Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 mol photon m^–2 s^–1 at 26 °C and 4.07 mol photon m^–2 s^–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m^–2 s^–1 at 26 °C and 65 mol photon m^–2 s^–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m^–2 s^–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day^–1 at 28 °C and 25 mol photon m^–2 s^–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.     

Isolation of membrane bound light-harvesting-complexes from the dinoflagellates Heterocapsa pygmaea and Prorocentrum minimum

We have isolated Chl a-Chl c-carotenoid binding proteins from the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown under high (500 mol m^–2 s^–1, HL) and low (35 mol m^–2 s^–1, LL) light conditions. We compared various isolation procedures of membrane bound light harvesting complexes (LHCs) and assayed the functionality of the solubilized proteins by determining the energy transfer efficiency from the accessory pigments to Chl a by means of fluorescence excitation spectra. The identity of the newly isolated protein-complexes were confirmed by immunological cross-reactions with antibodies raised against the previously described membrane bound Chl a-c proteins (Boczar et al. (1980) FEBS Lett 120: 243–247). Spectroscopic analysis demonstrated the relatedness of these proteins with the recently described Chl-a-c ₂-peridinin (ACP) binding protein (Hiller et al. (1993) Photochem Photobiol 57: 125–131; Iglesias Prieto et al. (1993) Phil Trans R Soc London B 338: 381–392). The water-soluble peridinin-Chl a binding-protein (PCP) was not detectable in P. minimum. Two functional forms of ACP with different pigmentation were isolated. A variant of ACP which was isolated from high-light grown cells, that specifically binds increased amounts of diadinoxanthin was compared to the previously described ACPs that bind proportionately more peridinin.Abbreviations ACP Chl a-Chl c-peridinin binding protein - AEBSF 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride - DDM dodecyl -d maltoside - Deriphat 160 N-lauryl-beta-iminopropionic acid - HEPES (N-2-hydroxyethylpiparizine-N-2-ethanesulphonic acid) - HL high light (500 mol m^–2 s^–1) - LL low light (35 mol m^–2 s^–1) - ₇₃₀ fluorescence yield (emission at 730 nm) - PCP peridinin-Chl a-binding protein - PMSF phenyl-methyl-sulfonyl-fluoride - PS I Photosystem I - PS II Photosystem II     

Changes in Photosystem II fluorescence in Chlamydomonas reinhardtii exposed to increasing levels of irradiance in relationship to the photosynthetic response to light

The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 mol m^–2s^–1 on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780 mol m^–2s^–1 where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600 mol m^–2s^–1 where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of Q_B-reducing centers and 3) a second photoinhibitory range above 1600 mol m^–2s^–1 where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS II centers and a large increase in spill-over in energy to PS I.Abbreviations Chl chlorophyll - DCMU 3,(3,4-dichlorophenyl)-1,1-dimethylurea - F_M maximal fluorescence yield - F_pl intermediate fluorescence yield plateau level - F₀ non-variable fluorescence yield - F_v total variable fluorescence yield (F_M-F₀) - initial slope to the light response curve, used as an estimate of initial quantum yield - convexity (rate of bending) of the light response curve of photosynthesis - LHC light-harvesting complex - P_max maximum rate of photosynthesis - PQ plastoquinone - Q photosynthetically active photon flux density (400–700 nm, mol m^–2s^–1) - PS photosystem - Q_A and Q_B primary and secondary quinone electron acceptor of PS II     

Response of maize and rice to 9-β-L(+) adenosine applied under different environmental conditions

The increase in growth, determined by dry weight gain, of rice (Oryza sativa L.) and maize (Zea mays L.) caused by foliar applications of 9--L(+) adenosine, a putative second messenger elicited by triacontanol, was studied under different environmental conditions. Maize seedlings cultured in the greenhouse under approximately 100 mol m^–2s^–1 of light prior to treatment with L(+) adenosine did not respond unless they received supplemental light (250–300 mol m^–2s^–1) after treatment. Exposure of rice seedlings growing for 16 h at 150 mol m^–2s^–1 to short periods of 450 mol m^–2s^–1 (< than 20 min) had no effect on the positive response of rice to L(+) adenosine; however, exposure for 60 min or more increased the growth of rice and obviated the effect of L(+) adenosine. Rice seedlings treated with L(+) adenosine at different times during the day responded only when treated 9 to 12h after initiation of the photoperiod. Normal growing temperatures under different light intensities had little or no direct effect on the response of plants to L(+) adenosine.     

