Supercooling ability of Rhododendron flower buds in relation to cooling rate and cold hardiness

The freezing process and supercooling ability in flower budsof 11 native Rhododendron species were examined with referenceto the cooling rate and cold hardiness by differential thermalanalysis. The freezing patterns of the excised whole buds variedwith the season: in autumn, buds froze as whole units, whilein winter, freezing was initiated in the scales and propagatedto each floret. The supercooling ability of florets was enhancedduring winter. The freezing patterns in winter buds were stronglyinfluenced by the cooling rate (1 to 30°C/hr). Althoughthe first exotherm in scales occurred at –5 to –10°Gand was rate-independent, the occurrence of several floret exothermsshifted considerably to lower subzero temperatures at slowerrates. The most reliable cooling rate for testing maximum supercoolingability was l°C/hr. The exotherm in florets of hardier speciesoccurred at –20 to –25°C and at –7 to–20°C for less hardy ones, and were well correlatedwith their killing temperatures. Water relations within budtissues in response to freezing are briefly discussed. (Received June 26, 1980; )     

Supercooling ability of Rhododendron flower buds in relation to cooling rate and cold hardiness

The freezing process and supercooling ability in flower budsof 11 native Rhododendron species were examined with referenceto the cooling rate and cold hardiness by differential thermalanalysis. The freezing patterns of the excised whole buds variedwith the season: in autumn, buds froze as whole units, whilein winter, freezing was initiated in the scales and propagatedto each floret. The supercooling ability of florets was enhancedduring winter. The freezing patterns in winter buds were stronglyinfluenced by the cooling rate (1 to 30°C/hr). Althoughthe first exotherm in scales occurred at –5 to –10°Gand was rate-independent, the occurrence of several floret exothermsshifted considerably to lower subzero temperatures at slowerrates. The most reliable cooling rate for testing maximum supercoolingability was l°C/hr. The exotherm in florets of hardier speciesoccurred at –20 to –25°C and at –7 to–20°C for less hardy ones, and were well correlatedwith their killing temperatures. Water relations within budtissues in response to freezing are briefly discussed. (Received June 26, 1980; )     

Supercooling Ability, Water Content and Hardiness of Rhododendron Flower Buds during Cold Acclimation and Deacclimation

The relationship between supercooling ability and water contentand killing temperature of flower buds during cold acclimationand deacclimation were studied using R. kiusianum and R. x akebono.The occurrence of multiple floret exotherms and their shiftto a narrow range at lower subzero temperatures, as well asthe marked decrease of florets water content, were observedas the symptoms of cold acclimation occuring in flower budsfrom fall to winter, and vice versa in spring buds during deacclimation.In R. kiusianum, the fully acclimated period was from Novemberto March and two months longer than that of R. x akebono. Thesupercooling ability of the former was about –25°Cand about –20°C in the latter. Although the watermigration within bud tissues during the freezing process wasdetermined in the acclimated and deacclimated buds for R. xakebono, no significant water changes could be observed, evenin the acclimated buds. Thus, it is conceivable that deep supercoolingin florets may result not necessarily from water migration fromflorets and bud axes to scales in response to freezing, butfrom low water content in situ of cold-acclimated or artificiallydehydrated flower buds. (Received July 29, 1981; Accepted October 12, 1981)     

Collapse of Peroxide-Scavenging Systems in Apple Flower-Buds Associated with Freezing Injury

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 the‘McIntosh’ 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 10^–4 to10^–5 M and 10^–5 M, respectively, and the levelsof GSH decreased to about 10^–5 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 ‘Jonathan’apple 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)     

Cold hardiness in various organs and tissues of Rhododendron species and the supercooling ability of flower buds as the most susceptible organ

The freezing resistance of various organs and tissues was determined in 24 Rhododendron species (mainly Subgenus Tsutsutsi) having different ecological distributions. The order of hardiness for organ or tissue is as follows: leaf bud > wood ≧ bark > flower bud, and the flower bud is characterized as the most cold-susceptible organ. The relationship of killing temperature (KT) to northern distribution was the most significant in leaf buds compared to other organs and tissues. KTs of leaf buds for the most hardy species were ?45 °C (or below) and those for the most tender species were about ?23 °C, while KTs of flower buds were about ?28 °C for the former and ?16 °C for the latter. Although KTs of flower buds native to southwestern Japan were well correlated with the exothermic temperature distribution (ETD) of florets, those in the more northern species were generally lower than ETDs. The supercooling ability of flower buds appears to be sufficient to avoid the freezing stress since the extreme minimum temperature (EMT) at the northern limit of natural distribution for each tree species examined was not lower than the KT and ETD of the flower buds.     

