bluuebunny/crossref_metadata_2025 huggingface dataset:
Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches
Authors: Tsai C.H.I.‐W.E.I. , Lee H.O.W.‐J.I.N.G.
Published: March 2003

Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroaches with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28°C and DD (constant darkness). In B. bisignata, males and virgin females cockroaches entrained by light–dark cycles show free‐running rhythmicity in DD, and most activities occur during the subjective night. Daily locomotor activities of virgin females show cyclic changes that coincided with ovarian development. Virgin females also exhibit calling behaviour during the subjective night, and this shows a free‐running rhythm. Male mate‐finding locomotion and female calling behaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free‐running rhythm under DD conditions. Our results indicate that only mated females could not express a circadian locomotor rhythm. Pregnancy reduces a female’s locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms between these two species to their living environments and mate‐finding strategies.
Orientation of specialist and generalist fungivorous ciid beetles to host and non‐host odours
Authors: Guevara Roger , Rayner Alan D. M. , Reynolds Stuart E.
Published: March 2003

Most ciids (Ciidae) are strict fungivores specialized on fruit bodies of wood‐rotting fungi. The Ciidae includes both specialist and generalist species. Recent evidence suggests that ciids locate and discriminate their potential hosts based mainly on fungal odours. In this study, we investigated the field distribution of ciids in a local woodland near Bath, U.K. We also evaluated experimentally the behavioural responses of ciids to host and non‐host fungi in an olfactometer, and explored potential differences in putative aroma compounds in host fungi.

Our field data showed that Octotemnus glabriculus, Cis boleti and Cis nitidus have preference for one host species, whereas C. bilamellatus has no preference. The experimental evidence was in accordance with the field observations. The specialists O. glabriculus, C. boleti and C. nitidus were specifically attracted to odour compounds of their preferred host fungi: Coriolus versicolor for the first two beetles and Ganoderma adspersum for the latter one. By contrast, the generalist C. bilamellatus was attracted to odours from C. versicolor, G. adspersum and Piptoporus betulinus.

The evidence from this and other published studies suggest that ciids depend mainly on fruit body odours for location and discrimination of their host fungi. In accordance with this, we observed diffierential behavioural responses of ciids to aroma compounds of host and non‐host species.
Sexual dimorphism in the pyrgomorphid grasshopper Phymateus morbillosus: from wing morphometry and flight behaviour to flight physiology and endocrinology
Authors: Gäde Gerd
Published: March 2003

Abstract In the field, adult males of the grasshopper Phymateus morbillosus are able to fly for up to 1 min and cover up to c. 100 m, whereas females, although fully winged, are apparently unable to get airborne. Morphometric data indicate that the males are lighter, have longer wings, a higher ratio of flight muscles to body mass, and a lower wing load value than females. It was investigated whether this inability of females to fly is related to fuel storage, flight muscle enzymatic design and/or the presence and quantitative capacity of the endocrine system to mobilize fuels. In both sexes, readily available potential energy substrates are present in the haemolymph in similar concentrations, and the amount of glycogen in flight muscles and fat bodies does not differ significantly between males and females. Mass‐specific activities of the enzymes GAPDH (glycolysis), HOAD (fatty acid oxidation) and MDH (citric acid cycle) in flight muscles are significantly lower in females compared with males, and mitochondria are less abundant in the flight muscles of females. There is no significant difference between the ability of the two sexes to oxidize various important substrates. Both sexes contain three adipokinetic peptides in their corpora cardiaca; the amount of each peptide in female grasshoppers is higher than in males.

Thus, despite some differences listed above, both sexes appear to have sufficient substrates and the necessary endocrine complement to engage in flight. It seems more likely, from the morphometric data above, that the chief reason for flightlessness is that P. morbillosus females cannot produce sufficient lift for flight; alternatively, the neuronal functioning associated with the flight muscles may be impaired in females.
The photosynthesis of young Panicum C4 leaves is not C3‐like
Authors: Ghannoum O. , Siebke K. , Von Caemmerer S. , Conroy J. P.
Published: March 2003

Evidence is presented contrary to the suggestion that C4 plants grow larger at elevated CO2 because the C4 pathway of young C4 leaves has C3‐like characteristics, making their photosynthesis O2 sensitive and responsive to high CO2. We combined PAM fluorescence with gas exchange measurements to examine the O2 dependence of photosynthesis in young and mature leaves of Panicum antidotale (C4, NADP‐ME) and P. coloratum (C4, NAD‐ME), at an intercellular CO2 concentration of 5 Pa. P. laxum (C3) was used for comparison. The young C4 leaves had CO2 and light response curves typical of C4 photosynthesis. When the O2 concentration was gradually increased between 2 and 40%, CO2 assimilation rates (A) of both mature and young C4 leaves were little affected, while the ratio of the quantum yield of photosystem II to that of CO2 assimilation (ΦPSII/ΦCO2) increased more in young (up to 31%) than mature (up to 10%) C4 leaves. A of C3 leaves decreased by 1·3 and ΦPSII/ΦCO2 increased by 9‐fold, over the same range of O2 concentrations. Larger increases in electron transport requirements in young, relative to mature, C4 leaves at low CO2 are indicative of greater O2 sensitivity of photorespiration. Photosynthesis modelling showed that young C4 leaves have lower bundle sheath CO2 concentration, brought about by higher bundle sheath conductance relative to the activity of the C4 and C3 cycles and/or lower ratio of activities of the C4 to C3 cycles.
The effects of solar ultraviolet‐B radiation on the growth and yield of barley are accompanied by increased DNA damage and antioxidant responses
Authors: MAZZA C. A. , BATTISTA D. , ZIMA A. M. , SZWARCBERG‐BRACCHITTA M. , GIORDANO C. V. , ACEVEDO A. , SCOPEL A. L. , BALLARÉ C. L.
Published: March 2003

