bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of host responder types after a single Cooperia oncophora infection: kinetics of the systemic immune response
Authors: Kanobana K. , Vervelde L. , Van Der Veer M. , Eysker M. , Ploeger H.W.
Published: March 2003

After primary infection with 100 000 third stage larvae of the intestinal nematode Cooperia oncophora in 3‐month‐old calves, a high variability in egg output and worm counts is observed. Based on this variability, infected animals can be divided in different responder types. The three major phenotypes can be classified as high, intermediate and low responder animals. We investigated whether calves classified into different responder types show different immune responses during infection. Peripheral blood eosinophil counts and flow cytometric analysis of different lymphocyte subsets of the blood did not reveal major differences between infected and control animals, nor between responder types. However, the levels of Cooperia‐specific immunoglobulin (Ig)G1 and IgA during primary infection were significantly higher in intermediate responders than in low responders. In the intermediate responders, isotype specific responses were negatively correlated with parasitological parameters expressing worm expulsion and influence on worm fecundity. Total serum IgE levels were elevated in most of the infected animals. A quantitative positive relationship between worm counts and total serum IgE levels was observed. Based on the observed correlations, we propose a role for the humoral response against the maintenance of the infection in the gut.
Relationship between reactive nitrogen intermediates and total immunoglobulin E, soluble CD21 and soluble CD23: comparison between cerebral malaria and nonsevere malaria
Authors: Nacher Mathieu , Singhasivanon Pratap , Kaewkungwal Jaranit , Silachamroon Udomsak , Treeprasertsuk Sombat , Tosukhowong Thanawat , Vannaphan Suparp , Looareesuwan Sornchai
Published: March 2003

To search for evidence of a protective role of the CD23/NO pathway against cerebral malaria, concentrations of reactive nitrogen intermediates (RNI) and sCD21, total immunoglobulin (Ig)E and sCD23 were compared between 17 cases of cerebral malaria and 33 controls. The geometric mean of sCD23 concentration was higher among cerebral malaria cases than among controls (optical density 2643/1495, P = 0·01). The ratio between sCD21 and sCD23 was significantly lower in cerebral malaria cases than in controls (0·67 ± 0·02 versus 0·77 ± 0·02, respectively, P = 0·009). Multiple linear regression analysis showed that, among cerebral malaria cases, there was a clear correlation between RNI and both IgE (P = 0·007) and sCD21 (P < 0·0001). Among controls, there was a strong negative correlation between RNI and sCD23 concentrations (r = −0·61, P < 0·0001). However, multivariate analysis unmasked the fact that, in controls, there was also a positive correlation between RNI and IgE (P = 0·045). Logistic regression showed that increased RNI concentrations were associated with a cerebral malaria adjusted odds ratio of 1·05 per unit increase [95% confidence interval (CI) 1·006–1·1, P = 0·02] and that an increased ratio between sCD21 and sCD23 was associated with protection from cerebral malaria (adjusted OR = 0·00001 per unit increase (95% CI 0–0·03, P = 0·005). These different immunological profiles suggest that, among controls, the CD23/NO pathway was chronically stimulated whereas, in cerebral malaria, its stimulation was acute, which could explain why some patients developed cerebral malaria and others did not.
Amino acids as taste stimuli for tsetse flies
Authors: VAN DER WYNAND M. , VAN NATERS GOES , DEN OTTER CORNELIS J.
Published: March 2003

Abstract.This paper reports the responses of taste cells on the legs of the blood‐feeding tsetse fly Glossina fuscipes fuscipes Newstead 1910 (Diptera: Glossinidae) to twenty protein amino acids and to their mixture as it is present in human sweat. It is investigated whether the mixture is sensed differently than the amino acids singly. The taste cells are most sensitive to phenylalanine (K≈ 1 μm) and tyrosine; and they respond in a lesser degree to methionine, valine, isoleucine, cysteine, tryptophan, histidine, alanine, and threonine. The amino acids serine, proline, asparagine, arginine, glutamine, lysine, aspartic acid, glutamic acid, and glycine give little or no response even at 10 mm. As the succession of effectiveness of the amino acids appears to be the same for all cells, it is deduced that the flies are unable to discriminate the amino acids by comparing responses across sensory cells. A temporal coding of quality does not seem feasible either. Thus, the properties of the taste cells limit the sense to assessing the intensity of an amino acid stimulus and not its identity. Although several parameters in the response adaptation curves are concentration‐dependent, it is suggested that the flies judge intensity of a stimulus only from the first 50 or so milliseconds. Although other studies and these indicate that a multiplicity of binding sites may be responsible for the reception of amino acids, the response to the mixture can be predicted from a no‐interaction model, whereby each ligand's access to the binding sites is proportional to its mole fraction. It is argued that this may be the case for more of the naturally occurring mixtures which comprise structurally similar ligands. The responses to the mixture and to phenylalanine alone are equally susceptible to inhibition by sodium chloride. It is suggested that, although discrimination of hosts probably requires another sense, the sense of taste is an excellent tool to detect a host underfoot during the local search for a feeding site.
Respiratory gas exchanges of termites from the Sabah (Borneo) assemblage
Authors: Jeeva D. , Bignell D. E. , Eggleton P. , Maryati M.
Published: March 2003

Abstract.Oxygen uptake and carbon dioxide release at 28°C were determined in worker castes of twenty‐six species of forest termites from the Danum Valley Conservation Area, south‐east Sabah, by Warburg manometry.

