bluuebunny/crossref_metadata_2025 huggingface dataset:
Maize stomatal conductance in the field: its relationship with soil and plant water potentials, mechanical constraints and ABA concentration in the xylem sap
Authors: TARDIEU F. , KATERJI N. , BETHENOD O. , ZHANG J. , DAVIES W. J.
Published: April 2006

Abstract. Stomatal conductance, leaf water potential, soil water potential and concentration of abscisic acid (ABA) in the xylem sap were measured on maize plants growing in the field, in two treatments with contrasting soil structures. Soil compaction affected the stomatal conductance, but this effect was no longer observed if the soil water potential was increased by irrigation. Differences in leaf water potential did not account for the differences in conductance between treatments. Conversely, the relationship between stomatal conductance and concentration of ABA in the xylem sap was consistent during the experiment. The proposed interpretation is that stomatal conductance was controlled by the root water potential via an ABA message. Control of the stomatal conductance by the leaf water potential or by an effect of mechanical stress on the roots is unlikely.
Simulated influence of altitude on photosynthetic CO2 uptake potential in plants
Authors: SMITH W. K. , DONAHUE R. A.
Published: April 2006

Abstract. A simulation of the quantitative influence of altitude on photosynthetic CO2 uptake capability (AP) included the effects of predicted changes (1) in air temperature (lapse rate) and (2) leaf temperature, (3) ambient pressure and CO2 concentration, and (4) the diffusion coefficient for CO2 in air. When a dry lapse rate (0.01°C m−1) in air temperature was simulated, significant declines (up to 14%) in AP were predicted from sea level to 4km altitude. A moist lapse rate of 0.003°C m−1 resulted in less than a 4% decrease in AP over the same altitude range. When natural leaf temperatures (predicted from heat balance analyses) were simulated, AP was significantly greater (∼20%) than when leaf temperatures were considered equal to air temperature for all lapse conditions. There was virtually no change in AP with altitude when predicted leaf temperatures and moist lapse conditions were simulated. There was a significant (∼10%) increase in AP with altitude when leaf temperature was held constant at 30°C (regardless of altitude) under moist lapse conditions. Future studies evaluating the effects of elevation on photosynthesis could benefit from the above considerations of the effects of natural leaf temperature regimes and prevailing lapse conditions on CO2 uptake potential.
Potential effects of elevated CO2 and changes in temperature on tropical plants
Authors: HOGAN K. P. , SMITH A. P. , ZISKA L. H.
Published: April 2006

Abstract. Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO2 concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO2 concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO2 concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO2 concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.
Physiology of inorganic C acquisition and implications for resource use efficiency by marine phytoplankton: relation to increased CO2 and temperature
Authors: RAVEN J. A.
Published: April 2006

Abstract. Photosynthesis by many marine phytoplankton algae is saturated by the inorganic C concentration in air‐equilibrated sea water. These organisms appear to use an active inorganic C transport process (CO2‐concentrating mechanism) which increases the CO2 concentration around rubisco and saturates this enzyme with CO2 and suppresses its oxygenase activity. A minority of marine phytoplankton algae have photosynthetic characteristics more suggestive of diffusive CO2 entry; the inorganic C concentration present in sea water does not saturate photosynthesis by these organisms. Theoretical considerations, tested when possible against observation, suggest that the organisms with a CO2‐concentrating mechanism could have a lower cost of photons, nitrogen, iron, manganese and molybdenum to achieve a given rate of carbon accumulation by the cells than is the case for the organisms with diffusive CO2 entry. Zinc and selenium costs may show the reverse effect. The increased sea‐surface inorganic C, and CO2 concentrations which will result from anthropogenic increases in atmospheric CO2 content are predicted to increase the rate of photosynthesis, and of growth when other resources are abundant, and to reduce, or reverse, the higher resource (photons, nitrogen, iron, manganese and molybdenum) cost of a given rate of CO2 assimilation in organisms with CO2 diffusion relative to those which have CO2 concentrating mechanisms and do not repress them at higher inorganic C concentrations. These effects may well alter species composition, and overall resource cost of growth, of phytoplankton; any influence that these effects may have on CO2 removal from the atmosphere are severely constrained by other trophic levels and, especially, oceanic circulation patterns. Changed sea‐surface temperatures are unlikely to qualitatively alter these conclusions.
Growth at elevated CO2: photosynthetic responses mediated through Rubisco
Authors: BOWES G.
Published: April 2006