There is limited information on the impacts of present‐day solar ultraviolet‐B radiation (UV‐B) on biomass and grain yield of field crops and on the mechanisms that confer tolerance to UV‐B radiation under field conditions. We investigated the effects of solar UV‐B on aspects of the biochemistry, growth and yield of barley crops using replicated field plots and two barley strains, a catalase (CAT)‐deficient mutant (RPr 79/4) and its wild‐type mother line (Maris Mink). Solar UV‐B reduced biomass accumulation and grain yield in both strains. The effects on crop biomass accumulation tended to be more severe in RPr 79/4 (≈ 32% reduction) than in the mother line (≈ 20% reduction). Solar UV‐B caused measurable DNA damage in leaf tissue, in spite of inducing a significant increase in UV‐absorbing sunscreens in the two lines. Maris Mink responded to solar UV‐B with increased CAT and ascorbate peroxidase (APx) activity. No effects of UV‐B on total superoxide dismutase (SOD) activity were detected. Compared with the wild type, RPr 79/4 had lower CAT activity, as expected, but higher APx activity. Neither of these activities increased in response to UV‐B in RPr 79/4. These results suggest that growth inhibition by solar UV‐B involves DNA damage and oxidative stress, and that constitutive and UV‐B‐induced antioxidant capacity may play an important role in UV‐B tolerance.
The cellular basis of guard cell sensing of rising CO2
Authors: ASSMANN S. M.
Published: March 2003

Numerous studies conducted on both whole plants and isolated epidermes have documented stomatal sensitivity to CO2. In general, CO2 concentrations below ambient stimulate stomatal opening, or an inhibition of stomatal closure, while CO2 concentrations above ambient have the opposite effect. The rise in atmospheric CO2 concentrations which has occurred since the industrial revolution, and which is predicted to continue, will therefore alter rates of transpirational water loss and CO2 uptake in terrestrial plants. An understanding of the cellular basis for guard cell CO2 sensing could allow us to better predict, and perhaps ultimately to manipulate, such vegetation responses to climate change. However, the mechanisms by which guard cells sense and respond to the CO2 signal remain unknown. It has been hypothesized that cytosolic pH and malate levels, cytosolic Ca2+ levels, chloroplastic zeaxanthin levels, or plasma‐membrane anion channel regulation by apoplastic malate are involved in guard cell perception and response to CO2. In this review, these hypotheses are discussed, and the evidence for guard cell acclimation to prevailing CO2 concentrations is also considered.
Subcellular compartmentation of proline in the leaves of the subantarctic Kerguelen cabbage Pringlea antiscorbutica R. Br. In vivo13C‐NMR study
Authors: AUBERT S. , HENNION F. , BOUCHEREAU A. , GOUT E. , BLIGNY R. , DORNE A.‐J.
Published: March 2003

Proline is one of the major solutes accumulated upon salt stress in leaves, stem and roots of the subantarctic Brassicaceae Pringlea antiscorbutica R. Br. (Kerguelen cabbage). Using in vivo13C‐NMR techniques, it was possible for the first time to visualize the subcellular compartmentation of proline between cytoplasmic and vacuolar compartments in Pringlea leaves. We observed that this osmolyte accumulated at a 2–3 times higher concentration in the cytoplasm than in the vacuole.
Interacting determinants of specific leaf area in 22 herbaceous species: effects of irradiance and nutrient availability
Authors: MEZIANE D. , SHIPLEY B.
Published: March 2003

We measured specific leaf area (SLA) and six of its determinants (the thickness of lamina, mesophyll, epidermis, mid‐vein and mid‐vein support tissues and leaf water content) in a collection of 22 herbaceous species grown in factorial combinations of high μ1100 (mol m–2 s–1) and low (200) irradiance crossed with high (1 : 1) and low (1 : 6 dilution) concentrations of a modified Hoagland hydroponic solution. SLA increased with both decreasing irradiance and with increasing nutrient availability but there was a strong interaction between the two. Lamina and mesophyll thickness both increased with increasing irradiance and nutrient availability without any interaction. The experimental treatments had complicated effects on mid‐vein thickness and its support tissues. Leaf water content (a measure of leaf tissue density) decreased with increasing irradiance levels and with decreasing nutrient supply, but with an interaction between the two treatments. Changes in nutrient supply had no effect on SLA at high irradiance because leaf thickness and leaf tissue density changed in a compensatory way. A path analysis revealed that each of the components affected SLA when the others were statistically controlled but the strengths of the effects of mesophyll thickness, mid‐vein thickness and water content differed between treatment groups. The effect of epidermal thickness on SLA was constant across environments and it showed no significant covariation with the other determinants. There was significant covariation between mesophyll thickness, mid‐vein thickness and water content and this covariation was constant across the treatment groups.
Intramolecular deuterium distributions reveal disequilibrium of chloroplast phosphoglucose isomerase
Authors: SCHLEUCHER J. , VANDERVEER P. , MARKLEY J. L. , SHARKEY T. D.
Published: March 2003

