bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasmodium falciparum malaria blood stage parasites preferentially inhibit macrophages with high phagocytic activity
Authors: LEITNER WOLFGANG W. , KRZYCH URSZULA
Published: November 2003

Exposure to malaria blood stage antigens results in several defects of macrophages/monocytes one of which is an irreversible reduction of phagocytic activity. In the present study we analysed phagocytic activity of subpopulations of human monocyte‐derived‐macrophages (MDM) based on the capacity of individual cells to ingest FITC‐labelled microbeads. The results demonstrate that malaria infection affected predominantly MDM subpopulations with high level of phagocytosis. This population decreased during parasitaemia, however, during recovery from the infection the highly phagocytic cells replaced the damaged cells. The exposure of MDM cultures to blood stage antigens showed that the highly active macrophages from persons with active malaria infection decreased further, while the population increased during recovery. Furthermore, we observed that while ingestion of a few parasitized RBC (3 schizonts) stimulated phagocytosis, larger amounts or longer exposure periods eventually paralysed the entire phagocytic system. Accordingly, by selectively blocking actively phagocytizing macrophages, the malaria parasite prevents both specific and non‐specific immune responses, which are initiated by macrophages as phagocytes and professional antigen presenting cells.
A comparison of mucosal inflammatory responses to Giardia muris in resistant B10 and susceptible BALB/c mice
Authors: ENKATESAN P. , FINCH R.G. , WAKELIN D.
Published: November 2003

In the first three weeks of primary Giardia muris infections B10 mice clear infection more rapidly than BALB/c mice. There is evidence that interferon‐γ contributes to the relative resistance of B10 mice. The nature of the functional contribution of interferon‐γ is unclear and does not relate to the secretory or serum antibody response. Mucosal inflammatory events in these strains have been studied. Apart from a small rise in both strains of goblet cell and mucosal mast cell numbers, associated with release of mast cell protease‐1 in serum, no inflammatory infiltrate was observed at the time trophozoites were cleared from the intestinal lumen. Inhibition of mast cell products (5‐hydroxytryptamine and histamine) by cyproheptadine enhanced the intensity of infection in both strains. The relative resistance of B10 mice could not be explained in terms of the mucosal inflammatory response.
Recognition of Schistosoma mansoni Cathepsins B and L by human IgG1 and IgG4 antibodies
Authors: GROGAN JANE , ROTMANS PETER , GHONEIM HOSSAM , DEELDER ANDRÉ , YAZDANBAKHSH MARIA , KLINKERT MO‐QUEN
Published: November 2003

Human schistosome infections are chronic in nature and elevated IgG4 levels are associated with length of exposure. To examine how structure, localization and dynamics of exposure of a protein to the immune system can affect antibody isotype expression, specific antibody levels against two Schistosoma mansoni recombinant cathepsin molecules were determined in S. mansoni‐infected individuals. Cathepsin B (rCatB, secreted in the gut) and cathepsin L (rCatL, localized in the reproductive structures) were used to determine IgG1 reactivity, as a measure of the stimulation of the immune response, and the switch to IgG4 as an indicator of the dynamics and rate of presentation to the immune system. Sera from three groups of S. mansoni‐infected patients were used: individuals with life‐long exposure in an endemic area in Burundi, a group from a recent endemic focus in Senegal, and of acutely infected European travellers. We report for the first time the ability of rCatL to trigger an immune response and show distinct antibody isotype reactivity between rCatB versus rCatL. Patients harbouring long‐term chronic infections had elevated levels of IgG4 to both antigen, whereas individuals infected for less than four years had high IgG4 to rCatB but not to rCatL. Acutely infected travellers developed IgG1 to rCatB only. Our results demonstrate that an immune response is mounted more rapidly against a cathepsin molecule secreted in the gut of the worm than against an internally localized cathepsin.
Vaccination against Haemonchus contortus with denatured forms of the protective antigen H11
Authors: MUNN EDWARD A. , SMITH TREVOR S. , SMITH HOWARD , JAMES FIONA M. , SMITH FIONA C. , ANDREWS STUART J.
Published: November 2003

As part of a systematic examination of the protective epitopes on H11, groups of sheep were vaccinated with preparations of purified H11 used untreated (group A), or progressively denatured (linearized) by incubation with sodium dodecyl sulphate (SDS) (group B) or by boiling with SDS in the presence of dithiothreitol (group C). All the sheep developed antibodies which bound to the untreated H11. When challenged with 10 000 infective larvae of Haemonchus contortus the mean levels of protection relative to the mean values for adjuvant controls were 99.8%, 85% and 79% for faecal egg counts and 95%, 79% and 54% for worm burden at post‐mortem for groups A, B and C respectively. The H11‐specific antibodies inhibited the microsomal aminopeptidase activity of H11 in vitro up to 80%. The levels of inhibition by sera from individual animals correlated with levels of protection with r2, of 0.69–0.87.
Sensitivity of Entamoeba histolytica and Entamoeba dispar patient isolates to human complement
Authors: WALDERICH BRIGITTE , WEBER ANNE , KNOBLOCH JÜRGEN
Published: November 2003

