bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative sensitivity of ‘Prior Lisbon’ lemon and ‘Valencia’ orange trees to foliar sodium and chloride concentrations
Authors: LLOYD J. , KRIEDEMANN P.E. , ASPINALL D.
Published: April 2006

Abstract While citrus rootstocks differ in capacity for sodium and chloride ion exclusion, citrus scion species also vary in foliar sensitivity to NaCl salinisation. Of two common scions, ‘Lisbon’ lemon appears more sensitive, whereas ‘Valencia’ orange in less sensitive to leaf salt. In an attempt to explain this difference. ‘Valencia’ orange (Citrus sinensis [L.] Osbeck) and ‘Prior Lisbon’ lemon (Citrus limon [L.] Burm. F.) were budded to rootstocks known to differ in their ability to exclude sodium ions viz, the strong excluder Trifoliata (Poncirus trifoliata [L.] Raf.), and the weaker excluder Troyer citrange (C. sinensis×P. trifoliata); neither rootstock shows strong exclusion of chloride ions. Budded trees were held under a photosynthetic photon flux density of 450 μmol m 2 S 1 and watered with nutrient solution containing either 0 or 50 mol m 3 NaCl. Growth and photosynthetic responses were measured over 58 d following onset of salinization: salinity effects on leaf gas exchange were studied in relation to changes in leaf water status, compatible solutes and foliar content of sodium and chloride ions, over that same period.

Once root‐zone salinization began to influence leaf solutes (day 30 onwards), lemon showed a steeper increase in leaf chloride than occurred for orange. Although rootstock differences were without effect on this ingress of chloride ions for either scion, sodium ions were excluded from both scions to a larger extent by Trifoliata than by Troyer citrange.

Carbon dioxide assimilation of scion foliage was reduced earlier and to a much larger extent by rootzone salinization in lemon than in orange. Furthermore, comparisons of CO2 assimilation in relation to leaf tissue solutes between scions (on either rootstock) showed stronger responses for both sodium and chloride ions in lemon than in orange. Faster ingress of chloride into lemon leaves was identified as the crucial factor which predisposed towards expression of that contrast between scions.

Although contrasts between scions in photosynthetic responses to salinization matched a faster ingress of chloride into lemon than into orange leaves, the sharper photosynthetic response of ‘Prior Lisbon’ lemon to salinity was not solely attributable to higher concentrations of chloride ions (cell sap basis). A difference between species in subcellular compartmentation of the chloride ion under saline conditions was invoked.
Expression of C4‐like photosynthesis in several species of Flaveria
Authors: MOORE B. D. , KU M. S. B. , EDWARDS G. E.
Published: April 2006

Abstract Photosynthetic metabolism was investigated in leaves of five species of Flaveria (Asteraceac), all previously considered to be C4 plants. Leaves were exposed to 14CO2 for different intervals up to 16s. Extrapolation of 14C‐product curves to zero time indicated that only F. trinervia and F.bidentis assimilated atmospheric CO2 exclusively through phosphoenolpyruvate carboxylase. The proportion of direct fixation of 14CO2 by ribulose‐I, 5‐bisphosphate carboxylase/oxygenase (Rubisco) ranged from 5 to 10% in leaves of F. australasica. F. palmeri and F. vaginata.

Protoplasts of leaf mesophyll and bundle sheath cells were utilized to examine the intercellular compartmentation of principal photosynthetic enzymes. Leaves of F. australasica, F. palmeri and F. vaginata contained 5 to 7% of the leaf's Rubisco activity in the mesophyll cells, while leaves of F. trinervia and F. bidentis contained at most 0.2 to 0.8% of such activity in their mesophyll cells. Thus, F. trinervia and F. bidentis have the complete C4 syndrome, while F. australasica, F. palmeri and F. vaginata are less advanced, C4‐like species.
Na‐Ca interactions in barley seedlings: relationship to ion transport and growth
Authors: CRAMER G. , EPSTEIN E. , LÄUCHLI A.
Published: April 2006

Abstract Salt‐stressed plants often show Ca deficiency symptoms. The effects of NaCl salinity (1 to 150 mol m‐3) and supplemental Ca (10 mol m‐3) on Na and Ca transport in barley (Hordeum vulgare L.) and their relationship to growth were investigated. The adjustment of Na and Ca transport was investigated by examining young seedlings exposed to short‐term (immediate) and long‐term (7 d) exposure to salinity. When the plants were exposed to long‐term treatments of salinity, the rate of sodium accumulation in roots was approximately 10 to 15% of short‐term treatments. No significant adjustment in the transport to the shoot was observed. Rates of tracer (22Na) transport were compared to calculated rates based on relative growth rates and tissue element concentrations. Comparisons between measured tracer and calculated rates of transport indicate that 22Na transport may underestimate transport to the shoot because of dilution of the tracer in the root cytoplasm. Calcium uptake showed only minor adjustment with time. Measured rates of tracer transport to the shoot correlated well with calculated values. The transport and tissue concentrations of Na were significantly affected by supplemental Ca. Calcium transport and tissue concentrations were markedly inhibited by salinity. Supplemental Ca increased Ca transport and accumulation at all NaCl treatments above that of control plants without supplemental Ca. Salinity inhibited plant growth at 150 mol m ‐3NaCl, but not at 75 mol m‐3.

