bluuebunny/crossref_metadata_2025 huggingface dataset:
A controlled‐environment chamber for measurement of canopy photosynthesis by small stands of lettuce (Lactuca sativa L.)
Authors: CAPORN S. J. M. , WOOD W. A.
Published: April 2006

Abstract. A controlled‐environment chamber constructed from a standard chest freezer was used to grow and measure the CO2 exchange of small stands of lettuce (Lactuca sativa L. ev. Ambassador). The chamber, with horizontal air flow, provided good control of air temperature (c. 6 to 16°C), irradiance (0–300 μmol PAR m 2S1 and CO2 (350–1000 μmol mol−1). The photosynthetic response to changes in these variables was measured using an inexpensive CO2 dosing system which recorded the input rate required to maintain a constant concentration of CO2 (to ± 2.5%). Characteristis of the growth environment and the changes in response to temperature and irradiance are described.
Perception of gravity expressed by vascular differentiation
Authors: GERSANI M. , SACHS T.
Published: April 2006

Abstract. The differentiation of new vessels was induced by local applications of auxin to isolated pieces of turnip storage roots. This differentiation was compared in varied relative orientations of the location of auxin application, the shoot‐root polarity and the direction of gravity. Vessel differentiation was restricted to the cambial region and its course was determined primarily by the location of auxin application and the original, determined polarity of the tissues. Within this framework, the course of vessel differentiation was significantly modified by gravity: individual vessels tended to curve downwards and to be concentrated on the lower half of the tissue. The results can be understood as an observable expression of an influence of gravity on auxin transport.
Vascular transport and soybean nodule function. III: Implications of a continual phloem supply of carbon and water
Authors: WALSH K. B.
Published: April 2006

Abstract.In soybean, stores of carbon within the leaf have been demonstrated to support nodule metabolism under both photosynthetic and non‐photosynthetic conditions. Indeed, a net depletion of nodule starch is observed only under conditions of suboptimal rates of nodule metabolism. Therefore, maximal rates of nodule metabolism are associated with a continual supply of phloem sap to the nodule, delivering water, carbon and other solutes. A restriction of phloem supply to the nodule may result in changes in turgor between the apoplast of the export pathway and the symplast of the nodule. This change may cause the observed decrease in the permeability to gases and to the rate of product export from nodules deprived of a phloem supply. It is suggested that nodule metabolism is homeostatically regulated in terms of internal O2levels by the delivery of phloem water and solutes.
An examination of the advantages of C3‐C4 intermediate photosynthesis in warm environments
Authors: SCHUSTER W. S. , MONSON R. K.
Published: April 2006

Abstract. The photosynthetic responses to temperature in C3, C3‐C4 intermediate, and C4 species in the genus Flaveria were examined in an effort to identify whether the reduced photorespiration rates characteristic of C3‐C4 intermediate photosynthesis result in adaptive advantages at warm leaf temperatures. Reduced photorespiration rates were reflected in lower CO2 compensation points at all temperatures examined in the C3‐C4 intermediate, Flaveria floridana, compared to the C3 species, F. cronquistii. The C3‐C4 intermediate, F. floridana, exhibited a C3‐like photosynthetic temperature dependence, except for relatively higher photosynthesis rates at warm leaf temperatures compared to the C3 species, F. cronquistii. Using models of C3 and C3‐C4 intermediate photosynthesis, it was predicted that by recycling photorespired CO2 in bundle‐sheath cells, as occurs in many C3‐C4 intermediates, photosynthesis rates at 35°C could be increased by 28%, compared to a C3 plant. Without recycling photorespired CO2, it was calculated that in order to improve photosynthesis rates at 35°C by this amount in C3 plants, (1) intercellular CO2 partial pressures would have to be increased from 25 to 31 Pa, resulting in a 57% decrease in water‐use efficiency, or (2) the activity of RuBP carboxylase would have to be increased by 32%, resulting in a 22% decrease in nitrogen‐use efficiency. In addition to the recycling of photorespired CO2, leaves of F. floridana appear to effectively concentrate CO2 at the active site of RuBP carboxylase, increasing the apparent carboxylation efficiency per unit of in vitro RuBP carboxylase activity. The CO2‐concentrating activity also appears to reduce the temperature sensitivity of the carboxylation efficiency in F. floridana compared to F. cronquistii. The carboxylation efficiency per unit of RuBP carboxylase activity decreased by only 38% in F. floridana, compared to 50% in F. cronquistii, as leaf temperature was raised from 25 to 35°C. The C3‐C4 intermediate, F. ramosissima, exhibited a photosynthetic temperature temperature response curve that was more similar to the C4 species, F. trinervia, than the C3 species, F. cronquistii. The C4‐like pattern is probably related to the advanced nature of C4‐like biochemical traits in F. ramosissima The results demonstrate that reductions in photorespiration rates in C3‐C4 intermediate plants create photosynthetic advantages at warm leaf temperatures that in C3 plants could only be achieved through substantial costs to water‐use efficiency and/or nitrogen‐use efficiency.
Poly(γ‐glutamylcysteinyl)glycines or phytochelatins and their role in cadmium tolerance of Silene vulgaris
Authors: VERKLEIJ J. A. C. , KOEVOETS P. , VAN‘T RIET J. , BANK R. , NIJDAM Y. , ERNST W. H. O.
Published: April 2006