Effects of Irradiance and Temperature on Flowering of Chrysanthemum morifolium Ramat. in Continuous Light

The short-day plant Chrysanthemum morifolium cv. Polaris initiatedflower buds in all irradiances of continuous light from 7.5to 120 W m^–2. As the irradiance increased, the transitionto reproductive development began earlier and the number ofleaves initiated before the flower bud was reduced. The autumn-floweringcultivars Polaris and Bright Golden Anne, and the summer-floweringGolden Stardust were also grown in continuous light at differenttemperatures; all initiated flower buds at temperatures from10 to 28 °C but only the buds of Golden Stardust developedto anthesis and then only at 10 and 16°C. Flower initiationbegan earliest at 16–22 °C, and the number of leavesformed before the flower bud was increased at 28°C. GoldenStardust was exceptional in that the number of leaves formedwas also increased at 10 °C. Axillary meristems adjacentto the terminal meristem initiated flower buds rapidly at 10°C but not at 28 °C in all three cultivars. These resultsare discussed in relation to the autonomous induction of flowerinitiation and the effects of the natural environment on floweringof chrysanthemum. Chrysanthemum morifolium Ramat, flowering, irradiance, temperature     

Freezing avoidance mechanism of primordial shoots of conifer buds

Excised winter buds of very hardy fir supercooled to —30or — 35?C, though primordial shoots excised from thesewinter buds (freezing point: about —5.5?C) supercooledonly to —12 to — 14?C. Also, excised primordialshoots did not tolerate freezing, but were rather resistantto desiccation. Differential thermal analysis (DTA) of primordialshoots revealed that the capability of supercooling increasedwith decreasing water content and that no exotherm could bedetected in the primordial shoots with a water content belowabout 20%. When excised whole buds were cooled very slowly,the exotherm temperature shifted markedly to a lower value andthe exotherm became much smaller. Also, masses of needle icewere observed, mainly beneath the crown of the primordial shoot.From these results, it may be concluded that most of the waterin primordial shoots gradually migrates out through the crownand freezes as the temperature decreases (extraorgan freezing),which enables primordial shoots to survive at very low temperatures.Winter buds of Abies balsamea held at — 20?C for 30 daysand then slowly cooled down to —50 or —60?C remainedalive. Thus, there seems to be no low temperature limit to thisfrost avoidance mechanism, if the primordial shoots can resistintensive freeze-dehydration. Low temperature exotherms wereobserved in all genera which belong to Abietoideae and Laricoideaeof Pinaceae, all of which have a crown in the primordial shoots,but not in other conifers. ¹ Contribution No. 2037 from the Institute of Low TemperatureScience. (Received June 25, 1979; )     

Pigment Production by Cultured Florets of Chrysanthemum morifolium

Individual florets (4–5 mm long) of a purple cultivar(Fandango) of the horticultural chrysanthemum (Chrysanthemummorifolium Ramat) were taken from flower buds just prior toopening and cultured in a sterile liquid medium (containinginorganic salts and sucrose) at 15 °C under a 12-h day.For the first 14 days increase in wet weight was exponential.Anthocyanin appeared on the third day and was then synthesizedrapidly. Chlorophyll and carotenoid were present initially:carotenoid levels rose quickly while chlorophyll remained almostconstant. Highest pigment content and most growth were foundwhen the florets were grown on 3 per cent sucrose. However,the highest anthocyanin concentration was found with 4 per centsucrose, the highest carotenoid concentration with 0.6 per centsucrose. No anthocyanin was produced when the florets were grownat 6 or 30 °C; maximum yield was at 15 °C. Most carotenoidwas formed at 30 °C and most chlorophyll was found at 20–5°C. All florets from 1 to 7 mm long could be cultured. Theseresults are discussed in relation to flower colour and pigmentformation in vivo.     

