bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative efficacy of the Schistosoma mansoni nucleic acid vaccine, Sm23, following microseeding or gene gun delivery
Authors: Da’dara Akram A. , Skelly Patrick J. , Fatakdawala Mufaddal , Visovatti Scott , Eriksson Elof , Harn Donald A.
Published: March 2003

Sm23 is an integral membrane protein expressed widely in the human parasitic worm Schistosoma mansoni. Sm23 has already been shown to elicit protective immune responses following immunization with peptides or DNA constructs. In this study, we evaluated the immunogenicity and the protective efficacy of the Sm23 DNA vaccine using two different intradermal DNA delivery methods: microseeding and gene gun. Using both techniques, all mice immunized with the Sm23‐pcDNA construct generated Sm23‐specific immunoglobulin (Ig)G antibody, while mice immunized with the control plasmid, pcDNA, did not. Antibody isotypes analysis revealed that microseeding elicited mainly IgG2a and IgG2b antibodies, with relatively low levels of IgG1 and IgG3. The relative IgG1/IgG2a ratio was 0·03, indicative of a Th1 type immune response. In contrast, gene gun immunization resulted in significantly higher levels of IgG1 and IgG3. The relative IgG1/IgG2a ratio in this case was 11, indicative of a Th2 type immune response. No significant difference in the levels of IgG2b was observed. Coimmunization with plasmid DNA encoding either interleukin (IL)‐12 or IL‐4 by microseeding did not affect the levels of IgG1, while the levels of IgG2a and IgG2b were reduced. On the other hand, the levels of IgG3 were significantly increased by IL‐4, but unchanged by IL‐12. Importantly, in all experiments, the Sm23‐pcDNA vaccine provided statistically significant levels of protection against challenge infection. Microseeding immunizations resulted in higher levels of protection (31–34% protection) than gene gun immunization (18% protection). This suggests that the Th1 type immune response elicited by microseeding immunization was responsible for the higher protection levels. However, the protective effect of the vaccine was not affected by coadministering plasmids encoding either IL‐12 or IL‐4 using the microseeding technique.
Cystatins of filarial nematodes up‐regulate the nitric oxide production of interferon‐γ‐activated murine macrophages
Authors: Hartmann Susanne , Schönemeyer Annett , Sonnenburg Bettina , Vray Bernard , Lucius Richard
Published: March 2003

Cystatins of two filarial nematodes were studied with regard to their capacity to up‐regulate the production of nitric oxide (NO) in vitro, and the effects were analysed. Recombinant cystatin of the human pathogenic filaria Onchocerca volvulus and of the rodent filaria Acanthocheilonema viteae significantly enhanced the NO production of interferon (IFN)‐γ‐activated macrophages of BALB/c and C3H/HeJ mice. Truncated cystatins lacking the N‐terminal protease inhibitory active site, and showing marginal protease inhibitory activity, up‐regulated the NO production to the same extent as the full‐length proteins, indicating that the effect on the NO production is independent of cysteine protease inhibition. NO did not contribute to the suppression of proliferative T cell responses exerted by filarial cystatins, as shown in other studies, since NO synthase inhibitors did not restore proliferative responses. The up‐regulation of NO production induced by filarial cystatins was partly dependent on the production of interleukin‐10 and tumour necrosis factor‐α, since depletion of both cytokines by antibodies led to a diminution of the enhanced NO production by 22–48%. Our data suggest that filarial cystatins are potent triggers of the production of NO, a mediator which was shown to have a role as an effector molecule against filarial worms in vitro and in vivo.
Chemokine responses in schistosomal antigen‐elicited granuloma formation*
Authors: Chiu Bo‐Chin , Chensue Stephen W.
Published: March 2003

Host immune systems have evolved specialized responses to multicellular parasites. This is well represented by the type 2 granulomatous response to Schistosoma mansoni egg antigens, which is an eosinophil‐rich inflammatory response mediated by Th2‐associated cytokines. Using Ag‐bead models of pulmonary granuloma formation in mice, we defined characteristic chemokine (CK) profiles in the granulomatous lungs. Our findings point to a role for C‐C chemokine receptor‐2 (CCR2) and CCR3 agonists such as monocyte chemotactic proteins (MCPs) 1/CCL2, 3/CCL7 and 5/CCL12 as important participants that are subject to regulation by Th2 cytokines interleukin (IL)‐4 and IL‐13. CCR4 and CCR8 agonists are also likely contributors. Analysis of CK receptor knockout mice revealed that CCR2 ligands (e.g. MCP‐1 and 5) promoted early phase granuloma macrophage accumulation, whereas anti‐MCP‐3 (CCL7) antibody treatment abrogated eosinophil recruitment. CCR8 knockout mice also demonstrated impaired eosinophil recruitment but this appeared to be related to impaired Th2 cell function. Transcript analysis of CD4+ T cells generated during schistosome granuloma formation failed to show biased CCR8 expression but, having a more limited receptor repertoire, these cells were likely more dependent on CCR8 ligands. Together, these studies indicate an intricate involvement of chemokines in various stages and aspects of schistosomal egg Ag‐elicited granuloma formation.
Positive anemotaxis by Varroa mites: responses to bee odour plumes and single clean‐air puffs
Authors: KUENEN L. P. S. , CALDERONE N. W.
Published: March 2003

