bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the concentration of ABA in xylem sap as a function of changing soil water status can account for changes in leaf conductance and growth
Authors: ZHANG J. , DAVIES W. J.
Published: April 2006

Abstract. Maize seedlings (Zea mays L. John Innes F1 hybrid) were grown in a greenhouse in l‐m‐long tubes of soil. When the plants were well established, water was withheld from half of the tubes. Control plants were watered every day during the 20‐d experimental period. The soil drying treatment resulted in a substantial restriction of stomatal conductance and a limitation in shoot growth, even though there was no detectable difference in the water relations of watered and unwatered plants. From day 7 of the soil drying treatment, xylem ABA concentrations (measured using the sap exuded from detopped plants) were substantially increased in unwatered plants compared to values recorded with sap from plants watered every day. Measurements of water potential through the profile of unwatered soil suggest that xylem ABA concentrations reflects the extent of soil drying. Leaf ABA content was a much less sensitive indicator of the effect of soil drying and during the whole of experimental period there was no significant difference between ABA concentration in leaves of well watered and unwatered plants. In a second set of experiments, ABA was fed to part of the roots of potted maize plants to manipulate xylem ABA concentration. These manipulations suggested that the increases in ABA concentration in xylem sap, which resulted from soil drying, were adequate to explain the observed variation in stomatal conductance and might also explain the restriction in leaf growth rate. These results are discussed in the light of recent work which suggests that stomatal responses to soil drying are partly attributable to an as‐yet unidentified inhibitor of stomatal opening.
Abscisic acid mimics effects of dehydration on area expansion and photosynthetic partitioning in young soybean leaves
Authors: BUNCE J. A.
Published: April 2006

Abstract. Leaf area expansion, photosynthetic carbon dioxide uptake and leaf dry mass accumulation were compared for expanding leaves of well‐watered soybean (Glycine max [L.] Merr.) plants, mildly dehydrated plants and well‐watered plants treated with abscisic acid (ABA). Both ABA treatment and dehydration reduced area expansion in the light and over a 24 h period without decreasing the photosynthetic rates of expanding leaves. Dry mass accumulation during the light was less in ABA‐treated and water‐stressed leaves than in control leaves, with no differences among treatments in leaf mass per unit of area. ABA treatment and water stress both increased export of carbon from expanding leaves in the light. ABA applied near the end of the light period also increased export of carbon during the following dark period. However, it is unlikely that decreased availability of photosynthate caused slow expansion in the ABA and dehydration treatments, because expansion rates were not slowed in plants kept in dim light, even though photosynthetic rates and dry mass accumulation rates were greatly reduced. The data suggest that ABA may mediate the effects of mild dehydration on leaf area expansion and partitioning of photosynthate.
Salinity tolerance of Kosteletzkya virginica. I. Shoot growth, ion and water relations
Authors: BLITS K. C. , GALLAGHER J. L.
Published: April 2006

Abstract. Kosteletzkya virginica (L.) Presl., a dicotyledonous halophyte native to brackish tidal marshes, was grown on nutrient solution containing 0. 85, 170 or 255 mol m‐3 NaCl, and the effects of external salinity on shoot growth and ion content of individual leaves were studied in successive harvests. Growth was stimulated by 85 mol m‐3 NaCl and was progressively reduced at the two higher salinities. Growth suppression at high salinity resulted principally from decreased leaf production and area, not from accelerated leaf death. As is characteristic of halophytic dicots. K. virginica accumulated inorganic ions in its leaves, particularly Na+ and K+. However, the Na+ concentration of individual leaves did not increase with time, but remained constant or even declined, seeming to be well‐coordinated with changes in water content. A striking feature of the ion composition of salinized plants was the development of a dramatic gradient in sodium content, with Na+ partitioned away from the most actively growing leaves. Salt‐treated plants exhibited a strong potassium affinity, with foliar K+ levels higher in salinized plants than unsalinized plants after an initial decrease. These results suggest that selective uptake and transport, foliar compartmentation of Na+ and K+ in opposite directions along the shoot axis, and the regulation of leaf salt loads over time to prevent build‐up of toxic concentrations are whole‐plant features which enable K. virginica to establish favourable K+‐Na+ relations under saline conditions.
Salinity tolerance of Kosteletzkya virginica. II. Root growth, lipid content, ion and water relations
Authors: BLITS K. C. , GALLAGHER J. L.
Published: April 2006

