bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iron deficiency‐induced changes in the photosynthetic pigment composition of field‐grown pear (Pyrus communis L) leaves
Authors: MORALES F. , ABADÍA A. , BELKHODJA R. , ABADÍA J. 
Published: April 2006

ABSTRACTIn this work we characterize the changes induced by iron deficiency in the pigment composition of pear (Pyrus communis L.) leaves grown under high light intensities in field conditions in Spain. Iron deficiency induced decreases in neoxanthin and β‐carotene concomitantly with decreases in chlorophyll a, whereas lutein and carotenoids within the xanthophyll cycle were less affected. Iron deficiency caused major increases in the lutein/chlorophyll a and xanthophyll cycle pigments/chlorophyll a molar ratios. The chlorophyll a/chlorophyll b ratio increased in response to iron deficiency. The carotenoids within the xanthophyll cycle in iron‐deficient and in iron‐sufficient (control) leaves underwent epoxidations and de‐epoxidations in response to ambient light conditions. In control leaves dark‐adapted for several hours, most of the xanthophyll cycle pigment pool was in the epoxidated form vio‐laxanthin, whereas iron‐deficient leaves had significant amounts of zeaxanthin. Iron‐deficient leaves also exhibited an increased non‐photochemical quenching, supporting the possibility of a role for pigments within the xanthophyll cycle in photoprotection.
Insects and fungi on a C3 sedge and a C4 grass exposed to elevated atmospheric CO2 concentrations in open‐top chambers in the field
Authors: THOMPSON G. B. , DRAKE B. G. 
Published: April 2006

ABSTRACTThe effects of elevated atmospheric CO2 concentration on plant‐fungi and plant‐insect interactions were studied in an emergent marsh in the Chesapeake Bay. Stands of the C3 sedge Scirpus olneyi Grey, and the C4 grass Spartina patens (Ait.) Muhl. have been exposed to elevated atmospheric CO2 concentrations during each growing season since 1987. In August 1991 the severities of fungal infections and insect infestations were quantified. Shoot nitrogen concentration ([N]) and water content (WC) were determined. In elevated concentrations of atmospheric CO2, 32% fewer S. olneyi plants were infested by insects, and there was a 37% reduction in the severity of a pathogenic fungal infection, compared with plants grown in ambient CO2 concentrations. S. olneyi also had reduced [N], which correlated positively with the severities of fungal infections and insect infestations. Conversely, S. patens had increased WC but unchanged [N] in elevated concentrations of atmospheric CO2 and the severity of fungal infection increased. Elevated atmospheric CO2 concentration increased or decreased the severity of fungal infection depending on at least two interacting factors, [N] and WC; but it did not change the number of plants that were infected with fungi. In contrast, the major results for insects were that the number of plants infected with insects decreased, and that the amount of tissue that each insect ate also decreased.
The plasmalemma surface area exposed to the soil solution is markedly reduced by maturation of the exodermis and death of the epidermis in onion roots
Authors: KAMULA S. A. , PETERSON C. A. , MAYFIELD C. I. 
Published: April 2006

ABSTRACTThe dimorphic exodermis of the root of onion (Allium cepa L.) consists of long and short cells, both of which have Casparian bands. The long cells and some of the short cells also have suberin lamellae. The proportion of short cells with lamellae increases with distance from the root tip and with plant age, but is not influenced by drought stress. In young regions of onion roots, characterized by a mature endodermis and an immature exodermis, the plasmalemma surface area that can be contacted by the soil solution is 90·9 mm2 per mm length of root, i.e. the sum of the plasmalemma surface areas of the epidermis, immature exodermis, cortical parenchyma and endodermis external to the Casparian band. This is reduced to 14·5–14·7 mm2 by the development of a Casparian band in the exodermis, which cuts off access to the cortical parenchyma, and by the development of suberin lamellae, which cut off access to the plasmalemmae of the long and some of the short cells of the exodermis. Death of all the epidermal cells, a consequence of drought, further reduces this area to 0·205–0·0183 mm2, i.e. the area of the outer tangential plasmalemmae of the short cells without suberin lamellae. In this condition, the root's capacity for ion uptake should be reduced but its capacity to resist water loss to the soil should be increased.
Replacement of nitrate by ammonium as the nitrogen source increases the salt sensitivity of pea plants. II. Inter‐ and intracellular solute compartmentation in leaflets
Authors: SPEER M. , KAISER W. M. 
Published: April 2006