Twenty‐one Entamoeba histolytica and 56 Entamoeba dispar patient isolates were investigated for their sensitivity to the classical and alternative pathway of human complement. E. histolytica and E. dispar patient isolates were differentiated by polymerase chain reaction and hexokinase isoenzyme typing. It was found that 90.3% (±12.0%) of the trophozoites of E. histolytica were lysed after 30 min by the alternative pathway of complement in the presence of 50% human serum (19 isolates showed lysis rates higher than 80%), whereas E. dispar cells were less susceptible to the alternative pathway as 68.8% (±28.2%) of lysis occurred. However, 23 of the E. dispar isolates were lysed between 100 and 80% (90.9%±9.1%), demonstrating that about half of the tested E. dispar isolates were highly sensitive to complement lysis. Only 11 of the E. dispar isolates were proven to be ‘resistant’ to the alternative pathway of complement and were lysed less than 40%. These results are in conflict to earlier publications, describing resistance of E. dispar to complement lysis (Hamelmann et al. 1992, 1993).
Immune response to the filaria Litomosoides sigmodontis in susceptible and resistant mice
Authors: MARÉCHAL P. , LE GOFF L. , HOFFMAN W. , RAPP J. , OSWALD I.P. , OMBROUCK C. , TAYLOR D.W. , BAIN O. , PETIT G.
Published: November 2003

Comparisons were made between the immune responses evoked during the course of chronic and patent infections of Litomosoides sigmodontis in susceptible BALB/c mice and non‐patent infections in resistant B10.D2 mice. Early antigen specific responses of spleen cells were weak in both mouse strains. However, by day 58 post infection a strong Th2 response, as determined by production of IL‐4, IL‐5 and IL‐10, was observed in BALB/c mice but not in B10.D2 mice. Antibody responses seemed to appear sooner in B10.D2 than in BALB/c mice, and these differentially recognised two antigens of 15 kD and 80 kD.
Zinc deficiency and energy restriction modify immune responses in mice during both primary and challenge infection with Heligmosomoides polygyrus (Nematoda)
Authors: SHI HAI NING , KOSKI KRISTINE G. , STEVENSON MARY M. , SCOTT MARILYN E.
Published: November 2003

This study characterized the consequences of zinc‐sufficient (Zn+, 60 mg zinc/kg diet, ad libitum), zinc‐deficient (Zn−, 0.75 mg zinc/kg diet, ad libitum) and energy‐restricted (ER, 60 mg zinc/kg diet which was restricted to match food intake of Zn− mice) diets on the in vivo and in vitro immune response of BALB/c mice during both primary and challenge infection with Heligmosomoides polygyrus. In Zn+ mice, both primary and challenge infection with H. polygyrus induced not only a strong Th2 response (IgE, IgG1, eosinophilia, IL‐4, IL‐5, IL‐10), but also elements of a Th1 response (IgG3, IFN‐γ). Zinc deficiency significantly depressed Th2‐dependent antibody production during both primary and challenge infection, and reduced mitogen and antigen‐induced T cell proliferation during the challenge infection. Th2 cytokine production was reduced by zinc deficiency (IL‐4), energy restriction (IL‐5) and by zinc deficiency possibly in combination with energy restriction (IL‐10) during the primary infection whereas Th1 cytokine production (IFN‐γ) was depressed during the challenge infection by zinc deficiency, possibly together with energy restriction. Both zinc deficiency and energy restriction reduced eosinophilia with the more profound effect being exerted by zinc deficiency. Thus, both zinc deficiency and its concurrent energy restriction modify immune responses in the mice during primary and challenge infection with H. polygyrus.
Phytochrome degradation
Authors: CLOUGH R. C. , VIERSTRA R. D.
Published: November 2003

Plants actively modulate the levels of the various phyto‐chrome isoforms during their life cycle to optimize light absorption and perception. For phytochrome A (phyA), one of the most influential methods of control is selective turnover of the photoreceptor upon photoconversion from the red‐absorbing form (Pr) to the far‐red‐absorbing form (Pfr). Whereas the Pr form has a half‐life of approximately 1 week, the Pfr form is rapidly degraded with a half‐life of 1–2 h. The ubiquitin/26S proteasome pathway has been implicated in phyA breakdown. In this proteolytic pathway, multiple ubiquitins are covalently attached to proteins committed for degradation; these ubiquitin‐protein conjugates then serve as intermediates in the breakdown of the target protein by the 26S proteasome, a multi‐subunit proteolytic complex. In several plant species, ubiquitin‐phyA conjugates have been detected in vivo following Pfr formation that show accumulation and decay kinetics expected for Pfr degradation intermediates. Analyses of phyA mutants and phyA/phyB chimeras expressed in transgenic plants have been particularly useful in mapping domains within the chromoprotein that are necessary for Pfr degradation. Several domains have been identified within both the N‐ and C‐terminal portions of the photoreceptor that presumably serve as recognition and/or acceptor sites for ubiquitination
An emerging molecular map of the phytochromes
Authors: QUAIL P. H.
Published: November 2003