Abstract.The stimuli and mechanisms mediating host location and host choice by the bee mite, Varroa jacobsoni (Oudemans), are currently unknown. It is shown that Varroa can use single clean‐air puffs and bee‐odour plumes in a wind tunnel as directional cues. Varroa turned nearly straight upwind in response to single 0.1‐s puffs of clean air directed at 90° to the their anterior‐posterior axis. They turned significantly further to their left side (104°) than to their right (76°), but showed no difference in latency to initiation of the turns (means of 63.3 ms vs. 62.6 ms, respectively). They also followed bee‐odour plumes in a wind tunnel. When released in odour and control plumes mid‐way between the plume's origin and the downwind end of the tunnel, mites responding to bee‐odour walked upwind in, or along the edge of, the odour plume with 38% making contact with the odour delivery tube; mites in clean air did not walk upwind along the air stream, and none made contact with the air delivery tube. Walking speeds were not different between the bee‐odour and control groups (0.28 vs. 0.29 cm s–1); there were also no differences in the turning rates (96.85 vs. 97.16 deg s–1 and 388.08 vs. 379.18 deg cm–1, respectively). Under all conditions, mites walked in a zigzag fashion.
Flight tone of field‐collected populations of Anopheles gambiae and An. arabiensis (Diptera: Culicidae)
Authors: WEKESA J. W. , BROGDON W. G. , HAWLEY W. A. , BESANSKY N. J.
Published: March 2003

Abstract.Laboratory colonies of the human malaria vectors Anopheles gambiae Giles and An. arabiensis Patton have distinct flight tones. If flight tone similarly distinguishes natural populations of these sympatric sibling species, it may play a role in reproductive isolation of swarms that are otherwise behaviourally identical. To assess the fidelity of flight tone differences in natural populations, flight tone was measured in the F1 progeny of mosquitoes of both species captured in western Kenya. Flight tone distributions of wild An. gambiae and An. arabiensis were similar to their laboratory conspecifics. However, interspecies comparisons of flight tone of wild mosquitoes revealed significantly different but overlapping distributions for both sexes. Furthermore, when the effect of body size on flight tone was determined, there was a positive correlation between wing length and flight tone for both sexes of An. gambiae and An. arabiensis, suggesting that mosquito size is a significant variable affecting flight tone. Although these findings diminish any practical benefit of flight tone as a diagnostic tool in species identification, its potential role in pre‐mating species recognition needs further investigation.
Modulation of whitefly take‐off and flight orientation by wind speed and visual cues
Authors: Isaacs Rufus , Willis MarK. A. , Byrne David N.
Published: March 2003

The effect of different wind speeds on take‐off and flight orientation of the sweetpotato whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), was studied in the presence of a green visual stimulus which reflected 550 ± 10 nm light, or a white stimulus of the same intensity. When the white light was present, take‐off was negatively correlated with wind speed. Analysis of the flight tracks of whiteflies in 0, 15 and 30 cm/s wind with the white light present showed that flight was not directed toward the stimulus in zero wind, and that insects were carried downwind as the wind increased. Net displacement downwind was significantly slower than the wind speed, indicating that B. tabaci can control its rate of displacement relative to its surroundings, and is not always passively transported by the wind. In the presence of the green visual stimulus, take‐off and flight behaviour of B. tabaci was markedly different to that observed in the presence of the white light. Taking off was more likely and whiteflies made upwind orientated flights, landing on the illuminated section of the screen when it reflected green light. At all wind speeds tested, the mean ground speeds of B. tabaci were approximately 20 cm/s whether the insects were flying upwind or downwind. This uniformity of ground speed regardless of the changing effects of wind‐induced drift in different directions strongly suggests that whiteflies actively control their ground speed using visual flow fields in a manner similar to all other flying insects examined thus far.
The titres of lectins in the haemolymph of Lacanobia oleracea and the effects of parasitism by the ectoparasitoid wasp Eulophus pennicornis
Authors: Mosson Helen J. , Richards Elaine H. , Marris Gay C. , Edwards John P.
Published: March 2003

Serum from larvae of Lacanobia oleracea L. (Lepidoptera; Noctuidae) parasitized by Eulophus pennicornis (Hymenoptera; Eulophidae) and from normal non‐parasitized larvae is capable of agglutinating rabbit, sheep, calf, goat, chicken, horse and human erythrocytes, but not yeast. Studies with a range of inhibitory carbohydrates showed that serum lectins(s) had specificity for sugars containing galactose and for rhamnose, and for the glycosubstances fetuin and asialofetuin. Lectin activity is heat‐labile and is not dependent on calcium. Parasitism by E. pennicornis caused an increase in the agglutination titre of the serum from larvae of L. oleracea but not an increase in specific activity (titre per mg protein per ml). However, when venom from the venom gland of female wasps was injected into L. oleracea larvae, both the agglutinating activity and the specific activity of the larval serum increased. The possible causes of this increase are discussed. It is suggested that venom contains antigenic components which, when injected into the haemocoel of the L. oleracea larva, may be increasing lectin synthesis and/or release into the serum.
Distribution of lysozyme and protease, and amino acid concentration in the guts of a wood‐feeding termite, Reticulitermes speratus (Kolbe): possible digestion of symbiont bacteria transferred by trophallaxis
Authors: Fujita Ai , Shimizu Isamu , Abe Takuya
Published: March 2003

