bluuebunny/crossref_metadata_2025 huggingface dataset:
Sapwood water storage: its contribution to transpiration and effect upon water conductance through the stems of old‐growth Douglas‐fir
Authors: WARING R. H. , RUNNING S. W.
Published: April 2006

Abstract Enough water is stored in the sapwood of large Douglas‐fir to significantly contribute to transpiration. Sapwood water content falls through the season, causing the wood's conductivity to fall. This leads to low leafwater potentials, stomatal closure, and reduced photosynthesis by the trees.

The amount of water stored in the sapwood of Douglasfir 50‐60 m tall, growing in the Cascade Mountains of Oregon, was estimated periodically over two seasons from measurements of sapwood relative water content (Rs). The relationship between Rs and volume of water contained in the sapwood was determined in the laboratory, and an equation describing the variation of relative conductivity (K) with Rs was derived from the literature. Stomatal conductance (ks) and leaf water potentials were measured in the field.

The relative conductivity of the sapwood was calculated from estimates of the flow rate through the tree and differences in water potential between dawn and the time of comparison. Flow rate was assumed to equal transpiration rate, calculated from the Penman‐Monteith equation using measured ks values. A sixfold decrease in K during the summer was attributed to changes in Rs. The maximum observed diurnal variation in K would require a change in RS estimated at 25%.

About 270 m3 ha−1 (27 mm) of water were stored in sapwood, and 75% of that was in the stemwood. Withdrawal from this store reached 1.7 mm day−1 on clear days after cloudy or rainy weather. Recharge could be almost as fast (up to 1.6 mm day−1) after rain, but was very slow if the foliage remained wet.
Dawn signal as a rhythmical timer for the seasonal adaptive variation of CAM: a model
Authors: MOREL C. , QUEIROZ O.
Published: April 2006

Abstract Photoperiodism, known to control the level of CAM in different types of CAM plants (e.g. Kalanchoe blossfeldiana, Bryophyllum daigremontianum), would act as a reliable timer for seasonal coherent adaptation. Two different endogenous rhythms (malic enzyme activity, PEP carboxylase capacity) appear to be separately coupled to dawn and dusk, respectively, thus achieving time‐compartmentation of CAM; this feature suggests involvement of an ‘internal coincidence’ type of clock mechanism.

Persistence in continuous darkness of the rhythm of malic enzyme activity (measured by label incorporation into pyruvate or by CO2 output) establishes its endogenous character and shows that light is not necessary for malate decarboxylation. The role of the dawn signal would be to entrain the CAM system, i.e. to phase the endogenous rhythm of malic enzyme activity correctly to local time. The possibility of an effect of the phase of the PEP carboxylase rhythm on the phase of the decarboxylation rhythm is ruled out by the presence of the intermediary malate storage step. Phase responses to red and to far‐red show that phytochrome is involved in rephasing the rhythm of malic enzyme activity.

The relative position of dusk affords a ‘measurement’ of the season by the CAM system entrained by dawn. According to the dusk‐dawn interval, the level of PEP carboxylase capacity (amount of active enzyme) is modified, resulting in changes of CAM level (high activity under short days).
Light dark modulation of glycogen phosphorylase activity in the blue‐green alga, Anacystis nidulans
Authors: LEHMANN M. , WÖBER G.
Published: April 2006

Abstract The photoautotrophic procaryote, Anacystis nidulans, accumulates glycogen as a carbon reserve during illumination and nitrogen limitation. Glycogen phosphorylase participates in the mobilization of the polysaccharide in a dark period and was found to be a point of regulatory control of glycogen degradation. Specific enzyme activity of non‐dividing cells increased twofold upon transfer from light to dark and decreased again upon re‐illumination. This dark stimulation of enzyme activity was not inhibited by either rifampicin or chloramphenicol, whereas a light‐induced decrease was abolished by DCMU, an inhibitor of photosynthetic electron transport. Deactivation of glycogen phosphorylase could be simulated by dithiothreitol in vitro. A spheroplast lysate either with or without chromatophores and a partially purified glycogen‐enzyme complex responded to dithiothreitol.

These results are compatible with an interpretation in terms of redox changes taking place with the enzyme in an activation/deactivation cycle. The inactive form maintained in a reduced state by photosynthetic electron transport is thought to be converted into an active form in the dark.
Dissociation of H + extrusion from K+ uptake by means of lipophilic cations
Authors: BELLANDO M. , TROTTA A. , BONETTI A. , COLOMBO R. , LADO P. , MARRE E.
Published: April 2006

Abstract Dissociation of active H+ extrusion (−ΔH+) from K+ uptake in pea and maize root segments was attempted by substituting K+ in the incubation medium with lipophilic cations assumed to enter the cell by passive, non‐specific, permeation through the lipid component of the plasmalemma. Among the compounds tested, tributylbenzylammonium significantly stimulated −ΔH+ in the absence of other monovalent cations in the medium. This effect was much more evident when the experiment was carried out in the presence of fusicoccin, which strongly stimulates proton extrusion and monovalent cation uptake, and hyperpolarizes the trans‐membrane electric potential in these materials. Also the lipophilic cations tetraphenylphosphonium, dimethyldibenzylammonium and hexylguanidine markedly stimulated FC‐promoted −ΔH+. Octylguanidine at a low concentration induced an early stimulation followed by a strong inhibition of −ΔH+. A complete lack of additivity was observed between the effects of lipophilic cations and that of K+ on H+ extrusion. Lipophilic cations severely inhibited K+ uptake.