Molecular mapping studies and sequence comparisons are providing provocative new insights into regions of the phytochrome polypeptide important to the functional activities of the photoreceptor. The NH2‐terminal structural domain contains the determinants for photoperception, and for the differences in photosensory specificity and photolability between phyA and phyB. However, a contiguous COOH‐terminal domain is also required for the transfer of perceived informational signals downstream to transduction pathway components and for PfrA‐specific degradation to proceed. The COOH‐terminal domains of phyA and phyB are functionally interchangeable in these processes and a core sequence at the proximal end of this domain contains determinants necessary for signal transfer from both phyA and phyB, suggesting a common biochemical mechanism of signal transfer for the two photoreceptors. Striking sequence similarity between the NH2‐terminal domain of aSynechocystisprotein, ORF SLR0473, and the phytochromes indicates that the cyanobacteria contain phytochrome‐related photoreceptors. The COOH‐terminal domains of ORF SLR0473 and the phytochromes are also related to one another and both show sequence similarities to the sensor histidine kinases. These data raise the possibility that the cyanobacteria have a functional photoregulated histidine kinase signalling system and that the plant phytochromes represent remnants of that system.
Photoreceptors and signals in the photoperiodic control of development
Authors: JACKSON S. , THOMAS B.
Published: November 2003

Many plant species are sensitive to changes in the seasons, especially with regard to their reproductive behaviour. Sexual or vegetative reproductive structures are often only formed at times of the year when days are sufficiently long, or short. Plants perceive daylength in the leaves, but reproductive changes occur in shoot apices in response to the movement of signals throughout the plant. There is good evidence that phytochrome A is an essential component of the daylength‐sensing mechanism in long‐day plants, and preliminary evidence suggests a potential interaction between phytochrome C and daylength sensitivity in short‐day plants. The sensitivity of reproductive processes to photoperiodic control is directly altered by photoreceptor action, particularly in the case of phytochrome B, which has a major influence on whether flowering or tuberization occurs under non‐inductive conditions in both long‐ and short‐day plants, but is not involved in daylength measurement. The signals which move from leaves to the sites of reproductive development are not known, but there is good evidence that gibberellins may be important and some preliminary indication that brassinosteroids might also be involved in photoperiodic signalling.
The function of phytochrome A
Authors: CASAL J. J. , SANCHEZ R. A. , YANOVSKY M. J.
Published: November 2003

Knowledge of the photoperceptive function of phytochrome A has improved substantially thanks to the availability of mutants lacking phytochrome A and transgenic plants transformed with the PHYA gene in sense or anti‐sense orientation. In imbibed seeds, phytochrome A mediates very‐low‐fluence responses. In etiolated seedlings, phytochrome A mediates very‐low‐fluence responses, high‐irradiance responses under continuous far‐red light, responsivity amplification to phytochrome B and red‐light enhancement of the phototropic response to blue light. In light‐grown seedings, phytochrome A modulates the extent of response to reductions in red/far‐red ratio perceived by phytochrome B, perceives daylength extensions and night interruptions affecting flowering, and perceives light treatments resetting endogenous rhythms. Under natural radiation these abilities are manifested during seed germination and seedling de‐etiolation under dense canopies or extremely low light fluences, and during early neighbour detection, but other processes await experimental evaluation. Phytochrome A affects growth and development throughout the whole life cycle of angiosperms.
Cryptogam phytochromes
Authors: WADA M. , KANEGAE T. , NOZUE K. , FUKUDA S.
Published: November 2003

Phytochrome responses in cryptogams are well characterized. However, the properties of cryptogam phytochromes are not well understood, because of the difficulty in obtaining suitable material. Recent advances in molecular biology offer the possibility of studying cryptogam phytochromes at the molecular level. The functional domains in cryptogam phytochromes have been predicted from the homology of the deduced amino acid sequences to known sequences of different functional proteins. Cryptogam phytochrome gene families are highly variable in size and composition. The most structurally unusual cryptogam phytochrome, found in the moss Ceratodon and the fern Adiantum, has a protein kinase catalytic domain in the C‐terminal half, although the N‐terminal half is homologous to conventional phytochromes. In conventional phytochrome, modules homologous to the bacterial two‐component (transmitter) protein kinase have also been found in the C‐terminal ends. While phytochromes lack membrane‐spanning sequences, some types may have microtubule attachment sequences. The relationship of these to dichroic phytochrome is discussed. Phytochrome mRNA and proteins are also discussed, as well as the use of mutants in elucidating signal transduction pathways.
Transpiration does not control growth and nutrient supply in the amphibious plant Mentha aquatica
Authors: PEDERSEN O. , SAND‐JENSEN K.
Published: November 2003

