bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of CO2, temperature and their interaction on the growth and yield of carrot (Daucus carota L.)
Authors: WHEELER T.R. , MORISON J. I. L. , ELLIS R.H. , HADLEY P.
Published: April 2006

Stands of carrot (Daucus carota L.) were grown in the field within polyethylene‐covered tunnels at a range of soil temperatures (from a mean of 7·5°C to 10·9°C) at either 348 (SE = 4·7) or 551 (SE = 7·7) μmol mol−1 CO2. The effect of increased atmospheric CO2 concentration on root yield was greater than that on total biomass. At the last harvest (137d from sowing), total biomass was 16% (95% CI = 6%, 27%) greater at 551 than at 348 μmol mol−1 CO2, and 37% (95% CI = 30%, 44%) greater as a result of a 1°C rise in soil temperature. Enrichment with CO2 or a 1°C rise in soil temperature increased root yield by 31% (95% CI = 19%, 45%) and 34% (95% CI = 27%, 42%), respectively, at this harvest. No effect on total biomass or root yield of an interaction between temperature and atmospheric CO2 concentration at 137 DAS was detected. When compared at a given leaf number (seven leaves), CO2 enrichment increased total biomass by 25% and root yields by 80%, but no effect of differences in temperature on plant weights was found. Thus, increases in total biomass and root yield observed in the warmer crops were a result of the effects of temperature on the timing of crop growth and development. Partitioning to the storage roots during early root expansion was greater at 551 than at 348 μmol mol−1 CO2. The root to total weight ratio was unaffected by differences in temperature at 551 μmol mol−1CO2, but was reduced by cooler temperatures at 348 μmol mol−1 CO2. At a given thermal time from sowing, CO2 enrichment increased the leaf area per plant, particularly during early root growth, primarily as a result of an increase in the rate of leaf area expansion, and not an increase in leaf number.
Effects of low temperature on lateral diffusion in plasma membranes on maize (Zea mays L.) root cortex protoplasts: relevance to chilling sensitivity
Authors: KOSTER K. L. , TENGBE M. A. , FURTULA V. , NOTHNAGEL E. A.
Published: April 2006

The effects of temperature on the lateral diffusion of fluorescent phospholipids, sterols and proteins in the plasma membranes of maize root cortex protoplasts were monitored using fluorescence photobleaching recovery (FPR). Diffusion parameters were measured in two cultivars of maize having different chilling tolerance. Hydrodynamic theory predicts that the diffusion coefficient, D, should increase with increasing temperature. In the more chilling‐tolerant cultivar, however, D for all three probes was nearly insensitive to temperature. In the more chilling‐sensitive cultivar, D was also insensitive to temperature over the range from 12 to 21°C, but D for the lipid probes tended to be higher and more variable at lower temperatures. The proportion of probe molecules free to diffuse in the membrane was less than 1 for all probes, and increased significantly with increasing temperature for the protein probe. These results, taken together, support the concept that the plasma membrane contains domains having differing diffusional characteristics. Temperature effects on membrane diffusion are moderated by the existence of these domains to limit significant changes. The observed tendency for higher diffusion coefficients at low temperatures in the chilling‐sensitive cultivar may correlate to morphological changes observed with protoplasts of that cultivar at low temperatures.
Loss of intracellular glycerol from Dunaliella by electroporation at constant osmotic pressure: subsequent restoration of glycerol content and associated volume changes
Authors: SHARIATI M. , LILLEY R. McC.
Published: April 2006

The effect of electroporation on Dunaliella tertiolecta at constant osmotic pressure (or water activity) was investigated. The following metabolic and physiological parameters were determined: extracellular and intracellular glycerol content, soluble protein content, photosynthetic oxygen evolution, mitochondrial oxygen uptake, cell volume and cell density. Electroporation conditions are described that released about 10% of intracellular glycerol to the external medium with minimal apparent effects on metabolism. Glycerol release originated from most cells rather than by total rupture of a small proportion of cells. Cell volume, measured on motile cells by video microscopy, reduced by 23% immediately after electroporation. Cell density did not increase. The uptake of mannitol, the major solute in the electroporation medium, was less than 20% of glycerol release. Following electroporation, the intracellular glycerol content and the cell volume both returned to pre‐electroporation values after about 30min. Because the cells were maintained at constant external osmotic pressure throughout the procedure, it is concluded that the regulatory mechanism responsible for setting the intracellular glycerol content does not sense external osmotic pressure per se. These findings are consistent with a mechanism that senses a parameter linked directly to cell volume to set the intracellular glycerol content.
Modelling forest response to increasing CO2concentration under nutrient‐limited conditions
Authors: KIRSCHBAUM M. U. F. , KING D. A. , COMINS H. N. , MCMURTRIE R. E. , MEDLYN B. E. , PONGRACIC S. , MURTY D. , KEITH H. , RAISON R. J. , KHANNA P. K. , SHERIFF D. W.
Published: April 2006

The growth rates of woody plants depend on both the rate of photosynthetic carbon gain and the availability of essential nutrients. Instantaneous carbon gain is known to increase in response to increasing atmospheric CO2concentration, but it is uncertain whether this will translate into increased growth in the longer term under nutrient‐limited conditions. An analytical model to address this question was developed by Comins & McMurtrie (1993,Ecological Applications3, 666–681). Their model was further tested and analysed. Manipulation of various assumptions in the model revealed its key assumptions and allowed a more confident prediction of expected growth responses to CO2enrichment under nutrient‐limited conditions.

