Seedling responses of four Australian tree species to toxic concentrations of manganese in solution culture

Little is known about the responses of Australian plants to excess metal, including Mn. It is important to remedy this lack of information so that knowledgeable decisions can be made about managing Mn contaminated sites where inhabited by Australian vegetation. Acacia holosericea, Melaleuca leucadendra, Eucalyptus crebra and Eucalyptus camaldulensis were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Mn treatments viz., 1, 8, 32, 128, 512 and 2048 M. The order of tolerance to toxic concentrations of Mn was A. holosericea E. crebra < M. leucadendra < E. camaldulensis, the critical external concentrations being approximately 5.1, 5.0, 21 and 330 M, respectively. The critical tissue Mn concentrations for the youngest fully expanded leaf and total shoots were, respectively, 265 and 215 g g^–1 DM for A. holosericea, 445 and 495 g g^–1 DM for M. leucadendra, 495 and 710 g g^–1 DM for E. crebra and 7230 and 6510 g g^–1 DM for E. camaldulensis. The high tolerance of E. camaldulensis (as opposed to the sensitivity of E. crebra) to excess Mn raises concern about fauna feeding on the plant and is consistent with hypotheses suggesting the Eucalyptus subgenus Symphomyrtus is particularly tolerant of stress, including excess Mn. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the management of Mn toxic sites.     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

In vitro plant regeneration via somatic embryogenesis from root culture of some rhizomatous irises

A method for plant regeneration of Iris via somatic embryogenesis is described. Root and leaf pieces from in vitro-grown plants of several genotypes of rhizomatous Iris sp. were cultured in vitro. Callus induction occurred only on root cultures incubated under low light intensity (35 mol m^-2 s^-1) on two induction media containing 2,4-D (4.5 or 22.5 M), NAA (5.4 M) and kinetin (0.5 M). Somatic embryos developed after transfer of callus onto four regeneration media containing 9 or 22 M BA, or 5 M kinetin and 2 M TIBA or 9 M BA and 4 M TIBA. Plantlets could be obtained from these somatic embryos. Genotypic differences were found both in callus induction and somatic embryo formation, with I. pseudacorus responding better than I. versicolor or I. setosa. Cytological analysis performed on root tips of 80 regenerated plants revealed that two of the I. pseudacorus regenerants were tetraploid.Abbreviations 2,4-D dichlorophenoxy acetic acid - NAA naphthaleneacetic acid - BA 6-benzyladenine - TIBA 2,3,5-triiodobenzoic acid - IBA indolebutyric acid     

Effect of aluminium on yield and plant chemical concentrations of some temperate legumes

The aluminium (Al) tolerance of 34 temperate legume species (143 genotypes, including 57 from Trifolium repens) was determined in 60 experiments over a 3 year period in a low ionic strength (2.7 × 10^-3 M) solution culture. For each genotype, the relationship between solution Al³⁺ activity (M) and relative yield was determined and the Al³⁺ activity associated with a 50% reduction in yield (Al_RY50) calculated. In addition, plant chemical concentrations were determined in at least one genotype from most species. For white clover, Al_RY50 over all genotypes had an approximately normal distribution with mean of 1.31 M for the tops and 1.51 M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritance. For the other species tested, Al_RY50 ranged from 0.15 to 4.53 M in the tops and from 0.21 to 4.89 M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an Al_RY50 less than 1 M, including all species tested in the genera Melilotus and Medicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an Al_RY50 greater than 2, including all genotypes in the species Lotus pedunculatus. Except for Lotus, there were no consistent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all elements except B in the roots were lower than that of the other species. The Al_RY50 of the species was not related to plant chemical concentrations in the absence of Al. Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemical concentrations for 56–94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K concentrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P concentrations decreased in the tops but increased in the roots. Increasing Al in solution increase plant Al at the average rate of 44 g g^-1 M ^-1 (range 20–87) in the tops and 333 g M ^-1 (range 162–616) in the roots.     

Development of high frequency multiple shoot formation in Persian clover (<Emphasis Type="Italic">Trifolium resupinatum</Emphasis> L.)