Supplemental Ca significantly improved root length but not fresh weight after 7d of salinity, although differences in fresh weight were detected after 9d. There were significant Na‐Ca interactions with ion transport, ion accumulation, and growth. The effects of salinity on Na and Ca transport to the shoot do not appear to play a major role in shoot growth of barley.
Photosynthetic and stomatal responses of the halophyte,Plantago maritima L. to fluctuations in salinity
Authors: FLANAGAN L. B. , JEFFERIES R. L.
Published: April 2006

Abstract Measurements of photosynthesis as a function of intercellular CO2 (A‐C1 curve) were made on single. attached leaves of Plantago maritima L. while plants were exposed to changes in salinity. Salinity was increased in steps from 50 to 500 mol m‐3 NaCl and then returned to 50 mol m‐3 NaCl at two rates, 75 mol m‐3 (NaCl) day‐1 (experiment 1) and 150 mol m‐3 (NaCl) day‐1 (experiment 2). In experiment one, the CO2 assimilation rate declined at high CO2 concentrations, but the initial slope of the A‐C1 curve was unaffected in young leaves after salinity was increased to 500 mol m‐3 NaCl. The insensitivity of photosynthesis to increases in CO2 concentration above air levels was not associated with insensitivity to a reduction in oxygen concentration. In experiment two increasing the rate at which salinity was changed resulted in larger declines in photosynthesis and leaf conductance than were observed in experiment one. Both the initial slope and the CO2 saturated region of the A‐C1 curve were substantially reduced at high salinity suggesting that mesophyll biochemical capacity had been inhibited. However, concurrent measurements of photosynthesis as oxygen evolution under 5% CO2 indicated no effect of increased salinity on photosynthetic capacity. This suggests that the apparent non‐stomatal limitations indicated by A‐C1 measurements were artifacts caused by strong, nonuniform stomatal closure.
The nature of protein differentiation in the growing pea root
Authors: ALLAN E. , TREWAVAS A.J.
Published: April 2006

Abstract Sections of the growing root of pea (Pisum sativum) have been microdissected into stele, cortex and epidermis. Using labelled amino acids, two dimensional separations employing non‐equilibrium pH gel electrophoresis (NEPHGE) and isoelectric focusing (IEF), and silver staining, the complexity of protein differences between the cortex and the stele has been assessed. Analyses commenced as cells in these two tissues appear in the meristem (0.7—1 mm from the tip) and continued up to 30 mm from the tip as they subsequently mature. From the earliest stages at which the cortex and stele can be distinguished and dissected apart the protein patterns differ substantially. However these tissue differences, involving over one third of the detected protein species, are almost all quantitative. Very few qualitative (i.e. tissue specific) proteins were detected. Many proteins also show quantitative stage‐specific variation, detected using successively older root segments. In vitro translation studies involving isolated mRNA showed only a very limited stage‐specific variation in translated proteins. This supports the notion that translational controls may contribute significantly to the development of these two tissue types.
Signal perception, differential expression within multigene families and the molecular basis of phenotypic plasticity
Authors: SMITH H.
Published: April 2006

Abstract. This Introduction to the Special Issue of Plant, Cell and Environment on ‘Sensing the Environment’is concerned with the molecular mechanisms that may link the perception of environmental signals with the evocation of those specific developmental responses that collectively are known as phenotypic plasticity. The significance of phenotypic plasticity at the evolutionary, developmental and ecological levels is outlined, and it is argued that the extent of an individual's adaptability to environmental conditions must be a reflection of the extent and sophistication of the controls over the synthesis and action of specific proteins. Reviewing evidence from a selected range of plant enzymes and regulatory proteins, it is proposed that differential regulation of the expression of members of multigene families may represent the molecular basis of phenotypic plasticity.
Light‐driven leaf movements*
Authors: KOLLER D.
Published: April 2006

Abstract. Mature leaves of many plants re‐orientate their laminae photonastically in response to non‐directional light signals, and/or phototropically in response to directional light signals, by flexing of pulvini, most commonly subtending their bases. Physiological and structural specializations of the pulvinus enable it to flex, by rapidly undergoing differential and repeatedly reversible axial volume changes (expansion/contraction) in opposite sectors of its motor tissue. Light‐driven leaf movements are adaptations that contribute to the efficiency of the photosynthetic apparatus in the leaf. The phototropic response maximizes the harvesting of photosynthetically radiant energy. The photonastic response to dark‐to‐light transitions increases the interception of light by unfolding the lamina. Another photonastic response modulates the interception of radiant energy by the lamina, allowing it to evade damage by light in excess of its photosynthetic capacity when the leaf is under stress. The same unidentified blue‐absorbing pigment system appears to be involved in all these responses. Non‐directional light signals are perceived in the pulvinus. Perception of directional light signals may be localized in other parts of the leaf in different plants: for example, the pulvinus in most leguminous species, and the lamina in malvaceous and at least one leguminous species. The perception of non‐directional and directional light signals, their transduction to differential volume changes in the target cells, and their transmission between the two where the sites are separate, are discussed.
Phototropism: mechanisms and ecological implications
Authors: IINO M.
Published: April 2006