The analysis indicated that conclusions about the CO2sensitivity of production were strongly influenced by assumptions about the relationship between foliar and heartwood nitrogen concentrations. With heartwood nitrogen concentration proportional to foliar nitrogen concentration, the model predicted a strong response of plant productivity to increasing CO2concentration, whereas with heartwood nitrogen concentration set constant, the model predicted only a very slight growth response to changing CO2concentration. On the other hand, predictions were only slightly affected by: (1) assumptions about the extent of nitrogen retranslocation out of senescing roots and foliage or wood during heartwood formation; (2) the effects of nitrogen status on specific leaf area or (3) leaf longevity; (4) carbon allocation between different plant parts; or (5) changes in the N:C ratio of organic matter sequestered in the passive pool of soil organic matter. Modification of the effect of foliar nitrogen concentration on the light utilization coefficient had only a small effect on the CO2sensitivity for pines. However, this conclusion was strongly dependent on the chosen relationship between single‐leaf photosynthesis and leaf nitrogen concentration. Overall, the analysis suggested that trees growing under nitrogen‐limited conditions can respond to increasing atmospheric CO2concentration with considerable increases in growth.
Adaptation of the tonoplast V‐type H+‐ATPase of Mesembryanthemum crystallinum to salt stress, C3–CAM transition and plant age
Authors: RATAJCZAK R. , RICHTER J. , LÜTTGE U.
Published: April 2006

Plants of the facultative halophyte and CAM species Mesembryanthemum crystallinum L. (Aizoaceae) were stressed for 8 d with 400 mol m−3 NaCl in the root medium. NaCl was then removed from the substratum, and the plants were watered again with NaCl‐free solution. A second set of plants was maintained as controls. A small degree of CAM, as indicated by day‐night changes in malate levels, was expressed during ageing of the plants. Salinity‐stress‐dependent CAM induction was reversible by the removal of salt, as indicated by similar Δ malate levels in previously salt‐stressed plants and in non‐stressed plants on day 19 of the experiment. Tonoplast vesicles were isolated from leaves during the time‐course of stress application, stress removal and ageing. Parameters of the tonoplast H+‐ATPase were correlated to the application of salinity, the expression of CAM and ageing. It was concluded, first, that a pronounced increase in the amount of tonoplast H+‐ATPase is related to salinity per se and a smaller increase to ageing; secondly, that there is an increase in the specific activity of the enzyme related to ageing; thirdly, that the induction of two new polypeptides with molecular masses of 32 and 28 kDa is correlated in time with the expression of CAM, and, fourthly, that the two new polypeptides are part of the tonoplast H+‐ATPase holoenzyme.
The influence of nitrogen availability on carbon and nitrogen storage in the biennial Cirsium vulgare (Savi) Ten. II. The cost of nitrogen storage
Authors: MONSON R.K. , SCHULZE E.‐D. , FREUND M. , HEILMEIER H.
Published: April 2006

The cost of nitrogen storage to current growth was examined in relation to N availability in the biennial Cirsium vulgare. Plants were grown outdoors, in sand culture, with continuous diel drip irrigation of fertilization medium containing one of five different N concentrations. Plants grown at the highest N concentration stored twice as much N in their tap roots as did plants grown at the lowest N concentration. In high‐N‐grown plants, the storage of N reserves occurred during the period of maximum growth, at the same time as tap‐root production. At the time of maximum biomass, stored N was also at a maximum. During the period following maximum biomass, no additional storage of N occurred. This pattern was observed despite frequent late‐season leaf senescence which resulted in a large pool of potentially mobile N which could have been stored at no cost to growth. In low‐N‐grown plants, the production of tap‐root storage tissue and the filling of that tissue with stored N were staggered. Tap‐root production and growth occurred during the period of maximum growth, as in the high‐N‐grown plants. However, filling of the storage tissue with N occurred late in the growing season, when the pool of mobile N from senescent leaves was large. The utilization of this late‐season N source occurred with little or no cost to growth, and this N is labelled, according to previous definitions, as ‘accumulated’. The costs of storing N in plants of the different N treatments were calculated using two models based on different growth constraints. In one model, the cost of N storage was represented as lost growth due to allocation of N to storage, rather than to the photosynthetic shoot (i.e. growth was assumed to be limited by carbon acquisition). In the second model, the storage cost was calculated as lost growth due to allocation of N to storage, rather than to the nitrogen‐acquiring fine‐root system (i.e. growth was assumed to be limited by nitrogen acquisition). In both models, the total cost of N storage was predicted to decrease as N availability decreased due to smaller storage pool sizes in plants of the low‐N treatments. The cost of filling the tap root with stored N as a percentage of the total storage cost was also reduced as N availability decreased due to the occurrence of late‐season accumulation. By relying, at least in part, on late‐season accumulation, plants grown at the lowest three levels of N availability reduced total storage costs by 15 to 22%. The results demonstrate that plants are capable of adjusting their storage patterns in response to low nitrogen availability such that the costs of storage are reduced.
Comparison of electric and growth responses to excision in cucumber and pea seedlings. I. Short‐distance effects are a result of wounding
Authors: STAHLBERG R. , COSGROVE D. J.
Published: April 2006