D, deuterium δD(NMR), chemical shift axis in a deuterium NMR spectrum F6P, fructose‐6‐phosphate G6P, glucose‐6‐phosphate IRMS, isotope ratio mass spectrometry NMR, nuclear magnetic resonance PGI, phosphoglucose isomerase  Intramolecular deuterium distributions of the carbon‐bound hydrogens of glucose were measured using deuterium nuclear magnetic resonance. Glucose isolated from leaf starch of common bean (Phaseolus vulgaris cv. Linden) or spinach (Spinacia oleracea cv. Giant nobel) was depleted in deuterium in the C(2) position, compared with glucose isolated from leaf sucrose or bean endosperm starch. In beans, the depletion of C(2) was independent of the light intensity during growth (150 or 700 μmol photons s–1 m–2). The ratio of glucose‐6‐phosphate to fructose‐6‐phosphate ([G6P]/[F6P]) in bean chloroplasts was 0·9 in high light, indicating that the phosphoglucose isomerase reaction was not in equilibrium ([G6P]/[F6P]) ≈ 3). This implies that the kinetic isotope effect of phosphoglucose isomerase depleted deuterium in the C(2) position of G6P. Because the depletion was the same, the chloroplastic ([G6P]/[F6P]) ratio was in disequilibrium irrespective of the light intensity. If the ([G6P]/[F6P]) ratio was in equilibrium, a large chloroplastic pool of G6P would be unavailable for regeneration of ribulose‐1,5‐bisphospate. We argue that chloroplast phosphoglucose isomerase activity is regulated to avoid this. The deuterium depletion of C(2) explains the known low overall deuterium abundance of leaf starch. This example shows that measurements of intramolecular deuterium distributions can be essential to understand overall deuterium abundances of plant material.
Morphological factors determining salt tolerance in citrus seedlings: the shoot to root ratio modulates passive root uptake of chloride ions and their accumulation in leaves
Authors: Moya J. L. , Primo‐Millo E. , Talon M.
Published: March 2003

The results presented in this work were obtained with two citrus genotypes, the chloride‐tolerant Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and the chloride‐sensitive Carrizo citrange [Citrus sinensis (L.) Osb. ×Poncirus trifoliata (L.) Raf.]. The data show that chloride uptake under salinization is driven by passive forces. In both species, net rates of chloride root uptake increased linearly, without saturation, with the increase of external NaCl concentrations (30–240 mol m–3). Uptake rates, on a μg g root dry weight–1 h–1 basis, in Cleopatra and Carrizo decreased (from 38 to 21) and increased (from 21 to 35), respectively, with the increase (about three‐fold) of the shoot to root ratio. With the appropriate shoot to root ratio in each genotype, it was demonstrated that at identical external doses of NaCl, Cl– uptake rates and Cl– xylem concentrations in the two species were very similar. Root pruning and defoliation showed that the amount of chloride taken by the plant was a function of the size of the root system, whereas leaf chloride concentration, the parameter responsible for salt damage, was dependent upon leaf biomass. Measurements of water transpiration suggested that chloride root uptake and leaf accumulation might be linked to water absorption and transpiration rates, respectively. The data indicate that plant morphology is a crucial factor determining salt‐tolerance in citrus.
The effects of high temperature on isoprene synthesis in oak leaves
Authors: Singsaas E. L. , Sharkey T. D.
Published: March 2003

Isoprene emission from plants is highly temperature sensitive and is common in forest canopy species that experience rapid leaf temperature fluctuations. Isoprene emission declines with temperature above 35 °C but the temperature at which the decline begins varies between 35 and 44 °C. This variability is caused by the rate at which leaf temperature is increased during measurement with lower temperatures associated with longer measurement cycles. To investigate this we exposed leaves of red oak (Quercus rubra L.) to temperature regimes of 35–45 °C for periods of 20–60 min. Isoprene emission increased during the first 10 min of high temperature exposure and then decreased over the next 10 min until it reached steady state. This phenomenon was common at temperatures above 35 °C but was not noticeable at temperatures below that. The response was reversible within 30 min by lowering leaf temperature to 30 °C. Because there is no storage of isoprene inside the leaf, this behaviour indicates regulation of isoprene synthesis in the leaf. We demonstrated that the variability in isoprene decline results from regulation and explains the variability in the temperature response. This is consistent with our theory that isoprene protects leaves from damage caused by rapid temperature fluctuations.
Distribution of Zn in functionally different leaf epidermal cells of the hyperaccumulator Thlaspi caerulescens
Authors: Frey B. , Keller C. , Zierold K.
Published: March 2003