Abstract. Phototropism in seed plants, either etiolated or de‐etiolated, is mediated by unidentified photoreceptor(s) sensitive to blue and near‐UV regions of the light spectrum. Green plants may have an additional phototropic system sensitive to red light. Fluence‐response studies of the blue light‐sensitive phototropism, initially made on oat coleoptiles, have indicated the occurrence of multiple response types. Of those, two are found to be general: the first pulse‐induced positive phototropism (fPIPP), or the so‐called first positive curvature, and the time‐dependent phototropism (TDP) or the second positive curvature. The fPIPP, elicited by a pulse stimulus shorter than a few minutes, is characterized by a bell‐shaped fluence‐response curve and the validity of reciprocity. The TDP, elicited by prolonged irradiation, is characterized by its dependence on the exposure time and the invalidity of reciprocity. Studies made on these two response types have revealed the following: (1) plants acquire directional light information for phototropism by sensing internal light gradients created by light scattering and absorption; (2) phototropism results from redistribution of growth, i.e. inhibition on the irradiated side and compensating stimulation on the shaded side; (3) lateral movement of growth regulators, the principle of the Cholodny‐Went theory, can account for the growth redistribution, and auxin is clearly the mediating regulator in maize coleoptiles. This review further describes some mechanistic implications of fPIPP. Experimental results indicate that (1) fPIPP is mediated by a single step of photoreaction, (2) the responsiveness, reflected in the height of the fluenceresponse curve, is reduced by pre‐irradiation with blue light and recovers gradually afterward, and (3) the light sensitivity, reflected in the position of the fluence‐response curve along the log fluence axis, is also reduced by the pre‐irradiation and recovers gradually. Analyses of these results, based on kinetic models, suggest that the bell‐shaped fluence‐response curve is caused by the difference in the amounts of a photoproduct between irradiated and shaded sides, and that fPIPP represents a mechanism of TDP. It is also indicated that phytochrome in the red‐absorbing form exerts two separate effects on phototropism: reduction of the light sensitivity and enhancement of the responsiveness. Along with the discussion of the mechanisms of phototropism, their ecological implications are considered.
Plant response to atmospheric humidity
Authors: GRANTZ D. A.
Published: April 2006

Abstract. Plants growing in environments differing in prevailing humidity exhibit variations in traits associated with regulation of water loss, particularly cuticular and stomatal properties. Expansive growth is also typically reduced by low humidity. Nevertheless, there is little evidence in plants for a specific sensor for humidity, analogous to the blue light or phytochrome photoreceptors. The detailed mechanism of the stomatal response to humidity remains unknown. Available data suggest mediation by fluxes of water vapour, with evaporation rate assuming the role of sensor. This implies that stomata respond to the driving force for diffusional water loss, leaf‐air vapour pressure difference. Induction of metabolic stomatal response to humidity may involve signal metabolites, such as abscisic acid, that are present in the transpiration stream. These materials may accumulate in the vicinity of guard cells according to the magnitude and location of cuticular transpiration, both of which could change with humidity. Such a mechanism remains hypothetical, but is suggested to account for feedforward responses in which transpiration decreases with increasing evaporative demand, and for the apparent insensitivity of stomatal aperture in isolated epidermis to epidermal water status. Other responses of plants to humidity may involve similar indirect response mechanisms, in the absence of specific humidity sensors.
Phytochrome, a family of photoreceptors with multiple physiological roles
Authors: SMITH H. , WHITELAM G. C.
Published: April 2006

Abstract.Photoperception by phytochrome is crucially important at many stages of the plant life cycle in allowing adaptation to a changing light environment. Phytochrome is encoded by a family of genes subject to differential expression in response to environmental and developmental factors. Multiple forms of phytochrome exist with, in some cases, identifiably different spectrophotometric, biochemical and physiological characteristics. This article reviews the regulation of development by phytochrome and discusses evidence from physiological studies of wild type, mutant and transgenic plants consistent with the proposal that different members of the phytochrome family have different photosensory roles. We speculate briefly on the possible evolutionary relationship between the different photosensory roles, and suggest approaches towards further elucidation of the nature of phytochrome‐mediated photoperception and adaptation to the natural light environment.
Sensing of atmospheric CO2 by plants
Authors: MOTT K. A.
Published: April 2006

Abstract. Despite recent interest in the effects of high CO2 on plant growth and physiology, very little is known about the mechanisms by which plants sense changes in the concentration of this gas. Because atmospheric CO2 concentration is relatively constant and because the conductance of the cuticle to CO2 is low, sensory mechanisms are likely to exist only for intercellular CO2 concentration. Therefore, responses of plants to changes in atmospheric CO2 will depend on the effect of these changes on intercellular CO2 concentration. Although a variety of plant responses to atmospheric CO2 concentration have been reported, most of these can be attributed to the effects of intercellular CO2 on photosynthesis or stomatal conductance. Short‐term and long‐term effects of CO2 on photosynthesis and stomatal conductance are discussed as sensory mechanisms for responses of plants to atmospheric CO2. Available data suggest that plants do not fully realize the potential increases in productivity associated with increased atmospheric CO2. This may be because of genetic and environmental limitations to productivity or because plant responses to CO2 have evolved to cope with variations in intercellular CO2 caused by factors other than changes in atmospheric CO2.
Light perception in guard cells
Authors: ZEIGER E.
Published: April 2006