These data are interpreted as supporting the view of an electric, rather than a chemical, (namely, involving the same carrier system) nature of the coupling of active H+ extrusion with K+ influx.
Farnesol‐like antitranspirant activity and stomatal behaviour in maize and Sorghum lines of differing drought tolerance
Authors: WILSON J. A. , DAVIES W. J.
Published: April 2006

Abstract Potted seedlings of four lines of maize and Sorghum of differing drought tolerance were subjected to a single soil drying cycle and were only rewatered when the plants showed the first signs of wilting. Other plants remained well‐watered throughout the experimental period. As plant water potentials decreased in the unwatered plants of three of the lines investigated (Sorghum Piper and M35‐1, V‐4146 and maize Farz 27), endogenous levels of farnesol‐like antitranspirants increased. Closure of stomata correlated well with the increase in endogenous antitranspirant. In the fourth line (Sorghum M35‐1, V‐4184), stomata did not close as the level of plant water stress increased, although leaf diffusion resistance of even the well‐watered plants of this line was quite high. In this line, there was no consistent relationship between plant water stress and antitranspirant level or between stomatal behaviour and antitranspirant level. The involvement of farnesol‐like antitranspirants in the control of stomatal behaviour in water‐stressed plants is discussed.
Phytochrome photoequilibria in green leaves under polychromatic radiation: a theoretical approach
Authors: HOLMES M. G. , FUKSHANSKY L.
Published: April 2006

Abstract Phytochrome photoequilibria within a model green leaf have been calculated. The results show a gradient in photoequilibria within the leaf lamina due to selective attenuation of incident light by the leaf tissue. Large differences were observed between photoequilibria calculated for a leaf under natural daylight and photoequilibria calculated for a leaf receiving daylight filtered through a vegetation canopy.
Effect of ethylene on auxin transport and metabolism in midrib sections in relation to leaf abscission of woody plants
Authors: RIOV J. , GOREN R.
Published: April 2006

Abstract The relationship between ethylene‐induced leaf abscission and ethylene‐induced inhibition of auxin transport in midrib sections of the leaf blade of Citrus sinensis L. Osbeck, Populus deltoides Bart, and Eucalyptus camaldulensis Dehn. was studied. These species differed greatly in their abscission response to ethylene. The kinetic trend of abscission resembled that of the inhibition of auxin transport in all three species. It is suggested that one of the main actions of ethylene in the leaf blade is to inhibit auxin transport in the veinal tissues, thus reducing the amount of auxin transported from the leaf blade to the abscission zone.

Ethylene inhibited transport of both IAA (indole‐3‐acetic acid) and NAA (α‐naphthaleneacetic acid) in the midrib sections. However, while ethylene enhanced the conjugation of IAA with aspartic acid and glucose in the apical (absorbing) segment of the midrib sections, it had little effect on the conjugation of NAA. The data indicate that auxin destruction through conjugation does not play a major role in the inhibition of auxin transport by ethylene.
The synthesis, transport and metabolism of endogenous cytokinins
Authors: VAN STADEN J. , DAVEY J. E.
Published: April 2006

Abstract Present evidence indicates that only the root systems of plants have been shown conclusively to synthesize cytokinins. Although most of these compounds are apparently exported to the shoot via the xylem, there are indications that more attention should be given to the possibility of translocation through the phloem. Within mature leaves the cytokinins derived from the roots are converted to inactive or storage forms by means of glucosylation. While it would appear that glucosylation could occur in all living plant cells whenever the cytokinins are no longer required for active growth, and could provide the plant with a potential reservoir of cytokinins, very little is known with regard to the transport and reutilisation of these compounds.
The electroosmotic theory of phloem transport: a final restatement
Authors: SPANNER D. C.
Published: April 2006

Abstract The electroosmotic theory as published in 1974 is subjected to a detailed re‐examination, mainly in connection with the problems of anion transport and of the sheer magnitude of the transmembrane potassium current it necessitates. The result is a fundamental modification of the theory which appears very promising. A proton excretion pump replaces the potassium pump; anion transport now presents little difficulty. A modification of the scheme is proposed to incorporate plants like Cucurbita whose P‐protein is basic. The new suggestions appear to offer themselves fairly readily to experimental test. Anion transport in the phloem appears to differ somewhat fundamentally from cation transport.
Transport of copper and manganese to the xylem exudate of sunflower
Authors: GRAHAM ROBIN D.
Published: April 2006