Chlorophyll fluorescence as an indicator of photosynthetic functioning of in vitro grapevine and chestnut plantlets under ex vitro acclimatization

This study reports the effects of light availability during the acclimatization phase on photosynthetic characteristics of micropropagated plantlets of grapevine (Vitis vinifera L.) and of a chestnut hybrid (Castanea sativa × C. crenata). The plantlets were acclimatized for 4 weeks (grapevine) or 6 weeks (chestnut), under two irradiance treatments, 150 and 300 mol m^–2 s^–1 after in vitro phases at 50 mol m^–2 s^–1. For both treatments and both species, leaves formed during acclimatization (so-called `new leaves') showed higher photosynthetic capacity than the leaves formed in vitro either under heterotrophic or during acclimatization (so-called `persistent leaves'), although lower than leaves of young potted plants (so-called `greenhouse leaves'). In grapevine, unlike chestnut, net photosynthesis and biomass production increased significantly with increased light availability. Several parameters associated with chlorophyll a fluorescence indicated photoinhibition symptoms in chestnut leaves growing at 300 mol m^–2 s^–1. The results taken as a whole suggest that 300 mol m^–2 s^–1 is the upper threshold for acclimatization of chestnut although grapevine showed a better response than chestnut to an increase in light.     

Seasonality of brown macroalgae from Antarctica—a long-term culture study under fluctuating Antarctic daylengths

Summary The seasonal development of the endemic Antarctic Desmarestiales Himantothallus grandifolius, Phaeurus antarcticus, Desmarestia anceps, of a ligulate Desmarestia sp., of the Antarctic cold-temperate Adenocystis utricularis (Dictyosiphonales) and of the endemic Antarctic Ascoseira mirabilis (Ascoseirales) was monitored in a 2-year culture study under fluctuating daylengths mimicking the daylength conditions on King George Island (Antarctica). Temperature was kept constant at 0° C and nutrient levels were maintained at 0.6 moles m^–3 nitrate and 0.025 moles m ^–3 phosphate. Sporophytes were initiated between (April-) June and July in all Desmarestiales. This event was controlled either by induction of gametophyte fertility (in H. grandifolius and D. anceps) or by induction of spore formation (in Desmarestia sp. and P. antarcticus). Young sporophytes of all species showed a growth optimum from September to December (-February). Desmarestia sp. and P. antarcticus produced spores and degenerated subsequently after one year of culture at 3 mol photons m^–2 s^–1 or after 22 months of culture at 2 mol m^–2 s^–1. In D. anceps spores were released without degeneration of the mother plants after 20 and 19 months of culture at 3 and 10 olm^–2 s^–1, respectively. In H. grandifolius spore formation was not observed. Adult one year old plants of the latter two perennial species showed growth optima between September and November. Microthalli of A. utricularis were the dominant life phase of this alga in winter. Macrothalli started to develop from June onwards at 3 mol m^–2 s^–1 or from August to September at 2 mol m^–2 s^–1. Growth rates of macrothalli cultivated at 9 mol m^–2 s^–1 showed a growth optimum from September to November. The macrothalli released spores from January to February. Macrothalli cultivated at 3 mol m^–2 s^–1 maximally grew in January. They became fertile after almost 2 years of culture at 3 mol m^–2 s^–1 and remained vegetative at 2 mol m^–2 s^–1. A. mirabilis exhibited a prominent growth optimum from August to October, at photon fluence rates between 2 and 47 mol m^–2 s^–1. A second optimum was evident from January to March in plants cultivated at 9 mol m^–2 s^–1. The results closely correspond to available field data and indicate that the phenology of the studied species can be controlled in the laboratory solely by simulating Antarctic daylengths conditions. The light requirements for growth were very low in microthalli and in juvenile macrothalli and growth was mostly light saturated at 4–12 mol m^–2 s^–1. Few-celled sporophytes of H. grandifolius and D. anceps tolerated at least 8 and 11 months of darkness. The minimum light demands for completion of the life cycle are 31.4 mol m^–2 year^–1 in Desmarestia sp., P. antarcticus and probably also in the 2 perennial Desmarestiales; 47.1 mol m^–2 year^–1 are needed in A. utricularis and probably also in A. mirabilis. These values predict a lower distribution limit of the investigated species at 53±23 m or 48±21 m in clear offshore waters and at 28±5 m or 26±5 m, respectively, in inshore fjords of the Antarctic Peninsula region.Contribution No. 281 of the Alfred-Wegener-Institut für Polar-u. Meeresforschung     