ABSTRACTPea plants (Pisum sativum L. cv. ‘Kleine Rheinländerin’) grown on ammonium or nitrate as the sole nitrogen source were treated with 50 mol m−3 NaCl. Four days after salt addition, ammonium‐grown plants developed the first visible damage symptoms (wilting of leaflets, starting from the margins). Salt‐treated, nitrate‐grown plants were not affected during the experimental period. In order to obtain a better understanding of this differential salt sensitivity, we investigated the inter‐ and intracellular ion compartmentation of leaflets under both nutritional conditions by analysing ion concentrations in the apoplastic space, in chloroplasts and in protoplasts. When the leaves of nitrate‐ and ammonium‐grown plants had attained similar sodium and chloride contents (after different times of exposure to salinity), the latter had a considerably lower chloroplastic chloride (and also sulphate) concentration. The results suggest that the intracellular compartmentation capacity of ammonium‐grown plants is considerably lower than that of nitrate‐grown plants. Ion toxicity appeared to initiate breakdown of metabolism in parts of the mesophyll tissue of ammonium‐grown plants, causing an abrupt release of solutes into the apoplast, which coincided with the appearance of visible damage. Although the ammonium concentrations in leaves increased dramatically in the later phases of damage development, they were too low to cause the collapse of electrochemical gradients at the time at which damage became visible. Thus, the reason for a lower compartmentation capacity under ammonium nutrition remains as yet unclear.
Long‐term responses of Melilotus segetalis to salinity. II. Nutrient absorption and utilization
Authors: ROMERO J. M. , MARAÑÓN T. , MURILLO J. M. 
Published: April 2006

ABSTRACTSpecific absorption rates (SAR) and specific utilization rates (SUR) of sodium, chloride, potassium, calcium, magnesium and phosphate ions were determined for Melilotus segetalis (Brot.) Ser. (annual sweetclover) grown under both control and salinized conditions (NaCl treatment of CE=15 dS m−1) for a complete life cycle with sequential harvests.The behaviour over time of the SARs and SURs of the mineral elements was in general correlated with relative growth rate (RGR) kinetics, with a parabolic trend during the vegetative phase and a progressive linear decrease during the reproductive stage.Salinity significantly reduced the SARs of K and Mg but did not affect the SARs of Ca and P during the vegetative phase. During the reproductive stage, however, the SARs of K, Ca and P of salt‐stressed plants were higher than in control plants. The similar SARs of total cations (TC) found in control and salt‐stressed plants may indicate compensatory mechanisms to maintain a constant total cation content.Salt‐stressed plants showed lower SURs of K, Ca and P during the vegetative phase, and lower SURs of K and P but a higher SUR of Mg during the reproductive stage.A nutrient imbalance, caused by a lower root efficiency in absorbing K and Mg and a lower leaf efficiency in producing biomass per unit of K, Ca and P, apparently contributed to the salt‐induced reduction in growth during the vegetative phase of M. segetalis. The switch to non‐reduced, compensated growth during the reproductive phase may have been caused by a higher nutrient demand which increased the root efficiency in absorbing K, Ca and P and the leaf efficiency in utilizing Mg.
Pine needle growth and fine structure after prolonged acid rain treatment in the subarctic
Authors: BÄCK J. , NEUVONEN S. , HUTTUNEN S. 
Published: April 2006

ABSTRACTThe growth and morphology of Scots pine needles were studied in a long‐term acid rain experiment in the far north of Finnish Lapland. Pine trees 5 m tall of age 50–70 years were exposed, by spraying the foliage and soil from a height of 2 m, to either clean water (IC) or acidified water over the period 1985–1992, the acidification site being divided into sub‐areas in which the precipitation contained two levels of either sulphuric (Sm, Sh) or nitric (Nm, Nh) acid, or both (SNm, SNh). The treatments with medium and high sulphate‐S over eight consecutive years yielded a total sulphur deposition of 3·4 and 17·1 gm−2, respectively, and those with medium and high nitrate‐N a total nitrogen deposition of 1·1 and 5·9 g m−2. Needles were collected for light and electron microscopy, growth measurements and morphometry. Growth in branch height had decreased by about 40% after 6 years of SNm or SNh treatment, and needle growth by 15% in the SNh trees as compared with the irrigated control trees (IC), although decreases were statistically significant only with respect to the non‐irrigated control trees (DC). Growth of branches and needles was slightly better in the Nh treatment than in the IC group. The areas of the whole needle, the mesophyll and the phloem decreased in response to SNh treatment as compared with IC or DC, and a statistically significant decrease of about 30–40% was seen in the area of the xylem in comparison with DC. Cellular damage was observed following the acid treatments, especially with a high acid load. The damage was manifested in collapse of the cellular compartments, increases in lipid accumulations and swelling or disorganization of the protoplast. Increased vacuolization of the cytoplasm, plasmalemma irregularities and chilling‐type damage to the mitochondria were also observed.
Consequences of growth at two carbon dioxide concentrations and two temperatures for leaf gas exchange in Pascopyrum smithii (C3) and Bouteloua gracilis (C4)*
Authors: MORGAN J. A. , HUNT H. W. , MONZ C. A. , LECAIN D. R. 
Published: April 2006