Abstract. Kosteletzkya virginica (L.) Presl., a dicot halophyte native to brackish tidal marshes, was grown on nutrient solution containing 0. 85, 170 or 255 mol m 3 NaCl, and the effects of external salinity on root growth, ion and water levels, and lipid content were examined in successive harvests. Root growth paralleled shoot growth trends, with some enhancement observed at 85 mol m 3 NaCl and a reduction noted at the higher salinities. Root Na+ content increased with increasing external NaCl, but remained constant with time for each treatment. K+ content, although lower in salt‐grown plants after 14 d salinization, subsequently increased to levels comparable to unsalinized plants. A strong K+ affinity was reflected in the increased K+/Na+ selectivity of salt‐grown plants and by their low Na+/K+ ratios. Cl levels rose in salinized plants and values were double or more those for Na+, indicating the possibility of a sodium‐excluding mechanism in roots. Root phospholipids and sterols, principal membrane constituents, were maintained or elevated and the free sterol/phospholipids ratio increased in salinized K. virginica plants, suggesting retention of overall membrane structure and decreased permeability. This response, considered in light of root calcium maintenance and high potassium levels, suggests that salinity‐induced changes in membrane lipid composition may be important in preventing K+ leakage from cells.
Effects of low‐level ozone exposure under ambient conditions on photosynthesis and stomatal control of Vicia faba L.
Authors: ABEN J. M. M. , JANSSEN‐JURKOVIČOVÁ M. , ADEMA E. H.
Published: April 2006

Abstract. Gas exchange rates of 4‐week‐old faba bean plants were measured after exposure to ozonc (120 μg m3) in an open top chamber for 8 h per day over a period of 2 weeks. The exchange rates were compared with those of control plants. Plants exposed between mid‐May and the end of July 1987 showed a minor negative effect on stomatal conductance, while there was no effect on photosynthesis and respiration. Plants exposed between the end of August and early October showed a negative effect on both stomatal conductance and photosynthesis. In addition, the dark respiration rate was slightly increased. It is concluded that ozone can have a direct effect on the stomata as well as on the photosynthetic system and that the stomata are more sensitive than the photosynthetic system.
Effects of inorganic nitrogen sources on spore germination and gametophyte growth in Botrychium dissectum
Authors: MELAN M. A. , WHITTIER D. P.
Published: April 2006

Abstract. The effects of variations in nitrogen source upon spore germination and gametophyte growth of the eusporangiate fern Botrychium dissectum forma obliquum were investigated. Spore germination and early gametophyte growth were directly related to the oxidation level of the supplied nitrogen source. Nitrate and nitrite inhibited spore germination and at concentrations above 0.035 mol m‐3 prevented it entirely. Ammonium promoted germination well above the levels attained on media without nitrogen. Concentrations of ammonium greater than 0.035 mol m‐3 often resulted in germination above 90%. The growth of young gametophytes from spores was reduced on media without nitrogen or on media with high concentrations of nitrate. Ammonium stimulated the growth of both young and older gametophytes. However, older gametophytes were able to grow on media containing nitrate as the sole nitrogen source. We conclude that a reduced nitrogen source is necessary for spore germination and early growth of Botrychium gametophytes. This requirement has several ecological implications which may be related to the distribution of these ferns and the establishment of mycorrhizal associations.
Interaction of enriched CO2 and water stress on the physiology of and biomass production in sweet potato grown in open‐top chambers
Authors: BHATTACHARYA N. C. , HILEMAN D. R. , GHOSH P. P. , MUSSER R. L. , BHATTACHARYA S. , BISWAS P. K.
Published: April 2006

Abstract. The objective of this study was to investigate the effects of water stress in sweet potato (Ipomoea batatas L. [Lam] ‘Georgia Jet’) on biomass production and plant‐water relationships in an enriched CO2 atmosphere. Plants were grown in pots containing sandy loam soil (Typic Paleudult) at two concentrations of elevated CO2 and two water regimes in open‐top field chambers. During the first 12 d of water stress, leaf xylem potentials were higher in plants grown in a CO2 concentration of 438 and 666 μmol mol−1 than in plants grown at 364 μmol mol−1. The 364 μmol mol−1 CO2 grown plants had to be rewatered 2 d earlier than the high CO2‐grown plants in response to water stress. For plants grown under water stress, the yield of storage roots and root: shoot ratio were greater at high CO2 than at 364 μmol mol−1; the increase, however, was not linear with increasing CO2 concentrations. In well‐watered plants, biomass production and storage root yield increased at elevated CO2, and these were greater as compared to water‐stressed plants grown at the same CO2 concentration.
How does a mistletoe affect the water, nitrogen and carbon balance of two mangrove ecosystem species?
Authors: OROZCO A. , RADA F. , AZOCAR A. , GOLDSTEIN G.
Published: April 2006

Abstract.The effect of a mistletoe,Phthirusa maritima, on the water, nitrogen and carbon balance of two mangrove host species,Conocarpus erectusandCoccoloba uvifera, was studied. Several daily cycles of water potential and its components (pressure‐volume curves); leaf nitrogen content (Kjeldahl method); leaf conductance, transpiration rates and carbon assimilation (portable gas exchange system) were measured on mistletoe, infested and uninfested plants in the Caribbean coast of Venezuela. The mistletoe on both host species showed higher transpiration rates and lower CO2assimilation rates, and therefore lower water use efficiencies. With respect to infested and uninfested plants,C. erectusdid not show large differences in the parameters measured with the exception of assimilation rates which were significantly lower in the infested plants. On the other hand,C. uviferadid show differences in all parameters and, therefore, was affected to a greater degree by the mistletoe. The behaviour of mistletoeinfested and uninfested plants, with respect to habitats with different degrees of water stress and with respect to the salinity gradient in which these mangroves grow, is discussed.
Water stress leads to a change of partitioning in favour of sucrose in heterotrophic cell suspension cultures of Chenopodium rubrum
Authors: DANCER J. , DAVID M. , STITT M.
Published: April 2006

