Molecular thermal telemetry of free-ranging adult Drosophila melanogaster

The expression of two temperature-sensitive reporter genes, hsp70 and an hsp70-LacZ fusion, in free-ranging adult Drosophila melanogaster indicates that natural thermal stress experienced by such small and mobile insects may be either infrequent or not severe. Levels of the heat-shock protein Hsp70, the major inducible Hsp of Drosophila, were similar in most wild Droso- phila captured after warm days to levels previously reported for unstressed flies in the laboratory. In a transgenic strain transformed with an hsp70-LacZ fusion (i.e., the structural gene encoding bacterial β-galactosidase under control of a heat shock promoter), exposure to temperatures ≥32°C in the laboratory typically resulted in β-galactosidase activities exceeding 140 mOD₄₅₀ h^–1μg^–1 soluble protein. Flies caged in sun frequently had β-galactosidase activities in excess of this level, whereas flies caged in shade and flies released and recaptured on cool days did not. Most flies (>80%) released on warm, sunny days had low β-galactosidase activities upon recapture. Although the balance of recaptured flies had elevated β-galactosidase activities on these days, their β-galactosidase activities were <50% of levels for flies caged in direct sunlight or exposed to laboratory heat shock. These data suggest that even on warm days most flies may avoid thermal stress, presumably through microhabitat selection, but that a minority of adult D. melanogaster undergo mild thermal stress in nature. Both temperature-sensitive reporter genes, however, are limited in their ability to infer thermal stress and demonstrate its absence. Received: 14 July 1999 / Accepted: 21 December 1999     

Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 μmol m⁻²s⁻¹) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 μmol m⁻²s⁻¹, while net CO₂ assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 μmol m⁻²s⁻¹, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 μmol m⁻²s⁻¹. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 μmol m⁻²s⁻¹. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 μmol m⁻²s⁻¹was suitable for acclimatisation when plants were transferred from in vitro conditions.     

Differences in photosynthetic apparatus of leaves from different sides of the chestnut canopy

In crowns of chestnut trees the absorption of radiant energy is not homogeneous; leaves from the south (S) side are the most irradiated, but leaves from the east (E) and west (W) sides receive around 70 % and those from north (N) face less than 20 % of the S irradiation. Compared to the S leaves, those from the N side were 10 % smaller, their stomata density was 14 % smaller, and their laminae were 21 % thinner. N leaves had 0.63 g(Chl) m⁻², corresponding to 93 % of total chlorophyll (Chl) amount in leaves of S side. The ratios of Chl a/b were 2.9 and 3.1 and of Chl/carotenoids (Car) 5.2 and 4.8, respectively, in N and S leaves. Net photosynthetic rate (P _N) was 3.9 μmol(CO₂) m⁻² s⁻¹ in S leaves, in the E, W, and N leaves 81, 77, and 38 % of that value, respectively. Morning time (10:00 h) was the period of highest P _N in the whole crown, followed by 13:00 h (85 % of S) and 16:00 h with 59 %. Below 500 μmol m⁻² s⁻¹ of photosynthetic photon flux density (PPFD), N leaves produced the highest P _N, while at higher PPFD, the S leaves were most active. In addition, the fruits from S side were 10 % larger than those from the N side.     

Developmental changes in carboxylase activities in in vitro cultured coconut zygotic embryos: comparison with corresponding activities in seedlings

Phosphoenolpyruvate Carboxylase (PEPC; EC: 4.1.1.31) and Ribulose 1,5-bisphosphate Carboxylase/Oxygenase (RubisCO; EC: 4.1.1.39) enzyme specific activities were measured during the in vitro development of coconut (Cocos nucifera L.) zygotic mature embryos into plantlets and compared with those of palms produced by conventional seed germination. At the time of initiation of germination, high PEPC and low RubisCO activities were measured in both cultured and conventionally germinated embryos, thus indicating an anaplerotic CO₂ fixation. During both in vitro and in planta development, RubisCO progressively took over and became the main route for inorganic carbon fixation. The in vitro-grown coconut plantlets showed a faster decrease in their PEPC:RubisCO ratio than the seedlings, suggesting that an earlier transition from a heterotrophic to an autotrophic mode of carbon fixation takes place in the in vitro-derived material. Just before acclimatization, the RubisCO activity in in vitro-derived plantlets (2.83 μmol CO₂h⁻¹mg⁻¹ _TSP) was lower than that in seedlings (6.98 μmol CO₂h⁻¹mg⁻¹ _TSP) of the same age. Nevertheless, after acclimatization, RubisCO activities were comparable in both in vitro and in planta germinated material This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of culture medium and illumination on the acid invertase activity in callus of Medicago strasseri

