bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal morphometric variation in sexual and asexual, North American and Australian, populations of the aphid, Acyrthosiphon pisum
Authors: Smith M. A. H. , Mackay P. A. , Lamb R. J. 
Published: March 2003

SummaryThe lengths of the body and appendages of the aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae) vary seasonally in sexual North American and asexual Australian populations. The first generation of spring aphids in North America and winter aphids in Australia have short appendages in relation to body length. Excluding this phenotype, North American and Australian aphids cannot be discriminated morphometrically. The short appendages in North America are associated with a specialized morph called a fundatrix; the short appendages of Australian aphids are caused by exposure to low temperatures during prenatal development. The same temperature‐sensitive mechanism operates in sexual and asexual North American aphids, but does not explain the short appendages of the fundatrix, which appear to arise through a separate mechanism. The short appendages are caused neither by a maternal effect from winged mothers, although such an effect exists, nor by seasonal changes in body length and allometry, nor by microevolutionary changes. The temperature‐induced shortening of appendages is a seasonal polymorphism, which mimics the short appendages seen in fundatrices. The two types of phenotypic plasticity have the same consequence in sexual and asexual populations of the same species and may be an example of convergent evolution.
Water loss in desert ants: caste variation and the effect of cuticle abrasion
Authors: Johnson Robert A. 
Published: March 2003

SummaryWater loss rates (WLRs) varied across castes (workers > alate males > alate females) for desert ants in the generaAphaenogaster, MessorandPogonomyrmex. Exposure to soil caused increased WLRs in workers and foundresses (mated, dealate females), apparently because of cuticular abrasion caused by nest excavation. Moreover, field‐collected workers and foundresses from incipient nests (those exposed to soil) had similar WLRs, as did unabraded workers and alate females (those unexposed to soil). These data call into question previous adaptive scenarios for differences in WLRs across ant species and castes. For live alate females, WLRs increased over two stages. The first increase occurred immediately after mating, and the second occurred for foundresses collected 2 days later from incipient nests. By contrast, WLRs of HCN‐killed females were unaffected by mating, but increased significantly for foundresses collected from 2‐day‐old nests.
Responses of male Helicoverpa zea to single pulses of sex pheromone and behavioural antagonist
Authors: Quero Carmen , Fadamiro Henry Y. , Baker Thomas C. 
Published: March 2003

SummaryMale Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) flying in a pheromone plume respond to the loss of pheromone when they fly into a large pocket of clean air by going into crosswind casting flight in a mean of 0.48 s; 0.62 s after re‐contacting pheromone presented as a single pulse, they surge upwind in a kind of narrow zigzagging flight. After 0.36 s of surging, they lapse into casting flight once again in the clean air following the pulse. The addition of a known behavioural antagonist (Z)‐11‐hexadecenyl acetate (Z11–16:Ac), to the pheromone significantly increases the mean latency of the response to a single pulse to 0.85 s. No other aspects of the surge were significantly changed by the presence of antagonist in the single pulse of pheromone. Thus, unlike males of the related species, Heliothis virescens, which show significant changes in track and course angles when antagonist is present in single pulses, only an increased latency of response to a filament containing antagonist occurred in H. zea males. The increased latency could act cumulatively when the male is exposed rapidly and repeatedly to filaments in a natural plume and explain the profound arrestment effect of the antagonist in such plumes. The latencies to casting and surging in response to a pulse of pheromone blend are longer than those of the smaller species, H. virescens, and may be due to size‐related differences in manoeuverability of H. zea vs. H. virescens.
Solute fluxes from tobacco to the parasitic angiosperm Orobanche cernua and the influence of infection on host carbon and nitrogen relations
Authors: Hibberd J. M. , Quick W. P. , Press M. C. , Scholes J. D. , Jeschke W. D. 
Published: March 2003

ABSTRACT Orobanche species are holoparasites which are very efficient sinks for host‐derived solutes. Here, we report the use of direct measurements of xylem sap solute concentrations and water fluxes, together with a modelling procedure to calculate element fluxes within an association between Orobanche cernua and its tobacco host. Infection of tobacco by the parasite markedly influenced carbon acquisition and partitioning; net fixation of carbon was 20% higher in infected tobacco compared with controls. Orobanche cernua caused a 84% increase in net carbon flux moving downward from the tobacco shoot and 73% of this carbon was intercepted by the parasite, almost entirely through the phloem (>99%). Further, the parasite also exerted a large impact on the nitrogen relations of the plant, notably nitrate uptake was stimulated and the amino acid content of xylem sap was lower. The parasite also relied heavily on host phloem for the supply of other resources, with only 5 to 15% of N, and 16% of K, 23% of Na, 63% of Mg and 13% of S being derived from the xylem. Thus, we provide quantitative information on the phloem dependency of the parasite and show that host carbon and nitrogen metabolism is stimulated as a consequence of infection.
Developmental changes in enzymes involved in the conversion of hexose phosphate and its subsequent metabolites during early tuberization of potato
Authors: Appeldoorn N. J. G. , De Bruijn S. M. , Koot‐Gronsveld E. A. M. , Visser R. G. F. , Vreugdenhil D. , Plas L. H. W. Van Der 
Published: March 2003