The local electric response to stem excision in both pea epicotyls and cucumber hypocotyls is a depolarization of the cells in the wound area. If we define wound area as the region of local depolarization, we find that it extends for approximately 10 mm from the cut or wound site in pea epicotyls, whereas it can reach up to 40 mm in cucumber hypocotyls. The wound‐induced depolarization in pea cells is transient, reaching its maximal amplitude within 1–2 min, whereas in cucumber cells this depolarization is more sustained. A third difference between wound responses in pea and cucumber is the intermittent appearance of spikes, i.e. very short, rapidly reverted depolarizations which frequently accompany the basic depolarization in cucumber but not in pea cells. These spikes can propagate in both directions along the hypocotyl axis. The cause of the different responses of pea and cucumber cells is unknown. A possible explanation might be found in different degrees of electrical cell coupling in the two species. This possibility was investigated in cucumber hypocotyls by measuring the cell input resistance (Rin) of epidermal cells at various axial distances from the cut. Shorter distances increase the likelihood of shunting the cell membrane resistance through the shortened symplastic path to the cut surface. With a series of cuts made at decreasing distances from the measured site, cell depolarization increased without comparable changes in Rin. Two conclusions were drawn. Firstly, wound‐induced depolarizations are not brought about by shunting of the cell resistance in the wound area. Secondly, the depolarization is probably not carried by ion channels but may be caused by an inhibition of proton pump activity. Parallel to its depolarizing effect on the membrane potential, excision led to a severe and sustained decline in the cucumber hypocotyl growth rate only when carried out sufficiently close to the growing region (45 mm from the hook). Similar excision in pea epicotyls failed to change the growth rate. Both electrical and growth data support the concept that the high and sustained responsiveness of cucumber seedlings to wounding is caused by a particular sensitivity of their proton pump mechanism.
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

In 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

The 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

The 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

Pea 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

Specific 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

The 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

Continually 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

Two 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

The 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

A 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

Patchy 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

Tomato 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

This 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

Significant 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.
Water relations and growth of tomato fruit pericarp tissue
Authors: GRANGE R. I.
Published: April 2006

The water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA3) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.
Proton flux measurements from tissues in buffered solution
Authors: ARIF I. , NEWMAN I. A. , KEENLYSIDE N.
Published: April 2006

Proton movement across plant cell membranes is part of many important physiological processes. The net proton flux to or from tissues can be determined non‐invasively by measuring the proton electrochemical potential gradient in the adjacent solution. In buffered solution, some of the protons crossing the tissue boundary diffuse as proto‐nated buffer whose flux is not included in the flux calculated from the proton (hydrogen ion) electrochemical gradient. In this theoretical paper, it is shown how experimenters can calculate the protonated buffer flux from the measured proton flux in solution. The ratio of these two components of total proton flux depends on the pH of the solution and on the concentration and pK of the buffer. For a given concentration of a buffer which has a single pK, the flux ratio rises with pH when the solution pH is lower than the buffer pK. The slope is about 2 on a log10 scale. As the pH increases above the pK, the flux ratio levels off to approach its maximum. With mixed buffers, or one having two or more pK values, the flux ratios are additive: each buffer acts independently based on its concentration and its pK value. Unbuffered solutions always have the buffering effects of water itself and also of carbonates due to carbon dioxide dissolved from the atmosphere. In unbuffered solutions at pH 6, the flux carried by water and carbonate is about 1 % of the measured proton flux. This validates measurements of proton flux from tissues, made by a number of workers, in unbuffered solutions below pH 6.
Effects of aluminium on nitrate uptake and assimilation
Authors: RUFTY T. W. , MacKOWN C. T. , LAZOF D. B. , CARTER T. E.
Published: April 2006

