bluuebunny/crossref_metadata_2025 huggingface dataset:
ATP‐dependent carbon transport in perfused Chara cells
Authors: MIMURA T. , MÜLLER R. , KAISER W. M. , SHIMMEN T. , DIETZ K.‐J.
Published: April 2006

Carbon 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

The 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

In 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

In 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

The 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

Responses 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

Tissue‐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

Potato 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.
Growth responses of individual roots of Opuntia ficus‐indica to salinity
Authors: GERSANI M. , GRAHAM E. A. , NOBEL P. S.
Published: April 2006

Responses of individual roots of the widely cultivated cactus Opuntia ficus‐indica to salinity stress were evaluated using a split‐root system. Three roots from a plant with at least 20 roots were isolated from the remainder of the root system and exposed to 0, 30 or 100 mol m‐3 NaCl for up to 28 d. Cortical cells became shorter and lateral root development was substantially reduced as salinity increased. Compared with the control, the increase in dry weight for the isolated roots was reduced 40% by 30 mol m‐3 NaCl and 93% by 100mol m‐3 NaCl. The sodium content of roots increased only two‐fold with increasing salinity. Respiration rates of roots exposed to 30 or 100 mol m‐3 NaCl were higher than those of the control. Carbon accumulation in roots measured 2 d after exposing shoots to 14CO2 was not initially affected by 30 mol m‐3 NaCl but was substantially reduced at 100 mol m‐3 NaCl. Thus, roots exposed to short periods of moderate salinity stress maintained sufficient carbon sink strength for continued growth of the roots. Moreover, increased salinity led to decreased efficiency of carbon usage for the expansion of root surface area.
Stored xylem sap from wheat and barley in drying soil contains a transpiration inhibitor with a large molecular size
Authors: MUNNS R. , PASSIOURA J. B. , MILBORROW B. V. , JAMES R. A. , CLOSE T. J.
Published: April 2006

Xylem sap was collected from wheat and barley growing in a drying soil, and the effect of the sap on transpiration was detected by a bioassay with detached wheat leaves. The inhibitory activity of fresh sap was small, and could be largely accounted for by the abscisic acid content (about 2×10‐5mol m‐3). When fresh sap was stored at ‐20°C for several days, the activity increased. Maximum activity developed after a week. This increase in activity was due to a compound that increased in size with storage at ‐20°C. When fresh sap was fractionated with filters of different molecular size exclusion characteristics, and the separated fractions stored at ‐20°C for a week, activity developed only in the fraction containing compounds smaller than 0·3 kDa. However, when sap already stored at ‐20°C was fractionated, activity was only in fractions containing compounds larger than 0·3 kDa. The increase in activity and in size did not occur with storage in liquid nitrogen (‐196°C) or at ‐80°C. These results suggest that storage at ‐20°C causes the aggregation or polymerization of a small compound with low activity to form a large compound with high activity. This change is not catalysed by an enzyme because it can occur in a fraction from which molecules larger than 0·3 kDa are removed. It is probably promoted by high solute concentrations when ice crystals form. Sap collected from plants in soils of high water potential had little or no activity after storage at ‐20°C.
Growth and onto‐morphogenesis of soybean (Glycine max Merril) in an open, naturally CO2‐enriched environment
Authors: MIGLIETTA F. , RASCHI A. , RESTI R. , BADIANI M.
Published: April 2006