The aim of this study was to show the potential of Thlaspi caerulescens in the cleaning‐up of a moderately Zn ‐contaminated soil and to elucidate tolerance mechanisms at the cellular and subcellular level for the detoxification of the accumulated metal within the leaf. Measured Zn concentrations in shoots were high and reached a maximum value of 83 mmol kg−1 dry mass, whereas total concentrations of Zn in the roots were lower (up to 13 mmol kg−1). In order to visualize and quantify Zn at the subcellular level in roots and leaves, ultrathin cryosections were analysed using energy‐dispersive X‐ray micro‐analysis. Elemental maps of ultrathin cryosections showed that T. caerulescens mainly accumulated Zn in the vacuoles of epidermal leaf cells and Zn was almost absent from the vacuoles of the cells from the stomatal complex, thereby protecting the guard and subsidiary cells from high Zn concentrations. Observed patterns of Zn distribution between the functionally different epidermal cells were the same in both the upper and lower epidermis, and were independent of the total Zn content of the plant. Zinc stored in vacuoles was evenly distributed and no Zn‐containing crystals or deposits were observed. From the elemental maps there was no indication that P, S or Cl was associated with the high Zn concentrations in the vacuoles. In addition, Zn also accumulated in high concentrations in both the cell walls of epidermal cells and in the mesophyll cells, indicating that apoplastic compartmentation is another important mechanism involved in zinc tolerance in the leaves of T. caerulescens.
The effect of ozone in Scots pine (Pinus sylvestris L.): gene expression, biochemical changes and interactions with UV‐B radiation
Authors: Zinser C. , Jungblut T. , Heller W. , Seidlitz H. K. , Schnitzler J.‐P. , Ernst D. , Jr H. Sandermann
Published: March 2003

Increased levels of both ozone and ultraviolet‐B radiation (UV‐B) are typical for high‐altitude sites. Here we report on interactive effects of both stresses on Scots pine (Pinus sylvestris L.). Scots pine seedlings were exposed in a phytotron to a simulated outdoor climate. To assess effects of ozone and of UV‐B radiation on the plants, ozone was added at ambient or at twice‐ambient levels, and UV‐B was eliminated or added at a low ambient level. Visible needle damage became apparent at enhanced ozone concentrations after 10 d of exposure and increased continuously. The accumulated exposure over a threshold value of 40 nL L−1 ozone (AOT40) revealed that an ozone exposure dose of 10 μL L−1 h was necessary for the development of needle injury, regardless of the UV‐B conditions. Cinnamyl alcohol dehydrogenase (CAD) and stilbene synthase (STS) have been reported to be induced by ozone. The mRNAs of these stress‐related enzymes were induced only under twice‐ambient ozone concentrations. Ozone‐induced transient STS transcript levels reached their maximal values between day 1 and day 5, and were more pronounced in the presence of UV‐B. Similarly, pinosylvin, as well as pinosylvin methyl ether contents, showed moderate transient increases under these conditions. In contrast, CAD mRNA content and CAD enzyme activity increased continuously under enhanced ozone concentrations. Additional UV‐B resulted in suppressed transcript level and enzymatic activity of CAD. The data indicate that in conifer needles, at the level of gene expression, there is an interaction between responses to UV‐B and ozone.
Xylem sap flow and stem hydraulics of the vesselless angiosperm Drimys granadensis (Winteraceae) in a Costa Rican elfin forest
Authors: Feild T. S. , Holbrook N. M.
Published: March 2003

For decades, botanists have considered Winteraceae as the least modified descendents of the first angiosperms primarily because this group lacks xylem vessels. Because of a presumed high resistance of a tracheid‐based vascular system to water transport, Winteraceae have been viewed as disadvantaged relative to vessel‐bearing angiosperms. Here we show that in a Costa Rican cloud forest, stem hydraulic properties, sapwood area‐ and leaf area‐specific hydraulic conductivities of Drimys granadensis L. (Winteraceae) are similar to several co‐occurring angiosperm tree species with vessels. In addition, D. granadensis had realized midday transpiration rates comparable to most vessel‐bearing trees. Surprisingly, we found that D. granadensis transpired more water at night than during the day, with actual water loss being correlated with wind speed. The failure of stomata to shut at night may be related to the occlusion of stomatal pores by cutin and wax. Our measurements do not support the view that absence of xylem vessels imposes limitations on water transport above those for other vesselled plants in the same environment. This, in turn, suggests that a putative return to a tracheid‐based xylem in Winteraceae may not have required a significant loss of hydraulic performance.
Two distinct regions of response drive differential growth in Vigna root electrotropism
Authors: Wolverton C. , Mullen J. L. , Ishikawam H. , Evans M. L.
Published: March 2003

