bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light use efficiency of dry matter gain in five macro‐lichens: relative impact of microclimate conditions and species‐specific traits
Authors: Palmqvist K. , Sundberg B. 
Published: March 2003

ABSTRACTRelations between irradiance (I) and lichen growth were investigated for five macro‐lichens growing at two sites in Sweden. The lichens represented different mycobiont–photobiont associations, two morphologies (foliose, fruticose) and two life forms (epiphytic, terricolous). The lichens were transplanted at two geographically distant sites in Sweden (1000 km apart) from Sept 1995 to Sept 1996 in their typical microhabitats, where microclimate and growth were followed. Between April/May and Sept 96, the terricolous species had a dry matter gain of 0·2 to 0·4 g (g DW)–1 and the epiphytes 0·01 to 0·02 g (g DW)–1. When related to area, growth amounted to 30 to 70 g m−2 for the terricolous species and to 1 to 4 g m−2 for the epiphytes. There was a strong correlation between growth and intercepted irradiance when the lichens were wet (Iwet), with 0·2 to 1·1 g lichen dry matter being produced per MJ solar energy. Across the 10 sets of transplants, light use efficiencies of dry matter yield (e) ranged between 0·5 and 2%, using an energy equivalent of 17·5 kJ g−1 of lichen dry matter. The higher productivity of the terricolous species was due to longer periods with thallus water contents sufficient for metabolic activity and because of the higher mean photon flux densities of their microhabitat. A four‐fold difference in photosynthetic capacity among the species was also important. It is concluded that lichen dry matter gain was primarily related to net carbon gain during metabolically active periods, which was determined by light duration, photon flux density and photosynthetic capacity.
Variation in dynamics of phytochrome A inArabidopsisecotypes and mutants
Authors: Eichenberg K. , Hennig L. , Martin A. , Schäfer E. 
Published: March 2003

ABSTRACTPhytochromes are photoreceptors in plants which can exist in two different conformations: the red light‐absorbing form (Pr) and the far‐red light‐absorbing form (Pfr), depending on the light quality. The Pfrform is the physiologically active conformation. To attenuate the Pfrsignal for phytochrome A (phyA), at least two different mechanisms exist: destruction of the molecule and dark reversion. Destruction is an active process leading to the degradation of Pfr. Dark reversion is the light‐independent conversion of physiologically active Pfrinto inactive Pr. Here, we show that dark reversion is not only an intrinsic property of the phytochrome molecule but is modulated by cellular components. Furthermore, we demonstrate that dark reversion of phyA may be observed inArabidopsisecotype RLD but not in otherArabidopsisecotypes. For the first time, we have identified mutants with altered dark reversion and destruction in a set of previously isolated loss of function PHYA alleles (Xuet al. Plant Cell1995, 7, 1433–1443). Therefore, the dynamics of the phytochrome molecule itself need to be considered during the characterization of signal transduction mutants.
Stomatal responses to non‐local changes in PFD: evidence for long‐distance hydraulic interactions
Authors: Buckley Thomas N. , Mott Keith A. 
Published: March 2003

ABSTRACTInteractions among stomata within a single areole have recently been reported, and evidence suggests that hydraulic mechanisms may be responsible for these interactions. Such interactions may play a role in patchy stomatal behaviour by coordinating stomatal behaviour within areoles. However, models suggest that longer‐distance interactions may be required to produce the large‐scale discoordination that is characteristic of stomatal patchiness. This study was undertaken to characterize long‐distance interactions between ‘artificial patches’ of stomata under varying conditions of evaporative demand and soil water stress. Gas‐exchange was monitored in two adjacent regions (‘patches’) of a wheat leaf by two independent gas mixing and analysis systems. When photon flux density (PFD) was changed in only one of these patches, stomatal conductance responded in both patches in a manner consistent with hydraulic interactions propagated by changes in xylem water potential. These data are discussed in the context of mechanisms for patchy stomatal conductance and implications for the design and analysis of gas‐exchange experiments.
Physiological factors limit fruit set of tomato (Lycopersicon esculentum Mill.) under chronic, mild heat stress
Authors: Sato S. , Peet M. M. , Thomas J. F. 
Published: March 2003