Abstract. The global uptake of CO2 in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco), which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO2 and O2 are substrates; CO2 also activates the enzyme. In C3 plants, rubisco has a low catalytic activity, operates below its Km (CO2), and is inhibited by O2. Consequently, increases in the CO2/O2 ratio stimulate C3 photosynthesis and inhibit photorespiration. CO2 enrichment usually enhances the productivity of C3 plants, but the effect is marginal in C4 species. It also causes acclimation in various ways: anatomically, morphologically, physiologically or biochemically. So, CO2 exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO2 enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/Pi‐regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/Pi regeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/Piregeneration capacities, or chloroplast disruption. As exemplified by field‐grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO2 enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C4 and CAM plants have genetically adapted to a decline in the external CO2/O2 ratio, by the development of mechanisms to concentrate CO2 internally; thus circumventing O2 inhibition of rubisco. Here rubisco affinity for CO2 is less, but its catalytic activity is greater, a situation compatible with a high‐CO2 internal environment. In aquatic autotrophs, the CO2 concentrating mechanisms acclimate to the external CO2, being suppressed at high‐CO2. It is unclear, whether a doubling in atmospheric CO2 will be sufficient to cause a de‐adaptive trend in the rubisco kinetics of future C3 plants, producing higher catalytic activities.
The effects of increasing CO2 on crop photosynthesis and productivity: a review of field studies
Authors: LAWLOR D. W. , MITCHELL R. A. C.
Published: April 2006

Abstract. Only a small proportion of elevated CO2 studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO2 increases photosynthesis, dry matter production and yield, substantially in C3 species, but less in C4, it decreases stomatal conductance and transpiration in C3 and C4 species and greatly improves water‐use efficiency in all plants. The increased productivity of crops with CO2 enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield‐forming structures than in their size. There is little evidence of a consistent effect of CO2 on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO2 in combination with temperature, water and nutrition are essential; they should be related to the development and improvement of mechanistic crop models, and designed to test their predictions.
Molecular responses of plants to an increased incidence of heat shock
Authors: HOWARTH C. J.
Published: April 2006

Abstract. Climatic change as a result of the greenhouse effect is widely predicted to increase mean temperatures globally and, in turn, increase the frequency with which plants are exposed to heat shock conditions, particularly in the semi‐arid tropics. The consequences of extreme high‐temperature treatments on plants have been considered, particularly in relation to the synthesis of heat shock proteins (HSPs) and the capacity to acquire thermotolerance. The heat shock response is described using results obtained with seedlings of the tropical cereals, sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum). A gradual temperature increase, as would occur in the field, is sufficient to induce thermotolerance. The synthesis of HSPs is a transient phenomenon and ceases once the stress is released. Despite the persistence of the HSPs themselves, de novo synthesis of HSPs is required for the induction of thermotolerance each time high temperatures are encountered. The effect of a repeated, diurnal heat shock was investigated and genotypic differences found in the ability to induce the heat shock response repeatedly.
The molecular and biochemical analyses of CO2‐concentrating mechanisms in cyanobacteria and microalgae
Authors: COLEMAN J. R.
Published: April 2006

Abstract. The supply of dissolved inorganic carbon for photosynthesis in the aquatic environment is much more variable than that experienced by terrestrial plants. In response to this variability, cyanobacteria and many species of microalgae acclimate to rapid changes in the availability of dissolved inorganic carbon by the induction of high affinity/high capacity CO2‐concentrating systems (CCMs). Biochemical and molecular analyses of the acclimation response have recently identified several components that are required for efficient operation of the CCMs and CO2 assimilation. This has been accomplished using in vivo labelling studies, and characterization of high inorganic carbon (Ci) requiring cyanobacterial and algal mutants. The identification and regulation of expression of polypeptides synthesized in response to limiting Ci concentrations, and the proposed role of the carboxysome and the pyrenoid in the functioning of the CCMs are examined.
Leaf age and season influence the relationships between leaf nitrogen, leaf mass per area and photosynthesis in maple and oak trees
Authors: REICH P. B. , WALTERS M. B. , ELLSWORTH D. S.
Published: April 2006

Abstract. Seasonal changes in photosynthesis, leaf nitrogen (N) contents and leaf mass per area (LMA) were observed over three growing seasons in open‐grown sun‐lit leaves of red maple (Acer rubrum), sugar maple (A. sacchamm) and northern pin oak (Quereus ellipsoidalis) trees in southern Wisconsin. Net photosynthesis and leaf N were highly linearly correlated on both mass and area bases within all species from late spring until leaf senescence in fall. Very early in the growing season leaves had high N concentrations, but low photosynthetic rates per unit leaf N, suggesting that leaves were not fully functionally developed at that time. Leaf N per unit area and LMA had nonparallel seasonal patterns, resulting in differing relationships between leaf N/area and LMA in the “early versus late growing season. As a result of differences in seasonal patterns between leaf N/area and LMA, net photosynthesis/area was higher for a given LMA in the spring than fall, and the overall relationships between these two parameters were poor.
Dunaliella acidophila: an algae with a positive zeta potential at its optimal pH for growth*
Authors: GIMMLER H. , SCHIEDER M. , KOWALSKI M. , ZIMMERMANN U. , PICK U.
Published: April 2006

