bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of pH on stomatal sensitivity to abscisic acid
Authors: PATERSON N. W. , WEYERS J. D. B. , A'BROOK R.
Published: April 2006

Abstract.The sensitivity of stomata ofCommelina communisL. to abscisic acid (ABA) was evaluated by analysing the initial rates of response to the compound at different hormone concentrations. This was carried out at pH 6.8 and pH 5.5. The data were modelled and statistically analyzed by means of a computer program employing non‐linear regression techniques and step‐down analysis of variance. The response kinetics as quantified in terms of three sensitivity parameters were found to differ significantly between the two pH values. This finding is discussed in relation to previous research on purified ABA‐binding proteins.
Rhodamine 123 as a vital stain for mitochondria of plant cells
Authors: VANNINI G. L. , PANCALDI S. , POLI F. , FASULO M. P.
Published: April 2006

Abstract. Rhodamine 123 (Rh 123), a relatively new mitochondrial marker, little used in the study of plant cells, was tested on excized leaves of Elodea canadensis Michx. and on suspension‐cultured cells of Ranunculus serbicus Vis. In both preparations, the dye accumulated rapidly and selectively in the mitochondria whose number, morphology and cell distribution could be easily observed. In the presence of Rh 123, cytoplasmic movements could also be perceived and the spatial arrangement of the mitochondria with respect to that of the auto‐fluorescent chloroplasts was studied in connection with a normal or altered cytoskeletal framework. The specific uptake of Rh 123 by the organdies seemed to be potential‐dependent since it was influenced by cations, ionophores and inhibitors of electron transport. Short exposures to the stain were practically non‐toxic, whereas prolonged treatments (6–20 h) provoked specific alterations in structure of the mitochondria. The data reported here indicate that Rh 123 may be an excellent vital stain to study the morphology, function and dynamics of the mitochondria in living plant cells.
The citrus leaf cuticle in relation to measurement of leaf water potential using thermocouple psychrometers*
Authors: OOSTERHUIS D. M. , PARKER M. L. , WULLSCHLEGER S. D. , KIM K. S.
Published: April 2006

Abstract. Cuticular resistance to water vapour diffusion is an important aspect of thermocouple psychrometry and may introduce significant error in the measurement of leaf water potential (Ψ). The effect of the citrus (Citrus mitis Blanco) leaf cuticle on water vapour movement was studied using the times required for vapour pressure equilibration during thermocouple psychrometric measurement of Ψ. Cuticular abrasion with various carborundum powders was used to reduce the diffusive resistance of both the adaxial and abaxial leaf surfaces, and the extent of the disruption to the leaf was investigated with light and electron microscopy.

Cuticular abrasion resulted in reduced equilibration times due to decreased cuticular resistance and greater water vapour movement between the leaf and the psychrometer chamber. Equilibration times were reduced from over 5 h in the unabraded control leaves to 1 h with cuticle abrasion. This was associated with the decrease in diffusive resistance with cuticular abrasion from over 55 s cm−1 to less than 8 s cm−1 for both the adaxial and abaxial leaf surfaces.

Scanning electron micrographs of the abraded leaf tissue revealed considerable disruption of the stomatal ledge and of the guard cells, surface smoothing and displacement of waxes into the stomatal aperture, and damage to veins. Observations with the transmission electron microscope revealed frequent disruption of epidermal cell walls, and damage to both the cytoplasmic and vacuolar membranes.
Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures
Authors: SCHONBECK MARK W. , EGLEY G. H.
Published: April 2006

Abstract. Germination responses of redroot pigweed (Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log‐linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm3 m−3 were observed after 32 d, compared to 0.18−1.6 cm3 m−3 after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose‐response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.
Ecophysiological studies on Sonoran Desert plants, VI. Seasonal photosynthesis and production of Machaeranthera gracilis, a winter ephemeral*
Authors: ANDERSON D. A. , SZAREK S. R.
Published: April 2006

Abstract. A comparative study of two chromosomal races of the winter‐active ephemeral Machaeranthera gracilis showed that the seasonal magnitudes of photosynthesis were only slightly greater for a progeny desert race than for an ancestral foothills race. Maximum observed photosynthetic capacity and the seasonal reduction in foliar photosynthesis occurred earlier in the year for the desert race. The relative growth rate was higher in this race up until the time of its peak seasonal biomass. A ratio of harvested net production to estimated gross primary production decreased until anthesis. Photosynthesis contributing to net growth continued into periods with moderate environmental stress. The continuation of growth by the desert race was enhanced by maintenance of a higher root‐shoot ratio, as well as greater relative stem growth. During reproduction, foliar CO2 assimilation could not solely provide the measured dry matter accumulation, suggesting the importance of assimilate contribution by photosynthetic stems. Seasonal increases in the enthalpy content of whole plants and plant organs occurred for both races, indicating the absence of significant translocation during reproduction and the potential for stem photosynthesis.
Ultrastructural features of chilling‐injury in Episcia reptans
Authors: MURPHY COLETTE , WILSON J. M.
Published: April 2006