Abstract. When heterotrophic cell suspension cultures of Chenopodium rubrum were subjected to water stress by incubation in increasing concentrations of sorbitol there was an immediate shrinking of the protoplast volume. Glucose uptake decreased in parallel. When the external water potential was greater than 0.5 MPa, a change in the partitioning of this incoming carbon was observed, resulting in a doubling of the ratio of sucrose to starch. This was accompanied by an increase in the concentration of the glycolytic intermediates and a particularly pronounced increase in the levels of fructose‐2,6‐bisphosphate and malate. The extractable activity of sucrose phosphate synthase was determined using a new method which overcomes the problem of uridine‐diphosphate loss from the assay medium. It was found that sucrose phosphate synthase activity decreased in the water stressed cells. Therefore, the higher sucrose concentration in these cells is attributed to the increase in metabolite concentrations alone.
Buoyancy effect on forced convection in the leaf boundary layer
Authors: KITANO M. , EGUCHI H.
Published: April 2006

Abstract. Mixed convection (forced convection plus free convection) in the leaf boundary layer was examined by air flow visualization and by evaluation of the boundary layer conductance at different leaf‐air temperature differences (TL‐TA) under low wind velocities. The visualized air flow was found to become more unstable and buoyant at higher TL‐TA. An ascending longitudinal plume was induced along the upper surface, and the air flow along the lower surface ascended after passing the trailing leaf edge. The air flow modified by buoyancy was considered to result in an increase in boundary layer conductance (GA) for mixed convection, which became higher with higher TL‐TA as compared with the conductance for pure forced convection without buoyancy. This increase in GA appeared larger at larger Grashof number (Gr) and at smaller Reynolds number (Re). The dependences of buoyancy effect on Gr and Re were related to ‘edge‐effects’.
Nocturnal citrate accumulation and its response to environmental stress in the CAM plant Kalanchoe pinnata (Lam.) Pers.
Authors: LÜTTGE U.
Published: April 2006

Abstract. Kalanchoe pinnata (Lam.) Pers., a plant having crassulacean acid metabolism (CAM), was grown in high light (16–23 mol photons m−2 d−1) and in the shade (0.8–2.1 mol photons m−2 d−1), respectively. Plants were stressed in three ways, i.e. by transfer from high light to shade or vice versa just before measurements, and by withholding nitrogen and/or water. During the day‐night cycle of CAM, K. pinnata showed day‐night changes of citrate levels (Δ citrate) in addition to malate changes (Δ malate). Changes of leaf‐cell sap osmotic pressure. Δπ, were linearly correlated with these changes of organic‐acid anion levels with a relation of Δπ/(Δ citrate +Δ malate) = 1/1. The environmental stressor, i.e. limited N‐nutrition, drought and higher or lower irradiance than experienced during growth, affected the absolute and relative contributions made by Δ citrate and Δ malate to total nocturnal organic‐acid accumulation. In the high‐light‐grown plants transferred to the shade, changes of citrate levels were much less affected than changes of malate levels by the generally decreased metabolic activity and inhibition of CO2 uptake. In the shade‐grown plants, Δ citrate increased in response to stress imposed by interactive effects of the three stressors.
The effect of light intensity and daylength on the β‐dimethylsulphoniopropionate (DMSP) content of marine green macroalgae from Antarctica*
Authors: KARSTEN U. , WIENCKE C. , KIRST G. O.
Published: April 2006

Abstract. The β‐dimethylsulphoniopropionate (DMSP) concentrations of 5 Antarctic green algae grown at 2, 30 and 55 μmol photons m−2 s−1 were determined during a period of one year, cultivated under fluctuating daylengths mimicking the conditions of the natural habitat at King George Island. Antarctica. The intracellular DMSP content of all species decreased simultaneously with decreasing daylengths and vice versa. Additionally, the DMSP level was affected by the light intensity: the higher the photon fluence rate the greater the algal DMSP concentration. Under conditions of darkness, there was a degradation of the DMSP pool in members of the Acrosiphoniales, while the DMSP content in members of the Ulvales did not change. The results indicate a light‐dependent DMSP accumulation in algae. Therefore, they may help to explain the seasonal variability of DMSP and its cleavage product dimethylsulphide (DMS) in coastal waters.
Pressure‐volume relationships in non‐rehydrated tissue at various water deficits
Authors: KUBISKE M. E. , ABRAMS M. D.
Published: April 2006

