bluuebunny/crossref_metadata_2025 huggingface dataset:
Tobacco phytochromes: genes, structure and expression
Authors: ADAM E. , KOZMA‐BOGNAR L. , SCHAFER E. , NAGY F.
Published: November 2003

Photomorphogenesis in tobacco, like in other higher plant species, is regulated by at least three different types of photoreceptors, among which the best characterized is phytochrome. Three genes, designated Nt‐PHYA1, Nt‐PHYA2 and Nt‐PHYBl, have been isolated from the allotetraploid Nicotiana tabacum encoding phytochrome A (phyA)‐like and phytochrome B (phyB)‐like apoproteins, respectively. The deduced amino acid sequences of the encoded tobacco phyA and B proteins exhibit significant homology (>75%) to phyA and phyB proteins described in Arabidopsis and in other plant species including potato, tomato and pea. Expression patterns and levels of the tobacco PHYA‐ and PHYB‐like genes have been characterized in detail. Expression of the PHYB1 gene is regulated mainly, while that of the PHYA genes is regulated partially, at the level of transcription, which is initiated at multiple start sites and produces at least three different types of transcripts differing in length and abundance. Analysis of trans‐genic tobacco plants showed that expression patterns of the Nt‐PHYA/GUS and Nt‐PHYB/GUS transgenes exhibit well‐defined organ/tissue‐specific patterns. Transcription of the endogenous Nt‐PHYA genes as well as of the Nt‐PHYA/GUS transgenes is down‐regulated by light, and this regulation is mediated by phytochrome. Expression of the Nt‐PHYB gene is insensitive to light. Expression of several light‐induced tobacco genes is mediated by phytochrome and further modulated by a circadian clock. Although phytochrome plays a significant role in synchronizing/setting this endogenous oscillator, transcription of the Nt‐PHYA and Nt‐PHYB genes is not regulated by the circadian rhythm in developing tobacco seedlings. In the absence of well‐characterized mutants, the precise biological function of tobacco phyA and phyB molecules, in contrast to the phyA and phyB proteins in Arabidopsis, is not yet understood.
Patterns of leaf surface wetness for montane and subalpine plants
Authors: BREWER C. A. , SMITH W. K.
Published: November 2003

The frequency and duration of water on leaf surfaces have important consequences for plant growth and photosynthetic gas exchange. The objective of the present study was to compare the frequency and duration of leaf wetness under natural field conditions among species and to identify variation in structural features of leaves that may reduce surface wetness. During June–September 1992 in the central Rocky Mountains (USA), natural leaf wetting due to rain and dewfall was observed on 79 of 89 nights in open meadow habitats compared to only 29 of 89 nights in the understorey. Dew formation occurred at relative humidities that were often well below 100% because of radiational heat exchange with cold night skies and low wind speeds (< 0.5 m s−1). A survey of 50 subalpine/montane species showed that structural characteristics associated with the occurrence and duration of leaf surface wetness differed among species and habitats. Both adaxial and abaxial surfaces accumulated moisture during rain and dewfall events. Leaf surfaces of open‐meadow species were less wettable (P= 0.008), and had lower droplet retention (P= 0.015) and more stomata P= 0.017) than adjacent understorey species. Also, leaf trichomes reduced the area of leaf surface covered by moisture. Ecophysiological importance is suggested by the high frequency of leaf wetting events in open microsites, influences on growth and gas exchange, and correspondence between leaf surface wettability and habitat.
Elevated CO2 stimulates cells to divide in grass meristems: a differential effect in two natural populations of Dactylis glomerata
Authors: KINSMAN E. A. , LEWIS C. , DAVIES M. S. , YOUNG J. E. , FRANCIS D. , VILHAR B. , OUGHAM H. J.
Published: November 2003

In this study, we tested the hypothesis that elevated [CO2] shortens the cell cycle in meristems of Dactylis glomerata, more in a Portuguese population (38°53′N) than in a Swedish population (63°09′N). In the shoot meristem, the cell cycle shortened to about the same extent (∼ 26%) in both populations exposed to the elevated [CO2] treatment. In the root meristem, the cell cycle shortened by 17% in the Portuguese and by 8% in the Swedish population. However, the proportion of rapidly cycling cells increased in the Portuguese much more than in the Swedish population in both meristems. In the root meristem, there was a 1.86‐fold increase in the Portuguese compared with a 1.31‐fold increase in the Swedish. In the shoot meristem, the increases were 1.5–3‐fold for the Portuguese and 1.2‐fold for the Swedish. The data are consistent in showing that a major response to the elevated [CO2] treatment was an increase in the proportion of cells that were cycling and that this was more marked for the Portuguese population. A more general response to the elevated [CO2] treatment was a shortening of the cell cycle regardless of population.
Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes
Authors: POLLE A. , EIBLMEIER M. , SHEPPARD L. , MURRAY M.
Published: November 2003