Springs emitting carbon dioxide are frequent in Central Italy and provide a way of testing the response of plants to CO2 enrichment under natural conditions. Results of a CO2 enrichment experiment on soybean at a CO2 spring (Solfatara) are presented. The experimental site is characterized by significant anomalies in atmospheric CO2 concentration produced by a large number of vents emitting almost pure CO2 (93%) plus small amounts of hydrogen sulphide, methane, nitrogen and oxygen. Within the gas vent area, plants were grown at three sub‐areas whose mean CO2 concentrations during daytime were 350,652 and 2370 μmol mol‐1, respectively. Weekly harvests were made to measure biomass growth, leaf area and ontogenetic development. Biomass growth rate and seed yield were enhanced by elevated CO2. In particular, onto‐morphogenetic development was affected by elevated CO2 with high levels of CO2 increasing the total number of main stem leaf nodes and the area of the main stem trifoliolate leaves. Biochemical analysis of plant tissue suggested that there was no effect of the small amounts of H2S on the response to CO2 enrichment. Non‐protein sulphydryl compounds did not accumulate in leaf tissues and the overall capacity of leaf extracts to oxidize exogenously added NADH was not decreased. The limitations and advantages of experimenting with crop plants at elevated CO2 in the open and in the proximity of carbon dioxide springs are discussed.
Fructose‐containing carbohydrates in the tuberous root of Gomphrena macrocephala St.‐Hil. (Amaranthaceae) at different phenological phases
Authors: VIEIRA C. C. J. , FIGUEIREDO‐RIBEIRO R. C. L.
Published: April 2006

Gomphrena macrocephala St.‐Hil. (Amaranthaceae) is a perennial herb that grows spontaneously in the cerrado and is characterized by well‐defined phenological phases throughout the year. Soluble carbohydrates are the main reserve compounds of the tuberous root and constitute approximately 50% of the dry weight. These sugars were partially characterized as fructans forming a single homologous series, different from inulin, the most common fructan of dicotyledons. The mean molecular weight of polysaccharides was high and reached 37 kDa in the dormant phase. Fructan spherocrystals were detected in the tuberous root after treatment with ethanol, being associated with the parenchyma of secondary xylem. The content, composition and mean molecular weight of fructans were related to phenology. In late dormancy, there was a marked increase in monosaccharides, particularly fructose, and a concomitant decline of polysaccharides, probably as a result of fructan breakdown. During sprouting and in the vegetative phase, the contents of oligosaccharides and low molecular weight polysaccharides increased. A gradual rise in the molecular weight of polysaccharides occurred during the reproductive phase and at early dormancy, concurrently with decreasing levels of oligosaccharides. The capacity of G. macrocephala to accumulate readily accessible sugars, such as fructans, instead of starch, in response to environmental changes, may be of considerable advantage, since the cerrado is often subjected to seasonal drought and burnings.
Photosynthetic acclimation to shade: probing the role of phytochromes using photomorphogenic mutants of tomato
Authors: SMITH H. , SAMSON G. , FORK D. C.
Published: April 2006

Photomorphogenic mutants of tomato were used to probe the possible involvement of phytochrome A in photosynthetic acclimation to shade. Plants of wild‐typeLycopersicon esculentum, the near isogenic mutantsaurea(au, deficient in phytochrome A, and also possibly other phytochromes) andhigh pigment(hp, exhibiting exaggerated photomorphogenic responses), and theau/hpdouble mutant were grown in a greenhouse under either unfiltered daylight, or daylight attenuated by neutral density filters or green filters that simulated the spectral effects of vegetation shade. Growth and photosynthetic parameters were measured over a growing period of 15 d. Typical effects of simulated vegetation shade on extension growth were observed only in the wild‐type andhpstrains; the presence of theaulesion resulted in reduced capacity to respond to vegetation shade by increased extension. Photosynthetic light saturation curves obtained using infrared gas analysis at 15 d indicated that neither theaunor thehpmutations caused serious reductions in maximum net photosynthetic rate in plants acclimated to full daylight, although theau/hpdouble mutant showed a significantly reduced maximum rate. In the wild‐type andhpstrains grown under both neutral and simulated vegetation shade, the photosynthetic light saturation curves were similar. Plants with theaulesion showed a significantly lower capacity to acclimate to vegetation shade, as seen by their reduced maximum rate of net photosynthesis. However,in situmeasurements of photosynthetic rate in the greenhouse were indistinguishable between the four strains. Thylakoid stoichiometry measurements revealed a very large increase in PSII/PSI ratio under simulated vegetation shade as compared with either unfiltered daylight or neutral density shade. These increases were not diminished in the phytochrome‐deficientaustrains, and were even larger in thehpstrains. The results indicate that theaulesion has little effect on the capacity of tomato to exhibit photoadaptation to simulated vegetational shade when measured at the thylakoid level. On the other hand, net leaf photosynthesis under vegetation shade can be significantly affected by the phytochrome deficiency caused by theaumutation, implying a possible role for one or more of the phytochromes in photoadaptation at the leaf level.
Modelling carbon isotope fractionation in tree rings based on effective evapotranspiration and soil water status
Authors: DUPOUEY J.‐L. , LEAVITT S. , CHOISNEL E. , JOURDAIN S.
Published: April 2006