Abstract.The purpose of this paper is to examine a technique for estimating the weight at full saturation (Ws) from pressure‐volume (P‐V) analysis of non‐rehydrated plant tissue at various water deficits. Tissue samples are typically rehydrated prior to P‐V analysis to determine Ws, necessary to calculate many tissue water parameters. However, several studies have indicated that artificial rehydration may significantly alter P‐V relationships, such as the plateau effect, resulting in erroneous measurements of tissue elasticity and osmotic potentials. The results of this study suggest that linear regression of P‐V data at and above the turgor loss point may be used to extrapolate Wsfrom non‐rehydrated samples at various moisture deficits, thus eliminating the plateau effect and other potential rehydration problems. Determination coefficients and standard errors of the Y‐intercept indicated a strong linear relationship between tissue fresh weight and water potential (Ψ), and a high degree of predictability of Wsin all but one of the species‐treatment combinations evaluated in this study, despite predawn Ψ as low as ‐ 1.0 MPa.
Primordium initiation at the stem apex as the primary event controlling plant development: preliminary evidence from wheat for the regulation of leaf development
Authors: HAY R. K. M. , KEMP D. R.
Published: April 2006

Abstract. The results from field studies of 12 crops of winter wheat (two seasons, four sites in the U.K., four cultivars), in which leaf appearance and events at the mainstem apex were fully documented, were used to investigate the inter‐relationship between leaf initiation and appearance. It was shown that the progress of leaf appearance could be divided into two phases around collar initiation. During the first phase, which was common to all crops examined, leaf appearance was linearly related to leaf initiation, indicating that leaf appearance was not independently regulated by the environment but dependent on initiation. The slope of the second phase relationship varied between crops, indicating the intervention of an additional controlling factor. This shows that, for the first phase at least, the time course of leaf appearance was predetermined by the rate of leaf initiation at the stem apex.
Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO2 enrichment
Authors: CONROY J. P. , MILHAM P. J. , MAZUR M. , BARLOW E. W. R.
Published: April 2006

Abstract Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO2 mol 1 for 2 years to establish if growth responses to high CO2 would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO2 concentration were subjected to phosphorus deficiency and to periodic drought. CO2 enrichment increased whole‐plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole‐plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO2 and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO2 levels but differed between families. These results suggest that, as the atmospheric CO2 concentration rises, field‐grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.
Control of photosynthetic carbon dioxide fixation by the boundary layer, stomata and ribulose 1,5‐biphosphate carboxylase/oxygenase
Authors: WOODROW I. E. , BALL J. T. , BERRY J. A.
Published: April 2006

Abstract Coefficients describing the sensitivity of the rate of photosynthetic carbon dioxide fixation to small changes in the stomatal conductance and boundary layer conductance are derived. These sensitivity or ‘control’ coefficients, together with those for the carboxylase and oxygenase activities of ribulose 1,5‐bisphosphate carboxylase/oxygenase, are calculated from standard gas exchange data and apply under conditions where leaf temperature and water vapour concentration at the leaf surface remain largely constant. It is shown that the magnitude of the control coefficients depends on conditions such as photon flux density, ambient CO2 concentration and relative humidity at the leaf surface. The extension of this analysis to encompass the sensitivity of the photosynthetic fluxes to changes in enzyme concentrations and kinetic properties is also discussed.
Photosynthetic and stomatal conductance responses to acid mist of red spruce seedlings
Authors: EAMUS D. , FOWLER D.
Published: April 2006

AbstractTwo‐year‐old seedlings ofPicea rubens, growing in open‐top chambers in Scotland were treated twice weekly from July 1987 to December 1987, with mist containing ammonium sulphate and nitric acid at a pH of either 2.5 or 5.0. The response of photosynthesis and stomatal conductance to light flux density and carbon dioxide concentration were measured in March 1989. Leaf chlorophyllaandbcontents were also measured. Acid mist (pH 2.5) resulted in several significant changes. First, both the rate of light saturated photosynthesis (Amax) and CO2‐ saturated rate of photosynthesis (J) were substantially increased, when expressed per unit leaf area. Second, the apparent quantum yield and chlorophyllsaandbcontent increased. Third, as a consequence of the greater chlorophyll content of the leaves treated with acid mist, the rate of Amax, and J, expressed per unit chlorophyll, was substantially reduced in pH 2.5 treated branches. Stomatal conductance was enhanced at all but the highest light flux densities, and was independent of the CO2concentration, remaining high for all values of CO2concentration used. These results show that acid mist caused a number of responses in the gas exchange and photosynthetic properties of red spruce.
Seasonal dynamics of carbohydrate and nitrogenous components in the roots of perennial weeds
Authors: CYR D. R. , BEWLEY J. D. , DUMBROFF E. B.
Published: April 2006

Abstract Chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale L.) are persistent weeds, the aerial portions of which do not survive in winter. However, subterranean tissues remain viable and facilitate the rapid resumption of growth in early spring. The source of nutrients for growth prior to the establishment of foliage is the roots. Carbohydrate and N reserves are accrued during late summer and autumn, respectively. Hydrolysis of fructans during late autumn occurs coincidentally with increments in sucrose, the latter providing a readily accessible C pool. Nitrate, free amino acids and soluble protein all play substantial roles in nitrogen storage. Asparagine is the predominant amino acid in the free pool during winter, followed by glutamine, ornithine, serine, aspartic acid and glutamic acid. Storage reserves remain at peak levels throughout winter and deeline prior to the resumption of growth. The patterns observed here provide evidence that N is an important currency of storage metabolism and, thus, a framework has been provided for the examination of regulation of N storage in perennial weeds.
Photosynthesis in chloroplasts rapidly isolated from primary leaves of oat (Avena sativa L.): effects of orthophosphate, metal ion and chelators
Authors: YU J. , WOO K. C.
Published: April 2006

