Effects of Light and Temperature on Flower-opening of Pharbitis nil

Flower buds of Pharbitis nil cut from plants growing in thefield opened rapidly when kept in darkness for 8 hr followedby continuous light at 20–25°C, but those kept indarkness for 4 hr opened promptly oniy when the temperatureduring the following light period was kept at 23°C or lower.Buds exposed to continuous light at 25°C did not open, butthose exposed to continuous light at 23°C opened slowly.At a lower temperature, the buds opened rapidly even in continuouslight. When the buds were placed in darkness at 25°C at13:30, 17:30 and 21:30 (artificial light from 17:30 to 21:30),they opened about 10 hr after the onset of darkness regardlessof the time of the onset of darkness, but when the buds werekept at 20°C in light from 13:30, 17:30 and 21:30, theyopened at 3:30–5:30 regardless of the time of transferto the lower temperature. The biological clock which controlsthe time of flower-opening is suggested to be easily reset bya light-off signal, but not by a shift from a normal to lowertemperature (20°C). At the lower temperature, the time offlower-opening probably is determined by the time of the latestpreceding light-off (or light-on) signal. ¹Dedicated to Professor Dr. Erwin Biinning on the occasion ofhis 75th birthday. (Received October 23, 1980; Accepted December 15, 1980)     

Physical Basis of Flower-opening in Pharbitis nil

Flower buds of Pharbitis nil cut from plants growing in thefield open rapidly when subjected to darkness (20–25°C)or low temperature (20°C) in light. Petals of the buds arethe sites of photo- and thermo-perception; flower-opening iscaused mainly by the epinasty of petal midribs. ¹Dedicated to Professor Dr. Erwin Bunning on the occasion ofhis 75th birthday. (Received October 23, 1980; Accepted December 15, 1980)     

Studies on the light controlling the time of flower-opening in Pharbitis nil

Flower buds of Pharbitis nil, strain Violet, open about 10 hrafter the onset of darkness at 24?C. Daylight fluorescent lightat 0.3–3 W/m² given during the first 4 hr of this darkperiod delayed the time of flower-opening, but that given laterhad only a slight effect or was ineffective. Red light was mosteffective in delaying the time of flower-opening, and a 5-minred light pulse given every 30 min also was effective. The effectof this 5-min red light was partly reversed by a subsequentfar-red light pulse which suggests that the absence of P_fr duringthe first 4 hr in the dark is necessary for normal timing offlower-opening. Five minutes of red light given 10 hr after the onset of darknessadvanced the phase of the circadian rhythm which controls thetime of flower-opening; buds opened about 7 hr earlier on thefollowing day. This effect of red light was also reversed bya subsequent exposure to far-red light, which suggests the participationof phytochrome in this reaction. (Received October 8, 1979; )     

The Metabolism of Abscisic Acid

The light-catalysed isomerization of (+)-abscisic acid (ABA)to its trans isomer during isolation from leaves was monitoredby the addition of (±)-[2-¹⁴C]ABA to the extraction medium.(+)Trans-abscisic acid (t-ABA) was found to occur naturallyin rose (Rosa arvensis) leaves at 20µg/kg fresh weight;(+)-ABA was present at 594µg/kg. (±)-[2-¹⁴D]Trans-abscisicacid was not isomerized enzymically to ABA in tomato shoots. (±)-Abscisic acid was converted by tomato shoots to awater-soluble neutral product, ‘Metabolite B’, whichwas identified as abscisyl-ß-D-glucopyranoside. When(±)-[2-¹⁴C]trans-abscisic acid in an equimolar mixturewith (±)-[2-¹⁴C}ABA was fed to tomato shoots it was convertedto its glucose ester 10 times faster than was ABA. Trans-abscisyl-ß-D-glucopyrano8ide only was formedfrom (±)-[2-¹⁴C]t-ABA in experiments lasting up to 30h. Glucosyl abscisate was formed slowly from ABA and the freeacid fraction contained an excess of the unnatural (–).ABAas did the ABA released from abscisyl-ß-D-glucopyranosideby alkaline hydrolysis. The (+).ABA appeared to be the solesource of the acidic ‘Metabolite C" previously noted. The concentrations of endogenous (+)-, (+)-[2-¹⁴C]-, and (–)-[2-¹⁴C]ABAremaining as free acid, and also in the hydrolysate of abscisyl-ß-D-glucopyranoside,were measured by the ORD, UV absorption, and scintillation spectrometryof highly purified extracts of ABA from tomato shoots whichhad been supplied with racemic [2-^l4C]ABA.     

