bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blue‐green fluorescence excited by UV laser on leaves of different species originates from cutin and is sensitive to leaf temperature
Authors: BONGI G. , PALLIOTTI A. , ROCCHI P. , MOYA I. , GOULAS Y. 
Published: April 2006

ABSTRACTUnder ultra‐violet excitation, intact leaves generate a strong blue‐green fluorescence emission with several bands. Their integrated energy is 6 to 11 times the energy released by chlorophyll a bands (Chappelle et al. 1984, Applied Optics 23, 134–138). This paper provides evidence that the blue‐green fluorescence emission comes mainly from outer epidermal layers of the leaves and can be transferred on a quartz lamina by quickly dipping the leaves in organic solvents with subsequent solvent evaporation. Blue‐green fluorescence displays a diffusion‐controlled quenching of fluorescence intensity between 4°C (high fluorescence) and 37°C (low fluorescence). The blue‐green fluorescence emissivity is not linked to short‐term metabolic effects other than leaf temperature, but epidermis adaptations both to drought and to excessive radiation increase emissivity.
Far‐red light reflected from neighbouring vegetation promotes shoot elongation and accelerates flowering in spring barley plants
Authors: DAVIS M. H. , SIMMONS S. R. 
Published: April 2006

ABSTRACTField experiments were conducted in St Paul, MN, USA, to test the hypothesis that early season declines in the red:far‐red ratio (R:FR) associated with FR reflection from neighbouring leaves have a role in regulating barley development. Treatment plants were grown adjacent to densely sown border rows of barley. The borders functioned to reflect far‐red (FR), which reduced R:FR within the treatment plant light environment without shading treatment plants. Barriers were set in the soil to minimize root interactions between treatment plants and borders. Treatment plants were spaced either 2 or 16 cm apart. The presence of borders significantly increased shoot leaf and internode lengths at both plant spacings. Leaf sheath length data suggest that interactions between 2 cm spaced treatment plants enhanced plant responsiveness to the presence of borders. Border treatments shortened the period of vegetative growth prior to initiation of main shoot floral primordia. Bordered plants formed fewer main shoot leaves, initiated internode elongation at a lower node, and had slightly earlier heading dates than unbordered controls. Leaf appearance rate was not influenced by border treatments. We conclude that barley shoot development is photomorphogenically modulated by R:FR. Early season shifts in R:FR could have a significant influence on shoot development given that barley has the capacity to detect and developmentally respond to declines in R:FR associated with FR reflection from neighbours.
Molecular evolution of phosphoeno/pyruvate carboxylase
Authors: TOH H. , KAWAMURA T. , IZUI K. 
Published: April 2006

ABSTRACTPhosphoenolpyruvate carboxylase is an enzyme involved in a wide variety of important metabolic pathways of plants such as anaplerotic reactions and C4 and CAM photosynthetic pathways. The accumulation of molecular sequence data of phosphoenolpyruvate carboxylases has enabled us to investigate the function and molecular evolution of the enzymes by computer‐assisted sequence comparison. Here we report the results of sequence comparison of phosphoenolpyruvate carboxylases: (1) Phosphoenofpyruvate carboxylases were classified into four groups; a subgroup of bacterial enzymes and three subgroups of plants enzymes. (2) The divergence time of the monocot enzymes involved in the C4 pathways was roughly estimated to be 150—300 million years. On the other hand, the phylogenetic tree of the enzymes suggested that those for the dicot enzymes involved in the C4 and CAM pathways might be close to the divergence time between the monocots and the dicots. (3) The evolutionary positions of the enzymes prevalent in roots or root nodules were identified. (4) Although sorghum and maize contained at least three genes for the enzymes in their genomes, the rates of amino acid substitution of the enzymes were different from gene to gene. The difference could not be explained by either lineage effects nor bias in base contents.
The effect of ultraviolet‐B radiation on gene expression and pigment composition in etiolated and green pea leaf tissue: UV‐B‐induced changes are gene‐specific and dependent upon the developmental stage
Authors: JORDAN B. R. , JAMES P. E. , STRID Å. , ANTHONY R. G. 
Published: April 2006