Abstract Absorption of copper and manganese by sunflower roots from solution cultures of varying composition was followed by measuring the concentrations of the metals appearing in whole roots, root cell sap and xylem exudate. Total copper in the fibrous roots was linearly related to the concentration of copper in the external solution but the concentration of copper released to the xylem exudate was buffered somewhat against the changes made externally. No such buffering was observed for managenese. A copper‐sensitive electrode, responsive only to free cupric ions was used in conjunction with total copper analysis by atomic absorption spectrophotometry to show that little of the copper (usually < 1%) existed as a free ion in any phase of the system. Copper in the xylem exudate may be strongly complexed. An electron paramagnetic resonance spectrum of the xylem exudate indicated that manganese probably was a free divalent ion. Calculation of the electrochemical potential gradient for free cupric ions showed that no special metabolically‐linked mechanism need be postulated to account for absorption of copper (or manganese) other than that necessary to maintain the transmembrane potential.
An analysis of the changes in growth rate occurring during the initial stages of geocurvature in shoots
Authors: DIGBY J. , FIRN R. D.
Published: April 2006

Abstract A detailed study of the changes in growth rate on the two sides of a shoot prior to, and following geostimulation has been undertaken. Data from etiolated Zea seedlings, and cucumber hypocotyls, and from light grown sunflower hypocotyls are presented. In all cases, the differential growth which brings about geocurvature begins simultaneously along the length of the organ. This is contrary to previous reports in the literature which suggested that curvature begins first at the tip of an organ and progresses basipetally. The feature which is common to all species investigated is that growth of the upper side of the shoot ceases following geostimulation. In some cases there is also a marked acceleration in growth rate on the lower side of the shoot (sunflower) but other species show no such acceleration of growth (cucumber). It has been assumed for many years that the major factor causing upward curvature was an acceleration of growth on the lower side of the organ. The data presented here show that the cessation of growth on the upper side is a major, and in some cases the only factor bringing about geocurvature. The data are discussed in relation to the mechanisms which might control geotropic curvature.
A study of the autotropic straightening reaction of a shoot previously curved during geotropism
Authors: FIRN R. D. , DIGBY J.
Published: April 2006

Abstract The growth of marked zones on horizontal sunflower and maize shoots was measured over long periods. Subsequent to a period of geocurvature, a period of autotropic straightening occurred in most zones of these shoots. The patterns of differential growth causing this straightening were determined. The straightening appeared in the more apical zones initially and subsequently in the basal zones. The magnitude of the differential growth causing the straightening in any zone was similar to that which caused geocurvature in the same zone. It was found that autotropic straightening became evident in some zones before those zones had reached a vertical orientation thus it is suggested that gravity is not directly involved in the initiation of autotropism.
Correlation between far‐red absorbing phytochrome and response in phytochrome‐mediated anthocyanin synthesis
Authors: STEINITZ B. , SCHÄFER E. , DRUMM H. , MOHR H.
Published: April 2006

Abstract Mustard seedlings were light treated at 24 h after sowing (25°C) to induce phytochrome‐mediated anthocyanin synthesis in cotyledons and hypocotylar hook. All light treatments were performed within the range of the reciprocity law. The in situ photoconversion kinetics of phytochrome (Pr→ Pfr) were measured under the same light treatment. It was found that between 0.4 and 1.0 relative Pfr level the amount of anthocyanin extracted from the organs at 52 h after sowing was linearily correlated with the amount of Pfr produced at 24 h in cotyledons and hypocotylar hook. It is concluded that an explanation of the fluence response function for red light mediated anthocyanin synthesis in the mustard seedling does not require the concept of active vs. bulk phytochrome.
The role of calcium in buffering soils
Authors: BACHE B. W.
Published: April 2006

Abstract. Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH‐buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity; dAB/dpH ≃ 1000 Eq. m−3.

In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non‐calcareous soils is caused by specific ion adsorption at variable‐charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non‐calcareous soils vary from 10 Eq. m−3 for sandy soils to 100 Eq. m−3 for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in liming materials.
Calcium and plant action potentials
Authors: BEILBY M. J.
Published: April 2006

Abstract. Under normal conditions the action potential in Characeae is dependent on the presence of both Cl− and Ca2+. Cl− seems to play a straightforward part as a transient depolarizing flow. The role of Ca2+, however, is emerging as an increasingly complex one: there are Ca2+ concentration changes in the cytoplasm, as well as transient Ca2+ currents across the plasmalemma and possibly the tonoplast. In most Characeae Ca2+ is necessary for the Cl− channel to function, and it is also involved in the cessation of the cytoplasmic streaming observed at the time of excitation.

The function of Ca2+ at the time of the action potential is being revealed by experimental techniques of increasing sophistication. The development of these methods and possible associated artefacts are considered.
Calcium and plant organelles
Authors: MOORE ANTHONY L. , ÅKERMAN KARL E. O.
Published: April 2006

