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1.
Freeze Desiccation: a Second Mechanism for the Survival of Hydrated Lettuce (Lactuca sativa L.) Seed at Sub-zero Temperatures 总被引:1,自引:0,他引:1
Differential Thermal Analysis of hydrated lettuce cv. GreatLakes achenes using a rapid cooling rate (20 °C h1)produced two exotherms per achene. Both exotherms representedthe freezing of supercooled water. The high temperature exothermoccurred at 93 °C and was produced by freezing ofwater inside the pericarp but exterior to the endosperm. Thetemperature at which it occurred could be altered by the additionof nucleating agents. The low temperature exotherm produced by freezing of the embryooccurred at 162 °C and marked the death of the seed.Its temperature was not changed by the addition of nucleatingagents but its occurrence required the structural integrityof the endosperm. At low cooling rates (1 and 2 °C h1)low temperature exotherms were not recorded and samples removedat 25 °C had high viability. Slow cooling causeda redistribution of water within the seed whereby ice formingoutside the endosperm caused desiccation of the embryo and preventedits freezing. A mechanism is proposed, in terms of established supercoolingand nucleation theory, to explain the observed results and thevalue of freeze tolerance to the species in its natural habitatis discussed. Cooling rate, differential thermal analysis, freezing avoidance, Lactuca sativa L., lettuce, seed, supercooling, water migration 相似文献
2.
Effects of cooling and rewarming rates on the survival of carnationshoot apices frozen to the temperature of liquid nitrogen wereinvestigated. Ten percent dimethyl sulfoxide (DMSO), alone orin combination with 5% glucose, sucrose or sorbitol was mosteffective as a cryoprotectant for carnation shoot apices. Theshoot apices survived slow freezing at about 70?C inthe presence of 10% DMSO. About 80% of the shoot apices survivedfreezing at the temperature of liquid nitrogen after prefreezingat 50?C or below, regardless of the rewarming rates.Shoot apices in the presence of 10% DMSO were cooled at differentrates then rewarmed rapidly. The survival rate gradually decreasedto zero as the cooling rate increased from about 0.5?C/min to50?C/min. At cooling rates higher than 50?C/min, no survivalwas observed even at 5?104?C/min. However, in apices prefrozenat 15?C or below then cooled ultrarapidly at 104?C/min,all remained alive with subsequent rapid rewarming. These apicesdeveloped normal young plants. This ultrarapid cooling methodcombined with prefreezing seems to be useful for the cryopreservationof shoot apices from various plants.
1Contribution No. 2207 from the Institute of Low TemperatureScience, Hokkaido University. This work was supported in partby a Grant-in-Aid (No. 434035) for Scientific Research fromthe Ministry of Education, Science and Culture. (Received November 13, 1979; ) 相似文献
3.
Low temperature tolerance was investigated in the imbibed seedof 15 seed lots compnsmg seven cultivars of Lactuca sativa L.During rapid cooling (20 °C h1) some seeds of allseed lots survived to 16 °C but none to 20°C. The majority of seed lots retained over 50 per centviability above 14 °C due to isolation of the embryofrom external ice by the endosperm, and subsequent embryo super-cooling.Certain seed lots, including all three seed lots of cv. TomThumb, showed high mortality at temperatures above 10°C. Correlation of mortality with the formation of externalice suggested that the endosperm is not an effective nucleationbarrier in these seed lots. Survival to 20 °C was increased at slower coolingrates (6 to 1 °C h1) due to freeze desiccation ofthe embryo, but seed lots varied considerably in their toleranceof specific cooling rates. A model to explain this variationwas developed incorporatmg (1) seed lot super-cooling limittemperature, (2) the rate at which freeze dehydration of thesupercooled embryo took place, (3) the moisture content at whichnucleation (at 20 °C) was no longer certain and (4)the.initial equilibrium moisture content of the fully imbibedseed. Factors (1), (2) and (3) were found to be relatively constant,but low (or artificially reduced) seed moisture content wasclosely correlated with high survival at natural cooling rates.Seed size fractions of similar moisture content from a singlecultivar showed that more small seeds survive cooling at 3 °Ch1 to 20 °C than larger seed. Seed with pierced endosperms or ineffective nucleation barrierswere capable of surviving to at least 10 °C if cooledslowly (1 °C h1) but were killed by rapid (20 °Ch1) cooling. Lactuca sativa L, lettuce, seed germination freezing tolerance, super-cooling 相似文献
4.