Metabolic rate varied inversely with body weight in a suite of soil‐, wood/soil‐ and wood‐feeding species, giving a slope (in a log–log plot) of – 0.63. However, a number of large species, actively foraging forms such as Macrotermes malaccensis, M. gilvus, Havilanditermes atripennis and Hospitalitermes hospitalis, but also the wood‐feeding Schedorhinotermes sarawakensis, showed an oxygen consumption greater than expected for their body weight. Rates of methane emission were above 0.100 μmol g–1 h–1 in seventeen species, with very high fluxes in two wood/soil‐feeders, Termes borneensis (0.546 ± 0.163 μmol g–1 h–1) and Prohamitermes mirabilis (0.303 ± 0.123 μmol g–1 h–1). Of the fifteen remaining species, seven were soil‐feeders, five were wood‐feeders, two were wood/litter‐feeders and a single species fed on lichen and moss. Low or negligible CH4 emissions (< 0.100 μmol g–1 h–1) were observed in three other species, all wood‐feeders.

An apparent respiratory quotient (RQapp) was calculated using xCO2 and xO2 (corrected for methane emission, but not hydrogen). Mean RQapp was at or above 1.00 in eleven species and between 0.95 and 1.00 in a further six species, the two sets of species together representing all trophic groups, including lichen‐feeders. This is argued to be consistent with carbohydrate being the principal substrate supporting respiration.
The effect of temperature on the photoperiodic ‘counters’ for female morph and sex determination in two clones of the black bean aphid, Aphis fabae
Authors: Nunes Marlies VaZ. , Hardie JiM.
Published: March 2003

Experiments were performed on two clones of the black bean aphid, Aphis fabae Scopoli – one from Aberdeen, Scotland (57°N), the other from Cambridge, England (52°N) − to determine the number of long‐ or short‐night cycles required for 50% induction of winged versus wingless females on the one hand and males versus females on the other (i.e. required day number, RDN), at three temperatures, 12.5, 15 and 17.5°C. In the case of female morph determination, the RDN for long‐night cycles was temperature compensated, whereas that for short‐night cycles was highly temperature dependent. For sex determination, the RDN for long‐night cycles was again temperature compensated, whereas, due to the mechanism of sex determination, male production was close to 100% in our protocol, even with a maximal number of short‐night cycles, and the RDN could therefore not be assessed. Model‐generated response curves, using the recently developed ‘double circadian oscillator model’ for photoperiodic time measurement in insects and mites, closely resembled the observations. It could also be shown that differences observed between response curves of female morph and sex determination in the Scottish clone were due, according to the model, to differences in their photoperiodic ‘counters’, rather than to differences in their clocks.
Reproductive development and ontogeny of queen pheromone production in the fire ant Solenopsis invicta
Authors: Vargo Edward L.
Published: March 2003

Queens of the fire ant, Solenopsis invicta Buren, produce several releaser and primer pheromones. Using bioassays, the ontogeny of three of these pheromones related to reproductive development was investigated. Virgin queens, in which the process of wing‐shedding (dealation) serves as an indicator of the initiation of reproductive development, were studied. First, the production of two queen pheromones produced in the poison gland was examined. The pheromone responsible for initiation and maintenance of retinue formation, a releaser effect, was found to be produced in detectable quantities 2 days after dealation, at which time queens showed significant ovary development and many (30%) had started laying eggs. A primer pheromone that inhibits alate virgin queens from dealating was detected in queens 3 days following wing‐shedding, when 80% of the queens were ovipositing. Second, I examined the onset of a pheromone of unknown glandular origin produced by reproductively active virgin queens which leads to their destruction in queenright colonies by stimulating workers to attack and kill them. This pheromone is secreted in quantities detectable by bioassay 2 days after dealation. Thus, in S. invicta, the ontogeny of three distinct queen pheromones is tightly linked with ovary development and initiation of egg laying. These results demonstrate reproductive and communicative functions are closely associated during the transition from potential to functional queen.
The dark‐colour‐inducing neurohormone of locusts in relation to an albino mutant of Schistocerca gregaria
Authors: Yerushalmi Yoram , Livshits Leonid , Pener Meir Paul
Published: March 2003

In the albino mutant of an Okinawa strain of Locusta migratoria (L.) (Orthoptera: Acrididae), albinism is caused by the absence of the dark‐colour‐inducing neurohormone (DCIN), which is present in the corpora cardiaca (CC) of normally coloured phenotypes. This study tests whether the absence of DCIN is responsible for albinism in an albino mutant of another locust, Schistocerca gregaria (Forsk.) (Orthoptera: Acrididae). This seemed feasible because a single Mendelian unit controls albinism in both species. However, implantation of CC, or injection of an extract of CC, from albino donors of S. gregaria, induce dark coloration in crowded nymph recipients of the Okinawa albino mutant of L. migratoria, as effectively as do implanted CC, or injections of extract of CC, from normal phenotype donors of S. gregaria. Therefore, DCIN is present in the albino mutant of S. gregaria, and consequently, the albinism in this mutant is not caused by its absence.