Xanthophyll cycle activity in detached barley leaves senescing under dark and light

Senescence-induced changes in the xanthophyll cycle activity and chlorophyll (Chl) fluorescence parameters were compared in detached barley (Hordeum vulgare L.) leaf segments kept for 6 d in darkness or under continuous white light (90 mol m^–2 s^–1). Before detachment of the leaf segments, the plants were grown at periodic regime [12 h light (90 mol m^–2 s^–1)/12 h dark]. The de-epoxidation state of the xanthophyll cycle pigments (DEPS) in the leaf samples was determined immediately (the actual DEPS), after 1 h of dark-adaptation (the residual DEPS), and during 14 min of a high-irradiance (HI) exposure (500 mol m^–2 s^–1) (HI-induced DEPS). In the light-senescing segments, senescence was delayed pronouncedly compared to dark-senescing ones as the Chl content, the photosystem 2 photochemistry, and electron transport processes were highly maintained. Further, the actual DEPS increased, probably due to the increased mean photon dose. The HI-induced increase in the DEPS was stimulated in the light-senescing segments, whereas it was slowed down in the dark-senescing ones. However, after the 14 min HI-exposure of the dark-senescing segments the HI-induced DEPS was not markedly lower than in the mature leaves, which indicated the maintenance of the xanthophyll cycle operation.     

Ex Vitro Phenotype Stability is Affected by In Vitro Cultivation

Plant phenotype stability during ex vitro growth, one of the main requirements of plant micropropagation, was tested on tobacco. Plants cultivated in vitro in the presence of 3 % sucrose under photon flux density (PFD) of 200 mol m^–2 s^–1 (3 % HL plants) showed the best growth and photosynthetic parameters in the course of 7-day acclimation. However, significant change in phenotype of these plants appeared under a decrease in PFD to 50 mol m^–2 s^–1 during further ex vitro growth (in the period of 7^th – 17^th day). Much higher internodia elongation was found in 3 % HL plants in comparison with plants grown in vitro on sucrose media under PFD of 50 mol m^–2 s^–1 (3 % LL) or without sucrose either under PFD of 50 mol m^–2 s^–1 or 200 mol m^–2 s^–1 (0 % LL, 0 % HL). It can be presumed that 3 % HL plants show permanent demand for high PFD. Neither ABA or chlorophyll contents nor de novo thylakoid membrane synthesis were related to the morphogenic effect of low PFD. Changeable contents of hexoses in leaves of 3 % HL and 3 % LL plants were in no direct correlation to the elongated growth.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Application of N-15 dilution for simultaneous estimation of nitrification and nitrate reduction in soil-water columns

Nitrification and denitrification rates were estimated simultaneously in soil-floodwater columns of a Crowley silt loam (Typic Albaqualfs) rice soil by an¹⁵N isotopic dilution technique. Labeled NO ₃ ^– was added to the floodwater of soil-water columns, half were treated with urea fertilizer. The (NO ₃ ^– +NO ₂ ^– )–N and (NO ₃ ^– +NO ₂ ^– )–N concentrations in the floodwater were measured over time and production and reduction rates for NO ₃ ^– calculated. Nitrate reduction in the urea amended columns averaged 515 mol N m^–2h^–1 and nitrification averaged 395 mol N m^–2h^–1 over the 35–153 d incubation. The nitrification rate for 4–19 d sampling period (1,560 mol N m^–2h^–1) in the urea amended columns was almost 9 times greater than the reduction rate (175 mol N m^–2h^–1) over the same period. Without the addition of urea the NO ₃ ^– production rate averaged 32 mol N m^–2h^–1 and reduction 101 mol N m^–2h^–1.     