Abstract. The zeta potential (which approximates the surface potential) of the acid resistant green alga Dunaliella acidophila (optimal growth at pH 1.0) and the salt resistant D. parva (grown at pH 7.6) were calculated from the electrophoretic mobility of cells as determined by means of free‐flow electrophoresis. Dunaliella acidophila cells exhibit a positive zeta potential (+5 to +20mV) at acidic external pH values, whereas negative zeta potentials (‐30 mV) were measured at neutral pH values. Negative zeta potentials of the same order of magnitude were also measured for D. parva cells (pH 7.6). Low concentrations of La3+ and A13+ did not affect the positive zeta potential of D. acidophila at acidic pH values, whereas higher concentrations caused a shift to more positive potentials. However, at neutral pH these cations caused a significant decrease of the negative zeta potential. The impermeant polycation poly‐L‐lysine acted in a similar manner to A13+ or La3+. The effect of Impermeant cations and anions on various physiological reactions also supports the existence of a positive zeta potential for D. acidophila and of a negative zeta potential for D. parva: polycations such as DEAE‐dextran and poly‐L‐lysine strongly inhibitied photosynthesis and mobility of D. parva, but did not affect these reactions in D. acidophila. Comparable differential inhibitions were also observed for A13+ and La3+. Impermeant anions such as Dextran‐sulfate exhibited effects in the opposite direction: inhibition was stronger with D. acidophila and weaker with D. parva. However, the differential inhibition by impermeant anions was much less pronounced in comparison with impermeant cations due to the relatively high pKa values of anionic solutes and consequently relatively high protonation at pH 1.0. The physiological consequences of an asymmetrically charged plasma membrane (excess of positive charges outside, excess of negative charges on the cytoplasmic side) of D. acidophila are discussed in regard to the extreme acid resistance of this alga and its resistance to cationic toxic solutes in industrial wastes.
Ion accumulation in the cell walls of rice plants growing under saline conditions: evidence for the Oertli hypothesis
Authors: FLOWERS T. J. , HAJIBAGHERP M. A. , YEO A. R.
Published: April 2006

Abstract. When plants of rice (Oryza saliva L.) are subjected to mildly saline (50mol m−3 NaCl) conditions, the leaves show symptoms of water deficit, even though ion accumulation has been more than sufficient to adjust to the decrease in external water potential. After a few days of exposure to salt, there is a negative correlation, in a population of leaves, between the leaf water concentration (g water per g dry weight) and their sodium concentration (mmol Na per g dry weight). Ion concentrations in the cell walls and the cytoplasm of cells of plants grown in low salinity were measured by X‐ray microanalysis. The NaCl concentration in solution in the apoplast was calculated to be around 600mol m−3 in leaves of plants whose roots were exposed to only 50 mol m−3 NaCl. This constitutes strong evidence that an important factor in salt damage in rice is dehydration due to the extracellular accumulation of salt as suggested in the Oertli hypothesis. The implication, that changes in tissue ion concentration and solute potentials equivalent to the external medium is not evidence of plant osmotic adjustment to salinity, is discussed.
Modification of paraheliotropic leaf movement in Phaseolus vulgaris by photon flux density
Authors: FU Q. A. , EHLERINGER J. R.
Published: April 2006

Abstract. The effects of modification of photon flux density (PFD, 400‐700 nm) on paraheliotropic leaf movement were examined in Phaseolus vulgaris L. under controlled environmental conditions. The cosine of the angle of incidence to directional PFD (cos(i)), a measure of leaf movement, was linearly and negatively related to PFD. That is, leaflets progressively oriented away from a direct light beam in response to increasing PFD. The minimum PFD causing paraheliotropic movement was approximately 25 μmol m−2 s−1. When PFD was varied, tissue temperature changed due to an altered energy balance. Since a change in pulvinus temperature can affect leaf movement, experiments were conducted to distinguish the effects of PFD signal and pulvinis temperature. Leaflets oriented to reduce incident PFD levels in response to increasing PFD (either white light or blue light) when pulvinis temperature was kept constant. From these results, we conclude that changes in PFD signals alone can control paraheliotropic leaf movements. Phaseolus vulgaris grown outdoors oriented their leaflets to face towards the sun in the morning and again in late afternoon, but avoided the sun's direct rays at midday. This diurnal pattern of paraheliotropic leaf movements can be explained on the basis of known paraheliotropic movements in response to PFD and air temperature.
CO2 enrichment of sour orange trees: 2.5 years into a long‐term experiment
Authors: IDSO S. B. , KIMBALL B. A. , ALLEN S. G.
Published: April 2006

Abstract. Eight sour orange trees have been grown from seedling stage in the field at Phoenix, Arizona, U.S.A., in four identically‐vented, open‐top, clear‐plastic‐wall chambers for close to 2.5 years. Half of the chambers have been maintained at ambient atmospheric CO2 concentrations over this period, while half of them have been maintained at 300 ppm (300 μlmol CO2 per mol air) above ambient. Initially, the trees in each treatment were essentially identical; but in less than 2 years, the trunks of the CO2‐enriched trees had become twice as large as their ambient‐treatment counterparts. After 2 full years of growth, the enriched trees had 79% more leaves, 56% more primary branches with 172% more volume, 70% more secondary branches with 190% more volume, and 240% more tertiary branches with 855% more volume. In addition, the CO2‐enriched trees also had fourth‐, fifth‐ and sixth‐order branches, while the ambient‐treatment trees had no branches above third order. Total trunk plus branch volume of the CO2‐en‐riched trees was 2.79 times that of the ambient‐treatment trees after 2 fulf years of growth.
Does climatic warming increase the risk of frost damage in northern trees?
Authors: HÄNNINEN H.
Published: April 2006

