The effects of food deprivation, prey density and volume on clearance rates and ingestion rates of Diacyclops thomasi

The ingestion rates of the copepod, Diacyclops thomasi, on thesoft-bodied rotifer, Synchaeta pectinata, increased 10-fold(0.07–0.77 Synchaeta h^–1) over the range 50–250prey l^–1. The saturating functional response curve appearedsigmoid but was statistically indistinguishable from a parabola.The response curve was more linear and 10 times lower over thesame range of density when Diacyclops was offered Kerarellacochleans, a species having a stiffened lorica. Diacyclops maximizedits ingestion rate on Synchaeta as a function of the availablegut space. Predation effort, measured as clearance rates, waslinked tentatively to changes in swimming speed of Diacyclopsand was a function of hunger level. Diacyclops, which were starvedfor varying periods of time, increased their ingestion rateson Synchaeta up to a maximum (-3.0 h^–1) after 7–10h of food deprivation. The gut passage time of Diacyclops wasestimated to be 7–8 h. Therefore, ingestion rates (andclearance rates) appeared to be strongly correlated to the volumeof food in the gut.     

The Hydration-Induced Ca2+ Release Is a General Phenomenon in Characeae

When an internodal cell of Nitella axilliformis that had beentreated with 10 mM KCl and 1 mM EGTA was examined for transcellularosmosis, an increase in the cytosolic concentration of Ca²⁺on the endoosmotic side was observed, as was the case in Nitellaflexilis even though the increase was much smaller in Nitellaaxilliformis. The hydration-induced calcium release (HICR) wasalso observed in other species of Characeae, namely, Chara corallinaand Nitellopsis obtusa. HICR was also demonstrated in cytoplasmisolated from Nitella axilliformis and Chara corallina as fromNitella flexilis. Thus, it appears that HICR is not specificto Nitella flexilis but may be a general phenomenon in Characeae. ²Present adress: Department of Biology, Faculty of Science,Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263 Japan     

Sodium Accumulation in Pappophorum I. Uptake, Transport and Recirculation

The uptake, transport and accumulation of sodium were comparedin two grasses: Pappophorum pappifervm (Lam.) O. Kuntze, a glycophyteand P. philippianum L. R. Parodi, a facultative halophyte. Atlow salinity levels, (50 mM NaCl) shoots of salt-treated P.pappiferum accumulated lower Na⁺ concentrations than the otherspecies. This difference does not seem to be related to Na⁺uptake, as in short-time experiments (< I h), whole plantsof both species showed similar rates of Na⁺ uptake and transport Sodium recirculation was assessed in split-root experiments.It was similar in control (previously non-salinized) plantsof both species, but in salt-treated plants it was more significantin P. pappiferum. This mechanism, along with increased lossof recently acquired Na⁺, could contribute to keep Na⁺ levelslower in shoots of P. pappiferum than in P. philippianum. Pappophorum, Gramineae, sodium recirculation, salinity     

Boron Mobility in Two Coniferous Species

In contrast to earlier beliefs, it is now known that boron (B)can be retranslocated complexed with sugar alcohols in someplant species. Conifers had been thought not to translocatesugar alcohols in the phloem. However, 1 d after applying¹⁰Benriched boric acid to shoots of Scots pine and Norway spruceseedlings, we found increases in both the amount and proportionof¹⁰B in the root systems in both species. We conclude thatB is translocated in the phloem from shoots to roots in spruceand pine, and therefore it is possible that these species retranslocateB. Copyright 2000 Annals of Botany Company Scots pine, Pinus sylvestris, Norway spruce, Picea abies, conifers, boron retranslocation, roots, stable isotopes, sugar alcohols, boron complexes, mineral nutrition, forest trees     

Excitable Channels in Nitellopsis obtusa as Part of an Active Ion-Transport System

The present paper is a study on the rapid and the slow excitablechannels of Nitellopsis obtusa. The working hypothesis is thatduring the excitation of these cells a Ca²⁺-dependent activeion-transport system in the plasmalemma is activated (Gyenesand Bulychev, 1979; Gyenes, Bulychev, and Kurella, 1980) whichmay interact with a light-dependent active transport systemalso present in the plasmalemma. It is found that under conditionsof maximal light-induced current changes, registered in voltageclamp experiments, the amplitudes of both action current componentsare relatively small (10–15 µA cm²) and they increaseup to 100–150 µA cm^–2 during 15–30 minin the dark. Cells may also be excited chemically under conditionsof unchanged voltage across the plasmalemma. It is suggestedthat in the excitation process of Nitellopsis obtusa two typesof ion channels take part/emdash electrically excitable passiveand chemically excitable active channels-both incorporated inone proteolipid complex of a Ca²⁺-dependent ATPase of the plasmalemma.     