Abstract. Guard cells perceive light via two photoreceptor systems: a blue‐light‐dependent photosystem and the guard cell chloroplast. Chloroplasts stimulate stomatal opening by transducing photosynthetic active radiation into proton pumping at the guard cell plasma membrane. In addition, guard cell chloroplasts fix CO2 photosynthetically. Sugar from guard cell photosynthesis can contribute to the osmotic build‐up required for opening. The blue‐light‐dependent photosystem activates proton pumping at the guard cell plasma membrane and stimulates starch hydrolysis. Available information on the photobiological properties of guard cells makes it possible to describe stomatal function in terms of the cellular components regulating stomatal movements. The blue light response is involved in stomatal opening in the early morning and stomatal responses to sunflecks. The guard cell chloroplast is likely to be involved in stomatal adaptations to sun, shade and to temperature. Interactions between these photosystems, a third photoreceptor in guard cells, phytochrome, and other mechanisms transducing stomatal responses such as VPD and carbon dioxide, provide the cellular basis for stomatal regulation.
Boundary layer properties of highly dissected leaves: an investigation using an electrochemical fluid tunnel
Authors: GUREVITCH J. , SCHUEPP P. H.
Published: April 2006

Abstract. A method for modelling heat and mass transfer by diffusion‐controlled electrode reactions in a fluid tunnel is described. In this procedure, a nickelplated leaf functions as a test electrode, and the convective transfer of ions to the leaf cathode in an electrolyte‐filled flow tunnel is measured as a function of flow rate. The method permits the simulation of water vapour and heat transfer, and in particular, the determination of boundary layer conductances, by analogy with observed ion transfer. The approach is applicable to many problems in modelling heat and mass transfer between leaves and their surroundings, and is especially useful in examining the properties of leaves in which surface characteristics or overall shape are complex. Using this method, the properties of the highly dissected leaves of Achillea lanulosa with regard to forced convection were investigated. The leaves showed high transfer conductances, indicating that the effective unit of heat transfer was probably the individual leaf subelements. Conductances tended to be greater and effective characteristic dimensions smaller for the larger, more open leaves of a lower altitude population in contrast with leaves from high altitude plants. While the results provide insight into the properties of these complex leaf shapes, difficulties in interpreting the findings are discussed, and a number of exploratory approaches are suggested for data analysis and interpretation.
Epidermal focussing and effects upon photosynthetic light‐harvesting in leaves of Oxalis
Authors: POULSON M. E. , VOGELMANN T. C.
Published: April 2006

Abstract. In Oxalis, epidermal cells on both the adaxial and abaxial surface of the leaf concentrated light within the leaf by a lens mechanism. Focal lengths of epidermal cells were estimated using two methods: they were calculated from radius of curvature measurements taken from individual epidermal cells, and were measured directly in agarose replicas of the leaf surface. In the three species of Oxalis examined, light that was incident upon the adaxial leaf surface was concentrated within the palisade, whereas light that was incident upon the abaxial leaf surface was concentrated within the spongy mesophyll. Using sensiometric analysis, theoretically maximal focal intesifications were measured in leaf replicas at the focal maximum and at intermediate positions corresponding to the mid‐region of the palisade and spongy mesophyll tissues. Focal intensifications ranged from 2.2 to 10.4 times incident light at the focal maximum, and 1.3 to 4.5 in the palisade or spongy mesophyll layers. Elimination of epidermal focussing, by covering the leaf surface with a thin layer of mineral oil, strongly affected chlorophyll fluorescence induction curves resulting in a decrease of 10–40% in the initial (F0) and variable fluorescence (Fv). These results are consistent with the interpretation that the chloroplasts were adapted to their light microenvironment within the leaf and that focussing by the epidermis channelled light to a population of chloroplasts that were adapted to high light.
Regulation of phytochrome mRNA abundance in green oat leaves
Authors: EDWARDS C. L. , COLBERT J. T.
Published: April 2006

Abstract. Avena sativa L. (oat) seedings were grown 4 d in continuous white light followed by 3 d in darkness. Probes derived from an oat phytochrome cDNA clone (pAP 3.2) were used in slot blot analyses to measure the abundance of phytochrome mRNA in the distinct etiolated and green portions of the leaves produced by these seedlings. Both the green and etiolated portions accumulated phytochrome mRNA to a level of about 85% of the etiolated seedling level. Subsequent experiments with similar seedlings showed that both the green and etiolated portions were capable of inducing a dramatic decline in phytochrome mRNA abundance in response to a saturating red light pulse. Despite the ability of green portions of oat leaves to accumulate phytochrome mRNA and to down‐regulate phytochrome mRNA abundance in response to light, no substantial variation in phytochrome mRNA abundance was observed in green oat seedlings maintained on a 12‐h day/12‐h night cycle. In the same oat seedlings, the abundance of chlorophyll a/b binding protein mRNA fluctuated dramatically during the day/night cycle.
A novel interaction of magnesium translocation with the supply of phosphorus to roots of grapevine (Vitis viniferaL.)*
Authors: SKINNER P. W. , MATTHEWS M. A.
Published: April 2006