Cell volume distribution dynamics of <Emphasis Type="Italic">Chlorella</Emphasis><Emphasis Type="Italic">vulgaris</Emphasis> Beij. in batch cultures under continuous light

Cell volume distribution in Chlorella vulgaris cultures coming out of senescence was measured by flow cytometry every 6 h for 114 h in a full-factorial experiment with initial nitrate (420–4200 g NO₃-N l^–1), phosphate (9–186 g PO₄-P l^–1), and continuous light (50–330 E m^–2 s^–1) as treatments. The maxima in median and median absolute deviation (MAD) of cell volume were achieved within 6 h of each other and their timing was not affected by any treatment. Population specific growth rate during the first 66 h calculated from volume distribution changes was significantly affected by light treatment only (p=0.002).Revisions requested 4 November 2004; Revisions received 17 January 2005     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

Photosynthetic gas exchange response of poplars to steady-state and dynamic light environments

The steady-state and dynamic photosynthetic response of two poplar species (Populus tremuloides and P. fremontii) to variations in photon flux density (PFD) were observed with a field portable gas exchange system. These poplars were shown to be very shade intolerant with high light saturation (800 to 1300 mol photons m^–2 s^–1) and light compensation (70 to 100 mol m^–2 s^–1) points. Understory poplar leaves showed no physiological acclimation to understory light environments. These plants become photosynthetically induced quickly (10 min). Activation of Rubisco was the primary limitation for induction, with stomatal opening playing only a minor role. Leaves maintained high stomatal conductances and stomata were unresponsive to variations in PFD. Leaves were very efficient at utilizing rapidly fluctuating light environments similar to those naturally occurring in canopies. Post-illumination CO₂ fixation contributed proportionally more to the carbon gain of leaves during short frequent lightflecks than longer less frequent ones. The benefits of a more dynamic understory light environment for the carbon economy of these species are discussed.     

Ecophysiological characterization of carnivorous plant roots: Oxygen fluxes,respiration, and water exudation

Various ecophysiological investigations on carnivorous plants in wet soils are presented. Radial oxygen loss from roots of Droseraceae to an anoxic medium was relatively low 0.02 – 0.07 mol(O₂) m^{– 2} s^–1 in the apical zone, while values of about one order of magnitude greater were found in both Sarracenia rubra roots and Genlisea violacea traps. Aerobic respiration rates were in the range of 1.6 – 5.6 mol kg^–1 (f.m.) s^–1 for apical root segments of seven carnivorous plant species and 0.4 – 1.1 mol kg^–1 (f.m.) s^–1 for Genlisea traps. The rate of anaerobic fermentation in roots of two Drosera species was only 5 – 14 % of the aerobic respiration. Neither 0.2 mM NaN₃ nor 0.5 mM KCN influenced respiration rate of roots and traps. In all species, the proportion of cyanide-resistant respiration was high and amounted to 65 – 89 % of the total value. Mean rates of water exudation from excised roots of 12 species ranged between 0.4 – 336 mm 3 kg^–1 (f.m.) s^–1 with the highest values being found in the Droseraceae. Exudation from roots was insensitive to respiration inhibitors. No significant difference was found between exudation rates from roots growing in situ in anoxic soil and those kept in an aerated aquatic medium. Carnivorous plant roots appear to be physiologically very active and well adapted to endure permanent soil anoxia.     

