bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predicting responses of photosynthesis and root fraction to elevated [CO2]a: interactions among carbon, nitrogen, and growth*
Authors: LUO Y. , FIELD C. B. , MOONEY H. A. 
Published: April 2006

ABSTRACTAt elevated atmospheric CO2 concentrations ([CO2]a), photosynthetic capacity (Amax) and root fraction (ηR, the ratio of root to plant dry mass) increased in some studies and decreased in others. Here, we have explored possible causes of this, focusing on the relative magnitudes of the effects of elevated [CO2]a on specific leaf (nm) and plant (np) nitrogen concentrations, leaf mass per unit area (h), and plant nitrogen productivity (α). In our survey of 39 studies with 35 species, we found that elevated [CO2]a led to decreased nm and np in all the studies and to increased h and α in most of the studies. The magnitudes of these changes varied with species and with experimental conditions.Based on a model that integrated [CO2]a‐induced changes in leaf nitrogen into a biochemically based model of leaf photosynthesis, we predicted that, to a first approximation, photosynthesis will be upregulated (Amax will increase) when growth at increased [CO2]a leads to increases in h that are larger than decreases in nm. Photosynthesis will be downregulated (Amax will decrease) when increases in h are smaller than decreases in nm. The model suggests that photosynthetic capacity increases at elevated [CO2]a only when additional leaf mesophyll more than compensates the effects of nitrogen dilution.We considered two kinds of regulatory paradigms that could lead to varying responses of ηR to elevated [CO2]a, and compared the predictions of each with the data. A simple static model based on the functional balance concept predicts that ηR should increase when neither np nor h is very responsive to elevated [CO2]a. The quantitative and qualitative agreement of the predictions with data from the literature, however, is poor. A model that predicts ηR from the relative sensitivities of photosynthesis and relative growth rate to elevated [CO2]a corresponds much more closely to the observations. In general, root fraction increases if the response of photosynthesis to [CO2]a is greater than that of relative growth rate.
Interacting effects of CO2 concentration, temperature and nitrogen supply on the photosynthesis and composition of winter wheat leaves
Authors: DELGADO E. , MITCHELL R. A. C. , PARRY M. A. J. , DRISCOLL S. P. , MITCHELL V. J. , LAWLOR D. W. 
Published: April 2006

ABSTRACTWinter wheat (Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO2 concentrations (350 and 700 μmol mol−1), two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4°C] and two rates of nitrogen supply (equivalent to 489 kg ha−1 and 87 kg ha−1). Leaves grown at 700 μmol mol−1 CO2 had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO2 concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long‐term exposure to elevated CO2 concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO2 concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO2 concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity.
Effective stomatal and boundary‐layer resistances of heterogeneous surfaces
Authors: McNAUGHTON K. G. 
Published: April 2006

ABSTRACTIn nature surfaces are rarely uniform, so terms such as ‘surface’, ‘stomatal’ or ‘canopy’ resistance usually indicate some kind of average over a population of sub‐areas, each with its own separate resistance. Questions then arise as to how gross measurements of these resistances should be interpreted in terms of the components, or how components should be aggregated into representative single values. Aggregation schemes have been published by Raupach (1991, Vegetatio 91, 105–120) and Lhomme (1992, Agriculture and Forest Meteorology 61, 11–21), but these are different for reasons that were not explained. This paper develops the idea that averaging schemes should be designed to serve particular purposes, and that they can be varied to suit these purposes. It is shown that the ‘effective’ resistances defined by Raupach and Lhomme preserve different quantities. A further averaging scheme is developed which preserves both correct transpiration rate and CO2 flux when used in the Penman‐Monteith equation and an equation describing assimilation. All of these schemes are fairly complex, so the work provides a warning against naive use of effective variables.
Endocytosis in plants: fact or artefact?
Authors: HAWES C. , CROOKS K. , COLEMAN J. , SATIAT‐JEUNEMAITRE B. 
Published: April 2006

ABSTRACTWhilst plant cells are apparently equipped with all the necessary molecular machinery for receptor‐mediated endocytosis, the physiological role of this process in these cells remains an enigma. In this article, we consider current opinions of endocytosis in plants and define some of the problems that have impeded progress in our under‐standing of the part played by endocytosis in the vesicle trafficking pathway.
Alteration in carbon partitioning induced by the movement protein of tobacco mosaic virus originates in the mesophyll and is independent of change in the plasmodesmal size exclusion limit
Authors: BALACHANDRAN S. , HULL R. J. , VAADIA Y. , WOLF S. , LUCAS W. J. 
Published: April 2006