ABSTRACTThe effects of chronic, mild heat stress on fruit set, fruit production, release of pollen grains, photosynthesis, night respiration and anther dehiscence were examined in tomatoes (Lycopersicon esculentum Mill.) differing in high‐temperature sensitivity. Plants were grown under three temperature regimes: (1) 28/22 or 26/22 °C (optimal temperature); (2) 32/26 °C (high temperature); and (3) 32/26 °C day/night temperatures relieved at 28/22 °C for 10 d before anthesis, then returned to 32/26 °C (relieving treatment). FLA 7156 was the only cultivar with fruit set at 32/26 °C. All five cultivars, however, had fruit set under the relieving treatment (RT). The longer the relief, the higher the percentage of fruit set. Longer periods of relief also increased the number of pollen grains released, and linear regression analysis showed a significant relationship between the number of pollen grains released and the percentage of fruit set. Germination of pollen grains was also lowered in high‐temperature‐grown plants. The number of pollen grains produced, photosynthesis and night respiration did not limit fruit set under chronic, mild heat stress, however. This suggested that cultivar differences in pollen release and germination under heat stress are the most important factors determining their ability to set fruit.
Memories of winter: vernalization and the competence to flower
Authors: Michaels S. D. , Amasino R. M. 
Published: March 2003

ABSTRACTThe promotion of flowering in response to a prolonged exposure to cold temperatures (i.e. winter) is a useful adaptation for plant species that flower in the spring. This promotion is known as vernalization and results in a permanent memory of cold exposure. While the physiology of vernalization has been extensively studied in many species, the molecular mechanism of vernalization remains largely unknown. Recent studies, however, have revealed some of the molecular events that create the requirement for vernalization. In Arabidopsis, naturally occurring late‐flowering ecotypes and plants containing late‐flowering mutations in the autonomous floral‐promotion pathway are relatively late flowering unless cold treated. The vernalization requirement of these late‐flowering ecotypes and autonomous‐pathway mutants is largely created by an upregulation of the floral inhibitor FLOWERING LOCUS C (FLC). After cold treatment, as imbibed seeds or young seedlings, FLC transcript levels are downregulated and remain low for the remainder of the plant's life, but return to high levels in the next generation. Plants containing a constitutively expressed 35S:FLC construct remain late flowering after cold treatment, indicating that FLC levels must be downregulated for vernalization to be effective. Thus the epigenetic downregulation of FLC appears to be a major target of the vernalization pathway and provides a molecular marker of the vernalized state.
Data analysis in plant physiology: are we missing the reality?
Authors: Amzallag G. N. 
Published: March 2003

AbstractIn plant physiology, data analysis is based on the comparison of mean values. In this perspective, variability around the mean value has no significance per se, but only for estimating statistical significance of the difference between two mean values. Another approach to variability is proposed here, derived from the difference between redundant and deterministic patterns of regulation in their capacity to buffer noise. From this point of view, analysis of variability enables the investigation of the level of redundancy of a regulation pattern, and even allows us to study its modifications. As an example, this method is used to investigate the effect of brassinosteroids (BSs) during vegetative growth in Sorghum bicolor. It is shown that, at physiological concentrations, BSs modulate the network of regulation without affecting the mean value. Thus, it is concluded that the physiological effect of BSs cannot be revealed by comparison of mean values. This example illustrates how a part of the reality (in this case, the most relevant one) is hidden by the classical methods of comparison between mean values. The proposed tools of analysis open new perspectives in understanding plant development and the non‐linear processes involved in its regulation. They also ask for a redefinition of fundamental concepts in physiology, such as growth regulator, optimality, stress and adaptation.
Nutrient transfer from soil nematodes to plants: a direct pathway provided by the mycorrhizal mycelial network
Authors: Perez‐Moreno J. , Read D. J. 
Published: March 2003

AbstractA pathway for the transfer of nutrients from dead nematodes to mycorrhizal plants is described for the first time. Plants of Betula pendula were grown in transparent microcosms in the mycorrhizal (M) or non‐mycorrhizal (NM) condition, either with or without nematode necromass of known nitrogen (N) and phosphorus (P) contents as the major potential source of these elements. Plants colonized by the mycorrhizal fungus Paxillus involutus produced greater yields and had larger N and P contents in the presence of nematodes than did their NM counterparts. The symbiotic systems were shown to exploit the N and P originally contained in necromass more effectively, and to transfer the nutrients to the plants in quantities approximately double those seen in NM systems. Even so, NM plants obtained sufficient N and P from dead nematodes to enable some enhancement of growth. Our observations confirm that mycorrhizal fungi provide the potential for the recycling of nutrients contained in this quantitatively important component of the soil mesofauna and demonstrate that the symbiotic pathway is considerably more effective than that provided by saprotrophs alone. The consequences of this nutrient transfer pathway for nutrient recycling in temperate forest ecosystems are considered.
Spectral dependence of flavonol and betacyanin accumulation in Mesembryanthemum crystallinum under enhanced ultraviolet radiation
Authors: Ibdah M. , Krins A. , Seidlitz H. K. , Heller W. , Strack D. , Vogt T. 
Published: March 2003