The different acid invertase activity (total, soluble, wall-bound and extracellular) in calli induced on explants (cotyledon, petiole, hypocotyl and leaf) originated from Medicago strasseri seedlings were evaluated. In cultures subjected to 16 h photoperiod, the highest total, soluble and extracellular activities were found in calli from leaves cultured in medium 12 (MS with 0.01 mg·dm⁻³ (0.045 μM) of TDZ), elevated amounts of total and wall-bound invertase being found in calli induced on petioles in 12G medium (MS with 0.01 mg·dm⁻³ (0.045 μM) TDZ and 3.104 mg·dm⁻³ glycerol). In cultures maintained in darkness, the activity detected was lower than that observed in cultures under light conditions. The highest amounts of enzyme was bound in calli cultured on medium 12 (total and extracellular invertase) -leaves- and medium 12D (MS with 0.001 mg·dm⁻³ (0.0045 μM) TDZ) (soluble invertase) -using hypocotyls. In general, the different forms of invertase activity studied seem to appear in greatest amounts in calli induced under light conditions using leaves as explant and TDZ as growth regulator.     

Photosynthetic characteristics of Dunaliella salina (Chlorophyceae,Dunaliellales) in relation to β-carotene content

Photosynthetic characteristics of Dunaliella salina with high (red form) and low β-carotene (green form) concentrations were studied. D. salina growing in brine saltworks exhibited a high level of β-carotene (15 pg cell⁻¹). The rate of oxygen evolution as a function of irradiance was higher in the red than in the green form (on chlorophyll basis). Photosynthetic inhibition of the green form was observed above 500 μmol m⁻² s⁻¹. The red form appeared more resistant to high irradiance and no inhibition in O₂ evolution was observed up 2000 μmol m⁻² s⁻¹. However, when these results are expressed on a cell number basis the rate of oxygen evolution was significantly higher in the green form. Carbonic anhydrase (CA) activity (total, soluble, membrane bound) was found in red and green forms. CA was higher in the red form on a chlorophyll basis, but lower if expressed on a protein basis. The light dependent rate of oxygen evolution and photoinhibition depends on the concentration of β-carotene in D. salina cells.     

Cadmium effects and accumulation in cultures ofProrocentrum micans (dinophyta)

Effects and accumulation of cadmium were studied in unialgal 10-1 batch-culture experiments with the dinoflagellateProrocentrum micans Ehrenberg. Tests were made using sterile filtered North Sea water enriched with nitrate and phosphate only in order to avoid disturbances by complex formation. Cadmium was added to the cultures in amounts of 100 to 0.13μg l⁻¹. In one series it was added at the start of the experiments and in a second one after a growth period of 1 week. Addition of only 1.2μg Cd l⁻¹ reduces multiplication rates and maximum cell densities of the algae. Not until 0.4μg Cd⁻¹ does growth correspond to that of the controls. Cadmium concentrations were measured, after filtration, in the culture medium and in the biomass by means of flameless AAS. The cadmium content in algae increased from 2.7μg g⁻¹ (dry weight) in controls to 500μg g⁻¹ (dry weight) in media containing 100μg Cd l⁻¹. Uptake occurred rapidly during the first few days of the experiments, slowed down somewhat during exponential growth stage, and increased during decay of the cultures. Cadmium content of culture media remained nearly constant (Series 1) or decreased only slowly during experimental time (Series 2). The highest concentration factor was measured in the controls. It decreased with increasing metal concentration in the medium and increased with experimental time. Structural modifications of the cells were visible after Lugol fixation only, indicating brittleness of the cell walls.P. micans has shown to be extremely sensitive to cadmium and to accumulate this metal.     

