Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya--Lakes Bogoria, Nakuru and Elmenteita

For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaiasminor Geoffroy) have been observed at alkaline-saline KenyanRift Valley lakes. To estimate the potential influence of toxiccyanobacteria on these mass deaths, the phytoplankton communitieswere investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterialtoxins were analyzed both in the phytoplankton from the threelakes and in isolated monocyanobacterial strains of Arthrospirafusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidiumterebriformis. Lake Bogoria was dominated by the cyanobacteriumA. fusiformis. In L. Nakuru and L. Elmenteita the phytoplanktonmainly consisted of A. fusiformis, A. abijatae and Anabaenopsisarnoldii, and in L. Nakuru an unknown Anabaena sp. was alsofound. Furthermore, this is the first time A. abijatae and theunknown Anabaena sp. have been found in Kenyan lakes. Phytoplanktonwet weight biomass was found to be high, reaching 777 mg L^–1in L. Bogoria, 104 mg L^–1 in L. Nakuru and 202 mg L^–1in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxinsmicrocystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-awere detected in phytoplankton samples from L. Bogoria and L.Nakuru. Total microcystin concentrations amounted to 155 µgmicrocystin-LR equivalents g^–1 DW in L. Bogoria, and 4593µg microcystin-LR equivalents g^–1 DW in L. Nakuru,with anatoxin-a concentrations at 9 µg g^–1 DW inL. Bogoria and 223 µg g^–1 DW in L. Nakuru. In L.Elmenteita phytoplankton, no cyanobacterial toxins were found.A. fusiformis was identified as one source of the toxins. Theisolated strain of A. fusiformis from L. Bogoria was found toproduce both microcystin-YR (15.0 µg g^–1 DW) andanatoxin-a (10.4 µg g^–1 DW), whilst the A. fusiformisstrain from L. Nakuru was found to produce anatoxin-a (0.14µg g^–1 DW). Since A. fusiformis mass developmentsare characteristic of alkaline-saline lakes, health risks towildlife, especially the Arthrospira-consuming Lesser Flamingo,may be expected.     

Hormonal responses to partial drying of the root system of Helianthus annuus

Plants of Helianthus annuus were pot-grown in soil, with approximately30% of the root system protruding through the base. After 7d, the upper part of the root system of half of the plants wasexposed to drought (internal roots) while the lower part waskept in aerated nutrient solution (protruding root). The treatmentrapidly reduced the internal roots' water content from 26.1to 21.9 g g^–1 dry weight (DW), while in protruding rootsof stressed plants it slowly and continuously decreased from31.9 to 25.2 g g^–1 DW. Leaf water content rapidly decreasedin treated plants from 7.4 to 6.4 g g^–1 DW in the first2d and then reached a plateau. In stressed plants leaf stomatalresistance was significantly higher in the first 3 d while leafwater potential was lower only on the last day. Abscisic acid (ABA) concentration in treated plants increasedsignificantly compared to the controls. In treated internalroots, ABA rose from the first day, reaching a maximum of 1.48±0.49nmol g^–1 DW after 3 d. In treated protruding roots a maximumof 0.99±0.09 nmol g^–1 DW was reached after 1 d.ABA concentration in the xylem sap increased 2 d and 3 d afterthe start of soil drying, with a maximum of 113±12nmoll^–1 during the third day. The ABA rise in the leaves oftreated plants was less significant. Indol-3yl-acetic acid (IAA) concentration in internal rootsof treated plants reached a maximum of 22.54±3.34 nmolg^–1 DW on the third day, then decreased dramatically.The protruding root system of control plants showed a maximumvalue of 16.05±1.77 nmol g^–1 DW on the sixth day. Little difference in cytokinin content of xylem sap was notedbetween control and treated plants. Hormonal variations in different parts of the plant are discussedin relation to drought stress. Key words: Soil drying, roots, ABA, IAA, cytokinins     

Cytological Analysis of Seedling Roots, Transformed Root Cultures and Roots Regenerated from Callus of Swainsona galegifolia (Andr.) R. Br.