Environmental influences on carbon isotope fractionation in tree rings require further elucidation in order to use this parameter as a biological marker of climatic variations. δ13C values in tree‐ring cellulose of beech (Fagus sylvaticaL.) were analysed for the period from 1950 to 1990. A bioclimatic model of water balance was used to give the actual evapotranspiration as well as the soil water content on a daily basis. δ13C shows a significant decrease from –24·5‰ to –25‰ over this period. Internal CO2concentration changes from 200 to 220 ppm in relation with the rise of atmospheric CO2. Beside a slight non‐significant inter‐individual variation, a large year‐to‐year variation exists. The relative extractable soil water of July, combined with the value of δ13C for the previous year, predicts as much as 70% of this variance. Air temperature or precipitation accounted for less variation. δ13C is strongly correlated with basal area increment, but appeared a more reliable indicator of water status at the stand level.
Solute analysis and water relations of gametophyte mutants tolerant to NaCl in the fern Ceratopteris richardii
Authors: VOGELIEN D. L. , HICKOK L. G. , AUGÉ R. M. , STODOLA A. J. W. , HENDRIX D.
Published: April 2006

The stl1 and stl2 mutations confer low and high levels of NaCl tolerance to gametophytes of the fern Ceratopteris richardii, respectively. As an initial characterization of these mutations, the levels of various organic solutes, tissue ion content and water relations were examined in the wild‐type and mutant strains in the absence and presence of 60 mol m‐3 NaCl stress (a level which results in a 20, 15 and 0% reduction in gametophyte growth in the wild‐type, stl1 mutant and stl2 mutant, respectively). All strains exhibited major changes in organic and inorganic solute levels and water relations in response to 60 mol m‐3 NaCl stress. Differences in organic solute levels and water relations between the wild‐type and mutant strains in the absence and in response to 60 mol m‐3 NaCl stress were minimal. Analysis of tissue ion content showed that stl1 was associated with a slight reduction in Na+ accumulation during 60 mol m‐3 NaCl stress. stl2 was associated with (1) higher constitutive levels of K+ and (2) continued selective accumulation of K+ and reduced accumulation of Na+ during 60 mol m‐3 NaCl stress. A K+/Na+ ratio close to 1 was observed in the wild‐type during 60 mol m‐3 NaCl stress, while higher ratios were detected in stl1 and stl2 (1·7 and 4·0, respectively). The findings of this study suggest that the tolerance imparted by stl1 and stl2 is associated with altered ion accumulation during NaCl stress, rather than an enhanced ability to accumulate organic solutes to be used for osmotic adjustment of the cytoplasm.
Immunocytochemical localization of indole‐3‐acetic acid in primary roots of Zea mays
Authors: SHI L. , MILLER I. , MOORE R.
Published: April 2006

Colloidal gold‐labelled antibody was used to localize indole‐3‐acetic acid in caps of primary roots of Z. mays cv. Kys. Gold particles accumulated on the nucleus, vacuoles, mitochondria, and some dictyosomes and dictyosome‐derived vesicles. This is the first localization of indole‐3‐acetic acid in dictyosomes and dictyosome‐derived vesicles and indicates that dictyosomes and vesicles constitute a pathway for indole‐3‐acetic acid movement in and secretion from root cap cells. Our findings provide cytochemical evidence to support the hypothesis that indole‐3‐acetic acid plays an important role in root gravitropism.
The effect of a long‐term water stress on the metabolism and emission of terpenes of the foliage of Cupressus sempervirens
Authors: YANI A. , PAULY G. , FAYE M. , SALIN F. , GLEIZES M.
Published: April 2006