A study was conducted to examine the hypothesis that the effects of external Al on NO3− uptake and assimilation depend upon the concentration of Al present. Young soybean seedlings [Glycine max (L.) Merrill, cv. Essex], growing under moderate acidity stress at pH 4‐2, were exposed to a range of {A13+} in solution for 3d, and to labelled 99 atom %15NO3− during the final hour of Al exposure. Uptake of 15NO3−g−1 root dry weight was increased by about 28% in the presence of Al at {A13+} below 10 mmolm−3, and NO3− uptake was decreased by about 12% when the {A13+} increased to 44mmoln−3. The stimulation phase closely paralleled stimulation of root elongation. At higher {A13+}, the inhibition of root elongation was much more severe than that of NO3− uptake. There was no indication of a separate effect of Al on root 15NO3− reduction in situ, as the accumulation of reduced 15N in the root remained a similar percentage of 15NO3− uptake at all {A13+}. At higher {A13+}, the atom %15N enrichment of the insoluble reduced‐N (protein) fraction of root tips increased. This suggests that the Al inhibition of root elongation did not result from disruption of the N supply to the root apex.
The impact of mycorrhizal colonization upon nitrogen source utilization and metabolism in seedlings of Eucalyptus grandis Hill ex Maiden and Eucalyptus maculata Hook
Authors: TURNBULL M. H. , GOODALL R. , STEWART G. R.
Published: April 2006

Analysis of soil solution from forest sites dominated by Eucalyptus grandis and Eucalyptus maculata indicates that soluble forms of organic nitrogen (amino acids and protein) are present in concentrations similar to those of mineral nitrogen (nitrate and ammonium). Experiments were conducted to determine the extent to which mycorrhizal associations might broaden nitrogen source utilization in Eucalyptus seedlings to include organic nitrogen. In isolation, species of ectomycorrhizal fungi from northern Australia show varying abilities to utilize mineral and organic forms of nitrogen as sole sources. Pisolithus sp. displayed strongest growth on NH4+, glutamine and asparagine, but grew poorly on protein, while Amanita sp. grew well both on mineral sources and on a range of organic sources (e.g. arginine, asparagine, glutamine and protein). In sterile culture, non‐mycorrhizal seedlings of Eucalyptus grandis and Eucalyptus maculata grew well on mineral sources of nitrogen, but showed no ability to grow on sources of organic nitrogen other than glutamine. In contrast, mycorrhizal seedlings grew well on a range of organic nitrogen sources. These observations indicate that mycorrhizal associations confer on species of Eucalyptus the ability to broaden their resource base substantially with respect to nitrogen. This ability to utilize organic nitrogen was not directly related to that of the fungal symbiont in isolation. Seedlings mycorrhizal with Pisolithus sp. were able to assimilate sources of nitrogen (in particular histidine and protein) on which the fungus in pure culture appeared to grow weakly. Experiments in which plants were fed 15N‐labelled ammonium were undertaken in order to investigate the influence of mycorrhizal colonization on the pathway of nitrogen metabolism. In roots and shoots of all seedlings, 15N was incorporated into the amide group of glutamine, and label was also found in the amino groups of glutamine, glutamic acid, γ‐aminobutyric acid and alanine. Mycorrhizal colonization appeared to have no effect on the assimilation pathway and metabolism of [15N]H4+; labelling data were consistent with the operation of the glutamate synthase cycle in plants infected with either Pisolithus sp. (which in isolation assimilates via the glutamate synthase cycle) or Elaphomyces sp. (which assimilates via glutamate dehydrogenase). It is likely that the control of carbon supply to the mycorrhizal fungus from the host may have a profound effect on both the assimilatory pathway and the range of nitrogen sources that can be utilized by the association.
Evidence that photoperiodic, dark time measurement in Pharbitis nil involves a circadian rather than a semidian rhythm
Authors: LUMSDEN P. J. , YOUNGS J. A. , THOMAS B. , VINCE‐PRUE D.
Published: April 2006

Experiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far‐red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night‐break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night‐break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo‐period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is described.
Diurnal variations in growth rate and growth substrate levels of spinach (Spinacia oleracea L.) under nitrogen‐limiting conditions
Authors: BUYSSE J. , MERCKX R.
Published: April 2006

Spinach plants were grown in hydroponic culture provided with variable limiting amounts of N. During a complete diurnal cycle, growth of the root and shoot parts, as well as levels of soluble and insoluble sugars and of free amino acids, were monitored. No clear relationship could be detected between the level of N feeding and the levels of free sugars and amino acids. Analysis of variance revealed that the variances in the relative growth rates of plant root and shoot could be correlated with the levels of sugars and amino acids. Root amino acid concentration could be correlated with shoot amino acid concentration and root sugar concentration. No relationship was found between the variances in root and shoot free sugar concentrations.