The stability of chromosome number was investigated in culturesof roots from Swainsona galegifolia. Roots from germinated seedsor plants grown in vitro when cultured in liquid medium howed90% or more cells with the diploid number of 2n = 32. The remainingcells showed aneuploidy mostly below 32. The stability of chromosomenumbers was not affected by transformation with Agrobacteriumrhizogenes although when roots were transformed with A. rhizogenesLB 9042 the range of chromosome numbers in the few aneuploidcells present was higher than in roots for which strain A4 wasused. In contrast, roots regenerated from callus had only 15%of cells with 2n = 32 and showed a modal number of 18. Six rootcultures established from individual roots regenerated fromcallus showed a wide variation in number (8–83). Fivecultures had a modal number around 18, the sixth, a modal numberof 39 which is above the diploid number. The implication ofthe results for the production of secondary metabolites fromroot culture is discussed. Key words: Agrobacterium rhizogenes, callus cultures, chromosome number, root cultures, Swainsona galegifolia     

The shikonin derivatives and pyrrolizidine alkaloids in hairy root cultures of Lithospermum canescens (Michx.) Lehm.

Hairy root cultures of Lithospermum canescens were established using three strains of Agrobacterium rhizogenes: ATCC 15834, LBA 9402 and NCIB 8196. Eight lines resulting from infection with A. rhizogenes ATCC 15834 demonstrated sufficient biomass increase and were submitted to further investigations. The contents of acetylshikonin (ACS) and isobutyrylshikonin (IBS) in transformed hairy roots made up ca. 10% of those observed in natural roots of L. canescens (24.35 and 14.48 mg g⁻¹ DW, respectively). One line, Lc1-D, produced the largest amounts of ACS (2.72 mg g⁻¹ DW) and IBS (0.307 mg g⁻¹ DW). Traces of pyrrolizidine alkaloids (PA), canescine and canescenine, were found in all lines of transformed hairy roots.     

Use of a Disarmed Ri Plasmid Vector in Analysis of Transformed Root Induction

Nicotiana glauca, N. tabacum, Solanian dulcamara and S. nigrumwere transformed by Agrobacteriun rhizogenes strain BN1010 (TL^–TR⁺).The TR-DNA stimulated agropine-positive root induction and wastransformation competent in the absence of the TL-DNA. An unusualpattern of root induction was seen when stem explants were inoculatedwith this strain; occasionally, agropine-positive roots wereinduced at the inoculation sites, but prolific agropine-negativeroots were formed in profusion down the stems. The utility ofBN1010 as an efficient co-integrating vector was demonstratedby the separate transfer of a fragment containing rol ABC (BN1010::pEM15) and of a chimeric nopaline synthase-kanamycin resistancegene (BN1010:: Neo) into plants. Root cultures of S. dulcamaratransformed with BN1010:: Neo had an unusual, positively geotropicphenotype. Strain BN1010:: pEM15 (rol ABC⁺D^–TR⁺) incitedmore roots down stem explants than strain A4T. This indicatesthat rol D may act to suppress agropine-negative root productionin N. glauca and N. tabacum. Key words: Agrobacterium rhizogenes, TL-DNA, TR-DNA, disarmed Ri vector, transformed roots, Nicotiana glauca, N. tabacun, Solatium dulcamara, S. nigrum     

Hairy root culture of <Emphasis Type="Italic">Picrorhiza kurroa</Emphasis> Royle ex Benth.: a promising approach for the production of picrotin and picrotoxinin

Picrorhiza kurroa Royle ex Benth. is an endangered plant producing various compounds of medicinal importance. Hairy roots of P. kurroa were obtained following cocultivation of shoot tip explants with Agrobacterium rhizogenes strains A 4 and PAT 405. Bacterial strain A 4 appeared to be better than the strain PAT 405 in terms of both growth of respective hairy root cultures and secondary metabolite production. The optimal growth of both the hairy root cultures occurred on half-strength semisolid medium with 3% sucrose. Picrotin and picrotoxinin from the roots of wild type field grown plants were compared with 8-week-old hairy root cultures induced by the A 4 and PAT 405 strains of A. rhizogenes. Picrotin and picrotoxinin content were evaluated in hairy root cultures as well as roots of field grown plant of P. kurroa. In terms of the production of picrotin and picrotoxinin, the A 4 induced hairy roots appeared to be a better performer than the PAT 405 induced hairy root cultures. The picrotin and picrotoxinin content was highest in 8-week-old A 4 induced hairy roots (8.8 μg/g DW and 47.1 μg/g DW, respectively). Rapid growth of the hairy roots of P. kurroa with in vitro secondary metabolite production potential may offer an attractive alternative to the exploitation of this endangered plant species.     

