bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and shoot:root partitioning of spinach plants as affected by nitrogen supply
Authors: SMOLDERS E. , MERCKX R. 
Published: April 2006

ABSTRACTSpinach plants (Spinacia oleraceaL.) were grown hydroponically in fixed environmental conditions either at full nitrate availability (11·8mol m‐3) or at a suboptimum relative nitrate addition rate of 0·20d‐1, 0·15d‐1or 0·10d‐1respectively, the other nutrients being adequately provided. The relative growth rate (RGR) of the plants varied significantly with the nutrition treatment and decreased during development in all treatments. The concentration of reduced nitrogen in the plants grown at full nitrate availability did not change significantly during the experimental growth period and nitrate accumulation was substantial. After an adaptation period, the concentration of reduced nitrogen in the plants at the suboptimum nitrate addition rates increased during growth and was lowest at the lowest relative nitrate addition rate. Nitrate uptake was almost complete in the suboptimum treatments and nitrate accumulation was negligible as long as the concentration of reduced nitrogen was below 2·0 mmol (g dry weight)‐1. The RGR of all plants was proportional to the concentration of reduced nitrogen in the plant minus a minimal tissue concentration required for growth. However, the proportionality factor was inversely related to the plant mass. This relationship was summarized in an empirical model which explained 98·7% of the variance of the dry weight (log scale) data of all treatments at all harvests. The model was compared with other growth models found in the literature. The shoot/root weight ratio increased from 2 to 4 if nitrate provision was not limiting, and initially, this ratio decreased at suboptimum nitrate provision but increased at higher growth stages. Possible explanations of the dynamics of dry matter partitioning are discussed in relation to models.
Differential effects of drought and light levels on accumulation of citric and malic acids during CAM in Clusia
Authors: FRANCO A. C. , BALL E. , LÜTTGE U. 
Published: April 2006

ABSTRACTNight‐time citrate accumulation has been proposed as a response to stress in CAM plants. To address this hypothesis, gas exchange patterns and nocturnal acid accumulation in three species of Clusia were investigated under controlled conditions with regard to water stress and responses to low and high photosynthetic photon flux density (PPFD). Under high PPFD, leaves of Clusia nocturnally accumulated large amounts of both malic and citric acids. Under low PPFD and well‐watered conditions, substantial night‐time citrate accumulation persisted, whereas malate accumulation was close to zero. Malate accumulation and night‐time CO2 uptake from the atmosphere declined in all three species during prolonged drought periods, whereas citrate accumulation remained similar or increased. Recycling of respiratory CO2 was substantial for both well‐watered and water‐stressed plants. The suggestion that citrate accumulation is energetically more favourable than malate accumulation is not supported if the source of CO2 for the formation of malate is respiratory CO2. However, the breakdown of citric acid to pyruvate in the light period releases three molecules of CO2, while the breakdown of malic acid releases only one CO2 per pyruvate formed. Thus, citric acid should be more effective than malic acid as a mechanism to increase CO2 concentration in the mesophyll and may help to prevent photoinhibition. Organic acid accumulation also affected the vacuolar pH, which reached values of 2·6–3·0 at dawn. At these pH values, the transport of 2H+/ATP is still feasible, suggesting that it is the divalent form of citrate which is being transported in the vacuoles. Since citrate is a well‐known buffer, and Clusia spp. show the largest day‐night changes in organic acid levels measured in any CAM plant, it is possible that citrate increases the buffer capacity of the vacuoles. Indeed, malate and titratable acidity levels are positively related to citrate levels. Moreover, Clusia species that show the highest nocturnal accumulation of organic acids are also the ones that show the greatest changes in citric acid levels.
Photosynthetic gas exchange and the stable isotope composition of leaf water: comparison of a xylem‐tapping mistletoe and its host
Authors: FLANAGAN L. B. , MARSHALL J. D. , EHLERINGER J. R. 
Published: April 2006