Implantation of CC, or injection of extracts of CC, from albino donors of S. gregaria to conspecific albino nymphs does not induce darkening. Only extremely high doses of synthetic DCIN injected into albino nymphs of S. gregaria are effective, inducing some darkening. The dose to induce such darkening in albino nymphs of S. gregaria is 50 nmol, ≈ 5 × 106 times higher than that (10 femtomol) needed to induce equivalent darkening in nymphs of the Okinawa albinos of L. migratoria. The results are discussed and some possible explanations of the observed effects outlined.
Measuring the heart rate of the spider, Aphonopelma hentzi: a non‐invasive technique
Authors: Coelho FlÁvio C. , Amaya Carlos C.
Published: March 2003

In this work we describe a non‐invasive and precise technique to record the heartbeats of a spider. A linear output Hall effect transducer in conjunction with a small magnet was used to monitor the micromovements on the dorsal surface of the abdomen of the tarantula Aphonopelma hentzi (Girard) (Theraphosidae). The exoskeleton in this region is in direct contact with suspensory ligaments connected to the heart, and the dorsal cuticle of the opisthosoma moves with each heartbeat. The technique allowed the discrimination of the different stages of the spider's cardiac cycle. The method can be also adapted for a smaller spider or other arthropods. We believe that the method proposed in this paper allows investigators to gain insights into a spider's natural heart rate by gathering unbiased data with a non‐invasive and very precise technique. We have found the resting heart rate of A. hentzi to be 5.6 ± 1.47 beats/min, which is lower than previously reported values.
The function of female accessory reproductive gland secretion and a cost to polyandry in the yellow dung fly
Authors: Hosken D. J. , Uhía E. , Ward P. I.
Published: March 2003

Abstract Female yellow dung flies have large paired accessory reproductive glands, the function of which remains unclear. However, gland contents are secreted during copula and egg laying. Other female flies produce a range of anti‐bacterial substances in their accessory reproductive glands that protect them and their eggs from pathogens, and it is possible that gland secretion acts similarly in yellow dung flies. A series of experiments was conducted to test this idea. Because the volume of secretion remaining in the glands is negatively related to copula duration, egg hatchability and longevity of females was compared in groups that copulated experimentally once or three times. A zone inhibition assay was used to see if gland extract inhibited bacterial growth. Egg number was positively associated with female body size, but the proportion of eggs hatching was not. Neither copula number nor duration influenced egg number or hatch number or proportion. In accordance with this, gland extract did not inhibit bacterial growth. However, female longevity was reduced in females that copulated with more males. This suggests that gland secretion does not serve to protect eggs, but as with a number of taxa, copula is costly to female yellow dung flies.
Allatotropic and allatostatic activities in extracts of brain and the effects of Manduca sexta allatotropin and Manduca sexta allatostatin on juvenile hormone synthesis in vitro by corpora allata from the Eri silkworm, Samia cynthia ricini
Authors: Li Sheng , Jiang Rong‐Jing , Cao Mei‐Xun
Published: March 2003

Both allatotropic and allatostatic activities were found in crude extracts of brain from adult and larval Eri silkworm, Samia cynthia ricini, but it seems that allatotropic activity dominates in each stage. There was a high level of allatotropic activity in the crude extract of brain from newly emerged female adults, but allatostatic activity appeared in the bioassay when excessive amounts of crude extracts of brain were added. Crude extracts of brain from premoulting fourth‐instar larvae and from newly ecdysed fifth‐instar larvae exhibited allatotropic activities, whereas extracts of brain from the second and third day of the fifth‐instar larvae inhibited juvenile hormone (JH) release slightly. Allatotropic activity from the brains of adults and larvae stimulated both adult and larval corpora allata (CA) to synthesize JH. Manduca sexta allatotropin (AT) (Mas‐AT) and M. sexta allatostatin (AST) (Mas‐AST) also stimulated and inhibited both adult and larval S. cynthia ricini CA to synthesize JH, respectively. Higher concentrations of Mas‐AT (10−4 or 10−3 M) showed an inhibitory effect on adult CA. CA from newly emerged female adults were the most sensitive to inhibition by Mas‐AST, whereas CA from female pharate adults at about 6 h before adult emergence were the most sensitive to stimulation by Mas‐AT and S. cynthia ricini brain allatotropic activity. An extract of brain and Mas‐AT induced some of the non‐active female pharate adult CA at 12 h before emergence to synthesize a small amount of JH.
Photosynthetic acclimation to elevated CO2 is modified by source:sink balance in three component species of chalk grassland swards grown in a free air carbon dioxide enrichment (FACE) experiment
Authors: Bryant J. , Taylor G. , Frehner M.
Published: March 2003

Artificial chalk grassland swards were exposed to either ambient air or air enriched to 600 μmol mol–1 CO2, using free‐air CO2 enrichment technology, and subjected to an 8 week simulated grazing regime. After 14 months of treatment, ribulose‐1,5‐bisphosphate carboxylase (Rubisco) activity (Vc,max) and electron transport mediated ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity (Jmax), estimated from leaf gas exchange, were significantly lower in fully expanded leaves of Anthyllis vulneraria L. (a legume) and Sanguisorba minor Scop. grown in elevated CO2. After a change in source:sink balance brought about by defoliation, photosynthetic capacity was fully restored in A. vulneraria and S. minor, but acclimation continued in the grass Bromopsis erecta (Hudson) Fourr. Changes in net photosynthesis (Pn) with growth at elevated CO2 ranged from a 1·6% reduction in precut leaves of A. vulneraria to a 47·1% stimulation in postcut leaves of S. minor. Stomatal acclimation was observed in leaves of A. vulneraria (reduced stomatal density) and B. erecta (reduced stomatal conductance). The results are discussed in terms of whole‐plant resource‐use optimization and chalk grassland community competitive interactions at elevated CO2.
Dissecting the roles of osmolyte accumulation during stress
Authors: Hare P. D. , Cress W. A. , Van Staden J.
Published: March 2003