SPAWNING SEASON AND EGG PRODUCTION IN FORTH ESTUARY RETUSA OBTUSA (MONTAGU) (GASTROPODA: OPISTHOBRANCHIA)

Retusa obtusa held individually in the laboratory carried largeoocytes in the gonad but did not spawn in December-late January.In late Jan-early Feb, however, the first few individuals producedbatches of 8–17 eggs and, by early February, most individualswere producing means of 2–4 eggs d^–1 and maximain late Feb of <7.9 d^–1. Spawning declined to low levelsin few individuals in late March. By early April, spawning hadvirtually ceased prior to the drastic loss of adults in thepopulation by May. Larger R. obtusa generally produced more eggs than smaller onesand the few specimens shorter than 3.8 mm produced markedlyfewer than those of 3.8–5.0 mm shell length. Twenty of the 34 R. obtusa held in the main breeding period(4 sets started 29 Jan-3 Mar) spawned in 3 or more successiveweeks whereas only 6 of them failed to spawn in 2 consecutiveweeks, so indicating that several successive batches of eggsare commonly produced. Yet in virtually all individuals (exceptat the start of breeding) more eggs were produced in the firstweek of captivity than subsequently. These first-week valuesimply total production by individuals in the spawning seasonof some 112-305 eggs comprising about 2.8-7.6 mg dry weightor, by the Forth estuary population, of 26880-73200 eggs m^–2comprising 0.67-1.83 g dry weight m^–2. (Received 19 August 1988; accepted 30 September 1988)     

Effects of light intensity and quality on the relative N and P requirement (the optimum N:P ratio) of marine planktonic algae

The relative requirement of N and P (the optimum N:P ratio)by Dunaliella tertiolecta, Phaeodactylum tricornutum, Prymnesiumparvum and Thalassiosira pseudonana was studied under variouslight intensities and spectra. The ratio was determined as theratio of the minimum cell N and P concentrations (q₀N and q₀pwhen either nutrient was limiting. The ratio varied widely amongspecies; under light-saturation for growth (116 µEin ^m–2s^–1 it ranged from 11.8 in ^D. tertiolecta to 36.6 in P.tricornutum. The ratio appeared to be higher at a sub-saturatingintensity (24 µEin m^–2 s^–1 in all except P.tricornutum, mainly because of higher q_oN with little changein q_oP. In T. pseudonana Q_oP also increased, resulting in aninsignificant change in the ratio. The ratio varied little withinthe range of saturation intensity. Light quality affected q_oNand q_oP as well as the ratio, and the pattern of change variedfrom species to species. The optimum ratio of individual specieswas linearly correlated to their q_oN except in P. tricornutum.q_oN for all species showed a linear correlation with cell proteinconcentrations irrespective of light conditions. The changeof optimum N:P ratios in the three species thus appears to berelated to changes in cell protein contents. The ratio of carbohydratesto protein remained constant regardless of light intensity orquality and was higher in P-limited cultures. We conclude thatchanges in light regime can strongly influence algal nutrientrequirements and species interrelationships by altering theoptimum cellular N:P ratio.     