Abstract. The role of intracellular organelles in the regulation of cytosolic Ca2+ levels and whether changes in these levels affect organelle metabolism is considered. We have assessed the biochemical properties of the Ca2+ transporting systems in mitochondrial, chloroplast and microsomal fractions. It is proposed that although all of these organelles can transport Ca2+ to varying extents it would appear that in some tissues at least mitochondria do not play a significant role in the maintenance of cytosolic Ca2+. The most important Ca2+ transporting systems are probably the ATP dependent Ca2+ extrusion across the plasma membrane and Ca2+ uptake by endoplasmic reticulum, as well as light driven Ca2+ uptake by chloroplasts. Changes in cytoplasmic [Ca2+] do appear to regulate the activity of NAD kinase in chloroplasts, the mitochondrial external NADH dehydrogenase and intra‐mitochondrial glutamate dehydrogenase, all of which play a key role in plant cell metabolism. Since some of these enzymes are affected by primary stimuli such as light or hormones, it is concluded that Ca2+ may act as a second messenger mediating some of the primary responses.
Calcium and the plant cytoskeleton
Authors: WILLIAMSON RICHARD E.
Published: April 2006

Abstract. The regulation of the plant cytoskeleton by the concentration of free ionized Ca2+ in the cytosol is discussed. The effect is illustrated by considering the role of Ca2+ in regulating cytoplasmic streaming in Physarum and characean algae, and flagellar beating in Chlamydomonas. Examples are given of cytoskeletal processes in other plant cells that may be Ca2+ ‐regulated, together with an appraisal of some technical difficulties that currently limit their study.
Calcium and the cell wall
Authors: DEMARTY MAURICE , MORVAN CLAUDINE , THELLIER MICHEL
Published: April 2006

Abstract. From this brief review it appears that the interactions between calcium ions and cell walls play a key role in plant physiology. Calcium ions are involved in many mechnisms: for example, stabilization of cell wall structures, acidic growth, ion exchange properties, control of the activities of wall enzymes. All these properties originate from the tight binding of calcium ions to the pectins present in the cell walls. The factor most important for controlling wall behaviour is the density of non‐diffusible charges and, due to its high affinity, calcium can significantly affect this factor. We also discuss the theoretical ion exchange models in relation to the specific role of calcium ions.
Calcification in aquatic plants
Authors: BOROWITZKA MICHAEL A.
Published: April 2006

Abstract. The CaCO3 deposits of aquatic plants may be intra‐, inter‐ and extracellular. Calcification is mainly the result of photosynthetic CO2 or HCO−3 assimilation. This raises the local pH and CO2−3 concentration resulting from shifts in the dissolved inorganic carbon equilibrium, due to either net CO2 depletion as in Halimeda or localized OH− efflux (or H+ influx) as in Chara. The plant cell wall may be important in CaCO3 nucleation by acting as an epitaxial substratum or template, or by creating a microenvironment enriched in Ca2+ compared to Mg2+. Hypotheses on the reason for the lack of calcification in many aquatic plants are presented.
Regulation of nitrate uptake into Chara corallina cells via NH+4 stimulation of NO−3 efflux
Authors: DEANE‐DRUMMOND C.E.
Published: April 2006

Abstract. Net NO3 uptake by NO−3 deficient Chara cells was used to calculate [NO−3]c assuming that the cytoplasm occupies 10% total volume and that nitrate reduction and storage are negligible (i.e. maximum [NO−3]c was calculated). A linear relationship was found between NO−3 efflux and [NO−3]c. There was an initial burst of NO−3 efflux when NH+4 was added, followed by a slower efflux rate which matched influx rate such that net NO−3 uptake was zero. Over 50% of NO−3 that had been taken up in 2 h was lost within the first 5 min of NH+4 addition. The Nernst equation was used to predict the direction of the electrochemical driving force for NO−3 entry. Under the experimental conditions used NO−3 efflux is actively transported. The differential involvement of both NO−3 influx and NO−3 efflux in the regulation of NO−3 uptake is discussed and a model is proposed to account for these results which envisages discrete NO−3 influx and NO−3 efflux carriers.
Regulation of the loss of frost hardiness in Pinus radiata by photoperiod and temperature
Authors: GREER D. H. , STANLEY C. J.
Published: April 2006

Abstract. In controlled environments, the interactive effects of warm (16: 8°C, day: night) and cool (12: 4°C, day: night) temperatures and long (13.5 h) and short (10 h) photoperiods on the dehardening of seedlings of Pinus radiata D. Don were investigated. In another experiment, the effect of four photoperiods from 9 to 14 h was examined. In a third, dehardening at constant temperatures from 5 to 17°C was followed. There was no evidence for an interaction between photoperiod and temperature. Dehardening was temporarily delayed by photoperiods below about 10 h, but there was no other quantitative effect of photoperiod. At constant temperatures, the rate of dehardening was initially constant but declined as the minimum summer frost hardiness was reached. In the initial phase the rate of dehardening was a linear function of temperature, increasing from 0.05°C day−1 at 8°C to 0.30 °C day−1 at 17°C. Temperature controlled the loss of frost hardiness by regulating the rate of dehardening.
The dual role of oxygen in avocado fruit respiration: Kinetic analysis and computer modelling of diffusion‐affected respiratory oxygen isotherms
Authors: TUCKER M. L. , LATIES G. G.
Published: April 2006

Abstract. Oxygen plays a dual role in affecting the rate of respiration of avocado fruit (Persea americana Mill, cv. Hass). The respiration rate v. oxygen concentration curve for steady state avocado fruit respiration is biphasic. The curve becomes monophasic, however, when measured under conditions of rapidly changing oxygen concentration in a closed circulating system. The results are interpreted as indicating that oxygen at relatively high concentrations modulates respiration independent of its interaction with the terminal oxidase—presumably cytochrome oxidase.