Although exogenous electric fields have been reported to influence the orientation of plant root growth, reports of the ultimate direction of differential growth have been contradictory. Using a high‐resolution image analysis approach, the kinetics of electrotropic curvature in Vigna mungo L. roots were investigated. It was found that curvature occurred in the same root toward both the anode and cathode. However, these two responses occurred in two different regions of the root, the central elongation zone (CEZ) and distal elongation zone (DEZ), respectively. These oppositely directed responses could be reproduced individually by a localized electric field application to the region of response. This indicates that both are true responses to the electric field, rather than one being a secondary response to an induced gravitropic stimulation. The individual responses differed in the type of differential growth giving rise to curvature. In the CEZ, curvature was driven by inhibition of elongation, whereas curvature in the DEZ was primarily due to stimulation of elongation. This stimulation of elongation is consistent with the growth response of the DEZ to other environmental stimuli.
Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques
Authors: Stylinski C. D. , Oechel W. C. , Gamon J. A. , Tissue D. T. , Miglietta F. , Raschi A.
Published: March 2003

Lifelong exposure to elevated concentrations of atmospheric CO2 may enhance carbon assimilation of trees with unlimited rooting volume and consequently may reduce requirements for photoprotective pigments. In early summer the effects of elevated [CO2] on carboxylation and light utilization of mature Quercus pubescens trees growing under chronic [CO2] enrichment at two CO2 springs and control sites in Italy were examined. Net photosynthesis was enhanced by 36 to 77%. There was no evidence of photosynthetic downregulation early in the growing season when sink demand presumably was greatest. Specifically, maximum assimilation at saturating [CO2], electron transport capacity, and Rubisco content, activity and carboxylation capacity were not significantly different in trees growing at the CO2 springs and their respective control sites. Foliar biochemical content, leaf reflectance index of chlorophyll pigments (NDVI), and photochemical efficiency of PSII (ΔF/Fm′) also were not significantly affected by [CO2] enrichment except that starch content and ΔF/Fm′ tended to be higher at one spring (42 and 15%, respectively). Contrary to expectation, prolonged elevation of [CO2] did not reduce xanthophyll cycle pigment pools or alter mid‐day values of leaf reflectance index of xanthophyll cycle pigments (PRI), despite the enhancement of carbon assimilation. However, both these pigments and PRI were well correlated with electron transport capacity.
Excretion of two proteases by the ectomycorrhizal fungus Amanita muscaria
Authors: Nehls U. , Bock A. , Einig W. , Hampp R.
Published: March 2003

In the soils of mature forests, nitrogen availability is mainly the result of litter decomposition. Thus protein degradation is of major interest for nutrition. Two aspartic proteases were excreted in a pH‐dependent manner by the ectomycorrhizal fungus Amanita muscaria grown in liquid culture. AmProt1 with a molecular mass of approximately 45 kDa was mainly present at pH values up to 5·4, whereas the excretion of AmProt2 with a molecular mass of about 90 kDa was only detectable at pH values between pH 5·4 and 6·3. In addition, the pH optima of both enzymes differed significantly. AmProt1 had a narrow pH optimum around 3, whereas AmProt2 had a broad pH optimum between 3 and 5·5 and a higher affinity to the substrate methylcasein. One cDNA‐clone (AmProt1*) that presumably encodes AmProt1 was identified. Like AmProt1, this cDNA was expressed in a pH‐dependent manner. In addition, carbohydrate and to a lesser extent nitrogen depletion significantly enhanced AmProt1* expression. In fully developed Populus hyb./A. muscaria ectomycorrhizas the expression of AmProt1* was significantly higher in hyphae of the Hartig net compared with those of the fungal sheath. The role of AmProt1 and AmProt2 for fungal physiology and competitiveness is discussed.
Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors
Authors: De Beer D. , Larkum A. W. D.
Published: March 2003

With microsensors, we measured the steady‐state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m‐2 s‐1), Ca2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calcification cannot supply sufficient protons and CO2 to sustain photosynthesis.
Natural 15N abundance of epiphytes depends on the position within the forest canopy: source signals and isotope fractionation
Authors: Wania R. , Hietz P. , Wanek W.
Published: March 2003

The natural 15N abundance (δ15N) of epiphytes and its N sources were studied in the canopy of a lowland rainforest in Costa Rica. Vascular and non‐vascular epiphytes and canopy soils were collected from four canopy zones and analysed for N contents and δ15N signals. In addition, the N concentrations and δ15N signatures of bulk precipitation, throughfall and stemflow were measured during the wet and the dry season. The δ15N values of epiphyte leaves decreased significantly from the lower zones (means of −3·9 and −4·3‰) to the upper zones (means of −5·4 and −6·1‰) of the canopy. In contrast, δ15N signatures of canopy soils (average −0·3‰) differed little between the zones. Bulk deposition was enriched in 15N (+4·3‰) compared to all other potential N sources and was higher than throughfall and stemflow (+0·5 to −1·3‰). δ15N values of atmospheric deposition were inversely related to those of the epiphyte leaves, whereas N isotopic composition of canopy soils did not vary significantly. Consequently, it is concluded that the variations in foliar N isotope composition of epiphytes were not simply caused by utilization of isotopically different N sources, but by different 15N discrimination during N acquisition.
Natural variation in Arabidopsis seedling photomorphogenesis reveals a likely role for TED1 in phytochrome signalling
Authors: Pepper A. E. , Corbett R. W. , Kang N.
Published: March 2003