ABSTRACTThe influence of the 30 kDa movement protein of tobacco mosaic virus (TMV‐MP) on carbon partitioning in trans‐genie tobacco plants (Nicotiana tabacum cv. Xanthi) expressing the TMV‐MP was investigated. Using reciprocal grafting of transgenic tobacco plants expressing this movement protein and vector control plants, as well as transgenic tobacco plants expressing the TMV‐MP in phloem cells only, we showed that the interactive site involved in carbon allocation to roots is localized to the mesophyll tissue. Biomass partitioning experiments conducted on transgenic plants, in which various deletion mutant forms of the TMV‐MP (two of which included deletions in the domain responsible for increasing the size exclusion limit) were expressed, revealed that the TMV‐MP exerts its influence on carbon allocation via a mechanism that is completely independent of the TMV‐MP‐induced increase in the plasmodesmal size exclusion limit. Furthermore, small N‐ and C‐terminal deletions in the MP revealed the complexity of the interactions likely to be involved between the MP and an endogenous regulatory mechanism. We propose that the TMV‐MP interferes with an endogenous signal transduction pathway that involves macromolecular trafficking through plasmodesmata to regulate biomass partitioning between the source and various sink tissues.
Effects of photoinhibitory treatment on CO2 assimilation, the quantum yield of CO2 assimilation, D1 protein, ascorbate, glutathione and xanthophyll contents and the electron transport rate in vine leaves
Authors: CHAUMONT M. , MOROT‐GAUDRY J.‐F. , FOYER C.H. 
Published: April 2006

ABSTRACTThe responses of photosynthesis to high light and low temperature were studied in vines cultivated in the greenhouse in low light. Exposure to high light (1000 /umol m−2 s−1) or low temperature (5 °C) alone had no measurable effect on the photosynthetic processes, but the combination of high light and low temperature caused rapid loss of photosynthetic capacity and a decrease in the efficiency of photosynthetic energy conversion. After a 15 h exposure to 5°C at high light, the Fv/sb/Fmratio had decreased by 80% and the apparent quantum yield by 75%. Nevertheless, when the leaves were returned to low light at 22°C, these parameters recovered rapidly. The foliar pools of ascorbate and glutathione decreased in the first hours of photoinhibitory treatment while the zeaxanthin content increased from negligible levels to about 50% of the total foliar xanthophyll pool. There was a clear correlation between the zeaxanthin content of the leaves and their Fv/Fm ratio during both photoinhibition and recovery. However, there was also a good correlation between the decrease in theFv Fm ratio and the measured decrease in the total foliar levels of the antioxidants ascorbate and glutathione. The amount of D, protein diminished over the same period as the zeaxanthin levels were increasing. This approach, involving simultaneous measurements of several parameters considered to influence photosystemy II activity, clearly demonstrates that measured decreases in Fv/Fm may not simply be related to zeaxanthin levels or to amounts of D1 protein alone but result from multifactoral influences.
Calmodulin levels in radish (Raphanus sativus L.) seeds germinating at low calcium availability induced by EGTA treatments
Authors: NEGRINI N. , RIVETTA A. , COCUCCI M. 
Published: April 2006

ABSTRACTIncubation of radish (Raphanus sativus L.) seeds in the presence of 1 or Smol m−3 Ca‐EGTA, which increased Ca2+ activity in the incubation medium (c. 0.24 or 0.37 mol m−3 at 24 h with respect to c. 0.13 mol m−3 in the control), did not affect germination, the restoration of K+ net influx, the increase in DNA and RNA levels or protein synthesis. Incubation in 1 mol m−3 Na‐EGTA, which reduced Ca2+ activity in the incubation medium (20 mmol m−3 at 24 h), decreased the total Ca2+ level in embryo axes (‐21%), but only slightly inhibited the increase in fresh weight without affecting the restoration of K+ net influx, the increase in DNA and RNA levels or protein synthesis. In the presence of 5 mol m−3 Na‐EGTA (Ca2+ activity in the incubation medium was 0.6 mmol m−3), the decrease in the total Ca2+ level was greater (c. ‐27%) and the increases in fresh weight, DNA and RNA were inhibited by about 50, 39 and 40%, respectively. These results indicate that increased Ca2+ availability does not affect germination and suggest that the effect of Na‐EGTA, at least up to 5 mol m−3, is a result of an induction of Ca2+ deficiency. The amount and specific activity of calmodulin (CaM) present in the soluble fraction (100 000g) of radish embryo axes greatly increased during the first 24 h of incubation (c. 5‐fold and 7‐fold, respectively). This increase was very similar in the Ca‐EGTA‐treated seeds but was inhibited (c. ‐38%) by 1 mol m−3 Na‐EGTA, even if the increases in DNA and RNA levels and protein synthesis were not significantly reduced. The lower amount of CaM after 24 h of incubation in 1 mol m−3 Na‐EGTA (c. ‐30%) was due to a reduction in the fraction of CaM bound to a proteinaceous CaM inhibitor present in radish seeds [M. Cocucci & N. Negrini (1988) Plant Physiology 88, 910–914] and not involved in the metabolic reactivation of the seed. These results suggest that the level of CaM is controlled by Ca2+ availability and that the CaM inhibitor has a role in controlling the amount of Ca‐CaM available for the Ca‐CaM‐dependent enzymes.
Depolarization of tomato leaf cells by oligogalacturonide elicitors
Authors: THAIN J.F. , GUBB I.R. , WILDON D. C. 
Published: April 2006