ABSTRACTA highly synchronized in vitro tuberization system, based on single‐node cuttings containing an axillary bud, was used to investigate the activity patterns of enzymes involved in the conversion of hexose phosphates and related products during stolon‐to‐tuber transition of potato (Solanum tuberosum L.). At tuberization the activity of enzymes involved in glycolysis and the oxidative pentose phosphate pathway (OPPP) showed a small but clear increase. This increase reflects a higher capacity of respiratory(‐related) metabolism, presumably due to the onset of rapid cell division in the apical part of the tuberizing stolon. During the phase of successive tuber growth these enzymes decreased in activity, suggesting that the concomitant massive starch accumulation is not accompanied by a large increase in respiration. A high degree of positive correlation between the activities of these enzymes could be observed, implying that the level of respiratory metabolism‐related enzymes is co‐ordinately regulated by the same mechanism of coarse control. The activity pattern of pyrophosphate:fructose‐6‐phosphate phosphotransferase (PFP) showed no developmental change and does not resemble the activity pattern of the enzymes participating in respiratory(‐related) metabolism. Instead, its level of activity is very likely the result of metabolic regulation. The level of the content of the metabolites UDP‐glucose (UDPGlc) and glucose‐6‐phosphate (Glc6P) decreased after the onset of tuberization. This decline indicates that tuber induction is not accompanied by an appreciable increase in the level of the cytosolic hexose phosphate (hexose‐P) content but that it rather remains on a low level, which might be a prerequisite in order to maintain a high net rate of sucrose degradation during tuber development. In contrast to UDPGlc and Glc6P, the content of fructose‐1,6‐bisphosphate (Fru1,6bisP) showed an increase after tuber induction. The overall activities of ADP‐glucose pyrophosphorylase (AGPase) and starch phosphorylase (STP) both showed a large increase after tuber initiation, which is consistent with their presumed role in the process of starch synthesis and accumulation during rapid tuber growth.
Shoot structure, canopy openness, and light interception in Norway spruce
Authors: Stenberg P. , Kangas T. , Smolander H. , Linder S. 
Published: March 2003

ABSTRACTWe analysed changes in shoot structure with canopy openness in control (C) and irrigated–fertilized (IL) Picea abies trees. Canopy openness, which was used to characterize light availability, varied between 0·23 and 0·90 for C shoots and 0·07 to 0·75 for IL shoots. Needle width and thickness increased with canopy openness, but were similar for C and IL needles. The ratio of needle thickness to width remained fairly close to one throughout the canopy. This resulted in large values (3·0–4·0) of the ratio of total to projected needle area. The ratio of total to projected needle area did not correlate with canopy openness. Shoot silhouette to total needle area ratio (STAR) and specific needle area decreased with canopy openness. As a result, shoot silhouette area per unit needle mass was up to three times larger in shade shoots than in sun shoots. STAR and specific needle area were similar for C and IL shoots and needles. Needle nitrogen concentration varied between 0·7 and 1·1% (C), and between 1·0 and 1·6% (IL). On both plots, nitrogen content was linearly related to estimated relative light interceptance (RLI) (both expressed per needle area), but the ratio of nitrogen content to RLI increased with decreasing canopy openness.
Ethylene production and ACC‐accumulation in Agrobacterium tumefaciens‐induced plant tumours and their impact on tumour and host stem structure and function
Authors: Wächter R. , Fischer K. , Gäbler R. , Kühnemann F. , Urban W. , Bögemann G. M. , Voesenek L. A. C. J. , Blom C. W. P. M. , Ullrich C. I. 
Published: March 2003

ABSTRACTEthylene emission from wild‐type Agrobacterium tumefaciens (C58)‐induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo‐acoustic spectrometry. Ethylene production was as high as 700 pmol g FW–1 h–1, namely 140 times greater than emitted by non‐tumourized control stems. It was highest in 5‐week‐old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO‐production was discovered. Accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), the substrate of ACC‐oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour‐adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non‐transformed, tumour‐surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens‐induced tumours.
Leaf expansion and cell division are affected by reducing absorbed light before but not after the decline in cell division rate in the sunflower leaf
Authors: Granier C. , Tardieu F. 
Published: March 2003