Abstract. The effect of cadmium on growth of Cd‐tolerant and ‐sensitive plants of Silene vulgaris and on the production of metal‐binding compounds in both types of plants was studied. The Cd‐content of the roots and the Cd‐root/shoot ratio was higher in Cd‐tolerant plants. A Cd‐binding compound (Cd‐BC) with an apparent molecular mass of 14.5 kD was isolated from the roots of Cd‐tolerant and ‐sensitive plants, grown in 40 mmol m−3 Cd for 21 d. More than 60% of the total Cd in the roots was associated with this compound. Determination of the amino‐acid content of the purified Cd‐containing compound from both types of plants showed that they possessed a similar amino‐acid composition to that of phytochelatins. Only the bis‐ and tris‐forms were present. The amount of Cd and sulphide associated with phytochelatin was greater in tolerant plants than in sensitive ones suggesting that an increased sulphide content of complexes containing peptide, sulphide and Cd may form the basis of evolved Cd‐tolerance in Silence vulgaris.
Investigation of the limitations to photosynthesis induced by leaf water deficit in field‐grown sunflower (Helianthus annuus L.)
Authors: WISE R. R. , FREDERICK J. R. , ALM D. M. , KRAMER D. M. , HESKETH J. D. , CROFTS A. R. , ORT D. R.
Published: April 2006

Abstract. The diurnal cycling of leaf water potential (Ψleaf) in field‐grown sunflower (Helianthus annuus) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψleaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO2 concentrations. These and other observations suggest that the daily decline in photosynthesis represents a ‘down regulation’ of the biochemical demand for CO2 that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non‐stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψleaf) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well‐controlled adaptive responses by field‐grown sunflower plants to limited water availability.
Effects of water stress on oxygen, hydrogen and carbon isotope ratios in two species of cotton plants
Authors: YAKIR D. , DeNIRO M. J. , EPHRATH J. E.
Published: April 2006

Abstract. Two cotton species (Gossypium hirsutum L. cv. SJ‐2 and Gossypium barbadence cv. S‐5) were grown under irrigated (wet) and non‐irrigated (dry) conditions in the same field. Leaf water was enriched in 18O and deuterium in the dry treatment relative to the wet treatment for both species. Only in plants of S‐5 was a similar enrichment observed in leaf cellulose. In both species, the isotopic composition of leaf cellulose must reflect the isotopic composition of the actual water pool involved in cellulose synthesis. Therefore, our observations indicate that one species (SJ‐2) can maintain a relative isolation of this water pool from direct evapotranspirational effects. Such plant species will more faithfully record, in the isotopic composition of organic matter, the isotopic composition of ground water. In contrast, the isotopic composition of organic matter in plants such as S‐5 could be used as an integrated signal reflecting humidity conditions during growth. Water use efficiency, based on seed‐cotton yield and total water applied, correlated linearly with differences in carbon isotopic ratios between species in both the wet and dry treatments and between treatments in each species.
Ethylene‐promoted ascorbate peroxidase activity protects plants against hydrogen peroxide, ozone and paraquat
Authors: MEHLHORN H.
Published: April 2006

Abstract. In experiments where mung beans (Vigna radiata L.) and peas (Pisum sativum L.) have been pre‐exposed to ethylene and afterwards treated with ozone, it has been shown that such ethylenepretreated plants may become more resistant to ozone. Further experiments with hydrogen peroxide (H2O2) and the herbicide paraquat suggest that this increased resistance against ozone depends on the stimulation of ascorbate peroxidase activity which provides cells with increased resistance against the formation of H2O2 which is also formed when plants are fumigated with ozone. These results explain why increased production of ethylene can be observed in plants exposed with ozone or other oxidative stress and clearly demonstrate that in plants, as well as animals, peroxidases protect cells against harmful concentrations of hydroperoxides.
Differential responses of alpine and non‐alpine Aquilegia species to increased ultraviolet‐B radiation
Authors: LARSON R. A. , GARRISON W. J. , CARLSON R. W.
Published: April 2006

Abstract. Two species of columbines, Aquilegia caerulea (which lives in alpine environments) and A. canadensis (a lower‐elevation species) responded to artifically increased levels of solar UV‐B radiation by becoming significantly shorter and developing a significantly greater number of leaves. The degree of shortening was greater in A. canadensis, the non‐alpine species, while the number of leaves increased faster in A. caerulea. Significant differences in gashandling and water‐use physiological responses were noted, with UV‐B treatment leading to decreased water‐use efficiency in both species. Concentrations of flavonoids increased significantly in both species following light exposure, whereas alkaloids in A. caerulea appeared to be destroyed by UV‐B. No significant changes occurred in β‐carotene concentrations in either species.
Implications of non‐uniform stomatal closure on gas exchange calculations
Authors: VAN KRAALINGEN D. W. G.
Published: April 2006

Abstract. This paper discusses the consequences of non‐uniform (= patchwise) stomatal closure on the estimation of gas exchange parameters. The estimation of the partial pressure of internal CO2 (ci) appears to be little sensitive to complete non‐uniform stomatal closure. During the process of closure of these patches, however, a lower ci will be calculated. For gas exchange measurements done at low wind speeds, it can be shown that an error is made in the partitioning of the total vapour transfer resistance into boundary layer and stomatal resistance. This error influences the calculated total transfer resistance of gases other than water vapour (e.g. CO2). The apparent negative internal gas concentrations that have sometimes been found in fumigation experiments with SO2 can possibly be explained by this error.
Growth and carbon allocation in Pennisetum typhoides infected with the parasitic angiosperm Striga hermonthica
Authors: GRAVES J. D. , WYLDE A. , PRESS M. C. , STEWART G. R.
Published: April 2006