Abstract Mesembryanthemum crystallinum L. (Aizoaceae) is a drought‐ and salt‐tolerant halophyte that is able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200–1500 µmol m−2 s−1) it displays a rapid cell‐specific accumulation of plant secondary metabolites in the upper leaf epidermis; a phenomenon that is not detectable with salt or drought treatment. The accumulation of these compounds, the betacyanins and acylated flavonol glycosides, increases if the plants are exposed to polychromatic radiation with a progressively decreasing short‐wave cut‐off in the ultraviolet range. The response is localized in the epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. It is demonstrated that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential decrease of the response function of the plant with increasing wavelength.
Modelling the limits on the response of net carbon exchange to fertilization in a south‐eastern pine forest
Authors: Lai C.‐T. , Katul G. , Butnor J. , Siqueira M. , Ellsworth D. , Maier C. , Johnsen K. , Mckeand S. , Oren R. 
Published: March 2003

AbstractUsing a combination of model simulations and detailed measurements at a hierarchy of scales conducted at a sandhills forest site, the effect of fertilization on net ecosystem exchange (NEE) and its components in 6‐year‐oldPinus taedastands was quantified. The detailed measurements, collected over a 20‐d period in September and October, included gas exchange and eddy covariance fluxes, sampled for a 10‐d period each at the fertilized stand and at the control stand. Respiration from the forest floor and above‐ground biomass was measured using chambers during the experiment. Fertilization doubled leaf area index (LAI) and increased leaf carboxylation capacity by 20%. However, this increase in total LAI translated into an increase of only 25% in modelled sunlit LAI and in canopy photosynthesis. It is shown that the same climatic and environmental conditions that enhance photosynthesis in the September and October periods also cause an increase in respiration The increases in respiration counterbalanced photosynthesis and resulted in negligibleNEEdifferences between fertilized and control stands. The fact that total biomass of the fertilized stand exceeded 2·5 times that of the control, suggests that the counteracting effects cannot persist throughout the year. In fact, modelled annual carbon balance showed that gross primary productivity (GPP) increased by about 50% and that the largest enhancement inNEEoccurred in the spring and autumn, during which cooler temperatures reduced respiration more than photosynthesis. The modelled difference in annualNEEbetween fertilized  and  control  stands  (approximately  200 1;g 2;C 3;m−2y−1)  suggest that the effect of fertilization was sufficiently large to transform the stand from a net terrestrial carbon source to a net sink.
The role of CAM in high rainfall cloud forests: an in situ comparison of photosynthetic pathways in Bromeliaceae
Authors: Pierce S. , Winter K. , Griffiths H. 
Published: March 2003

AbstractCrassulacean acid metabolism (CAM), an advanced photosynthetic pathway conferring water conservation to plants in arid habitats, has enigmatically been reported in some species restricted to extremely wet tropical forests. Of these, epiphytic Bromeliaceae may possess absorbent foliar trichomes that hinder gas‐exchange when wetted, imposing further limitations on carbon dioxide (CO2) uptake. The hypothesis that the metabolic plasticity inherent to CAM confers an ecological advantage over conventional C3 plants, when constant rainfall and mist might inhibit gas‐exchange was investigated. Gas‐exchange, fluorometry and organic acid and mineral nutrient contents were compared for the bromeliads Aechmea dactylina (CAM) and Werauhia capitata (C3) in situ at the Cerro Jefe cloud forest, Panama (annual rainfall >  4 m). Daily carbon gain and photosynthetic nutrient use efficiencies were consistently higher for A. dactylina, due to a greater CO2 uptake period, recycling of CO2 from respiration and a dynamic response of CO2 uptake to wetting of leaf surfaces. During the dry season CAM also had water conserving and photoprotective roles. A paucity of CAM species at Cerro Jefe suggests a recent radiation of this photosynthetic pathway into the wet cloud forest, with CAM extending diversity in form and function for epiphytes.
Seasonal and diurnal variations in gene expression in the desert legume Retama raetam
Authors: MERQUIOL E. , PNUELI L. , COHEN M. , SIMOVITCH M. , RACHMILEVITCH S. , GOLOUBINOFF P. , KAPLAN A. , MITTLER R. 
Published: March 2003