Distribution of lysozyme and protease, and amino acid concentration in the guts of a wood‐feeding termite, Reticulitermes speratus (Kolbe) (Isoptera, Rhinotermitidae) were studied to examine the possibility that termites digest symbiont bacteria transferred by trophallaxis. Total lysozyme activity was found predominantly in the salivary gland and to a minor extent in the digestive tracts. However, specific lysozyme activity was high in the foregut as well as in the salivary gland. The similarity of the lysozyme pH profile of the salivary gland and of the foregut suggested that the foregut lysozyme came from the salivary gland. Major protease activity having the optimum pH of 7.5 was found in the midgut. Total free amino acid amount and concentration in the midgut was higher than elsewhere in the digestive tract. The possibility that lysozyme secreted from the salivary gland into the foregut digests hindgut bacteria transferred by trophallaxis was discussed.
Amino acid concentration and distribution of lysozyme and protease activities in the guts of higher termites
Authors: Fujita Ai , Abe Takuya
Published: March 2003

Abstract The distributions of lysozyme and protease activities and of amino acids was measured in the guts of five species of higher termites, Macrotermes annandalei, Odontotermes formosanus, Pericaproitermes nitobei, Termes comis and Nasutitermes takasagoensis. Lysozyme activity was found only in M. annandalei, P. nitobei and N. takasagoensis. Protease activity was high in the midgut of all species but negligible elsewhere in the gut. Amino acid concentration was highest in the midgut of all species of workers.
Flight behaviour ofCadra cautellamales in rapidly pulsed pheromone plumes
Authors: Justus Kristine A. , Schofield Steven W. , Murlis John , Cardé Ring T.
Published: March 2003

AbstractAirborne pheromone plumes in wind comprise filaments of odour interspersed with gaps of clean air. When flying moths intercept a filament, they have a tendency to surge upwind momentarily, and then fly crosswind until another filament is intercepted. Thus, the moment‐to‐moment contact with pheromone mediates the shape of a flight track along the plume. Within some range of favourable interception rates, flight tracks become straighter and are headed more due upwind. However, as the rate of interception increases, there comes a point at which the moth should not be able to discern discreet filaments but, rather, should perceive a ‘fused signal’. At the extreme, homogeneous clouds of pheromone inhibit upwind progress by representative tortricids. In a wind tunnel,Cadra cautella(Walker) (Lepidoptera: Pyralidae) were presented with 10 ms pulses of pheromone at a repetition rate of 5, 10, 17 and 25/s and a continuous, internally turbulent plume. Pulse size and concentrations were verified with a miniature photoionization detector sampling surrogate odour, propylene, at 100 Hz. Male moths maintain upwind progress even at plumes of 25 filaments/s. Furthermore, moths exhibited greater velocities and headings more due upwind at 17 and 25 Hz than at the lower frequencies or with the continuous plume. It is hypothesized that eitherC. cautellapossesses a versatile sensory system that allows the resolution of these rapidly pulsed pheromone plumes, or that this species does not require a ‘flickering’ signal to fly upwind.
Phenotypic plasticity of body pigmentation inDrosophila: influence of a developmental thermoperiodic regime in two sibling species
Authors: Pétavy Georges , Moreteau Brigitte , Gibert Patricia , David Jean R.
Published: March 2003

AbstractVariation of body pigmentation according to growth temperature was analysed in two European populations (Bordeaux and Cordoba) of the two sibling speciesDrosophila melanogaster(Meigen) andD. simulans(Sturtevant). Results obtained at constant temperatures were compared with those observed under alternating thermal regimes of various amplitudes and with a daily periodicity of 12–12 h. Abdominal pigmentation in segments 5, 6 and 7, and of their sum, was investigated in both species in females only. Thoracic trident pigmentation was studied in males and females but inDrosophila melanogasteronly.

Thoracic pigmentation exhibited curvilinear convex reaction norms under constant conditions, with a darker pigmentation in the population (Bordeaux) living in a colder climate. No specific effects of alternating regimes were seen. For abdomen pigmentation, slightly different reaction norms were observed under constant conditions between Bordeaux and Cordoba strains. There were also slight differences between the two species. Alternating temperatures produced a significant decrease in average pigmentation, roughly proportional to the thermal amplitude.

Alternating stressing conditions induced also an increase in the phenotypic variability of abdominal pigmentation, especially in segments 6 and 7. Finally, because an increase of growth temperature results in a monotonically decreasing reaction norm of both abdomen pigmentation in females and a size‐related trait, the wing/thorax ratio, we found a linear relationship between the two variables, with a very high overall correlation at constant temperatures (r = 0.99). The correlation was slightly less under alternating conditions, due to a broader dispersal of the experimental values around the regression lines.
Cuticular colour change after imaginal eclosion is time‐constrained: blacker beetles darken faster
Authors: Thompson John J. W. , Armitage Sophie A. O. , Siva‐Jothy Michael T.
Published: March 2003