Abstract Growth and gas exchange measurements are used in conjunction with a carbon balance model to describe the millet (Pennisetum typhoides)–witchweed (Striga hermonthica) host—parasite association. Striga hermonthica reduces the growth of millet by 28% and radically alters the architecture of infected plants. Whilst grain yield and stem dry weight are reduced (by 80 and 53%, respectively), leaf and root growth are stimulated (by 41 and 86%, respectively). The difference in production between infected and uninfected millet plants can be accounted for by two processes: first, export of carbon to the parasite (accounting for 16% of the dry weight not gained); and second, parasite‐induced reductions in host photosynthesis (accounting for 84% of the dry weight not gained). Striga hermonthica is dependent on carbon exported from the host, since the plant has low rates of photosynthesis coupled with high rates of respiration. The carbon balance model suggests that in mature S. hermonthica plants parasitic on millet, 85% of the carbon is host‐derived. Carbon fluxes are also estimated using δ13C measurements, since S. hermonthica is a C3 plant parasitizing a C4 host. In conjunction with gas exchange measurements, these suggest that in root, stem and leaf of S. hermonthica, 87, 70 and 49% of carbon is hostderived, respectively.
The coleoptile sheath of wheat impedes oxygen transport to seminal roots
Authors: THOMSON C. J. , ARMSTRONG W.
Published: April 2006

Abstract Wheat, Triticum aestivum cv. Gamenya, seedlings were grown for 4d in acrated 0.5 mol m−3 CaSO4 solution. A cylindrical platinum‐electrode and vernier microscope were used to examine the effects of the colcoptile sheath on O2 transport from shoots to seminal roots via the internal gas‐space system, and on the clongation of the root tip. By removing the colcoptile sheath, O2 concentrations at the root tip in an O2‐free medium at 5°C increased from 0.017 to 0.17 mol m−3 O2 when 100 kPa O2 was around the shoots. When the shoots were in air, the separation of the colcoptile sheath from the primary leaf caused the rate of root clongation in the anoxic medium to increase by two fold.
The refilling of embolized xylem in Pinus sylvestris L.
Authors: BORGHETTI M. , EDWARDS W. R. N. , GRACE J. , JARVIS P. G. , RASCHI A.
Published: April 2006

Abstract. The hypothesis that ray parenchyma cells are actively involved in the refilling of embolized xylem of Pinus sylvestris L. was tested by killing the ray parenchyma and comparing rehydration of killed stems with that of control material. Killing of ray parenchyma was achieved using hot water or sodium azide. In most experiments, the available water for refilling was at negative water potential. Experiments were done on three kinds of plant material: small branch segments, potted seedlings and small potted trees. In all experiments, there was no indication that the azide‐killed xylem was slower to refill than the control material and it was concluded that the parenchyma has no role in the refilling process, which therefore must be purely physical or physicochemical. Stems treated with hot water did not refill; we suggest that this may be caused by high temperatures decreasing the water permeability of the tracheid wall. The refilling of small branch segments may be explained by surface tension forces (capillary action), which inside the tracheid lumen may lower the water potential down to ‐9.7kPa; this may be enough to draw in water from the available water that in experiment one was at ‐2kPa. In the case of seedlings or saplings, capillary action cannot explain refilling, because the xylem water potentials were always lower than those estimated from tracheid radii. Condensation of water during diurnal cycles of warming and cooling is also unlikely to contribute to refilling significantly. To account for refilling in these cases, it is supposed that the tracheid wall may be chemically active and able to lower the water potential below the value expected by capillarity.
The acquisition and accumulation of inorganic carbon by the unicellular green alga Chlorella ellipsoidea
Authors: ROTATORE C , COLMAN B.
Published: April 2006

Abstract. The uptake and accumulation of inorganic carbon has been investigated in Chlorella ellipsoidea cells grown at acid or alkaline pH. Carbonic anhydrase (CA) was detected in ceil extracts but not in intact cells and CA activity in acid‐grown cells was considerably less than that in alkali‐grown cells. Both cell types demonstrates low K1/2 (CO2) values in the range pH 7.0–8.0 and these were unaffected by O2 concentration. The CO2 compensation concentrations of acid‐ and alkali‐grown cells suspended in aqueous media were not significantly different in the range of pH 6.0–8.0, but at pH 5.0, the CO2 compensation concentrations of acid‐grown cells (57.4cm3 m−3) were lower than those of alkali‐grown cells (79.2cm3 m−3). The rate of photo‐synthetic O2 evolution in the range pH 7.5–8.0 exceeded the calculated rate of CO2 supply two‐ to three‐fold, in both acid‐ and alkali‐grown cells, indicating that HCO3− was taken up by the cells. Accumulation of inorganic carbon was measured at pH 7.5 by silicone‐oil centri‐fugation, and the concentration of unfixed inorganic carbon was found to be 5.1 mol m−3 in acid‐grown and 6.4mol m−3 in alkali‐grown cells. These concentrations were 4.6‐ and 5.9‐fold greater than in the external medium. These results indicate that photorespiration is suppressed in both acid‐ and alkali‐grown cells by an intracellular accumulation of inorganic carbon due, in part, to an active uptake of bicarbonate.
The perturbation of the endomembrane network of the chlamydomonad alga Gloeomonas by the herbicide isopropyl N‐phenyl carbamate (IPC)
Authors: DOMOZYCH D. S.
Published: April 2006