Many plants accumulate organic osmolytes in response to the imposition of environmental stresses that cause cellular dehydration. Although an adaptive role for these compounds in mediating osmotic adjustment and protecting subcellular structure has become a central dogma in stress physiology, the evidence in favour of this hypothesis is largely correlative. Transgenic plants engineered to accumulate proline, mannitol, fructans, trehalose, glycine betaine or ononitol exhibit marginal improvements in salt and/or drought tolerance. While these studies do not dismiss causative relationships between osmolyte levels and stress tolerance, the absolute osmolyte concentrations in these plants are unlikely to mediate osmotic adjustment. Metabolic benefits of osmolyte accumulation may augment the classically accepted roles of these compounds. In re‐assessing the functional significance of compatible solute accumulation, it is suggested that proline and glycine betaine synthesis may buffer cellular redox potential. Disturbances in hexose sensing in transgenic plants engineered to produce trehalose, fructans or mannitol may be an important contributory factor to the stress‐tolerant phenotypes observed. Associated effects on photoassimilate allocation between root and shoot tissues may also be involved. Whether or not osmolyte transport between subcellular compartments or different organs represents a bottleneck that limits stress tolerance at the whole‐plant level is presently unclear. None the less, if osmolyte metabolism impinges on hexose or redox signalling, then it may be important in long‐range signal transmission throughout the plant.
Mycorrhizal sink strength influences whole plant carbon balance of Trifolium repens L.
Authors: Wright D. P. , Read D. J. , Scholes J. D.
Published: March 2003

A comparative analysis of daily carbon (C) budgets and aspects of the C physiology of clover (Trifolium repens L.) colonized by vesicular‐arbuscular (VA) mycorrhizal fungi was carried out over a 70 d growth period under conditions designed to ensure that shoots of mycorrhizal (M) and non‐mycorrhizal (NM) plants were of similar nutrient status. C budgets did not differ on day 24 but by day 42 M plants had a significantly higher rate of photosynthesis than their NM counterparts when expressed on a whole shoot basis or unit dry weight basis. As both sets of plants were of the same size it was concluded that this greater C gain was the result of increased sink strength provided by the mycorrhizal fungus. By day 53 M plants had become larger than their uncolonized counterparts and a sink‐induced stimulation in the rate of photosynthesis was no longer apparent. M plants had higher root sucrose, glucose and fructose pools from day 24. Analyses suggested that these sugars were utilized for trehalose and lipid synthesis, for the production of the large extramatrical mycelium and for the support of the respiratory demands of the M root system. Increased C allocation to roots of M plants was associated with a stimulation of the activities of cell wall and cytoplasmic invertases and of sucrose synthase in roots colonized by VA fungi. Such increases in enzyme activity may provide the mechanism enabling increased partitioning of carbohydrate both to the M root system and the fungal symbiont.
Importance of leaf versus whole plant CO2 environment for photosynthetic acclimation
Authors: Sims D. A. , Luo Y. , Seemann J. R.
Published: March 2003

The reduction of photosynthetic capacity in many plants grown at elevated CO2 is thought to result from a feedback effect of leaf carbohydrates on gene expression. Carbohydrate feedback at elevated CO2 could result from limitations on carbohydrate utilization at many different points, for example export of triose phosphates from the chloroplast, sucrose synthesis and phloem loading, transport in the phloem, unloading of the phloem at the sinks, or utilization for growth of sinks. To determine the relative importance of leaf versus whole plant level limitations on carbohydrate utilization at elevated CO2, and the possible effects on the regulation of photosynthetic capacity, we constructed a treatment system in which we could expose single, attached, soybean leaflets to CO2 concentrations different from those experienced by the rest of the plant. The single leaflet treatments had dramatic effects on the carbohydrate contents of the treated leaflets. However, photosynthetic capacity and rubisco content were unaffected by the individual leaflet treatment and instead were related to the whole plant CO2 environment, despite the fact that the CO2 environment around the rest of the plant had no significant affect on the total non‐structural carbohydrate (TNC) contents of the treated leaflets. These results necessitate a re‐evaluation of the response mechanisms to CO2 as well as some of the methods used to test these responses. We propose mechanisms by which sink strength could influence leaf physiology independently of changes in carbohydrate accumulation.
Rapid changes in xanthophyll cycle‐dependent energy dissipation and photosystem II efficiency in two vines, Stephania japonica and Smilax australis, growing in the understory of an open Eucalyptus forest
Authors: ADAMS III W. W. , DEMMIG‐ADAMS B. , LOGAN B. A. , BARKER D. H. , OSMOND C. B.
Published: March 2003

Leaves of Stephania japonica and Smilax australis were characterized in situ on the coast of north‐eastern New South Wales, Australia, where they were growing naturally in three different light environments: deep shade, in the understory of an open Eucalyptus forest where they received frequent sunflecks of high intensity, and in an exposed site receiving full sunlight. In deep shade the xanthophyll cycle remained epoxidized during the day and the vast majority of absorbed light was utilized for photosynthesis. In the exposed site both deepoxidation and epoxidation of the xanthophyll cycle and changes in the level of xanthophyll‐dependent thermal energy dissipation largely tracked the diurnal changes in photon flux density (PFD). In the understory the xanthophyll cycle became largely deepoxidized to zeaxanthin and antheraxanthin upon exposure of the leaves to the first high intensity sunfleck and this high level of deepoxidation was maintained throughout the day both during and between subsequent sunflecks. In contrast, thermal energy dissipation activity, and the efficiency of photosystem II, fluctuated rapidly in response to the changes in incident PFD. These findings suggest a fine level of control over the engagement of zeaxanthin and antheraxanthin in energy dissipation activity, presumably through rapid changes in thylakoid acidification, such that they became rapidly engaged for photoprotection during the sunflecks and rapidly disengaged upon return to low light when continued engagement might limit carbon gain.
C‐S lyase activities in leaves of crucifers and non‐crucifers, and the characterization of three classes of C‐S lyase activities from oilseed rape (Brassica napus L.)
Authors: KIDDLE G. A. , BENNETT R. N. , HICK A. J. , WALLSGROVE R. M.
Published: March 2003