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     

Environmental Factors Controlling Flower Opening and Closing in aPortulacaHybrid

To examine flower opening and closing of aPortulacahybrid, flowerbuds were placed in darkness for 12 h (2030–0830 h) at20 °C and then exposed to various light-temperature conditions.Flower buds exposed to light at 25, 30 or 35 °C opened within1 h, and wilted 10–14 h later. Flower buds exposed tolight at 20 °C started to open after 4 h but opened slowlyand not completely. Flower buds subjected to 25, 30 or 35 °Cin darkness also opened rapidly, but did not reach full opening.Flowers opened at 30 °C in light, and partially closed andopened repeatedly in response to cycles of a 2-h exposure to20 °C and a 2-h exposure to 30 °C at any time between1000 to 1600 h. Similar phenomena were observed when the flowersopened at 30 °C in light and then were subjected to darknessand light alternately at 30 °C, although the effect of lightwas less obvious than that of alternating temperature. Floweropening and closing were not affected by relative humidity.These results indicate that a rise in temperature is requiredfor rapid flower opening in the buds kept at 20 °C, andthat light intensifies the effect of high temperature. Exposureto light without a temperature change delayed and slowed floweropening which was never complete. The involvement of an endogenousrhythm in flower opening byPortulacais indicated. Portulacahybrid, flower opening, flower closing, temperature shift, endogenous rhythm.     

Stomatal Functioning of In Vitro and Greenhouse Apple Leaves in Darkness, Mannitol, ABA, and CO2

Leaves from in vitro and greenhouse cultured plants of Malusdomestica (Borkh.) cv. Mark were subjected to 4 h of darkness;4 h of 1 M mannitol induced water stress; 1 h of 10^–4M to 10^–7 M cis-trans abscisic acid (ABA) treatment; 1h of 0.12% atmospheric CO₂. Stomatal closure was determinedby microscopic examination of leaf imprints. In all treatments,less than 5% of the stomata from leaves of in vitro culturedplants were closed. The diameter of open stomata on leaves fromin vitro culture remained at 8 µm. In contrast, an averageof 96% of the stomata on leaves of greenhouse grown plants wereclosed after 4 h in darkness; 56% after 4 h of mannitol inducedwater stress; 90% after 1 h of 10^–4 M ABA treatment; 61%after 1 h in an atmosphere of 0.12% CO₂. Stomata of in vitroapple leaves did not seem to have a closure mechanism, but acquiredone during acclimatization to the greenhouse environment. Thelack of stomatal closure in in vitro plants was the main causeof rapid water loss during transfer to low relative humidity.     

Freezing Avoidance Mechanisms by Supercooling in Some Rhododendron flower Buds with Reference to Water Relations

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)     

Correlative Inhibition of Lateral Bud Growth in Pisum sativum L. and Phaseolus vulgaris L.: Studies of the Role of Abscisic Acid

The possibility has been investigated that abscisic acid (ABA)might act as a correlative inhibitor of lateral bud growth inPisum sativum and Phaseolus vulgaris. Application of ABA insmall quantities (2µg) to axillary buds on decapitatedplants of P. sativum caused appreciable inhibition of theirgrowth, and induced a compensatory growth of the bud on an adjacentnode. Application of this same quantity of ABA to axillary budson decapitated plants of Phaseolus vulgaris was without effect,but a high concentration in lanolin (1 mg g^–1) did substantiallyreduce bud outgrowth. Endogenous ABA-like substances in Phaseolusvulgaris, detected by bioassay and electron capture g.l.c.,were present in similar concentrations in shoot tips, lateralbuds on intact plants and lateral buds on plants decapitated24 h earlier. The effects of applied ABA suggested that it might be involvedin the mechanism of correlative inhibition in Pisum sativum,but it was not possible to test this hypothesis by determiningendogenous ABA levels in axillary buds because of their smallsize. The evidence presented here suggests that ABA is not acorrelative inhibitor in Phaseolus vulgaris even though at highconcentration it can inhibit the growth of axillary buds.     