Abstract.The role of phosphorus (P) in leaf magnesium (Mg) concentrations and photosynthesis was investigated in field and glasshouse experiments with grapevine (Vitis viniferaL., cvs. Chenin blane. Chardonnay, and Carignane). In the field, leaves of vines growing on soil with low available P exhibited symptoms of Mg deficiency and had low P and Mg concentrations. The rate of photosynthesis for leaves of untreated control vines was approximately 0.7 nmol CO2cm2s1. When P fertilizer was applied to the soil, Mg deficiency symptoms were eliminated, and leaf P and Mg concentrations increased to above critical levels. When Mg was applied as a foliar spray, leaf Mg increased to above critical levels, but leaf P did not change significantly. In both experiments, the rate of photosynthesis increased to greater than 1.0 nmol CO2cm2s1after nutrient applications. Thus, under low soil P conditions, leaf photosynthesis was limited by leaf Mg concentrations. In glasshouse experiments in which vines were grown with and without P for three seasons, Mg accumulated in large roots of ‐ P vines to approximately twice the concentration found in roots of + P vines. Analysis of the xylem exudate from detopped plants showed that Mg concentration in xylem sap of + P vines was twice as great as that in ‐ P vines. When P was supplied to ‐ P vines, the concentration of Mg increased to the concentration of + P vines within 2 days. The results show that the translocation of Mg from roots to shoots of grapevine is dependent upon P supply to the roots and suggest that Mg translocation is more sensitive than uptake to P supply.
Study of the inheritance of seed primary dormancy and the ability to enter secondary dormancy in Petunia: influence of temperature, light and gibberellic acid on dormancy
Authors: GIRARD J.
Published: April 2006

Abstract. The germination behaviour of two Petunia hybrida lines. M30 and Th7, and their reciprocal hybrids was studied. Two sets of experimental conditions appeared helped to distinguish between dormant and non‐dormant parental lines: (1) 25 and 35 °C in the dark, in the latter case after 2 months of dry storage at 20 °C; (2) 35 and 40 °C in the light. Photosensitivity was tested in the first case and sensitivity to GA3 in the second case. The predominance of paternal control over dormancy was evident. A maternal or tegumentary control of photosensitivity and of sensitivity to GA3 was also shown. Transferring the seeds, originally imbibed in conditions expressing primary dormancy, to conditions which previously supported their germination, allowed us to show that secondary dormancy could be easily induced when a deeper primary dormancy had already developed in the seeds.
Influence of nitrate and ammonium on the growth and 2,4‐diaminobutyric acid composition of flatpea (Lathyrus sylvestris L.)
Authors: SHEN L. , FOSTER J. G. , ORCUTT D. M.
Published: April 2006

Abstract. Presence of 2.4‐diaminobutyric acid (A2bu), a neurotoxin, in tissues of flatpea (Lathyrus sylvestris L.) necessitates a thorough understanding of the regulation of this nonprotein amino acid before the species can be recommended to livestock producers for forage applications. To determine how different concentrations and ratios of NO3 and NH+4 in growth media influence the levels of A2bu and other free amino acids in the ‘Lathco’flatpea cultivar, plants were grown hydroponically in controlled environments. The concentration of A2bu was highest in tissues when the NO3 to NH+4 ratio in the nutrient solution was low. Responses of amides and other nonprotein amino acids, especially in the roots, followed a similar trend. Free protein amino acids in leaves and stems were generally unaffected by changes in NO3 to NH+4 ratios. In roots, protein amino acids increased as the NO3 to NH+4 ratio in the growth medium increased. Ammonium inhibited shoot and root growth; NO3 alleviated the toxic effects of NH+4. Soluble protein concentrations were higher in the shoots of NO3‐fed plants and in the roots of plants supplied with NH+4. These results suggest that accumulation of A2bu and other nonprotein amino acids, as well as asparagine and glutamine, plays a role in detoxification of NH+4 and storage of N.
Air pollution in the past recorded in width and stable carbon isotope composition of annual growth rings of Douglas‐fir
Authors: MARTIN B. , SUTHERLAND E. K.
Published: April 2006

Abstract. Tree‐ring indices (TRIs) of annual growth rings in stems of Douglas‐fir (Pseudotsuga menziesii) growing near a copper smelter showed reduced growth during two multi‐year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO2 emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ13C) in cellulose purified from wood formed in such years. Based on current models for 13C/12C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO2 in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution‐related change in δ13C was superimposed on a change with time in δ13C, independent of growth, by ‐ 1.4 per mil from 1902 to 1984.
Sampling Atriplex bladders: a comparison of methods
Authors: BRECKLE S.‐W. , FREITAS H. , REIMANN C.
Published: April 2006

Abstract. A major objection to the convenient sampling of Chenopodiacean bladders by brushing in aqueous solutions is the suspected leakage of ions from the leaf blade. To overcome this problem, a new method of sampling bladder hair is described, which also achieves rapid and quantitative separation and, at the same time, yields bladder samples of undoubtedly high purity. Leakage is stopped by the aid of liquid nitrogen. Comparison of this method to removal of bladders by brushing in aquenous solutions effectively confirm the validity of the customary method beyond dispute.
Blue light effects on stomata are mediated by the guard cell plasma membrane redox system distinct from the proton translocating ATPase
Authors: RAGHAVENDRA A. S.
Published: April 2006

Abstract. The effects of blue light on stomata are critically analysed. Blue‐light‐induced increase in stomatal conductance is preceded by membrane hyperpolarization, proton efflux, potassium uptake and malate synthesis in guard cells. Hypothetically, a flavin containing plasma membrane redox system can pump protons out of guard cells on illumination with blue light. It is proposed that this electrogenic proton pump requires NAD(P)H but does not involve ATP/ATPase.
Net fluxes and pools of nitrogenous compounds during suspension culture of photoautotrophicChenopodium rubrumcells
Authors: BECK E. , RENNER U.
Published: April 2006