Photosynthetically versatile thin shade leaves: A paradox of irradiance-response curves

Thick sun leaves have a larger construction cost per unit leaf area than thin shade leaves. To re-evaluate the adaptive roles of sun and shade leaves, we compared the photosynthetic benefits relative to the construction cost of the leaves. We drew photosynthetically active radiation (PAR)-response curves using the leaf-mass-based photosynthetic rate to reflect the cost. The dark respiration rates of the sun and shade leaves of mulberry (Morus bombycis Koidzumi) seedlings did not differ significantly. At irradiances below 250 μmol m⁻² s⁻¹, the shade leaves tended to have a significantly larger net photosynthetic rate (P _N) than the sun leaves. At irradiances above 250 μmol m⁻² s⁻¹, the P _N did not differ significantly. The curves indicate that plants with thin shade leaves have a larger daily CO₂ assimilation rate per construction cost than those with thick sun leaves, even in an open habitat. These results are consistently explained by a simple model of PAR extinction in a leaf. We must target factors other than the effective assimilation when we consider the adaptive roles of thick sun leaves.     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

Structural and grazing responses of zooplankton community to biomanipulation of some Dutch water bodies

Structure and grazing activities of crustacean zooplankton were compared in five lakes undergoing manipulation with several unmanipulated eutrophic (shallow) and mesotrophic (deep) lakes in The Netherlands. The biomanipulated lakes had lesser number of species and their abundance, both of rotifers and crustaceans, and had much larger mean animal size (3–11 μg C ind.⁻¹) than in the unmanipulated eutrophic lakes (0.65 μG C ind.⁻¹). WhereasD. hyalina (=D. galeata) andD. cucullata generally co-occurred in the unmanipulated lakes, in the manipulated lakes bothD. hyalina and other large-bodied daphnids,D. magna,D. pulex (=D. pulicaria), were the important grazers. In the biomanipulated lakes an increase in the individual crustacean size and of zooplankton mass were reflected in a decrease in seston concentration, higher Secchi-disc depth and a marked decrease in the share in phytoplankton biovolume of cyanobacteria. Biomass relationship between seston (150 μm) and zooplankton indicated a Monod type relationship, with an initial part of the curve in which the zooplankton responds linearly to the seston increase up to aboutca. 2 mg C l⁻¹, followed by a saturation of zooplankton mass (0.39 mg C l⁻¹) at 3–4 mg C l⁻¹ seston, and an inhibitory effect on zooplankton mass at seston levels>4 mg C l⁻¹. This latter is related to predominance in the seston of cyanobacteria. In the biomanipulated lakes, the zooplankton grazing rates often exceeded 100% d⁻¹, during the spring, and food levels generally dropped to <0.5 mg C l⁻¹. The computed specific clearance rate (SCR) of zooplankton of 1.9 l mg⁻¹ Zoop C is well within the range of SCR values (1.7–2.2 l mg⁻¹ Zoop C) from deep and mesotrophic waters, but about an order of magnitude higher than in the eutrophic lakes, with the food levels 10-fold higher. For 25% d⁻¹ clearance of lake seston between 35 and 60 ind. l⁻¹ are needed in the biomanipulated lakes against 1200–1300 ind. l⁻¹ in eutrophic lakes. Similarly, about 10 to 15 times more crustacean grazers are required to eliminate the daily primary production in the eutrophic lakes than in the biomanipulated lakes. These numbers are inversely related to the differences in animal size. The corresponding biomass values of zooplankton needed to clear the daily primary production in the eutrophic waters were 0.1–0.2 mg C l⁻¹ in the biomanipulated lakes, but about 0.45 mg C l⁻¹ in the unmanipulated eutrophic waters. Only if the water was kept persistently clear by zooplankton was there a balanced seston budget between the inputvia primary production and elimination by zooplankton. Mostly, however, the input exceeded the assimilatory removal by zooplankton, such that the estimated seston loss could be attributed to sedimentation and mineralization.     