Effect of irradiance, temperature and salinity on growth and toxin production by Nodularia spumigena

The object of this work was to determine, using a full-factorial experiment, the influence of temperature, irradiance and salinity on growth and hepatotoxin production by Nodularia spumigena, isolated from Lake Alexandrina in the south-east of South Australia. Higher levels of biomass (determined as particulate organic carbon, POC), toxin production and intracellular toxin concentration per mg POC were produced under light limited conditions (30 mol m^–2 s^–1) and at salinities equal to or greater than those experienced in Lake Alexandrina. Both highest biomass and total toxin production rates were recorded at temperatures equal to or greater than those of the lake (20 and 30°C). The temperature at which maximum biomass and toxin production was recorded decreased from 30°C for cultures grown at 30 mol m^–2 s^–1 to 20°C when grown at 80 mol m^–2 s^–1. In contrast, intracellular toxin per mg POC was highest at the lowest growth temperature, 10°C, at both 30 and 80 mol m^–2 s^–1. It appears that the optimum temperature for biosynthetic pathways used in the production of toxin is lower than the optimum temperature for those pathways associated with growth. Intracellular toxin levels were higher in cells cultured at 10°C/30 mol m^–2 s^–1 whereas the majority of the toxin was extracellular in cells grown at 30°C/30 mol m^–2 s^–1. This implies that the highest concentration of toxin in lake water would occur under high temperature and high irradiance conditions. Individual environmental parameters of salinity, irradiance and temperature were all shown to influence growth and toxin production. Notwithstanding, the overall influence of these three parameters on toxin production was mediated through their effect upon growth rate.     

Simultaneous use of 14C and 3H to determine autotrophic production and bacterial protein production in periphyton

A method of simultaneously quantifying photoautotrophic (algae and cyanobacteria) and bacterial production in periphyton communities by ¹⁴C-bicarbonate and ³H-leucine incorporation was investigated and applied to communities subjected to specific intensities of photosynthetically active radiation (400–700 nm). Maximum photosynthetic output (2.23 ± 0.29 (SE) g C cm^-2 h^-1) and bacterial production (0.07 ± 0.006 g C cm^-2 h^-1) occurred at the highest photon flux density (400 mol m^-2 s^-1). Over a photon flux density range of 20–400 mol m^-2 s^-1, bacterial and autotroph productivity were significantly and positively correlated (r = 0.89). Furthermore, application of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, a photosystem 11 inhibitor, to periphyton films reduced bacterial production by 46%, but it had no such effect on bacteria-only cultures. Therefore, the magnitude of bacterial production in periphyton was coupled to the photosynthesis/metabolism of algae and/or cyanobacteria.     

Optimization of eicosapentaenoic acid production byPhaeodactylum tricornutumin the flat panel airlift (FPA) reactor

Biomass and eicosapentaenoic acid (EPA) productivities were investigated in a flat panel airlift loop reactor ideally mixed by static mixers. Growth with ammonium, urea and nitrate as nitrogen source were performed at different aeration rates. Cultures grew on ammonium but the decay of pH strongly inhibited biomass increase. On urea biomass productivity reached 2.35 g L^–1d^–1at an aeration rate of 0.66 vvm (24 h light per day, 1000 mol photon m^–2s^–1). Aeration rates between 0.33 vvm and 0.66 vvm and maximal productivities on urea were linearly dependent. Productivity on nitrate never exceeded 1.37 g L^–1d^–1. In the range of maximum productivity photosynthesis efficiency of 10.6% was reached at low irradiance (250 mol photon m^–2s^–1). Photosynthesis efficiency decreased to 4.8% at 1000 mol photon m^–2s^–1. At these high irradiances the flat panel airlift reactor showed a 35% higher volume productivity than the bubble column. At continuous culture conditions the influence of CO₂concentration in the supply air was tested. Highest productivities were reached at 1.25% (v/v) CO₂where the continuous culture yielded 1.04 g L^–1d^–1(16 h light per day, 1000 mol photon m^–2s^–1). The average EPA content amounted to 5.0% of cell dry weight, that resulted in EPA productivities of 52 mg L^–1d^–1(continuous culture, 16 h light per day) or 118 mg L^–1d^–1(batch culture, 24 h light per day).     