Abstract.Suspension cultured cells ofChenopodium rubrumwere grown photoautotrophically under a diurnal light‐dark cycle of 16‐8h. The following phases of the batch culture were differentiated: a short lag, a cell division phase terminated by a pronounced transition to stationary maintenance which finally gradually passed into senescence. Nitrogen fluxes typical of these stages were followed by measuring uptake of NO3and NH4+from the medium and their incorporation into the cellular fractions of nitrogenous compounds. Activities of seven N‐metabolizing enzymes were determined. Compartmentation of enzymes and nitrogenous compounds was analysed after isolation of intact chloroplasts and vacuoles from protoplasts. Eighty‐two per cent of the N originally present in the medium was taken up and incorporated to an extent of 80% into protein until the end of the division phase. Net protein synthesis ceased upon transition to the stationary phase. During the division phase a vacuolar pool of NO3was established and then maintained throughout the resting phase. Free cellular NH4+was not localized within the vacuole and responded to the ammonium content of the medium. Amino acids accumulated in the cells especially during the stationary phase, during which they were present in the vacuole. Typical nitrogen relations are portrayed as flux diagrams for one day of each of the essential developmental phases. The enzyme activities were easily sufficient to account for the observed flow rates of the corresponding nitrogenous compounds. Hence, uptake of NO3and NH4+must be considered as steps limiting N metabolism inChenopodium rubrumcell suspensions.
Stomatal response to humidity in sugarcane and soybean: effect of vapour pressure difference on the kinetics of the blue light response
Authors: ASSMANN S. M. , GRANTZ D. A.
Published: April 2006

Abstract. The effect of atmospheric humidity on the kinetics of stomatal responses was quantified in gas exchange experiments using sugarcane (Saccharum spp. hybrid) and soybean (Glycine max). Pulses of blue light were used to elicit pulses of stomatal conductance that were mediated by the specific blue light response of guard cells. Kinetic parameters of the conductance response were more closely related to leaf‐air vapour pressure difference (VPD) than to relative humidity or transpiration. Increasing VPD significantly accelerated stomatal opening in both sugarcane and soybean, despite an approximately five‐fold faster response in sugarcane. In contrast, the kinetics of stomatal recovery (closure) following the pulse were similar in the two species. Acceleration of opening by high VPD was observed even under conditions where soybean exhibited a feedforward response of decreasing transpiration (E) with increasing evaporative demand (VPD). This result suggests that epidermal, rather than bulk leaf, water status mediates the VPD effect on stomatal kinetics. The data are consistent with the hypothesis that increased cpidermal water loss at high VPD decreases the backpressure exerted by neighbouring cells on guard cells. allowing more rapid stomatal opening per unit of guard cell metabolic response to blue light.
Mechanism of calcium‐dependent salt tolerance in cells of Nitellopsis obtusa: role of intracellular adenine nucleotides
Authors: KATSUHARA M. , TAZAWA M.
Published: April 2006

Abstract. The tonoplasts of internodal cells of Nitellopsis were removed by perfusing the vacuoles with media containing a Ca2 chelator, EGTA. Treatment of tonoplast‐free cells with 100 mol m3 NaCl induces a large membrane depolarization, a drastic decrease in the membrane resistance and an increase in Na+ influx. These events are identical to those that occur in intact cells subjected to high NaCl. These responses to NaCl are prevented if 10 mol m3 Ca2+ is supplied together with 100 mol m3 NaCl. The protective effect of Ca2+ is evident only when the intracellular ATP concentration exceeds 0.1 mol m3 and does not occur full when the intracellular ATP is removed. AMP at concentrations greater than 0.5 mol m3 or 0.25 mol m3 AMPPNP can replace ATP. It is concluded that ATP does not act as an energy source nor as a substrate for protein phosphorylation. ATP seems to exert its effects as a coeffector with Ca2+ in regulating the Na+ permeability of the plasma membrane.
Sink control of nitrogen uptake and assimilation during regrowth after‐cutting of ryegrass (Lolium perenne L.)
Authors: OURRY A. , BOUCAUD J. , DUYME M.
Published: April 2006

Abstract. The 15N isotope was used to compare the uptake and the assimilation of NH4+ and NO3 nitrogen in ryegrass (Lolium perenne L.) during regrowth after cutting. Uptake of nitrate‐N, expressed per plant, was at all times greater than ammonium‐N uptake and assimilation decreased in roots and stubble while its assimilation was maintained at a high level in leaves. It has been suggested that ammonium assimilation is directly related to the availability of carbohydrates in the sink organ (leaves) resulting from their remobilization from the source organs (roots and stubble). Nitrate reduction decreased in all organs, while the uptake of NO3 was still high. After this first period of regrowth, nitrogen assimilation both from nitrate and ammonium increased in all the plants. Nitrate reduction capacity (expressed in μg NO3‐N reduced per g D.W. per d) is 7.5 and 22.5 times greater in leaves than in stubble and roots, respectively. Therefore, nitrogen assimilation in stubble and particularly in roots was mainly dependent on ammonium nitrogen.
Radial and axial turgor pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions
Authors: RYGOL J. , ZIMMERMANN U.
Published: April 2006