Long-term Respiratory Cost of Maintenance and Growth of Field-grown Young Hinoki Cypress (Chamaecyparis obtusa)

Respiration rate of the entire above-ground parts of field-grown8-year-old hinoki cypress [Chamaecyparis obtusa(Sieb. et Zucc.)Endl.] was measured at monthly intervals over a 5-year period,to evaluate the trend in proportion of maintenance and growthcomponents of respiration with stand development. Representativesample trees were selected for respiration measurements. Theannual respiration rates of individual sample trees were combinedand partitioned into maintenance and growth components by regressingspecific respiration rate on mean relative growth rate. Maintenanceand growth respiration coefficients generated in this way were5.2 mol CO₂kg^-1year^-1and 39 mol  CO₂kg^-1, which are equivalentto 14.3 mg C kg^-1C h^-1(at mean annual air temperature of 15.1°C) and 0.94 kg C kg^-1C. Considering the maintenance andgrowth respiration coefficients, and phytomass and phytomassincrement of individual trees in the stand, the maintenanceand growth respiration rates of the stand were estimated. Theproportion of the maintenance respiration increased, whereasthat of the growth respiration decreased with stand development,due to decreasing relative growth rate.Copyright 1997 Annalsof Botany Company Chamaecyparis obtusa; growth respiration coefficient; hinoki; maintenance respiration coefficient; stand respiration     

Rates of Photosynthesis in Characean Cells: II. PHOTOSYNTHETIC 14CO2 FIXATION AND 14C-BICARBONATE UPTAKE BY CHARACEAN CELLS

Photosynthetic ¹⁴C fixation by Characean cells in solutionsof high pH containing NaH¹⁴CO₃ gave a measure of the abilityof these cells to take up bicarbonate (H¹⁴CO₃^–). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 1–1.5µµmoles cm^–2 sec^–1, rates of 3–8µµmoles cm^–2 sec^–1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 5–6 µµmoles cm^–2 sec^–1 wereobtained with Chara australis, 3–8 µµmolescm^–2 sec^–1 with Nitellopsis obtusa, and 1–5µµmoles cm^–2 sec^–1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H¹⁴CO₃^– uptake would be maskedby rapid diffusion of ¹⁴CO₂ into the cells: the four Characeanspecies fixed ¹⁴CO₂ at maximum rates of 30–40 µµmolescm^–2 sec^–1 (at 21° C).     

DISTRIBUTION AND PRODUCTION OF THREE HYDROBIA SPECIES (GASTROPODA: HYDROBIIDAE) IN A SHALLOW COASTAL LAGOON IN THE BAY OF CADIZ, SPAIN

The abundance, life span, growth and production of the mud snailsHydrobia minoricensis, H. ulvae and H. ventrosa in a semi-naturallagoon system were studied by taking monthly samples at threesites during 1991 and 1992. The most abundant species, H. minoricensisoccurred at mean densities of 12834 to 26264 snails m^–2(10.7 to 25.8g dry weigh m^–2), depending on the site.The least abundant species, H. ulvae, occurred at mean densitiesof 185 to 353 snails m^–2 (3.2 to 2.2g dry weight m^–2).The numerical abundance and biomass of the three Hydrobia specieswere positively related to the biomass of benthic macroalgae(P<0.01). Although H. ulvae egg capsules were recorded throughoutthe year, newly hatched snailsof this species were not observed,in contrast to the other two species. The early spring and summercohorts of H. minoricensis and H. ventrosa seemed to be themost numerous. The average life spans of these two species wereestimated to be about 18 and 13 months respectively. Annualproduction estimates for the whole lagoon system were 29.0 (6.3),5.5 (0.8) and 5.2 (1.0)g dry weight (ash-free dry weight) m^–2yr^–1 for H. minoricensis, H. ulvae and H. ventrosa respectively.The annual P/B ratio was about 2 for H. minoricensis and H.ventrosa. (Received 5 July 1994; accepted 5 October 1994)     

The escape behavior of marine copepods in response to a quantifiable fluid mechanical disturbance