A computer model is presented which takes into account the effect of diffusion barriers on the kinetics of oxygen utilization as a function of concentration in avocado fruit. The model is used to make predictions concerning the apparent Km of the terminal oxidase or oxidases in avocado fruit. It is concluded that the apparent Km of the terminal oxidase of uninhibited avocado fruit is that of cytochrome oxidase, and that the alternative, cyanide‐resistant oxidase of avocado fruit does not contribute appreciably to the uninhibited respiration of preclimacteric or climacteric avocado fruit.
Chilling injury in coleus as influenced by photosynthetically active radiation, temperature and abscisic acid pretreatment. I. Morphological and physiological responses
Authors: KRIZEK D. T. , SEMENIUK P. , MOLINE H. E. , MIRECKI R. M. , ABBOTT J. A.
Published: April 2006

Abstract. Coleus blumei Benth. (PI No. 354190), a green‐leafed cultivar, was exposed to 5°C for 48 or 72 h after pretreatment for 48 h at two levels of photosynthetically active radiation (PAR) (8 and 320 μmol s−1 m−2), two temperatures (13 and 20°C), and two abscisic acid (ABA) levels (0 and 200 g m−3 of the racemic mixture). Plants given low PAR for only 48 h prior to chilling treatment (48 or 72 h at 5°C) showed increased protection against chilling injury while those given high PAR were severely injured. The former plants were darker green, contained greater concentrations of chlorophyll‐a, chlorophyll‐b, total chlorophyll and anthocyanin and generally had a lower abscission rate than the latter plants. There were no differences, however, in chlorophyll‐a/b ratio among plants grown at the two PAR levels, two temperatures or two ABA concentrations. Temperature and ABA pretreatment and number of hours at 5°C had no significant effect on chilling injury as measured by leaf chlorosis, but generally had a significant effect on leaf abcission, especially at 3 and 7 d after returning the plants to the greenhouse. Enclosing intact plants or excised shoots in plastic bags to maintain 100% relative humidity during 72 h chilling treatment failed to provide protection against chilling injury. These findings indicate that the protective effects of low PAR applied prior to chilling treatment may be as important or more important than that applied during chilling. They also indicate the importance of making careful measurements of PAR levels when conducting studies on chilling injury.
Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II
Authors: PAPPAS T. , MITCHELL C. A.
Published: April 2006

Abstract. Vegetative plants of soybean [Glycine max (L.) Merr. cv. Wells II] grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse‐grown (GG) plants after 16 d of treatment. Outdoor‐grown (OG) plants, which were subjected to additional environmental stresses including ultraviolet radiation, wind loading, and uncontrolled temperature and humidity fluctuations, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24–45% FL). Reduction in dry weight gain due to mechanical stress corresponded to a decrease in relative growth rate (RGR). Decreases in net assimilation rate and leaf area ratio contributed equally to the lower RGR of shaken plants, indicating that seismic stress inhibits dry weight accumulation by decreasing both the photosynthetic efficiency and the assimilatory surface of soybean.
A procedure for isolating vacuoles from leaves of the halophyte Suaeda maritima
Authors: DRACUP M. N. H. , GREENWAY H.
Published: April 2006

Abstract. A method is described here for isolating protoplasts and vacuoles from leaves of the halophyte Suacda maritima. Integrity of the protoplasts and vacuoles was tested by staining and shown to be more than 75%, while use of biochemical markers, staining and light microscopy suggested a high degree of purity of the vacuoles. Phosphatase and NADH cytochrome‐c‐reductase were associated with vacuoles; phosphatase showed an eight‐fold enrichment and NADH cytochrome‐c‐reductase a 3.5‐fold enrichment relative to protoplasts. The vacuoles contained only 15% of the protein in protoplasts.
An heuristic hypothesis of chilling injury in plants: a role for calcium as the primary physiological transducer of injury
Authors: MINORSKY P. V.
Published: April 2006

Abstract. It is suggested that increased levels of free cytosolic calcium ([Ca2+]cyt) may serve as the primary physiological transducer of chilling injury in plants. Numerous similarities between the effects of [Ca2+]cyt‐raising treatments on plants and the effects of chilling temperatures on chilling‐sensitive (CS) plants are noted. It is proposed that chilling temperatures may lead to increases in [Ca2+]cyt in CS plant cells by reducing the rate at which they exclude Ca2+ from their cytosol and that rapid cooling (coldshock) may cause rapid increases in [Ca2+]cyt due to the activation of voltage‐dependent cation channels. Chill‐induced increases in [Ca2+]cyt in the cells of CS plants may reflect either an inherent inability of such plants to maintain homeostatic levels of Ca2+ at low temperatures or a stress‐induced reaction which has evolved to enable such cells to cope more effectively with the short‐term hardships imposed by cold. Previous proposals concerning the physiological transduction of chilling injury are also discussed. It is argued that there is little evidence to suggest that the immediate effects of low temperatures on CS cells include either decreases in ATP levels, general increases in the passive permeability of membranes, or increased rates of fermentation.
Partitioning stomatal and non‐stomatal limitations to photosynthesis
Authors: JONES H. G.
Published: April 2006

Abstract. Plant scientists concerned both with crop improvement and with understanding the control mechanisms of complex processes such as photosynthesis need to identify those processes that are most important in restricting the overall rate and to quantify the relative importance of different components. The techniques that have been used for quantifying the relative importance of component processes in limiting net assimilation rate are reviewed and related to a fundamental definition based on sensitivity analysis. It is concluded that many methods currently in use, including standard resistance analysis, frequently give very misleading answers.