Gradient of photosynthetic pigments in the bark and leaves of lilac (Syringa vulgaris L.)

The concentration of chlorophyll and a carotenoids in the bark of stems of different age and in the leaves of lilac (Syringa vulgaris L.) was determined. The thickness of bark changes with the age of the stems, ranging from 0.73 mm in the current-year stems to 1.22 mm in 3-year-old ones. Chlorophyll and carotenoids were present through the whole thickness of the bark, except the cork. It was found that chlorophyll and carotenoids are located mainly in the outer layer of the bark, immediately under the cork, to a depth of 400 μm. In this layer the chlorophyll a/b ratio is the highest and the content of chlorophyll is four times larger than that of carotenoids. When penetrating deeper into the bark, the content of chlorophyll and carotenoids as well as the chlorophyll a/b ratio diminishes. Investigations of the leaves showed that most of the chlorophyll is found in the palisade parenchyma, the chlorophyll a/b ratio is the highest in the upper layer. The highest concentration of chlorophyll in the bark is 0.44 mg·dm⁻² and in leaves −1.2 mg⁻²·dm⁻². The highest value of the chlorophyll a/b ratio in the bark is 3.8, and the lowest 0.5, while in the leaves it varies from 4.5 to 3.8 Low values of the chlorophyll a/b ratio are due to the shade conditions existing in the bark and they are evidence of very great differentiation of light conditions within it.     

Stability of transgene expression, field performance and recombination breeding of transformed barley lines

Stable inheritance of the transgene, consistent expression and competitive agronomic properties of transgenic crops are important parameters for successful use of the latter. These properties have been analyzed with 18 homozygous transgenic barley lines of the cultivar Golden Promise. The lines originated from three independent primary transformants obtained by the biolistic method with three plasmids containing respectively, the bar gene, the uidA gene and the gene for a protein-engineered heat-stable (1,3–1,4)-β-glucanase. Three production levels of recombinant β-glucanase were identified in homozygous transgenic T₃ plants, and these remained constant over a 3-year period. In micro-malting experiments, the heat-stable enzyme reached levels of up to 1.4 μg·mg⁻¹ protein and survived kiln drying at levels of 70–100%. In the field trials of 1997 and 1998 the transgenic lines had a reduced 1000-grain weight as well as variable yield depressions compared to the Golden Promise progenitor. In 1999 large-scale propagations of the lines with the highest recombinant enzyme synthesis during germination and of Golden Promise were studied at three different locations. In an irrigated field transgenic lines yielded approximately 6 t·ha⁻¹ and Golden Promise 7.7 t·ha⁻¹. Cross-breeding was carried out to transfer the transgene into a more suitable genetic background. Crosses of the semi-dwarf ari-e mutant Golden Promise gave rise to the four morphological phenotypes nutans, high erect, erect, and ari-e. Two improvements were achieved: (1) F₃ lines homozygous for the expression of heat-stable (1,3−1,4)-β-glucanase were found among lines that were homozygous for each of the four morphological phenotypes; (2) improved 1000-grain weights and yields with respect to those of the original transformants were observed in some F₄ lines homozygous for the morphological phenotypes and for the transgene. In the case of a homozygous nutans line, the transgenic plants had a higher 1000-grain weight than those lacking the transgene. Like mutants providing useful output traits, transgenic plants will often have to be improved by relocating the gene into more suitable genotypes. Received: 6 March 2000 / Accepted: 14 April 2000     