The threshold shear values needed to elicit the escape reactionto a quantifiable fluid mechanical disturbance were comparedbetween five free-swimming oceanic copepod species. The resultsindicate a significant difference in the threshold for differentspecies of copepods and between different age groups withina single species. In general, animals captured from more energeticregimes required a higher threshold than those captured frommore pacific locations. Labidocera madurae required the highestshear values with 51.5 s^–1 for 50% of the animals testedto elicit an escape reaction (S₅₀). Acartia tonsa and Euchaetarimana, in contrast, were behaviorally the most sensitive requiringan S₅₀ of only 1.5 and 4.1 s^–1, respectively, to initiatean escape reaction. Pleuromamma xiphias and Oithona requiredintermediate shear values with an S₅₀ of 7.2 and 8.1 s^–1.When compared to literature values, the threshold needed toelicit an escape reaction was consistently higher than averageenvironmental shear values. Threshold shear values also variedsignificantly with developmental stage. Naupliar stages of A.tonsarequired greater than six times the S₅₀ value required by adultsof the same species. This suggests that the higher vulnerabilityto predation of naupliar stages of copepods may not only reflectinferior escape strength, but may also result from the higherthreshold needed to elicit an escape reaction. This study supportsthe hypothesis that selective feeding patterns exhibited bypredators of copepods may be the result of the differentialbehavioral sensitivities of different species and developmentalstages of copepods.     

Biochemical Limitations to Carbon Assimilation in C3 Plants--A Retrospective Analysis of the A/Ci Curves from 109 Species

Species-specific differences in the assimilation of atmosphericCO₂ depends upon differences in the capacities for the biochemicalreactions that regulate the gas-exchange process. Quantifyingthese differences for more than a few species, however, hasproven difficult. Therefore, to understand better how speciesdiffer in their capacity for CO₂ assimilation, a widely usedmodel, capable of partitioning limitations to the activity ofribulose-1,5-bisphosphate carboxylase-oxygenase, to the rateof ribulose 1,5-bisphosphate regeneration via electron transport,and to the rate of triose phosphate utilization was used toanalyse 164 previously published A/C_i, curves for 109 C₃ plantspecies. Based on this analysis, the maximum rate of carboxylation,Vc_max, ranged from 6µmol m^–2 s^–1 for the coniferousspecies Picea abies to 194µmol m^–2 s^–1 forthe agricultural species Beta vulgaris, and averaged 64µmolm^–2 s^–1 across all species. The maximum rate ofelectron transport, J_max, ranged from 17µmol m^–2s^–1 again for Picea abies to 372µmol m^–2 s^–1for the desert annual Malvastrum rotundifolium, and averaged134µmol m^–2 s^–1 across all species. A strongpositive correlation between Vc_max and J_max indicated that theassimilation of CO₂ was regulated in a co-ordinated manner bythese two component processes. Of the A/C_i curves analysed,23 showed either an insensitivity or reversed-sensitivity toincreasing CO₂ concentration, indicating that CO₂ assimilationwas limited by the utilization of triose phosphates. The rateof triose phosphate utilization ranged from 4·9 µmolm^–2 s^–1 for the tropical perennial Tabebuia roseato 20·1 µmol m^–2 s^–1 for the weedyannual Xanthium strumarium, and averaged 10·1 µmolm^–2 s^–1 across all species. Despite what at first glance would appear to be a wide rangeof estimates for the biochemical capacities that regulate CO₂assimilation, separating these species-specific results intothose of broad plant categories revealed that Vc_max and J_maxwere in general higher for herbaceous annuals than they werefor woody perennials. For annuals, Vc_max and J_max averaged 75and 154 µmol m^–2 s^–1, while for perennialsthese same two parameters averaged only 44 and 97 µmolm^–2 s^–1, respectively. Although these differencesbetween groups may be coincidental, such an observation pointsto differences between annuals and perennials in either theavailability or allocation of resources to the gas-exchangeprocess. Key words: A/C_i curve, CO₂ assimilation, internal CO₂ partial pressure, photosynthesis     