ABSTRACTThe effect of absorbed photosynthetic photon flux density (PPFD) on leaf expansion is a key issue for analysing the phenotypic variability between plants and for modelling feedback loops. Expansion and epidermal cell division in leaf 8 of sunflower were analysed in a series of five experiments where absorbed photosynthetic photon flux density (PPFD) was reduced either by shading or by covering part of the leaf area. These treatments were imposed at different times during leaf development. Expansion and cell division were affected by a reduction in absorbed PPFD only in the first part of leaf development, while the leaf area was less than 2% of its final value and while absolute expansion rate was slow. In contrast, it was not affected if imposed later when the leaf was visible and absolute expansion rate was at maximum. A reduction in absorbed PPFD caused the same reduction in expansion and in cell division whether it was due to a reduction in incident PPFD or to a reduction in photosynthetic leaf area, suggesting that carbon metabolism was involved. Relative expansion rate recovered to control levels when relative division rate began to decline, in all experiments and in all zones of a leaf. This was probably linked to the source–sink transition, after which the leaf had such a high priority in carbon allocation that it was largely insensitive to changes in absorbed PPFD. The final leaf area was therefore closely related to the cumulated PPFD absorbed by the plant from leaf initiation to the end of exponential cell division.
Novel approaches for examining the effects of differential soil compaction on xylem sap abscisic acid concentration, stomatal conductance and growth in barley (Hordeum vulgare L.)
Authors: Hussain A. , Black C. R. , Taylor I. B. , Mulholland B. J. , Roberts J. A. 
Published: March 2003

ABSTRACTNovel techniques were devised to explore the mechanisms mediating the adverse effects of compacted soil on plants. These included growing plants in: (i) profiles containing horizons differing in their degree of compaction and; (ii) split‐pots in which the roots were divided between compartments containing moderately (1·4 g cm−3) and severely compacted (1·7 g cm−3) soil. Wild‐type and ABA‐deficient genotypes of barley were used to examine the role of abscisic acid (ABA) as a root‐to‐shoot signal. Shoot dry weight and leaf area were reduced and root : shoot ratio was increased relative to 1·4 g cm−3 control plants whenever plants of both genotypes encountered severely compacted horizons. In bartey cultivar Steptoe, stomatal conductance decreased within 4 d of the first roots encountering 1·7 g cm−3 soil and increased over a similar period when roots penetrated from 1·7 g cm−3 into 1·4 g cm−3 soil. Conductance was again reduced by a second 1·7 g cm−3 horizon. These responses were inversely correlated with xylem sap ABA concentration. No equivalent stomatal responses occurred in Az34 (ABA deficient genotype), in which the changes in xylem sap ABA were much smaller. When plants were grown in 1·7 : 1·4 g cm−3 split‐pots, shoot growth was unaffected relative to 1·4 g cm−3 control plants in Steptoe, but was significantly reduced in Az34. Excision of the roots in compacted soil restored growth to the 1·4 g cm−3 control level in Az34. Stomatal conductance was reduced in the split‐pot treatment of Steptoe, but returned to the 1·4 g cm−3 control level when the roots in compacted soil were excised. Xylem sap ABA concentration was initially higher than in 1·4 g cm−3 control plants but subsequently returned to the control level; no recovery occurred if the roots in compacted soil were left intact. Xylem sap ABA concentration in the split‐pot treatment of Az34 was initially similar to plants grown in uniform 1·7 g cm−3 soil, but returned to the 1·4 g cm−3 control level when the roots in the compacted compartment were excised. These results clearly demonstrate the involvement of a root‐sourced signal in mediating responses to compacted soil; the role of ABA in providing this signal and future applications of the compaction procedures reported here are discussed.
An accurate method to quantify ribulose bisphosphate carboxylase content in plant tissue
Authors: Ferreira R. B. , Esquível M. G. 
Published: March 2003

ABSTRACTA method is described to accurately measure the content of ribulose bisphosphate carboxylase (RuBP carboxylase, EC 4·1.1·39) in plant tissues. This procedure, termed the internal standard method, involves extraction of the plant tissue (containing an unknown amount of 1H‐RuBP carboxylase) in a buffer containing a known amount of previously purified 3H‐RuBP carboxylase (internal standard). The rapid and efficient, single step copurification of 1H‐ and 3H‐RuBP carboxylases on the Mono Q column of the Fast Protein Liquid Chromatography System (FPLC), or by sucrose density gradient ultracentrifugation, allows the accurate estimation of the purification yield (3H in purified enzyme/3H in the extraction buffer). Knowing the amount of 1H‐RuBP carboxylase in the purified enzyme and the purification yield, one can calculate the concentration of 1H‐enzyme present in the plant tissue. This procedure overcomes some of the main constraints associated with the methods described in the literature: it takes into account the enzyme that is lost during the clarification of the protein extracts or during the isolation and purification processes; it is independent of the proteolysis that occurs in vitro by the action of cell proteases; it is not affected by the presence of RuBP carboxylase breakdown products; it is not influenced by any of the factors that control the catalytic activity or the activation state of the enzyme; and, it does not depend on the specificity of antigen‐antibody reactions.
Influence of temperature and soil drying on respiration of individual roots in citrus: integrating greenhouse observations into a predictive model for the field
Authors: Bryla D. R. , Bouma T. J. , Hartmond U. , Eissenstat D. M. 
Published: March 2003