Agrobacterium rhizogenes Mediated Transformation of the Forage Legumes Medicago sativa and Onobrychis viciifolia

Three cultivars of M. sativa and one cultivar of O. viciifoliawere evaluated for their response to inoculation with A. rhizogenesstrain A4T (containing pRiA4b). A cultivar-dependent responsewas observed in M. sativa with 94%, 25%, and 4% of infectedstem explants producing transformed roots in the cultivars Vertus,Regen-S, and Rangelander, respectively. In O. viciifolia cv.Hampshire Giant, an explant-dependent response was observedwith 78% and 50% of seedling cotyledon and hypocotyl explantsresponding, respectively. Leaf explants failed to produce transformedroots. Transformed roots showed plagiotropic and negativelygeotropic growth on hormone-free agar MS medium. Productionof transgenic shoots from O. viciifolia root cultures occurredspontaneously. Recovery of transgenic plants from M. salivacv. Rangelander was achieved by transfer of callus (inducedon UM medium containing 2·0mg dm^–3 2,4-D and 0·25mg dm^–3 kinetin) to MS medium containing 0·5 ingdm^–3 BAP and 0·05 mg dm^–3 NAA. Cultured rootsof both species synthesized opines (agropine and mannopine).Extensive morphological variation was observed in plants ofM. sativa (clone Al) and O. viciifolia (clone A4Tl) establishedin the glasshouse. DNA sequences homologous to TL-DNA and TR-DNAwere present in root clones and regenerated plants. Key words: Agrobacterium rhizogenes, Medicago sativa, Onobrychis viciifolia, transformed roots, transgenic plants     

Root Nodules of Phaseolus: Efficient Scavengers of Molybdenum for N2-fixation

Molybdenum is thought to be of intermediate mobility in thephloem and this may limit N₂-fixation by restricting the supplyof molybdenum to the nodules of legumes. When no molybdenumwas supplied to Phaseolus vulgaris nodule Mo content increasedat the expense of shoots and roots even when seed molybdenumcontent was large. Nodules sampled from plants receiving molybdenumin the feeding solution had a concentration of 21–78 µgMo g^-1. In the absence of molybdenum and with deficient seedcontent (<0.5 µg Mo seed^-1) nodule concentrations rangedfrom 1.9 to 3.5 fig Mo g^-1 in a small seeded genotype and 8.7±0.48µg Mo g^-1 in a large seeded genotype. N₂-fixation in theseplants was not impaired except in one instance where noduleconcentration was 1.9 µg Mo g^-1. Evidence that molybdenumis effectively translocated from leaves to roots and noduleswas obtained using foliar treatments. All of the 3.3 µgMo applied to a leaf was recovered in the plant after 10 d.Mo content of the nodules increased by 81%, whilst Mo contentof shoots increased by 56%. Root Mo content was eight timesgreater than that in plants not receiving a foliar treatmentof molybdenum. We conclude that when molybdenum was scarce inthe plant it was mobile and was translocated from roots andshoots to the nodules. As a result, nodule concentrations andcontents of molybdenum were frequently maintained at amountssufficient for N₂-fixation even when the plant was entirelydependent on a small seed reserve of molybdenum.     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta I. Photocontrol of Carotenoid Production

Rhodotorula minuta cells, which have only traces of carotenoidswhen grown in the dark, started carotenoid production with theonset of illumination and the amount increased almost linearlyuntil 70 hr then remained constant thereafter when incubationwas continued under illumination, with the number of cells continuingto increase. The rate of carotenoid production [Vc (µgg^–1 hr^–1)] depended on the intensity of light [I(ergcm^–2 sec^–1)], with the relationship of Vc=0.74 logI–1.46. The final carotenoid content [C(µg g^–1)]of cells incubated under continuous light was also controlledby the light intensity [I], with the relationship of C=52 logI–81. Control of carotenoid production by light occursas a two-phase process consisting of a temperatureindependentphotochemical reaction and light-independent biochemical reactions. (Received September 12, 1981; Accepted February 20, 1982)     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Root Distribution, Growth, Respiration, and Hydraulic Conductivity for Two Highly Productive Agaves

Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha^–1yr^–1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d^–1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C₃ and C₄ agronomic species. The respiration rateof attached main roots was 32 µmol CO₂ evolved kg^–1dry weight s^–1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C₃ and C₄ agronomic species.The root hydraulic conductivity had a maximal value of 3 x 10^–7ms^–1 MPa^–1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake     

Relationship Between the Development and Growth of Rye (Secale cereale L.) and the Potassium Concentration in Solution