An efficient and reliable micropropagation system for Persian clover (Trifolium resupinatum L.) was developed using different explants and media. Node, hypocotyl and cotyledonary node explants were cultured on Murashige and Skoog (MS) medium supplemented with combinations of either 6-benzyladenine (BA) and indole-3-butyric acid (IBA) or BA, Kinetin (KIN) and IBA. Direct multiple shoots developed within 6weeks in all explants in most media tested. The best shoot multiplication capacity was obtained from cotyledonary node explants on MS medium containing 7.1M BA and 1M IBA or 14.1M BA and 1M IBA. Elongated shoots were rooted on either MS medium alone or combination with different concentrations of indole-3-butyric acid (IBA), indole-3-acetic acid (IAA) and -naphthaleneacetic acid (NAA). High rooting was achieved in half strength MS medium containing 8M IBA.     

Sisal plant regeneration via organogenesis

Callus was initiated from in vitro grown immature leaf and ex vitro grown mature leaf and rhizome explants of Agave sisalana Perr. ex. Engelm, on MS medium containing 2,4-D (9.05 M) and kinetin (4.6 M) or 2,4-D (9.05 M), kinetin (4.6 M) and CH (1000 mg l^–1) or mod. MS (NH₄NO₃, 1500 mg l^–1) containing 2,4-D (9.05 M) and kinetin (4.6 M). Light was essential for callus formation which, however, was different in three types of explants on three different media compositions. Increasing NH₄ ⁺had a negative impact while addition of CH had a positive impact on callus formation. Shoot regeneration from callus from CH-supplemented medium only was achieved for rhizome and immature leaf tissues. The highest rate of regeneration was obtained with BA (26.6 M) as the sole hormone. Shoot buds g^–1 callus varied according to BA concentrations. Shoot proliferation rate increased on half-strength MS medium containing BA (8.9 M). Microshoots developed on MS medium containing BA (2.22 M) and GA₃ (1.44 M) and finally rooted on MS medium containing IAA (11.42 M). Acclimatized rooted plantlets are growing satisfactorily in ex vitro. This is the first report on plant regeneration via organogenesis of A. sisalana.     

Plant regeneration via somatic embryogenesis in Styrian pumpkin: cytological and biochemical investigations

Somatic embryo formation was induced from cotyledon explants of Styrian pumpkin (Cucurbita pepo L. subsp. pepo var. styriaca Greb.) by using a solid MS medium supplemented with 16.11M NAA and 4.44M BA or 26.85M NAA and 13.32M BA. The callus proliferation was more efficient on medium supplemented with 26.85M NAA and 13.32M BA. In contrast, the embryogenic response was higher on medium with lower concentrations of growth regulators (16.11M NAA and 4.44M BA). The time needed for embryo induction did not depend on medium composition. Embryos in globular stage were transferred to three different maturation media, containing 2.89M GA₃ in combination with 0.54M NAA, 11.42M IAA and growth regulator-free medium. The germination rate was the highest when embryos were cultured on medium with 11.42M IAA. Plantlets grown on this medium achieved maturity suitable for transplantation into soil within 9 to 10weeks. The regenerated plants were successfully transferred into field and developed fertile flowers and set fruits. Biochemical analysis showed significant lower total glutathione levels among in vitro grown plantlets compared to seedlings grown in soil. When the plantlets were transferred into soil, they reached a normal size within a month and the glutathione concentration was comparable to seed-derived plants at the same developmental stage. Transmission electron microscopy was used to investigate possible differences in the ultrastructure of cells from callus cultures, and leaf cells of regenerated and seed-derived plants. Differences in the ultrastructure were found within chloroplasts which contained only single thylakoids, large starch grains and small plastoglobuli in callus cells in comparison to leaf cells, which possessed a well developed thylakoid system, small starch grains and large plastoglobuli.     

Minimal growth in vitro conservation of coffee (Coffea spp.)