Down regulation of CYP 1A1 by glucocorticoids in trout hepatocytes in vitro

Summary Short-term culture of rainbow trout (Onchorhynchus mykiss) hepatocytes was used to examine the effect of dexamethasone (DEX) on microsomal CYP 1A1 protein content and 7-ethoxyresorufin-O-deethylase (EROD) activity in vitro. Hepatocytes prepared by controlled collagenase digestion and plated at a density of 0.25 × 10⁶ cells/cm² in plastic culture dishes precoated with trout skin extract (7.6 μg skin protein/cm²) to facilitate cell attachment were maintained at 16° C. Cells were treated with DEX (10⁻⁹ to 10⁻⁷ M) or vehicle (dimethyl sulfoxide, DMSO) at 24 h. Microsomal CYP 1A1 protein content and EROD activities were measured at 72 h. Both CYP 1A1 protein as measured by Western blots using CYP 1A1 specific anti-sera and EROD activity were significantly lower in DEX (10⁻⁸ to 10⁻⁷ M)-treated hepatocytes compared to untreated (control) or DMSO-treated cells. The effect was dose dependent in that a gradual decrease of CYP 1A1 protein and EROD activities were seen with increasing doses of DEX (10⁻⁸ to 10⁻⁷ M). DEX at 10⁻⁹ M was ineffective. Concomitant addition of 10⁻⁶ M RU486, a type II specific glucocorticoid receptor antagonist, to hepatocytes treated with 10⁻⁷ M DEX abolished the DEX effect. RU486 at 10⁻⁸ M was ineffective. Spironolactone (10⁻⁸ to 10⁻⁶ M), a type I specific glucocorticoid receptor antagonist, did not counteract the DEX effect. RU486 or spironolactone (10⁻⁶ M) alone had no effect on CYP 1A1 under similar conditions. DEX thus down regulates CYP 1A1 in fish cultured hepatocytes and this regulation is mediated through the type II glucocorticoid receptor(s).     

Quantitative and Qualitative Changes in Peroxidase of Cucurbita Pepo Cultivars Stressed with Heavy Metals

Seedlings of two cultivars of zucchini (Cucurbita pepo L.) Courgette d'Italie (CI) and Courgette d'Alger (CA) were pre-treated with various concentrations of cadmium, copper and zinc for 30 d. High accumulation of heavy metals especially in the roots was showed. Peroxidase activity was affected according to the type of metal added, concentration, and the plant cultivar used. In leaves and roots of the CI control plants peroxidase activities were 50 and 17 % higher than in the CA control plants. Treatment with Cd (5 μg g⁻¹), Cu (200 μg g⁻¹), and Zn (500 μg g⁻¹) increased peroxidase activities in CA but decreased it in CI both in leaves and roots. Heavy metals tested lead also to some qualitative changes characterized by appearance of new isoforms of peroxidase. The results show the possibility to use the activities of peroxidase as biomarkers for Cd, Cu and Zn stresses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Susceptibility of green leaves and green flower petals of CAM orchid <Emphasis Type="Italic">Dendrobium</Emphasis> cv. Burana Jade to high irradiance under natural tropical conditions

Photosynthetic rates of green leaves (GL) and green flower petals (GFP) of the CAM plant Dendrobium cv. Burana Jade and their sensitivities to different growth irradiances were studied in shade-grown plants over a period of 4 weeks. Maximal photosynthetic O₂ evolution rates and CAM acidities [dawn/dusk fluctuations in titratable acidity] were higher in leaves exposed to intermediate sunlight [a maximal photosynthetic photon flux density (PPFD) of 500–600 μmol m⁻² s⁻¹] than in leaves grown under full sunlight (a maximal PPFD of 1 000–1 200 μmol m⁻² s⁻¹) and shade (a maximal PPFD of 200–250 μmol m⁻² s⁻¹). However, these two parameters of GFP were highest in plants grown under the shade and lowest in full sun-grown plants. Both GL and GFP of plants exposed to full sunlight had lower predawn F_v/F_m [dark adapted ratio of variable to maximal fluorescence (the maximal photosystem 2 yield without actinic irradiation)] than those of shade-grown plants. When exposed to intermediate sunlight, however, there were no significant changes in predawn F_v/F_m in GL whereas a significant decrease in predawn F_v/F_m was found in GFP of the same plant. GFP exposed to full sunlight exhibited a greater decrease in predawn F_v/F_m compared to those exposed to intermediate sunlight. The patterns of changes in total chlorophyll (Chl) content of GL and GFP were similar to those of F_v/F_m. Although midday F_v/F_m fluctuated with prevailing irradiance, changes of midday F_v/F_m after exposure to different growth irradiances were similar to those of predawn F_v/F_m in both GL and GFP. The decreases in predawn and midday F_v/F_m were much more pronounced in GFP than in GL under full sunlight, indicating greater sensitivity in GFP to high irradiance (HI). In the laboratory, electron transport rate and photochemical and non-photochemical quenching of Chl fluorescence were also determined under different irradiances. All results indicated that GFP are more susceptible to HI than GL. Although the GFP of Dendrobium cv. Burana Jade require a lower amount of radiant energy for photosynthesis and this plant is usually grown in the shade, is not necessarily a shade plant.     