ABSTRACTThe effect of ultraviolet‐B radiation (UV‐B: 280–320nm) on gene expression and pigment composition has been investigated in pea tissue at different stages of development. Pea (Pisum sativum L., cv. Feltham First) seedlings were grown for 17d and then exposed to supplementary UV‐B radiation. Chlorophyll a per unit fresh weight decreased by more than 20% compared with control levels after exposure to UV‐B radiation for 7d. In contrast, chlorophyll b content remained the same or increased slightly. Leaf protein biosynthesis, as determined by 35S‐methionine incorporation, was rapidly inhibited by UV‐B radiation, although the steady‐state levels of proteins were either unchanged or only slightly altered. RNA transcripts for the chlorophyll a/b binding protein (cab) were also rapidly reduced to low or even undetectable levels in the expanded third leaf or younger leaf bud tissue after exposure to UV‐B radiation. In contrast, cab RNA transcripts were either low or undetectable in etiolated pea tissue, but increased substantially in light and during exposure to UV‐B radiation. The cab RNA transcripts were still present at control levels in pea plants after 7d of greening under supplementary UV‐B radiation or UV‐B alone. The protein composition changed significantly over the 7d of greening, but no differences could be detected between the light treatments. The increase in chlorophyll content was slightly greater during de‐etiolation under supplementary UV‐B radiation than under control irradiance. Under UV‐B radiation alone, chlorophyll was synthesized at a greatly reduced rate. Changes in protective pigments were also determined. Anthocyanins did not change in either etiolated or green tissue exposed to UV‐B radiation. However, other flavonoids increased substantially in either tissue during exposure to light and UV‐B radiation. The RNA levels for chalcone synthase were measured in green and etiolated tissue exposed to UV‐B radiation. The chs RNA transcripts were present in low or undetectable amounts in control tissues. In green leaf tissue exposed to supplementary UV‐B, a transient increase was detected. The transcripts for chs reached a maximum level after approximately 8 h UV‐B exposure, and then declined to lower levels over subsequent days of diurnal photoperiods. However, a constant increase in chs was found after continuous exposure to UV‐B for up to 30 h. In etiolated tissue, either white‐light, supplementary UV‐B or UV‐B alone gave small increases in chs, only 8 h of UV‐B radiation alone gave any substantial increase in chs expression. Overall, these results clearly demonstrate that the response to increased levels of UV‐B radiation is dependent upon the developmental stage of the tissue and involves complex changes in gene expression.
The CO2‐concentrating mechanism is absent in the green alga Coccomyxa: a comparative study of photosynthetic CO2 and light responses of Coccomyxa, Chlamydomonas reinhardtii and barley protoplasts
Authors: PALMQVIST K. , ÖGREN E. , LERNMARK U. 
Published: April 2006

ABSTRACTPhotosynthesis was characterized for the unicellular green alga Coccomyxa sp., grown at low inorganic carbon (Ci) concentrations, and compared with Chlamydomonas reinhardtii, which had been grown so that the CO2 concentrating mechanism (CCM) was expressed, and with protoplasts isolated from the C3 plant barley (Hordeum vulgare). Chlamydomonas had a significantly higher Ci‐use efficiency of photosynthesis, with an initial slope of the Ci‐response curve of 0.7 mol(gChl)−1 h−1 mmol Cim−3)−1, as compared to 0.3 and 0.23 mol(gChl)−1 h−1 (mmol Cim−3)−1 for Coccomyxa and barley, respectively. The affinity for Ci was also higher in Chlamydomonas, as the half maximum rate of photosynthesis [K0.5 (Ci)] was reached at 0.18 mol m−3, as compared to 0.30 and 0.45 mol m−3 for Coccomyxa and barley, respectively. Ethoxyzolamide (EZ), an inhibitor of the enzyme carbonic anhydrase (CA) and the CCM, caused a 17‐fold decrease in the initial slope of the photosynthetic Cj‐response curve in Chlamydomonas, but only a 1.5‐ to two‐fold decrease in Coccomyxa and barley. The photosynthetic light‐response curve showed further similarities between barley and Coccomyxa. The rate of bending of the curve, described by the convexity parameter, was 0.99 (sharp bending) and 0.81–0.83 (gradual bending) for cells grown under low and high light, respectively. In contrast, the maximum convexity of Chlamydomonas was 0.85. The intrinsically lower convexity of Chlamydomonas is suggested to result from the diversion of electron transport from carbon fixation to the CCM. Taken together, these results suggest that Coccomyxa does not possess a CCM and due to this apparent lack of a CCM, we propose that Coccomyxa is a better cell model system for studying C3 plant photosynthesis than many algae currently used.
The origin and theoretical correction of thermal gradients in thermocouple psychrometers
Authors: VANDERCHMITT E. , DAUDET F.‐A. 
Published: April 2006