Mentha aquatica L. was grown at different nutrient availabilities in water and in air at 60% RH. The plants were kept at 600 mmol m−3 free CO2 dissolved in water (40 times air equilibrium) and at 30 mmol m−3 CO2 in air to ensure CO2 saturation of growth in both environments. We quantified the transpiration‐independent water transport from root to shoot in submerged plants relative to the transpiration stream in emergent plants and tested the importance of transpiration in sustaining nutrient flux and shoot growth. The acropetal water flow was substantial in submerged Mentha aquatica, reaching 14% of the transpiration stream in emergent plants. The transpiration‐independent mass flow of water from the roots, measured by means of tritiated water, was diverted to leaves and adventitious shoots in active growth. The plants grew well and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in fertile sediments. Restricted O2 supply to the roots of submerged plants may account for the smaller nutrient concentrations, though these exceeded the levels required to saturate growth. In hydroponics, the root medium was aerated and circulated between submerged and emergent plants to minimize differences in medium chemistry, and here the two growth forms behaved similarly and could fully exploit nutrient enrichment. It is concluded that the lack of transpiration from leaf surfaces in a vapour‐saturated atmosphere, or under water, is not likely to constrain the transfer of nutrients from root to shoot in herbaceous plants. Nutrient deficiency under these environmental conditions is more likely to derive from restricted development and function of the roots in waterlogged anoxic soils or from low porewater concentrations of nutrients.
Floral transition mutants in Arabidopsis
Authors: KOORNNEEF M. , PEETERS A. J. M.
Published: November 2003

An inventory of genetic differences in flowering time in Arabidopsis is presented and discussed. Many genes influence the transition to flowering in a quantitative way. Two groups of mutants and natural variants can be distinguished: those that are responsive to environmental factors and those that are less responsive or unresponsive. It is possible that all late/early‐flowering mutants isolated to date carry a mutation with an effect, either promotive or repressive, on a floral repressor. The interaction between light perception and flowering has been studied by analysis of phytochrome‐ and cryptochrome‐deficient mutants, which showed that phyA and probably also cryptochrome have a promotive role in flowering, whereas phyB and other stable phytochromes have an inhibitory role. A circadian rhythm is important in establishing daylength sensitivity, as was shown by the phenotype of the elf 3 mutants.
Phytochrome A, phytochrome B and other phytochrome(s) regulate ATHB‐2 gene expression in etiolated and green Arabidopsis plants
Authors: STEINDLER C. , CARABELLI M. , BORELLO U. , MORELLI G. , RUBERTI I.
Published: November 2003

The expression of the Arabidopsis ATHB‐2 gene is light‐regulated both in seedlings and in adult plants. The gene is expressed at high levels in rapidly elongating etiolated seedlings and is down‐regulated by a pulse of red light (R) through the action of a phytochrome other than phytochrome A or B, or by a pulse of far‐red light (FR) through the action of phytochrome A. In green plants, the expression of the ATHB‐2 gene is rapidly and strongly enhanced by lowering the R:FR ratio perceived by a phytochrome other than A or B. Returning the plant to a high R:FR ratio results in an equally rapid decrease of the ATHB‐2 mRNA. Consistently, plants overproducing ATHB‐2 show developmental phenotypes characteristic of plants grown in low R:FR: elongated petioles, reduced leaf area, early flowering, and reduced number of rosette leaves. Taken together, the data strongly suggest a direct involvement of ATHB‐2 in light‐regulated growth phenomena throughout Arabidopsis development.
A spatially explicit model of patchy stomatal responses to humidity
Authors: HAEFNER J. W. , BUCKLEY T. N. , MOTT K. A.
Published: November 2003

Stomata of leaves can exhibit either temporally stable, spatially homogeneous behaviour or complex spatial and temporal dynamics, depending on environmental and physiological conditions. To test the ability of accepted physiological mechanisms to describe these patterns, we developed a simple, spatially explicit model of stomatal responses to humidity that incorporated hydraulic interactions among stomata. Model results showed qualitative agreement with experimental evidence for a number of phenomena: (1) at high humidities, whole‐leaf steady‐state conductance is a monotonic function of humidity; (2) the initial stomatal response following a perturbation in humidity is in the direction opposite to the final response, and (3) spatial dynamics include patch formation and self‐organization similar to that observed in actual leaves. These comparisons do not eliminate other explanations, but do suggest that novel mechanisms need not be invoked to explain the diversity of spatial and temporal patterns of stomatal behaviour in leaves.
Salinity resistance and plant growth revisited
Authors: NEUMANN P.
Published: November 2003

This article reconsiders a recent hypothesis concerning the physiology of growth inhibition by salinity and its relevance to the breeding of salt‐resistant crops (Munns 1993, Plant, Cell and Environment 16, pp. 15–24). The hypothesis states that the osmotic effects of salinity on water availability will strongly and equally inhibit the growth of related species and varieties. The genotypic diversity needed for breeding increased resistance to growth inhibition by salinity is only expected to appear after weeks or months. Higher rates of salt accumulation in more sensitive varieties then lead to accelerated leaf senescence. This further inhibits new growth, as compared with more resistant varieties. Accordingly, breeders aiming to increase crop growth under salinity should focus efforts on manipulating genes which can decrease rates of salt accumulation. However, the osmotic inhibition of growth by salinity appears to involve regulatory physiogical changes. Thus, some genotypic diversity might be expected. Clear evidence is presented for genotypic diversity in early growth responses to salt or PEG‐induced osmotic stress, in several species and varieties. The conclusion is that development of plants with increased resistance to inhibition of growth by the osmotic effects of external salinity (in addition to increased resistance to salt accumulation) is both feasible and desirable.
The apparent feedforward response of stomata to air vapour pressure deficit: information revealed by different experimental procedures with two rainforest trees
Authors: FRANKS P. J. , COWAN I. R. , FARQUHAR G. D.
Published: November 2003