Abstract Adult mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), show density dependent polyphenism in adult cuticular colour that is correlated with prophylactic immunity (Barnes & Siva‐Jothy, 2000). The degree of cuticular colour is important in understanding the biology of a number of insect‐related phenomena (e.g. industrial melanism, thermoregulation). In this paper, the extent of variation in cuticular colour in a large outbred population is documented; the rate of darkening under three different rearing protocols including experimental selection for cuticular colour is examined; and the time taken for cuticular colouring to be completed is determined. The results show that cuticular colouring after eclosion is time‐constrained in T. molitor, regardless of whether beetles are reared in large outbred cultures, inbred cultures, or cultures subjected to selection for darkness or lightness. Blacker beetles always darkened faster. The potential reasons for the constraint and the potential costs of rapid darkening are discussed.
Immune investment and sperm competition in a beetle
Authors: Drnevich Jenny M. , Barnes Andrew I. , Siva‐Jothy Michael T.
Published: March 2003

Individuals that invest more in immunity may not be able to invest as much in o\ther life history traits. The overall effects on fitness depend on the balance of investment in life history traits and unnecessary investment in immunity may lower fitness. Adult mealworm beetles (Tenebrio molitor L.) modulate their investment according to the perceived risk of infection as larvae; the amount of investment can be assessed by body coloration. This prophylactic investment in immunity can be used to assess the costs of investment when no immune challenge is present. Whether investment in immunity is traded off against sperm competitive ability, another important fitness trait in insects, was investigated. Males that had invested more in immunity (dark males) competed against males that had invested less (light males) for fertilization of offspring. Dark males did lose sperm precedence over time, whereas light males did not. However, this decrease in sperm offensive ability may not result in decreased fitness for darker males under normal female mating frequencies; the decrease in offspring did not occur for 1 week, but females that have constant access to males mate once a day, which would negate any long‐term effects of male mating order. Thus, prophylactic investment in immunity does not produce immediate reductions in a male's ability to gain fertilizations. The costs to immune investment may be born by other fitness traits in T. molitor.
Effects of maternal age on reproductive traits and fitness components of the offspring in the bruchid beetle, Callosobruchus chinensis (Coleoptera: Bruchidae)
Authors: Yanagi Shin‐Ichi , Miyatake Takahisa
Published: March 2003

In many insect species, the size and number of eggs decrease with maternal age. Thus, both the size and number of eggs must be considered to know the exact cost of reproduction with maternal age. The resource depletion hypothesis was examined in the bruchid beetle Callosobruchus chinensis. The hypothesis explains why the egg size decreases with maternal age based on the decline of the female's reproductive capacity. A decrease was found in reproductive effort (= egg size × the number of eggs) and the fitness component of offspring with maternal age. The effects of the female's nutritional status on the relationship between maternal age and the reproductive effort of females with and without food and water were also examined. The results indicate that the decrease in size and number of eggs with maternal age can be explained by the resource depletion hypothesis in C. chinensis.
Variability and genetic components of innate fruit odour recognition in a parasitoid of Drosophila
Authors: Campan E. , Couty A. , Carton Y. , Pham‐Delègue M. H. , Kaiser L.
Published: March 2003

Abstract This study aims to investigate the genetic variability of olfactory responses to odours from the host habitat, involved in host selection by insect parasitoids. The probing response of females to fruit and non‐fruit odours was studied in Leptopilina boulardi Barbotin et al. (Hymenoptera, Figitidae), a parasitoid of the frugivorous Drosophila melanogaster larvae. Responses of two strains (from Nasrallah, Tunisia, and from Brazzaville, Congo) and their hybrids were compared. Probing is a searching mode by repeated ovipositor insertions into the breeding substrate to locate digging larvae. Most Brazzaville females exhibited innate ovipositor probing into agar in response to the fruit aromas (banana, orange, pear, prickly pear), whereas this was rare in the Nasrallah strain. These four fruits are all breeding sites for D. melanogaster, whereas mushroom is not. Mushroom odour did not trigger any probing response in either strain. In addition, the latency of the probing response was shorter in Brazzaville females. Results from hybrid females (F1 and Backcross) showed that both probability to probe in response to a fruit aroma and latency of the response were strongly heritable. Regarding the probability to probe, there was an apparent complete dominance of Nasrallah characteristics, whereas additive inheritance was found in the Brazzaville lineage. The contrast between reciprocal F1 hybrids suggested a strong interaction with non‐chromosomal factors. It is suggested that a cytoplasmic factor in the Nasrallah strain decreases females' propensity to probe in response to significant odours. The latency of probing appeared to be under a chromosomal influence. Thus, this study identifies a strong genetic component in the responses to odours from the host habitat. It also provides information on the genetic basis of the two characters studied.
Spatial distributions of tissue expansion and cell division rates are related to irradiance and to sugar content in the growing zone of maize roots
Authors: Muller B. , Stosser M. , Tardieu F.
Published: March 2003