C‐S lyases in plants are involved in primary and secondary metabolism, and in glucosinolate‐containing species may be involved in glucosinolate biosynthesis. Extracts from oilseed rape (Brassica napus) leaves were assayed for several C‐S lyase activities. Four activities [using L‐cystine, L‐cystathionine, S‐(2‐benzothiazolyl)‐L‐Cys (SBC) and S‐benzyl‐L‐Cys] were investigated in detail. All are developmentally regulated (highest in youngest leaves), and differentially inhibited by iodoacetamide, N‐ethylmaleimide (NEM) and ethylenediaminetetraacetic acid (EDTA). Thermal stabilities and pH optima were also distinct. Competitive inhibition of the SBC lyase activity with a variety of sulphur‐containing compounds indicated that cystine lyase contributes to SBC degradation, and this enzyme may cleave a wide range of compounds, both aliphatic and aromatic, but other ‘SBC lyases’ were also present. Putative aromatic glucosinolate intermediates were cleaved by the rape enzymes. Developmental and biochemical studies indicate that at least three classes of C‐S lyase activity are present in rape leaves: cystathionine β‐lyase, cystine lyase and a group of relatively non‐specific lyases. C‐S lyase preparations from other glucosinolate‐ and non‐glucosinolate‐containing species were capable of cleaving a number of aliphatic and aromatic conjugates. The highest activities were detected in glucosinolate‐containing species and Allium cepa (onion). C‐S lyase activities in non‐glucosinolate‐containing species (tobacco, Nicotiana tabacum, and barley, Hordeum vulgare) were much lower.
Ultrastructural characterization of maize (Zea mays L.) kernels exposed to high temperature during endosperm cell division
Authors: COMMURI P. D. , JONES R. J.
Published: March 2003

This study reports the ultrastructural changes in maize endosperm that result from exposure to high temperature during cell division. Kernels were grown in vitro at 25 ºC continuously (control) and at 5 d after pollination (DAP) subsamples were transferred to continuous 35 ºC for either 4 or 6 d. The 4 d treatment reduced kernel mass by 40% and increased kernel abortion three‐fold. The 6‐d high‐temperature treatment resulted in a 77% reduction in kernel mass and a 12‐fold increase in kernel abortion. Evaluation of the kernels at 11 DAP using scanning and transmission electron microscopy revealed that the reduced kernel mass and/or abortion was associated with the disruption of cell division and amyloplast biogenesis in the periphery of the endosperm. This was further confirmed by the presence of an irregular‐shaped nucleus, altered size of the nucleolus, highly dense nucleoplasm, and a decrease in the number of proplastids and amyloplasts. Thus, the endosperm cavity was not filled, the total number of endosperm cells was reduced by 35 and 70%, and the number of starch granules was decreased by 45 and 80% after exposure to 4 and 6 d of high‐temperature treatments, respectively. This also resulted in a 35–70% reduction in total starch accumulation. KI/I2 staining and light microscopy revealed that starch accumulation in the peripheral endosperm cells was reduced more severely than in the central zones. However, the scanning electron micrographs of cells from the central endosperm showed that the number and the size of apparently viable amyloplasts were reduced and isolated granules were smaller and/or showed enhanced pitting. These ultrastructural data support the hypothesis that high temperature during endosperm cell division reduces kernel sink potential and subsequently mature kernel mass, mainly by disrupting cell division and amyloplast biogenesis in the peripheral and central endosperm.
A comparative study of fluxes and compartmentation of nitrate and ammonium in early‐successional tree species
Authors: Min X. , Yaeesh Siddiqi M. , Guy R. D. , Glass A. D. M. , Kronzucker H. J.
Published: March 2003

13NO3– and 13NH4+ compartmental analyses were carried out in seedling roots of trembling aspen (Populus tremuloides Michx.), lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and interior Douglas‐fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) at 0·1 and 1·5 mol m–3 external NO3– or NH4+ concentrations ([NO3–]o or [NH4+]o, respectively). At the lower [NO3–]o, the capacities and efficiencies of acquisition and accumulation of NO3–, based upon NO3– fluxes and cytoplasmic NO3– concentrations ([NO3–]c), were in the order aspen >> Douglas‐fir > pine. At 1·5 mol m–3[NO3–]o, the NO3– influx increased 18‐fold in pine, four‐fold in Douglas‐fir and approximately 1·4‐fold in aspen; in fact, at 1·5 mol m–3[NO3–]o, the NO3– influx in pine was higher than in aspen. However, at high [NO3–]o, efflux also increased in the two conifers to a much greater extent than in aspen. In aspen, at both [NO3–]o, approximately 30% of the 13N absorbed was translocated to the shoot during 57 min of 13N loading and elution, compared with less than 10% in the conifers. At 0·1 mol m–3[NH4+]o, influx and net flux were in the order: aspen > pine > Douglas‐fir but the differences were much less than in NO3– fluxes. At 1·5 mol m–3[NH4+]o, NH4+ influx, efflux and [NH4+]c greatly increased in aspen and Douglas‐fir and, to a much lesser extent, in pine. In aspen, 29 and 12% of the 13N absorbed was translocated to the shoot at 0·1 and 1·5 mol m–3[NH4+]o, respectively, compared with 5 to 7% in the conifers at either [NH4+]o. These patterns of nitrogen (N) uptake, particularly in the case of NO3–, and the observed concentration responses of NO3– uptake, reflect the availability of N in the ecological niches, to which these species are adapted.
Significance of antioxidants and electron sinks for the cold‐hardening‐induced resistance of winter rye leaves to photo‐oxidative stress
Authors: Streb P , Feierabend J.
Published: March 2003

