue and the development of necrotic areas. Applicationof antimicrotubular drugs such as colchicine, demecolcine orpodophyllotoxin during chilling significantly accelerated andenhanced tissue damage. Lumicolchicine, the stereoisomer ofcolchicine, was ineffective. Non-chilled tissues showed hardlyany damage when treated with the same levels of antimicrotubulardrugs. Prior treatment with 10^–5 M abscisic acid (ABA)prevented the appearance of symptoms of damage caused by chillingand the antimicrotubular drugs during the first 2 to 3 daysand greatly reduced it at later stages. Our present resultssuggest that chilling damage may be due at least in part, tothe cold-induced disassembly of microtubules. Furthermore, themode of action of ABA might be related to factors which influencethe physiological stability of the microtubule network. ¹Preliminary report of this work was presented at the 10th InternationalConference on Plant Growth Substances, Madison, Wisconsin, 1979. ³Incumbent of the Seagram Chair in Plant Sciences. (Received April 15, 1980; )     

Chilling injury in cotton (Gossypium hirsutum L.) Prevention by abscisic acid

Cotton (Gossypium hirsutum L.) intact seedlings and isolatedcotyledonary discs were exposed to chilling (4?C) under humidconditions which prevented dehydration. The damage resultingfrom chilling was estimated by means of electrolyte leakageand survival in whole seedlings and by the electrolyte leakageand necrotic areas in isolated cotyledonary discs. Also, theeffect of chilling on membrane phospholipids and cellular reducedglutathione was determined. Within the first two and three daysof chilling, there was a marked reduction in the reduced glutathioneand membrane phospholipid levels without electrolyte loss andnecrosis. This reduction was completely prevented by pretreatmentwith abscisic acid. Prolonging the chilling period resultedin decreased survival in whole seedlings and in progressiveincrease in electrolyte leakage and necrosis in isolated cotyledonarydiscs. Pretreatment with abscisic acid prior to chilling almostcompletely prevented this chilling injury when exposure to 4?Cwas less than 5 days. Even with longer chilling periods, theabscisic acid pretreatment greatly reduced the damage. ³Incumbent of the Seagram Chair in Plant Science. (Received July 21, 1979; )     

Long-Term Chilling of Young Tomato Plants under Low Light. IV. Differential Responses of Chlorophyll Fluorescence Quenching Coefficients in Lycopersicon Species of Different Chilling Sensitivity

Temperature dependences of chlorophyll fluorescence quenchingcoefficients were studied in the cultivated tomato (Lycopersiconesculentum) and three lines of the chilling-tolerant L.peruvianumfrom different altitudes, i.e. LA 1373 (20 m a.s.l.), LA 2157(1,650 m a.s.l.) and LA 385 (2,400 m a.s.l.). At actinic lightintensity near light saturation of photosynthesis (370 µEm^–2 s^7minus;1), photochemical quenching (qP) increasedwith increasing temperature between 5 and 30°C. The temperature,at which qP reached the numerical value 0.5 [T (qP=0.5)] decreasedby 2.5–4.5°C after a chilling treatment of 14 daysat 10°C in L. peruvianum, indicating acclimation of thephotosynthetic dark reactions in this species. The final T (qP=0.5)attained after chilling could be arranged in the order L.esculentum>LA1373>LA 2157>LA 385. The fast relaxing non-photochemicalquenching (qN) component (qf, consisting mainly of energy-dependentquenching, qE) exhibited minima near the optimum temperaturefor photosynthesis. These minima shifted to lower temperaturesupon chilling in L. peruvianum. Photoinhibitory quenching (ql)was unaffected by chilling in the high altitude lines, but-increasedstrongly in LA 1373 and L. esculentum. Under low actinic light(40 µE m^–2 s^–1), temperature dependences ofqP and qN were nearly identical in L. esculentum and LA 385and revealed abrupt changes at approx. 8°C. It is concludedthat qP and ql, measured after defined chilling treatments,are valuable screening parameters for chilling tolerance inearly growth stages of Lycopersicon plants. (Received November 2, 1993; Accepted February 28, 1994)     

Influence of Root and Content on the Temperature Response of Net and Uptake in Chilling Sensitive and Chilling Resistant Lycopersicon Taxa