We have studied the influence of low concentrations of 6-benzyladenine on growth limitation, in order to preserve coffee germplasm through a microcutting collection. Concentrations of 0 M, 1.3 M and 4.4 M were compared in four species: Coffea congensis, C. canephora, C. liberica and C. racemosa. After six months, microcutting behaviour varied between the different treatments, and a species effect was observed. The slow growing species (C. liberica and C. congensis) needed 1.3 M; the others coffee species (C. canephora and C. racemosa) exhibited moderate caulogenesis on 6-benzyladenine-free medium. Zero and low concentrations did not affect survival rates. In conclusion 1.3 M seems most appropriate for conserving all four species.Abbreviation BA 6-benzyladenine     

Ultrastructure of Sporothrix schenckii treated with iodine-potassium iodide solution

The ultrastructural changes produced by iodine-potassium iodide solution on yeast cells of Sporothrix schenckii were investigated by transmission electron microscopy in order to clarify the mechanism of oral potassium iodide therapy for sporotrichosis. Yeast cells were dipped with solutions containing various concentrations of iodine. The rate of germination decreased markedly between the range of iodine concentrations from 0.63 g/ml to 5.0 g/ml. No significant ultrastructural changes were seen at the concentration of the iodine of 1.25 g/ml (80% germination) or less. In the concentration of 2.5 g/ml (50% germination), normal cells and degenerated cells coexisted. When the cells were treated with 5.0 g of iodine per ml (0% germination) or more, their interior structures were completely destroyed. It is assumed that iodine treatment of the organism causes rapid destruction in the whole cell.     

In vitro propagation of Asparagus maritimus – A rare Mediterranean salt-resistant species

Asparagus maritimus L. Miller is a rare species growing of the Mediterranean region and is morphologically similar to A. officinalis. In order to establish an efficient in vitro propagation protocol, explants were excised from spear segments and cultured on Murashige and Skoog (1962) medium containing 3% sucrose and various concentrations of growth regulators. The best shoot initiation (3–4 per explant) was achieved on a medium containing 0.88 M N⁶-benzyladenine (BA), 0.93 M kinetin, 1.07 M -naphthaleneacetic acid (NAA) and 3.90 M ancymidol. Shoot initiation could also be achieved without ancymidol but the shoots were thinner and longer. A very high shoot multiplication rate was achieved on media supplemented with 3% sucrose, 1.07 M NAA, 0.93 M kinetin, 0.44 M BA and various concentrations of ancymidol. The lowest concentration of ancymidol (0.39 M) significantly promoted the highest shoot multiplication rate (11.9 shoots/crown). For root formation, media were supplemented with 6% sucrose, 1.07 M NAA and various concentrations of ancymidol. Rooting frequency increased with higher ancymidol concentration up to 5.07 M (82.0% rooting). The number of ex vitro shoots formed was strongly correlated (r=0.66) with the length of roots formed in vitro, which was the highest at a 1.95 M ancymidol.     

Different regeneration potential of mesophyll protoplasts from cultivated and a wild species of tomato

Mesophyll protoplasts were isolated from leaves of three cultivars of Lycopersicon esculentum (L.) Mill., namely Hilda 72, Rutgers and Rentita, and from the wild tomato species Lycopersicon peruvianum (L.) Mill. Protoplasts from L. peruvianum divided and grew actively in a liquid medium according to Zapata et al. (1977), whereas protoplasts from the tomato cultivars Hilda 72 and Rutgers showed comparable rates for cell division only, when the content of major elements in this medium was reduced to one half of the original concentration and when mannitol as osmoticum was replaced by glucose. In Rentita protoplasts no cell division could be observed in about 15 different modifications of the five basic culture media tested. The morphogenetic potential of these tomato cells was assessed by comparing the root and shoot formation of protoplasts and of leaf explants. L. peruvianum exhibited the highest potential. Calli derived from protoplasts regenerated roots on Murastrige-Skoog agar containing 1 M benzylaminopurine (BAP) plus 10 M indole-3-acetic acid (IAA) and 0.1 M BAP plus 1 M IAA. Shoot formation occurred in the combinations of 10 M BAP with 0.1, 1.0, and 10 M IAA. Plantlets regenerated from the L. peruvianum calli could be grown in soil. No shoots or roots were regenerated from calli of Hilda 72 and Rutgers protoplasts in all combinations of BAP and IAA tested in the range from 0.1 M to 100 M, thus indicating the rather low morphogenetic potential of these protoplasts as compared to protoplasts from L. peruvianum leaves.Abbreviations BAP benzylaminopurine - IAA indole-acetic acid - TMV tobacco mosaic virus     