Freezing Avoidance Mechanisms by Supercooling in Some Rhododendron flower Buds with Reference to Water Relations 总被引:3,自引:0,他引:3
Excised florets of some hardy Rhododendron species did not toleratefreezing at 5°C when ice-inoculated due to intracellularfreezing. Florets in intact December buds, however, could besupercooled to about 30°C. When flower buds of R.japonicum were slowly cooled with daily decrements of 5°Cto temperatures ranging from 0 to 20°C, the exothermtemperatures of the florets drastically decreased. This wasaccompanied by a decrease in water content of florets and peduncleand an increase in that of scales. The water in florets andthe peduncle is thought to migrate to scales and other tissuesduring the early stages of freezing; the dehydrated floret hasa lower freezing point which enhances its supercooling abilityand the dehydrated peduncle helps to maintain the supercooledstate of the florets. This hypothesis would explain the dependenceon the cooling rate of supercooling in Rhododendron flower buds.Water migration within flower buds was observed in other hardyRhododendron species with some variation in ice formation siteand the quantity of migrated water. The exotherm temperatureof excised florets was inversely proportional to their watercontent. Dehydration of flower buds by wind at 0°C alsoenhanced their supercooling ability. Mechanisms of freezingavoidance by supercooling in Rhododendron flower buds and therelationship of supercooling to freezing tolerance are discussed.
1 Contribution No. 2254 from the Institute of Low TemperatureScience
2 This is a revised form of the master's thesis of the seniorauthor (M.I.) which is cited in the present and previous papers(Sakai 1979a, b, etc.). (Received August 11, 1980; Accepted June 1, 1981) 相似文献
5.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m3 CaCl2 r, P, Y and were20.7±4.6 µm min1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min1MPa1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m3 KC1 these parametersbecame 12.3±3.5 µm min1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min1MPa1. After 24 h osmotic adjustment in 150 mol m3mannitol/0.5 mol m3 CaCl2 r= 19.6±4.2 µmmin1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min1 MPa01, respectively.After 24 h growth in 350 mol m3 mannitol/0.5 mol m3CaCl2 r= 13.3±4.1 µm min1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min1MPa1. During osmotic adjustment in 200 mol m3mannitol/0.5 mol m3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min1MPa1. Therefore, Y and are influenced by 10 mol m3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur 相似文献
6.
Thermal analyses of freezing events in hydrated lettuce (LactucasativaL.) seeds show a correlation between low temperature exotherms(LTEs) (evidence of ice crystal formation) and seed death. Yet,weather patterns common to the Northern Great Plains of NorthAmerica regularly create conditions where non-dormant seedsof native plants hydrate with snow melt and are subsequentlyexposed to -30 °C or colder conditions. To determine ifsuch weather patterns decimate dispersed seeds, we measuredthe effects of freezing on fully hydrated winterfat (Eurotialanata(Pursh) Moq.) seeds harvested from the Northern Plainsat two USA and one Canadian location. Survival of hydrated seedsto -30 °C at a cooling rate of 2.5 °C h-1was similarto that of seeds not subjected to cooling, even though botha high temperature exotherm (HTE) and an LTE were observed.Although the LTE was not related to winterfat seed survival,freeze-stressed seeds had reduced germination rates and reducedseedling vigour, particularly for the collection with the lightestseeds. The temperature of LTEs was similar among seed collectionswith a mean of -17.6 °C, but was warmer when the seeds wereimbibed at 0 °C compared to 5, 10 or 20 °C. We founda significant correlation between the HTE and LTE temperatures.The difference and the correlation may be due to the highermoisture content of seeds imbibed at 0 °C. After pericarpremoval, only one exotherm in the range of the LTE was observed.This was also true for the naked embryo. We conclude that anLTE indicates ice formation in the embryo, but that it doesnot signal the death of a winterfat seed.Copyright 1998 Annalsof Botany Company Eurotia lanata(Pursh) Moq.,Krascheninnikovia, Ceratoides,winterfat, exotherm, freezing tolerance, freezing avoidance, seedbed ecology, germination, D50, seedling vigour, seed collection 相似文献
7.
CLARKE ANDREW; LEESON ELSPETH A.; MORRIS G. JOHN 《Journal of experimental botany》1986,37(9):1285-1293
86Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, 86Rb uptake was abolished. Cells cooled rapidlyto 5°C in the absence of ice accumulated 86Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and 86Rb uptake, albeit slow, was measurable at5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced 86Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate 86Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, 86Rb uptake, membrane 相似文献
8.