We have investigated the way in which the radiation absorbed by leaves affects the rate of elongation of maize (Zea mays L.) roots. In five repeated growth chamber experiments, plants previously grown at a photon irradiance of 23 mol m–2 d–1 received either 7 or 34 mol m–2 d–1 from day 10 to day 20 after germination. The elongation rate of primary roots steadily decreased for 4 d after reduction in irradiance and then stabilized at 60% of that in plants at high irradiance. The elongating zone was slightly shorter after 2 d at low irradiance, and was further reduced after 8 d. The concentrations of sucrose and glucose in the elongating zone were greatly decreased after 2 d at low irradiance and the gradient of both sugars was suppressed. The longer period at low irradiance affected neither sugar content nor gradient. In the same way, cell production rate was reduced after 2 d at low irradiance and was not appreciably decreased afterwards. The root zone with cell division was shorter in plants at low irradiance, but cell division rate remained nearly constant temporally and spatially, and was unaffected by the irradiance treatment. Our results suggest that primary events after a reduction in irradiance were a change in cell flux and sugar content in the elongating zone. Change in elongation rate was slower and probably the result of a time‐related developmental effect, which may be related to the change in cell production.
Is thermal time adequate for expressing the effects of temperature on sunflower leaf development?
Authors: Granier C. , Tardieu F.
Published: March 2003

We have tested whether the effects of temperature on sunflower leaf growth could be documented by using thermal time. The rates of leaf expansion and of cell division were analysed in leaves located at two positions on the stem, and a spatial analysis of expansion rate was carried out. Experiments were performed in growth chamber (stable conditions), in the field or in a greenhouse (fluctuating conditions). We compared three methods for characterizing the rate and the duration of expansion. Responses to leaf temperature were consistent only when expansion was characterized as a two‐phase process — a period of exponential expansion (constant relative expansion rate, RER) followed by a decrease in RER. RER and relative cell division rate (RDR) responded linearly to temperature with a common response curve for all studied conditions. This response curve was also common to all studied zones within a leaf and to leaves at two positions on the stem. The reciprocals of the durations of the periods of exponential expansion, non‐zero expansion and non‐zero division were also linearly related to leaf temperature with common response curves in a given leaf zone. The x‐intercepts of all these response curves and of the response curve of leaf initiation rate to temperature did not significantly differ in an analysis of covariance, with a common value of 4·8 °C. The expression of time in cumulative degree days, with a base temperature of 4·8 °C, resulted in a unique time course of RER and cell division rate regardless of temperature. These results suggest that a powerful ‘program’ of leaf development exists in a sunflower plant.
Sucrose cycling, Rubisco expression, and prediction of photosynthetic acclimation to elevated atmospheric CO2
Authors: Moore B. D. , Cheng S.‐H. , Rice J. , Seemann J. R.
Published: March 2003

Photosynthetic acclimation to elevated CO2 cannot presently be predicted due to our limited understanding of the molecular mechanisms and metabolic signals that regulate photosynthetic gene expression. We have examined acclimation by comparing changes in the leaf content of RuBP carboxylase/oxygenase (Rubisco) with changes in the transcripts of Rubisco subunit genes and with leaf carbohydrate metabolism. When grown at 1000 mm3 dm–3 CO2, 12 of 16 crop species at peak vegetative growth had a 15–44% decrease in leaf Rubisco protein, but with no specific association with changes in transcript levels measured at midday. Species with only modest reductions in Rubisco content (10–20%) often had a large reduction in Rubisco small subunit gene mRNAs (> 30%), with no reduction in large subunit gene mRNAs. However, species with a very large reduction in Rubisco content generally had only small reductions in transcript mRNAs. Photosynthetic acclimation also was not specifically associated with a change in the level of any particular carbohydrate measured at midday. However, a threshold relationship was found between the reduction in Rubisco content at high CO2 and absolute levels of soluble acid invertase activity measured in plants grown at ambient or high CO2. This relationship was valid for 15 of the 16 species examined. There also occurred a similar, albeit less robust, threshold relationship between the leaf hexose/sucrose ratio at high CO2 and a reduced photosynthetic capacity ≥ 20%. These data indicate that carbohydrate repression of photosynthetic gene expression at elevated CO2 may involve leaf sucrose cycling through acid invertase and hexokinase.
Interactive effects of elevated atmospheric CO2, mycorrhization and drought on long‐distance transport of reduced sulphur in young pedunculate oak trees (Quercus robur L.)
Authors: Schulte M. , Herschbach C. , Rennenberg H.
Published: March 2003

Pedunculate oak (Quercus robur L.) was germinated and grown under nutrient non‐limiting conditions for a total of 10–15 weeks at ambient CO2 concentration and 1100 μmol mol–1 CO2 either in the presence or the absence of the mycorrhizal fungus Laccaria laccata. Half of the oak trees of these treatments were exposed to drought during final growth by suspending the water supply for 21 d. Mycorrhization and elevated atmospheric CO2 each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO2 was mainly attributed to increased growth of lateral roots, mycorrhization promoted shoot growth. Water deficiency reduced biomass accumulation without affecting relative water content, but this effect was more pronounced in mycorrhizal as compared to non‐mycorrhizal trees. Elevated CO2 partially prevented the development of drought stress, as indicated by leaf water potential, but did not counteract the negative effects of water deficiency on growth during the time studied. Enhanced biomass accumulation requires adaption in protein synthesis and, as a consequence, enhanced allocation of reduced sulphur produced in the leaves to growing tissues. Therefore, allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH, the main long‐distance transport form of reduced sulphur, to mature oak leaves. Export of radiolabel proceeded almost exclusively in basipetal direction to the roots. The rate of export of radioactivity out of the fed leaves was significantly enhanced under elevated CO2, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO2 as compared to ambient CO2. Mycorrhization did not affect 35S export out of the fed leaves, but the distribution of radiolabel between stem and roots was altered in preference of the stem. Trees exposed to drought did not show appreciable export of the 35S radioactivity fed to the leaves when grown under ambient CO2. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO2 seemed to counteract this effect of drought stress to some extent, since higher leaf water potentials and improved 35S export out of the fed leaves was observed in oak trees exposed to drought and elevated CO2 as compared to trees exposed to drought and ambient CO2.
Sap flow in Scots pines growing under conditions of year‐round carbon dioxide enrichment and temperature elevation
Authors: Kellomäki S. , Wang K.‐Y.
Published: March 2003