Abstract A simple mechanical method for the rapid isolation of chloroplasts with high rates of photosynthesis from young leaves of oat (Avena sativa L.) was described. The photosynthetic activity of these chloroplasts was stable for at least 2 h with rates of CO2‐dependent O2 evolution of 30–40 μmol g 1 Chl s 1. The photosynthetic properties of these chloroplasts were similar to those reported for spinach and pea chloroplasts isolated by mechanical disruption. The pH optimum for photosynthetic O2 evolution was pH 7.6. The induction time was 0.5–2 min. Maximal rates of photosynthetic O2 evolution in these chloroplast preparations were obtained in the absence of both divalent cations and EDTA. Addition of divilent cations strongly inhibited photosynthesis which could be partially restored by the subsequent addition of EDTA. But when these cations were not present in the assay medium the addition of EDTA greater than 1 mol m 3 decreased photosynthetic activity. The optimal orthophosphate concentration required for photosynthesis in these chloroplast preparations was 0.2–0.3 mol m 3. In contrast, the addition of pyrophosphate either in the light or dark inhibited photosynthesis. In a comparative study, chloroplasts were also isolated from oat and wheat (Triticum aestivum L., cultivar Hybrid C306) protoplasts. These chloroplast preparations were found to have properties similar to those determined for oat chloroplasts isolated by the mechanical method reported above.
Different stomatal responses of maize leaves after blue or red illumination under anoxia
Authors: VAVASSEUR A. , LASCÈVE G. , COUCHAT P.
Published: April 2006

Abstract In normal air, illumination with a low level of blue or red light (40 μmol m−2 s−1) did not induce stomatal opening in maize plantlets. In CO2‐free air, 40 μmol m−2 s−1 of blue or red light promoted an enhancement in stomatal opening. At the same quantum flux, blue light was more efficient than red light and stomatal closure occurred more rapidly with a significantly shorter lag phase after blue light. Anoxia inhibited light‐dependent stomatal opening, even under 320 μmol m−2 s−1 illumination. However, after 60 min of illumination with 40 μmol m−2 s−1 of blue light in anoxia, transient stomatal opening was observed when the plant was returned to darkness and normal air. This transient stomatal opening was weaker after pretreatment with red light. We conclude that a blue‐light‐dependent process induced under anoxia leads to stomatal opening provided oxygen is present. Possible mechanisms associated with blue‐light‐effect and the nature of the oxygen‐consuming processes are discussed.
The active uptake of carbon dioxide by the unicellular green algae Chlorella saccharophila and C. ellipsoidea
Authors: ROTATORE C. , COLMAN B.
Published: April 2006

Abstract. Mass spectrometry has been used to measure the rates of CO2 uptake of acid‐ and alkali‐grown cells of the green algae Chlorella ellipsoidea (UTEX 20) and C. saccharophila (UTEX 27). The time course of CO2 formation on addition of 100mmol m−3 K2CO3 to cells in the dark was used as an assay for external carbonic anhydrase (CA). No external CA was detected in acid‐grown cells of either species or in alkali‐grown cells of C. ellipsoidea but was present in alkali‐grown C. saccharophila. In the absence of external CA, or when it was inhibited by 5mmol m−3 acetazolamide, cells of both species, on illumination, rapidly depleted the free CO2 in the medium at pH 7.5 to near zero concentrations before maximum photosynthetic O2 evolution rates were established. Addition of bovine CA rapidly restored the equilibrium CO2 concentration in the medium, indicating that the cells were selectively taking up CO2. Transfer of cells to the dark caused a rapid increase in the CO2 concentration in the medium largely due to the efflux of inorganic carbon from the cells as CO2. This rapid light‐dependent CO2 uptake takes place against pH and concentration gradients and, thus, has the characteristics of active transport.
Fusicoccin‐induced membrane depolarization, K+ efflux and extracellular alkalinization in leaves of Vigna unguiculata
Authors: ULLRICH C. I. , PIKE S. , BELEID EL‐MOSHATY F. I. , LENZ S. , POPHAM P. , NOVACKY A. J.
Published: April 2006

