bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of flowering by photoperiod in Arabidopsis
Authors: COUPLAND G. 
Published: November 2003

ABSTRACTThe flowering time of Arabidopsis thaliana is strongly influenced by light quality and photoperiod length. Broadly, two classes of mutations have been characterized that disrupt the response to photoperiod. The first of these, which includes early flowering 3 (elf3), probably influences flowering time by affecting the endogenous cir‐cadian rhythm that enables the duration of the photoperiod to be measured. The genes affected by the second class of mutations, which includes constans (co), are required to promote flowering in response to long photoperiods. The CONSTANS gene has been cloned, and analysis of transgenic plants in which the gene is expressed from a strong viral promoter indicates that transcriptional regulation of CO is an important determinant of flowering time in response to photoperiod. I describe recent progress in understanding these two classes of mutations, and how they influence flowering time in response to photoperiod.
The role of COP1 in light control of Arabidopsis seedling development
Authors: TORII K. U. , DENG X. W. 
Published: November 2003

ABSTRACTThe Arabidopsis seedling can follow two contrasting developmental programmes, photomorphogenesis in light and skotomorphogenesis in darkness. CONSTITUTIVE PHOTOMORPHOGENIC I (COP1) is an essential regulatory gene required for repression of seedling photomorphogenic development in darkness. Recent mutational and overexpression analyses of the COP1 gene suggest a central role for COP1 in light control of seedling development and point to functional implications of its structural domains. Cell biological studies of COP1 have provided a clue to how light regulates the repressive activity of COP1 and thus seedling development.
The role of mutants in the search for the photoreceptor for phototropism in higher plants
Authors: BRIGGS W. R. , LISCUM E. 
Published: November 2003

ABSTRACTEarly attempts to identify the chromophore of the photoreceptor for phototropism are reviewed. Carotenoids and flavins were the principal candidates, but studies with grass coleoptiles devoid of carotenoids suggest that at least in these organs carotenoids are most unlikely to play that role. The status of characterization of a gene for a putative photoreceptor protein is also reviewed. As the action spectrum for phototropism resembles the absorption spectrum of a flavoprotein, flavoproteins are attractive candidates at present, especially since the CRY1 photoreceptor in Arabidopsis thaliana that mediates blue light‐dependent hypocotyl growth suppression has flavin adenine dinucleotide as one of its two chromophores. As the second chromophore appears to be pterin, pterins should not be ruled out as candidate chromophores for the photoreceptor for phototropism.
The phytochrome gene family in tomato (Solarium lycopersicum L.)
Authors: PRATT L. H. , CORDONNIER‐PRATT M.‐M. , KELMENSON P. M. , LAZAROVA G. I. , KUBOTA T. , ALBA R. M. 
Published: November 2003

ABSTRACTPhytochrome apoproteins in angiosperms are encoded by a small gene family. Tomato (Solatium lycopersicum L.) serves well as a dicotyledonous model system for elucidating the extent of this gene family, its expression patterns, and the roles of individual members of the family. Five phytochrome genes (PHYA, PHYB1, PHYB2, PHYE and PHYF have been characterized in tomato. Quantitative measurements of transcript abundances from each tomato PHY throughout the life cycle indicate that transcript levels generally range from 10 to 100 μmol mol−1 total mRNA, in the following order of decreasing abundance: PHYA, PHYB1, PHYE, PHYB2 and PHYF. PHYA transcripts were found to be most abundant in seedling roots, while PHYB2 and PHYF transcripts were expressed preferentially in fruit. PHYA mutants (fri) have been found to be the consequence of a single nucleotide substitution adjacent to the 3′ terminus of an intron. What are almost certainly PHYB1 mutants have also been described, although the molecular nature of these mutants remains to be revealed. Efforts to obtain PHYB2, PHYE and PHYF mutants are currently underway.
Tobacco phytochromes: genes, structure and expression
Authors: ADAM E. , KOZMA‐BOGNAR L. , SCHAFER E. , NAGY F. 
Published: November 2003

ABSTRACTPhotomorphogenesis 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

ABSTRACTThe 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

ABSTRACTIn 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

ABSTRACTTo 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

ABSTRACTThe 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

ABSTRACTMitochondria 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

ABSTRACTUsing 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

ABSTRACTWhile 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

ABSTRACTThe 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

ABSTRACTAn 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

ABSTRACTThe 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

ABSTRACTThe 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.