We studied the influence of internal ammonium and nitrate contenton the temperature response of ammonium and nitrate uptake inboth chilling sensitive and chilling resistant tomatoes. Threetaxa were examined: Lycopersicon esculentum Mill. cv. T-5, achilling sensitive cultivar, Lycopersicon hirsutum Humb. andBompl. LA 1264, a wild, chilling sensitive accession from thelowlands of Ecuador, and Lycopersicon hirsutum LA1778, a chillingresistant accession from the highlands of Peru. Short exposures(4 h) of L. esculentum cv. T-5 to chilling temperatures irreversiblyinhibited ammonium absorption for at least 6 h. Nitrate absorptionin this taxon and ammonium and nitrate absorption in the L.hirsutum accessions recovered fully and immediately from suchexposures. The chilling resistant accession, L. hirsutum LA1778,showed a lower Q₁₀ for ammonium absorption (1?54?0?10, mean?s.e.)than its chilling sensitive relatives, L. hirsutum LA1264 (2?37?0?35)and L. esculentum cv. T-5 (1?92?0?11). The temperature responseof nitrate absorption depended on internal nitrate status; plantsgrown at high levels of ammonium and nitrate (200 mmol m^–3)showed higher Q₁₀'s for nitrate uptake (2?29?0?10) than thosedepleted of internal (1?86?0?12). Key words: Lycopersicon, ammonium, nitrate, temperature response, chilling     

Gas Chromatography-Flame Thermionic Detector Analysis of Cytokinins in Etiolated Squash Seedlings using 14C-BA as an Internal Standard

Cytokinin contents in cotyledon, hypocotyl and root of etiolatedsquash (Cucurbita maxima Duch.) seedlings were determined byinstrumental analysis using ¹⁴C-benzyladenine (¹⁴C-BA) as aninternal standard. Crude extracts were purified using insolublepolyvinylpyrrolidone, cellulose-phosphate column and SEP-PAKC18 cartridge, then applied to a Sephadex LH-20 column to separatezeatin riboside (ZR), isopentenyl adenosine, isopentenyl adenine,¹⁴C-BA and a mixture of zeatin (Z) and dihydrozeatin (DHZ).The recovery rate for the cytokinin fractions after LH-20 wascorrected by ¹⁴C-BA. Each cytokinin fraction was further purifiedby HPLC which also separated Z and DHZ in the LH-20 fraction.Before permethylation, ¹⁴C-BA was added to each of the cytokininfractions to correct the methylation rates. Each methylatedcytokinin fraction was again purified by HPLC, then subjectedto gas chromatography with a capillary column and flame thermionicdetector. The detection limit of cytokinins by this system was0.1 ng. cis-ZK was the most abundant cytokinin in all tissues of theetiolated squash seedlings. Active cytokinins such as trans-ZRand trans-Z were mostly found in cotyledons with lesser amountsin the roots. DHZ was most abundant in the cotyledon. All cytokininsisolated by this procedure were confirmed by gas chromatographyselectedion monitoring. (Received December 26, 1986; Accepted June 1, 1987)     

Phase progress under low temperature treatment of the potassium uptake rhythm in a duckweed, Lemna gibba G3

Potassium uptake rhythm in the long-day duckweed Lemna gibbaG3 grown at 26?C disappeared at temperatures below 12?C. However,when the plants were returned to 26?C, the rhythm immediatelyrestarted from circadian time 12 with its normal wave form.Temperature steps from 20 to 30?C or from 30 to 20?C did notmodify the phase of the rhythm, although a step from 15 to 30?Cor from 30 to 15?C evoked a distortion in the wave form withoutintroducing any reproducible phase shift. Various periods of 9 or 4?C given during the subjective dayphase reduced the pace of rhythm progress by 40 or 60%, whilethose given during the subjective night phase did not. Theseresults suggest that the subjective day and night phases arethe energy charge and discharge phases for the underlying oscillator,respectively. Energy fluxes for the oscillators are brieflydiscussed. ¹Present address: National Institute for Basic Biology, Okazaki444, Japan. ²Present address: Aichi Gakuin University, Chikusa, Nagoya 464,Japan. (Received August 25, 1979; )     

Diurnal change in temperature sensitivity gibba G3 induced by acetylcholine in continuous light