ABSTRACTTemperature‐compensated psychrometers are explained and a theoretical correction for temperature gradients, with its boundaries, is given. The correction was elaborated for in situ determination of water potential on soybean and tomato stems where it was indispensable. The origin of the thermal gradients in the psychrometric chamber is then discussed. Cooling of the conducting tissue by the circulation of xylem sap seemed to be the major cause for these gradients, while the heating of the psychrometer (thermally insulated) by the surroundings through radiative or conductive transfer was negligible.
Photon requirement for O2‐Revolution in red (λ= 680 nm) light for some C3 and C4 plants and a C3–C4 intermediate species*
Authors: OSBORNE B. A. 
Published: April 2006

ABSTRACTPhoton requirements for O2‐evolution in red (λ=680nm) light (Фr) were measured for six C3 species, one C3‐like, C3–C4 intermediate species, and three C4 species, including examples of NADP‐malic enzyme and PEP‐carboxykinase C4 sub‐groups. Variation in Фr within the C3 species was small with a mean value of 7.96 ±0.12 mol photon mol−1 O2, whereas the mean value for the C4 species was 12.27± 1.53 mol photon mol−1 O2, with the lowest value, 9.24 ±0.13 mol photon mol−1 O2, for the PEP‐carboxykinase C4 species Spartina townsendii. The C3–C4 intermediate species Panicum milioides had a value of 9.05 ±0.29 mol photon mol−1 O2, approximately 1 mol photon mol−1 O2 greater than the C3 species. The possibility that this extra cost is due to PEP‐carboxylase‐dependent recycling of CO2 is discussed. No correlation was found between Фr and chlorophyll content or leaf absorptance. Based on white (ФW) and red light measurements of the photon requirement, values in red light were approximately 20% higher than white‐light estimates. These results are discussed with reference to accepted mechanisms of energy transduction in thylakoid membranes (Z‐scheme), expected inefficiencies and losses during light‐harvesting and electron transport reactions, and the influence of respiratory processes.
Spectral balance and UV‐B sensitivity of soybean: a field experiment
Authors: CALDWELL M. M. , FLINT S. D. , SEARLES P. S. 
Published: April 2006

ABSTRACTSoybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV‐B radiation (280–320 nm) under different combinations of UV‐A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV‐B and UV‐A lamps electronically modulated to track ambient radiation. Significant UV‐B‐caused decreases in total aboveground production and growth were seen only when PFD and UV‐A were reduced to less than half their flux in sunlight. When PFD was low, UV‐A appeared to be particularly effective in mitigating UV‐B damage. However, when PFD was high, substantial UV‐A did not appear to be required for UV‐B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV‐B, leaves in all experiments exhibited increased UV‐absorbing pigments and decreased whole‐leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV‐B experiments conducted in glasshouse or growth cabinet conditions to plant UV‐B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.
Hardening of root cell walls: a growth inhibitory response to salinity stress
Authors: NEUMANN P. M. , AZAIZEH H. , LEON D. 
Published: April 2006

ABSTRACTPrimary roots of intact maize plants (Zea mays L.) grown for several days in nutrient solutions containing 100 mol m−3 NaCl and additional calcium, had relatively inhibited rates of elongation. Possible physical restraints underlying this salt induced inhibition were investigated. The inhibition did not involve reductions in osmotic potential gradients and turgor in the tip tissues responsible for root elongation growth. The apparent yield threshold pressure, which is related to capacity of cell walls to undergo loosening by stress relaxation, was estimated psychrometrically in excised root tips. Salinity increased yield threshold values. Comparative root extensibility values were obtained for intact plants by determining the initial (1 min) increase in root elongation rate induced by an 0.1 MPa osmotic jump. Comparative extensibility was significantly reduced in the salinized root tips. Salinity did not reduce capacities for water efflux and associated elastic contraction in root tip tissues of intact plants exposed to hypertonic mannitol. We conclude that cell wall hardening in the elongating root tips is an important component of root growth inhibition induced by long‐term salinization.
Day‐to‐day variation in nitrogenase activity of Alnus incana explained by weather variables: a multivariate time series analysis
Authors: EKBLAD A. , LUNDQUIST P.‐O. , SJÖSTRÖM M. , HUSS‐DANELL K. 
Published: April 2006