ABSTRACTPhotosynthetic gas exchange and the stable isotopic composition of foliage water were measured for a xylem tapping mistletoe, Phoradendron juniperinum, and its host tree, Juniperus osteosperma, growing in southern Utah. The observed isotopic composition of water extracted from foliage was compared to predictions of the Craig‐Gordon model of isotopic enrichment at evaporative sites within leaves. Assimilation rates of juniper were higher and stomatal conductance was lower than the values observed for the mistletoe. This resulted in lower intercellular/ ambient CO2 values in the juniper tree relative to its mistletoe parasite. For mistletoe, the observed foliage water hydrogen and oxygen isotopic enrichment was less than that predicted by the model. In juniper, foliage water hydrogen isotopic enrichment was also lower than that predicted by the evaporative enrichment model. In contrast, the oxygen isotopic enrichment in juniper foliage water was slightly greater than that predicted for the evaporative sites within leaves. Hydrogen isotopic enrichment in mistletoe foliage shows systematic variation with stem segment, being highest near the tips of the youngest stems and decreasing toward the base of the mistletoe, where isotopic composition is close to that of stem water in the host tree. In a correlated pattern, mid‐day stomatal conductance declined abruptly in mistletoe foliage of increasing age.
The coupling between extra‐ and intracellular electric potentials in Bidens pilosa L.
Authors: FRACHISSE‐STOILSKOVIĆ J. M. , JULIEN J. L. 
Published: April 2006

ABSTRACTThe extracellular electrical potential in Bidens pilosa has been compared with the transmembrane potential in hypocotyl cells. We found that variations in the extracellular electrical potential, induced by different KCI concentrations, were identical to the variations of the transmembrane potential. In order to explain the strong correlation between the extracellular potential and the transmembrane potential, an interpretative model based on the electrical diagram of the plant was tested. From our data, we found that: (1) the symplast behaves as a low resistance pathway compared with the apoplast; and (2) the cell wall contributes weakly (20% at the most) to the transmembrane potential. It is concluded that each hypocotyl cell is strongly coupled electrically with its neighbour. This property, together with the high apoplast resistance, accounts for the similarity in the extracellular and transmembrane potential measurements. These properties, which are characteristic of excitable organs, support the existence of action potentials in Bidens.
Effects of ozone on the photosynthetic apparatus and leaf proteins during leaf development in wheat
Authors: NIE G.‐Y. , TOMASEVIC M. , BAKER N. R. 
Published: April 2006

ABSTRACTLeaves of Triticum aestivum cv. Avalon were grown in an atmosphere that contained 150 nmole mol‐1 ozone for 7h each day. After leaves had reached maximum size, the leaf blade was divided into three sections to provide tissue of different age, the youngest at the base of the blade and the oldest at the leaf tip. The ozone treatment was found to decrease significantly the light‐saturated rate and quantum yield of CO2 assimilation and the maximum quantum yield of photosystem II photochemistry in the oldest leaf section. No effects were found on the basal and middle sections of the leaf. These ozone‐induced decreases in the photosynthetic parameters were associated with decreases in the efficiency of utilization of light for CO2 assimilation at the photon flux density under which the leaves were grown. The depression in photosynthetic performance of tissue near the leaf tip was accompanied by large decreases in the contents of total, soluble and thylakoid proteins and chlorophyll. There was also found to be a preferential loss of ribulose‐1,5‐carboxylase‐oxygenase. These ozone‐induced changes in chlorophyll and protein contents and the photosynthetic activities of the leaf tissue were similar to changes normally associated with leaf senescence. Two‐dimensional polyacrylamide gel analyses of leaf proteins demonstrated the loss of some minor, and unidentified, proteins, whilst another group of minor proteins appeared. It is concluded that daily exposure of the leaf to 150 nmol mol‐1 ozone for 7h had no effect on the development of the photosynthetic apparatus and its activities during leaf expansion, but it did promote the onset of premature senescence in fully expanded tissue that resulted in a loss of pigments, proteins and photosynthetic capacity and efficiency.
ATP‐dependent carbon transport in perfused Chara cells
Authors: MIMURA T. , MÜLLER R. , KAISER W. M. , SHIMMEN T. , DIETZ K.‐J. 
Published: April 2006