AbstractStudying plants growing naturally within their habitat can contribute greatly to our understanding of molecular and biochemical processes involved in the response of plants to changes in environmental conditions. Seasonal and diurnal variations in the expression of several transcripts involved in the defence of plants against abiotic stresses, i.e. transcripts encoding dehydrins, heat shock proteins, and antioxidative enzymes, were followed in Retama raetam plants that grow naturally within an arid dune ecosystem. These were associated with changes in environmental parameters simultaneously recorded at the research sites. It was found that the expression pattern of some transcripts correlated with changes in environmental conditions in the different plants during the year. In contrast, the expression pattern of other transcripts appeared to be plant specific and may be associated with phenotypic variability (plasticity). Transcripts encoding different heat shock proteins were induced in a co‐ordinated manner, suggesting that their corresponding products function as a chaperone network. Measurements of photosynthetic activity revealed a diurnal cycle in R. raetam. Photosynthesis was highest during early morning, declined toward the stressful midday hours and recovered at late afternoon. The present analysis suggests that R. raetam uses a combination of different avoidance strategies in co‐ordination with active defence mechanisms to withstand the stressful conditions that prevail within the desert ecosystem.
Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature
Authors: KAKANI V. G. , PRASAD P. V. V. , CRAUFURD P. Q. , WHEELER T. R. 
Published: March 2003

AbstractAir temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (Tmin, Topt and Tmax) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and Tmax for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related (R2 = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.
Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling
Authors: LEAKEY A. D. B. , PRESS M. C. , SCHOLES J. D. , WATLING J. R. 
Published: March 2003

AbstractThe survivorship of dipterocarp seedlings in the deeply shaded understorey of South‐east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO2 upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO2. Equal total daily photon flux density (PFD) (∼7·7 mol m−2 d−1) was supplied as either uniform irradiance (∼170 µmol m−2 s−1) or shade/fleck sequences (∼30 µmol m−2 s−1/∼525 µmol m−2 s−1). Photosynthesis and growth were enhanced by elevated CO2 treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO2 but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO2 were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post‐irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO2 under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition.
Allelism of rice blast resistance genes in two Chinese rice cultivars, and identification of two new resistance genes
Authors: Pan Q. , Wang L. , Tanisaka T. , Ikehashi H. 
Published: March 2003

Blast, caused by Pyricularia grisea, is a major constraint on rice production. To broaden genetic diversity for resistance to this disease, two rice cultivars, GA20 and GA25 from Yunnan Province, China, were analysed for the genetic basis of their high resistance to blast. GA20 was crossed with 10 Japanese differential cultivars, and GA25 was crossed with nine of them and with the susceptible Chinese cultivar Lijiangxintuanheigu (LTH). The resistance of GA20 was governed by two dominant genes allelic to genes at the Pi‐k and Pi‐ta loci. The allele at the Pi‐k locus was new, based on a reaction pattern different from known alleles at this locus. It could not be shown whether or not the allele at the Pi‐ta locus is new, because races with virulence for Pi‐ta were not tested. GA25 has one resistance gene, which is not allelic to genes at the loci Pi‐a, Pi‐k, Pi‐z, Pi‐ta, Pi‐b, and Pi‐t, but is linked to the Pi‐i gene on chromosome 9 with a recombination frequency of 15.1 ± 2.8%.The new allele at the Pi‐k locus in GA20 is designated as Pi‐kg(t), and the new resistance gene in GA25 as Pi15(t).
Occurrence of two serotypes of sweet potato chlorotic stunt virus in East Africa and their associated differences in coat protein and HSP70 homologue gene sequences
Authors: Alicai  , Fenby  , Gibson  , Adipala  , Vetten  , Foster  , Seal  
Published: March 2003

Amongst samples of the sweet potato chlorotic stunt crinivirus (SPCSV) obtained from crops of sweet potato in Uganda, two serotypes (SEA1 and SEA2) were distinguished using a panel of monoclonal antibodies (Mabs) to a Kenyan isolate of SPCSV. SEA1 serologically resembled the Kenyan isolate of SPCSV whereas SEA2 has not previously been reported. SEA1 was predominant in eastern Uganda whereas SEA2 was predominant in southern and western Uganda. SEA2 tended to occur in more severely diseased sweet potato plants than SEA1. RNA was extracted from eight plants and replicate clones representing the heat shock protein 70 (HSP70) homologue and coat protein (CP) genes were generated by reverse transcription and PCR. Sequence analyses revealed substitutions at two nucleotide positions in the HSP70 homologue gene, although neither affected deduced amino‐acid sequences. Nucleotide substitutions in the CP gene region, which led to 11 amino‐acid substitutions, revealed two major groupings plus other minor variants.The EMBL accession numbers of the sequences reported in this paper are AJ010754 through to AJ01769 (coat protein sequences) and AJ010914 through to AJ010929 (partial HSP70 homologue gene sequences).