Abstract. In leaves of three different cultivars of cowpeas (Vigna unguiculata), the fungal toxin fusi‐coccin (FC) induced a plasmalemma depolarization from ‐175 to ‐100mV, a value slightly below the N2‐determined diffusion potential in the dark, and to a lesser extent in the light. The depolarization was preceded by the usual initial membrane hyperpolarization (up to 18mV). The membrane depolarization was accompanied by considerable K+ efflux and extracellular alkalinization. Primary and secondary leaves as well as stem tissue of plants, grown under long‐day conditions or in the dark responded similarly. Dark O2 uptake in leaves and hypocotyls was stimulated by FC by up to 77 and 87%, respectively. In contrast, FC caused a typical Em hyperpolarization, K+ influx, extracellular acidification and smaller stimulation of respiration (50%) in leaves of other legumes such as mungbean (Vigna radiata), or soybean (Glycine max). Leaves of navy beans (Phaseolus vulgaris) revealed an intermediate response to FC. The unusual effect of FC in Vigna might be related to the production of toxic catabolites during degradation and fermentation of storage products necessary to meet the strong energy requirement of the pm‐H+ ATPase.
Distribution of aluminium in accumulator plants by X‐ray microanalysis in Richeria grandis Vahl leaves from a cloud forest in Venezuela
Authors: CUENCA G. , HERRERA R. , MÉRIDA T.
Published: April 2006

Abstract. The leaf cells of a tropical tree which accumulates more than 1mg per gram dry weight of Al in its leaves were studied by X‐ray microanalysis. The analyses made in cell walls, vacuoles and chloroplasts of a mature leaf showed that A1 is accumulated preferentially in the cell wall. In the pre‐senescent leaf, A1 also invades the interior of cells and is deposited in chloroplasts and vacuole. Aluminium was found also in xylem vessels but only in traces in phloem tissue. It was not found in spongy parenchyma cells. The observed A1 distribution, i.e. at the adaxial leaf face, coincides with observed damage in tissues of pre‐senescent leaves. The means by which this plant copes with Al under natural conditions seems to be partially preventing it from entering the cell by deposition in cell walls. A hypothesis about the pathways of Al in accumulator plants is proposed.
A dynamic model of photosynthesis in varying light taking account of stomatal conductance, C3‐cycle intermediates, photorespiration and Rubisco activation
Authors: GROSS L. J. , KIRSCHBAUM M. U. F. , PEARCY R. W.
Published: April 2006

Abstract. A dynamic model of whole leaf C3 photosynthesis is constructed using a modified version of the Farquliar‐von Caemmerer approach. The model is designed to provide a physiological basis to understand observations of assimilation in environments with varying photon flux densities, including induction phenomena. The model couples the effect of light activation and dark deactivation of enzymes, stomatal conductance responses, and variations in the pools of carbon cycle intermediates. The dynamic components are viewed on three time scales, the slowest of which (min to h) involves changes in stomatal conductance and the activation stale of Rubisco. On a time scale of seconds to a few minutes, adjustments in pools of biochemical components of the photosynthetic pathway occurs. The most rapid time scale corresponds to the equilibration time of intercelluar CO2 concentration through gaseous diffusion and is here assumed to occur instantaneously. The model form includes a single pool for reduced intermediates including RuBP, a single pool for components of the glycolate pathway, and a third component corresponding to the activation state of Rubisco. This is coupled to a previously described model for the dynamics of stomatal conductance, giving a final model form consisting of six non‐linear ordinary differential equations, of which three control conductance dynamics and three control assimilation. The coupling between these occurs through the variable pi, the intercellular partial pressure of CO2. Only three of the parameters for the assimilation portion of the model require dynamic data to estimate. The remaining parameters are estimated from steady‐state data. The model is calibrated using previously collected data on the tropical understory plant Alocasia macrorrhiza and is shown to have qualitatively similar behaviour to that of experimental measurements using simple changes in PFD, as well as a complex sequence of such changes.
Use of a model of photosynthesis and leaf microenvironment to predict optimal stomatal conductance and leaf nitrogen partitioning
Authors: FRIEND A. D.
Published: April 2006

Abstract. A model of photosynthesis (PGEN) is presented. The model assumes that optimal use is made of the leaf nitrogen available for partitioning between the carboxylase and thylakoid components. This results in predictions of Rubisco and chlorophyll concentrations very similar to those measured elsewhere. A function is incorporated which represents the detrimental effects of negative leaf water potentials on the Calvin cycle, producing a quantitative and mechanistic trade‐off between CO2 entering, and H2O leaving, the leaf. Thus, an optimal stomatal conductance and associated internal partial pressure of CO2 exists for any given set of environmental conditions. The model calculates this optimal state for the leaf, which is its output. The model was subjected to changes in the following parameters: soil water potential, irradiance, ambient CO2 partial pressure, leaf temperature, leaf‐to‐air vapour pressure deficit, wind speed, atmospheric pressure, leaf nitrogen content, root dry weight and leaf width. These perturbations resulted in changes in predicted optimal conductance which were very similar to what has been observed. In general, as the capacity of the leaf to fix CO2 increased, so did the predicted optimal conductance, with the internal partial pressure of CO2 being maintained close to 22Pa.
Plants can grow on internal water
Authors: MATYSSEK R. , TANG A.‐C. , BOYER J. S.
Published: April 2006