Shoot and flower primordia of vegetative and flower buds ofextremely or very hardy conifers belonging to the subfamilyAbietoideae of the Pinaceae, survived between 40 and70?C by extraorgan freezing, which differed greatly dependingupon species. The water in these organs gradually froze outwith decreasing temperatures when cooled very slowly, whichenabled these organs to survive %40?C or below. The same icesegregation in shoot and flower primordia by extraorgan freezingwas observed in most of the temperate conifers belonging toTaxaceae, Cephalotaxaceae, Taxodiaceae and Cuppressaceae, makingthem resistant to temperatures between 15 and 25?C.In these conifers, scales acted as an ice sink, unlike the conifersof Abietoideae. The rates of cooling and exosmosis of waterin the shoot or flower primordia, their size, and their abilityto tolerate freeze-dehydration or its related stress play animportant role in determining whether death is caused by freeze-dehydrationor intraorgan freezing. Even in very hardy conifers, low temperature exotherms fromfreezing within the shoot primordia appeared between 30and 35?C on the DTA profiles when cooled continuouslyunder laboratory conditions from 5?C to 50?C at 2 to5?C/h. Appearance of low temperature exotherms always resultedin death. However, in the coldest area of Hokkaido, where theair temperature cools down to 40?C or below nearly everyyear, such an intraorgan freezing seems seldom to occur, especiallyin natural stands. On the other hand, low temperatures below25?C seldom occur in warm-temperate climates. Thus, itmay be considered that in both boreal and temperate coniferstheir shoot and flower primordia seem to tolerate freeze dehydrationby extraorgan freezing under natural conditions.
1 Contribution No. 2431 from the rnstitute of Low TemperatureScience. (Received March 27, 1982; Accepted August 12, 1982) 相似文献
9.
SCAGLIARINI SANDRA; PUPILLO PAOLO; VALENTI VINCENZO 《Journal of experimental botany》1988,39(8):1109-1119
Scagliarini, S., Pupillo, P. and Valenti, V. 1988. Isoformsof NADP-dependent malic enzyme in tissues of the greening maizeleaf.J. exp. Bot. 39: 11091119. The compartmentation of the isoforms of NADP-dependent malicenzyme (E.C. 1.1.1.40
[EC]
) has been studied in cell-free extractsand in enzymatically-isolated protoplasts of mesophyll tissue(MT) and bundle sheath (BS) strands of greening maize leaves.The etiolated leaf of 10-d-old seedlings contains a cytosolicisozyme with a pl of 5.4 ?0.1 at low specific activity (s.a,45 ? 3 nmol min1 mg1 protein), found both in MTand BS. The green leaf on the other hand contains the dominantBS chloroplast isozyme with pl 4.6 ? 0.2 at a s.a, of 370 ?40 nmol min1 mg1 protein (3.2 ? 0.5 µmolmin1 mg1 chl) and a minor, previously undescribedisoform with pl 6.5 ? 0.1 also localized in the BS at a s.a.of 38 ? 6 nmol min1 mg1 protein. Green MT protoplastshave only traces of pl 4.6 isozyme. After illumination of dark-grown seedlings, the total leaf activityshows a rapid increase (1.5-fold within 2 h), attributed mainlyto the pl 5.4 isozyme of MT protoplasts and BS strands. Thisis followed by a large increase of enzyme activity due to thecontinued rise of pl 5.4 isozyme for about 24 h and, after aninitial lag of a few hours, to the accumulation of pl 4.6 isozyme.After 18 h illumination, pl 4.6 and 5.4 isozyme activities tendto decline in the MT whereas they are still increasing in theBS, particularly the former. This pl 4.6 species has becomethe major one by 48 h illumination. The final pattern of greenleaves is established around 96 h light, when the chloroplastisozyme has attained its maximum level, the pl 5.4 isozyme ofBS strands has been superceded by the pl 6.5 species (also supposedto be cytosolic) and MT protoplasts retain little residual activity.Some metabolic implications of the changing pattern of NADP-dependentmalic isozymes during maize leaf greening are discussed. Key words: C4, isozymes, malic enzyme, photodifferentiation, Zea mays 相似文献
10.