Effect of zooplankton type and abundance on prey consumption by the fairy shrimp, Streptocephalus proboscideus (Anostraca: Crustacea)

Laboratory cultured Streptocephalus proboscideus (three sizes (mm), viz. 8.44 ± 0.95 (virgin), 14.18 ± 1.49 (adult I) and 19.24 ± 1.52 (adult II)) were offered (separately for males and females) field collected zooplankton (12 prey types) at three levels of abundance (1.0 ml⁻¹, 2.0 ml⁻¹ and 4.1 ind. ml⁻¹ in 30-minute feeding experiments. Gut contents, analyzed for abundance and diversity of prey type, showed that predator size, sex and their interaction had strong effects on prey consumption. Regardless of their size, and of prey density, S. proboscideus females consumed 25–90% more prey than males. Their filtration rates (adult II) were higher (125 ml ind.⁻¹ h.⁻¹) than those of males (30 ml ind.⁻¹ h.⁻¹) too. Rotifers had the highest numerical percentage in the gut, regardless of predator size or sex. Cladocerans were only consumed by adults I and II. Adult II females consumed 28.5–43.3 μg zooplankton dry weight ind.⁻¹ h.⁻¹. Size distribution of B. longirostris in the field and in the gut were closely similar. This study confirms S. proboscideus as a non-selective filter feeder. Since it did not eat jumping rotifers, copepod nauplii and copepodites, it may contribute to structuring its prey communities, because good escapers will be enriched in the medium, while poor escapers will be depleted.     

Carbon fixation and carbonic anhydrase activity in Haslea ostrearia (Bacillariophyceae) in relation to growth irradiance

The metabolic pathway of primary carbon fixation was studied in a peculiar pennate marine diatom, Haslea ostrearia (Bory) Simonsen, which synthesizes and accumulates a blue pigment known as “marennine”. Cells were cultured in a semi-continuous mode under saturating [350 μmol(photon) m⁻² s⁻¹] or non-saturating [25 μmol(photon) m⁻² s⁻¹] irradiance producing “blue” (BC) and “green” (GC) cells, characterized by high and low marennine accumulation, respectively. Growth, pigment contents (chlorophyll a and marennine), ¹⁴C accumulation in the metabolites, and the carbonic anhydrase (CA) activity of the cells were determined during the exponential growth phase. Growth rate and marennine content were closely linked to irradiance during growth: higher irradiance increased both growth rate and marennine content. On the other hand, the Chl a concentration was lower under saturating irradiance. The distribution between the Calvin-Benson (C₃) and β-carboxylation (C₄) pathways was very different depending on the irradiance during growth. Metabolites of the C₃ cycle contained about 70 % of the total fixed radioactivity after 60 s of incorporation into cells cultured under the non-saturating irradiance (GC), but only 47 % under saturating irradiance (BC). At the same time, carbon fixation by β-carboxylation was 24 % in GC versus about 41 % in BC, becoming equal to that in the C₃ fixation pathway in the latter. Internal CA activity remained constant, but the periplasmic CA activity was higher under low than high irradiance.     