Starting in rrrr, individual trees of Scots pine (Pinus sylvestris L.) aged 30 years were grown in closed‐top chambers and exposed to normal ambient conditions (CON), elevated CO2 (Elev. C), elevated temperature (Elev. T) and a combination of elevated CO2 and temperature (Elev. C + T). Using the constant‐power heat balance method, sap flow was monitored simultaneously in a total of 16 trees, four for each treatment, over a 32 d period (after the completion of needle expansion and branch elongation in 1997). An overall variation in diurnal sap flow totals (Ft) was evident during the period of measurement (days 167–198, 1997) regardless of the treatments, with a range from 0·15 to 2·82 kg tree–1 d–1. Elev. C reduced Ft by 4·1–13·7% compared with CON on most days (P varies from 0·042 to 0·108), but slightly increased it on some days (P≥ 0·131), depending on the weather conditions. Although the decrease in Ft caused by Elev. C was statistically significant on only a few days (P≤ 0·042), the cumulative Ft for the 32 d decreased by 14·4% (P = 0·047), indicating that Elev. C may have an important influence on seasonal water use of the Scots pine. Analysis of the diurnal courses of sap flow combined with corresponding weather factors indicated that the CO2‐induced decrease in Ft could be largely attributed to an increase in stomatal sensitivity to vapour pressure deficit (VPD), whereas the CO2‐induced increase in Ft related to an increase in stomatal sensitivity to low light levels. Elev. T increased Ft by 11·2–35·6% throughout the measuring period and the cumulative Ft for the 32 d by 32·5% (P = 0·019), which could be largely attributed to the temperature‐induced increase in current‐year needle area and decrease in stomatal sensitivity to high levels of VPD. There were no significant interactive effects of CO2 and temperature on sap flow, so that Elev. C + T had approximately the same Ft as Elev. T and similar diurnal patterns of sap flow, suggesting that the temperature factor played a dominant role in the case of Elev. C + T.
Relationship of nitrate supply with growth rate, plasma membrane‐bound and cytosolic nitrate reductase, and tissue nitrate content in tobacco plants
Authors: STÖHR C.
Published: March 2003

cNR, cytosolic nitrate reductase PM‐NR, plasma membrane‐bound nitrate reductase  Activities of plasma membrane‐bound nitrate reductase (PM‐NR) and cytosolic nitrate reductase (cNR) in tobacco (Nicotiana tabacum L. cv. Samsun) are regulated differently, depending upon the nitrate supply to the culture medium (in sand culture). The cNR activity of roots was higher at low nitrate concentrations with the maximum at 5 mM nitrate supply and declined to low values beyond 5 mM. In contrast, the PM‐NR activity of roots increased with higher nitrate concentrations with the maximum at 25 mM nitrate and clearly decreased only at 40 mM. This high PM‐NR activity correlated with a low growth rate and might be one of the responses to excess nitrate. Internal nitrate and total nitrogen content of the tissues, however, showed a relative minimum in shoots and in roots of between 15 and 25 mM external nitrate. With declining PM‐NR activities beyond 25 mM external nitrate, the nitrate content in the tissue increased indicating an inverse relationship between tissue nitrate content and root PM‐NR activity. In leaves both NR activities (cNR and PM‐NR) correlated with the internal nitrate content, but with a different response at low nitrate.
The response of carrot (Daucus carota L.) and onion (Allium cepa L.) seedlings to mechanical impedance and water stress at sub‐optimal temperatures
Authors: WHALLEY W. R. , FINCH‐SAVAGE W. E. , COPE R. E. , ROWSE H. R. , BIRD N. R. A.
Published: March 2003

The response of pre‐emergent shoots of carrot and onion to mechanical impedance, water stress and suboptimal temperature was studied. We used model laboratory systems in which mechanical impedance and water stress could be varied independently of each other and independently of other complicating factors (e.g. aeration and hydraulic conductivity). Our results showed that mechanical impedance reduced the rate and extent of shoot development in both carrot and onion. Roots of both carrot and onion were less sensitive to mechanical impedance than shoots. The recovery of shoot length following the removal of impedance was studied. The data were used to develop a new model of shoot elongation as a function of mechanical stress, water stress, temperature, shoot length and time. Our results also provide a new insight into the physiology of shoot development in strong soils. We contrast the effect of mechanical impedance on pre‐emergent seedling development in carrot and onion.
Carbon metabolism in the subantarctic Kerguelen cabbage Pringlea antiscorbutica R. Br.: environmental controls over carbohydrates and proline contents and relation to phenology
Authors: AUBERT S. , ASSARD N. , BOUTIN J.‐P. , FRENOT Y. , DORNE A.‐J.
Published: March 2003