Abstract. The effect of climatic warming on the timing of bud burst and the subsequent risk of frost damage on trees in central Finland was assessed with the aid of a computer model, 73 years of temperature data and a climatic scenario corresponding to doubled level of atmospheric CO2. In general, climatic warming hastened bud burst, due to ontogenetic development during warm spells in autumn, winter and spring. During the years with the warmest winters in the scenario conditions: (a) bud burst took place during mid‐winter; and (2) depending on the year, the trees were subsequently exposed to temperatures between −27 and −10°C. This finding suggests that the risk of frost damage to trees will be increased if the predicted climatic warming occurs. Because of the assumptions used in the model, the results are not conclusive, but they do point out the importance of further experimental studies on genetic and environmental regulation of timing of bud burst in trees.
The kinetics of stomatal responses to VPD in Vicia faba: electrophysiological and water relations models
Authors: ASSMANN S. M. , GERSHENSON A.
Published: April 2006

Abstract. An Ohm's law analogy is frequently employed to calculate parameters of leaf gas exchange. For example, resistance to water vapour loss is calculated as the quotient of vapour pressure difference (VPD) and vapour loss by transpiration. In the present research, this electrical analogy was extended. Steady‐state transpiration as a function of VPD, assayed in leaflets of Vicia faba using gas exchange techniques, was compared with steady‐state K+ current magnitude as a function of voltage in isolated guard cell protoplasts of Vicia faba, assayed using the patch clamping technique in the whole cell configuration. An electrophysiological model originally developed to explain the kinetics of current changes following step changes in voltage across a cell membrane was used to fit the kinetics of transpiration changes following step changes in VPD applied to leaflets of Vicia faba. Following step increases in VPD, transpiration exhibited an initial increase, reflecting the increased driving force for water loss and, for large step increases in VPD, a transient decrease in stomatal resistance. Transpiration subsequently declined, reflecting stomatal closure. By analogy to electrophysiological responses, it is hypothesized that the humidity parameter that is sensed by guard cells is VPD. Two models based on epidermal water relations were also applied to transpiration kinetics. In the first model, the transient increase in transpiration following a step increase in VPD was attributed partially to an increase in the Physical driving force (VPD) and partially to a transient decrease in stomatal resistance resulting from reduced epidermal backpressure. In the second model, the transient decrease in stomatal resistance was attributed to a direct response of the guard cells to VPD. Both models based on water relations gave good fits of the data, emphasizing the need for further study regarding the metabolic nature of the guard cell response to humidity.
Studies of the relationship between isoprene emission rate and CO2 or photon‐flux density using a real‐time isoprene analyser
Authors: MONSON R. K. , HILLS A. J. , ZIMMERMAN P. R. , FALL R. R.
Published: April 2006

Abstract. Studies of the isoprene emission rate in response to changes in photon‐flux density and CO2 partial pressure were conducted using a recently developed on‐line isoprene analyser combined with a gas exchange system and chlorophyll fluorometer. Upon darkening, the isoprene emission rate from leaves of aspen (Populus tremuloides Michaux.) began to decline immediately, demonstrating that the internal pool of isoprene, or its precursors, is small and that the instantaneous emission rate is tightly coupled to the rate of synthesis. A post‐illumination burst of isoprene was observed within 5 min after darkening and lasted for 15–20 min in four isoprene‐emitting species that were examined. In leaves of eucalyptus (Eucalyptus globulus Labill.), the magnitude of the post‐illumination burst was dependent on the photon‐flux density that existed before darkening, but not on ambient CO2 partial pressure. The dependence of the post‐illumination burst on photon‐flux density paralleled that for the steady‐state rate of isoprene emission. A step‐wise increase in intercellular CO2 partial pressure from 24.5 to 60 Pa resulted in an immediate decrease in isoprene emission rate and non‐photochemical fluorescence quenching, but an increase in CO2 assimilation rate. Given the several recent studies that link isoprene emission to chloroplastic processes, the results of this study indicate that the linkage is not dependent on the rate of CO2 flux through the reductive pentose phosphate pathway, but rather on more complex relationships involving metabolites not appreciably influenced by CO2 partial pressure.
A model of water flow through plants incorporating shoot/root ‘message’ control of stomatal conductance
Authors: JOHNSON I. R. , MELKONIAN J. J. , THORNLEY J. H. M. , RIHA S. J.
Published: April 2006