ABSTRACTA modelling system is described that indicates the extent to which day‐to‐day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field‐grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x‐variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x‐variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early‐season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten‐fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x‐variables, information that is non‐accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day‐to‐day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.
Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus‐indica
Authors: CUI M. , NOBEL P. S. 
Published: April 2006

ABSTRACTGas exchange and dry‐weight production in Opuntia ficus‐indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol−1 CO2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m−2 d−1). Elevated CO2 and PPFD enhanced the growth of basal cladodes and roots during the 12‐week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO2 enhanced the growth of first‐daughter cladodes but decreased the growth of the second‐daughter cladodes produced on them. CO2 enrichment enhanced daily net CO2 uptake during the initial 8 weeks after planting for both basal and first‐daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol−1 CO2. Cladode chlorophyll content was lower in elevated CO2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO2. The effect of elevated CO2 on net CO2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol−1 CO2. Averaged for the two CO2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.
Regulation of transpiration in coffee hedgerows: covariation of environmental variables and apparent responses of stomata to wind and humidity
Authors: GUTIÉRREZ M. V. , MEINZER F. C. , GRANTZ D. A. 
Published: April 2006

ABSTRACTStomatal regulation of transpiration was studied in hedgerow coffee (Coffea arabica L.) at different stages of canopy development encompassing a range of leaf area indices (L) from 0·7 to 6·7. Stomatal (gs) and crown (gc) conductance attained maximum values early during the day and then declined as both leaf‐to‐bulk air water vapour mole fraction difference (Va) and photosynthetically active photon flux density (I) continued to increase. Covariation of environmental variables during the day, particularly V, I, and wind speed (u), obscured stomatal responses to individual variables. This also caused diurnal hysteresis in the relationship between gc and individual variables. Normalization of gs and gc by I removed the hysteresis and revealed a strong stomatal response to humidity. At the crown scale, transpiration (E) increased linearly with net radiation (Rn) and seemed to increase with increasing wind speed. Increasing wind speed imposed higher leaf interior to leaf surface water vapour mole fraction differences (Vs) at given levels of Va. However, strong relationships between declining gc and E and increasing wind speed were obtained when gc and E were normalized by I and Rn, respectively, without invoking additional potential interactions involving temperature or CO2 concentration at the leaf surface. Apparent stomatal responses to wind were thus at least partially a reflection of the stomatal response to humidity.
Investigations of mechanisms of resistance to bipyridyl herbicides in Arctotheca calendula (L.) Levyns
Authors: PRESTON C. , BALACHANDRAN S. , POWLES S. B. 
Published: April 2006

ABSTRACTThe mechanism of resistance to diquat and paraquat was investigated in a bipyridyl‐herbicide‐resistant biotype of Arctotheca calendula (L.) Levyns. No differences were observed in the interactions of these herbicides with Photo‐system I, the active site, in thylakoids isolated from resistant and susceptible biotypes. Likewise, absorption of herbicide through the cuticle and gross translocation were identical in plants of the two biotypes. Foliar application of either 25 g ha−1 diquat or 200 g ha−1 paraquat rapidly inhibited CO2‐dependent O2 evolution of leaf segments of the susceptible biotype. O2 evolution of leaf segments of the resistant biotype was less affected by these treatments. Fluorescence imaging was used to observe visually, as fluorescence quenching, the penetration of herbicide to the active site. These experiments demonstrated that diquat appears at the active site more slowly in the resistant biotype compared to the susceptible biotype. HCO3‐dependent O2 evolution of thin leaf slices was less inhibited by diquat in the resistant biotype than in the susceptible biotype. The mechanism of resistance to the bipyridyl herbicides in this biotype of A. calendula is not a result of changes at the active site, decreased herbicide absorption or decreased translocation, but appears to be due to reduced herbicide penetration to the active site.
Xylem water transport: is the available evidence consistent with the cohesion theory?
Authors: ZIMMERMANN U. , MEINZER F. C. , BENKERT R. , ZHU J.J. , SCHNEIDER H. , GOLDSTEIN G. , KUCHENBROD E. , HAASE A. 
Published: April 2006

ABSTRACTSince its introduction in the late 19th century, the so‐called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m−1. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension‐driven water transport as the exclusive mechanism of long‐distance water transport in plants.