The subantarctic Brassicaceae Pringlea antiscorbutica R. Br. (Kerguelen cabbage) was used as a model to study the physiological adaptations of higher plants to the subantarctic environment. 13C‐nuclear magnetic resonance permitted, in combination with biochemical methods, the identification and quantification of the major solutes in leaves, stem and roots. As characterized in many Brassicaceae, proline was a major solute in all organs of the plants, and its accumulation was mainly controlled by salt stress rather than temperature. Glucose was the major soluble sugar in the leaves, whilst sucrose and starch accumulated in stems and roots. Over a period of 1 year we found strong correlations between (i) glucose content in leaves and irradiance, and (ii) starch content in non‐photosynthetic organs and air temperature. The pattern of carbohydrate accumulation indirectly indicated that photosynthetis was sustained throughout the year, even during cold days when the temperature remained near 0 °C. This is consistent with the direct gas exchange measurements showing that photosynthetic capacity is mainly influenced by irradiance and weakly by temperature. Taken together, these characteristics demonstrated that the growth and development cycle occurs without a period of dormancy.
Root hydraulic conductivity of Larrea tridentata and Helianthus annuus under elevated CO2
Authors: HUXMAN K. A. , SMITH S. D. , NEUMAN D. S.
Published: March 2003

While investigations into shoot responses to elevated atmospheric CO2 are extensive, few studies have focused on how an elevated atmospheric CO2 environment might impact root functions such as water uptake and transport. Knowledge of functional root responses may be particularly important in ecosystems where water is limiting if predictions about global climate change are true. In this study we investigated the effect of elevated CO2 on the root hydraulic conductivity (Lp) of a C3 perennial, Larrea tridentata, and a C3 annual, Helianthus annuus. The plants were grown in a glasshouse under ambient (360 μmol mol–1) and elevated (700 μmol mol–1) CO2. The Lp through intact root systems was measured using a hydrostatic pressure‐induced flow system. Leaf gas exchange was also determined for both species and leaf water potential (ψleaf) was determined in L. tridentata. The Lp of L. tridentata roots was unchanged by an elevated CO2 growth environment. Stomatal conductance (gs) and transpiration (E) decreased and photosynthetic rate (Anet) and Ψleaf increased in L. tridentata. There were no changes in biomass, leaf area, stem diameter or root : shoot (R : S) ratio for L. tridentata. In H. annuus, elevated CO2 induced a nearly two‐fold decrease in root Lp. There was no effect of growth under elevated CO2 on Anet, gs, E, above‐ and below‐ground dry mass, R : S ratio, leaf area, root length or stem diameter in this species. The results demonstrate that rising atmospheric CO2 can impact water uptake and transport in roots in a species‐specific manner. Possible mechanisms for the observed decrease in root Lp in H. annuus under elevated CO2 are currently under investigation and may relate to either axial or radial components of root Lp.
Photosynthesis, carbohydrate levels and chlorophyll fluorescence‐estimated intercellular CO2 in water‐stressed Casuarina equisetifolia Forst. & Forst.
Authors: SÁnchez‐RodrÍguez J. , PÉrez P. , MartÍnez‐Carrasco R.
Published: March 2003

The effect of long‐term water stress on photosynthetic carbon metabolism in Casuarina equisetifolia Forst. & Forst. was analysed by measuring CO2 assimilation, stomatal conductance, the quantum yield of photosystem II (ΦPSII), enzyme activities, and the levels of photosynthetic intermediates and carbohydrates. CO2 assimilation decreased under water stress while the intercellular CO2 concentration (Ci) as estimated by gas exchange measurements remained high. However, the estimates of Ci from measurements of ΦPSII suggest that the decrease in photosynthesis can be explained in terms of stomatal closure. Water stress decreased total stromal fructose‐1,6‐bisphosphatase activity and did not alter the activities and activation states of ribulose bisphosphate carboxylase oxygenase and NADP‐dependent malate dehydrogenase (NADP‐MDH). The concentration of photosynthetic metabolites, glucose, fructose and sucrose decreased, whereas starch concentrations increased under drought conditions.
Increased cytokinin levels in transgenic PSAG12–IPT tobacco plants have large direct and indirect effects on leaf senescence, photosynthesis and N partitioning
Authors: Jordi W. , Schapendonk A. , Davelaar E. , Stoopen G. M. , Pot C. S. , De Visser R. , Rhijn J. A. Van , Gan S. , Amasino R. M.
Published: March 2003

We studied the impact of delayed leaf senescence on the functioning of plants growing under conditions of nitrogen remobilization. Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco (Nicotiana tabacum L.) plants showing delayed leaf senescence through a novel type of enhanced cytokinin syn‐thesis, i.e. targeted to senescing leaves and negatively auto‐regulated (PSAG12–IPT), thus preventing developmental abnormalities. Plants were grown with growth‐limiting nitrogen supply. Compared to the wild‐type, endogenous levels of free zeatin (Z)‐ and Z riboside (ZR)‐type cytokinins were increased up to 15‐fold (total ZR up to 100‐fold) in senescing leaves, and twofold in younger leaves of PSAG12–IPT. In these plants, the senescence‐associated declines in N, protein and Rubisco levels and photosynthesis rates were delayed. Senescing leaves accumulated more (15N‐labelled) N than younger leaves, associated with reduced shoot N accumulation (–60%) and a partially inverted canopy N profile in PSAG12–IPT plants. While root N accumulation was not affected, N translocation to non‐senescing leaves was progressively reduced. We discuss potential consequences of these modified sink–source relations, associated with delayed leaf senescence, for plant productivity and the efficiency of utilization of light and minerals.
Dynamic changes in petiole specific conductivity in red maple (Acer rubrum L.), tulip tree (Liriodendron tulipifera L.) and northern fox grape (Vitis labrusca L.)
Authors: Zwieniecki Maciej A. , Hutyra Lucy , Thompson Matthew V. , Holbrook N. Michele
Published: March 2003