ABSTRACTCarbon transport across the plasma membrane, and carbon fixation were measured in perfused Chara internodal cells. These parameters were measured in external media of pH 5·5 and pH 8·5, where CO2 and HCO3‐ are, respectively, the predominant carbon species in both light and dark conditions. Cells perfused with medium containing ATP could utilize both CO2 and HCO3‐ from the external medium in the light. Photosynthetic carbon fixation activity was always higher at pH 5·5 than at pH 8·5. When cells were perfused either with medium containing hexokinase and 2‐deoxyglucose to deplete ATP from the cytosol (HK medium) or with medium containing vanadate, a specific inhibitor of the plasma membrane H+‐ATPase (V medium), photosynthetic carbon fixation was strongly inhibited at both pH 5·5 and 8·5. Perfusion of cells with medium containing pyruvate kinase and phosphoenolpyruvate (PEP) to maximally activate the H+‐ATPase (PK medium), stimulated the photosynthetic carbon fixation activities. Oxygen evolution of isolated chloroplasts and the carbon fixation of cells supplied 14C intracellularly were not inhibited by perfusion media containing either hexokinase and 2‐deoxyglucose or vanadate. The results indicate that Chara cells possess CO2 and HCO3‐ transport systems energized by ATP and sensitive to vanadate in the light. In the dark, intact cells also fix carbon. By contrast, in cells perfused with medium containing ATP, no carbon fixation was detected in 1 mol m ‐3 total dissolved inorganic carbon (TDIC) at pH 8·5. By increasing TDIC to 10 mol m‐3, dark fixation became detectable, although it was still lower than that of intact cells at 1mol m‐3 TDIC. Addition of PEP or PEP and PEP carboxylase to the perfusion media significantly increased the dark‐carbon fixation. Perfusion with vanadate had no effect on the dark‐carbon fixation.
Influence of flooding with diluted sea water on morphological and physiological characteristics in hexaploid triticale
Authors: KARIM M. A. , NAWATA E. , SHIGENAGA S. 
Published: April 2006

ABSTRACTThe influence of flooding with tap water, and with 10 and 20% sea water on the growth, yield and physiological characteristics in hexaploid triticale (X Triticosecale Wittmack) were analysed. The plants were grown in a glasshouse and flooded at the booting stage for 19 d. Flooding seriously affected the growth, yield and physiological activities of the plants. However, the growth and yield were greater in plants flooded with diluted sea water than in plants flooded with tap water. The amount of newly developed roots, photosynthetic rate and accumulation of mineral nutrients in the leaves was greater in sea water‐flooded plants as compared to tap water‐flooded plants. Oxygen concentrations in the diluted sea water were lower than in the tap water 6 d from the beginning of flooding. Leaf water potentials in the plants flooded with diluted sea water were lower than in the plants flooded with tap water until 7 d from the beginning of flooding when the position reversed. Transpiration was slower and stomatal resistance was greater in flooded plants, and were similar irrespective of water quality.
The effects of host carbon dioxide, nitrogen and water supply on the infection of wheat by powdery mildew and aphids
Authors: THOMPSON G. B. , BROWN J. K. M. , WOODWARD F. I. 
Published: April 2006

ABSTRACTIn two experiments, winter wheat (Triticum aestivum cv. Cerco) was grown in 350 (ambient) and 700 μmol mol‐1 (elevated) atmospheric CO2 concentrations. In the first experiment, plants were grown at five levels of nitrogen fertilization, and in the second experiment, plants were grown at three levels of water supply. All plants were infected with powdery mildew, caused by the fungus Erysiphe graminis. Plants grown in elevated atmospheric CO2 concentrations had significantly reduced % shoot nitrogen contents and significantly increased % shoot water contents. At elevated atmospheric CO2 concentrations, where plant nitrogen content was significantly reduced, the severity of mildew infection was significantly reduced, and where host water content was significantly increased, the severity of mildew infection was significantly increased. In a moderate water supply treatment, the plants grown in elevated atmospheric CO2 concentrations had significantly reduced nitrogen contents (9·9%) and significantly increased water content (4%), the amount of mildew infection was unchanged. The severity of mildew infection appeared to be more sensitive to host water content than to host nitrogen content.
Penetration of UV‐B radiation in foliage: evidence that the epidermis behaves as a non‐uniform filter
Authors: DAY T. A. , MARTIN G. , VOGELMANN T. C. 
Published: April 2006