The effects of long‐term water stress on water and terpene contents of the foliage of Cupressus sempervirens were studied. A great deal of water was lost over 2 months before a remarkable stabilization. A strong decrease of all the classes of terpenes accompanied this dehydration. Mono‐ and sesquiterpene hydrocarbons and free terpenols were almost entirely metabolized, whereas esters and terpene glycosides rose slightly and remained at a constant level when the water content had stabilized. Although a significant part of the mono‐ and sesquiterpene hydrocarbons was emitted in the early stage of stress application, the major part was used by the plant in response to the drought conditions.
Mathematical models of the photosynthetic response of tree stands to rising CO2 concentrations and temperatures
Authors: McMURTRIE R. E. , WANG Y.‐P.
Published: April 2006

Two published models of canopy photosynthesis, MAESTRO and BIOMASS, are simulated to examine the response of tree stands to increasing ambient concentrations of carbon dioxide (Ca) and temperatures. The models employ the same equations to described leaf gas exchange, but differ considerably in the level of detail employed to represent canopy structure and radiation environment. Daily rates of canopy photosynthesis simulated by the two models agree to within 10% across a range of CO2 concentrations and temperatures. A doubling of Ca leads to modest increases of simulated daily canopy photosynthesis at low temperatures (10% increase at 10°C), but larger increases at higher temperatures (60% increase at 30°C). The temperature and CO2 dependencies of canopy photosynthesis are interpreted in terms of simulated contributions by quantum‐saturated and non‐saturated foliage. Simulations are presented for periods ranging from a diurnal cycle to several years. Annual canopy photosynthesis simulated by BIOMASS for trees experiencing no water stress is linearly related to simulated annual absorbed photosynthetically active radiation, with light utilization coefficients for carbon of ɛ= 1.66 and 2.07g MJ−1 derived for Ca of 350 and 700 μmol mol−1, respectively.
Estimating transpiration from 6‐year‐old Eucalyptus grandis trees: development of a canopy conductance model and comparison with independent sap flux measurements
Authors: DYE P. J. , OLBRICH B. W.
Published: April 2006

Daily patterns of stomatal conductance (gs), xylem pressure potential (P) and canopy microclimatic variables were recorded on 11 sample days as part of a one‐year study of the water use of Eucalyptus grandis Hill ex Maiden in the eastern Transvaal, South Africa. Measured gs was found to be largely controlled by quantum flux density (Q) and ambient vapour pressure deficit (D). Canopy conductance (gc) was determined for hourly intervals using gs measurements and leaf areas in four different canopy levels. A simple model was constructed to allow the prediction of gc and transpiration from Q, D and season of year. The model was used to estimate transpiration rates from 10 trees in a later study of similarly‐aged E. grandis trees, in which sap flow in each tree was measured using the heat pulse velocity (HPV) technique. Five of the trees were monitored on a summer day and five on a winter day. Correspondence between HPV sap flow and modelled transpiration was good for the summertime comparisons, but measured winter‐time sap flow rates were underestimated by the model, especially under conditions of high sap flow. The discrepancy is believed to result from having insufficient data from the conductance study to describe the response of gs to relatively high D in winter. Marked variation in transpiration per unit leaf area indicates that a relatively large number of trees must be sampled for the HPV technique to be used to obtain a mean rate for an entire stand in winter.
Daily fluctuations of titratable acidity, content of organic acids (malate and citrate) and soluble sugars of varieties and wild relatives of Ananas comosus L. growing under natural tropical conditions
Authors: MEDINA E. , POPP M. , OLIVARES E. , JANETT H.‐P. , LÜTTGE U.
Published: April 2006