A decrease in steady‐state leaf transpiration rate with increased vapour pressure difference between leaf and air, which is reversible and independent of leaf water status, is evidence for feedforward control of stomatal aperture (Cowan 1977). A recent survey of gas exchange data by Monteith (1995), covering 52 sets of measurements on 16 species, reported that evidence for feedforward control was rare and usually reliant on a single point. We conducted gas exchange experiments on an additional 13 species and observed an apparent feedforward response in only two. However, the response was not reversible and depended upon experimental procedure. In view of this we discuss the appropriate use of the term ‘feedforward’.
Growth and water use of the mangroves Rhizophora apiculata and R. stylosa in response to salinity and humidity under ambient and elevated concentrations of atmospheric CO2
Authors: BALL M. C. , COCHRANE M. J. , RAWSON H. M.
Published: November 2003

Two mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m−3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO2 concentration (340 and 700 cm3 m−3). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt‐tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients.
Sodium and potassium transport to the xylem are inherited independently in rice, and the mechanism of sodium: potassium selectivity differs between rice and wheat
Authors: GARCIA A. , RIZZO C.A. , UD‐DIN J. , BARTOS S.L. , SENADHIRA D. , FLOWERS T.J. , YEO A.R.
Published: November 2003

The heritability of sodium and potassium transport to the xylem was measured by the regression of Fn+1, on Fn means in two segregating breeding populations of rice (Oryza sativa L.). The narrow‐sense heritabilities of shoot sodium concentration were 0.42 and 0.43 in the two populations, respectively, and the corresponding values for the heritability of shoot potassium concentration were 0.46 and 0.52. The sodium: potassium ratio was apparently heritable (0.36 and 0.40) because it was regressed positively on sodium concentration and negatively on potassium concentration. There was no significant relationship between the shoot sodium and potassium concentrations themselves. It is concluded that sodium and potassium uptake in rice are controlled by different genes which segregate independently. The magnitude of the transpirational bypass flow was estimated to be some 10 times greater in rice than in wheat (Triticum aestivum L.) and was found to be highly correlated with sodium uptake in rice but not in wheat. It is concluded that the bypass flow provides an additional pathway for sodium uptake in rice and that this accounts for the functional and genetic independence of sodium and potassium uptake in rice and consequently for the lesser prominence of potassium:sodium discrimination in rice than in wheat.
Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought
Authors: BALDOCCHI D.
Published: November 2003

Forests in the south‐eastern United States experienced a prolonged dry spell and above‐normal temperatures during the 1995 growing season. During this episode, nearly continuous, eddy covariance measurements of carbon dioxide and water vapour fluxes were acquired over a temperate, hardwood forest. These data are used to examine how environmental factors and accumulating soil moisture deficits affected the diurnal pattern and magnitude of canopy‐scale carbon dioxide and water vapour fluxes. The field data are also used to test an integrative leaf‐to‐canopy scaling model (CANOAK), which uses micrometeorological and physiological theory, to calculate mass and energy fluxes. When soil moisture was ample in the spring, peak rates of net ecosystem CO2 exchange (NF) occurred around midday and exceeded 20 μmol m−2 s−1. Rates of NK were near optimal when air temperature ranged between 22 and 25°C. The accumulation of soil moisture deficits and a co‐occurrence of high temperatures caused peak rates of daytime carbon dioxide uptake to occur earlier in the morning. High air temperatures and soil moisture deficits were also correlated with a dramatic reduction in the magnitude of NE. On average, the magnitude of NE decreased from 20 to 7 μmol m−2 s−1 as air temperature increased from 24 to 30°C and the soil dried. The CANAOK model yielded accurate estimates of canopy‐scale carbon dioxide and water vapour fluxes when the forest had an ample supply of soil moisture. During the drought and heat spell, a cumulative drought index was needed to adjust the proportionality constant of the stomatal conductance model to yield accurate estimates of canopy CO2 exchange. The adoption of the drought index also enabled the CANOAK model to give improved estimates of evaporation until midday. On the other hand, the scheme failed to yield accurate estimates of evaporation during the afternoon.
Apparent responses of stomata to transpiration and humidity in a hybrid poplar canopy
Authors: MEINZER F. C. , HINCKLEY T. M. , CEULEMANS R.
Published: November 2003