ABSTRACTContinually rising atmospheric CO2 concentrations and possible climatic change may cause significant changes in plant communities. This study was undertaken to investigate gas exchange in two important grass species of the short‐grass steppe, Pascopyrum smithii (western wheat‐grass), C3, and Bouteloua gracilis (blue grama), C4, grown at different CO2 concentrations and temperatures. Intact soil cores containing each species were extracted from grasslands in north‐eastern Colorado, USA, placed in growth chambers, and grown at combinations of two CO2 concentrations (350 and 700 μmol mol−1) and two temperature regimes (field average and elevated by 4°C). Leaf gas exchange was measured during the second, third and fourth growth seasons. All plants exhibited higher leaf CO2 assimilation rates (A) with increasing measurement CO2 concentration, with greater responses being observed in the cool‐season C3 species P. smithii. Changes in the shape of intercellular CO2 response curves of A for both species indicated photosynthetic acclimation to the different growth environments. The photosynthetic capacity of P. smithii leaves tended to be reduced in plants grown at high CO2 concentrations, although A for plants grown and measured at 700μmol mol−1 CO2 was 41% greater than that in plants grown and measured at 350 μmol mol−1 CO2. Low leaf N concentration may have contributed to photosynthetic acclimation to CO2. A severe reduction in photosynthetic capacity was exhibited in P. smithii plants grown long‐term at elevated temperatures. As a result, the potential response of photosynthesis to CO2 enrichment was reduced in P. smithii plants grown long‐term at the higher temperature.
Isoforms of glutamine synthetase in asparagus spears: the cytosolic enzyme increases after harvest
Authors: DOWNS C. G. , BORST W. M. , HURST P. L. , STEVENSON D. G. 
Published: April 2006

ABSTRACTTwo distinct forms of glutamine synthetase (GS) have been identified in the spear tip tissues of harvested asparagus (Asparagus officinalis L. cv. Limbras 10). The GS activities were separated by anion exchange chromatography. They have distinct kinetic properties and contain polypeptides of different sizes, and the abundances of the GS isoforms change differently after harvest. Plastid GS has a 44 kD polypeptide, and during the post‐harvest period the abundance of this polypeptide declined dramatically. After 5 d, the activity of plastid GS had declined to just 20% of that at harvest. Cytosolic GS has a 40 kD polypeptide and is the major constituent of the GS activity present at harvest (73% of total). After harvest, cytosolic GS activity declined by half and then, at 3 or 4 d after harvest, rose to 80% of the cytosolic GS activity present at harvest. The nitrogen metabolism of asparagus spears is significantly altered as the tissues deteriorate rapidly after harvest. We demonstrate that cytosolic GS activity increases during the post‐harvest period and is likely to be a critical feature of the physiology of the tip of a harvested asparagus spear.
Influence of temperature on the rhythmic emission of volatiles from Ribes nigrum flowers in situ
Authors: HANSTED L. , JAKOBSEN H. B. , OLSEN C. E. 
Published: April 2006

ABSTRACTThe floral volatiles of blackcurrant (Ribes nigrum) were collected in situ using the headspace technique. Eleven compounds were identified, including monoterpenes hydrocarbons and monoterpene ethers. The fragrance was emitted in a rhythmic manner, the maximum being in the middle of the photoperiod. Emission at 20°C was significantly higher than at 10°C. The rhythmic nature of emission seemed to cease under conditions of constant light. However, a slight rise in emission during the second period in continuous light may indicate a circadian control of emission. The significance of flower volatiles in relation to pollination is discussed.
Nitrogen partitioning and assimilation: methods for the extraction, separation and mass spectrometric analysis of nitrate, amino acid and soluble protein pools from individual plants following 15N labelling
Authors: ROBE W. E. , GRIFFITHS H. , SLEEP D. , QUARMBY C. 
Published: April 2006