Abstract. A model of water flow from the soil into the plant, and from the plant to the atmosphere is described. There are three state variables in the model: the soil, root and shoot water contents. The flow rate of water from the soil to the root is calculated by dividing the gradient in water potential by a resistance, comprising the resistance from the bulk soil to the root surface, and that from the root surface to the root interior. The resistance in the soil depends on the soil hydraulic conductivity, which in turn depends on the soil water potential. The flow rate from the root to the shoot is given by the gradient in water potential divided by a resistance, which depends on the structural dry mass of the plant. Transpiration is described by the Penman‐Monteith equation. The plant water characteristics can be modified to take account of osmotic and cell wall rigidity parameters. The model incorporates the concept of shoot/root ‘messages’ of water stress, which influence stomatal conductance. The message works through the generation of a hormone as the pressure potential in the shoot (mesophyll) or root falls. This hormone induces a shift of osmoticum from the guard cells to the surrounding mesophyll cells, which causes an increase (i.e. closer to zero) in the osmotic potential in these cells. This, in turn, causes a decrease in their pressure potential, and so reduces stomatal conductance. The model is used as a framework to address some of the issues that have recently been raised concerning the role of water potential in describing water flow through plants. We conclude that, with the hormone present, there is unlikely to be a unique relationship between stomatal conductance and shoot total water potential, since stomatal conductance depends on the pressure potential in the guard cells, which may differ from that in other cells. Nevertheless, this does not imply that water potential is not an important, and indeed fundamental, component for describing water flow through plants. Other aspects of water flow through plants are also considered, such as diurnal patterns of shoot, root and soil water potential components. It is seen that these may differ from the commonly held view that, as the soil dries down, they all attain the same values during the dark period, and which, as we show, is largely unsubstantiated either theoretically or experimentally.
Ion currents and the nitrogen status of roots of Hordeum vulgare and non‐nodulated Trifolium repens
Authors: MILLER A.L. , SMITH G. N. , RAVEN J. A. , GOW N. A. R.
Published: April 2006

Abstract. Profiles of self‐generated ion currents associated with the growing primary root tips of intact Hordeum vulgare L. and Trifolium repens L. (nonnodulated) seedlings were measured using a highly sensitive vibrating electrode in media containing NH+4 or NO‐3, and compared to control roots growing in nitrogen free media. Under these three nutrient regimes, positive current entered the root at regions corresponding to the meristematic tissues and main elongation zones of root tips and left from the mature root tissues. Mapping the surface of the roots with a pH‐sensitive microelectrode revealed regions of external alkalinity where positive electrical current entered the root, and external acidity where positive current exited. The correlation between pH‐profile and the pattern of ion current generation in these experiments suggests that H+ ions were responsible for carrying the bulk of the root‐generated current. Assimilation of NHJ results in net H+ extrusion while assimilation of NO‐3, results in net OH‐3 efflux. Growth on NH+4, as compared to growth on NO‐3, stimulated the magnitude of the electrical current but did not affect significantly the growth rate of the roots. However, despite the differing stresses on internal pH regulation that arise due to growth on the two exogenous forms of combined nitrogen, the current profiles were qualitatively similar under the different conditions that were examined. The role of the circulating proton current is not yet known; however, the constancy of the current profile under different nutrient regimes sustains the hypothesis that the current may have a role in the regulation of root polarity.
Acclimation of rice to changing atmospheric carbon dioxide concentration
Authors: ROWLAND‐BAMFORD A. J. , BAKER J. T. , ALLEN L. H. , BOWES G.
Published: April 2006

Abstract. The effects were studied of season‐long (75 and 88d) exposure of rice (Oryza sativa L. cv. IR‐30) to a range of atmospheric CO2 concentrations in outdoor, computer‐controlled, environment chambers under natural solar radiation. The CO2 concentrations were maintained at 160, 250, 330, 500, 660 and 900μmol mol‐1 air. Photosynthesis increased with increasing growth CO2 concentrations up to 500u.mol moP1, but levelled off at higher CO2 values. Specific leaf area also increased significantly with increasing CO2. Although leaf dry weight and leaf area index increased, the overall response was not statistically significant. Leaf nitrogen content dropped slightly with elevated CO2, but the response was not statistically significant. The specific activity of ribulose bisphosphate carboxylase/oxygenase (rubisco) declined significantly over the CO2 concentration range 160 to 900μmol mol‐1. When expressed on a leaf area basis, rubisco activity decreased by 66%. This was accompanied by a 32% decrease in the amount of rubisco protein as a fraction of the total soluble leaf protein, and by 60% on a leaf area basis. For leaves in the dark, the total rubisco activity (CO2/Mg2+‐activated) was reduced by more than 60%. This indicates that rice accumulated an inhibitor in the dark, probably 2‐car‐boxyarabinitol 1‐phosphate (CA‐1‐P). However, the inhibitor did not seem to be involved in the acclimation response. The degree of carbamylation of the rubisco enzyme was unchanged by the CO2 growth regime, except at 900 [μmol mol‐1 where it was reduced by 24%. The acclimation of rice to different atmospheric CO2 conditions involved the modulation of both the activity and amount of rubisco protein in the leaf.
Growth and photosynthesis of soybean (Glycine max (L.) Merr.) in simulated vegetation shade: influence of the ratio of red to far‐red radiation*
Authors: PAUSCH R. C. , BRITZ S. J. , MULCHI C. L.
Published: April 2006