To study whether responses of antioxidative enzymes to enhanced atmospheric CO2 concentrations are affected by plant nutrition, the activities of superoxide dismutase, catalase and peroxidase were investigated in leaves of 3‐year‐old beech trees grown with low (0.1 × optimum), intermediate (0.5 × optimum) and high (2 × optimum) nutrient supply rates in open‐top chambers at either ambient (∼ 355 μmol mol−1) or elevated (700 μmol mol−1) CO2 concentrations. These treatments resulted in foliar C/N ratios of about 20 in the presence of high and > 30 in the presence of low nutrient supply rates. Pigment and malon‐dialdehyde contents were determined to assess plant stress levels. Low nutrient supply rates caused pigment loss, whereas elevated CO2 had no effect on pigmentation. Guaiacol peroxidase activities did not respond to either CO2 or nutrient treatment. Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO2. Superoxidase dismutase activity was affected by both nutrient supply and CO2 concentration. In leaves from trees grown with the high‐nutrient treatment, superoxide dismutase activity was low irrespective of CO2 concentration. In chlorotic leaves, superoxide dismutase activity was increased, suggesting an enhanced need for detoxification of reactive oxygen species. Leaves from plants grown under elevated CO2 with medium nutrient supply rates showed decreased malondialdehyde contents and superoxide dismutase activities. This suggests that the intrinsic oxidative stress of leaves was decreased under these conditions. These results imply that intrinsic oxidative stress is modulated by the balance between N and C assimilation.
The influence of (photo)respiration on carbon isotope discrimination in plants
Authors: GILLON J.S. , GRIFFITHS H.
Published: November 2003

The contribution which (photo)respiration makes to carbon isotope discrimination (Δ13C) was examined by conducting simultaneous gas exchange measurements and isotopic analysis of carbon dioxide passing over leaves of Triticum aestivum and Phaseolus vulgaris, via manipulations of the carbon isotope composition (δ13C) of source CO2 during growth and measurement. Dark respiration only altered net Δ13C (Δobs) at low CO2 assimilation, and was sensitive to source CO2δ13C during measurement. Photorespiration reduced Δobs relative to Δ13C predicted from pi/pa (Δi) over the full range of CO2 assimilation, to a greater degree under elevated oxygen partial pressure (pO2), indicating fractionation during photorespiration (f) in T. aestivum. For P. vulgaris, Δobs was insensitive to elevated pO2 at higher assimilation rates, suggesting that f was minimal. A model was developed to calculate gross discrimination (Δps), independent of (photo)respiration, from which estimates of f were obtained for T. aestivum (3.3‰) and P. vulgaris (0.5‰). Because photorespiratory fractionation varies interspecifically, and influences net Δ13C which is directly reflected in leaf δ13C, consideration of (photo)respiratory fractionation is necessary when interpreting δ13C of leaf material, especially under conditions where (photo)respiratory CO2 losses make a large relative contribution to total plant carbon budgets.
Expression and kinetics of the mitochondrial alternative oxidase in nitrogen‐fixing nodules of soybean roots
Authors: MILLAR A. H. , FINNEGAN P. M. , WHELAN J. , DREVON J. J. , DAY D. A.
Published: November 2003

Mitochondria from nitrogen‐fixing soybean nodules had previously been found to display very low rates of cyanide‐insensitive O2 consumption and to contain little protein immunoreactive with alternative oxidase (AOX) antibodies (A. Reams et al. 1992, Plant Physiology 99, pp. 712–717). Following the recent identification of novel regulatory mechanisms for AOX, we have re‐investigated AOX activity in nodule mitochondria. When AOX is fully activated by adding pyruvate and a reductant, significant AOX activity can be measured in nodule mitochondria when substrates that cause the ubiquinone (Q) pool to become > 90% reduced are provided. These nodule mitochondria contain ∼10% of the immunoreactive protein observed in soybean root or cotyledon mitochondria. Furthermore, transcripts from all three members of the soybean AOX multigene family were significantly less abundant in total RNA from nodules than from other tissues. The ratio of transcripts from the three AOX genes varied between the outer cortex and the inner infected region of the nodule. Measurements of Q redox state (Qr/Qt) versus O2 consumption showed that much higher levels of Q reduction were required for AOX to be active in mitochondria from nodules than in mitochondria from roots and cotyledons, and that root and nodule mitochondria were more dependent on added pyruvate for maximum AOX activity. Kinetic modelling suggests that these differences were simply the result of differences in the relative amount of active AOX protein, rather than differences in Q content or the AOX isoform expressed, in the different tissues.
Contribution of sucrose synthase, ADP‐glucose pyrophosphorylase and starch synthase to starch synthesis in developing pea seeds
Authors: DÉJARDIN A. , ROCHAT C. , WUILLÈME S. , BOUTIN J.‐P.
Published: November 2003

Using genetic variability existing amongst nine pea genotypes (Pisum sativum L.), the biochemical basis of sink strength in developing pea seeds was investigated. Sink strength was considered to be reflected by the rate of starch synthesis (RSS) in the embryo, and sink activity in the seed was reflected by the relative rate of starch synthesis (RRSS). These rates were compared to the activities of three enzymes of the starch biosynthetic pathway [sucrose synthase (Sus), ADP‐glucose pyrophosphorylase and starch synthase] at three developmental stages during seed filling (25, 50 and 75% of the dry seed weight). Complete sets of data collected during seed filling for the nine genotypes showed that, for all enzyme activities (expressed on a protein basis), only Sus in the embryo and seed coat was linearly and significantly correlated to RRSS. The contribution of the three enzyme activities to the variability in RSS and RRSS was evaluated by multiple regression analysis for the first two developmental stages. Only Sus activity in the embryo could explain, at least in part, the significant variability observed for both the RSS and the RRSS at each developmental stage. We conclude that Sus activity is a reliable marker of sink activity in developing pea seeds.
Ultrasound acoustic emissions from dehydrating leaves of deciduous and evergreen trees
Authors: KIKUTA S. B. , LO GULLO M. A. , NARDINI A. , RICHTER H. , SALLEO S.
Published: November 2003