Variation in the DNA Content of Glycine Species

Nuclei were isolated from cotyledons of a range of accessionsfrom 14 species of Glycine. These were stained with ethidiumbromide and the relative fluorescence for each genotype wasmeasured by flow cytometry. The DNA content was estimated bycomparison of relative fluorescence with that from nuclei fromseedling leaves of Allium cepa, whose DNA content has been calculatedpreviously by chemical assay. The 4C amounts for diploid Glycineranged from 3.80 to 6.59 pg. Two groups of diploid species appearedfrom the analysis. The first consisted of species with amountsranging from 3.80 to 5.16 pg and included G. canescens (AA),G. argyrea (A₁ A₁), G. clandestina (A²A²), G. microphylla(BB),G. latifolia (B₁B₁), G. tabacina 2n=40 (B²B²), G. tomentella2n=38 (EE) and 2n=40 (DD), G. max and G. soja (GG), G. arenariaand G. latrobeana. A second group had higher DNA contents rangingfrom 5.27 to 6.59 pg, and consisted of G. curvata, G. cyrtoloba(CC), and G. falcata (FF). The polyploid species, G. tabacina2n=80 (AABB, BBB¹B¹), G. tomentella 2n=78 and 2n=80 (AAEE andDDEE, respectively) contained amounts approximating to the sumsof the respective parental diploid species thought to have givenrise to these allotetraploids. Intraspecific variation was detectedin the DNA content of G. canescens. Within the overall distributionof DNA amounts found in A genome species, each genome containeda range of DNA contents specific to that species. This phenomenonwas also detected amongst B genome species.     

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

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

The Effect of Salinity Changes Upon the Physiology of Eulittoral Green Macroalgae from Antarctica and Southern Chile: II INTRACELLULAR INORGANIC IONS AND ORGANIC COMPOUNDS

The effects of hypo- and hypersaline treatments ranging from7–68% on the intracellular inorganic ion and organic soluteconcentrations were determined in the eulittoral green macroalgaeUlothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa,Acrosiphonia arcta, and Ulva rigida from Antarctica and SouthernChile. The main inorganic cations were K⁺, Na⁺, and Mg²⁺ inall species. The major osmolyte in E. bulbosa, A. arcta, andU. rigida was K⁺ at increasing salinities. In both Ulothrixspecies, however, K⁺ levels declined during hypersaline stressand Na⁺ concentrations rose significantly. The main inorganicanions were Cl^-, SO²_4-, and PO³_4- in all algae, while E. bulbosaand U. rigida also contained NO⁺₃. A. arcta showed an extremelyhigh SO^2-₄ content. The organic solutes proline, sucrose, andß-dimethylsulphoniopropionate (DMSP) played an importantrole in osmotic acclimation. The occurrence of three organicosmolytes suggests an additional function of these solutes ascryoprotectants in the cold-water macroalgae investigated.     

Experimental studies into the feeding biology of rotifers in brackish water

Mass developments of rotifers of the genus Brachionus, and especiallyof B.quadridentatus, occur regularly in the largely hypertrophicchain of shallow waters (‘boddens’) south of theDarss-Zingst peninsula (Southern Baltic). Interest in the autecologyof the species is, therefore, considerable. Various food sourceswere used in laboratory experiments to ascertain the food requirementsof B.quadridentatus, determine its filtration and ingestionrates, and assess its food particle size-selection ability.Growth experiments showed that the chlorophyceans Nannochlorissp. and Chlorella vulgaris possess considerable nutritionalvalue for the species, whereas abundances declined when Microcystisfirma, detritus from Enteromorpha sp. and only bacteria (Pseudomonas),respectively, were provided as food sources. Filtration ratesvaried between 0.02 and 1.73 µl ind.^–1 h^–1,and ingestion rates between 121 and 5560 cells ind.^–1h^–1, depending on the filtration rate and algal concentration.Investigations into food particle size selection using fluorescentlatex particles revealed that particle size influences foodparticle intake. When particles of different sizes were mixed,the animals showed a preference for the larger particles andingested the smaller ones with a diameter of 1–2 µmless efficiently. The brackish water species Brachionus plicatiliswas studied besides B.quadridentatus in all experiments. Theformer species proved to be superior both in its range of utilizableparticle sizes and its growth rate. The experiments with laboratorycultures were backed up by studies performed with various rotiferspecies taken from natural populations.     

Annual cycle of tintinnids in Admiralty Bay with an emphasis on seasonal variability in Cymatocylis affinis/convallaria lorica morphology

In water samples collected from the middle of Admiralty Bay(King George Island 62°08'S 58°25'W) between February1990 and January 1991, 17 Tintinnina species were noted. TotalTintinnina numbers in summer were very high (up to 5000 cellsm^–3), but species diversity was low, consisting mainlyof Cymatocylis affnislconvallaria, forma convallaria. Duringaustral winter, cell numbers were very low, but species compositionwas diverse. Cymatocylis affnislconvallaria, forma affinis,and C.affmis/convallaria, forma convallaria, the polymorphicforms of one species C.affinis/convallaria, appear to be interchangeableduring the year. The transition from one form to the other occursin the spring and autumn. The typical Tintinnina polymorphismcan be attributed to the prevailing environmental conditions.     