Abstract. Water uptake is required when plants enlarge but growth may also occur when no external water is present. To determine whether this growth also depends on water, we studied etiolated seedlings of soybean (Glycine max L. Merr.) deprived of external water by transplanting to vermiculite of low water content or by transferring to water‐saturated air. When the external water supply was decreased or removed, the roots continued to grow rapidly but the stems abruptly decreased in growth (in 1 min) and continued to grow slowly. The stem tissues gained water content in the upper elongating region and lost water content in the basal region. Removal of the basal stem caused growth to slow further. When all tissues surrounding the stem elongating region were removed simultaneously, stem growth decreased abruptly to near zero. Control experiments showed that the decreased growth was not caused by wounding or the removal of the auxin or nutrient supply. It is concluded that growth always depended on a source of water and, when external supplies were absent, internal water was mobilized to enlarging tissues of shoots and roots mostly from the basal stem tissues in these seedlings.
Avena fatua L. seed and seedling nutrient dynamics as influenced by mycorrhizal infection of the maternal generation
Authors: LU X. , KOIDE T.
Published: April 2006

Abstract. The objective of this study was to determine how mycorrhizal infection of one generation of plants influences the nutrient dynamics of seeds and seedlings comprising the subsequent generation. We showed that, for Avena fatua L., seeds produced by mycorrhizal (M) plants consistently contained significantly more phosphorus (particularly the phytate P and residual P fractions) than seeds produced by non‐mycorrhizal (NM) plants. We also followed the development of spikelets produced by M and NM plants. The rates of increase in spikelet dry weight and nitrogen content were largely unaffected by mycorrhizal infection. However, the rate of P accumulation into spikelets was significantly increased by mycorrhizal infection. Greater endosperm P reserves in seeds produced by M plants were associated with greater rates of P accumulation in resultant seedlings. Moreover, offspring plants (all NM) produced by M mother plants had significantly higher root and rhizosphere phosphatase, ATPase and phytase activities than offspring plants produced by NM mother plants. This persistent maternal effect has never before been described. Our results suggest that mycorrhizal infection of one generation of plants may have substantial positive effects on the offspring generation, and thus, may influence plant population dynamics.
Responses of photosynthesis and carbohydrate‐partitioning to limitations in nitrogen and water availability in field‐grown sunflower*
Authors: FREDEEN A. L. , GAMON J. A. , FIELD C. B.
Published: April 2006

Abstract. Sunflower plants (Helianthus annuus L., cv. CGL 208) were field‐grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient‐stress (N‐stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen‐limited. Water‐stress (H2O‐stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient‐stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen‐use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O‐stress treatments. In addition, N‐stress reduced photosynthetic water‐use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O‐stress. In addition, sunflower plants responded to H2O‐stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O‐stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field‐grown sunflower manages a trade‐off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.
The polarity of gravitropism in the moss Physcomitrella patens is reversed during mitosis and after growth on a clinostat
Authors: KNIGHT C. D. , COVE D. J.
Published: April 2006

Abstract. We report two situations in which the polarity of gravitropism of single protonemal cells of the moss Physcomitrella patens is reversed. Dark‐grown protonemata of wild‐type P. patens grow negatively gravitropically. Time‐lapse video‐microscopy reveals that a temporary reversal of growth polarity occurs during mitotic division which is independent of the cells’ growth rate. A transitory reversal of growth direction is also observed when the unidirectional gravitropic stimulus is interrupted by a period of growth on a clinostat. A third situation, in which a mutant class responds by growing positively gravitropically, has been described previously (Jenkins, Courtice & Cove, 1986). These observations are discussed in terms of possible mechanisms for cell morphogenesis and tropic growth.
Terrestrial carbon storage resulting from CO2 and nitrogen fertilization in temperate grasslands
Authors: THORNLEY J. H. M. , FOWLER D. , CANNELL M. G. R.
Published: April 2006

Abstract. A temperate grassland model has been used to simulate carbon sequestration under various environmental conditions. The results suggest that the CO2 and nitrogen fertilization that has occurred may contribute appreciably to the so‐called missing carbon sink, which it has been suggested must exist to balance the global carbon budget.
Studies of Elodea nuttallii grown under photorespiratory conditions. III. Quantitative cytological characteristics
Authors: FAGERBERG W. R. , EIGHMY T. T. , JAHNKE L. S.
Published: April 2006

Abstract. Elodea nuttallii was grown in primary effluent from domestic wastewater under conditions in which CO2 may be limiting. However, high photosynthetic inorganic carbon uptake rates have been reported for Elodea under these conditions. In order to determine if leaf cell structure showed modifications which would support proposed models of a plasma membrane (PM) bicarbonate transport system and observed high photo‐synthetic rates, leaf cell ultrastructure was analysed using quantitative techniques (stereology). A Fold Index (FI) calculated for the PM showed that infolding increased surface area to 2.15 times that of an idealized cell of the same shape and size. Association Indices (Sa) showed a significant association of the mitochondria with the PM. These observations support models for an ATPase‐driven HCO3‐cation cotransport system in Elodea cells. High chloroplast thylakoid surface density values (Sv) were similar to C4:monocots and indicated high light‐gathering potential. The granal/stromal (g/s), granal/cristae (g/c), and stromal/cristae (s/c) membrane ratios were similar to those of C3 plant cells. Thus, Elodea chloroplasts and cells exhibited some structural features similar to both C3 and C4 plants. Membrane‐bound inclusion bodies, which occupied 1% of the cell volume, were also observed in the leaf cells. Cell walls and nucleoid regions were absent in these bodies and X‐ray (EDAX) analysis failed to detect any element (above the resolution limit of atomic no. 12) in substantial quantities. Inclusion bodies were observed in both the cytoplasm and the periplast and remain unidentified. A model is proposed for Elodea using an ATPase proton pump in the plasma membrane which extrudes protons into the periplast space between the cell wall and plasma membrane. This proton gradient is coupled to a bicarbonate symport.
Experiments on the control capacity of stomata of Picea abies (L.) Karst. after fumigation with ozone and in environmentally damaged material
Authors: MAIER‐MAERCKER U. , KOCH W.
Published: April 2006