ABSTRACTA simple procedure is described for the separation of nitrate, amino acid and soluble protein pools in small volumes of plant extract. Recent developments in mass spectrometry and automated, on‐line sample preparation facilitate the precise analysis of the 15N content of samples containing low concentrations of N (≤5 to ≥50μg) with enrichments close to the natural abundance level. When combined, these separation and analysis techniques make it possible to investigate and quantify the relationships between nitrogen uptake, storage, assimilation, and partitioning between discrete pools of N within individual plants, following 15N labelling.
Dynamics of patchy stomatal movements, and their contribution to steady‐state and oscillating stomatal conductance calculated using gas‐exchange techniques
Authors: CARDON Z. G. , MOTT K. A. , BERRY J. A. 
Published: April 2006

ABSTRACTPatchy stomatal movements were induced in leaves of Helianthus annuus L. and Xanthium strumarium L. by increasing Δw and decreasing light in a gas‐exchange cuvette. The dynamics of the patchy movements were recorded and analysed using images of chlorophyll fluorescence, and the influence of heterogeneous stomatal activity on gas‐exchange measurements of whole‐leaf stomatal conductance was explored. Image series and gas‐exchange measurements from two contrasting 100 min experiments are presented. One series of images, taken using Helianthus annuus, was characterized by strongly oscillating stomatal conductance induced by a decrease in light at high Δw. Fluorescence analysis revealed that individual patches of the leaf displayed a variety of behaviours (from static to strongly oscillating fluorescence), which, when averaged, matched the time dependence of the oscillating stomatal conductance measured by gas‐exchange techniques. During the second series of images, taken using Xanthium strumarium, stomatal conductance (measured with gas exchange) declined slightly after an increase in Δw, and then maintained a steady state. Again, some patches in this leaf showed highly dynamic qNP, although on the whole qNP varied without any obvious pattern or frequency. When all patch activity in this series was averaged, it paralleled the steady whole‐leaf stomatal conductance determined by gas‐exchange measurements. It is clear from this work that coordinated patchy stomatal movements can contribute significantly to the dynamics of whole‐leaf stomatal conductance, and, in contrast, that dynamic but uncoordinated patchy movements can average to produce a steady gas‐exchange trace.
Some relationships between the gas exchange, biochemistry and molecular biology of photosynthesis during leaf development of tomato plants after transfer to different carbon dioxide concentrations
Authors: VAN OOSTEN J.‐J. , BESFORD R. T. 
Published: April 2006

ABSTRACTTomato plants were exposed to four concentrations of CO2 (350, 700, 1050 or 1400 μmol CO2 mol−1) for 31 d. The light‐saturated rate of photosynthesis (A) of the unshaded fifth leaf was measured at either an ambient CO2 concentration of 350 μmol CO2 mol−1 [A (350)] or at the level of CO2 at which the plants were grown. The chloroplast protein composition and the level of transcripts of nuclear or plastid photosynthesis‐associated genes (PAGs), as well as the main carbohydrate content of the fifth leaf maintained horizontal and unshaded, were also measured during leaf development. At 60 and 95% leaf expansion, the A of high‐CO2‐grown plants measured at growth CO2 was higher than the A (350) of the plants grown at ambient CO2. However, in the fully mature leaves, A (growth CO2) declined linearly as growth CO2 concentration increased. The A (350) of plants exposed to elevated CO2 up to 60% leaf expanion had not acclimated to high CO2. At 95% leaf expansion, A (350) was lower in plants grown at high CO2. A versus CO2 (Ci) for mature leaves showed that A of the plants grown at high CO2 was lower over the entire range than that for plants grown at present ambient CO2 concentration. Lines fitted to the linear part of the A/Ci curves were concurrent at a Ci of 49μmol CO2 mol−1 and A=−1.21μmol CO2 m−2s−1. This Ct value is close to Λ* (46 μmol CO2 mol−1), the compensation point at 27°C calculated from the equation described in Brooks & Farquhar (1985, Planta 165, 397–406). This A is an estimate of respiration in the light (R1) and was not affected by acclimation to elevated CO2. Thylakoid proteins (photo‐system I core protein, D1 and D2 of the photosystem II core complex, cytochrome f) were all reduced by elevated CO2 only in the fully mature leaves (31d exposure), whereas the large and small subunits of Rubisco and Rubisco activase proteins had already declined after 22 d exposure. Transcript levels of the plastid‐encoded PAG (rbcL, psbA, psaA‐B) were reduced in the mature leaves by elevated CO2 when expressed on a total RNA basis, but they were not sensitive to elevated CO2 when expressed on a chloroplast 16S rRNA basis. However, rbcS, rca and cab mRNA transcripts were lower in the plants grown at high CO2 than in control plants after 22 d exposure when expressed on a nuclear rRNA basis. The loss of these nuclear PAGs was correlated with an accumulation of soluble sugars and starch.
Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using 15N
Authors: MULLER B. , TILLARD P. , TOURAINE B. 
Published: April 2006