Life history, biomass and production of two planktonic cyclopoid copepods in a shallow subtropical reservoir

Two planktonic cyclopoid copepods (Tropocyclops prasinus andMesocyclops longisetus) were raised in the laboratory to obtainlife history information (duration of embryonic and post-embryonicdevelopment, reproductive performance, longevity, and stage-specificlength and weight values). Animals were maintained at 20 and25°C, and fed ad libitum. Development times were temperaturedependent when food was not limiting, with shorter periods ofembryonic and post-embryonic development and decreased longevityat 25°C. Laboratory data on the duration of developmentand biomass, together with population dynamics data obtainedin the field, were used to estimate summer and winter biomassand production of these species in a shallow reservoir, LagoaDourada, Brazil. The maximum production rate of T. prasinus,attained during summer, was 2.8 mg dry weight (DW) m^–3day^–1 and the highest daily production:biomass (P:B) ratiowas 0.29, whereas for M. longisetus the maximum production ratewas 1.4 mg DW m^–3 day^–1 and the highest daily P:Bratio was 0.39, in the winter. Over short time intervals (everyother day), there was great variability of the species productionrates. Species production rates were low compared to valuesreported in the literature for the same or other species ofequivalent sized copepods from both tropical and subtropicalregions.     

Ultrastructural observations on marine choanoflagellates (Choano-flagellida, Acanthoecidae) from the coast of Thailand: species of Apheloecion gen.nov

Three species of loricate choanoflagellates (Choanoflagdlida,Acanthoecidae), collected from the Andaman Sea near Phuket Island(SW Thailand), have been described and referred to Apheloeciongen.nov. (holotype: A. quadrispinum sp.nov.). All species possessa single-chambered lorica composed of one transverse costs overlaidby a limited number of longitudinal costae which converge posteriorly.Anteriorly the longitudinal costae protrude above the transversecosta as sharp pointed spines. In A. quadrispinum sp.nov. andA. pentacanthum sp.nov. the lorica is terminated by a shortposterior spine, whereas in A. articulatum sp.nov. the pedicelis much more prominent, consisting of several costal stripswhich are joined end-to-end. The species of Apheloecion appearto be most closely related to species of Calliacantha and Monocosta.None of the species described are so far known from localitiesoutside the Andaman Sea.     

Nuclear DNA Content of 26 Orchid (Orchidaceae) Genera with Emphasis onDendrobium

2C DNA content values for 70 orchid species from 26 genera,including 37Dendrobiumspecies from eight taxonomic sections,were analysed using flow cytometry. The resulting nuclear DNAcontent values for species other thanDendrobiumranged from 1.91pg 2C^-1to 15.19 pg 2C^-1nuclei forCadetia tayloriandVanilla phaeantha,respectively.Dendrobiumnuclear DNA content values ranged from1.53 pg 2C^-1to 4.23 pg 2C^-1nuclei forD. cruentumandD. spectabile,respectively. DNA content measurements varied greatly withinDendrobiumsectionsLatouria and Spatulata. Nuclear DNA content values for the sixspecies analysed within Latouria ranged from 1.88 pg 2C^-1nucleiforD. macrophyllumto 4.23 pg 2C^-1nuclei forD. spectabile. NuclearDNA content values for the 16 species analysed within Spatulataranged from 1.69 pg 2C^-1nuclei forD. discolorto 4.05 pg 2C^-1nucleiforD. samoense. The least variation in DNA content was foundwithin the section Phalaenanthe, with nuclear DNA content valuesof 1.79 pg  2C^-1, 1.86 pg 2C^-1and 1.98 pg 2C^-1forD. bigibbum,D.affineandD. phalaenopsis, respectively.Copyright 1998 Annalsof Botany Company Orchidaceae,Dendrobium, flow cytometry, propidium iodide, nuclear DNA, genome size, 2C values.