The genus Ananas has its centre of origin in northern South America. In this area, several varieties of Ananas comosus are widely cultivated, and a number of wild species are found growing under variable conditions of light intensity, soil fertility and water availability. Here we report detailed daily courses of titratable acidity, and malate, citrate and free‐sugars content of several cultivated varieties of A. comosus and of A. ananassoides, a closely related species growing on granitic rock‐outcrops in southern Venezuela. Day‐night oscillations of both malate and citrate were detected in plants growing under full sun, but malate was by far the most important organic anion associated with CAM performance in ail populations sampled. Fructose was the dominant compound in the neutral fraction, but only sucrose showed a consistent inverse relation with the cycle of titratable acidity. The diel oscillations of free sugars measured were not always enough to account for the amount of organic anions accumulated during the night. Plants cultivated under shady conditions always showed a lower night‐time increase in titratable acidity and organic acids, and also smaller oscillations in the amount of free sugars than sun exposed plants. In all populations growing under full sun, osmolality increased during the night, but it was not always possible to explain these changes on the basis of variations in molar concentrations of organic acids and sugars. Besides, no diel variations in the cations K+, Ca2+ and Mg2+ were detected. K+ was always the dominant cation (K/Ca ratios ∼ 19), while Mg2+ was always higher than Ca2+ (Mg/Ca ∼ 2).
The functional significance of palisade tissue: penetration of directional versus diffuse light
Authors: VOGELMANN T. C. , MARTIN G.
Published: April 2006

Light gradients were measured in leaves that had different types of anatomical development of the mesophyll but similar pigment content. Leaves of the legume, Thermopsis montana, had columnar palisade and spongy mesophyll whereas leaves of the monocot, Smilacina stellata, had spongy mesophyll only. Light gradients were measured at 550 nm in both types of leaves when they were irradiated with collimated or diffuse light. When irradiated with collimated light, light gradients were steeper in leaves with spongy mesophyll in comparison to those that had palisade tissue. On the other hand, light gradients were similar between both leaf types when they were irradiated with diffuse light. Thus, columnar palisade cells facilitated the penetration of collimated light over diffuse light. These results suggest that palisade tissue may help distribute light more uniformly to chloroplasts within the leaf. Moreover, the functional significance of palisade tissue may be related to the amount of collimated light within the natural environment.
Influence of ultraviolet‐B (UV‐B) radiation on photosynthetic and growth characteristics in field‐grown cassava (Manihot esculentum Crantz)
Authors: ZISKA L. H. , TERAMURA A. H. , SULLIVAN J. H. , McCOY A.
Published: April 2006

The effects of ultraviolet‐B (UV‐B between 290 and 320 nm) on photosynthesis and growth characteristics were investigated in field grown cassava (Manihot esculentum Crantz). Plants were grown at ambient and ambient plus a 5.5kJ m−2 d−1 supplementation of UV‐B radiation for 95 d. The supplemental UV‐B fluence used in this experiment simulated a 15% depletion in stratospheric ozone at the equator (0°N). Carbon dioxide exchange, oxygen evolution, and the ratio of variable to maximum fluorescence (Fv/Fm) were determined for fully expanded leaves after 64–76 d of UV‐B exposure. AH plants were harvested after 95 d of UV‐B exposure, assayed for chlorophyll and UV‐B absorbing compounds, and separated into leaves, petioles, stems and roots. Exposure to UV‐B radiation had no effect on in situ rates of photosynthesis or dark respiration. No difference in the concentration of UV‐B absorbing compounds was observed between treatments. A 2‐d daytime diurnal comparison of Fv to Fm ratios indicated a significant decline in Fv/Fm ratios and a subsequent increase in photoinhibition under enhanced UV‐B radiation if temperature or PPF exceeded 35°C or 1800μmol m−2 s−1, respectively. However, UV‐B effects on fluorescence kinetics appeared to be temporal since maximal photosynthetic rates as determined by oxygen evolution at saturated CO2 and PPF remained unchanged. Although total biomass was unaltered with UV‐B exposure, alterations in the growth characteristics of cassava grown with supplemental UV‐B radiation are consistent with auxin destruction and reduced apical dominance. Changes in growth included an alteration of biomass partitioning with a significant increase in shoot/root ratio noted for plants receiving supplemental UV‐B radiation. The increase in shoot/root ratio was due primarily to a significant decrease in root weight (–32%) with UV‐B exposure. Because root production determines the harvest‐able portion of cassava, UV‐B radiation may still influence the yield of an important tropical agronomic species, even though photosynthesis and total dry biomass may not be directly affected.
Relationship between leaf water spin‐lattice relaxation time and water relation parameters in three wheat cultivars
Authors: NAGARAJAN S. , CHAHAL S. S. , GAMBHIR P. N. , TIWARI P. N.
Published: April 2006