It has been proposed that the stomatal response to humidity relies on sensing of the transpiration rate itself rather than relative humidity or the saturation deficit per se. We used independent measurements of stomatal conductance (gs), transpiration (E), and leaf‐to‐air vapour pressure difference (V) in a hybrid poplar canopy to evaluate relationships between gs and E and between gs and V. Relationships between E, V and total vapour phase conductance or crown conductance (gc) were also assessed. Conductance measurements were made on exposed and partially shaded branches over a wide range of incident solar radiation. In exposed branches, gs appeared to decline linearly with increasing E and increasing V at both high and low irradiance. However, in a partially shaded branch, a bimodal relationship between gs and E was observed in which gs continued to decrease after E had reached a maximum value and begun to decrease. The relationship between gs and V for this branch was linear. Plots of gc against E always yielded bimodal or somewhat variable relationships, whereas plots of gc against V were invariably linear. It was not possible to derive a unique relationship between conductance and E or V because prevailing radiation partially determined the operating range for conductance. Normalization of data by radiation served to linearize responses observed within the same day or type of day, but even after normalization, data collected on partly cloudy days could not be used to predict stomatal behaviour on clear days and vice versa. An additional unidentified factor was thus also involved in determining operating ranges of conductance on days with different overall radiation regimes. We suggest that the simplest mechanism to account for the observed humidity responses is stomatal sensing of the epidermal or cuticular transpiration rate rather than the bulk leaf or stomatal transpiration rate.
Sink‐stimulated photosynthesis and sink‐dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa–Ricinus communis
Authors: JESCHKE W. D. , HILPERT A.
Published: November 2003

Ricinus communis L. was grown under limiting N supply in quartz sand culture, fed with 0.2, 1 or 5 mol m−3 NO3−, or in liquid culture with 0.022, 0.05 or 0.5 mol m−3 NO3−. Some of the plants were infected with Cuscuta reflexa Roxb. As occurred for the host, dry matter production and growth of C. reflexa were severely depressed with decreasing N supply to the host. When parasitized by C. reflexa, the shoot and root dry weight of Ricinus was diminished at all levels of N nutrition, but the total dry weight of host plus parasite was almost the same as that of uninfected Ricinus. In contrast to the situation in Lupinus albus (Jeschke et al. 1994b), infection by Cuscuta resulted in increased tissue N levels in the host and the N content of the system Ricinus plus C. reflexa was the same or even somewhat larger than that of uninfected plants. This indicated a sink‐dependent stimulation of nitrate uptake. As a result of decreased root weights, nitrate uptake g−1 FW was stimulated by 80, 60 or only 40% at 0.2, 1 or 5 mol m−3 nitrate supply. Increased nitrate uptake was reflected, particularly at low N supply, in xylem transport; xylem sap nitrate concentrations were substantially elevated, while those of amino acids were decreased in parasitized plants. This indicated an inhibition of nitrate assimilation in roots of parasitized plants under limiting N supply. Besides these effects on N relations, C. reflexa induced a substantial sink‐dependent stimulation of net photosynthesis in host leaves and a concomitant increase in stomatal opening and transpiration. This stimulation depended on the relative sink size induced by Cuscuta, on nitrogen nutrition and on leaf age, indicating that delayed senescence of leaves contributes to the overall effects of Cuscuta on its host. The Cuscuta‐induced inhibition of nitrate assimilation in the roots and the increase in nitrate uptake suggest that nitrate reduction was shifted towards the leaves in the presence of C. reflexa. The stimulating effects of C. reflexa in the Ricinus‐Cuscuta association are compared with the strongly inhibitory effects occurring in the tripartite association L. albus–Rhizobium–Cuscuta reflexa.
Waterlogging and fire impacts on nitrogen availability and utilization in a subtropical wet heathland (wallum)
Authors: SCHMIDT S. , STEWART G.R.
Published: November 2003

Protein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90‐ and 60‐fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate. During waterlogging soil amino acids increased, particularly γ‐aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non‐mycorrhizal wallum species were significantly (P < 0.05) 15N‐enriched (0.3–4.3‰) compared to species with mycorrhizal associations (ericoid‐type, ecto‐, va‐mycorrhizal) which were strongly depleted in 15N (‐6.3 to ‐1.8‰). Lignotubers and roots had δ15N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto‐, ecto/va‐, and ericoid type mycorrhizal species which were enriched in 15N (0.1–2.4‰). The 515N signatures of δ15Ntotal soil N and δ15Nsoil NH4+ were in the range 3.7–4.5‰, whereas δ15Nsoil NO3− was significantly (P < 0.05) more enriched in 15N (9.2–9.8‰). It is proposed that there is discrimination against 15N during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium.
NaCl homoeostasis as a factor for the survival of the evergreen halophyte Armeria maritima (Mill.) Willd. under salt stress in winter
Authors: KÖHL K. I.
Published: November 2003

The combination of NaCl and low temperature stress makes winter a critical time for evergreen halophytes at temperate latitudes. As part of a study of ecotypic differentiation of the evergreen Armeria maritima (Mill.) Willd., inland and salt‐marsh populations were compared with respect to their growth and survival, osmotic adjustment and NaCl concentrations (based on dry weight) under salt stress in pot experiments in winter. Increased leaf necrosis in all populations under salt stress indicated a higher NaCl sensitivity in winter than in summer. Plants from inland populations were more sensitive than salt‐marsh populations. Inland and salt‐marsh populations showed similar capacities for seasonal osmotic adjustment, high seasonal increase of praline concentration and long‐term betaine accumulation. Inland and salt‐marsh populations allocated Na and Cl preferentially to the shoot. In inland populations, Na and Cl accumulated to high concentrations in leaves, whereas the much lower NaCl concentration in salt‐marsh populations suggested that in these plants, Na uptake was regulated to match the growth‐dependent ion demand of the shoot. The prevention of NaCl accumulation in times of slow growth by a NaCl homoeostasis system seemed to be an important adaptation with respect to the survival of evergreen plants in salt marshes.
Seasonal water use characteristics of tall wheatgrass [Agropyron elongatum (Host) Beauv.] in a saline environment
Authors: BLEBY T. M. , AUCOTE M. , KENNETT‐SMITH A. K. , WALKER G. R. , SCHACHTMAN D. P.
Published: November 2003