Natural genetic variation present among accessions of Arabidopsis thaliana (L.) Heynh. (commonly referred to as ‘ecotypes’) is a valuable, yet under‐exploited genetic resource for the study of plant developmental, physiological. and evolutionary responses to the environment. Seedling photomorphogenic responses were surveyed in a set of 11 Arabidopsis accessions collected from a variety of edaphic habitats and geographic locations. We observed substantial variation in light‐dependent hypocotyl growth responses in a variety of light conditions (white, red, blue, far‐red enriched light). The genetic basis for differences in hypocotyl growth responses to light between the Columbia (Col‐0) and Bensheim (Be‐0) accessions was examined in an F2 population. Quantitative genetic and quantitative trait locus (QTL) analyses were consistent with a model in which differences in light responses were conditioned by a single major gene with semi‐dominant effect, located on chromosome 4. Further experiments suggested that the genetic difference governing hypocotyl variation in this cross may be allelic to ted1, an extragenic suppressor of the de‐etiolated mutant det1, that was identified as an ethylmethane sulphonate‐induced mutation. This finding supports a role for ted1 in photomorphogenic signalling.
Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communities
Authors: Martínez F. , Lazo Y. O. , Fernández‐Galiano R. M. , Merino J. A.
Published: March 2003

The construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non‐significant (mean value: 1·64 ± 0·13 g glucose g−1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g−1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g−1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g−1 versus 1·78 ± 0·02 g glucose g−1). The differences observed in construction cost appeared to be due more to habitat‐induced differences in chemical composition than to any intrinsic difference between the species studied.
Do anthocyanins function as antioxidants in leaves? Imaging of H2O2 in red and green leaves after mechanical injury
Authors: Gould K. S. , McKelvie J. , Markham K. R.
Published: March 2003

Purified anthocyanin extracts show strong antioxidant properties in vitro, but it is not known whether they can scavenge reactive oxygen in living cells. The oxidative responses in red and green portions of Pseudowintera colorata leaf laminae were compared by the real‐time imaging of H2O2 in cells after mechanical injury. An oxidative burst was elicited almost immediately from chloroplasts in the palisade mesophyll, as evidenced using the fluorochromes dichlorofluorescein and scopoletin. H2O2 accumulated in green lamina regions for 10  min, and then decreased slowly. By contrast, red regions recovered rapidly, and maintained consistently low levels of H2O2. Infusion of cells with N‐acetyl‐l‐cysteine accelerated the depletion of H2O2 from green regions. Wounded leaves ultimately developed a localized necrotic lesion and an intense anthocyanic band. The red regions were enriched in anthocyanins, flavonols, dihydroflavonols, and hydroxycinnamic acids. Only the anthocyanins were suitably located to account for the enhanced rates of H2O2 scavenging. The data support the hypothesis that red cells have elevated antioxidant capabilities in vivo.
Anthocyanin accumulation in the illuminated surface of maize leaves enhances protection from photo‐inhibitory risks at low temperature, without further limitation to photosynthesis
Authors: Pietrini F. , Iannelli M. A. , Massacci A.
Published: March 2003

At     suboptimal     temperatures,     anthocyanins     accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo‐inhibition but also photo‐synthesis. To investigate this phenomenon, gas exchange, fluorescence,   superoxide   dismutase   activity   and  xantho‐phyll composition of anthocyanin‐containing HOPI and anthocyanin‐deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO2 supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The ΔF/Fm (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than ΔF/Fm of W22 with either light source. This probably compensated for the lower white light absorption of HOPI chloroplasts compared with W22 because of the presence of anthocyanins and led to similar rates of calculated electron transport for both genotypes. After exposure to high white light at 5 °C, xanthophyll de‐epoxidation and superoxide dismutase activity were lower in HOPI than in W22. Further, HOPI could be exposed to a much higher irradiance than W22 before Fv/Fm was reduced to that of W22.
Diurnal changes in the expressionof glutamate dehydrogenase and nitrate reductase are involved in the C/N balance of tobacco source leaves
Authors: Masclaux‐Daubresse C. , Valadier M.‐H. , Carrayol E. , Reisdorf‐Cren M. , Hirel B.
Published: March 2003

A novel cDNA encoding glutamate dehydrogenase (GDH) from tobacco(Nicotiana tabacum), namedgdh1,was characterized.Thegdh1mRNA was detected in roots, stems and source/senescentleaves. In order to investigate diurnal regulation ofgdh1inleaves, the content ingdh1mRNA was measured every 3 h overa 48 h period and compared toniaandgs2mRNAlevels, encoding, respectively, nitrate reductase (NR) and chloroplasticglutamine synthetase (GS2). In source leaves,gdh1mRNA levelsexhibit diurnal fluctuations. A 12 h shift was observedbetween the day–night rhythms ofgdh1andniaexpression.Metabolite contents were also measured and a shift in the day–nightfluctuations of both glutamate (GLU) andγ‐aminobutyricacid (GABA) was observed between sink and source leaves, whereasthe diurnal rhythm ofα‐ketoglutarate showed no change.A possible role of GDH in the shift of GLU and GABA contents isdiscussed. Leaf disc experiments showed thatgdh1expressionis enhanced in conditions of continuous darkness. This trend isinhibited by sucrose feeding. The opposite was observed forniaexpression.An important outcome of this work is the reverse regulation ofgdh1andniagenes.A possible role of sugars and amino acids in the co‐regulation ofgdh1andniagenesis suggested.
Phloem loading and unloading of sugars and amino acids
Authors: LALONDE S. , TEGEDER M. , THRONE‐HOLST M. , FROMMER W. B. , PATRICK J. W.
Published: March 2003