Freezing of healthy and rust (Puccinia lagenophorae) infectedleaves of Senecio vulgaris was compared calorimetrically bythermal analysis. In fully expanded leaves the threshold freezingtemperature was in the range 6.8 to 8.4 °Cin controls but 3.0 to 5.1 °C in leaves withsporulating rust sori. Comparable values in expanding leaveswere 5.0 to 8.9 °C and 3.9 to 6.7°C for healthy and rusted tissues, respectively. The bulktissue freezing point was between 1.0 and 4.0°C in both fully expanded and expanding healthy leaves,and was increased by infection by between +0.2 and 2.5 °C.Whereas healthy leaves supercooled by 3.15.8 °C,rusted leaves supercooled by only 1.84.9 °C Supercoolingof control leaves was reduced by dusting with aeciospores, particularlywhen leaves were wounded to simulate the rupture of the surfacecaused by sporulation, but wounding alone had no significanteffect. Supercooling of distilled water was also significantlyreduced by aeciospores, suspended at a concentration of 105spores ml1. It is concluded that rust-induced changes in leaf freezing inS. vulgaris grown in controlled environments were due to anincrease in the number of sites for ice nucleation, caused bythe presence of the aeciospores, and increased penetration ofice into internal tissues, resulting from damage to the cuticleand epidermis. Although data for frost resistance obtained inthe growth-room are similar to previous field observations,the role of the above mechanisms under field conditions remainsunproven. Senecio vulgaris (groundsel), Puccinia lagenophorae (rust), low temperature, freezing resistance 相似文献
11.
BUTLER DECLAN M.; ?STGAARD KJETILL; BOYEN CATHERINE; EVANS LEONARD V.; JENSEN ARNE; KLOAREG BERNARD 《Journal of experimental botany》1989,40(11):1237-1246
In an investigation of the main factors determining protoplastyield in Laminaria saccharina and L. digitata, protoplasts wereisolated from epidermal, cortical and medullary cells of vegetativethallus by incubation with commercial cellulases, crude andpurified mannuronate lyases and purified guluronate lyases.Treatment of the tissue with the calcium chelator EGTA beforeenzymatic digestion greatly increased the protoplast yield.Preplasmolysis was also necessary to obtain large numbers ofhealthy protoplasts and this was most effective when carriedout during chelation with EGTA. Purification of the mannuronatelyases by ion exchange chromatography reduced the toxicity ofthe crude enzyme preparation. The activities of the wall degradingenzymes were differentially influenced by pH and the optimumfor alginate-lyase activity (8.0) was higher than that for cellulaseactivity (<6.0). Protoplast yield decreased linearly withincreasing pH in the enzyme medium over the range tested (6.08.0),and this suggests that cellulases are more critical to walldigestion than alginate-lyases. Ionic osmotica gave improvedyields compared with sugar alcohols or sugars. Increasing thecalcium concentration of the enzyme medium brought about anexponential decrease in protoplast yield and wall digestionwas almost completely inhibited at concentrations exceeding8.0 mol m3. However, low levels of calcium (<2.0 molm3) were beneficial to protoplast viability. Yields of107 to 108 protoplasts g1 fr. wt. were consistently obtainedand 20% to 30% of these regenerated new cell walls within 12d of culture. Key words: Laminaria protoplasts, cell wall, alginate-lyases 相似文献
12.
Changes in the freezing tolerance for Silene acaulis L., a subarcticand arctic species of circumpolar distribution, were examinedto understand the extent of cold hardening and dehardening thatoccurs seasonally and with changes in plant phenology. Shootsof whole plants collected on a mountain ridge near Tromsø,Norway (69° N, 700 m above sea level) were frozen undercontrolled conditions at cooling rates of 3 to 4°C h-1.The extent of freezing-induced injury was examined both by chlorophyllfluorescence and by visual inspection with a microscope. A freezingtolerance level of -30°C was observed in mid-winter, basedon a 50% lethal point for freezing injury. Loss of cold hardinesswas substantial in mid-summer, with freezing tolerance of -8·5to -9°C observed in mid-July. Plants still covered by snowin mid-July had a freezing tolerance of -12·5 to -13°C.The maintenance of a basic level of freezing tolerance throughoutthe summer may be adaptive in the northern latitude-regionsbecause of the occurrence of episodic frosts during the growingseason.Copyright 1993, 1999 Academic Press Silene acaulis L., Caryophyllaceae, freezing tolerance, chlorophyll fluorescence, cushion plant 相似文献
13.