The contents of ascorbate and glutathione and the activities of superoxide dismutase and glutathione reductase were increased to levels as high as those in cold‐hardened leaves (CHL) by incubating non‐hardened leaves (NHL) of winter rye (Secale cereale L.) with the precursor substrates
L‐galactonic acid‐γ‐lactone and 2‐oxothiazolidine‐4‐carboxylate. Reduced glutathione was rapidly depleted from NHL after application of
D,
L‐buthionine sulfoximine, an inhibitor of its biosynthesis. In spite of greatly divergent antioxidant contents the rates of photo‐inactivation of photosystem II (PSII) and catalase observed in the presence of translation inhibitors did not differ greatly. The paraquat‐induced catalase inactivation and chlorophyll degradation in light were reduced in NHL with increased antioxidant levels. Paraquat‐induced photo‐inactivation of PSII was, however, not mitigated. The CHL had a higher capacity to prevent paraquat‐induced oxidation of ascorbate and glutathione than NHL with increased antioxidant contents. Increased antioxidant contents did not establish resistance to low temperature‐induced photo‐inactivation of PSII and catalase in NHL. The resistance of CHL to low temperature‐induced photo‐inactivation of PSII and catalase required repair at low temperature and active carbon assimilation but was only little affected when photorespiration was suppressed by phosphinothricin. Protection of PSII depended also on non‐photochemical quenching of excitation energy.
The isolation of wall‐bound proteins regulating yield threshold tension in glycerinated hollow cylinders of cowpea hypocotyl
Authors: Okamoto‐Nakazato A. , Nakamura T. , Okamoto H.
Published: March 2003

To isolate and purify the factor regulating the yield threshold tension (y) through acidification of the cell wall, proteins were extracted from hypocotyls of Vigna unguiculata L. Their effects on the pH‐dependencies of the wall extensibility (φ) and y were examined with reconstitution experiments by incorporating them into the heat‐denatured glycerinated hollow cylinders (GHCs). The wall mechanical properties of the reconstituted GHCs were determined using stress–strain experiments. Only the proteins extracted with 1 kmol m–3 of NaCl from the wall of elongation region restored the pH‐dependencies of φ and y once extinguished with heat‐denaturation, but proteins extracted from the other cell constituents or from the mature region of hypocotyl affect neither properties. Fractionation of the wall‐bound proteins by a hydrophobic column chromatography showed that the two different fractions affected φ or y independently. The sodium dodecyl sulphate‐polyacrylamide gel electrophoresis showed that the active fraction which restored the pH‐dependency of y still consists of two proteins of 30 and 32 kDa after purification by the sequential fractionation with cation‐exchange and gel filtration. These two proteins were named as ‘yieldin 30’ and ‘32’. Western blotting analysis using the rabbit‐antiserum against the cucumber expansin indicated that the yieldins are independent of cucumber expansin.
Molecular cloning of yieldins regulating the yield threshold of cowpea cell walls: cDNA cloning and characterization of recombinant yieldin
Authors: Okamoto‐Nakazato A. , Takahashi K. , Kido N. , Owaribe K. , Katou K.
Published: March 2003

cDNA for yieldin of Vigna unguiculata L. was cloned with reverse transcriptase‐polymerase chain reaction using synthetic oligonucleotides as primers. The primers were designed on the basis of the N‐terminal amino acid sequence of the yieldins isolated from the wall preparation of cowpea hypocotyls. The 1·2 kbp cDNA for yieldin contained an open reading frame of 981 base pairs, encoding 327 amino acids including 23 amino acids as a putative signal sequence. An homology search of the deduced amino acid sequence revealed that the yieldin was homologous to acidic class III endochitinases (EC 3·2.1·14) and concanavalin B. A cDNA fragment containing the yieldin‐coding region was introduced to Escherichia coli cells using an expression vector to express the recombinant protein. The recombinant yieldin was obtained from the recombinant E. coli and its effect on the wall mechanical properties was examined by reconstitution experiments. The recombinant yieldin fully restored the acid‐induced change of the yield threshold tension (y) of heat denatured glycerinated hollow cylinders (GHCs) of cowpea hypocotyls. Northern hybridization analysis revealed that the yieldin mRNA was expressed mainly in the rapid and moderate elongation region of the etiolated hypocotyl of Vigna unguiculata L.
Induction of 1‐aminocyclopropane‐1‐carboxylate oxidase mRNA by ethylene in mung bean roots: possible involvement of Ca2+ and phosphoinositides in ethylene signalling
Authors: Jung T. , Lee J. H. , Cho M. H. , Kim W. T.
Published: March 2003