The development and growth of rye (Secale cereale L. cv. Rheidol)was studied in seedlings grown hydroponically in complete nutrientsolutions containing between 10 and 600 µM K⁺. The phyllochron(defined as the interval between the appearance of successiveleaves) was used as a developmental timescale to compare plants.The pattern of both shoot and root development was strictlyordered on a phyllochron basis and was unaffected by solutionK⁺ concentration, with the exception that tillers in plantsgrown at the lowest K⁺ concentrations were occasionally eithernot initiated or aborted at an early stage of development. However,both the rate of leaf appearance on the main stem and successivetillers and the rate of tiller appearance were slower in plantsgrown at lower K⁺ concentrations. The rate of leaf appearanceon the main stem was reduced to below 90% of its maximal valueat solution concentrations below about 50 µM K⁺. Plantrelative growth rate (RGR) was also reduced by lowering theK⁺ concentration of the nutrient solution and fell to below90% of its maximal value at solution concentrations below about200 µM K⁺. There was a complex relationship between tissueK⁺ concentration and the K⁺ concentration of the nutrient solution,which differed between leaves and root. Leaf K⁺ concentrationincreased steadily from about 50 µmol g^-1 f. wt to about200 µmol g^-1 f. wt as solution K⁺ concentration was increasedfrom 10 to 400 µM. In contrast, root K⁺ concentrationexhibited a sigmoidal dependence on solution K⁺ concentration,maintaining a minimal value of approximately 20 µmol g^-1f. wt at concentration below 100 µM K⁺, then increasingprogressively to about 120 µmol g^-1 f. wt at a solutionconcentration of 600 µM K⁺. The 'critical' leaf K⁺ concentration,i.e. the concentration at which either plant RGR or plant developmentwas reduced 90% of its maximal value, was 86 µmol g^-1f. wt for plant RGR and 150 µmol g^-1 f. wt for plant development.The 'critical' root K⁺ concentration was 24 µmol g^-1 f.wt K⁺ for both RGR and development. A decline in tissue K⁺ concentrationbelow these thresholds reduced plant growth considerably. RootK⁺ concentration was a sensitive indicator of the K⁺ statusof the plant with respect to potential growth since plant growthdeclined abruptly as root K⁺ concentration approached its 'critical'value, whereas plant growth showed a less defined relationshipwith shoot K⁺ concentration.Copyright 1993, 1999 Academic Press Critical K⁺ concentration, development, potassium, relative growth rate (RGR), rye, Secale cereale L. cv. Rheidol     

Absorption and Distribution of Copper in Plants with Sufficient or Deficient Supplies

Wheat, red clover and ryegrass were grown in flowing solutionculture with sufficient (+ Cu) and deficient (–Cu) suppliesof copper. The rates of Cu absorption (µg g^–1 dryroot day^–1) did not differ greatly between species ineither treatment. Wheat plants, when transferred from the –Cu to the +Cu treatment, absorbed Cu at a much slower rate thanthose which had remained throughout in the + Cu treatment. Inall plants considerable proportions of the absorbed Cu wereretained in the roots, even when the plants were Cu-deficient,and the concentration in roots usually exceeded that in anypart of the shoots in both treatments. Transferring wheat plantsfrom the +Cu to the –Cu treatment decreased the concentrationin all plant parts except old leaves; similarly, transferringfrom the –Cu to +Cu treatment increased the concentrationin all parts of the shoots, execept old leaves, and in the roots. Lolium perenne, Trifolium pratense, Triticum aestivum, ryegrass, red clover, wheat, absorption, copper, flowing solution culture     

Xylem fluxes of fixed N through nodules of the legume Acacia littorea and haustoria of an associated N-dependent root hemiparasite Olax phyllanthi

Nodulated 1-1.5-year-old plants of Acacia littorea grown inminus nitrogen culture were each partnered with a single seedlingof the root hemiparasite Olax phyllanthi. Partitioning of fixedN between plant organs of the host and parasite was studiedfor the period 4–8 months after introducing the parasite.N fluxes through nodules of Acacia and xylem-tapping haustoriaof Olax were compared using measured xylem flows of fixed Nand anatomical information for the two organs. N₂ fixation duringthe study interval (635 µg N g FW nodules^–1 d^–1)corresponded to a xylem loading flux of 0.20 µg N mm^–2d^–1 across the secretory membranes of the pencycle parenchymaof the nodule vascular strands. A much higher flux of N (4891µg mm^–2 d^–1) exited through xylem at the junctionof nodule and root. The corresponding flux of N from host xylemacross absorptive membranes of the endophyte parenchyma of Olaxhaustorium was 1.15 µg N mm^–1 d^–1, six timesthe loading flux in nodules. The exit flux from haustorium toparasite rootlet was 20.0 pg N mm^–1 d^–1, 200-foldless than that passing through xylem elements of the nodule.Fluxes of individual amino compounds in xylem of nodule andhaustorium were assessed on a molar and N basis. N flux valuesare related to data for transpiration and partitioning of Cand N of the association recorded in a companion paper. Key words: Olax phyllanthi, host-parasite relationships, N flux, Acacia, N₂ fixation     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta II. Aspects of Photoregulative Reaction