Diurnal variation in petiole specific hydraulic conductivity and simultaneous measurements of leaf water potential were recorded in red maple, tulip tree and fox grape. Petiole specific conductivity was determined from in situ measurements of water flow into the distal (leaf‐bearing) end of an attached petiole as a function of applied hydrostatic pressure and petiole dimensions. The hydraulic properties of the petiole dominated the measurements, indicating that this technique can be used for rapid estimates of petiole hydraulic conductivity. There was a significant decrease in petiole specific conductivity associated with increasingly more negative leaf water potentials in maple and tulip tree, but not in grape. Petiole specific conductivity increased during the afternoon while the plant was actively transpiring and the xylem sap was under tension. The recovery of petiole conductivity during the afternoon suggests that hydraulic conductivity reflects a dynamic balance between a loss of hydraulic conductivity with increasing water stress, and its restoration as tension within the xylem decreases. Three experimental manipulations were applied to red maple and tulip tree to examine the sensitivity of diurnal changes in petiole conductivity to various physiological perturbations. Both phloem girdling and application of HgCl2 to the transpiration stream resulted in a marked decrease in the degree to which petiole specific conductivity recovered as xylem tension relaxed during the afternoon. Delivery of a surfactant to the xylem, however, did not significantly alter the relation between leaf water potential and petiole hydraulic conductivity.
DNA endoreduplication in maize endosperm cells: the effect of exposure to short‐term high temperature
Authors: Engelen‐Eigles G. , Jones R. J. , Phillips R. L.
Published: March 2003

DNA endoreduplication in Zea mays L. (cv. A619 × W64A) endosperm peaks between 16 and 18 d after pollination (DAP). The physiological function of DNA endoreduplication is not known but it is believed to be important in maize kernel development. In the present study, we investigated how 2, 4 or 6 d of high temperature (35 °C) affected DNA endoreduplication and maize kernel development in comparison with control kernels grown at 25 °C. Data were collected on fresh weight (FW), nuclei number, mitotic index, and DNA endoreduplication. Maize endosperm FW and nuclei number were reduced by exposure to 4 or 6 d of high temperature. At 18 DAP, the 2 d high temperature treatment (HTT) caused a reduction in FW and nuclei number, but had no effect on DNA endoreduplication and average DNA content per endosperm. However, when the exposure to high temperature was increased to 4 or 6 d, FW, nuclei number and the magnitude of DNA endoreduplication were progressively reduced, and the peak mitotic index was delayed compared with the control endosperm. At 18 DAP, the 4 d treatment showed 54·7% of the cells were 3 or 6 C, whereas only 41·2% were 12 C or higher. Six days of high temperature also resulted in a reduction in endosperm FW, nuclei number and a delay in the peak of mitotic index. DNA endoreduplication occurred in the kernels exposed to this treatment, although the magnitude was severely reduced compared with the control kernels. Nuclear DNA content was highly correlated (r= 0·93) with kernel FW, suggesting an important role of DNA endoreduplication in determining endosperm FW. The data suggest that high temperature during endosperm cell division exerted negative effects on DNA endoreduplication by dramatically reducing the nuclei number, leaving fewer nuclei available for DNA endoreduplication. However, the data also suggest that prolonged exposure to high temperature restricts entry of mitotic cells into the endoreduplication phase of the cell cycle.
Degradation of phytochrome A and the high irradiance response in Arabidopsis: a kinetic analysis
Authors: Hennig Lars , Büche Claudia , Schäfer Eberhard
Published: March 2003

The ability to respond to far‐red‐rich light is essential for seedlings germinating below dense canopies. Physiological and genetic studies have demonstrated that phytochrome A is the only photoreceptor mediating responses to far‐red light. However, all phytochromes including phytochrome A are believed to be activated by red light and to be inactivated by far‐red light. To address the fundamental question of why phytochrome A has its highest physiological activity at presumably inactivating wavelengths, we analysed light‐induced degradation of phytochrome A in Arabidopsis. Rate constants were obtained for all reaction events in a two‐step model of degradation. Based on biochemical data, the model includes a tagging mechanism preceding degradation. The parameterized model describes Pr accumulation, wavelength dependencies of degradation kinetics and steady‐state levels as well as Pfr‐induced Pr degradation. Subsequently, experimentally derived fluence rate response curves, action spectrum and response curves to dichromatic irradiation were compared to simulations based on the model of degradation. Two kinetically defined phytochrome subspecies, untagged Pfr and tagged Pr, have steady‐state levels closely matching the physiological response curves. Therefore, sensing of far‐red light by phytochrome A can be quantitatively explained based exclusively on regulated protein degradation.