In terrestrial higher plants, phloem transport delivers most nutrients required for growth and storage processes. Some 90% of plant biomass, transported as sugars and amino nitrogen (N) compounds in a bulk flow of solution, is propelled though the phloem by osmotically generated hydrostatic pressure differences between source (net nutrient export) and sink (net nutrient import) ends of phloem paths. Source loading and sink unloading of sugars, amino N compounds and potassium largely account for phloem sap osmotic concentrations and hence pressure differences. A symplasmic component is characteristic of most loading and unloading pathways which, in some circumstances, may be interrupted by an apoplasmic step. Raffinose series sugars appear to be loaded symplasmically. However, sucrose, and probably certain amino acids, are loaded into minor veins from source leaf apoplasms by proton symporters localized to plasma membranes of their sieve element/companion cell (se/cc) complexes. Sucrose transporters, with complementary kinetic properties, are conceived to function as membrane transporter complexes that respond to alterations in source/sink balance. In contrast, symplasmic unloading is common for many sink types. Intervention of an apoplasmic step, distal from importing phloem, is reserved for special situations. Effluxers that release sucrose and amino acids to the surrounding apoplasm in phloem loading and unloading are yet to be cloned. The physiological behaviour of effluxers is consistent with facilitated membrane transport that can be energy coupled. Roles of sucrose and amino acid transporters in phloem unloading remain to be discovered along with mechanisms regulating symplasmic transport. The latter is hypothesized to exert significant control over phloem unloading and, in some circumstances, phloem loading.
Differences between rice and wheat in ribulose‐1,5‐bisphosphate regeneration capacity per unit of leaf‐N content
Authors: SUDO E. , MAKINO A. , MAE T.
Published: March 2003

The photosynthetic rates under saturating CO2 conditions per unit of leaf‐N content were higher in wheat than in rice. This suggested that ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity is greater in wheat. Therefore, the biochemical factor(s) for this difference were examined between rice and wheat. Soluble protein‐N, insoluble‐N, and trichloroacetic acid (TCA) soluble‐N contents were found not to differ between the two species. The activities of several Calvin cycle enzymes such as RuBP carboxylase, NADP‐glyceraldehyde‐3‐phosphate dehydrogenase, phosphoglycerate kinase and chloroplastic fructose‐1,6‐bisphosphatase (cpFBPase) activities per unit of leaf‐N content were all higher in wheat than in rice. Among them, cpFBPase activity was most highly correlated with CO2‐saturated photosynthesis. The Vmax activity of sucrose‐phosphate synthase (SPS) for UDP‐glucose was almost the same between the two species and its Km value was a little lower in rice. Chlorophyll content and its a/b ratio did not differ. Cytochrome (Cyt) f content was greater in wheat, whereas coupling factor 1 content was greater in rice. Cyt f content was highly correlated with CO2‐saturated photosynthesis, irrespective of the two species. The results thus suggested that higher RuBP regeneration capacity in wheat leaves is most closely related to a greater Cyt f content and that another candidate is cpFBPase.
Molecular, physiological and pathological characterization of Corynespora leaf spot fungi from rubber plantations in Sri Lanka
Authors: Silva W. P. K. , Deverall B. J. , Lyon B. R.
Published: March 2003

The plant pathogenic fungus Corynespora cassiicola causes a severe leaf spot disease on more than 70 host plant species including Hevea brasiliensis. Genetic variability in 32 isolates of C. cassiicola collected from diverse hosts and locations in Sri Lanka and Australia was assessed using restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer (ITS) region of ribosomal DNA and random amplified polymorphic DNA‐polymerase chain reaction (RAPD‐PCR) analysis of total fungal DNA. Amplified ITS fragments from all 32 C. cassiicola isolates exhibited an identical size, and restriction analysis with seven different restriction endonucleases revealed identity in all of the detected DNA fragments. This finding of high genetic relatedness was further supported by the cloning and DNA sequencing of the ITS2 region from one Sri Lankan and one Australian isolate. However, RAPD‐PCR profiles generated by 15 oligonucleotide decamer primers revealed significant polymorphism between groups of organisms. Genetic relationships among the isolates were determined by cluster analysis of the RAPD‐PCR data and seven different RAPD groups were identified. Isolates showed strong correlations between the assigned RAPD group and the location and host plant genotype from which the isolate was collected. Correlations were also observed between the RAPD group, growth of the isolate and pathogenicity on different plant hosts.
The effect of temperature on colony growth by Erysiphe sp. infecting Rhododendron
Authors: Kenyon D. M. , Dixon G. R. , Helfer S.
Published: March 2003