Cytoplasmic pH (pHc) in Chara corallina was measured (from [14C]stribution)as a function of external pH (pH0)and temperature. With pH0near 7, pHc at 25?C is 7.80; pHcincreases by 0.005 pH units?C1 temperature decrease, i.e. pHc at 5 ?C is 7.90. WithpH? near 5.5, the increase in pHc with decreasing temperatureis 0.015 units ?C1 between 25 and 15?C, but 0.005 units?C1 between 15 and 5?C. This implies a more precise regulationof pHc with variations in pHo at 5 or 15 ?C compared with 25?C. The observed dp Hc/dT is generally smaller than the 0.017units ?C1 needed to maintain a constant H+/OH1,or a constant fractional ionization of histidine in protein,with variation in temperature. It is closer to that needed tomaintain the fractional ionization of phosphorylated compoundsor of CO2HCO3 The value of dpHc/dT has importantimplications for several regulatory aspects of cell metabolism.These include (all as a function of temperature) the rates ofenzyme reactions, the H+ at the plasmalemma(and hence the energy available for cotransport processes),and the mechanism for pHc regulation by the control of bidirectionalH+ fluxes at the plasmalemma. 相似文献
14.
Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s1 m2 photon flux density in a16 h photoperiod. The rate of CO2 output per fruit increasedquickly from 0.005 to 0.018 mg CO2 min1 during fruitelongation and subsequently more slowly to 0.030 mg CO2 min1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO2 g1 min1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO2 g1 min1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g1 d. wt day1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg1 d. wt day1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg1 nitrogen day1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g1growth (equivalent to a conversion efficiency, YG, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration 相似文献
15.
Plant Regeneration Through Meristem Culture from Vegetative Buds of Mulberry (Morus bombycis Koidz.) Stored in Liquid Nitrogen 总被引:3,自引:0,他引:3
Intact vegetative buds of mulberry (Morus bombycis) attachedto shoot segments were prefrozen, stored in liquid nitrogen,thawed, and the meristems excised for culture on Murashige andSkoog's medium supplemented with 1 mg 11 BA to regenerateplants. Either prefreezing at 10 °C or 20°C along with rapid thawing at 37 °C or prefreezingat 20 °C or 30 °C along with slow thawingat 0 °C was a suitable condition for high percentages ofsurvival and shoot regeneration. Potted mulberry plants couldbe finally obtained from the cryopreserved material. The systemusing intact buds as the material for cryopreservation is quitesimple when compared to conventional systems using isolatedmeristems together with cryoprotectants. Morus bombycis Koidz., mulberry, cryopreservation, meristem culture, plant regeneration 相似文献
16.
Cold hardiness in actively growing plants of Saxifraga caespitosaL., an arctic and subarctic cushion plant, was examined. Plantscollected from subarctic and arctic sites were cultivated ina phytotron at temperatures of 3, 9, 12 and 21 °C undera 24-h photoperiod, and examined for freezing tolerance usingcontrolled freezing at a cooling rate of 34 °C eitherin air or in moist sand. Post-freezing injury was assessed byvisual inspection and with chlorophyll fluorescence, which appearedto be well suited for the evaluation of injury in Saxifragaleaves. Freezing of excised leaves in moist sand distinguishedwell among the various treatments, but the differences werepartly masked by significant supercooling when the tissue wasfrozen in air. Excised leaves, meristems, stem tissue and flowerssupercooled to 9 to 15 °C, but in rosettesand in intact plants ice nucleation was initiated at 4to 7 °C. The arctic plants tended to be more coldhardy than the subarctic plants, but in plants from both locationscold hardiness increased significantly with decreasing growthtemperature. Plants grown at 12 °C or less developed resistanceto freezing, and excised leaves of arctic Saxifraga grown at3 °C survived temperatures down to about 20 °C.Exposure to 3 °C temperature for up to 5 d did notsignificantly enhance the hardiness obtained at 3 °C. Whenwhole plants of arctic Saxifraga were frozen, with roots protectedfrom freezing, they survived 15 °C and 25°C when cultivated at 12 and 3 °C, respectively, althougha high percentage of the leaves were killed. The basal levelof freezing tolerance maintained in these plants throughoutperiods of active growth may have adaptive significance in subarcticand arctic environments. Saxifraga caespitosa L., arctic, chlorophyll fluorescence, cold acclimation, cushion plant, freezing stress, freezing tolerance, ice nucleation, supercooling 相似文献
17.
Gut clearance rates of starving and continuously feeding Acartiatonsa were estimated. During the initial 30 min the rates weresimilar (0.045 and 0.048 min1, respectively; 14°C)but thereafter starving animals expelled the remains of theirgut contents at half the rate (0.019 min1) of fed ones(0.048). Pigment destruction was estimated by (i) incubationexperiments over 34 days, (ii) silica to pigment ratioin algae and faeces and (iii) by gut filling experiments. Theincubations showed that 8% of the ingested pigments were destroyedto nonfluorescent residues during gut passage. The silica topigment ratio method gave an average of 11 % (1 24) destructionand gut-filling experiments showed no systematic differencebetween ingestion measured as gut filling rate (fluorescence)and particle reduction.