While drying, detached leaves produced ultrasound acoustic emissions (UAE) comparable to emissions from stem and twig wood. Experiments on Ilex aquifolium L. showed that the main source of these signals was cavitation in the veins, to which conduits and fibres probably both contributed. Regions of the leaf blade with abundant mesophyll and only small veins emitted few signals. More signals were counted on the adaxial side of the midrib than on the abaxial one and on the proximal third than on the distal one, in accordance with the anatomical structure. Sound attenuation was pronounced. Eight species were compared with respect to cavitation behaviour, field water relations and pressure–volume curves, and the data showed differences in cumulative number of events and resistance of leaves to cavitation. Data were generally in good agreement with anatomical structure and habitat preferences. The number of signals per conduit counted on cross‐sections was in some leaves much higher than unity, which suggests short xylem elements or an acoustic activity of cells other than conduits. There was no correlation between cavitation threshold or cumulative number of signals and the degree of sclerophylly; unexpectedly, there was a correlation between the cumulative number of signals at a water potential of ‐1.3 MPa and the bulk modulus of elasticity.
Ultraviolet‐B effects on transcript levels for photosynthetic genes are not mediated through carbohydrate metabolism
Authors: MACKERNESS S. A.‐H. , SURPLUS S. L. , JORDAN B. R. , THOMAS B.
Published: November 2003

The relationship between UV‐B‐induced changes in gene expression and carbohydrate levels in pea seedlings has been investigated. The effect of supplementary UV‐B radiation on the transcript abundance for two photosynthetic genes, photosynthesis, respiration and the levels of carbohydrates was determined in fully expanded leaves of 17‐d‐old pea seedlings under high (HL: 350 μmol m−2 s−1) and low (LL: 150 μmol m−2 s1) light. Supplementary UV‐B caused down regulation of the photosynthetic genes in green leaves under LL and to a lesser extent under HL. In contrast to previous studies, UV‐B radiation resulted in a decrease in glucose levels rather than an increase under LL. Sucrose and starch levels were not affected until longer exposure. Effects of UV‐B on carbohydrate levels were, however, minimal under HL. The effects on transcript levels were most marked under LL and therefore could not be attributed to elevated carbohydrate levels. Comparison of UV‐B effects on carbohydrates in source (leaf) and sink (green buds) organs indicated that changes in carbohydrates in response to UV‐B are probably indirect and arise from effects of UV‐B on photosynthesis in source organs.
An instrument capable of imaging chlorophyll a fluorescence from intact leaves at very low irradiance and at cellular and subcellular levels of organization
Authors: OXBOROUGH K. , BAKER N. R.
Published: November 2003

An instrument capable of imaging chlorophyll a fluorescence, from intact leaves, and generating images of widely used fluorescence parameters is described. This instrument, which is based around a fluorescence microscope and a Peltier‐cooled charge‐coupled device (CCD) camera, differs from those described previously in two important ways. First, the instrument has a large dynamic range and is capable of generating images of chlorophyll a fluorescence at levels of incident irradiance as low as 0.1 μmol m−2 s−1. Secondly, chlorophyll fluorescence, and consequently photosynthetic performance, can be resolved down to the level of individual cells and chloroplasts. Control of the instrument, as well as image capture, manipulation, analysis and presentation, are executed through an integrated computer application, developed specifically for the task. Possible applications for this instrument include detection of early and differential responses to environmental stimuli, including various types of stress. Images illustrating the instrument's capabilities are presented.
Effect of leaf structure and water status on carbon isotope discrimination in field‐grown durum wheat
Authors: ARAUS J. L. , AMARO T. , ZUHAIR Y. , NACHIT M. M.
Published: November 2003

The relationships between leaf and kernel carbon isotope discriminations (Δ) and several leaf structural parameters that are indicators of photosynthetic capacity were studied in durum wheat grown in the field under three water regimens. A set of 144 genotypes were cultivated in two rain‐fed trials, and 125 of these were grown under supplementary irrigation before heading. Total chlorophyll and nitrogen (N) contents, the dry mass per unit leaf area (LDM, the reciprocal of specific leaf area) and carbon isotope discrimination (Δ) were measured in penultimate leaves and Δ of mature kernels was also analysed. Both LDM and N per unit area showed significant (P≤ 0.001) negative correlation (r=–0.60 and r=–0.36, respectively) with leaf Δ in the wettest trial. Little or no correlation was found for any structural parameter and leaf Δ in the rain‐fed trials. In contrast, in the two rain‐fed trials LDM was the parameter with the strongest positive correlation (P≤ 0.001) with kernel Δ (r= 0.47 and 0.30) and grain yield (r= 0.43 and 0.29), whereas no correlation was found in the irrigation trial. These correlations, rather than representing a causal link between the amount of photosynthetic tissue and Δ, were probably indirect associations caused by a parallel effect of water status and phenology on leaf structure, grain Δ and yield. Correlations across trials (i.e. environments) between leaf structure and either Δ and yield were very high, although also spurious. Our results suggest that LDM should be used to cull segregating population differences in leaf Δ based on the internal photosynthetic capacity only in the absence of drought. Selecting for kernel Δ and grain yield on the basis of LDM is worthwhile for rain‐fed trials.
The effects of photooxidative stress on photosystem I measured in vivo in Chlamydomonas
Authors: MARTIN R. E. , THOMAS D. J. , TUCKER D. E. , HERBERT S. K.
Published: November 2003