In addition, possible methods for apportioning the contributions of different component processes to observed changes in net photosynthetic rate (for example after stress) are also reviewed and compared against a fundamental approach based on sensitivity analysis. Unfortunately, the detailed time course of changes in mesophyll and stomatal properties that is required for application of the basic sensitivity analysis is seldom likely to be available, so that it is usually necessary to adopt an approximate method. The standard approximation that is recommended for calculating the contributions of different component processes to a change in assimilation rate, involves measurements at the initial and final states only. The various methods discussed in this paper are compared using published photosynthetic data for a range of species.
Possible effects of rising C02 on climate
Authors: CRANE A. J.
Published: April 2006

Abstract Two factors will determine the rate at which CO2 levels in the atmosphere increase in the future: the rate of input to the atmosphere, primarily from fossil fuel burning, and the way in which this CO2 is partitioned between atmosphere, ocean and biosphere. A brief review is given of the current state of knowledge of these aspects of the CO2 issue prior to a discussion of the changes in climate that might be expected from increased levels of CO2, whenever these might occur. The basis of climate modelling upon which our expectations rest is explained, indicating the nature of the uncertainty that currently exists in the model results. While some of the gross features of the likely climatic change seem reasonably well established qualitatively, considerable model development will be needed before reliable information on the likely regional effects is forthcoming. Observations have yet to confirm the occurrence of temperature change attributable to CO2 increases. Nevertheless, the possibility exists of a change in climate during the coming century that may be substantial relative to past experience. Although direct measures to control CO2 emissions would certainly be premature, long‐term planning of infrastructures, closely tuned to present climatic conditions, should ensure their robustness in the face of the uncertain climatic changes that may lie ahead.
Physical, chemical and biological characteristics* of CO2 gas flux across the air‐water interface
Authors: SMITH S. V.
Published: April 2006

Abstract Carbon dioxide gas flux across the air‐water interface is most often treated as a ‘simple’ physical process, primarily responding to wind speed and water temperature. Available experimental data yield an exponential regression equation relating wind speed to the thickness of a stagnant boundary film through which gas diffuses to or from the water. Flux of CO2 is influenced by CO2 hydration reactions in the stagnant boundary layer. High pH and a thick stagnant boundary layer favour chemical enhancement of the CO2 gas flux.

The rate of CO2 flux reflects the sum of net organic metabolism plus CaCO3 reactions. Some interesting gas‐flux constraints on the rate of net organic carbon production and on global geochemical cycling of CaCO3 emerge. At high pH (circa 10), the maximum net organic carbon production which can be supported by CO2 flux across the air‐water interface is about 0.06 mol C m&2 d&1. On a global scale, organic C, not atmospheric C, appears to account for the ‘CO2’ term in the classical CaCO3 dissolution‐precipitation reaction.
Exchange of carbon dioxide between vegetation and the atmosphere
Authors: LEGG B. J.
Published: April 2006

Abstract Carbon dioxide is transported from the atmosphere to leaf surfaces very efficiently, and atmospheric diffusion resistances rarely affect photo‐synthetic rates by more than 10%. The largest single resistance is in the boundary layer of individual leaves, and this is a well‐known function of leaf size, wind speed, and leaf to air temperature difference. For uniform vegetative canopies a fully turbulent boundary layer exists above; this layer is also well understood and well‐proven equations can be used to relate the carbon dioxide flux to the concentration gradient. Transport in the air within and just above vegetative canopies is less well understood. Turbulent diffusion theory has been shown to be inadequate, and consequently the diffusion resistance analogy cannot be used. Recent work, however, shows that Lagrangian theories of dispersion offer an alternative and more accurate description of transport within canopies.
Uptake of CO2 by aquatic vegetation
Authors: RAVEN J. A. , OSBORNE B. A. , JOHNSTON A. M.
Published: April 2006