Abstract. The highly complex and symmetric endomembrane network of the chlamydomonad alga, Gloeomonas kupferri, can be disrupted by the herbicide, isopropyl N‐phenyl carbamate (IPC). Upon incubation with IPC for between 30 min and 1 h, curling of the dictyosomes, proliferation of small vesicles from the trans face and swelling of the peripheral vacuolar complex takes place. Longer treatments result in degeneration of dictyosome cisternae into vesicular masses and the formation of supervacuolar complexes. Enzyme cytochemistry revealed that endomembrane ‘marker’ enzymes are altered/inhibited by IPC. A second but striking I PC‐induced effect is the production of branched, fibrillar inclusions in the cell nucleus. A discussion of I PC‐induced affects on ion regulation and microtubule/MTOC distribution in the cell is presented.
Zinc‐induced vacuolation in root meristematic cells of Festuca rubra L.
Authors: DAVIES K. L. , DAVIES M. S. , FRANCIS D.
Published: April 2006

Abstract. The effect of Zn on vacuole development in root meristematic cells was examined in three cultivars of Festuca rubra: a Zn‐tolerant cultivar (Merlin), a salt‐tolerant cultivar (Hawk) and a non‐tolerant cultivar (S.59) in order to determine whether or not vacuole development was related to Zn tolerance. Treatment with Zn greatly increased the percentage of cells in the apical meristem which were vacuolated in all three cultivars (7.01‐fold increase in Merlin, 3.61‐fold increase in Hawk and 5.39‐fold increase in S.59 over the range 0–0.5 μg Zn cm−3). Morphometric analyses on electromicrographs indicated that the percentage total vacuolar volume fraction of meristematic tissue was also increased by Zn treatment. Most of this increase was due to an increase in a particular component of the vacuole which was 0.2–0.5 μm in diameter, spherical or ovoid in outline and possessed a distinct amorphous electron dense matrix (Type A intravacuolar body). X‐ray microanalysis revealed that this matrix was rich in calcium and phosphorus in control plants. In Zn‐treated roots, elevated levels of Zn were found in the matrix in Merlin and Hawk, but not in S.59. In addition, intravacuolar membranous whorls or myelin bodies were more highly organized in Zn‐treated Merlin and Hawk but not S.59. Elevated Zn levels were not found in any other vacuolar component nor in nuclei, nucleoli, cell walls or ground cytoplasm. Control roots of Merlin possessed a greater type A vacuolar volume fraction than either Hawk or S.59 which may confer a greater capacity to compartmentalize Zn at the onset of exposure to toxic metals than the other cultivars. Predictably, the EM procedures resulted in loss of Zn from the roots to the fixative and dehydrating solutions. However, the rate of loss was the same (approximately 75–80%) regardless of cultivar. These findings are discussed in relation to their possible role in the mechanisms of Zn tolerance in these cultivars.
Effect of changes in nitrogen nutrition on the polyamine content of Alnus glutinosa
Authors: TONIN G. S. , WHEELER C. T. , CROZIER A.
Published: April 2006

Abstract. The principal polyamines in Alnus glutinosa roots, nodules and root pressure sap, putrescine, spermidine and spermine, were quantified by reversed‐phase, high‐performance liquid chromatography with fluorescence detection following precolumn derivatization with 9‐fluorenylmethyl chloroformate and 1‐ada‐mantanamine. Putrescine was the major component of all tissues and sap. It comprised 70% or more of the polyamine pool except in roots of KNO3‐fed plants, in which similar amounts of putrescine and spermidine were present at levels five‐fold lower than plants fed (NH4)2SO4. Polyamine levels in nodules were 50% greater than in roots. The polyamine content of roots and nodules was not altered significantly when the nitrogen nutrition was changed from sole reliance on nitrogen fixation to partial or complete utilization of (NH4)2SO4. However, the polyamine content of root pressure sap from nodulated plants increased almost four‐fold when they were fed with increasing concentrations of NH4NO3, although the total polyamine content remained low (5mmol m−3 sap). The polyamine content of the Alnus root system changed with plant age. In particular, the spermidine content of both roots and nodules was higher in 10‐ as compared to 16‐week‐old plants.
Surface potentials and hydraulic signals in wheat leaves following localized wounding by heat
Authors: MALONE M. , STANKOVIĆ B.
Published: April 2006