ABSTRACTThis study was undertaken to determine which of the two NO3− fluxes (influx or efflux) across plasma membranes of root cells is the target of those amino acids which have been shown to inhibit net NO3− uptake (Muller & Touraine 1992, Journal of Experimental Botany43, 617–623). Parallel experiments were performed to mea‐sure either the time course of 15NO3− release from roots of soybean seedlings previously labelled with this isotope into non‐labelled solution, or the time course of 15N accumulation from labelled 15NO3− solution in non‐labelled seedlings. Focusing on the fate of 15NO3− in the cytoplasmic compartment, a model is developed to describe the time courses of the accumulation and release of tracer across the plasma membranes of root cells. Both time courses can be described by the sum of an exponential plus a linear term. In our material, the linear part of the accumulation time course is obscured by the NO3− fluxes exiting the cytoplasm, and the curve thus appears to be quasilinear over several minutes. However, we show that the use of the net tracer accumulation rate during this time period as an estimate of NO3− influx does not provide accurate estimates of influx and efflux. By contrast, 15NO3− efflux analysis permits calculation of the unidirectional fluxes across plasma membranes of root cells and the kinetic parameters of the cytoplasmic NO3− pool. Under our experimental conditions, efflux accounted for 30 to 50% of influx, and the cytoplasmic NO3− content was found to be in the 70–400nmol g−1 fw range. Using this methodology, the effect of amino acid accumulation on unidirectional fluxes of nitrate was then examined. Pretreatments of the seedlings with an amino acid which has been shown to inhibit net NO3− uptake led to concomitant decreases in net accumulation rates of 15NO3− and of reduced 15N in roots and total 15N in cotyledons. NO3− influx was markedly inhibited by these treatments, while NO3− efflux remained essentially unaffected, or even decreased. It is concluded that the target of the regulation of NO3− uptake by phloemtranslocated amino acids is the influx system.
Regulation of proline accumulation in Arabidopsis thaliana (L.) Heynh during development and in response to desiccation
Authors: CHIANG H.‐H. , DANDEKAR A. M. 
Published: April 2006

ABSTRACTSignificant differences were observed in the amount and proportion of free amino acids in different organs of Arabidopsis thaliana (L.) Heynh, ecotype Columbia. The most notable were found for proline, which formed 17–26% of the total free amino acid concentration in reproductive tissues (floret and seed), but only 1–3% of the total free amino acid concentration in vegetative tissues (rosette leaf and root). Proline accumulation was associated with tissues that had relatively low water contents. Tissues which displayed high water contents, such as rosette leaves, contained low levels of proline. A significant increase in the levels of proline accumulation occurred in plants subjected to experimentally induced low water potentials as compared to unstressed plants. For instance, an 8–10‐fold increase in proline was observed in the presence of 120 mmol kg−1 NaCl or KCl, and a 20‐fold increase was stimulated by 60 mmol kg−1 PEG. However, in addition to the accumulation of proline, massive accumulation of Na+, K+ and Cl− ions occurred in tissues of plants stressed with salt. No significant differences were observed in mineral ions in plants stressed with PEG. Isotope tracer experiments with 14C compounds established that glutamate, ornithine and arginine are precursors of the proline biosynthesis induced by PEG in response to low water potentials in Arabidopsis thaliana. We conclude that the accumulation of proline in response to PEG occurs through increased biosynthesis.