Seasonal variations in freezing curves of stem sections of Cornus stolonifera MICHX.I

Comparisons of freezing curves have been used to determine theviability of plant parts exposed to stress. To gain understandingof the natural seasonal variations in freezing curves, uniformtwig sections of red-osier dogwood (Cornus stolonifera MICHX.)were collected throughout the year from a single clone and subjectedto controlled freezing while the tissue temperature was recorded.The supercooling of samples ranges from –2 to –7,but the variation was random and unpredictable. There was noapparent relationship between supercooling and the season ofthe year or the hardiness of the tissue. The freezing pointdepression, as estimated by the temperature of the first freezingplateau, was always between –0.25 and –1.0 andbore no relationship to hardiness or season. The freezing curveswere basically of three types: Summer and winter curves withtwo distinct freezing points; Early autumn curves with 3distinctfreezing points and spring curves with one prominent first freezingpoint which tended to mask the second freezing point. ¹Scientific Journal Series paper No. 6628, Minnesota AgriculturalExperiment Station. This research was supported in part by agrant from the Louis W. and MAUD HILL Family Foundation. ²Present Address: Horticulture Department, University of Wisconsin,Madison, Wisconsin, U.S.A.     

Freeze Desiccation: a Second Mechanism for the Survival of Hydrated Lettuce (Lactuca sativa L.) Seed at Sub-zero Temperatures

Differential Thermal Analysis of hydrated lettuce cv. GreatLakes achenes using a rapid cooling rate (20 °C h^–1)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 h^–1)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     

Low temperature exotherms of winter buds of hardy conifers

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; )     

Evidence for the Cell Wall Involvement in Temporal Changes in Freezing Tolerance of Jerusalem Artichoke {Helianthus tuberosus L.) Tubers during Cold Acclimation

We studied the mechanism of cold acclimation of Jerusalem artichoke{Helianthus tuberosus L.) tubers with special reference to therole of the cell wall. During the cold-acclimation process fromSeptember to January, the freezing tolerance of tubers increasedfrom – 2.8°C to –8.4°C (LT₅₀). By contrast,the isolated protoplasts con- stitutively showed a consistenthigh level of freezing toler ance (LT₅₀; below – 25°C)throughout the period. In tuber tissues, freezing injury waseffectively protected by the ex ternal addition of isotonicsolutions. Cryomicroscopic ob servations revealed that tissuecells mounted in isotonic so lutions plasmolyzed upon freezing;tissue cells mounted in water collapsed with a tight attachmentof plasma mem brane to the cell wall. Upon freezing of intacttissues in water to temperatures below the critical range, thecyto plasm was irreversibly acidified as revealed by a fluorescence pH-ratiometry, suggesting that occurrence of detri mentalcellular events leading to permanent cell injury. The freeze-inducedacidification of cytoplasm was also effective ly prevented bythe external addition of isotonic solutions. These results suggestthat the tight attachment of the plas ma membrane to the cellwall during freezing may have a harmful effect on cells, inparticular on the plasma mem brane, possibly due to mechanicalor some sort of chemi cal/physico-chemical interaction withthe cell wall. ¹Contribution no. 3946 from The Institute of Low TemperatureScience, Hokkaido University. This research was supported inpart by the grant from Japan Society for the Promotion of Science(JSPS-RFTF 96L00602) ²Present address: Tohoku National Agricultural Experiment Station, Morioka, Iwate, 020-01 Japan     

Changes in Tissue Freezing in Senecio vulgaris infected by Rust (Puccinia lagenophorae)

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 3.1–5.8 °C,rusted leaves supercooled by only 1.8–4.9 °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 ml^–1. 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     

The Freezing Response of an Arctic Cushion Plant, Saxifraga caespitosa L.: Acclimation, Freezing Tolerance and Ice Nucleation

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 3–4 °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     

Freezing Tolerance of Shoot and Flower Primordia of Coniferous Buds by Extraorgan Freezing

Shoot and flower primordia of vegetative and flower buds ofextremely or very hardy conifers belonging to the subfamilyAbietoideae of the Pinaceae, survived between –40 and–70?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 below–25?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)     

Extraorgan freezing in wintering flower buds of Cornus officinalis Sieb. et Zucc.