Pot culture studies were conducted using two drought‐tolerant and one susceptible cultivar of wheat (Triticum aestivum L.) under three different moisture regimes. Proton spin‐lattice relaxation time, T1, leaf water content, LWC, leaf water potential, Ψ, solute potential, Ψs and turgor potential, Ψp were measured from 45 to 75 d after sowing at weekly intervals. The three cultivars did not differ significantly in their values of LWC, leaf water potential, and their components in the stressed and unstressed plants; but they did differ significantly in their T1 values both under stressed and unstressed conditions on all days of measurement, with the drought tolerant cultivars having a higher T1 compared to the susceptible cultivar. This suggests that leaf water T1 is a better parameter for describing plant water status than the traditional water relation indices. The relation between Ψ and T1 was logarithmic, indicating the similarity between T1 and water activity of the cellular water.
Signal transmission during gravitropic curvature of primary roots of Zea mays
Authors: MOORE R. , MAIMON E.
Published: April 2006

Primary roots of Zea mays cv. Ageotropic are nonresponsive to gravity and elongate approximately 0.80 mm h−1. Applying mucilage‐like material (K‐Y Jelly) to the terminal 1.5 cm of these roots induces graviresponsiveness and slow elongation 28% (i.e. from 0.80 to 0.58mm h−1). Applying mucilage‐like material to one side of the terminal 1.5 cm of the root induces curvature toward the mucilage, irrespective of the root's orientation to gravity. Applying a 2‐mm‐wideband of mucilage‐like material to a root's circumference 8 to 10 mm behind the root cap neither induces gravicurvature nor affects elongation significantly. Similarly, applying mucilage‐like material to only the root cap does not significantly affect elongation or graviresponsiveness. Gravicurvature of mutant roots occurs only when mucilage‐like material is applied to the root/root‐cap junction. Reversing the caps of wild‐type and mutant roots produces gravitropic responses characteristic of the root cap rather than the host root. These results are consistent with the suggestion that gravitropic effectors are growth inhibitors that move apoplastically through mucilage between the root cap and root.
Field investigations of ammonia exchange between barley plants and the atmosphere. II. Nitrogen realiocation, free ammonium content and activities of ammonium‐assimilating enzymes in different leaves
Authors: SCHJOERRING J. K. , KYLLINGSBAEK A. , MORTENSEN J. V. , BYSKOV‐NIELSEN S.
Published: April 2006

The activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) in different leaves of field‐grown spring barley were measured during the reproductive growth phase in 2 consecutive years. Concurrently, the contents of soluble ammonium ions and free amides in the leaves were determined. The studies were carried out to investigate the relationship between variations in these parameters and emission of NH3 from the plant foliage. GS and GOGAT activities declined very rapidly with leafage. The decline in enzyme activities was followed by an increase in soluble ammonium ions and amides in the leaf tissues. During the same period, about 75% of leaf and stem nitrogen was reallocated to the developing ear. The amount of NH3 volatilized from the foliage during the reproductive growth phase amounted to about 1% of the reallocated nitrogen. The experimental years were characterized by very favourable conditions for grain dry matter formation and for re‐utilization of nitrogen mobilized from leaves and stems. Ammonia volatilization occurring under conditions with declining GS and GOGAT activities and increasing tissue concentrations of NH4+ may be useful in protecting the plant from accumulation of toxic NH3 and NH4+ concentrations in the tissues.
Effects of doubled atmospheric carbon dioxide concentration on the responses of assimilation and conductance to humidity
Authors: BUNCE J. A.
Published: April 2006