Abstract. Glycine max (L.) Merr. was grown under several light conditions to determine the role of red and far‐red radiation in plant adaptation to vegetation shade. Neutral density,‘neutral’ density with elevated far‐red radiation, and green shade treatments were used in a greenhouse, producing calculated phytochrome photostationary state (Pfr/Pr+Pfr) values of 0.68, 0.63 and 0.51, respectively. Cool‐white fluorescent lamps either alone or in conjunction with far‐red fluorescent lamps were used in a growth chamber, providing Pfr/Pr+Pfr of 0.79 and 0.61, respectively. Daily photo‐synthetically active radiation was about 25% of daylight and was approximately equal for both greenhouse (2.15MJ m−2) and growth chamber (2.57MJ m−2). Developmental stage 4 weeks after sowing was similar for all treatments, but axillary growth and rates of leaf area and dry matter accretion differed between plants from greenhouse and growth chamber. Light conditions simulating vegetation shade (i.e. a low ratio of red to far‐red radiation) significantly promoted petiole elongation and retarded the rate of stem elongation in both greenhouse and growth chamber experiments. Other aspects of growth either were not significantly altered by spectral quality or were not modified consistently in both greenhouse and growth chamber environments. Net photosynthetic rates measured under growth conditions for unifoliate and first trifoliolate (TF1) leaves of growth chamber plants between 9 and 21 d after sowing were generally unaffected by spectral quality, but supplemental FR enhanced TF1 leaf area expansion. The latter effect was not correlated with increased dry matter accumulation. The significance of spectral quality for adaptation of soybeans to canopy closure and intercropping is discussed.
Atmospheric CO2, plant nitrogen status and the susceptibility of plants to an acute increase in temperature
Authors: COLEMAN J. S. , ROCHEFORT L. , BAZZAZ F. A. , WOODWARD F. I.
Published: April 2006

Abstract. Elevated levels of CO2 in the atmosphere are expected to affect plant performance and may alter global temperature patterns. Changes in mean air temperatures that might be induced by rising levels of CO2 and other greenhouse gases could also be accompanied by increased variability in daily temperatures such that acute increases in air temperature may be more likely than at present. Consequently, we investigated whether plants grown in a CO2 enriched atmosphere would be differently affected by a heat shock than plants grown at ambient CO2 levels. Plants of a C3 annual (Abutilon theophrasti), a C3 annual crop (Sinapis alba) and a C4 annual (Amaranthus retroflexus) were grown from seed in growth chambers under either 400 or 700cm3 m−3 CO2, and were fertilized with either a high or low nutrient regime. Young seedlings of S. alba, as well as plants of all species in either the vegetative or reproductive phase of growth were exposed to a 4‐h heat shock in which the temperature was raised an additional 14–23°C (depending on plant age). Total biomass and reproductive biomass were examined to determine the effect of CO2, nutrient and heat shock treatments on plant performance. Heat shock, CO2, and nutrient treatments, all had some significant effects on plant performance, but plants from both CO2 treatments responded similarly to heat shocks. We also found, as expected, that plants grown under high CO2 had dramatically decreased tissue N concentrations relative to plants grown under ambient conditions. We predicted that high‐CO2‐grown plants would be more susceptible to a heat shock than ambient‐CO2‐grown plants, because the reduced N concentrations of high‐CO2 grown plants could result in the reduced synthesis of heat shock proteins and reduced thermotolerance. Although we did not examine heat shock proteins, our results showed little relationship between plant nitrogen status and the ability of a plant to tolerate an acute increase in temperature.
Effect of growth temperature on biomass production of nearly isonuclear triazine‐resistant and ‐susceptible common groundsel (Senecio vulgaris L.)
Authors: McCLOSKEY W. B. , HOLT J. S.
Published: April 2006

Abstract. The effect of growth temperature on biomass production and photosynthesis of nearly‐isonuclear triazine‐resistant and ‐susceptible Senecio vulgaris L. bio‐types was investigated. Plants were grown in growth chambers with day/night temperatures of 13/8, 20/15 and 30/25°C, and were harvested 35, 42, 49 and 56d after planting (DAP). The S biotype produced more shoot dry weight than the R × SBC6 biotype, and the S × RBC6 biotype produced more shoot dry weight than the R biotype at all DAP and growth temperature combinations. The S and S × RBC6 biotypes had greater photosynthetic rates than the R X SBC6 and R biotypes, respectively. Thus, plants containing the susceptible chloroplast genome produced more biomass and had greater photosynthetic rates than those with the resistant chloroplast genome, when in association with the same nuclear genome. There was no differential temperature effect on biomass production of isonuclear plants possessing resistant or susceptible chloroplast genomes. However, there was a large differential temperature effect on the amount of biomass produced by plants containing different nuclear genomes (R or S) in association with the same chloroplast genome. The R nuclear genome appeared to be better adapted to cooler growth temperatures while the S nuclear genome was better adapted to warmer growth conditions.
Interactions of Cd with Zn, Cu, Mn and Fe for lettuce (Lactuca sativa L.) in hydroponic culture
Authors: YS C. TH , VANTHOMME P. , SCHREVENS E. , DE PROFT M.
Published: April 2006