The effects of different photooxidative stresses on the function of photosystem I were measured in vivo in Chlamydomonas reinhardtii. Pholooxidative stresses included strong light, light combined with chilling to 0 °C, and light combined with several concentrations of methyl viologen. Photosystem I function was measured in vivo using the absorbance change at 820 nm associated with P700 oxidation. Photosystem II function was measured in vivo using chlorophyll fluorescence. Strong light or light combined with chilling caused inhibition of photosystem II function earlier than inhibition of photosystem I function. When photosystem I was inhibited, however, it did not recover. Light combined with 5 mmol m−3 methyl viologen caused inhibition of photosystem I function earlier than inhibition of photosystem II. If the methyl viologen concentration was reduced to 1 mmol m−3, the damage to PSI was accelerated by addition of 90 mmol m−3 chloramphenicol. This effect of chloroamphenicol suggests a role for chloroplast‐encoded proteins in protecting photosystem I against photooxidative damage caused by methyl viologen.
Correlating δ13C and δ18O in cellulose of trees
Authors: SAURER M. , AELLEN K. , SIEGWOLF R.
Published: November 2003

We measured the carbon and oxygen isotopic composition of stem cellulose of Pinus sylvestris, Picea abies, Fagus sylvatica and Fraxinus excelsior. Several sites along a transect of a small valley in Switzerland were selected which differ in soil moisture conditions. At every site, six trees per species were sampled, and a sample representing a mean value for the period from 1940 to 1990 was analysed. For all species, the mean site δ13C and δ18O of stem cellulose are related to the soil moisture availability, whereby higher isotope ratios are found at drier sites. This result is consistent with isotope fractionation models when assuming enhanced stomatal resistance (thus higher δ13C of incorporated carbon) and increased oxygen isotope enrichment in the leaf water (thus higher δ18O) at the dry sites. δ18 O‐δ13C plots reveal a linear relationship between the carbon and oxygen isotopes in cellulose. To interpret this relationship we developed an equation which combines the above‐mentioned fractionation models. An important new parameter is the degree to which the leaf water enrichment is reflected in the stem cellulose. In the combined model the slope of the δ18O‐δ13C plot is related to the sensitivity of the pi/pa of a plant to changing relative humidity.
Temporal and spatial expression of mRNAs encoding pathogenesis‐related proteins during ethylene‐promoted leaflet abscission in Sambucus nigra*
Authors: COUPE S. A. , TAYLOR J‐ E. , ROBERTS J. A.
Published: November 2003

Differential screening of a cDNA library generated from RNA extracted from ethylene‐treated leaflet abscission zones of Sambucus nigra resulted in the isolation of 20 abscission‐related clones. These clones could be grouped into seven families. Sequencing of members of these families revealed that the majority encoded pathogenesis‐related (PR) proteins, and these could be identified by sequence homology as a polyphenol oxidase (PPO), a PR‐1 type protein, a Chial type chitinase, a PR‐4 type protein similar to the potato win peptides, a PR‐6 type proteinase inhibitor, a Chia4 type chitinase and a metallothionein‐like protein (Coupe, Taylor & Roberts 1995, Planta 197, 442–447). Northern analysis revealed that these mRNAs were not expressed in freshly excised material but accumulated primarily in the abscission zone tissue after 18 h of exposure to ethylene at a time when abscission of the leaflet explants had reached 70%. Expression of the PPO and the Chia4‐type chitinase was ethylene‐dependent while that of the PR‐4 type was up‐regulated in the abscission zone tissue in the absence of the gas. The characterization of these mRNAs and their encoded proteins is presented and their possible roles during abscission are discussed.
Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over‐wintering at raised temperatures: indications of different sensitivities of spruce and pine
Authors: ÖGREN E. , NILSSON T. , SUNDBLAD L.‐G.
Published: November 2003

Long‐term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two‐year‐old seedlings with the same pre‐history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.
Mineral nutrient supply, cell wall adjustment and the control of leaf growth
Authors: SNIR N. , NEUMANN P. M.
Published: November 2003