It is essential to characterize the water use of plants that have potential for the stabilization of rising saline ground‐water which could lead to increases in soil salinity. In this study, several techniques were used to determine the seasonal water use characteristics of the perennial grass Agropyron elongatum (tall wheatgrass) growing in a moderately saline, dryland environment with a fluctuating shallow groundwater table varying in electrical conductivity between 0 and 10 dS m−1. Soil conditions were examined in terms of water potential measurements, plant water sources were identified using a stable isotope of water (deuterium, 2H) and evapotranspiration was estimated using hydrological and ventilated chamber methods. Seasonal changes in soil water potential were caused by salt accumulation and soil moisture leading to changes in plant water availability, particularly in the surface soil region over summer and autumn. Evapotranspiration in A. elongatum was high over summer during the peak period of growth (4 mm d−1), with evidence of water use from groundwater and from specific regions of the soil profile. Evapotranspiration was low during the period that A. elongatum was partially senescent in autumn (< 0.5 mm d−1) and the lowest leaf water potential of ‐3 MPa that was measured occurred during this period of moderate water stress. Intermediate levels of water use (1.5 mm d−1) were measured during winter when the entire soil profile was available for water uptake. Based on physiological characteristics, including aspects of summer water use, root morphology and salt tolerance in A. elongatum, we conclude that this species is suitable for stabilizing the level of moderately saline groundwater in parts of southern Australia, which could reduce the potential for soil salinization.
Does transpiration control stomatal responses to water vapour pressure deficit?
Authors: BUNCE J. A.
Published: November 2003

Three types of observations were used to test the hypothesis that the response of stomatal conductance to a change in vapour pressure deficit is controlled by whole‐leaf transpiration rate or by feedback from leaf water potential. Varying the leaf water potential of a measured leaf by controlling the transpiration rate of other leaves on the plant did not affect the response of stomatal conductance to vapour pressure deficit in Glycine max. In three species, stomatal sensitivity to vapour pressure deficit was eliminated when measurements were made at near‐zero carbon dioxide concentrations, despite the much higher transpiration rates of leaves at low carbon dioxide. In Abutilon theophrasti, increasing vapour pressure deficit sometimes resulted in both decreased stomatal conductance and a lower transpiration rate even though the response of assimilation rate to the calculated substomatal carbon dioxide concentration indicated that there was no ‘patchy’ stomatal closure at high vapour pressure deficit in this case. These results are not consistent with stomatal closure at high vapour pressure deficit caused by increased whole‐leaf transpiration rate or by lower leaf water potential. The lack of response of conductance to vapour pressure deficit in carbon dioxide‐free air suggests that abscisic acid may mediate the response.
Chlorophyll a fluorescence, enzyme and antioxidant analyses provide evidence for the operation of alternative electron sinks during leaf senescence in a stay‐green mutant of Festuca pratensis
Authors: KINGSTON‐SMITH A. H. , THOMAS H. , FOYER C. H.
Published: November 2003

Mutation of the sid gene in Festuca pratensis prevents chlorophyll degradation. The senescing leaves retain their chlorophyll complement and stay green. Nevertheless, CO2 assimilation and ribulose‐bisphosphate carboxylase/oxygenase content decline in both mutant and wild‐type plants. Photosynthesis and chlorophyll a fluorescence measurements were performed in air and at low oxygen to prevent photorespiration. The maximum extractable activity of ribulose 1,5 bisphosphate carboxylase was higher in the senescent mutant leaves than in those of the wild‐type control hut Mas much lower than that observed in the mature leaves of either genotype. The activation state of this enzyme was similar in mutant and wild‐type lines at equivalent stages of development. Analysis of chlorophyll a fluorescence quenching with varying irradianco showed similar characteristics for mature leaves of the two genotypes. Genotypic variations in photosystem II (I'SII) efficiency were observed only in the senescent leaves. Photochemical quenching and the quantum efficiency of PSII were greater in the senescent mutant leaves than in (he wild type at a given irradiance. The calculated electron flux through PSII was substantially higher in the mutant with a greater proportion of electrons directed to photorespiration.