Abstract Photosynthesis by aquatic plants based on the supply of CO2 from air‐equilibrated solutions may be limited by the low diffusion coefficient of CO2 in water. For plants in which the transport of CO2 from the bulk medium is by diffusion, and the initial carboxylation uses RUBISCO, CO2 supply can be increased by growth in habitats with fast water flow over the surface (reducing unstirred layer thickness), or with heterotrophically‐augmented CO2 levels, including the direct use of sediment CO2. Many aquatic plants using RUBISCO as their initial carboxylase counter the limitations on CO2 supply via the operation of biophysical CO2 concentrating mechanisms which are based on active transport of HCO−3, CO2 or H+ at the plasmalemma, and use bulk‐phase HCO−3 or CO2 as the C source. A final group of aquatic plants use biochemical CO2 concentrating mechanisms based on auxiliary carboxylation by PEPc: C4‐like and Crassulacean Acid Metabolism–like processes are involved. These various mechanisms for increasing CO2 supply to RUBISCO also help to offset the low specific reaction rate of aquatic plant RUBISCOs at low [CO2] and low [CO2]: [CO2]. In addition to overcoming restrictions on CO2 supply, the various methods of increasing inorganic C availability may also be important in alleviating shortages of nitrogen or photons.
The respiratory source of CO2
Authors: FARRAR J. F.
Published: April 2006

AbstractApproximately half of the carbon plants fix in photosynthesis is lost in dark respiration. The major pathways for dark respiration and their control are briefly discussed in the context of a growing plant. It is suggested that whole‐plant respiration may be largely ADP‐limited and that fine control of the respiratory network serves to select the respiratory substrate and to partition carbon between the numerous possible fates within the network. The striking stoichiometry between whole‐plant growth and respiration is reviewed, and the relationships between substrate‐limited growth and ADP‐limited respiration are discussed.
CO2 and intracellular pH
Authors: BOWN ALAN W.
Published: April 2006

Abstract The experimental determination of cytoplasmic and vacuolar pH values is discussed. Despite variation in these values evidence indicates that intracellular pH values are normally regulated within narrow limits. The regulatory mechanisms proposed involve the metabolic consumption of OH& and the active efflux of H +. The evidence for intracellular pH modification in response to CO2 hydration and the production of HCO−3 and H+ is examined. Theoretical calculations and experimental data indicate that CO2 concentrations as high as 5% will lower intracellular pH. Conversely, variation in CO2 levels around atmospheric concentrations is unlikely to perturb intracellular pH. High CO2 levels are found in bulky tissues, and flooded root systems. Evidence is presented that the slow diffusion of dissolved CO2 compared to gaseous CO2 results in its accumulation. It is proposed that the accumulation of respiratory CO2 may reduce intracellular pH values when plant tissues, cells or protoplasts are maintained in a liquid culture medium. Finally, the possible role of dark CO2 fixation and organic acid synthesis in the regulation of intracellular pH is examined.
Gravitropic responses of wild‐type and mutant strains of the moss Physcomitrella patens
Authors: JENKINS G I , COURTICE G. R. M. , COVE D. J.
Published: April 2006

Abstract The gravitropic responses of dark‐grown caulonemata and gametophores of wild‐type and mutant strains of the moss Physcomitrella patens have been investigated. In the wild‐type both caulonemata and gamelophores show negative orthogravitropism. No gravitropic response is observed when plants are rotated slowly on a clinostat and the inductive effect of gravity can be replaced by centrifugal force. The gravitropic response of caulonemanta is biphasic, consisting of an initial phase producing a bend of about 20° within 12 h of 90° reorientation and a subsequent slower phase leading to completion of the 90° curvature. No obvious sedimentation of statoliths accompanies this response. Several mutants have been isolated that are either partially or completely impaired in caulonemal gravitropism and one mutant shows a positive gravitropic response. Complementation analysis using somatic hybrids obtained following protoplast fusion indicates that at least three genes can mutate to give an altered gravitropic phenotype. None of these mutants is altered in gametophore gravitropism, suggesting that the gravitropic response of caulonemal filaments may require at least some gene products that are not required for the response of the multicellular gametophores. One class of mutant with impaired caulonemal gravitropism shows a pleiotropic alteration in leaf shape.
Cations stimulate proton pumping in Catharanthus roseus cells: implication of a redox system?
Authors: BELKOURA M. , RANJEVA R. , MARIGO G.
Published: April 2006

Abstract During growth, cultured Catharanthus oseus cells produce a transient acidification of the culture medium that may be controlled by cations. The removal of divalent ions from the medium by the chelator EGTA resulted in an inhibition of this acidification. Conversely, acidification can be stimulated by the addition of Ca2+, Mg2+ and La3+ in the basal medium.

This acidification process and the proton‐linked redox pump previously described (Marigo & Belkoura, 1985) respond in a similar manner to cations. These two systems, which are both inhibited by the Ca2+ ‐calmodulin antagonist calmidazolium, could be regulated by the Ca2+‐calmodulin complex. By using ionic surfactant (CP+, SDS−) it was demonstrated that the net surface charge of the plasmalemma plays a role in the activation of the two pumping processes. These results are interpreted to indicate that a transmembrane redox system could provide the energy for electrogenic proton extrusion.
Some water‐related physical properties of maize root‐cap mucilage
Authors: GUINEL F. C. , McCULLY M. E.
Published: April 2006