Abstract. Chilling the leaves of the extremely chill‐sensitive plant Episcia reptans for only a few hours at 5°C causes ultrastructural changes such as swelling and disorganization of chloroplasts and mitochondria, and vesiculation of cytoplasmic membranes. Rewarming plants after 5–6 h chilling causes further deterioration in chloroplast and mitochondrial structure and the appearance of fibrous material in the cytoplasm of epidermal, mesophyll and vascular cells. The nature of the deposit is not known but it may be the cause of the rapid development of chilling‐injury on return of plants to the warmth.
The utilization of bicarbonate ions by the macroalga Ascophyllum nodosum (L.) Le Jolis
Authors: JOHNSTON A. M. , RAVEN J. A.
Published: April 2006

Abstract A comparison of some of the methods used to determine whether aquatic plants have the ability to utilize bicarbonate ions as a source of inorganic carbon for photosynthesis has been applied to the intertidal macroalga Ascophyllum nodosum. These include: observing photosynthesis at a high pH (below the alga's CO2 compensation point), pH compensation point determinations, comparing the photosynthetic characteristics at low pH (5.20) and at high pH (7.95), estimating the maximal rates at which CO2 can diffuse through the unstirred layer and the rate at which CO2 can be produced from bicarbonate dehydration in the unstirred layer. All indicated that Ascophyllum nodosum can use bicarbonate ions for photosynthesis, though some were not always consistent. Calculating the total inorganic carbon concentration from pH measurements and acidification CO2 determinations revealed that the assumption that the alkalinity remains constant during pH drift experiments is not always valid.
Involvement of calcium ion in turgor regulation upon hypotonic treatment in Lamprothamnium succinctum
Authors: OKAZAKI Y. , TAZAWA M.
Published: April 2006

Abstract When internodal cells of Lamprothamnium succinetum were exposed to a hypotonic medium containing more than 1 mol m−3 Ca2+, the elevated turgor pressure decreased and reached a steady state within 30–60 min. The hypotonic treatment caused the membrane potential to depolarize, with a time lag of ca. 1 min. The membrane conductance increased transiently with the same time lag and reached a peak value within 2–3 min. When the external Ca2+ concentration was lowered to 0.01 mol m−3, both turgor regulation and change in the membrane conductance were strongly inhibited, although the membrane depolarization was not affected. When the Ca2+ level was returned to the normal level, the cells recovered their ability for turgor regulation and the membrane conductance attained a peak value after ca. 15–30 s. This response time is definitely shorter than that needed for the conductance change in cells exposed to a hypotonic medium having a normal level of Ca2+ from the beginning. We thus conclude that at least two sequential processes are involved in turgor regulation: a Ca2+ ‐independent process, followed by a Ca2+‐dependent process.
Water stress effects on guard cell anatomy and the mechanical advantage of the epidermal cells
Authors: SPENCE R. D. , WU H. , SHARPE P. J. H. , CLARK K. G.
Published: April 2006

AbstractVicia faba plants grown under water deficit were found to have guard cells considerably smaller than those of plants grown under well‐watered conditions. Stomala of plants adapted to drought conditions have been observed in past studies to maintain opening at plant water potentials lower than those of plants not so adapted. By employing the geometric interpretation of the mechanical advantage (Wu, Sharpe & Spence, 1985), an anatomical/mechanical basis was found that helps explain how such opening in drought conditions can occur. The geometry and resulting mechanical properties of small stomata, in contrast to larger stomata, give them the capability of opening or maintaining open pores with lower guard cell turgor pressures, relative to the turgor of the surrounding epidermal cells.
Photosynthetic electron transport and establishment of an associated trans‐thylakoid proton electrochemical gradient during development of the wheat leaf
Authors: WEBBER A. N. , BAKER N. R. , PAIGE CANDIDA D. , HIPKINS M. F.
Published: April 2006

Abstract Photosynthetic electron transport activities and the ability to generate and maintain a trans‐thylakoid proton electrochemical gradient were examined during chloroplast development in 4‐day‐old wheat leaves grown under a diurnal light regime. Polarographic and spectropholometric studies on leaf tissue demonstrated that poorly developed chloroplasls at the leaf base could photo‐oxidize water and transfer electrons from photosystem 2 to photosystem 1. The capacity for non‐cyclic whole‐chain electron transport increased during chloroplast development. Thylakoids isolated from the leaf base, although capable of pumping protons into the inlrathylakoid space, could not maintain a trans‐membrane proton electrochemical gradient; this ability developed at later stages of chloroplast biogenesis in the leaf. The implications of these results for the energetics of the developing leaf are discussed.
Physical, chemical and spectral properties of leaf surfaces of Berberis aquifolium (Pursh.)
Authors: SEYMOUR VIRGINIA
Published: April 2006