ABSTRACTIn some plants, particularly herbaceous species, a considerable proportion of incident ultraviolet‐B radiation (UV‐B, 280‐320 nm) penetrates into the leaf mesophyll where it is potentially damaging to nucleic acids and the photosyn‐thetic machinery. We used optical techniques to look at the spatial variation in UV‐B penetration through the epidermis of foliage of two herbaceous species (Chenopodium album and Smilacina stellata)and a conifer (Picea pun‐gens). Measurements of UV‐B penetration in intact foliage with a fibre‐optic microprobe revealed that 300 nm radiation reached 161±36μm (mean±SD) into leaves of C. album, 154±40μm in S. stellata and 17±2μm in P. pungens, with epidermal transmittance being 39±14%, 55±19% and 0%, respectively. A thin polymer film was developed which fluoresced blue when irradiated by UV‐B. Fresh epidermal leaf peels were placed over the film and irradiated with UV‐B, and microscopic examination of the film from below allowed us to determine the spatial pattern of UV‐B penetration through the epidermis. In herbaceous species, film fluorescence below cell walls, but not epidermal and guard cell protoplasts indicated that UV‐B transmittance was much greater through anticlinal cell wall regions than protoplasts. Ultraviolet‐B transmittance through large areas of epidermal cells could be induced by plasmolysis. Epidermal transmittance was also relatively high through stomal pores (and what appear to be nuclei in Smilacina), but relatively low through stomatal guard cells. Results from the fluorescing film technique were substantiated by direct measurements of UV‐B transmittance through epidermal peels with a fibre‐optic microprobe run paradermally along the bottom or inner side of irradiated peels. In Smilacina, we estimate that UV‐B epidermal transmittance was up to 90% through anticlinal cell wall regions, but <10% through protoplast areas. In contrast to herbaceous species, we did not detect any UV‐B transmittance through the epidermis of P. pungens with either the fluorescing film or the fibre‐optic microprobe technique. The epidermis appears to be a much more spatially uniform UV‐B filter in conifers than in these herbaceous species.
In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate‐deficient sunflower and maize leaves
Authors: JACOB J. , LAWLOR D. W. 
Published: April 2006

ABSTRACTThe effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi‐deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φe), the in vivo quantum yield of PSII photochemistry (φPSII) and the photochemical quenching co‐efficient (qP), and increased the non‐photochemical quenching co‐efficient (qN) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi‐deficient sunflower leaves reversed the long‐term effects of Pi‐deficiency on PSII photochemistry. Feeding Pi‐sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long‐term Pi‐deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long‐and short‐term responses of photosynthetic machinery to Pi deficiency. The relationship between φPSII and the apparent quantum yield of CO2 assimilation determined at varying light intensity and 21 kPa O2 and 35 Pa CO2 partial pressures in the ambient air was linear in Pi‐sufficient and Pi‐deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO2 assimilated by the Pi‐deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO2 reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi‐deficient leaves of sunflower and maize and that the decreased CO2 assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1‐5, bisphosphate, the acceptor for CO2.
Foliar gas exchange responses of two deciduous hardwoods during 3 years of growth in elevated CO2: no loss of photosynthetic enhancement
Authors: GUNDERSON C. A. , NORBY R. J. , WULLSCHLEGER S. D. 
Published: April 2006