1Present address: Kristineberg Marine Biological Station, S-45034 Fiskebäckskil, Sweden 相似文献
18.
Low temperature exotherms of winter buds of hardy conifers 总被引:2,自引:0,他引:2
Differential thermal analysis (DTA) of winter buds and the excisedprimordial shoots of sub-alpine or sub-cold firs revealed thatthese buds had all low temperature exotherms around 30?C.However, no low temperature exotherm below 15?C was detectedin the spring buds. In the winter bud of Abies firma, a temperatefir native to Japan, a low temperature exotherm was detectedaround 20?C, which is higher by 10?C than that of sub-alpineor sub-cold firs. The low temperature exotherms of these firsoccurred at nearly the same temperatures that result in thedeath of these primordial shoots. On the other hand, littleor no low temperature exotherm was detected in the winter budsof sub-cold spruces. In larch winter buds, numerous small exothermswere observed, which are probably due to the many leaf primordiain the buds. Unlike many temperate deciduous broad-leaved trees,no low temperature exotherm was detected below 15?C inwinter twig xylem of conifers such as Abies, Picea, Pinus, Larixand Pseudotsuga. Thus, very hardy coniferous twigs can tolerateextracellular freezing to 70?C.
1 Contribution No. 1907 from the Institute of Low TemperatureScience. (Received June 8, 1978; ) 相似文献
19.
The moisture content of newly germinated cabbage seed (radicles1 05 mm long) was reduced to 14% of f.wt without loss of viability.As the moisture content was reduced below 45%, the temperatureat which the germinated seeds froze, and therefore died, decreasedprogressively to a minimum of 34 C at 19% moisture content.No freezing exotherms were recorded in seeds with moisture contentsbelow 19%. Seeds with a moisture content between 14 and 16%maintained viability for at least 1 week when cooled at 26C.min1to 20 C and held at this temperature, indicating thepotential for prolonged storage of these low-moisture-contentgerminated (LMCG) seeds. Brassica oleracea, cabbage, germinated seed, seed storage, fluid drilling, freezing exotherm, thermal analysis 相似文献
20.
Collapse of Peroxide-Scavenging Systems in Apple Flower-Buds Associated with Freezing Injury 总被引:2,自引:0,他引:2
Changes in the metabolic activities of peroxide-producing systemsand peroxide-scavenging systems after freezing and thawing inflower buds of the apple, Malus pumila Mill., were studied withspecial reference to freezing injury. In flower buds of theMcIntosh apple that were frozen below lethal temperatures,the activity of NADH-Cyt c reductase (EC 1.6.99.3
[EC]
), one of theenzymes in the electron-transport chains that are related tothe peroxide-producing systems, decreased slightly, while thatof Cyt c oxidase (EC 1.9.3.1
[EC]
) hardly changed. By contrast, theactivities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49
[EC]
),dehydroascorbate reductase (EC 1.8.5.1
[EC]
) and ascorbate peroxidase(EC 1.11.1.11
[EC]
), which are involved in the peroxide-scavengingsystems, decreased to very low levels. The activity of glyceraldehyde-3-phosphatedehydrogenase (EC 1.2.1.12
[EC]
) also decreased markedly. However,little change was observed in the activities of hexokinase (EC2.7.1.1
[EC]
), glucosephosphate isomerase (EC 5.3.1.9
[EC]
), glutathionereductase (EC 1.6.4.2
[EC]
) and glutathione peroxidase (EC 1.11.1.9
[EC]
).Examination of substrates involved in the peroxide-scavengingsystems revealed that the levels of glucose-6-phosphate andfructoses-phosphate decreased to approximately 104 to105 M and 105 M, respectively, and the levelsof GSH decreased to about 105 M or became barely detectable.A decrease in the levels of GSSG also occurred while levelsof ascorbate rose slightly. Similar results were observed withflower buds from Starking Delicious and Jonathanapple trees. These results suggest that the freezing injury to apple flower-budsis closely related to the collapse of the peroxide-scavengingsystems that are coupled with the pentose phosphate cycle. Theresults also suggest that the dysfunction of these peroxide-scavengingsystems is caused by H2O2, which may be produced during freezingand thawing. (Received March 14, 1992; Accepted June 5, 1992) 相似文献