Somatic embryogenesis and plant regeneration from immature embryos of saw palmetto,an important landscape and medicinal plant

Somatic embryogenesis and plant regeneration from immature zygotic embryos was achieved for saw palmetto (Serenoa repens (Bartr.) Small). Embryos, isolated from immature fruit of native-grown plants, were cultured on Murashige and Skoog medium plus 0.15% (w/v) activated charcoal and supplemented with 452 M 2,4-dichlorophenoxyacetic acid (2,4-D) and 14.7 M N⁶-(2-isopentenyl)adenine (2iP). Clusters of somatic embryos developed from all immature zygotic embryos 5 weeks after culture initiation. After 12 weeks, explants were transferred to the same medium with the amount of 2,4-D reduced to 90.4 M which resulted in somatic embryo proliferation. Somatic embryos were then transferred to the basal medium containing 0.9, 9 M thidiazuron (TDZ), or no growth regulator for conversion into plantlets. The 9 M TDZ treatment was ineffective for plant regeneration. However, 12% of the embryos subcultured on 0.9 M TDZ were able to produce complete plantlets. Shoot production was obtained from 35% of the embryos subcultured in the absence of growth regulators. Rooting (100%) was achieved when these shoots were transferred onto medium containing 22.2 M -naphthaleneacetic acid (NAA).     

Promotion of flowering in apple trees with gibberellin A4 and C-3 epi-gibberellin A4

The proportion of spurs flowering on apple trees (Malus domestica Borkh. cv Golden Delicious) displaying a high degree of alternate-year flowering was increased in the off year by gibberellin A₄ (GA₄) and C-3 epi-GA₄ applied in the previous year. When applied 4.5 weeks after anthesis amounts of GA₄ ranging from 3 to 300 g per spur and 25 or 50 g of C-3 epi-GA₄ per spur were effective. Treatments with GA₄ made seven weeks after anthesis were less effective. A combination of 30 g GA₄ and 30 g zeatin (6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine) promoted flowering at both treatment times, and tended to be more effective than GA₄ alone.Abbreviation GA gibberellin or gibberellin-like substance Contribution No. 618     

Micropropagation of parsley through axillary shoot proliferation

A micropropagation protocol of parsley,Petroselinum crispum (Mill.) Nyman (curled type) has been developed. Surface-sterilized axillary buds cultured on Murashige and Skoog medium supplemented with benzyladenine, kinetin, or thidiazuron developed axillary shoots (rosettes). Kinetin resulted in only a low proliferation rate. The concentrations of thidiazuron or benzyladenine that were optimal for shoot proliferation, resulted in shoots with a low capability to root. During the rooting treatment, these shoots showed wilting signs. Rooting was increased significantly by using a two-week inductive stage with 2.5 M naphthaleneacetic acid directly followed by acclimatization. Two proliferation media (5 M benzyladenine and 0.5 M naphthaleneacetic acid or 5 M kinetin and 2.5 M naphthaleneacetic acid) resulted in moderate proliferation but produced shoots that were easy-to-root. These media have been tested by repeated axillary proliferation on the same medium. The medium with 5 M benzyladenine and 0.5 M naphthaleneacetic acid was optimal.Abbreviations BA 6-Benzyladenine - IBA Indole-3-butyric acid - MS Murashige & Skoog - NAA -Naphthaleneacetic acid     

Role of mitochondria in ethanol tolerance of Saccharomyces cerevisiae

The presence of active mitochondria and oxidative metabolism is shown to be essential to maintain low inhibition levels by ethanol of the growth rate (), fermentation rate (v) or respiration rate () of Saccharomyces cerevisiae wild type strain S288C. Cells which have respiratory metabolism show K _i (ethanol inhibition constant) values for , v and , higher (K _i>1 M) than those of petite mutants or grande strains grown in anaerobiosis (K _i=0.7 M). In addition, the relationship between or v and ethanol concentration is linear in cells with respiratory metabolism and exponential in cells lacking respiration. When functional mitochondria are transferred to petite mutants, the resulting strain shows K _i values similar to those of the grande strain and the inhibition of and v by increasing ethanol concentrations becomes linear.     