Chilling Injury in Cotton {Gossypium hirsutum L.): Light Requirement for the Reduction of Injury and for the Protective Effect of Abscisic Acid

Pretreatment by darkness increased chilling (4°C) injuryin whole cotton (Gossypium hirsutum L.) seedlings and isolatedcotyledonary tissue. Addition of sucrose in the dark periodprevented the effect of darkness. Application of the photosyntheticinhibitor DCMU in light simulated the effect of darkness. ABA(10^–5 M) decreased chilling injury when applied in lightas a pretreatment before the onset of chilling. The same pretreatmentin darkness was almost ineffective, unless sucrose was added.ABA applied in light together with DCMU was ineffective in decreasingchilling injury. Lower light intensity resulted in increasedchilling injury and a decreased effect of ABA in the preventionof chilling injury. The antimicrotubular drug colchicine increased the chillinginjury. Pretreatment with ABA in light decreased the chillingand colchicine injury while the same pretreatment in darknesswas ineffective. These results suggest that a deficiency of a photosyntheticproduct increases the chilling sensitivity of the tissue. ABAapparently increases chilling resistance through a metabolicprocess which depends on photosynthetic activity. ³ Incumbent of the Seagram Chair in Plant Sciences (Received November 20, 1980; Accepted January 31, 1981)     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Effect of abscisic acid on membrane-bound epidermal ATPase from tobacco leaves

Membrane-bound Mg⁺⁺-activated ATPase activity in epidermal stripsfrom tobacco leaves (Nicotiana tabacum L. Samsun NN) was stimulatedby abscisic acid (ABA) when the strips were floated on ABA solutionin light or in darkness. The optimum ABA concentrations in lightand in darkness were 10^–5 M and 10^–6 M, respectively.Carbonyl cyanide m-chlorophenylhydrazone (CCCP) and N, N'-dicyclohexylcarbodiimide(DCCD) completely blocked the basal level membrane-bound epidermalATPase activity. ABAinduced membrane-bound epidermal ATPaseactivity was completely inhibited by CCCP, but only partly byDCCD. H⁺-influx into epidermal strips on a solution in light was lowerthan that in darkness. ABA stimulated H⁺-influx into epidermalstrips in light and in darkness. CCCP suppressed basal levelH⁺-influx, whereas DCCD did not. CCCP also suppressed ABA-inducedH⁺-influx, whereas DCCD did not. Interaction between H⁺-influxand membranebound epidermal ATPase activity is discussed. (Received May 23, 1978; )     

Microelectrophoretic and 9-Aminoacridine Fluorescence Study of the Surface Electrical Properties of Suspension Cultured Catharanthus roseus Cells and Isolated Protoplasts: Effects of Abscisic Acid Treatment

The effects of abscisic acid (ABA) treatments on the surfaceelectrical properties of cells and isolated protoplasts fromCatharanthus roseus cell suspension cultures were studied byelectrophoretic mobility and 9-aminoacridine (9AA) fluorescencemeasurements. The surface charge densities of the cells andprotoplasts estimated from electrokinetic data were –0.064Cm^–2and –0.048 C m^–2 respectively. These values wereclose to that estimated by 9AA fluorescence technique i.e.,–0.053 Cm^–2 for the cells and –0.041 Cm^–2for the isolated protoplasts accordingly. The net negative surfacecharge density decreased after application of 10 µM and50 µM ABA in both cells and protoplats, the more pronouncedeffect being observed at 10 µM ABA. When 100 µMABA was supplemented to the cell suspension culture the oppositeeffect was observed. The average charge density increased to–0.074 C m^–2 for the cells, and to –0.055C m^–2 for protoplasts, as revealed from the 9AA measurements.The results are discussed in terms of specific concentrationdependent ABA-induced alterations of the electrostatic propertiesof cell and protoplast membranes. (Received December 12, 1994; Accepted April 3, 1995)     