When Lemna gibba G3 was in contact with 10^–5 M Ach oreserine, floral response to chilling changed diurnally under[24(0)], as was the case for control cultures exposed to [16(8)].On the other hand, with a rise in temperature, the min-[24(0)]decreased discontinuously in 24-hr units in Ach cultures subjectedto [24(0)], as did the min-[16(8)] in control cultures. Thusin the presence of Ach or eserine, this long-day plant tookthe continuous light regime, i.e. [24(0)], for another typeof long-day regime consisting of a long light period and a shortdark period, e.g. [16(8)]. In Ach cultures, the lower limitof the min-[24(0)] (72 hr) was attained at 22.5?C and remainedunaltered at the higher temperatures examined. The min-[16(8)]for control cultures, however, known to reach its lower limit(48 hr) at 26?C. Sodium lauryl sulphate (10^–5 M) and ouabain(10^–6 M) also caused a similar diurnal change in temperaturesensitivity of 24(0)] cultures. We surmised that exogenous Ach or inserted dark period modifiesthe relative rates chemical and physical component reactionsinvolved in the floral evocation processes, resulting in therhythmical floral response to chilling. (Received August 1, 1974; )     

Photosynthate Unloading from Seed Coats of Phaseolus vulgaris L.--Nature and Cellular Location of Turgor-Sensitive Unloading

Patrick, J. W., Jacobs, E., Offler, C. E. and Cram, W. J. 1986.Photosynthate unloading from seed coats of Phaseolus vulgarisL.—Nature and cellular location of turgor-sensitive unloading—J.exp. Bot. 37: 1006–1019. Unloading rates of ¹⁴C-Photosynthates from excised seed-coathalves of Phaseolus vulgaris L. plants were sharply increasedat cell turgor potentials in excess of 5 ? 10⁵ Pa. Turgor-sensitiveunloading occurred in the absence of any change in the passivepermeability of, and active sucrose influx across, the plasmalemmaand tonoplast membranes. The proton ionophore CCCP, and lowtemperature significantly slowed turgor-sensitive unloadingwhile PCMBS, a non-permeating sulphydryl-modifying compound,was without effect. Turgor-sensitive unloading significantlydepressed the ¹⁴C-Photosynthate content of the ground and branchparenchyma, but had no effect on the ¹⁴C-Photosynthate levelsin the vascular tissues. Cycling of cell turgor potentials aboveand below 5 ? 10⁵ Pa elicited reproducible responses in theunloading rate of ¹⁴C-Photosynthates. Increasing turgor above5 ? 10⁵ Pa resulted in a burst of ¹⁴C-Photosynthate unloading.Reversal to turgors less than 5 ? 10⁵ Pa caused a rapid depressionin unloading rate. It is proposed that turgor-sensitive unloadingis facilitated by a specific turgor-sensitive porter locatedon the plasmalemma of the ground and/or branch parenchyma cellsof bean seed coats. Key words: Bean, seed coat, turgor-sensitive unloading, phloem     

Effects of Chilling, Light and Nitrogen-containing Compounds on Germination, Rate of Germination and Seed Imbibition of Clematis vitalba L.

Effects of chilling (5 °C) period, light and applied nitrogen(N) on germination (%), rate of germination (d to 50% of totalgermination; T_50%) and seed imbibition were examined inClematisvitalba L. In the absence of chilling, light and N, germinationwas minimal (3%). When applied alone, both chilling and N increasedgermination. Chilling for 12 weeks increased germination to64%, and 2.5 mM NO^-₃or NH⁺₄increased germination to 10–12%.Light did not increase germination when applied alone, but didwhen applied in combination with chilling and/or N. Half theseed germinated when light was combined with 2.5 mM NO^-₃or NH⁺₄.The influence of chilling, light and/or N on germination wasgreater when combined, than when either factor was applied alone.Both oxidized (NO^-₃) and reduced (NH⁺₄) forms of N increasedgermination, but non-N-containing compounds did not, suggestingthe response was due to N and not ionic or osmotic effects. Without additional N, T_50%decreased from 16–20 d at zerochilling, to around 5 d at 8 and 12 weeks chilling. AlthoughT_50%was not influenced by an increase in NO^-₃or NH⁺₄from 0.5to 5.0 mM , it did increase with additional applied N thereafter.However, the magnitude of the N effect was small compared tothat of chilling. Like germination, seed imbibition increasedwith a longer chilling period, but in contrast imbibition decreasedslightly with increased applied NO^-₃or NH⁺₄. It is argued thatincreased imbibition is not directly related to an increasein total germination, but that it may be related to the rateof germination. Possible mechanisms involved in the reductionin dormancy ofC. vitalba seed are discussed. Clematis vitalba L.; germination; dormancy; imbibition; rate of germination; chilling; light; nitrate; ammonium; nitrogen; phytochrome     