Abstract. The effect and accumulation of cadmium (Cd) in lettuce grown by means of the hydroponic technique was investigated by multivariate analysis, and was found to be affected by the concentration of other trace elements. Particularly iron acted in a strongly antagonistic way against Cd. Consequently, no absolute toxicity limits for Cd can be drawn without considering other trace elements.
Measurement of chlorophyll fluorescence within leaves using a fibreoptic microprobe
Authors: BORNMAN J. F. , VOGELMANN T. C. , MARTIN G.
Published: April 2006

Abstract. The distribution of chlorophyll fluorescence was measured within leaves of Medicago saliva with a fibre optic microprobe. Leaves were irradiated with broad band blue light (1000 μmol m−2s−1) and chlorophyll fluorescence was measured at 688 nm. The amount of fluorescence measured within the leaf depended upon the direction in which the probe was inserted. When the probe was advanced directly through the leaf from the shaded towards the irradiated surface, the maximum amount of detected fluorescence occurred near the boundary between the palisade and spongy mesophyll. When the probe was advanced through the leaf from the opposite direction maximum detected fluorescence was at the boundary between the epidermis and palisade. These results appear to be a consequence of the blue light gradient, which declined exponentially within the palisade but was counterbalanced by increasing chlorophyll content within the leaf. Modelling indicates that the measured distribution of chlorophyll fluorescence can be explained by relatively uniform emission of fluorescence throughout the palisade layer, indicating that the chloroplasts may be photosynthetically specialized to their light environment within the leaf.
Modelling photosynthesis of cotton grown in elevated CO2
Authors: HARLEY P. C. , THOMAS R. B. , REYNOLDS J. F. , STRAIN B. R.
Published: April 2006

Cotton plants were grown in CO2‐controlled growth chambers in atmospheres of either 35 or 65 Pa CO2. A widely accepted model of C3 leaf photosynthesis was parameterized for leaves from both CO2 treatments using non‐linear least squares regression techniques, but in order to achieve reasonable fits, it was necessary to include a phosphate limitation resulting from inadequate triose phosphate utilization. Despite the accumulation of large amounts of starch (>50 g m−2) in the high CO2 plants, the photosynthetic characteristics of leaves in both treatments were similar, although the maximum rate of Rubisco activity (Vcmax), estimated from A versus Ci response curves measured at 29°C, was ∼10% lower in leaves from plants grown in high CO2. The relationship between key model parameters and total leaf N was linear, the only difference between CO2 treatments being a slight reduction in the slope of the line relating Vcmax to leaf N in plants grown at high CO2. Stomatal conductance of leaves of plants grown and measured at 65 Pa CO2 was approximately 32% lower than that of plants grown and measured at 35 Pa. Because photosynthetic capacity of leaves grown in high CO2 was only slightly less than that of leaves grown in 35 Pa CO2, net photosynthesis measured at the growth CO2, light and temperature conditions was approximately 25% greater in leaves of plants grown in high CO2, despite the reduction in leaf conductance. Greater assimilation rate was one factor allowing plants grown in high CO2 to incorporate 30% more biomass during the first 36 d of growth.
Physiological adaptation of waxapple to waterlogging
Authors: LIN C. H. , LIN C. H.
Published: April 2006

Waxapple (Syzygium samarangense Men. et. Perry) plants receiving up to 40d of continuous flooding treatment showed no symptoms of physiological disorder, but the treatment resulted in early flowering. In this report, several physiological parameters of flooded plants are compared with those of nonflooded plants. Both control plants and 9‐d‐flooding‐treated plants exhibited aerenchyma formation in the cortex tissue beginning 5 cm from the root tip. After 7d flooding treatment, the oxygen consumption rate of the root section was only 20% of that of the controls. Following flooding treatment, the roots showed an increase in alcohol dehydrogenase activity as well as an increase in three isozymes. However, malate dehydrogenase activity was decreased, and no significant change of NADP‐malic enzyme activity was observed. There were no significant differences in levels of ethylene, 1‐aminocyclopropane‐1‐carboxylic acid and 1‐(malonylamino) cyclopropane‐1‐carboxylic acid in petiole and roots of flooded and non‐flooded plants during the stage examined. It is inferred that the presence of aerenchyma in the root cortex allows a higher level of internal gas exchange, and thus, makes waxapple surprisingly flood tolerant. However, reduced root oxygen consumption rate may have limited root respiration rate and vegetative growth.
High annual productivity of certain agaves and cacti under cultivation
Authors: NOBEL P. S. , GARCÍA‐MOYA E. , QUERO E.
Published: April 2006