ABSTRACTThe electrical potential difference (Em) across the plasma membrane of tomato leaf mesophyll cells consists of a cyanide‐sensitive component, presumably produced by an H+‐ATPase, and a cyanide‐insensitive component. Variation of Em between different batches of tissue is mainly caused by variation in the cyanide‐sensitive component. Oligogalacturonide elicitors that induce the synthesis of proteinase inhibitors in tomato seedlings depolarize the Em of tomato leaf mesophyll cells. This depolarization closely resembles that caused by cyanide: they are of similar magnitude and vary in a similar manner with variation in the initial Em of different batches of tissue. Treatments with cyanide and with the elicitors have similar effects on the small depolarization caused by KCl at 10 mol m−3. The results suggest that the elicitors depolarize Em by inhibiting the plasma membrane H+‐ATPase, but that the detailed mechanism of inhibition by the elicitors is different from that caused by cyanide.
Growth of coniferous trees exposed to SO2 and O3 using an open‐air fumigation system
Authors: HOLLAND M. R. , MUELLER P. W. , RUTTER A. J. , SHAW P. J. A. 
Published: April 2006

ABSTRACTScots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2‐year‐old seedlings in an open‐air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO2 fumigation began in May 1987 and continued until December 1990. Long‐term mean SO2 concentrations were 4,13 and 22 nmol mo−1. Three plots, one at each SO2 level, were also exposed to O3 at an average of 1–3.times the ambient level. O3 fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO2 on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO2‐treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO2‐treated plots, in apparent response to codeposition of NH3‐N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O3 on growth were recorded for any species.
The Liphook Forest Fumigation Project: an overview
Authors: McLEOD A. R. , SKEFFINGTON R. A. 
Published: April 2006

ABSTRACTThe aim of the Liphook Project was to assess the effects of SO2 and O3, singly and in combination, on coniferous forest ecosystems. More than 4000 trees of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and Sitka spruce (P. sitchensis) were fumigated for nearly 4 years using an open‐air fumigation technique especially developed for the purpose. The technique eliminated artifacts due to chambers and enabled a variety of effects of the pollutant gases on forest ecosystems to be studied. Most symptoms of forest decline did not occur, but each species reacted in a different way to SO2 stress, providing no evidence for universal forest decline symptoms. However, some of the mechanisms hypothesized to underlie forest declines were observed as an effect of SO2 treatment, though others were not, notably any major effect of O3. The results are assessed against proposed regulatory standards (critical loads and levels) for the protection of forest ecosystems against pollution.
Interpretation of an empirical model for stomatal conductance in terms of guard cell function
Authors: DEWAR R. C. 
Published: April 2006

ABSTRACTAn empirical model for stomatal conductance (g), proposed by Leuning (1995, this issue) as a modification of Ball, Woodrow & Berry's (1987) model, is interpreted in terms of a simple, steady‐state model of guard cell function. In this model, stomatal aperture is a function of the relative turgor between guard cells and epidermal cells. The correlation between g and leaf surface vapour pressure deficit in Leuning's model is interpreted in terms of stomatal sensing of the transpiration rate, via changes in the gradient of total water potential between guard cells and epidermal cells. The correlation between g, CO2 assimilation rate and leaf surface CO2 concentration in Leuning's model is interpreted as a relationship between the corresponding osmotic gradient, irradiance, temperature, intercellular CO2 concentration and stomatal aperture itself. The explicit relationship between osmotic gradient and stomatal aperture (possibly describing the effect of changes in guard cell volume on the membrane permeability for ion transport) results in a decrease in the transpiration rate in sufficiently dry air. Possible extension of the guard cell model to include stomatal responses to soil water status is discussed.
Activated oxygen and antioxidant defences in iron‐deficient pea plants
Authors: ITURBE‐ORMAETXE I. , MORAN J. F. , ARRESE‐IGOR C. , GOGORCENA Y. , KLUCAS R. V. , BECANA M. 
Published: April 2006