Abstract. Localized burning of a leaf causes a rapid change in apoplastic electrical potential throughout the shoot of wheat seedlings (‘variation potential’). It also causes marked increases in turgor pressure in epidermal cells of adjoining leaves. These turgor increases indicate rapid propagation throughout the seedling, of a hydraulic pressure wave from the site of wounding. Evidence is presented that this pressure wave is caused by relief of xylem tension, by water released from damaged cells in the wounded region. It is demonstrated that, in the absence of wounding, pressure waves imposed at the tip of one leaf can travel to neighbouring leaves, and can there induce change in apoplastic electrical potential similar to a ‘variation potential’. This indicates that the hydraulic event produced by wounding is the signal responsible for systemic induction of the ‘variation potential’. This signal has been termed ‘Ricca's factor’. It is suggested that arrival of the hydraulic wave alters leaf water potential and thereby induces stomatal activity. Leaf surface potential may be dominated by electrogenic ion pumping or flux at stomatal cells, and the ‘variation potential’ may therefore be a reflection of stomatal activity induced by the hydraulic signal.
Changes in water relations and endogenous abscisic acid content of wheat and barley grains and embryos during development
Authors: MORRIS P. C. , JEWER P. C. , BOWLES D. J.
Published: April 2006

Abstract. Immature cereal embryo development can be controlled by in vitro culture on media containing ABA, or by media of low osmotic potential. To assess the possible in vivo roles of these factors, endogenous ABA levels and water relations of embryos and grains of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) were determined during development. ABA concentrations remained consistent with those required to inhibit precocious germination in vitro of early stage embryos but not of more mature embryos. With increasing maturity, a difference in water potential developed between grain and embryo, suggestive of an in vivo role for water status in controlling the development of the embryo.
Induction of exocytosis in characean internodal cells by locally restricted application of chlortetracycline and the effect of cytochalasin B, depolarizing and hyperpolarizing agents*
Authors: FOISSNER I.
Published: April 2006

Abstract. Local exocytosis with concomitant deposition of cell wall material (plugs) was induced in mature characean internodal cells by application of Sephadex beads loaded with a chlortetracycline (CTC)/CaCl2 solution. Plugs can be formed anywhere on the cells independently of structural and/or functional plasma membrane domains, provided that the pH of the CTC/CaCl2 solution is above 5.5. Plug formation is inhibited by cytochalasin B and membrane depolarizing agents. Treatment with fusicoccin enhances exocytosis. The results suggest that actin filaments are involved in the transport of vesicles and endoplasmic reticulum cisternae towards the cell membrane, and that the membrane potential determines the extent of CTC mediated Ca2+ influx.
Comparison of the effect of rapidly and gradually developing water‐stress on carbohydrate metabolism in spinach leaves
Authors: ZRENNER R. , STITT M.
Published: April 2006

Abstract. The effect of water‐stress on photosynthetic carbon metabolism in spinach (Spinacia oleracea L.) has been studied in experiments in which water‐stress was induced rapidly by floating leaf discs on sorbitol solutions or wilting detached leaves, and in experiments in which water‐stress was allowed to develop gradually in whole plants as the soil dried out. In both short‐ and long‐term water stress, the rate of photosynthesis in saturating CO2 did not decrease until leaf water potential decreased below ‐1.0 MPa. However, at smaller water deficits there was already an inhibition of starch synthesis, while sucrose synthesis remained constant or increased. This change in partitioning was accompanied by an increase in activation of sucrose‐phosphate synthase (revealed as an increase in activity assayed in the presence of low hexose‐phosphate and inorganic phosphate, while the activity assayed with saturating hexosephosphates remained unaltered). Water‐stressed leaves had a two‐ to three‐fold higher sucrose content at the end of the night, and contained less starch than non‐stressed leaves. When leaves were held in the dark, sucrose was mobilized initially, while starch was not mobilized until the sucrose had decreased to a low level; in water‐stressed leaves, starch mobilization commenced at a two‐fold higher sucrose content. It is concluded that water‐stressed leaves maintain higher sucrose and lower starch levels than non‐stressed leaves. This response is found in rapid and long‐term stress, and represents an inherent response to water deficits.
Do leaves contribute to the abscisic acid present in the xylem sap of ‘draughted’ sunflower plants?
Authors: NEALES T. F. , McLEOD A. L.
Published: April 2006

Abstract. The root systems of 30‐d‐old sunflower plants were treated with polyethylene glycol (PEG; osmotic potential ‐ 1.0MPa) for 2h, causing mild and transient wilting. Ten minutes before this treatment was applied, half the plants were defoliated. At varying times after the imposition of the PEG ‘drought stimulus’, the plant stems were cut and the sap exudate was collected and analysed for abscisic acid (ABA), using an elisa method. When stems were cut 2.25h after the treatments were applied, the ABA concentration in the sap of the controls did not vary with time: the mean concentration was 10.7 ± 1.0μ, mol m−3. However, in the treated plants, the first sample contained 78.1 ± 10.1 μmol m−3, decreasing to 13.6 ± 2.8 μmol m−3 over 8.75h. Defoliation did not affect the ABA concentration in the sap. When stems were cut at varying times (up to 25h) after treatment, the PEG treatment again caused an immediate increase in the ABA concentration in the sap, from 20 ± 1 to 136 ± 21 μmol m−3. However, defoliation reduced this increase, but only in plants sampled 4–25h after treatment. We conclude that, after the PEG treatment to the roots, the initial increase of the ABA content of sap, and its attenuation with time, may be ascribed to synthesis in the roots whereas, thereafter, ABA derived from the leaves makes a major contribution to the ABA found in the xylem sap.
An experimental test of the eddy correlation technique over a Mediterranean macchia canopy
Authors: VALENTINI R. , SCARASCIA MUGNOZZA G. E. , DE ANGELLS P. , BIMBI R.
Published: April 2006