Maximum catalytic activities of ascorbate peroxidase decreased in senescent compared to mature leaves of both genotypes, while glutathione reductase and monodehydroascorbate reductase were unchanged in both cases. Superoxide dismutase activity was approximately doubled and dehydroascorbate reductase activity was three times higher in senescent leaves compared with the mature leaves of both genotypes. In no case was there a difference in enzyme activities between mutant and wild type at equivalent growth stages. The pool of reduced ascorbate was similar in the mature leaves of the two genotypes, whereas it was significantly higher in the senescent leaves of the mutant compared with the wild type. Conversely, the hydrogen peroxide content was significantly higher in the mature leaves of the wild type than in those of the mutant, but in senescent leaves similar values were obtained. In leaves subjected to chilling stress the reduced ascorbate pool was higher in both mature and senescent leaves of the mutant than in their wild‐type counterparts. Similarly, the hydrogen peroxide pool was significantly lower in both mature and senescent leaves of the mutant than in the wild type. We conclude that, in spite of deceased CO2 assimilation, the mutant is capable of high rates of electron Slow. The high ascorbate/hydrogen peroxide ratio observed in the mutant, particularly at low temperatures, suggests that the senescent leaves are not subject to enhanced oxidative stress.
Mutational analysis of chilling tolerance in plants
Authors: TOKUHISA J. G. , FELDMANN K. A. , LaBRIE S. T. , BROWSE J.
Published: November 2003

A mutational approach was taken to identify genes required for low‐temperature growth of the chilling‐tolerant plant Arabidopsis thaliana. The screen identified mutants that were specifically compromised in their ability to grow at 5°C but were indistinguishable from wild type when grown at 22°C. The populations screened were mutated either by ethyl methanesulphonate or by T‐DNA insertion. In both cases symptoms at 5°C included chlorosis, reduced growth, necrosis and death. This diversity of phenotypes demonstrates roles for chilling‐tolerance responses in such diverse processes as organdie biogenesis, cell metabolism and cell and organ development. Co‐segregation analysis on the first five mutants isolated from the T‐DNA lines indicated that in three of them, pfc1, pfc2 and sop1, the chilling phenotype is the result of T‐DNA insertion in a gene required for chilling tolerance rather than the creation of a temperature‐conditional mutation in an essential housekeeping gene. This identification of T‐DNA tagged alleles will facilitate cloning of the PFC1, PFC2 and SOP1 loci and allow for the biochemical and molecular genetic characterization of these chilling‐tolerance genes and the proteins that they encode.
Expression of XET‐related genes and its relation to elongation in leaves of barley (Hordeum vulgare L.)
Authors: SCHÜNMANN P. H. D. , SMITH R. C. , LÅNG V. , MATTHEWS P. R. , CHANDLER P. M.
Published: November 2003

Five cDNA clones were isolated from barley (Hordeum vulgare L.) that encoded mRNAs related to xyloglucan endotransglycosylase (XET). One of the clones encoded a protein with XET activity in vitro. Sequence comparisons revealed five families of XET‐related sequences, one of which (containing two of the barley genes) was novel. Hybridization studies using clone‐specific probes indicated that the corresponding genes were represented once, or possibly twice, in the barley genome. Treatment of dwarf mutants with gibberellic acid (GA3), or homozygosity at the ‘slender’ (sln1) locus, resulted in a 2.5‐fold (approximately) stimulation of blade elongation rate. Three of the five clones detected mRNAs that were maximally expressed towards the base of the blade, and present in greater quantities in GA3‐treated or slender seedlings. The remaining two clones detected mRNAs that were maximally expressed in the middle of the blade. Relative elemental growth rate (REGR) profiles of leaves growing with or without GA3 treatment revealed similar maximal REGR values despite a 2.5‐fold difference in leaf elongation rate. Segments of GA3‐treated leaves attained their maximal REGR values more rapidly, this being associated with enhanced expression of the three ‘basal’ XET‐related mRNAs. Highest XET activities were detected in the base of the elongation zone, and in GA3‐treated seedlings a second activity peak was observed near the distal end of the elongation zone. We conclude that there are likely to be several XET isoenzymes with different expression patterns, and identify those XET‐related proteins potentially involved in leaf elongation.
Directed overexpression of PHYA locally suppresses stem elongation and leaf senescence responses to far‐red radiation
Authors: ROUSSEAUX M. C. , BALLARÉ C. L. , JORDAN E. T. , VIERSTRA R. D.
Published: November 2003

Ectopic overexpression of an oat PHYA cDNA in tobacco under the cauliflower mosaic virus 35S promoter results in plants with reduced morphological responses to far‐red radiation (FR). We have tested the hypothesis that it is possible to molecularly ‘mask’ steins and leaves to FR‐induced elongation and senescence responses by targeting the over‐expression of PHYA with appropriate promoters. Oat PHYA was expressed in tobacco (Nicotiana tabacum L. cv Xanthi) under the 35S and two Arabidopsis promoters: UBQ1 and CAB. The internodes of wild type, UBQ:PHYA, and CAB:PHYA plants, which exhibited little or no oat PHYA overexpression, responded to localized FR treatments with a marked increase in elongation. In contrast, 35S:PHYA plants, which overexpressed PHYA to high levels in all parts of the shoot, did not respond to FR treatments directed to their stems. Leaf senescence responses to FR were remarkably localized, and sensitivity to FR was also inversely correlated with the local PHYA expression level. Thus, chlorophyll content, specific leaf weight, and nitrate reductase activity in leaf spots treated with FR were highly reduced in wild type and UBQ:PHYA plants, but not in the CAB:PHYA and 35S:PHYA counterparts. Our results suggest that it may be feasible to obtain transgenic crop plants in which certain organs or tissues are made ‘blind’ to phytochrome‐perceived signals of canopy density, but whose general photomorphogenic competence is not greatly disturbed.