Ethylene markedly induces an increase in the mRNA level of 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase, the final step of its biosynthetic pathway, in mung bean roots. To investigate the second messengers that possibly participate in ethylene signalling various pharmacological reagents known to affect the cytosolic calcium level and phosphoinositide (PI) metabolism were applied to mung bean roots, and then the induction pattern of ACC oxidase (VR‐ACO1) by ethylene was monitored as a molecular paradigm for ethylene‐dependent responses in this tissue. The ethylene‐induced VR‐ACO1 gene expression was effectively inhibited by ruthenium red, a putative inhibitor of intracellular Ca2+ fluxes, and to a lesser extent by ethyleneglycotetraacetic acid, a calcium chelator and GdCl3, the plasma membrane calcium‐channel inhibitor. However, LaCl3 and verapamil, another type of plasma membrane calcium‐channel blockers, did not prevent the ethylene action. The calmodulin antagonist W‐7 significantly reduced the hormone‐dependent expression of VR‐ACO1. Treatment with neomycin or Li+, the antagonists of PI metabolism, almost completely blocked the ethylene‐induced accumulation of VR‐ACO1 transcript in a dose‐dependent manner, whereas the addition of exogenous Ca2+ along with antagonists effectively restored the ethylene‐induced VR‐ACO1 gene activation. The results showed that the ACC oxidase enzyme activities and protein levels were in parallel with the abundance of transcript in response to various antagonists and exogenous Ca2+. These results are discussed in light of suggestion that the PI‐derived second messenger and cytosolic calcium are necessarily involved in the ethylene‐induced ACC oxidase gene activation in mung bean root tissue.
Expression and activity of isoenzymes of superoxide dismutase in wheat roots in response to hypoxia and anoxia
Authors: Biemelt S. , Keetman U. , Mock H.‐P. , Grimm B.
Published: March 2003

We investigated the effects of hypoxia, anoxia and reaeration on enzymatic activity and expression of superoxide dismutase (SOD) isoforms in wheat roots (Triticum aestivum L.). Neither hypoxia nor subsequent re‐aeration caused significant changes in SOD isoenzyme pattern compared with aerated controls. However, anoxia led to the appearance of additional activity bands of SOD in native gels resulting in an increase in total activity. Additional isoformic bands remained also apparent in the following recovery period. Re‐aeration following both hypoxia and anoxia resulted in an increased content of hydrogen peroxide in roots. SOD transcript and protein levels were only slightly altered in response to hypoxia. Although SOD mRNA levels were diminished, protein content of different SOD isoforms increased with duration of anoxia. Incubation of roots with cycloheximide revealed that the additional activity bands and higher SOD protein content under anoxia were not due to de novo synthesis. Crude subcellular fractionation experiments implied that the anoxia‐responsive SOD isoforms might be plastid‐associated. We suggest that SOD is a very stable enzyme which, under anoxia, accumulates relative to total protein content and remains active even after protein modification under severe environmental stress conditions.
A comparative kinetic analysis of nitrate and ammonium influx in two early‐successional tree species of temperate and boreal forest ecosystems
Authors: Min Xiangjia , Siddiqi M. Yaeesh , Guy Robert D. , Glass Anthony D. M. , Kronzucker Herbert J.
Published: March 2003

Root NO3− and NH4+ influx systems of two early‐successional species of temperate (trembling aspen: Populus tremuloides Michx.) and boreal (lodgepole pine: Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forest ecosystems were characterized. NO3− and NH4+ influxes were biphasic, consisting of saturable high‐affinity (HATS) and constitutive non‐saturable low‐affinity transport systems (LATS) that were evident at low and relatively high N concentrations, respectively. NO3− influx via HATS was inducible (IHATS); nitrate pre‐treatment resulted in 8–10‐fold increases in the Vmax for influx in both species. By contrast, HATS for NH4+ were entirely constitutive. In both species, Vmax values for NH4+ influx were higher than those for NO3− uptake; the differences were larger in pine (6‐fold) than aspen (1·8‐fold). In aspen, the Km for NH4+ influx by HATS was approximately 3‐fold higher than for IHATS NO3− influx, while in pine the Km for IHATS NO3− influx was approximately 3‐fold higher than for NH4+ influx. The aspen IHATS for NO3− influx appeared to be more efficient than that of pine (Vmax values for aspen being approximately 10‐fold higher and Km values being approximately 13‐fold lower than for pine). By contrast, only small differences in values for the NH4+ HATS were evident between the two species. The kinetic parameters observed here probably result from adaptations to the N availabilities in their respective natural habitats; these may contribute to the distribution and niche separation of these species.
Photosynthesis, immediate export and carbon partitioning in source leaves of C3, C3‐C4 intermediate, and C4Panicum and Flaveria species at ambient and elevated CO2 levels
Authors: Leonardos E. D. , Grodzinski B.
Published: March 2003

Immediate export in leaves of C3‐C4 intermediates were compared with their C3 and C4 relatives within the Panicum and Flaveria genera. At 35 Pa CO2, photosynthesis and export were highest in C4 species in each genera. Within the Panicum, photosynthesis and export in ‘type I’ C3‐C4 intermediates were greater than those in C3 species. However, ‘type I’ C3‐C4 intermediates exported a similar proportion of newly fixed 14C as did C4 species. Within the Flaveria, ‘type II’ C3‐C4 intermediate species had the lowest export rather than the C3 species. At ambient CO2, immediate export was strongly correlated with photosynthesis. However, at 90 Pa CO2, when photosynthesis and immediate export increased in all C3 and C3‐C4 intermediate species, proportionally less C was exported in all photosynthetic types than that at ambient CO2. All species accumulated starch and sugars at both CO2 levels. There was no correlation between immediate export and the pattern of 14C‐labelling into sugars and starch among the photosynthetic types within each genus. However, during CO2 enrichment, C4Panicum species accumulated sugars above the level of sugars and starch normally made at ambient CO2, whereas the C4Flaveria species accumulated only additional starch.
Ionic and osmotic components of salt stress specifically modulate net ion fluxes from bean leaf mesophyll
Authors: Shabala S.
Published: March 2003