Abstract. Radial and axial turgor pressure profiles were measured with the pressure probe in untreated and salt‐treated intact roots of Mesembryanthemum crystallinum. The microcapillary of the pressure probe was inserted step‐wise into the root tissue 5, 25 and 50 mm away from the root cap. For evaluation of the data, only those recordings on a given root were used in which four discontinuous increases in turgor pressure occurred. These four turgor pressure increases could be related to the rhizodermal cells and to the cells in the three cortical layers. The measurements showed that a radial turgor pressure gradient of the same magnitude (directed from the third cortical layer to the external medium) existed along the root axis. The magnitude of this turgor pressure gradient decreased with increasing salinity (up to 400 mol m‐3 NaCl) in the growth medium. Addition of 10 mol m‐3 CaCl2 to the 400 mol m‐3 NaCl medium partly reduced the salt‐induced decrease in turgor pressure, but only in cells 25–50 mm away from the root tip. Combined with this effect, a small axial turgor pressure gradient was generated, therefore, in the cortex layers which was directed to the root tip. Measurements of the volumetric elastic modulus, ɛ, of the wall of the individual cells showed that the presence of salt considerably reduced the magnitude of this parameter and that addition of Ca2+ to the strongly saline medium partially diminished this decrease. This effect was strongest in cells 50 mm away from the root tip. The magnitude of ɛ of rhizodermal and cortical cells increased along the root axis both in untreated and in salt‐treated roots. The ɛ value was significantly smaller for rhizodermal cells compared to the cortical cells, with the exception of cells 50 mm from the tip. In this tissue, rhizodermal and cortical cells exhibited nearly the same values. The decrease of the ɛ‐values with salt and the increase along the root axis under the various growth conditions could be correlated with corresponding changes in cell volume. Diurnal changes in turgor pressure could not be detected in the individual root cells, with the notable exception of the rhizodermal and cortical cells located in the region 50 mm away from the root tip of the control plants. In these cells, an increase in turgor pressure was observed during the morning hours. Determination of the average osmotic pressure in tissue sections along the roots of control and salt‐treated plants revealed that at 400 mol m‐3 NaCl the osmotic pressure gradient between the tissue and the medium is exo‐directed, provided that the water is not (partly) immobilized.
Stomatal response to humidity in a sugarcane field: simultaneous porometric and micrometeorological measurements*
Authors: GRANTZ D. A. , MEINZER F. C.
Published: April 2006

Abstract. Gas exchange data obtained with wellventilated leaf cuvettes provide clear evidence of a stomatal response to leaf‐air vapour pressure difference (V). In contrast, remotely sensed leaf temperatures with specific assumptions regarding canopy boundary layer characteristics, have been interpreted to mean that stomata do not respond to V. We address this apparent discrepancy in a sugarcane field by simultaneous application of a single‐leaf, porometric technique and a whole‐canopy, Bowen ratioenergy balance technique. These methods indicated significant stomatal response to V in well‐irrigated sugarcane. Stomatal responses to V in the field were obscured by strong covariance of major environmental parameters so that opening responses to light and closing responses to V tended to offset each other. Low boundary layer conductance significantly uncoupled V at the leaf surface (Vs) from V determined in the bulk atmosphere (Va). This reduced the range of the stimulus, Vs, thereby reducing the range of the stomatal response, without indicating low stomatal sensitivity to V. Stomatal responses to Va may be smaller than expected from V response curves in cuvettes, since Vs rather than the conventionally measured Va is analogous to V in a well‐stirred cuvette. Recently published conclusions that remotely sensed canopy temperatures are inconsistent with stomatal response to V may be based on erroneous estimates of canopy boundary layer conductance and thus of Vs, use of air saturation deficit rather than V to express evaporative demand, and investigation at higher levels of evaporative demand than those eliciting maximal stomatal response.
Heat shock proteins in Sorghum bicolor and Pennisetum americanum. II. Stored RNA in sorghum seed and its relationship to heat shock protein synthesis during germination
Authors: HOWARTH C.
Published: April 2006

Abstract. During the germination of sorghum, heat shock proteins (HSPs) are synthesized in response to high‐temperature stress at the onset of imbibition. HSP72 and HSP83 are apparently synthesized without a heat shock induction in the first 2 h of imbibition. The presence of RNA encoding HSPs in the quiescent embryo, and in the 2 h imbibed embryo, was confirmed by in vitro translation of RNA isolated from dry mature sorghum seeds. By 24 h of imbibition at 35°C, no translatable RNA was evident for these HSPs unless a heat shock treatment was also given. Treatment of imbibing embryos with cordycepin inhibited RNA synthesis. Protein synthesis was not affected so greatly and HSP synthesis was still inducible although at reduced levels. The involvement of RNA stored in the seed and of de novo transcription in protein synthesis during imbibition is discussed.
The effect of chlorophyll content on changes of photochemical reactions in intact kidney bean leaves
Authors: KOIZUMI M. , KANO H. , KATSURA N. , INADA K.
Published: April 2006

Abstract. Activation spectra of photochemical reactions were measured by a flash spectrophotometer in leaves having varying chlorophyll contents at different stages of greening. The increase of chlorophyll concentration up to 30 nmol cm‐2 elevated the rates of photochemical reactions at all wavelengths of light used, and was found to be produced by an increase in the amounts of reaction centres. Further accumulation of chlorophyll up to 40 nmol cm‐2 was associated with an increase in light‐harvesting chlorophyll, an improved rate of photochemical reactions around 600 nm and at 700 nm, and self‐absorption and screening effects where chlorophyll absorbed maximally (400–450 nm and around 680 nm).
Stable carbon isotope fractionation by marine phytoplankton during photosynthesis
Authors: DESCOLAS‐GROS C. , FONTUNGNE M.
Published: April 2006

Abstract. In the marine environment, the range of values of carbon isotope fractionation between particulate tissue of phytoplankton and inorganic carbon can be more than 20‰ (− 35‰ < δ13C < − 14‰). This review considers the influence of seawater temperature, lipid content of phytoplanktonic cells, kinetic fractionation, and carbon pathway on δ13C values observed at sea.