Superoxide dismutase: An enzyme system for the study of micronutrient interactions in plants

The effect of different Mn levels on the isozyme pattern of superoxide dismutase was investigated. Pisum sativum L. plants were grown in nutrient solutions containing three Mn concentrations: 0.005 g/ml (deficient), 0.05 g/ml (low), and 0.5 g/ml (optimum). Leaf extracts contained three electrophoretically distinct superoxide dismutases (SOD), two of which were inhibited by cyanide and were probably Cu-Zn-SODs, while the third one was CN-insensitive and could be either an Mn- or an Fe-SOD. At 0.005 g/ml Mn supply the CN-insensitive SOD was significantly depressed at 15, 30, and 45 days of growth, whereas at 0.05 g/ml Mn this isozyme was significantly decreased only at 45 days growth. The two CN-sensitive SODs were inversely related to the CN-resistant enzyme, the activities of the former enzymes being significantly increased at Mn-deficient levels throughout plant growth. Metal determinations of the plants showed that at low concentrations of Mn in the nutrient media, copper and zinc content of leaves increased: the lower the Mn level, the higher the increase produced. The CN-resistant SOD activity, as judged by its dependency on Mn, appears to be an Mn-SOD rather than an Fe-SOD. In the light of the results obtained, the use of the enzyme system superoxide dismutase for the study of the role and interactions between Mn, Cu, and Zn in the plant cell is proposed.Abbreviations EDTA ethylenediaminotetraacetic acid - NBT nitro blue terazolium - SOD superoxide dismutase (EC 1.15.1.1)     

EDTA-assisted heavy-metal uptake by poplar and sunflower grown at a long-term sewage-sludge farm

Little information is available concerning the efficacy of chelates applied to biosolids (sewage-sludge)-treated soil for heavy-metal removal. The purpose of the experiment was to determine the availability to sunflower (Helianthus annuus L.) and hybrid poplar (Populus deltoides Marsh. × P. nigra L.) seedlings, of non-essential (Cd, Ni, Pb) and essential heavy metals (Cu, Fe, Mn, Zn) in field soil injected with biosolids since 1976 and treated with ethylenediamine-tetraacetic acid (EDTA) in 2001. Sunflower was grown at two densities, 20000 and 60000 plants/ha, and poplar at 10000 plants/ha. The tetrasodium salt of EDTA was applied at rates of 0, 0.5, 1, and 2 g EDTA salt per kg surface (25-cm depth) soil. The EDTA did not affect uptake by poplar of the three non-essential (Cd, Ni, Pb) and four essential (Cu, Fe, Mn, Zn) heavy metals. For sunflower, the 1.0 g/kg rate of chelate addition resulted in maximal removal of the three non-essential heavy metals (Cd, Ni, Pb). Uptake of the essential heavy metals by sunflower was little affected by the EDTA. At the 20000 plants/ha density, leaves of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than leaves of sunflower grown without the EDTA salt. At this density, concentrations of Cd in leaves of sunflower without EDTA and with 1.0 g/kg EDTA salt were 2.2 and 6.5 g/g, respectively; for Ni, they were 6.7 and 19.2 g/g, respectively; and for Pb, they were 15.6 and 46.9 g/g, respectively. At the 60000 plants/ha density, stems of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than stems of sunflower grown without the EDTA salt. At this density, concentrations of Cd in stems of sunflower without EDTA and with 1.0 g/kg EDTA salt were 0.6 and 4.6 g/g, respectively; for Ni, they were 1.7 and 17.6 g/g, respectively; and for Pb, they were 5.2 and 42.8 g/g, respectively. Removal of the non-essential heavy metals by sunflower was greater at the higher plant density (60000 plants/ha) compared to the lower one (20000 plants/ha).     

In vitro clonal propagation of Capsicum spp.