ABSTRACTIron (Fe) deficiency in pea leaves caused a large decrease (44–62&) in chlorophyll a, chlorophyll b and carotenoids, and smaller decreases in soluble protein (18&) and net photosynthesis (28&). Catalase, non‐specific peroxidase and ascorbate peroxidase activities declined by 51& in young Fe‐deficient leaves, whereas monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase activities remained unaffected. Ascorbate peroxidase activity was highly correlated (r2= 0. 99, P < 0. 001) with the Fe content of leaves, which allows its use as an indicator of the Fe nutritional status of the plant. Fe deficiency resulted in an increase of CuZn‐superoxide dismutase but not of Mn‐superoxide dismutase. The content of ascorbate decreased by only 24& and those of reduced and oxidized glutathione and vitamin E did not vary. The low‐molecular‐mass fraction of Fe‐sufficient leaves contained 30–65 μg (g dry weight)−1 Mn. This concentration was 15–60 times greater than that of Fe and Cu in the same fraction, and was further enhanced (1. 5‐ to 2. 5‐fold) by Fe deficiency without causing Mn toxicity. The concentration of catalytic Fe, that is, of Fe active for free radical generation, was virtually zero and that of catalytic Cu did not change with severe Fe deficiency. Because catalytic metals mediate lipid and protein oxidation in vivo, the above findings would explain why oxidatively damaged lipids and proteins do not accumulate in Fe‐deficient leaves.
Structural changes in the innercortex cells of soybean root nodules are induced by short‐term exposure to high salt or oxygen concentrations
Authors: SERRAJ R. , FLEURAT‐LESSARD P. , JAILLARD B. , DREVON J. J. 
Published: April 2006

ABSTRACTAfter a 2 h exposure of intact soybean nodules to high concentrations of NaCl (100mol m−3) or oxygen (8OkPa O2), morphometric computations carried out using an image analysis technique on semi‐thin sections showed that both treatments induced a decrease in the area of the inner‐cortex cells, which were then characterized by a tangential elongation. In contrast, no significant change in area occurred in the middle‐cortex cells although their elongation decreased. Electron microscopic observations showed that in the inner‐cortex cells changes included the presence of wall infoldings, an enlarged periplasmic space and a lobate nucleus whose chromatin distribution differed from that of the control. Structural changes also occurred in the endoplasmic reticulum, microbodies, mitochondria and plastids. From several of these changes, which are similar to those noted in osmocontractil cells in response to external stimuli, it can be hypothesized that the inner cortex may provide a potential mechanism for the control of oxygen diffusion through the nodules.
Response of the photosynthetic apparatus in maize leaves grown at low temperature on transfer to normal growth temperature
Authors: NIE G. ‐Y. , ROBERTSON E. J. , FRYER M. J. , LEECH R. M. , BAKER N. R. 
Published: April 2006

ABSTRACTLow temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves from 14 to 25°C, with a dramatic accumulation of thylakoid proteins and chlorophylls occurring after 3 d at 25°C. Thylakoid structure and organization also became similar to those observed in leaves grown at 25°C over this period. However, no comparable development of photosynthetic competence in photosystems I and II or in the rate of CO2 assimilation was observed on transfer of leaves from 14 to 25°C. Immunocytological analyses demonstrated heterogeneity in the distribution of a range of thylakoid proteins (cy tochrome f, the α and β subunits of the coupling factor, Dl of the photosytem II reaction centre, the 33kDa protein of the extrinsic oxygen‐evolving complex of photosystem II, and subunit II of photosystem I between mesophyll cells in leaves grown at 14°C, and in the responses of individual proteins to transfer of the leaves to 25°C. Such heterogeneity between mcsophyll cells would account for the inability of the leaves to develop the expected degree of photosynthetic competence on transfer to 25°C. The effects of low growth temperatures on chloroplast biogenesis are complex, as are the changes induced by the transfer ofleaves grown at low temperatures to optimal growth temperature, and both these factors may limit the canopy development and photosynthetic productivity of crops in temperate regions.
A chilling‐sensitive mutant of Arabidopsis is deficient in chloroplast protein accumulation at low temperature*
Authors: SCHNEIDER J. C. , NIELSEN E. , SOMERVILLE C. 
Published: April 2006

ABSTRACTMutations at the chsl locus in Arabidopsis thaliana (L.) confer a chilling‐sensitive phenotype in which plants become chlorotic and die after more than 3 d of exposure to temperatures in the range of 18 to 10°C. Within 8h after transfer of mutant plants from growth at 23 to 13°C, accumulation of the newly synthesized chloroplast‐localized polypeptides stearoyl‐ACP desaturase, glutamine synthetase and OEC 23 was severely impaired. By contrast, there was no apparent deleterious effect on the accumulation of two extrachloroplastic proteins examined: the elongation factor lα, and the phloem‐specific, extrachloroplastic isoform of glutamine synthetase. In one instance examined in detail, chilling did not decrease the accumulation of mRNA for stearoyl‐ACP desaturase, indicating that the effect was post‐transcriptional. Chloroplasts isolated from chilled wild‐type and chsl plants were equally able to process and protect from protease digestion in vitro synthesized pre‐plastocyanin. The results suggest that the chsl mutant may be defective in some aspect of chloroplast protein accumulation at low temperature.