Light- and Auxin-Induced Leaflet Opening in Detached Pinnae of Mimosa pudica

Leaflet pairs from detached pinnae of Mimosa pudica opened afterthe pinnae had been irradiated with light (2 W·m^–2)of 726 or 403 nm, whereas they remained almost closed with lightof 585 or 656 nm. Light-induced leaflet opening was observedonly in the daytime, from 6:00 to 16:00. Application of IAAat more than 30 µg/ml to the cut end of the pinna rachisesmade the leaflets open even in darkness with almost constantlag times of about 100 min which were independent of the concentration.NAA and 2,4-D also made the leaflet open at lower concentrationsthan IAA. Auxin-induced leaflet opening showed diurnal variation.Application of IAA for 2 to 6 min, depending on the concentration,was enough to open the leaflets. Autoradiography showed thatIAA was transferred from the cut end of a rachis throughouta pinna within 4 min. ¹Present address: Biological Institute, Faculty of Science,Kobe University, Kobe 657, Japan. (Received September 24, 1982; Accepted March 4, 1983)     

Feeding and growth rates of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

The goal of this research is to enhance our knowledge of thecontributions of doliolids to the planktonic community as consumersand secondary producers. The objectives are to quantify feedingand growth rates of Dolioletta gegenbauri gonozooids at fourfood concentrations and four temperatures in order to determinetheir impact as grazers throughout the water column. Althoughdoliolids are abundant in numerous regions of the coastal ocean,and are considered to be major planktonic grazers, data on ratesof feeding and growth are scarce. Laboratory experiments wereconducted at 16.5, 20, 23.5 and 26.5°C to quantify removalof a 50:50 volumetric concentration of Thalassiosira weissflogiiand Rhodomonas sp. at four different food concentrations of20, 60, 160 and 390 µg C l^–1. Results from theseexperiments suggest that clearance rates are similar at concentrationsfrom 20 to 60 µg C l ^–1, and decrease as the foodconcentrations increase to 160 and 390 µg C l ^–1.The ingestion rates increase over a range of phytoplankton concentrationsfrom 20 to 160 µg C l ^–1, then decrease when abnormallyhigh concentrations of 390 µg C l ^–1 are offered.Clearance and ingestion rates increase as temperature increasesfrom 16.5 to 26.5°C. The exponential growth rates rangefrom k = 0.2–0.7, with the lowest rates occurring at thehighest food concentration. Growth rates increase with increasingtemperature from K = 0.1–0.3 at 16.5°C to 0.45–0.7at 26.5°C. In each case, the small- and medium-sized zooidshad higher growth rates than the larger gonozooids. These resultssuggest that doliolid feeding and growth rates are a functionof environmental food concentrations and temperatures, and implythat they can be important consumers in a changing neritic environment.     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. Part I. A comparative study of the growth-irradiance relationship of three marine phytoplankton species: Skeletonema costatum, Olisthodiscus luteus and Gonyaulax tamarensis

Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m^–2 s^–1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O₂ and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 10^–3 µmol O₂ (µgChl a)^–1 h^–1 (µEinst m^–2 s^–1)^–1.Differences in maximum growth rate varied as the –0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m^–2s^–1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µ–Irelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµ–I curves and explained 97% of the observed interspecificvariability. ¹Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA     

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     

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     

Development of Eodiaptomus japonicus Burckhardt (Copepoda, Calanoida) reared on different sized fractions of natural plankton

The nutritional value of different sized fractions of naturalplankton was investigated for the growth of Eodiaptomus japonicusBurckhardt by comparing the development of its naupliar andcopepodid stages fed on differentially fractionated planktonicassemblages of a eutrophic pond, at 20°C. Water filteredthrough a 0.8 µm Nuclepore filter, containing mainly smallcoccoid bacteria (0.45–0.6 µm in cell diameter),at a concentration of 82.7 µg C 1^–1 could not supportthe development of E.japonicus. The 3 µm filtered water,containing bacteria and picoalgae. at a total concentrationof 259 µg C 1^–1, supported development but not eggproduction. The 20 µm filtered water, containing bacteria,picoalgae and large algae, at a total concentration of 2600µg C 1^–1, supported rapid development of the juvenilesand continuous egg production by the adults. The separated 3–20µm fraction, containing only large algae, could not supportthe development at concentrations of 131 and 196 µg C1^–1. However, the same rapid development of the juvenilesand continuous egg production by adults occurred at all of thetested concentrations between 261 and 3920 µg C1^–1of the large algae. The results suggest that E.japonicus favoursalgae larger than 3 µm during its complete lifespan, andthat the threshold food concentration for its development variesbetween 200 and 250 µg C 1^–1.