Abstract The leaves of Berberis aquifolium (Pursh.) exhibit either diffuse or specular (shiny) reflection, depending on the variety, but in no case are the leaves obviously glaucous. The dull‐surfaced leaves were less wettable than the glossy ones. Using scanning electron microscopy it was determined that the diffuse reflection was due to tubular crystals of wax 250 nm in diameter. The crystals were primarily composed of 19‐nonacosanol, a 29‐carbon secondary alcohol, as determined by gas chromatography‐mass spectrometry. The chemical constituents of the wax underlying the tubes appeared to be the same as those of the wax from glossy leaves, with 29‐carbon and 31‐carbon n‐alkanes and n‐heptacosanol as major constituents. The reflection spectra of dull‐surfaced (diffuse reflection) or glossy (specular reflection) leaves were the same, as were those of leaves with different amounts of epicuticular wax. Removing the epicuticular wax with chloroform did not change the spectrum.
A dynamic model for photosynthesis by an aquatic plant,Egeria densa
Authors: LAING W. A. , BROWSE J.
Published: April 2006

AbstractThis paper describes a dynamic model for photosynthesis by an aquatic plant,Egeria densa.The model takes into account an HCO−3pump, high diffusion resistances and PEP carboxylase, and develops a set of differential equations to form the time‐dependent solutions for photosynthesis. The predicted changes in pH, [CO2]aqand total inorganic carbon are compared with experimental data and the model is found to describe the data.

The model is then used to examine the effect of O2on photosynthesis under these conditions, and shows that the increase in internal CO2concentration due to the recycling of photorespiratory CO2directly stimulates gross CO2fixation and can more than compensate for the O2inhibition of gross photosynthesis. The importance of the HCO−3pump in O2inhibition is also examined.

The CO2compensation point (where inorganic carbon influx and efflux are equal) is examined and the importance of the HCO−3pump and PEP carboxylase in reducing the compensation concentration is discussed.

The model was developed in order to study the photosynthesis of an aquatic weed, which will be reported in a later paper.
Temperatures and thermal tolerances for cacti exposed to high temperatures near the soil surface
Authors: NOBEL P. S. , GELLER G. N. , KEE S. C. , ZIMMERMAN A. D.
Published: April 2006

Abstract Soil surface temperatures in deserts can reach 70 °C, far exceeding the high‐temperature tolerance of most vascular plants of about 55 °C. In this study a computer model indicated that the maximum temperatures of small spherical cacti would approach soil surface temperatures, in agreement with measurements on seedlings of Ferocactus acanthodes. Shortwave radiation was the most important environmental variable affecting maximum cactus temperatures: a 70% reduction in shortwave radiation by shading lowered both predicted and measured stem surface temperatures by 17 °C for plants 2 cm in diameter. High‐temperature tolerance, measured as the temperature that halved the fraction of cells taking up a vital stain after a 1 h high‐temperature treatment, could reach 60 °C for the detached stems of Opuntia bigelovii, which appears crucial for its vegetative reproduction, and 70 °C for O. ficus‐indica, apparently the greatest high‐temperature tolerance so far reported for higher vascular plants. Two‐fold increases in shortwave absorptance from Epithelantha bokei to Mammillaria lasiacantha to Ariocarpus fissuratus led to a 5 °C predicted increase in maximum temperature. However, compensatory differences in high‐temperature tolerances occurred for these dwarf cacti, helping to explain their occurrence in the same open habitat in the Chihuahuan Desert. All six species showed acclimation of their high‐temperature tolerance as ambient temperatures were increased, including acclimation by the roots of the dwarf cacti, where the greater sensitivity to high temperatures of roots would exclude them from the upper 2 cm of the soil. Using the model, the observed high‐temperature acclimation, and the temperatures needed to reduce stain uptake to zero, the three dwarf cacti were predicted to be able to survive soil surface temperatures of up to 74 °C.
Membrane deletion during plasmolysis in hardened and non‐hardened plant cells
Authors: JOHNSON‐FLANAGAN A. M. , SINGH J.
Published: April 2006