ABSTRACTResponses of photosynthesis and stomatal conductance were monitored throughout a 3‐year field exposure ofLiriodendron tulipifera(yellow‐poplar) andQuercus alba(white oak) to elevated concentrations of atmospheric CO2. Exposure to atmospheres enriched with +150 and +300 umol mol‐1CO2increased net photosynthesis by 12–144% over the course of the study. Net photosynthesis was consistently higher at +300 than at +150 umol mol‐1CO2. The effect of CO2enrichment on stomatal conductance was limited, but instantaneous leaf‐level water use efficiency increased significantly. No decrease in the responsiveness of photosynthesis to CO2enrichment over time was detected, and the responses were consistent throughout the canopy and across successive growth flushes and seasons. The relationships between internal CO2concentration and photosynthesis (e.g. photosynthetic capacity and carboxylation efficiency) were not altered by growth at elevated concentrations of CO2. No alteration in the timing of leaf senescence or abscission was detected, suggesting that the seasonal duration of effective gas‐exchange was unaffected by CO2treatment. These results are consistent with data previously reported for these species in controlled‐environment studies, and suggest that leaf‐level photosynthesis does not down‐regulate in these species as a result of acclimation to CO2enrichment in the field. This sustained enhancement of photosynthesis provides the opportunity for increased growth and carbon storage by trees as the atmospheric concentration of CO2rises, but many additional factors interact in determining whole‐plant and forest responses to global change.
Chloroplast thylakoid protein changes induced by low growth temperature in maize revealed by immunocytology
Authors: ROBERTSON E. J. , BAKER N. R. , LEECH R. M. 
Published: April 2006

ABSTRACTTissue‐specific effects of low growth temperature on maize chloroplast thylakoid protein accumulation were analysed using immunocytology. Sections of leaves from plants grown at 25 and 14°C were probed with antibodies to specific chloroplast thylakoid proteins from the four major protein multisubunit complexes of the thylakoid membrane followed by fluorescein‐conjugated goat anti‐rabbit antibodies. At a normal growth temperature of 25°C, the 32 kDa D1 protein of the photosystem II reaction centre and the 33 kDa protein of the extrinsic oxygen‐evolving complex of photosystem II are both accumulated to a greater degree in the mesophyll than in the bundle sheath chloroplasts. In contrast, subunit II of photosystem I, cytochrome f and the α‐ and β‐subunits of ATP synthetase are predominant in the bundle sheath thylakoids at 25°C. A striking difference between the 25°C‐grown and the 14°C‐grown leaf tissue was the presence in the latter of (20–30%) cells whose chloroplasts apparently completely lack several of the thylakoid proteins. In plants grown at 14°C, the accumulation of the 33 kDa protein of the extrinsic oxygen‐evolving complex of photosystem II was apparently unchanged, but other thylakoid proteins showed a significant reduction. The uneven distribution of proteins between the bundle sheath and mesophyll chloroplasts observed at 25°C was also maintained at 14°C. Reduction in the fluorescence at 14°C was manifested either as an overall reduction in the diffuse fluorescence across the chloroplast profiles or less frequently as a reduction to small discrete bodies of intense fluorescence. The significance of these results to low‐temperature‐induced reduction in the photosynthetic productivity of maize is discussed.
Changes in ethylene and polyamines in relation to mRNA levels of the large and small subunits of ribulose bisphosphate carboxylase/oxygenase in ozone‐stressed potato foliage
Authors: REDDY G. NAGI , ARTECA R. N. , DAI Y.‐R. , FLORES H. E. , NEGM F. B. , PELL E. J. 
Published: April 2006

ABSTRACTPotato plants (Solanum tuberosum L. cv‘Norland’) were subjected to acute and chronic exposures of ozone (O3). Periodically following or during the exposures, foliage of different physiological ages were sampled for tissue analysis. Measurement of the following parameters were included: ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), N‐malonyl 1‐aminocyclopropane‐1‐carboxylic acid (MACC), and ACC oxidase activity, putrescine, spermidine, and spermine levels, and ornithine decarboxylase (ODC) activity, and levels of mRNA transcripts for the large and small subunits of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) (rbcL and rbcS, respectively). Ozone increased emission of ethylene and the concentration and activity of all associated metabolites and enzymes. Putrescine titre increased in response to O3 as did ODC activity. Some increases in spermidine were also detected. Ozone decreased the levels of mRNA for rbcL and rbcS, with the latter transcript exhibiting greater sensitivity. After acute exposures were terminated, the rbcL and rbcS transcript in younger leaves returned to levels of nonstressed plants; effects were less likely to be reversed in older tissue. The potential relationship between the changes in rbcL and rbcS and ethylene and polyamines are discussed in the context of O3 induction of accelerated senescence.