In order to study the contribution of carboxylases (RUBISCO and the β‐carboxylases phosphoenolpyruvate carboxylase, phosphoenoplpyruvate carboxykinase and pyruvate carboxylase) to variations of particulate δ13C values at sea, we present results obtained simultenously on carboxylase activities and δ13C in various environmental conditions. The lowest δ13C values are clearly associated with predominance of ribulose‐1.5‐bisphosphate carboxylase activity, but it was more difficult to explain the high δ13C values. Different hypotheses are discussed.
The relationship between the Rubisco reaction mechanism and models of photosynthesis*
Authors: COLLATZ G. J. , BERRY J. A. , FARQUHAR G. D. , PIERCE J.
Published: April 2006

Abstract. A new model of photosynthesis published recently in this journal (H. Farazdaghi & G. E. Edwards, Plant, Cell and Environment (1988) 11, 789–798; 799–809) clams to have a more complete mechanistic basis than currently used models based on the paper of G. D. Farquhar, S. von Caemmerer & J. A. Berry (Planta (1980) 149, 78–90). In this paper, we examine the validity of the new kinetic expression for the rate of CO2 fixation by Rubisco, and the derivation of an equation for photosynthetic CO2 assimilation as a function of light intensity and CO2 concentration presented in the new model. In addition, we compare measured response curve of photosynthesis to CO2 and light with simulated curves using alternative models. We conclude that the new model is mechanistically misleading and, empirically, overestimates the extent to which light and CO2 co‐limit the rate of photosynthesis under most physiological conditions.
Physiological responses of the mangroveRhizophora manglegrown in the absence and presence of NaCl
Authors: WERNER A. , STELZER R.
Published: April 2006

Abstract.Propagules of the mangrove,Rhizophora mangleL., were precultivated for 9 months in a greenhouse. The young plants were transferred into unaerated nutrient solutions without and with 200 mol m3NaCl and subsequently their growth, their water relations and the photosynthetic properties of their leaves were studied. Growth of the salttreated plants was significantly increased, while the control plants gradually died off after finishing the experiments. The shoot water potential and the stomatal resistance of the leaves were lowered while the chlorophyll contents and the chlorophyll a/b ratio in the leaves of salt‐treated plants were increased by NaCl, the net result being an enhanced rate of CO2assimilation. The leaves of both sets of plants showed diurnal fluctuations in malic acid concentration which were more pronounced in the leaves of salt treated plants which, additionally, were more succulent. However, the plants showed no net CO2fixation at night, indicating thatRhizophora mangleis a CAM‐cycling plant. After 200 d of cultivation without or with NaCl, the Na+, Cl and K+concentrations in tissues and vacuoles were measured. Energy‐dispersive X‐ray microprobe analyses on root vacuoles of control plants reveal Na+preference, on those of salt treated plants a strong K+preference. Vacuolar K+concentrations are neither affected by NaCl nor do they vary across the root radius. High vacuolar Na+and Cl concentrations are found in the hypodermis followed by a stepwise decrease towards the inner root cortex cells. Ion concentrations of the photosynthetically active leaf tissues seem to be regulated by (1) radial filtration across the root cortex: (2) ion exchange of the xlem parenchyma cells: and (3) sequestration of Na+and Cl in the hypodermal water storage tissue of the leaves.
Photoinhibition in Vitis californica: interactive effects of sunlight, temperature and water status
Authors: GAMON J. A. , PEARCY R. W.
Published: April 2006

Abstract. In a series of factorial experiments with cultivated Vitis californica Benth. (California wild grape) growth outdoors in full sun, we examined the effects of sunlight, temperature and water status on net CO2 uptake and PSH chlorophyll fluorescence at 77K. Exposure to either high light or high temperature caused reductions in PSH activity followed by partial or complete overnight recovery. Upon simulataneous exposure to high light and high temperature, PSH inhibition was severe and persistent. The maximum chlorophyll fluorescence (FM) and the ratio of variable to maximum fluorescence (Fv/FM) differed in their responses to combinations of light and temperature. At both low and high light. FM declined with increasing temperature over a wide temperature range, while Fv/FM exhibited a similar sensitivity to temperature only at high light. Net CO2 uptake declined by mid‐afternoon and recovered by the next morning in most leaves, regardless of incident light or temperature. However, high‐light leaves exhibited severe and lasting declines if temperatures exceeded 45°C. Water‐stressed leaves exposed to high light exhibited greater reductions of net CO2 uptake than water‐stressed leaves exposed to low light. However, the degree of light‐dependent decline in PSH fluorescence (FM and Fv/FM) did not vary with water status, indicating that reduced PSH activity was not a primary cause of reduced carbon gain during water stress.