The possibility that changes in the plasticity of expanding cell walls are involved in regulating early leaf growth responses to nutrient deficiencies in monocot plants was investigated. Intact maize seedlings (Zea mays L.) which were hydroponically grown with their roots in low‐nutrient solution (1 mol m−3 CaCl2) showed early inhibition of first‐leaf growth, as compared with seedlings on complete nutrient solution. This early inhibition of leaf growth was not associated with reduced cell production. However, segmental elongation along the cell expansion zone at the base of the leaf and the lengths of mature epidermal cells were reduced by the low‐nutrient treatment. Solute (osmotic) potentials in the expanding leaf tissues were unchanged. In contrast, low‐nutrient treatments significantly altered leaf plasticity, i.e. the irreversible extension caused by applying a small force in the direction of leaf growth. For example, in vivo plasticity decreased, along with leaf growth, after transfer of seedlings from complete nutrient solution to low‐nutrient solution for 15 h. Conversely, in vivo plasticity increased, along with leaf growth, after transfer of plants previously grown on low‐nutrient solution to complete nutrient solution for 15 h. The nutrient treatments also induced similar changes in the in vitro plasticity of the expanding leaf cell walls. There were no consistent changes in elasticity. Thus, reductions in the plasticity of expanding leaf cell walls appear to be involved in controlling the early inhibition of maize leaf growth by root imposition of nutrient stress.
Effects of low and elevated CO2 partial pressure on growth and reproduction of Arabidopsis thaliana from different elevations
Authors: WARD J. K. , STRAIN B. R.
Published: November 2003

Atmospheric CO2 partial pressure may have been as low as 18 Pa during the Pleistocene and is expected to increase from 35 to 70 Pa before the end of the next century. Low CO2 reduces the growth and reproduction of C3 plants, whereas elevated CO2 often increases growth and reproduction. Plants at high elevation are exposed to reduced CO2 partial pressure and may be better adapted to the low CO2 of the Pleistocene. We examined genotypes of Arabidopsis thaliana from different elevations for variation in growth and reproduction at the CO2 levels of the Pleistocene, the present and the future. Genotypes exhibited limited genetic variation in the response of the production of biomass to changes in CO2, but showed significant variation in reproductive characters. We found evidence that plants from high elevations may be better adapted to low CO2 when considering seed number, which is an important component of fitness. Genotypes showed greater variation in the response of seed number between 35 and 20 Pa CO2 compared to 35 and 70 Pa CO2. We conclude that present‐day C3 annuals may have greater potential for evolution in response to the low CO2 of the Pleistocene relative to the elevated CO2 predicted for the future.
Interactions between inorganic phosphate (Pi) assimilation, photosynthesis and respiration in the Pi‐limited green alga Selenastrum minutum*
Authors: GAUTHIER D. A. , TURPIN D. H.
Published: November 2003

Inorganic phosphate (Pi)‐limited chemostat cultures of the green alga Selenastrum minutum were employed to investigate interactions between Pi assimilation, respiration and photosynthetic processes. Changes in net and gross gas exchange rates indicated that O2 evolution decreases during photosynthetic Pi assimilation. Room temperature and 77K Chi a fluorescence measurements revealed that this photosynthetic suppression is correlated with a transition from state 1 to state 2. Substantial photosynthetic Pi uptake rates occur in the presence of DCMU and KCN. Additionally, the cellular ratio of ATP:NADPH increases following Pi enrichment, suggesting that the ratio of cyclic to linear electron flow is enhanced in response to the high energy requirements of Pi uptake. Net starch degradation was observed during photosynthetic Pi assimilation and the cellular pool size of 3‐phosphoglycerate increased; however, gross gas exchange parameters and cellular metabolite pool sizes indicated that mitochondrial respiration plays a smaller role during Pi assimilation in the light than it does in the dark. These observations were used to formulate a model depicting possible interactions between photosynthetic electron flow, photosynthetic and respiratory carbon metabolism and metabolite exchange between the chloroplast, cytosol and mitochondrion during photosynthetic Pi assimilation.
Dual effect of phytochrome A on hypocotyl growth under continuous red light
Authors: MAZZELLA M. A. , ALCONADA MAGLIANO T. M. , CASAL J. J.
Published: November 2003

The role of phytochrome A in the control of hypocotyl growth under continuous red light (Rc) was investigated using phyA and phyB mutants of Arabidopsis thaliana, which lack phytochrome A (phyA) or phytochrome B (phyB), respectively, and transgenic seedlings of Nicotiana tabacum overexpressing Avena phyA, compared to the corresponding wild type (WT). In WT seedlings of A. thaliana, hypocotyl growth inhibition showed a biphasic response to the fluence rate of Rc, with a brake at 10−2μmol m−2 s−1. At equal total fluence rate, hourly pulses of red light caused slightly more inhibition than Rc. The response to very low fluences of continuous or pulsed red light was absent in the phyA and phyA phyB mutants and present in the phyB mutant. The second part of the response was steeper in the phyA mutant than in the WT but was absent in the phyB mutant. In WT tobacco the response to Rc was biphasic. Overexpression of Avena phyA enhanced the response only at very low fluence rates of Rc (< 10−2μmol m−2 s−1). In both species, the effect of hourly pulses of far‐red light was similar to the maximum inhibition observed in the first phase of the response to Rc. Using reciprocity failure (i.e. higher inhibition under continuous than pulsed light) as the operational criterion, a ‘true’ high‐irradiance reaction occurred under continuous far‐red light but not under Rc or red plus far‐red light mixtures. Native and overexpressed phyA are proposed to mediate very low fluence responses under Rc. In WT A. thaliana, this effect is counteracted by a negative action of phyA on phyB‐mediated low‐fluence responses.
Lognormal distribution of water permeability and organic solute mobility in plant cuticles
Authors: BAUR P.
Published: November 2003