Effects of exogenous methyl jasmonate in elicited anthocyanin-producing cell cultures of ohelo (Vaccinium phalae)

Summary Elicitation of anthocyanin-producing cells of ohelo (Vaccinium pahalae) by both biotic (purified β-glucan and chitosan) and abiotic [sodium ferric ethylenediamine di-(o-hydroxyphenylacetate) FeEDDHA, and CuSO₄] elicitors resulted in significant enhancement of anthocyanin accumulation. Anthocyanin production increased up to 1.8 and 1.5-fold over the control in the presence of abiotic elicitors (90 μM FeEDDHA and 20 μM CuSO₄, respectively), and increased 1.9 and 1.6-fold in the presence of biotic elicitors (10 mg L⁻¹ β-glucan and 100 mg L⁻¹ chitosan). Maximum anthocyanin production with the two most effective elicitors was achieved when cultures were treated on Day 3 (β-glucan) or Day 0 (FeEDDHA) after the initiation of fresh cell cultures. A concentration-dependent response was exhibited by cultures treated with exogenous methyl jasmonate (MJ). The addition of 0.5 μM MJ alone provoked a 2–3-fold increase in anthocyanin production over that of the control; however, no additive effect on anthocyanin production was observed in any treatments which combined MJ and β-glucan or FeEDDHA. Conditioning of the cells with a preculture in either MJ, β-glucan, or FeEDDHA similarly did not enhance anthocyanin production. Inoculation of cultures elicited by MJ or β-glucan with ibuprofen, a reported inhibitor of jasmonate biosynthesis, dramatically stimulated, rather than inhibited, anthocyanin production, resulting in levels of accumulation beyond any of the tested elicitor combinations. Hypotheses for the observed influence of ibuprofen in this system are discussed.     

Elevated CO<Subscript>2</Subscript> and temperature differentially affect photosynthesis and resource allocation in flag and penultimate leaves of wheat

Differences in acclimation to elevated growth CO₂ (700 μmol mol⁻¹, EC) and elevated temperature (ambient +4 °C, ET) in successive leaves of wheat were investigated in field chambers. At a common measurement CO₂, EC increased photosynthesis and the quantum yield of electron transport (Φ) early on in the growth of penultimate leaves, and later decreased them. In contrast, EC did not change photosynthesis, and increased Φ at later growth stages in the flag leaf. Contents of chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and total soluble protein were initially higher and subsequently lower in penultimate than flag leaves. EC decreased RuBPCO protein content relative to soluble protein and Chl contents throughout the development of penultimate leaves. On the other hand, EC initially increased the RuBPCO:Chl and Chl a/b ratios, but later decreased them in flag leaves. In the flag leaves but not in the penultimate leaves, ET initially decreased initial and specific RuBPCO activities at ambient CO₂ (AC) and increased them at EC. Late in leaf growth, ET decreased Chl contents under AC in both kinds of leaves, and had no effect or a positive one under EC. Thus the differences between the two kinds of leaves were due to resource availability, and to EC-increased allocation of resources to photon harvesting in the penultimate leaves, but to increased allocation to carboxylation early on in growth, and to light harvesting subsequently, in the flag leaves.     

Photoinhibition during acclimatization of micropropagatedSpathiphyllum “Petite” plantlets

Summary MicropropagatedSpathiphyllum “Petite” plantlets were acclimatized at low- or high-light intensities [photosynthetic photon flux density (PPFD) 100 or 300 μmol·m⁻²·s⁻¹]. During the first days chlorophyll fluorescence measurements show a partial photoinhibition of the photosynthetic apparatus, expressed by a decrease of the variable over maximal fluorescence ratio (F_v/F_m). This inhibition of F_v/F_m was significantly higher for plants grown at high-light intensity, leading to a photooxidation of chlorophyll. Newly formed leaves were better adapted to the ex vitro climatic condition (as shown by the increase of the F_v/F_m ratio) and had a higher net photosynthesis compared with in vitro formed leaves. Nevertheless, plants grown at 300 μmol·m⁻²·s⁻¹ were photoinhibited, compared with those at 100 μmol·m⁻²·s⁻¹. A sudden exposure to high-light intensity of 1-, 10- or 25-d-old transplanted plants (shift in PPFD from 100 to 300 μmol·m⁻²·s⁻¹) gave a linear decrease of F_v/F_m over a 12-h period, which was reflected in a 50% reduction of net photosynthesis. No significant interaction between day and hour was found, indicating high-light exposure causes the same photoinhibitory effect on in vitro and ex vitro formed leaves.