Abstract The dry weight (0.1%) and water potential ‐7 kPa) of root‐cap mucilage from 3‐d‐old axenically grown maize seedlings have been determined. The results suggest strong gelling properties and weak water‐holding capacity for the mucilage. Root tips from seedlings grown under low or high water stress were fixed by freeze‐substitution. Micrographs showed that in both conditions, mucilage was secreted into the periplasmic space and extruded through the cell wall, though in dry conditions, the mucilage was tightly pressed against the root‐cap surface. Histochemical and structural evidence is presented indicating chemical changes in the composition of the mucilage upon extrusion and a sharp increase in its hydration at increasing distance from the secretory cells. The possible functions of the root‐cap mucilage in the rhizosphere are examined in light of these findings.
Resistance of fully imbibed tomato seeds to very high salinities
Authors: KURTH E. , JENSEN A. , EPSTEIN E.
Published: April 2006

Abstract Seeds of Lyeopersicon esculentum cv. VF36 (a salt‐sensitive cultivar), L. esculentum var. Edkawi (which is fairly salt‐resistant), and a wild relative, L. cheesmanii, were exposed to various concentrations of NaCl, up to 460 mol m−3, either directly or following imbibition in non‐saline nutrient solution. After 10 d exposure to salt, they were transferred to non‐saline solution. All taxa showed some germination at the lowest salinity tested, 92 mol m−3 NaCl, but virtually no germination occurred at 184 mol m−3 NaCl or higher salinities. Within 2 d after removal of the salt stress, however, the seeds of L. esculentum reached control levels of germination, even if they had already been on the verge of germination when the stress was imposed. The seeds of L. cheesmanii were less resistant to NaCl. The physiological basis for the resistance of VF36 seeds is discussed.
Erythrosin B as an effective inhibitor of electrogenic H+ extrusion
Authors: COCUCCI M. C. , MARRÉ E.
Published: April 2006

Abstract In 24‐h‐genninaled radish seedlings erythrosin B (EB), an effective inhibitor of microsomal as well as of partially purified vanadate‐sensitive ATPase markedly inhibited the basal and the FC‐stimulated proton extrusion, and induced a rapid depolarization of FC‐hyperpolarized trans‐membrane electric potential (PD) without causing any significant change of ATP level. The effects of EB on H+ extrusion were partially additive with those of vanadatc, another inhibitor of plasma membrane H+‐ATPase. These effects are interpreted as due to a direct inhibition by EB on plasma membrane H+‐ATPase involved in H+ electrogenic transport in the higher plants.
Diurnal changes in water content of the stems of apple trees, as influenced by irrigation
Authors: BROUGH D. W. , JONES H. G. , GRACE J.
Published: April 2006

Abstract Groups of apple trees within an orchard were irrigated by either releasing a fine mist within the canopy or spraying water on the soil. Diurnal changes in the water content of the xylem were inferred from measurements of density made with a gamma probe. Transpiration rates were estimated from leaf temperatures, and water potentials and changes in radial dimension of the stem were recorded. Xylem water content and water potential declined each morning and recovered in the afternoon. Radial dimensions of the xylem followed a similar pattern, but the percentage change was very small in relation to the change in water content of the same tissue. The decline in water content is unlikely to have been caused by cavitation, as it was readily reversed in the afternoon. It is more likely to have been caused by changes in the volume of water occupying already‐cavitated fibres or intercellular spaces. Water potential and xylem water content were highest in the mist‐irrigated trees and least in the unirrigated controls.
Dependence of starch storage on nutrient availability and photon flux density in small birch Betula pendula Roth)
Authors: McDONALD A. J. S. , ERICSSON A. , LOHAMMAR T.
Published: April 2006

Abstract Small birch plants (Betula pendula Roth) were grown in a climate chamber at different levels of nutrient availability and at two photon flux densities. The extent to which starch storage was dependent upon nutrient availability and photon flux density was investigated.

Acclimated values of starch concentration in leaves were highest at low nutrient availability and high photon flux density. Starch storage in roots was only found at the lowest nutrient availability. However, the relative rate of starch storage (starch stored per unit plant dry weight and time) was higher in plants with good nutrition.

The data suggest that, at sub‐optimal nutrient availability, the momentary rate of net shoot photosynthesis is unlikely to limit the structural (as opposed to carbon storage) growth of the plant. Although photosynthetic rate per unit leaf area (as measured at the growth climate) was slightly lower in plants with poor nutrient availability, photosynthetic rate per unit leaf nitrogen was higher. These data suggest a priority of leaf nitrogen usage in photosynthesis, with limiting amounts of leaf nitrogen (and possibly other nutrients) for subsequent growth processes. This argument is consistent with the higher concentrations of starch found in plants with poor nutrient availability.
Plant cuticles sorb lipophilic compounds during enzymatic isolation
Authors: SCHÖNHERR J. , RIEDERER M.
Published: April 2006

Abstract Plant cuticles sorb large amounts of hexadecanoic acid, octadecanoic acid and other lipophilic compounds (not identified) when incubated in cell slurries obtained by enzymatically digesting leaves or fruits. These extraneous substances cannot be removed completely and selectively after cuticle isolation, nor is it possible to prevent sorption by optimizing isolation procedures. It is, therefore, impossible to estimate amounts and composition of intracuticular soluble lipids using enzymatically isolated cuticles, as has been done in the past. Extraneous substances sorbed during isolation do not affect water permeability of the cuticles.