It is shown that water permeabilities and organic solute mobilities in plant cuticles have a lognormal distribution. Seven‐hundred and fifty values for rate constants of desorption (∼mobility) of 2,4‐D from isolated Citrus aurantium L. cuticles from a population of leaves were pooled and analysed. A histogram of the rate constants of individual cuticles showed a skew distribution with a strong tail to higher values. Cuticular membranes with high values did not differ from others in visual appearance and were not leaky. After log‐transformation of original data an almost perfect normal distribution was obtained. Statistical tests showed that a normal distribution of original values is not acceptable. Inspection of older data for water permeability in the same species and experiments using large samples of cuticles from leaves of Pyrus communis L. and Stephanotis floribunda Brongn. and from fruits of Capsicum annuum L. showed a similar distribution, as did inspection of data for experiments with organic solutes. A lognormal distribution was found for cuticles of plants from growth chambers, glasshouses and outdoors as well as for water permeability of intact leaves of Hedera helix L. For small samples the overestimation from using the arithmetic mean of original data can be high, but use of the geometric mean or the median leads to smaller deviations. Removing cuticular waxes from cuticles produced normally distributed samples. A normal distribution was also obtained when organic compounds which increase solute mobility were sorbed into cuticles.
Water potential, turgor and cell wall properties in elongating tissues of the hydrotropically bending roots of pea (Pisum sativum L.)
Authors: HIRASAWA T. , TAKAHASHI H. , SUGE H. , ISHIHARA K.
Published: November 2003

The hydrotropic bending of roots of an ageotropic pea mutant, ageotropum, was studied in humid air in a chamber with a steady humidity gradient. We examined the effects of atmospheric humidity around the root on the water status of root tissues, as well as the wall growth and the hydraulic properties of the elongating tissues. Atmospheric humidity at the surface of the root was clearly lower on the side orientated towards the air with lower humidity than on the side orientated towards the air with higher humidity. However, there were no differences in water potential and osmotic potential between the tissues that faced air with higher and lower humidities in the elongating and mature regions. Plastic extensibility was higher in the tissues that faced the air with lower humidity than in the tissues that faced the air with higher humidity. No differences in turgor pressure and yield threshold were observed between the tissues that faced air with higher and lower humidities. Therefore, the extensibility of the cell wall appeared to be responsible for the different growth rates of tissues in root hydrotropism. A further probable cause of the hydrotropical bending of roots is changes in the hydraulic conductance in the elongating tissues. Since the hydrotropic bending of roots occurred only when a root tip was exposed to a humidity gradient, hydrotropism might occur after perception of a difference in humidity by the root tip, with accompanying changes in cell wall extensibility and hydraulic conductance.
Alterations in light‐induced stomatal opening in a starch‐deficient mutant of Arabidopsis thaliana L. deficient in chloroplast phosphoglucomutase activity
Authors: LASCÈVE G. , LEYMARIE J. , VAVASSEUR A.
Published: November 2003

Stomatal responses to light of Arabidopsis thaliana wild‐type plants and mutant plants deficient in starch (phosphoglucomutase deficient) were compared in gas exchange experiments. Stomatal density, size and ultrastructure were identical for the two phenotypes, but no starch was observed in guard cells of the mutant plants whatever the time of day. The overall extent of changes in stomatal conductance during 14 h light–10 h dark cycles was similar for the two phenotypes. However, the slow endogenous stomatal opening occurring in darkness in the wild type was not observed in the mutant plants. Stomata in the mutant plants responded much more slowly to blue light (70 μmol m−2 s−1) though the response to red light (250 μmol m−2 s−1) was similar to that of wild‐type plants. In paradermal sections, stomatal responses to red light (300 μmol m−2 s−1) were weak for wild‐type plants as well as for mutant plants. Stomatal opening was greater under low blue light (75 μmol m−2 s−1) than under red light for the two genotypes. However, in mutant plants, a high chloride concentration (50 mol m−3) was necessary to achieve the same stomatal aperture as observed for the wild‐type plants. These results suggest that starch metabolism, via the synthesis of a counter‐ion to potassium (probably malate), is required for full stomatal response to blue light but is not involved in the stomatal response to red light.
Whole‐plant ABA flux and the regulation of water loss in Cedrella odorata
Authors: JARVIS A. J. , DAVIES W. J.
Published: November 2003

Three‐month‐old Cedrella odorata seedlings were exposed to a soil‐drying treatment. During this period, xylem sap was periodically collected from the plant by applying pneumatic pressure to the roots. This also allowed whole‐plant water status to be measured by recording the balancing pressure applied. The concentration of ABA in xylem sap (C) was related to the whole‐plant transpiration rate (V) which was measured with a sap flow gauge. The analysis of these paired measurements centred on how the reciprocal of C (R) varied with respect to V. This revealed that (1) the observed increases in C could not be explained by the reductions in V alone, (2) initially, decreases in V were associated with proportional increases in the whole‐plant ABA flux (M), and (3) this relationship broke down at low values of V since zero flow was associated with a finite value for C estimated to be 41 pmol ABA mmol−1 H2O. A simple static model is developed from the observations that is able to explain the data well, and the results are discussed in terms of the effects of ABA on stomatal conductance (gsw).
Acclimation of photosynthesis to irradiance and spectral quality in British plant species: chlorophyll content, photosynthetic capacity and habitat preference
Authors: MURCHIE E. H. , HORTON P.
Published: November 2003