Ionic mechanisms of salt stress perception were investigated by non‐invasive measurements of net H+, K+, Ca2+, Na+, and Cl− fluxes from leaf mesophyll of broad bean (Vicia faba L.) plants using vibrating ion‐selective microelectrodes (the MIFE technique). Treatment with 90 m
M NaCl led to a significant increase in the net K+ efflux and enhanced activity of the plasma membrane H+‐pump. Both these events were effectively prevented by high (10 m
M) Ca2+ concentrations in the bath. At the same time, no significant difference in the net Na+ flux has been found between low‐ and high‐calcium treatments. It is likely that plasma membrane K+ and H+ transporters, but not the VIC channels, play the key role in the amelioration of negative salt effects by Ca2+ in the bean mesophyll. Experiments with isotonic mannitol application showed that cell ionic responses to hyperosmotic treatment are highly stress‐specific. The most striking difference in response was shown by K+ fluxes, which varied from an increased net K+ efflux (NaCl treatment) to a net K+ influx (mannitol treatment). It is concluded that different ionic mechanisms are involved in the perception of the ‘ionic’ and ‘osmotic’ components of salt stress.
Seasonal changes in hydraulic conductance, xylem embolism and leaf area in Eucalyptus tetrodonta and Eucalyptus miniata saplings in a north Australian savanna
Authors: Prior L. D. , Eamus D.
Published: March 2003

Eucalypt saplings in north Australian savannas commonly die back, sometimes to ground level, during the 5 months of the long dry season. Water potentials are lower in saplings than large trees during the dry season, and we hypothesized that low water potentials may lead to high levels of xylem embolism and consequent death of branches and whole shoots. As the dry season progressed, hydraulic conductance of terminal branches decreased by 50% in Eucalyptus tetrodonta but not in Eucalyptus miniata saplings. Hydraulic conductance per leaf area decreased seasonally by 34% in E. tetrodonta branches. These decreases may be associated with the loss of leaves recorded from E. tetrodonta but not E. miniata branches. We modelled the effect of sequential loss of parallel resistors, representing petioles on a branch. This showed there is a non‐linear decrease in flow as basal resistors are lost, which can lead to a decrease in mean flow per resistor due to increased mean path‐length. Thus the observed loss of basal leaves, together with xylem embolism, probably contributed to the seasonal loss of hydraulic conductance in E. tetrodonta saplings. Loss of hydraulic conductance due to xylem embolism was generally low (< 15%) in both species, and the seasonal increase in embolism could not fully account for the decline in hydraulic conductance of E. tetrodonta branches. There was little evidence that branch and shoot death was caused by these levels of embolism. Developing an embolism vulnerability curve for species with long vessels is problematic and this issue is discussed.
Reciprocal diurnal changes of phosphoenolpyruvate carboxylase expression and cytosolic pyruvate kinase, citrate synthase and NADP‐isocitrate dehydrogenase expression regulate organic acid metabolism during nitrate assimilation in tobacco leaves
Authors: Scheible W.‐R. , Krapp A. , Stitt M.
Published: March 2003

Diurnal changes of transcript levels for key enzymes in nitrate and organic acid metabolism and the accompanying changes of enzyme activities and metabolite levels were investigated in nitrogen‐sufficient wild‐type tobacco, in transfomants with decreased expression of nitrate reductase, and in nitrate‐deficient wild‐type tobacco. (i) In nitrogen‐sufficient wild‐type plants, transcript levels for nitrate reductase (NR, EC 1.6.6.1), nitrite reductase (NIR, EC 1.7.7.1) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were high at the end of the night and decreased markedly during the light period. The levels of these three transcripts were increased and the diurnal changes were damped in genotypes with decreased expression of nitrate reductase. The levels of these transcripts were very low in nitrate‐limited wild‐type plants, except for a small rise after irrigation with 0·2 mM nitrate. (ii) The levels of the transcripts for cytosolic pyruvate kinase (PK, EC 2.7.1.40), mitochondrial citrate synthase (CS, EC 4.1.3.7) and NADP‐isocitrate dehydrogenase (NADP‐ICDH, EC 1.1.1.42) were highest at the end of the light period and beginning of the night. These three transcripts increase and the diurnal changes were damped in genotypes with decreased expression of NR. (iii) The diurnal changes of transcript levels were accompanied by changes in the activities of the encoded enzymes. The activities of NR and PEPC were highest in the early part of the light period, whereas the activities of PK and NADP‐ICDH were highest later in the light period and during the first part of the night and CS activity was highest at the end of the night. Activity of PEPC, PK, CS and NADP‐ICDH increased and the diurnal changes were damped in genotypes with low expression of NR. Activity of all four enzymes decreased in nitrate‐limited wild‐type plants. (iv) In the light, malate accumulated, citrate decreased, and about 30% of the assimilated nitrate accumulated temporarily as glutamine, ammonium, glycine and serine. These changes were reversed during the night. (v) It is proposed that the diurnal changes of expression facilitate preferential synthesis of malate to act as a counter‐anion for pH regulation during the first part of the light period when NR activity is high, and preferential synthesis of 2‐oxoglutarate to act as a nitrogen acceptor later in the day when large amounts of nitrogen have accumulated in ammonium, glutamine and other amino acids including glycine in the photorespiration pathway, and NR activity has been decreased.