The growth and reproduction of powdery mildew pathogens is generally encouraged by increasing temperatures, up to 25°C. Germination and germ tube extension of Erysiphe sp. on Rhododendron cv. Elizabeth were optimal at 20°C for conidia originally formed at either 10 or 15°C. During a 50‐day period of colony growth, the viability of conidia formed at 15°C declined but for those formed at 10°C it increased. The expansion of Erysiphe colonies over an initial 12‐day period was favoured by incubation at 15°C compared with 10 or 20°C. In the first 8 to 10 days of growth, secondary and tertiary hyphae formed most rapidly at 20°C. After 12 days, expansion of colonies at 20°C was limited to the area initially infested by primary hyphae, whereas in colonies grown at 10 and 15°C secondary and tertiary hyphae had extended beyond the area first colonized. Small colonies of densely packed hyphae formed at 20°C compared with open spreading colonies observed at 10 and 15°C.
Occurrence and inheritance of resistance to powdery mildew (Oidium lycopersici) in Lycopersicon species
Authors: Ciccarese F. , Amenduni M. , Schiavone D. , Cirulli M.
Published: March 2003

Among 146 accessions of Lycopersicon pimpinellifolium, 132 of L. esculentum var. cerasiforme and 53 of L. peruvianum screened for resistance to powdery mildew, caused by Oidium lycopersici, a wide variation in reactions was found. Two plants of L. esculentum var. cerasiforme accession LA‐1230 were resistant. One resistant symptomless plant of accession LA‐1230, designated LC‐95, produced homozygous resistant progenies. LC‐95 was crossed with cv. Marmande (susceptible parent) and F1, F2 and backcrosses to the resistant and the susceptible parents were derived. These genotypes were grown in glasshouses at 23°C and 95–100% RH and inoculated with O. lycopersici. The F1 plants were susceptible. F2 and backcross segregations fitted the hypothesis of a single recessive gene which is here designated ol‐2.
Influence of light‐enhanced glycoalkaloids on resistance of potato tubers to Fusarium sulphureum and Fusarium solani var. coeruleum
Authors: Percival  , Karim  , Dixon
Published: March 2003

Increases in resistance to Fusarium sulphureum and Fusartium solani var. coeruleum were determined in seed tubers of cultivars Desiree, Pentland Hawk and Kerr's Pink with light‐enhanced glycoalkaloids. Glycoalkaloid concentration in the tubers ranged from 78.0 to 885.9 mg kg−1 fresh weight. Exposure of tubers to light prior to inoculation decreased fungal invasion, the greater reductions generally reflecting longer light exposure periods. In most cases, no direct relationship between resistance and glycoalkaloid concentrations was recorded for F. sulphureum. Surface infection indices and reduced depth of rot caused by F. solani var. coeruleum were closely correlated with tuber glycoalkaloid content. No significant effects on spore length and width were recorded. Exposure to light of seed tubers that are not destined for human or animal consumption could provide a pretreatment to reduce fungal invasion by F. sulphureum and F. solani var. coeruleum.
Effects of interrupted wet periods and different temperatures on the development of ascochyta blight caused by Mycosphaerella pinodes on pea (Pisum sativum) seedlings
Authors: Roger  , Tivoli  , Huber
Published: March 2003

The effect of interrupted wet periods on pycnidiospores of Mycosphaerella pinodes was studied by assessing spore viability, infection and disease development on pea seedlings. Pycnidiospores survived dry periods of up to 21 days after inoculation. Rewetting restored the infection capacity of the pycnidiospore, resulting in high levels of disease. The effects of wet–dry–wet cycles depended on when the dry period occurred during the infection process. No disease symptoms appeared when dry periods occurred during germination. A low level of disease occurred after rewetting in high relative humidity if the interruption of the wet period was long. However, a wet period resulting in leaf wetness after a dry period gave similar levels of infection to those achieved with a continuous wet period. Pycnidiospores formed appressoria but hyphae did not penetrate if a 6–12 h wet period preceded the dry period, and only a few flecks appeared during the dry period. Coalescent necrosis occurred when the dry period followed penetration. The disease was severe in each case when plants were returned to wet conditions after a period of dryness. Lesion development depended on the duration of the initial wet period, and the characteristics (temperature and duration) of both the dry period and the final wet period.
A new tool for entry and analysis of virulence data for plant pathogens
Authors: Herrmann  , Löwer  , Schachtel
Published: March 2003

The methods of Habgood (1970) and Gilmour (1973) for the assignment of pathogen race names are discussed and the advantages of a reversed octal system, based on Gilmour's octal code, are emphasized. A new spreadsheet, ‘HaGiS’, exploits these two designation systems to provide user‐friendly and fast access to some routine steps in the analysis of virulence data for plant pathogen populations. It produces graphs and tables for frequency distributions (of pathotypes, isolate complexities and cultivar susceptibilities); sorted lists (e.g. of the races ranked by predominance); indices (of sample diversity and of pathogenicity for each differential cultivar); and coloured proximity matrices. Use of HaGiS requires knowledge of only a few basic functions of MS Excel 97®. All graphs, tables, indices and matrices are generated automatically and displayed by switching to the corresponding worksheet. In addition to data analysis, the spreadsheet is convenient for the entry of experimental data, allowing for all commonly used assessment scales.