Abstract. With the aid of specifically designed potometer experiments, it is shown that, after ozone fumigation, twigs transpiring in gas exchange chambers show poor water balance in decreasing humidity. The quotient of water uptake to water loss never falls below 0.9 in healthy material because of the control capacity of the stomata. In twigs from a tree fumigated with ozone irregular and delayed stomatal closure results in values of < 0.5 or even lower, depending on the degree of damage. As a result, in dry air, the transpiration rates of fumigated twigs often fall far below those of the control material, even if they were higher than the latter in humid air. In analogous experiments, the difference in behaviour between twigs of densely (‘healthy’) and sparsely needled (‘damaged’) trees from the natural stand is comparable to the difference between controls and ozone‐fumigated trees in most respects. In soil that is more or less dried out and after the best possible saturation of the twigs during the night, the transpiration rates of fumigated trees increase fairly strongly in the humid chamber air at dawn, but finally decrease more or less suddenly to lower values than in the controls. The results are placed in the context of the basic research on plant water relations and compared with histological changes in the stomatal apparatus after a period of fumigation as described earlier. Therefore, long‐term effects of pollution can be explained as a specific distrubance of hydroregulation.
Adaptation to shade of the light‐harvesting apparatus inSilene dioica
Authors: McKIERNAN M. , BAKER N. R.
Published: April 2006

Abstract.The physiological characteristics and photo‐system composition of the photosynthetic apparatus ofSilene dioica, a woodland plant, grown in sun and natural shade are examined. As expected, shade leaves exhibited lower chlorophyll a/b ratios, light saturated rates of CO2assimilation (Asat), dark respiration (Rd,) and light compensation points (Г), with both sun and shade leaves having similar absorptances and quantum yields of CO2assimilation (φ). Shade leaves were able to utilize far‐red light for electron transport and carbon assimilation and reach the compensation point. Sun leaves in far‐red light had a rate of carbon assimilation equivalent to their dark respiration rate. Chlorophyll fluorescence kinetics from leaves at 77 K together with analyses of thylakoid contents of photosystems (PS) I and II and the light‐harvesting cholorphyll a/b protein complex associated with PSII (LHCII) demonstrated that the antenna size of PSII was similar in thylakoids of sun and shade leaves, but shade leaves containedca.20% more PSII andca.12% less PSI complexes. The increased PSII/PSI ratio in shade leaves accounted for their ability to achieve the compensation point in far‐red light. An important feature of photosynethic shade adaptation inS. dioicais an increase in the PSII/PSI ratio and not an increase in the antenna size of PSII. The adaptive response of sun leaves when placed in a shade environment was rapid and had a half‐time ofca.18h.
Solute concentrations of the phloem and parenchyma cells present in squash callus
Authors: LACKNEY V. K. , SJOLUND R. D.
Published: April 2006

Abstract. Glutaraldehyde fixation was used to determine the solute concentrations in the various cell types present in tissue cultures of squash (Cucurbita pepo). Small pieces of callus were plasmolyzed in a graded series of mannitol solutions and fixed in 20 kg m−3 glutaraldehyde adjusted to be isosmotic with the particular plasmolysing solution. The callus samples were further processed using standard electron microscopy techniques. Using this procedure, mature sieve elements that form in squash callus have an osmotic potentional of ‐2.4MPa. The osmotic potential of the callus sieve elements was comparable to values reported for the sieve tube members of the phloem in intact plants. This ability of callus sieve elements to develop high internal hydrostatic pressures demonstrates that they are capable of phloem loading. However, the osmotic potentials of the surrounding parenchymatous cells and companion cells were only –1.15 and –1.5 MPa, respectively. In contrast to the companion cells of the phloem in intact plant tissues, the osmotic potential of the callus companion cells indicated that they were not directly involved in phloem loading. Several immature sieve elements containing distinct nuclei and vacuoles were observed in the callus granules. These immature sieve elements were plasmolyzed in weaker mannitol solutions (below 0.6kmol m−3) than the enucleate sieve elements (1.01 kmol m−3 mannitol). The low solute concentrations in immature sieve elements indicated that the ability to load sugars occurs concomitantly with the maturation of the sieve element protoplast.