Abstract. Flux densities of water vapour and carbon dioxide were measured for a Mediterranean macchia canopy. Results show good agreement between the measured available energy and the sum of latent sensible and heat flux densities determined with the eddy correlation technique. Joint evaluation of the Bowen ratio, aerodynamic resistance, canopy resistance and the ‘omega factor’ suggests that the macchia canopy is intermediate in aerodynamic roughness between coniferous and deciduous canopies. Maximum daytime carbon flux densities ranged from ‐14 to ‐22(μnol m−2 s−1 on a ground area basis. The ratio of transpiration to assimilation (E/A) was a function of incident photo‐synthetic photon flux density below about 400 μmol m−2s−1 and above it was fairly constant at 272 mol mol−1 (H2O/CO2). The relationship between carbon influx and canopy conductance was linear. Results show promising applications of the eddy correlation technique for evaluating physiological features of canopies, treated as unitary functional systems.
Increased photosynthetic capacity of Scirpus olneyi after 4 years of exposure to elevated CO2
Authors: ARP W. J. , DRAKE B. G.
Published: April 2006

Abstract. While a short‐term exposure to elevated atmospheric CO2 induces a large increase in photosynthesis in many plants, long‐term growth in elevated CO2 often results in a smaller increase due to reduced photosynthetic capacity. In this study, it was shown that, for a wild C3 species growing in its natural environment and exposed to elevated CO2 for four growing seasons, the photosynthetic capacity has actually increased by 31%. An increase in photosynthetic capacity has been observed in other species growing in the field, which suggests that photosynthesis of certain field grown plants will continue to respond to elevated levels of atmospheric CO2
Studies ofElodea nuttalliigrown under photorespiratory conditions. I. Photosynthetic characteristics
Authors: JAHNKE L. S. , EIGHMY T. T. , FAGERBERG W. R.
Published: April 2006

Abstract.The photosynthetic characteristics ofElodea nuttalliigrown in wastewater in continuous flow reactors in a greenhouse were investigated. The diurnal changes in dissolved inorganic carbon (DIC), dissolved oxygen (DO) and pH were monitored. Photosynthesis removed both CO2(aq) and HCO3−from the reactors. A stoichiometry of 1.19:1 was observed between HCO3−removal during photosynthesis and OH−production during photosynthesis, consistent with theories regarding direct bicarbonate utilization. In laboratory experiments, the light compensation points (гPPFD) were similar (31–35μmol m−2s−1) to reported values for other macrophytes; however, the light saturation level was high (1100μmol m−2s−1) and similar to values reported for aerial portions Of heterophyllous macrophytes. The kinetics of photosynthetic oxygen evolution (Km(CO2) = 96mmol m−3; Vmax= 133mmol g−1Chl h−1) and the CO2compensation point (г= 44cm3m−3) suggested an adaptive, low photorespiratory state in response to low carbon concentrations. Photosynthetic Vmaxvalues were slightly, but significantly higher (P0.001) at pH 8.0 compared to pH 4.5. While CO2utilization at pH 8 could account for most of the observed phototsynthetic rates, an HCO3−component was present, suggesting two separate transport systems for HCO3−and CO2(aq) inE. nuttallii.The activity of RUBISCO (160.3 mmol g−1Chl h−1was one of the highest reported values for aquatic macrophytes. Compared to RUBISCO, we observed lower activities of the β‐carboxylating enzymes phophoenolpyruvate carboyxlase (PEPcase), 24.1 mmol g−1Chl h−1; phosphorenolpyruvate carboxykinase (PEPCKase), 14 mmol g−1Chl h−1. This suggests that the potential light‐independent fixation of carbon inE. nuttalliiwas much less than RUBISCO‐dependent fixation. The RUBISCO/PEPcase ratio was 6.6, indicating thatE. nuttalliiwas similar toMyriophyllumsp. in possessing a physiological adaptation to low CO2levels which is hypothesized to include carbonic anhydrase (CA) and an active transport system for HCO3−. CA levels were surprisingly low inE. nuttallii(14.2 EUmg Chl−).
Studies of Elodea nuttallii grown under photorespiratory conditions. II. Evidence for bicarbonate active transport
Authors: EIGHMY T. T. , JAHNKE L. S. , FAGERBERG W. R.
Published: April 2006

Abstract. Elodea nuttallii was grown under greenhouse conditions in domestic wastewater in an aquatic treatment system under conditions conducive to photorespiration. Initial research on the photosynthetic characteristics of E. nuttallii suggest that the submergent macrophyte possessed a carbon concentrating mechanism. Isotopic disequilibria H14CO3‐uptake studies (5‐80s) were used to assess the bicarbonate active‐transport capabilities in E. nuttallii leaves. Using a range of substrate concentrations (50‐50200mmol m−3), the accumulation of label (mmol g−1 Chl) over time due to transport was found initially to exceed accumulation due to fixation until steady state rates were observed. Internal steady state pools of dissolved inorganic carbon (DIC) ranged from 40 to 80 mol m−3. The concentration factor (CF: the ratio of internal cyroplasmic (DIC] to external medium [DIC]) decreased from 800 to 114 as external bicarbonate concentrations were increased. Inhibition of transport by uncouplers (2,4‐dinitrophenol (DNP), carbonyl cyanide‐m‐chlorophenylhydrazone (CCCP)); ATPase inhibitors (dicylcohexocarbodiamide (DCCD), phloridzin, arsenate); electron transport inhibitors (DCMU, Antimycin A), and carbonic anhydrase inhibitors (ethoxyzolamide, acetazolamide) suggest that bicarbonate transport required (1) a proton motive force, (2) a functional ATPase, (3) a chloroplast carbon sink, and possibly (4) a CA‐like moiety associated with the transport protein. While plasmalemmasomes were not observed, the plasmalemma was vesiculated and acid and alkaline banding was observed when leaves were incubated under light in the presence of bicarbonate. These data are consistent with the operation of a bicarbonate‐cation symport which concentrates substrate against a concentration gradient at the expense of metabolic energy. The presence of an active transport system for bicarbonate ensures that internal carbon concentrations are high when carbon dioxide, is scarce and bicarbonate is the only carbon species available in aquatic treatment systems during photorespiratory conditions. Therefore, E. nuttallii is particularly well suited for use in these systems.
Abrasive damage by wind to the needle surfaces of Picea sitchensis (Bong.) Carr. and Pinus sylvestris L.
Authors: van GARDINGEN P. R. , GRACE J. , JEFFREE C. E.
Published: April 2006