Twenty‐two common British angiosperms were examined for their ability to acclimate photosynthetically to sun and shade conditions. Plants were grown under low irradiance, far‐red enriched light (50 μmol m−2 s−1), selected to mimic as closely as possible natural canopy shade, and moderately high light of insufficient irradiance to induce photoinhibitory or photoprotective responses (300 μmol m−2 s−1). Light‐and CO2‐saturated photosynthetic rates of oxygen evolution (Pmax) and chlorophyll content were measured. Large variation was found in both parameters, and two ‘strategies’ for long‐term acclimation were identified: firstly a change in chlorophyll per unit leaf area which was found to correlate positively with photosynthetic capacity, and secondly changes in chlorophyll alb ratio and Pmax, indicative of alterations at the chloroplast level, which were not associated with a change in chlorophyll content per unit leaf area. Combinations of these two strategies may occur, giving rise to the observed diversity in photosynthetic acclimation. The extent and nature of photosynthetic acclimation were compared with an index of shade association, calculated from the association each species has with woodland. It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in ‘sun’ species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level. A framework for explaining the variation between plant species in leaf‐level photosynthetic capacity, in relation to the natural light environment, is presented. This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.
Chromoblastomycosis in India
Authors: Rajendran C. , Ramesh V. , Misra R. S. , Kandhari S. , Upreti H.B. , Datta K. K.
Published: November 2003

Background

Chromoblastomycosis is reported for the first time from the states of Jammu‐Kashmir and Bihar along with two additional cases from the stales of Assam and Uttar Pradesh. The work carried out on this disease in the Indian subcontinent is reviewed.

Methods

Relevant mycologic investigations, including direct microscopy, histopathology, and culture, were carried out of study the four cases. Treatment was given to two patients.

Results

The duration of the lesions varied from 5 to 32 years. In one case the lesion was a large erythematous plaque on the buttocks extending to the backs of the thighs, and in the others they were hypertrophic lesions on the extremities. Histopathologic study of specimens carried out in three patients revealed the causative organisms. On culture, Cladosporium carrionii was isolated in one and Fonsecaea species in the other three. The lesions in one patient were surgically excised and another patient responded well of a combined regimen of amphotericin B and 5‐fluorocytosine.

Conclusions

Although chromoblastomycosis is widely distributed in India, many patients remain undiagnosed due to a lack of proper facilities. Treatment is difficult and most patients are not able to afford the drugs prescribed for this condition.
Cost‐benefit of oral acyclovir in the treatment of herpes zoster
Authors: Kubeyinje Emmanuel Pandy
Published: November 2003

Background Oral acyclovir is a costly antiviral agent shown to be effective in the treatment of herpes zoster. Herpes zoster runs a relatively benign course in young, healthy individuals, as compared with elderly and immunologically compromised patients, in whom complications are common. This study attempts to assess the cost‐benefit of treatment with oral acyclovir in young healthy adults with herpes zoster.

Patients and methods The records of 42 healthy young adults suffering from herpes zoster and treated with oral acyclovir (800 mg five times daily for 7 days) were compared with those of 40 healthy young adults with herpes zoster seen during the same period but treated without oral acyclovir. The duration of zoster‐associated pain and the presence of complications were noted.

Results There was no statistically significant difference in the duration of zoster‐associated pain between the two groups of patients (P= 0.11). Other complications of herpes zoster were few and similar in the two groups.

Conclusions At a cost of $250 to $300 for a 7–day course of oral acyclovir, the use of this antiviral agent in healthy young individuals with herpes zoster is not justified, especially in developing countries with limited resources.
Angiocentric T‐cell lymphoma presenting as lethal midline granuloma
Authors: Lee Peter Y. , Freeman Nancy J. , Khorsand Jila , Weinstock Martin A.
Published: November 2003

Background Lethal midline granuloma (LMG) is a rare condition characterized by rapidly progressive midfacial destruction. Most LMG cases are angiocentric T‐cell lymphomas and an association with Epstein‐Barr virus (EBV) has been reported. Cutaneous involvement is poorly described and the prognosis not well documented.

Methods We report a case of angiocentric T‐cell lymphoma of the palate that presented as LMG with concurrent discrete skin lesions composed of two distinct morphologic appearances: indurated nodules and annular plaques. The English language literature for LMG‐type angiocentric T‐cell lymphoma is reviewed and a survival analysis of 58 cases with follow‐up data (including our own case) is performed.

Results The 1‐ and 5‐year survival rates were 45%± 7% and 22%± 9%, respectively. Poor survival was associated with advanced age and stage. EBV DNA was detected in 16 out of 21 reported cases in which it was sought (including our case).