Experiments were performed to determine if growth at elevated partial pressure of CO2 altered the sensitivity of leaf water vapour conductance and rate of CO2 assimilation to the leaf‐to‐air difference in the partial pressure of water vapour (Δw). Comparisons were made between plants grown and measured at 350 and 700 μPa Pa−1 partial pressures of CO2 for amaranth, soybean and sunflower grown in controlled environment chambers, soybean grown outdoors in pots, and orchard grass grown in field plots. In amaranth, soybean and orchard grass, both the absolute and the relative sensitivity of conductance to Δw at the leaf surface were less in plants grown and measured at the elevated CO2. In sunflower, there was no change in the sensitivity of conductance to Δw for the two CO2 partial pressures. Tests in soybeans and amaranth showed that the change in sensitivity resulted from elevated CO2 during the measurement of the Δw response. Assimilation rate of CO2 was not altered by Δw in amaranth, which has C4 metabolism. In sunflower, the assimilation rate of plants grown and measured at elevated CO2 was insensitive to Δw, consistent with the response of assimilation rate to intercellular CO2 partial pressure in the prevailing range. In soybean, the sensitivity of assimilation rate to Δw was not different between CO2 treatments, in contrast to what would be expected from the response of assimilation rate to intercellular CO2 partial pressure.
Photoinhibition of radish (Raphanus sativus L) seed germination: control of growth potential by cell‐wall yielding in the embryo
Authors: SCHOPFER P. , PLACHY C.
Published: April 2006

The biophysical mechanism underlying photoinhibition of radish (Raphanus sativus L.) seed germination was investigated using three cultivars differing in sensitivity to continuous irradiation with far‐red light (high‐irradiance reaction of phytochrome). Sensitivity of germination to the inhibitory action of light was assessed by probing germination under osmotic stress (incubation in media of low water potentials adjusted with polyethylene glycol 6000) and expressed in terms of ‘germination potential’ (positive value of the water potential at which germination is inhibited by 50%). Far‐red light decreases the germination potential to various degrees in the different cultivars, reflecting the light‐sensitivity of germination in water. Removal of the seed coat increases the germination potential by a constant amount in darkness and light. It is concluded that germination depends on the expansive force of the embryo which can be drastically diminished by far‐red light. Seed‐coat constraint and expansive force of the embryo interact additively on the level of the germination potential. Photoinhibition of germination was accompanied by an inhibition of water uptake into the seed. Analysis of seed water relations showed that osmotic pressure and turgor assumed higher levels in photoinhibited seeds, compared to seeds germinating in darkness, while the water potential was close to zero under both conditions. Far‐red light produced a shift (to less negative values) in the curve relating water‐uptake rate to external water potential, i.e. a reduction in the driving force for water uptake. It is concluded that photoinhibition of germination results from the maintenance of a high threshold of cell‐wall extensibility in the embryo.
Light induction of alternative pathway capacity in leaf slices of Belgium endive
Authors: ATKIN O. K. , CUMMINS W. R. , COLLIER D. E.
Published: April 2006

The effect of light on the development of the capacity for alternative pathway respiration was investigated in leaf slices of Belgium endive (Cichorum intybus L. cv. deliva). Dark‐grown plants possessed little capacity for the cyanide‐insensitive alternative pathway. In contrast, plants grown in continuous light had significant alternative pathway capacity. Light‐grown plants also had substantially higher concentrations of ethanol‐soluble carbohydrates in their leaves than plants grown in complete darkness. Despite these differences in leaf carbohydrate status and alternative pathway capacity of light‐ and dark‐grown leaf tissue, no differences were found in the activity of the alternative pathway, which was negligible in both treatments. Dark‐grown plants were adenylate restricted, as indicated by the increase in cytochrome pathway activity following uncoupling. Adenylates did not limit respiration in light‐grown leaf tissue. Plants that had been grown for 8d in complete darkness were also transferred to continuous light. Respiration of dark controls steadily declined over 11d following the transfer of plants to the light, due primarily to a decrease in cytochrome pathway activity. No such decline was observed in the plants transferred to continuous light. Transfer to continuous light led to significant increases in alternative pathway capacity relative to the dark controls. Alternative pathway activity remained negligible in both the dark controls and in plants transferred to continuous light. The results of this study suggest then that light per se may be responsible for the induction of alternative pathway capacity in Belgium endive.