AbstractIn citrus, the majority of fine roots are distributed near the soil surface – a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant’s below‐ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q10 = 1·8–2·0), provided that the changes in temperature were short‐term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 °C, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at <2% soil water content in sandy soil. A model was constructed from greenhouse data to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then validated in the field using data obtained by CO2 trapping on root systems of mature citrus trees. The trees were grown at a site where the soil temperature and water content were manipulated. Respiration predicted by the model was in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration for citrus.
Screening of cadmium‐responsive genes in Arabidopsis thaliana
Authors: Suzuki N. , Koizumi N. , Sano H. 
Published: March 2003

AbstractSeedlings of Arabidopsis thaliana were treated with Cd, and transcript populations that changed their levels were screened by a fluorescent differential display method. Among the 170 cDNAs initially identified, 31 were further characterized for their identity, expression profile and response to other stresses. Sequencing revealed 10, 12 and 15 to be related to signal transduction, protein denaturing stress and responses to active oxygen species, respectively. Many of these genes responded not only to Cd, but also to oxidative stress, Cu ions and a protein denaturation agent. Upon introduction into yeast cells, two genes, encoding ATMEKK1 and a putative farnesylated protein that has two metal binding motifs, endowed marked toleration of Cd toxicity. These results suggest that oxidative stress and protein denaturation are important components of Cd toxicity, and that to cope with such stresses, plants activate a set of genes involved in metal detoxification, protein refolding and wound healing. The results also suggested temporarily and spatially well‐regulated protein phosphorylation and activation of transcription factors, accompanied by their transcription.
Leaf ontogenetic dependence of light acclimation in invasive and native subtropical trees of different successional status
Authors: Yamashita N. , Koike N. , Ishida A. 
Published: March 2003

AbstractIn the Bonin Islands of the western Pacific where the light environment is characterized by high fluctuations due to frequent typhoon disturbance, we hypothesized that the invasive success of Bischofia javanica Blume (invasive tree, mid‐successional) may be attributable to a high acclimation capacity under fluctuating light availability. The physiological and morphological responses of B. javanica to both simulated canopy opening and closure were compared against three native species of different successional status: Trema orientalis Blume (pioneer), Schima mertensiana (Sieb. et Zucc.) Koidz (mid‐successional) and Elaeocarpus photiniaefolius Hook.et Arn (late‐successional). The results revealed significant species‐specific differences in the timing of physiological maturity and phenotypic plasticity in leaves developed under constant high and low light levels. For example, the photosynthetic capacity of T. orientalis reached a maximum in leaves that had just fully expanded when grown under constant high light (50% of full sun) whereas that of E. photiniaefolius leaves continued to increase until 50 d after full expansion. For leaves that had just reached full expansion, T. orientalis, having high photosynthetic plasticity between high and low light, exhibited low acclimation capacity under the changing light (from high to low or low to high light). In comparison with native species, B. javanica showed a higher degree of physiological and morphological acclimation following transfer to a new light condition in leaves of all age classes (i.e. before and after reaching full expansion). The high acclimation ability of B. javanica in response to changes in light availability may be a part of its pre‐adaptations for invasiveness in the fluctuating environment of the Bonin Islands.
Hydraulic architecture of leaf venation in Laurus nobilis L.
Authors: Zwieniecki M. A. , Melcher P. J. , Boyce C. K. , Sack L. , Holbrook N. M. 
Published: March 2003

AbstractVeins are the main irrigation system of the leaf lamina and an understanding of the hydraulic architecture of the vein networks is essential for understanding leaf function. However, determination of leaf hydraulic parameters is challenging, because for most leaves the vein system is reticulate, contains a hierarchy of different vein sizes, and consists of leaky conduits. We present a new approach that allows for measurements of pressure differences between the petiole and any vein within the leaf. Measurements of Laurus nobilis leaves indicate that first‐ and second‐order veins have high axial conductance and relatively small radial permeability, thus allowing water to reach distal areas of the leaf with only a small loss of water potential. Higher order veins tend to be more hydraulically resistant and permit greater radial leakage. This design allows for a relatively equitable distribution of water potential and thus reflects the capacity of the venation to provide a relatively homogeneous water supply across the leaf lamina, with only the leaf margins being hydraulically disadvantaged relative to the rest of the leaf.