To help ascertain the maximal productivity of plants with Crassulacean acid metabolism, measurements were undertaken on four potentially highly productive CAM species at optimal leaf or stem area indices of 4 to 6. Shoot area and shoot biomass were based on regression equations for material harvested from adjacent plants at 3‐month intervals; in addition, the monitored platyopuntias were harvested to determine their dry weight at the end of the observation period. Agave mapisaga and A. salmiana near Mexico City had a productivity averaging 40Mg ha−1 year−1 and exhibited higher maximal rates of net CO2 uptake than previously reported for CAM plants (29–34 μmol m −2 s−1). When irrigated and fertilized daily, Opuntia amyclea and O. ficus‐indica in Saltillo, Coahuila, Mexico, had an average productivity of 46Mg ha−1 year−1. These are among the highest productivities ever reported for any plant species.
Water balance in the arborescent palm, Sabal palmetto. I. Stem structure, tissue water release properties and leaf epidermal conductance
Authors: HOLBROOK N. M. , SINCLAIR T. R.
Published: April 2006

The functional importance of water storage in the arborescent palm, Sabal palmetto, was investigated by observing aboveground water content, pressure‐volume curve parameters of leaf and stem tissue and leaf epidermal conductance rates. The ratio of the amount of water stored within the stem to the leaf area (kg m−2) increased linearly with plant height. Pressure‐volume curves for leaf and stem parenchyma differed markedly; leaves lost turgor at 0.90 relative water content and –3.81 MPa, while the turgor loss point for stem parenchyma occurred at 0–64 relative water content and −0.96 MPa. Specific capacitance (change in relative water content per change in tissue water potential) of stem parenchyma tissue was 84 times higher than that of leaves, while the bulk modulus of elasticity was 346 times lower. Leaf epidermal conductance rates were extremely low (0.32–0.56 mmol m−2 s−1) suggesting that S. palmetto are able to strongly restrict foliar water loss rates. Structurally, stems of S. palmetto appear to be well suited to act as a water storage reservoir, and coupled with the ability to restrict water loss from leaf surfaces, may play an important role in tree survival during periods of low water availability.
Water storage in the wood and xylem cavitation in 1‐year‐old twigs of Populus deltoides Bartr.
Authors: LO GULLO M. A. , SALLEO S.
Published: April 2006

The possible role of water expelled from cavitated xylem conduits in the rehydration of water‐stressed leaves has been studied in one‐year‐old twigs of populus deltoides Bartr. Twigs were dehydrated in air. At desired values of leaf water potential (Ψl) (between near full turgor and ‐1.62 MPa), twigs were placed in black plastic bags for 1–2h. Leaf water content was measured every 3–5 min before bagging and every 10 min in the dark. Hydraulic conductivity and xylem cavitation were measured both in the open and in the dark. Cavitation was monitored as ultrasound acoustic emissions (AE). A critical Ψl value of ‐0.96 MPa was found, at which AE increased significantly while the leaf water deficit decreased by gain of water. Since the twigs were no longer attached to roots, it was concluded that water expelled from cavitated xylem conduits was transported to the leaves, thus contributing to their rehydration. Xylem cavitation is discussed in terms of a ‘leaf water deficit buffer mechanism’, under not very severe water stress conditions.
Differentiation of freezing tolerance and vernalization responses in Cruciferae exposed to a low temperature
Authors: LAROCHE A. , GENG X.‐M. , SINGH J.
Published: April 2006

High levels of freezing tolerance were induced in leaves of different Cruciferae species including Brassica napus, Arabidopsis thaliana, Barbarea vulgaris, Thlaspi arvenses and Descurainia sophia by low‐temperature acclimation. Concomitantly, the amount of total RNA doubled in these three species. Analyses of methylation patterns and dosage of rRNA genes were carried out to determine whether or not alterations occur in this DNA during development of freezing tolerance. Hybridizations of Southern transfers with an rDNA probe revealed two additional EcoRI sites in purified DNA isolated from freezing‐tolerant leaves of winter B. napus cv Jet Neuf and D. sophia (both of which require low temperatures for vernalization), but not in isolates of A. thaliana or spring B. napus cv Topas. An increase of rDNA cistrons was also observed in both B. napus cv Jet Neuf and D. sophia but not in A. thaliana or B. napus cv Topas upon cold acclimation. These results suggest that low temperature induced amplification of rDNA and the differential methylation of EcoRI sites may possibly be related to the vernalization process but may not be related to the development of freezing tolerance. However, the higher activity of RNA polymerase (2.5 times more) observed upon cold acclimation may explain the concomitant increase in total RNA and may be related to the development of freezing tolerance in the Cruciferae.