Effect of High-intensity Light Given Prior to Low-temperature Treatment on the Long-day Flowering of Pharbitis nil

Pharbitis nil, strain Violet which had been exposed to high-intensitylight (18,000 lux at 23?C) for 7 days followed by a low-temperaturetreatment (13–14?C) for 7 days initiated flower buds evenunder continuous light, but plants given these treatments inreverse order failed to bud. Three days of high-intensity lightat 23?C was most effective in promoting the flower-inducingeffect of the subsequent low-temperature period. Six days oflow temperature following the 3-day high-intensity light periodinduced near-maximum flowering response. DCMU (5?10^–6M) given during the high-intensity light period inhibited flowering,but when given during or after the low-temperature period itwas ineffective. DCMU at the same concentration given before,during or after an inductive 16-hr dark period at 26?C did notinhibit flowering. Sucrose, ATP, NADPH and some other reducingagents tested did not nullify the DCMU effect nor substitutefor the effect of high-intensity light. But, the high-intensitylight effect could be substituted, at least partly, by 5-chlorosalicylicacid, 3,4-dichlorobenzoic acid and some other benzoic acid derivatives,which are highly effective in inducing long-day flowering inthe short-day plant, Lemna paucicostata. (Received October 20, 1981; Accepted February 3, 1982)     

Induction of Low Molecular Weight Cadmium-Binding Compound in Soybean Roots

Blakeley, S. D., Robaglia, C, Brzezinski, R. and Thirion, J-P.1986. Induction oflow molecular weight cadmium-binding compoundin soybean roots.—J. exp. Bot. 37: 956–964. A Cd-binding compound has been identified in roots of Cd-treatedsoybean plants (Glycine max L.). Induction of synthesis of thiscompound after treatment with CdCl₂ was monitored by labellingwith either ¹⁰⁹Cd in vitro or with ³⁵S-cysteine or ³⁵S-methioninein vivo. The apparent molecular weight as determined by gelfiltration was about 14000 daltons. However, after carboxymethylationand electrophoresis under denaturing conditions its molecularweight was less than 3400 daltons. Simultaneous labelling with¹⁰⁹ and ³⁵S-cysteine demonstrated that the compound containscysteine residues. Gel electrophoresis of ³⁵S-cysteine or ³⁵S-methioninelabelled protein samples showed the compound to be rich in cysteinebut not in methionine, and that it was induced about 60-foldby 1?0 mol m^–3 CdCl₂ after 7 d. Key words: Soybean, cadmium, induction, root     

Heat shock proteins and chilling sensitivity of mung bean hypocotyls

Excised mung bean (Vigna radiata L.) hypocotyl sections wereexposed to 40 C for up to 4 h in the presence or absence of50 µM cycloheximide (CHX) before being held at a non-chilling(20 C) or chilling (2.5 C) temperature. Mung bean hypocotyltissue is chilling sensitive, and the rate of solute leakageis highly correlated with the extent of chilling injury. A 3h heat shock at 40 C reduced chilling-induced solute leakageby up to 40%, but leakage was similar to non-heat-shocked hypocotylswhen CHX was present. Specific proteins were labelled when hypocotylswere exposed to [³⁵S] methionine during the last hour of heatshock. The nine most intense bands on the autoradiographs ofSDS-PAGE gels of extracted protein corresponded to molecularweights of 114, 79, 73, 70, 60, 56, 51, 46, and 18 kDa. The18 kDa band reached a maximum after 1 h at 40 C and then rapidlydecreased in intensity as the heat shock continued, becomingundetectable at 4 h. The four most intense bands after 3 h at40 C corresponded to molecular weights of 79, 70, 51, and 46kDa. The synthesis of these four hsps was markedly reduced whenthe hypocotyl sections were exposed to CHX during heat shock.During chilling for 6 d, the levels of hsps 79 and 70 remainedsignificantly higher in tissue that was heat shocked prior tochilling than in tissue that was not heat shocked. In contrast,the levels of hsps 51 and 46 were similar in bothheat-shockedand control tissues. Heat-shock-induced chilling tolerance waslost between 6 and 9 d ofstorage at 2.5 C; this loss coincidedwith the decay of hsps 79 and 70 to control levels. These resultssuggest that heat shock induces an increase in both chillingtolerance and the de novo synthesis of specific heat shock proteins;namely hsps 79 and 70. This is the first report showing a relationshipbetween heat-shock-induced chilling tolerance and specific heat-shock-inducedproteins. Key words: Ion leakage, protein synthesis, Vigna radiata     