Conclusions We present photographic documentation of a broader spectrum of cutaneous lesions in the LMG‐type angiocentric T‐cell lymphoma than has previously been described, and have confirmed the association with EBV. The prognosis is poor. Aggressive therapy such as bone marrow transplantation should be considered early in the course.
Postpemphigus acanthomata: a sign of clinical activity?
Authors: Yesudian Paul Devakar , Krishnan Srivilliputtur G.S. , Jayaraman Muriugaiya , Janaki Vanakampadi R. , Yesudian Patrick
Published: November 2003

Background Pemphigus is a group of vesiculobullous disorders in which the blisters usually heal with hyper‐ or hypopigmentation. The appearance of acanthomata at sites of previous blisters has been noted in some cases.

Methods All cases of pemphigus admitted to the Madras Medical College hospitals during a 2‐year period from March 1993 to March 1995 were taken into the study and screened for the presence of acanthomata.

Results Fifty‐two cases of pemphigus were identified, 47 of pemphigus vulgaris and five of pemphigus foliaceus; and of these 13 developed acanthomata when the blisters healed. Ten of these cases were of pemphigus vulgaris and three were of pemphigus foliaceus; biopsy of these lesions showed hyperkeratosis, acanthosis, papillomatosis, and intraepidermal clefting. Immunofluorescence carried out in two of these acanthomata also showed intercellular fluorescence.

Conclusions The occurrence of acanthomata in healed lesions of pemphigus is not uncommon; because histopathologic and immunofluorescence evidence of disease activity is present, cases of this sort require careful follow‐up.
The association of chronic urticaria and angioedema with autoimmune thyroiditis
Authors: Turktas Ipek , Gokcora Nahide , Demirsoy Sadik , Cakir Nuri , Onal Esra
Published: November 2003

Background An increased frequency of autoimmune thyroiditis is seen in patients with chronic urticaria and angioedema (CUA) and it has been hypothesized that autoimmunity may be playing a role in the pathogenesis of CUA. The aim of this study was to learn the extent of autoimmune thyroid disease in a series of patients who presented with CUA.

Methods Thyroid function tests and thyroid autoantibodies were measured by radioimmunoassay and immunoradiometric assay respectively in 94 CUA patients and 80 age‐ and sex‐matched healthy volunteers.

Results Eleven patients (11.7%) were found to have thyroglobulin antibodies (TGA) and nine patients (9.57%) thyroid microsomal (TMA) titers ranging from 150 to 1340.37 and from 165.73 to 8000 lU/mL respectively. Both antibodies were detected in three control cases (3.7%). The association was statistically significant (P < 0.01). Six of 11 patients had thyroid dysfunction and the other five cases were euthyroid.

Conclusions Our results justified the use of TMA and TGA for the early diagnosis of autoimmune thyroiditis in combination with CUA. The higher frequency of these antibodies in our patients, along with results from previously published data, suggest that this entity may reflect an autoimmune basis in some CUA patients. Thyroid function tests are not enough to rule out thyroid disease, and thyroid antibody tests should be carried out in all patients with CUA.
Malignancy in adult dermatomyositis
Authors: Leow Yung‐Hian , Goh Chee Leok
Published: November 2003

Background Dermatomyositis has been reported to be associated with malignancies in 15%–34% of patients in Western countries, but in as many as two‐thirds of patients in Singapore. The aim of this study was to determine whether a diagnostic measure could be helpful in the diagnosis of a malignancy in patients with dermatomyositis.

Methods This is a retrospective study on 38 adult patients with dermatomyositis that were seen over a 6‐year period from 1989 to 1994.

Results All the patients presented with cutaneous features that suggest the clinical diagnosis of dermatomyositis; however, not all cases show all the key features of the disease. Of the studied patients, 86.8% were noted to have photosensitivity as a key cutaneous presentation. Thirty (78.9%) of our patients were above the age of 40 years, and 12 (31.6%) of these were found to have an associated malignancy. Nasopharyngeal carcinoma was the most commonly associated malignancy (38.4%) in our study population.

Conclusions In our study population, otorhinolaryngologic screening is an essential investigation for the evaluation of dermatomyositis in association with malignancy.
Tinea capitis in south‐western Ethiopia: a study of risk factors for infection and carriage
Authors: Figueroa Jose Ignacio , Hawranek Thomas , Abraha Aynalem , Hay Roderick James
Published: November 2003

Background Tinea capitis is a common dermatophyte infection which constitutes an important public health problem among children worldwide. The endemic nature of scalp ringworm in Africa is perpetuated mainly by the lack of knowledge about the prevalence and carrier status, and the absence of control measures.

Methods Two hundred and nineteen schoolchildren from urban and rural communities of the Illubabor district, south‐western Ethiopia, were examined, and scalp samples were taken. Children were classified according to clinical signs and mycologic findings.

Results Physical examination revealed that 29% of the children had clinical lesions compatible with tinea capitis. Dermatophytes were isolated from 33% of the children's scalp samples; of these, 16% had clinical lesions and 17% were identified as carriers. Trichophyton violaceum was responsible for 97% of infections.

Conclusions Tinea capitis was the second most prevalent cutaneous finding in these children, with a higher prevalence in the urban community; the predictive value of the clinical diagnosis was low and a high proportion of children were identified as carriers in these communities. No relationship between household overcrowding and scalp infection was found.