Abstract. Extraorgan freezing as a mechanism for increasing cold hardiness was shown using flower buds of Cornus officinalis Sieb. et Zucc. Differential thermal analysis (DTA) revealed that florets in flower buds of C. officinalis owed their cold hardiness to deep supercooling and also that slower cooling rates increased the supercooling ability of florets. During slow stepwise cooling (5°C h⁻¹), the water content of florets decreased and that of scales (involucral bracts) increased, which resulted in accumulation of ice within the scales. This was more extensive in early winter and early spring buds than mid-winter ones. Flower buds with silicone oil in the space between florets and scales also showed a similar decrease in water content of florets and an increase in that of scales. This indicated that water migration from the florets to the scales probably took place by way of the peduncles and the receptacle, possibly through their vascular traces, and not directly from the surface of the florets to the ice sink in the form of vapour. Possible mechanisms of extraorgan freezing are postulated along with this finding.     

Vacuolar Membrane Lesions Induced by a Freeze-Thaw Cycle in Protoplasts Isolated from Deacclimated Tubers of Jerusalem Artichoke (Helianthus tuberosus L.)

The processes of freezing injury in Jerusalem artichoke (Helianthustuberosus L.) tubers were studied using protoplasts isolatedfrom cold-acclimated and deacclimated tubers. Prior to freezing,protoplasts were preloaded with 10 µM fluorescein diacetate(FDA) in an isotonic sorbitol solution. After freeze-thawingat various temperatures, cell viability was evaluated undera fluorescence microscope. In cold-acclimated tubers, more than80% of protoplasts survived freezing to – 20°C. Bycontrast, in deacclimated tubers, the cell survival abruptlydeclined after freezing to temperatures below – 5°C.Thus, freezing tolerance differed significantly between protoplastsisolated from cold-acclimated and deacclimated tubers. Two distincttypes of cell injury, which were caused by either damage toplasma membrane (cell-lysis type) or by damage to the vacuolarmembrane (abnormal-staining type), were observed, dependingon the cold hardiness and freezing temperature. In the cellsof the abnormal-staining type, shrinkage of the central vacuolarspace and simultaneous acidification of the cytoplasmic spacewere characteristically observed immediately before completecell-rehydra-tion during thawing. The decrease in freezing toleranceof protoplasts after deacclimation was suggested to be due mainlyto destabilization of the vacuolar membrane by freeze-induceddehydration stress. ¹Contribution no. 3945 from The Institute of Low TemperatureScience, Hokkaido University. This research was supported inpart by the grant from Japan Society for the Promotion of Science(JSPS-RFTF 96L00602) ²Present address: Tohoku National Agricultural Experiment Station, Morioka, Iwate, 020-01 Japan     

Determinate Floral Buds of Plantain (Musa AAB) as a Site of Adventitious Shoot Formation

Floral buds of the ‘False Horn’ plantain clonesMusa (AAB) ‘Harton Verde’, ‘Harton Negra’,and ‘Currare’ terminate in a large single floralstructure. The apices of these floral buds are here designatedas determinate since they have lost the ability to produce additionalfloral initials or buds. Terminal peduncle segments can be culturedin a modified Murashige and Skoog (1962) medium supplementedwith N⁶-benzyl-aminopurine (5 mg I^–1). Under these conditions,this apparent inability to yield buds can be overcome as vegetativeshoot clusters form in the axils of the bracts. Rooted plantletsare obtainable by treating shoots with naphthaleneacetic acid(1 mg I^–1) and activated charcoal (0.025%). The adventitiousorigin of the shoots has been established. Musa cultivars, plantains, floral bud, adventitious buds, tissue culture     

Plant Regeneration Through Meristem Culture from Vegetative Buds of Mulberry (Morus bombycis Koidz.) Stored in Liquid Nitrogen

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 1^–1 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     

Effects of Gibberellic Acid and Naphthaleneacetic Acid on Petiole Senescence and Subtended Peduncle Growth of Cyclamen persicum Mill

Removal of the blade from the leaf subtending the first flowerbud on Cyclamen persicum ‘Swan Lake’ plants causedthe petiole of that leaf to senesce, but had no effect on thegrowth of the flower peduncle in the debladed petiole's axil.A 10 mg NAA l^–1 application generally had no effect onpetiole senescence, peduncle elongation or flowering date whenapplied to the cut end of the petiole after blade removal. A25 mg GA₃ l^–1 application or a combination of 25 mg GA₃l^–1 application or a combination of 25 mg GA₃ l^–1plus 10 mg NAA l^–1 delayed petiole senescence and enhancedpeduncle elongation and subsequent flowering. No treatment significantlyaltered peduncle length at the time of flowering. Cyclamen persicum Mill, ‘Swan Lake’, tissue receptivity, flowering, GA₃, NAA