Characteristic Changes in Relaxation Times of Water Protons in Vigna radiata Seedlings Exposed to Temperature Stress

Water protons in hypocotyl tissues from etiolated seedlingsof Vigna radiata that were exposed to temperature stress showedcharacteristic relaxation behaviors for ¹H-NMR. Cold stresstreatment (0C) caused gradual prolongation of NMR relaxationtimes (T₁). After exposure of tissues to cold stress for 24h, T₁ returned to the initial value as a result of subsequentincubation at normal temperature (20C). By contrast, heat stresstreatment (40C) induced a time-dependent decrease in T₁, whichdid not return completely to the initial value upon subsequentincubation at 20C after exposure to heat stress for 4 h. Weexamined changes in various physical factors that influencethe response of T₁ to temperature stress, namely, water contentand the concentrations of protein, diamagnetic (K⁺, Na⁺, Ca²⁺and Mg²⁺) and paramagnetic (Mn²⁺ and Fe²⁺) ions in the tissues.From the relationships between T₁ and these factors in vitro,we could not interpret the responses of T₁ to the temperaturestress only in terms of a change in water content. A synergisticeffect of an Mn²⁺ -protein complex and pH might be essentialfor the mechanism of changes in T₁ that are due to cold stress.The influence of heat stress on structural water in tissuesis discussed in terms of water-protein interactions. (Received December 28, 1992; Accepted May 6, 1993)     

Thermal Properties of Membrane Lipids from two Cyanobacteria, Anacystis nidulans and Synechococcus sp.

The composition and positional distribution of fatty acids inmonogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylglyceroland sulphoquinovosyldiacylglycerol from two cyanobacteria, Anacystisnidulans and Synechococcus sp. grown at 25°C have been determinedand compared with measurements of the phase separation temperaturesof the lipids. Only monogalactosyldiacylglycerol in Anacystisand sulphoquinovosyldiacylglycerol in Synechococcus showed phaseseparation temperatures above 0°C. The phase transitiontemperature of a sample of sulphoquinovosyldiacylglycerol containingover 90% of the dihexadecanoyl molecular species has been determinedto be 43°C for the Na⁺ salt and 38°C for the Mg⁺⁺ salt. ^*Deceased. September 14, 1986. (Received June 25, 1986; Accepted August 25, 1986)     

Solute Leakage from Solanum nigrum L. Seeds Exposed to High Temperatures during Imbibition

Exposure of Solanum nigrum L. seeds to high temperatures duringimbibition affected their leakage pattern: (1) The rate of leakageof total electrolytes was markedly increased with elevationof temperature. The increase was highest during the first 3h of imbibition but with a reduced rate thereafter. (2) Leakageof Na⁺ was almost complete after 6 h of imbibition at both temperatures,but much more Na⁺ leaked out at 50?C than at 25?C. (3) A markedincrease in leakage of K⁺ occurred after 24 h of exposure to50?C so that after 96 h three times more K⁺ leaked out at 50?Cthan at 25?C. (4) After 6 h of imbibition Ca11 and Mg⁺⁺ continuedto leak out at 25?C and at 50?C at a similar rate. (5) Imbibitionat an elevated temperature induced a marked increase in theleakage of both nucleic acids and proteins. (6) Malate dehydrogenasewas not detected in the leachate at 25?C, but was found after48 h at 50?C. It is assumed that this enzyme was of cytoplasmicorigin, indicating heat damage to membranes. The possible roleof the above phenomena in the loss of viability of the seedsdue to exposure to high temperature during imbibition is discussed. Key words: Leakage, Germination, S. nigrum