The photoregulation of carotenogenesis in Rhodotorula minutawas found to consist of tow phases, a temperature-independentphotochemical reaction (light process) and temperature-dependentbut light-independent biochemical reactions (dark process).These processes were separately examined by regulating the temperatureand were characterized as follows: 1) The quantity of carotenoid produced [C (µg g^–1)]and the rate of carotenoid production [Vc (µg g^–1hr^–1)] in the dark process were regulated by the lightdose [D (erg cm^–2)] to which cells were exposed in thelight process. These relationships were expressed by the equations:C=9.1 log D–62.0 and Vc=0.81 log D–5.60. This photoresponsefollowed the Roscoe-Bunsen reciprocity law. 2) The induced state toward carotenogenesis, once acquired inthe light process, was very stable, suggesting that the proposedphotochemical product is stable as an inducer of carotenogenesisand decreases only in conjunction with carotenoid biosynthesis. 3) The photochemical reaction was oxygen-independent, but subsequentdark reactions were completely dependent on oxygen. 4) Postulated compounds related to the photochemical reactionwere not metabolized in vivo. (Received September 12, 1981; Accepted February 20, 1982)     

Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.)

The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg^–1 s^–1for cable roots and 3·27±0·12 µmolkg^–1 s^–1 for fine roots. The Q₁₀ for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m^–3 and 3·4mol m^–3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma     

Solasodine production in transformed organ cultures (roots and shoots) of Solanum eleagnifolium Cav.

Summary Transformed organ cultures of Solanum eleagnifolium Cav. (roots and shoots) were obtained by infection with different Agrobacterium species (A. rhizogenes and A. tumefaciens). The growth index and the solasodine productivity of both kinds of cultures were determinated for several clones. Transformed roots (clone 5) shows a Growth Index of 39.07 and a solasodine yield of 1.90 ± 0.08 mg g^-1DW . Solasodine content in clone 5 of transformed roots (1.9 ± 0.08 mg g^-1 DW) is similar to those obtained by hormonal manipulation (1.00 – 1.68 mg g^-1DW) but higher than those found in shoots and leaves of the wild-grown plant (0.3–0.4 mg g^-1DW).     

The Uptake and Distribution of Copper in Some Forage Grasses as Affected by Nitrate-nitrogen Supply in Flowing Solution Culture

The effect of changes in nitrate-nitrogen supply on the absorptionand distribution of copper was examined in grasses grown inflowing solution culture with a maintained concentration ofcopper. Absorption by roots (µg Cu g^–1 dry root)decreased markedly when nitrogen had been depleted or was maintainedat 0.1 mg l^–1 N, but there was an immediate increase whennitrogen was maintained at 1.0 or 10.0 mg l^–1. There werealso large increases in the concentration of copper in the shootsof plants grown with 1.0 and 10.0 mg 1^–1 N. The rootsof plants grown with 0.1 or 1.0 mg 1^–1 N retained similarproportions of uptake, but a lower proportion was retained whenthe plants were grown with 10.0 mg 1^–1. Although a lowerproportion of the copper was associated with cell walls in theplants grown at 10.0 mg 1^–1 N this was the result of alower content of cell walls rather than an effect on copperitself. In a longer-term experiment in conventional solutionculture with a range of nitrogen concentration, the concentrationof copper in shoots was largely determined by shoot growth. Dactylis glomerata, Festuca arundinacea, Lolium perenne, cell walls, copper absorption, copper distribution, flowing solution culture, nitrate-nitrogen     

Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves

The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 12–19 days' duration reachedchl concentrations of 10–50 µg^–1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day^–1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30–100 µE m^–2S^–1and the growth rate was reduced by about 30% at 500–1000µE m^–2S^–1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm^–2S^–1 chl/C ratios were also below maximum at PFDsbelow 40–50 µE m^–2S^–1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)^–1h^–1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h^–1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1_sat (160–330 µE m^–2S^–1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for I_sat (560 µE m^–2S^–1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes.     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.