Abstract. After a period of one week at 11m s−1 in a wind tunnel, the leaf surface of Picea sitchensis and Pinus sylvestris had undergone structural modification. Low‐temperature scanning electron microscopy was used to examine these changes. Picea showed flattening and smearing of wax crystals, as well as cracks in some of the wax structures filling the stomatal antechambers. In Pinus, most damage was on the cells surrounding the stomatal antechamber or on needle ridges. Artificially abraded surfaces were of similar appearance. Minimum epidermal conductance to water vapour (geMIN) was determined gravimetrically. In PiceagcMIN was more than doubled by wind treatment and increased eightfold by rubbing. Similar but less extreme increases occurred in Pinus. Neither species showed recovery of geMIN after 1 week at low windspeed.
Level of endogenous indole‐3‐acetic acid in the stem of Pinus sylvestris in relation to the seasonal variation of cambial activity
Authors: SUNDBERG B. , LITTLE C. H. A. , CUI K. , SANDBERG G.
Published: April 2006

Abstract. Gas chromatography – selected ion monitoring – mass spectrometry was used to measure the level of indole‐3‐acetic acid (IAA) in the cambial region at the top and bottom of the branchless portion of the main stem of three large Scots pine trees, at weekly intervals from 28 April to 13 July. During this period, the cambium reactivated from the dormant state and entered its ‘grand’ period of xylem and phloem production, which was monitored by microscopy. The total amount of IAA (ng cm−2) increased steadily from 28 April until late June, and thereafter remained constant. In contrast, the concentration of IAA (ng g−1 fresh weight) was high at the start of cambial reactivation, declined when the number of differentiating tracheids began to increase, and then rose as the number of cells decreased. The timing and magnitude of the changes in xylem and phloem production and in IAA level were similar at the two sampling positions. It is concluded that the seasonal changes in cambial activity in the conifer stem cannot be ascribed simply to a fluctuation in the level of endogenous IAA in the cambial region.
Respiration in a future, higher‐CO2 world
Authors: AMTHOR J. S.
Published: April 2006

Abstract. Apart from its impact on global warming, the annually increasing atmospheric [CO2] is of interest to plant scientists primarily because of its direct influence on photosynthesis and photorespiration in C3 species. But in addition, ‘dark’ respiration, another major component of the carbon budget of higher plants, may be affected by a change in [CO2] independent of an increase in temperature. Literature pertaining to an impact of [CO2] on respiration rate is reviewed. With an increase in [CO2], respiration rate is increased in some cases, but decreased in others. The effects of [CO2] on respiration rate may be direct or indirect. Mechanisms responsible for various observations are proposed. These proposed mechanisms relate to changes in: (1) levels of nonstructural carbohydrates, (2) growth rate and structural phytomass accumulation, (3) composition of phytomass, (4) direct chemical interactions between CO2 and respiratory enzymes, (5) direct chemical interactions between CO2 and other cellular components, (6) dark CO2 fixation rate, and (7) ethylene biosynthesis rate. Because a range‐of (possibly interactive) effects exist, and present knowledge is limited, the impact of future [CO2] on respiration rate cannot be predicted. Theoretical considerations and types of experiments that can lead to an increase in the understanding of this issue are outlined.
Short‐ and long‐term effects of a change in the spatial distribution of nitrate in the root zone on N uptake, growth and root development of young lettuce plants
Authors: BURNS I. G.
Published: April 2006

Abstract. The effects of a change in the distribution of nitrate within the root zone on N uptake and growth were studied using young lettuce plants after reducing the proportion of their root systems supplied with nitrate from 100 to ca 10% in split‐root experiments in the glasshouse. The main effects of the localized nitrate supply were concentrated in a 2‐week period immediately after the treatment was imposed, when a temporary reduction in nitrate uptake caused the gradual development of N deficiency and a decline in plant growth rate. The plants adapted to the change in nitrate distribution, initially by increasing unit absorption rates (uptake rates per unit weight of root) and more gradually by increasing production of new roots in the high‐nitrate zone. As a result, relative N uptake rates and relative growth rates were restored to the same levels as for control plants (given a spatially uniform N supply throughout) after ca 12d, even though only ca 12–15% of their roots were exposed to nitrate at this time. Thereafter, the plants continued to adapt by concentrating new root growth in the nitrate‐containing zone, ultimately allowing unit absorption rates to return to normal. There was no evidence of any significant N deficiency in the plants after the initial adaptive response was complete, even though the total‐N concentrations of the plants given the localized supply were consistently less than those given the uniform N treatment, and nitrate concentrations in the petiole sap were generally lower in leaves on one side of the plant (because of limited lateral movement of nitrate between xylem vessels during its transport to the shoot).