The effect of various concentrations of benzyladenine (BA 4.4–177.5 M) or kinetin (4.7–185.9 M) on shoot proliferation from shoot-tip explants was investigated in C. praetermissum Heiser & Smith and C. annuum L. Maximum number of shoots were obtained on Murashige & Skoog's medium with 66.6 M BA or 92.9 M kinetin in C. praetermissum, and 88.8 M BA or 116.2 M kinetin in C. annuum after 4 weeks of culture. Combining 1 M 2, 3, 5-triiodobenzoic acid (TIBA) with low levels of BA or kinetin significantly increased shoot number as compared to using either cytokinin alone. Rooting of regenerated shoots was achieved on MS medium containing 5.7 M indoleacetic acid. Best rooting (80–100%) was observed in shoots from TIBA plus BA or kinetin media while only 40–50% of shoots from the BA or kinetin treatments were rootable. Plantlets obtained from TIBA plus BA or kinetin were normal diploids while those from BA or kinetin alone revealed distinct chromosomal aberrations in their root tip squashes. Regenerants from TIBA plus BA or kinetin media were successfully established in the soil (86% survival rate), where they flowered and showed normal meiotic behaviour with 100% pollen viability.Abbreviations BA benzyladenine - IAA indole-3-acetic acid - MS Murashige & Skoog's medium - TIBA 2, 3, 5-triiodobenzoic acid     

Storage,mobilization and interrelations of starch,sugars, protein and fat in the ray storage tissue of poplar trees

The seasonal pattern in starch, various sugars, protein, and fat, and their interrelationship, has been followed in 3-year-old branch wood of poplar trees (Populus x canadensis Moench robusta) under natural site conditions. The deposition of starch, protein and fat proceeds at different times. Starch accumulates from May until October, fat mainly during the summer months, and protein when the leaves are yellowing in September and October. The maximum concentrations in the branch wood were 15–18 g starch, 6–9 g protein, 4–8 g fat, 10–15 g sucrose, and up to 30 g total sugars per milligram dry weight (DW). During starch deposition periods no increased sucrose level is found in the tissue. The maximum daily starch deposition rate was 0.2–0.4 g starch/day/mg DW of wood. During starch hydrolysis in late autumn and winter, a dramatic increase in sucrose and its galactosides is measured (up to 15–27 g/mg DW in total). In early spring, before budbreak, the concentrations of these sugars diminishes sharply. In contrast to this clear-cut starch-to-sugar conversion in autumn no significant starch-to-fat conversion is detected. An elevated content of free glycerol, however, is found in winter. In spring, starch and storage protein are mobilized completely, or almost completely, in poplar twig wood. A noteworthy pool of maltose is found transiently during autumn (up to 8 g/mg DW) and again in spring. The results demonstrate that the individual storage materials, e.g. starch, protein, and fat, are accumulated fairly independently in the wood storage parenchyma. Tissue sugar levels, in contrast, appear to be closely related to the seasonal variations in starch content, on the one hand, and to the acclimation and deacclimation of the cells, on the other. The interrelations of the storage materials and sugars are discussed.     

Uptake of sewage derived nitrogen by<Emphasis Type="Italic"> Ulva rigida</Emphasis> (Chlorophyceae) in Bahía Nueva (Golfo Nuevo,Patagonia, Argentine)

Uptake kinetics of nitrogen derived from sewage–seawater mixtures (2.5–20% v/v effluent) were determined in the laboratory for Ulva rigida (Chlorophyceae) native from Bahía Nueva (Golfo Nuevo, Patagonia, Argentine). In terms of nitrogen concentration, experimental enrichment levels varied between 53.7 and 362.3M of ammonium and between 0.77 and 6.21M of nitrate+nitrite. Uptake rates were fitted to the Michaelis–Menten equation, with the following kinetic parameters: ammonium: V_max = 591.2molg^–1h^–1, K _s=262.3M, nitrate+nitrite: V _max=12.9molg^–1h^–1, K _s=3.5M). Both nutrients were taken up simultaneously, but ammonium incorporation was faster in all cases. The results show a high capability of Ulva rigida to remove sewage-derived nitrogen from culture media. In the field, most of the nitrogen provided by the effluent would be tied up in algal biomass, supporting low nitrogen levels found at a short distance away from the source.