Factors affecting in vitro microrhizome production in turmeric

In vitro microrhizome production was obtained in turmeric (Curcuma longa Linn.). Freshly sprouted buds with small rhizome portions excised from stored mature rhizomes were cultured on semi-solid culture initiation medium –- MS basal medium + 0.88 M BAP (6-benzylaminopurine) + 0.92 M kinetin + 5% coconut water + 2% sucrose + 0.5% agar –- resulting in bud elongation. Multiple shoots were produced from these elongated buds by culturing in liquid shoot multiplication medium –- MS basal medium + 2.2 M BAP + 0.92 M kinetin + 5% coconut water + 2% sucrose –- at 25±1°C and 16-h light (at 11.7 mol m^–2 s^–1)/8-h dark cycles. Clumps of four to five multiple shoots/single shoots were used in various experiments. Cultures were incubated in the dark at 25±1°C. Half strength MS basal medium supplemented with 80 g l^–1 sucrose was found to be optimal for microrhizome production. Cytokinin BAP had an inhibitory effect on microrhizome production. At the highest concentration of BAP tried (35.2 M) microrhizome production was totally inhibited. Microrhizome production depended on the size of the multiple shoots used. Microrhizomes produced were of a wide range in size (0.1–2.0 g) and, readily regenerated when isolated and cultured in vitro on culture initiation medium or shoot multiplication medium. Under in vivo conditions, small (0.1–0.4 g), medium (0.41–0.8 g) and big (>0.81 g) microrhizomes regenerated. Plantlets developed from big microrhizomes grew faster.     

Model aided design of repeated fed-batch penicillin fermentation

Structured models of antibiotic fermentation that quantify maturation and aging of product forming biomass are fitted to experimental data. Conditions of superiority of repeated fed batch cultivation are characterized on the basis of a performance criterion that includes penicillin productivity and costs of operation. Emphasis is placed on the relevance of such research to the model aided design of optimal cyclic operation.List of Symbols c IU/mg cost factor - D s^–1 dilution rate - J IU · cm^–3 · h^–1 net productivity - k _p IU · mg^–11 · h^–1 specific product formation rate - k _pm IU · mg^–1 · h^–1 maximum specific product formation rate - p IU/cm³ concentration of penicillin - T s final time of fermentation - t s fermentation time - X kg/m³ concentration of biomass dry weight - X ₁kg/m³ concentration of young, immature biomass - X ₂ kg/m³ concentration of mature product forming biomass - X _c kg/m³ biomass concentration of the end of growth phase - X _mkg/m³ maximum biomass concentration Greek Letters s^–1 specific maturation rate - s^–1 specific aging rate - s^–1 specific growth rate - _m s^–1 maximum specific growth rate - _p s^–1 specific growth rate during the product formation phase - s cycle time - % volume fraction of draw-off Abbreviations CC chemostat culture - RFBC repeated fed batch culture - RBC repeated batch culture     

UV-A mediated induction of carotenoid accumulation in Dunaliella bardawil with retention of cell viability

The effect of adding UV-A radiation (320–400 nm) to photosynthetically active radiation (PAR, 400–700 nm) during growth of the photosynthetic marine microalga Dunaliella bardawil was investigated in this work in terms of cell growth and carotenoid production. Although signs of slow cell growth (slight reduction of chlorophyll and protein content) were observed after 24 h of cell exposure to UV-A (40 mol photons m^–2 s^–1 and 70 mol photons m^–2 s^–1) plus 140 mol photons m^–2 s^–1 PAR , 84 h exposure to these UV-A conditions slightly stimulated cell growth and increased the photosynthetic efficiency of the exposed cultures. The enhanced cell growth was coupled with an increase in total carotenoid content. Besides -carotene as the major pigment, increases in the well-known antioxidants lutein and zeaxanthin of about 3-fold and 5-fold, respectively, were determined in cultures exposed to UV-A radiation of 70 mol photons m^–2 s^–1for 84 h. As a consequence, far from being negative to cell growth, low and medium UV-A radiation are stress factors that could be successfully applied to long-term processes for large scale carotenoid production using D. bardawil cultures with retention of cell viability. UV-A exposure has the advantage of being a factor either easily applied or removed as required, in contrast to other nutrient stresses, which require medium replacement for their application.