The delay in the initiation of an adaptive response caused a significant check in growth, and the resulting relative weight differences were maintained throughout the subsequent life of the plant. Plants in all treatments matured on the same date, so yields for those grown with the localized supply were less than those of the control, and could not be recovered by delaying final harvest without unacceptable loss of quality. The pattern of the changes in N uptake and plant growth, and the effect on final yield, were similar to those exhibited by young lettuce plants subjected to a temporary interruption in nitrate supply, suggesting that the reduction in final yield for plants grown with the localized supply was largely the effect of the check in growth which occurred whilst the Plants were adapting to the change in nitrate distribution during the early part of the experiment. This implies that the rate of dry matter production of young lettuce plants can be altered by N treatment without affecting their rate of physiological development.
Sugarcane proteins and messenger RNAs regulated by salt in suspension cells
Authors: RAMAGOPAL S. , CARR J. B.
Published: April 2006

Abstract. Changes in gene expression induced by salinity were investigated in a suspension culture of the tropical, graminaceous plant sugarcane (Sacchamm spp.). Three cell lines tolerant to 5, 10 and 15kg m−3 NaCl were adapted and the expression of newly synthesized proteins and translatable mRNAs in these cell lines were compared with those in unadapted cells on high‐resolution, two‐dimensional gels. Specific proteins and mRNAs altered by salinity were identified. At the protein level, the expression of 15 proteins was induced or enhanced, and that of three others was repressed or abolished. At the translatable mRNA level, the expression of 18 mRNAs was induced or enhanced, and that of eight others was repressed or abolished. The expression of some of these was also regulated, depending on the salt‐adapted cell line. The above changes were characteristic of salt‐adapted cells and were not found in unadapted cells undergoing a short‐term salt stress. Overall, 29 sugarcane proteins were regulated by salinity: for 15, translatable mRNAs were found; for three, no translatable mRNA was detected; and for six of the remaining 11, in vivo equivalents were not observed. These data suggest that a multitude of mechanisms at the transcriptional, post‐transcriptional and post‐translational levels may contribute to the control of gene expression in the sail‐adapted sugarcane cells.
Chilling stress and oxygen metabolizing enzymes in Zea mays and Zea diploperennis*
Authors: JAHNKE L. S. , HULL M. R. , LONG S. P.
Published: April 2006

Abstract. The activities of five active‐oxygen scavenging enzymes were compared for cold‐lability and three were compared for chilling induction in two Zea genotypes of contrasting susceptibility to photoinhibition during chilling. Activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GTR, EC 1.6.4.2) in leaf extracts from plants grown without chilling stress were assayed at 19°C and 5°C. Enzymes from the chilling‐susceptible Z. Mays cv. LG11 had lower specific activities at 5°C than did enzymes from the chilling‐tolerant Z. diploperennis, except for MDHAR where no significant differences were observed. The activities of SOD and APX from Z. diploperennis were double those of Z. mays at both assay temperatures. Monodehydroa‐scrobate reductase and glutathione reductase activities in both species were reduced by 63–78% at a 5°C assay temperature. The dehydroascorbate reductase (DHAR) showed the greatest low‐temperature lability losing 96% (Z. diploperennis) and 100% (Z. mays) of its activity at 5°C. To examine possible chilling‐induced changes in levels of enzyme activity, plants of both Zea genotypes were transferred to growth chambers at 10°C at moderate light intensities. Glutathione reductase activity was found to increase within 24h in Z. diploperennis, but it decreased slightly in Z. mays. MDHAR activity decreased by 50% in Z. diploperennis but showed only a transient increase in activity in Z. mays.
Low night temperatures have a differential effect on the diurnal cycling of gene expression in cold–sensitive and tolerant tomatoes*
Authors: VALLEJOS C. EDUARDO
Published: April 2006

Abstract. Comparisons were made between the changes in mRNA levels induced by low night temperatures in the cold–sensitive tomato and two altitudinal ecotypes of the wild species L. hirsutum. Changes in mRNA levels were detected by resolving in vitro translation products of poly(A)+ RNA by 2‐D PAGE. The treatment was applied by first growing plants in a thermoperiod of 25/18°C and then switching to 25/6°C. All tomatoes displayed a diurnal cycling in which a set of mRNAs accumulated at the end of the 18°C nights, whereas another accumulated at the end of the 25°C days. The accumulation of night specific mRNAs was inhibited by 6°C nights in the cold sensitive tomatoes while that of the tolerant one was only marginally affected. All tomatoes showed a similar reduction in the apparent turnover rate of the day specific mRNAs during the 6°C nights. Finally, low night temperatures induced the accumulation of six to eight mRNAs in all genotypes. This number increased by 15 in L. esculentum after the seventh night and are likely involved in stress response rather than acclimation/tolerance. The tomato is proposed as a genetic model to discriminate genes involved in acclimation/tolerance from those involved in stress response.