Abstract Video recordings of interference phase contrast microscopy were used to study plasmalemma deletion during plasmolysis in hardened and non‐hardened suspension cultured cells of Brassica napus, alfalfa, and cells isolated from rye seedlings. Although different hardening regimes and different cells were used, the responses to plasmolysis were consistent. Hardened cells uncoupled the volume to surface area ratio during plasmolysis both by forming a large number of strands between the cell wall and protoplast and by leaving rivulet‐like networks of membranes on the cell wall surface. Tonoplast membrane was deleted as sac‐like intrusions into the vacuole. Non‐hardened cells produced few strands during plasmolysis. They also deleted plasmalemma and tonoplast into the vacuole as endocytotic vesicles. During deplasmolysis of hardened cells both the individual membrane strands and the rivulets of membrane material vesiculated into strings of vesicles. The vesicles were osmotically active and were re‐incorporated into the expanding protoplast. Conversely, deplasmolysis in non‐hardened cells resulted in few osmotically active vesicles and many broken strands. The vacuolar sac‐like intrusions in hardened cells were re‐incorporated into the vacuole whereas the endocytotic vesicles in non‐hardened cells were not re‐incorporated. Therefore, the non‐hardened cells underwent expansion‐induced lysis.
C4 acid decarboxylation type in Eragrostis (Poaceae) patterns of variation in chloroplast position, ultrastructure and geographical distribution
Authors: PRENDERGAST H. D. V. , HATTERSLEY P. W. , STONE N. E. , LAZARIDES M.
Published: April 2006

Abstract We investigated the activity of C4 acid decarboxylating enzymes, the PCR (‘photosynthetic carbon reduction’, or ‘Kranz’) bundle sheath anatomy and ultrastructure, and the geographical distribution of Australian species of the C4 grass genus Eragrostis. Species had either the even sheath outline and centripetally located PCR cell chloroplasts characteristic of NAD‐malic enzyme (NAD‐ME) species (29 spp.), the uneven sheath outline and centrifugal PCR cell chloroplasts characteristic of PEP carboxykinase (PCK) species (28 spp.), or were intermediate between these types (7 spp.). The suberized lamella was present in PCR cell walls of species with PCK‐like and intermediate anatomy, and absent from those of species with NAD‐ME‐like anatomy. Biochemical determination of C4 type for 11 species, however, revealed only NAD‐ME activity, irrespective of anatomical type; no PCK activity was detected. PCK‐like species arc most numerous in northern, high rainfall, tropical Australia and also predominate in relatively humid coastal and subcoastal areas. NAD‐ME‐like species are numerically and proportionally dominant where rainfall is < 30 cm year−1. Overall, as many species occur in high as in low rainfall areas. Results are discussed in relation to previously established anatomical/ultrastructural/geographical/biochemical correlations and to Infrageneric taxonomy.
Flowering of Pharbitis nil is controlled by an endogenous semidian rhythm
Authors: KING R. W. , EVANS L. T. , HEIDE O. M.
Published: April 2006

Abstract Flowering of Pharbitis nil after an inductive dark period is greatly influenced by far‐red (FR) irradiation during the preceding light period. The response to FR is rhythmic in otherwise constant conditions, and the period of the oscillation is approximately 12 h (i.e. semidian). The rhythm also appears to operate under daily light‐dark cycles. The expression of this novel rhythm depends on the time from the beginning of FR pretreatment to the onset of the inductive dark period. The cotyledons are the site of response to both the pretreatment and inductive darkness, and both these conditions must be perceived by the same cotyledon.
NaCl effects on 4‐desmethylsterol composition of plasma‐membrane‐enriched preparations from citrus roots
Authors: DOUGLAS T. J.
Published: April 2006

Abstract The free 4‐desmethylsterol composition of plasma‐membrane‐enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m−3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE‐54 fused silica) columns and the sterols were identified by combined gas chromatography‐mass spectrometry (GC‐MS).

Only three 4‐desmethylsterols were positively identified by GC‐MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4‐desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m−3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes.

Salt‐induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl− in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl− exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl− exclusion ability in citrus is presented.
Phospholipid, galactolipid and free sterol composition of fibrous roots from citrus genotypes differing in chloride exclusion ability
Authors: DOUGLAS T. J. , SYKES S. R.
Published: April 2006

Abstract Fibrous roots of four citrus hybrids and parent rootstocks from which the hybrids were generated, all selected for their different Cl− exclusion abilities, were assayed for phospholipid, galactolipid and free 4‐desmethylsterol content. There was no correlation between a plant's ability to exclude Cl− and the level of either phospholipid, galactolipid, or total free sterol in the roots of control plants. However, an inverse correlation was established between the ratio of phospholipid to free sterol in control roots and total leaf Cl− levels of plants treated with 50 mol m−3 NaCl for 56 d.

With the exception of a significant decrease in hybrid 80‐05‐05, galactolipid levels were unaffected by salt treatment. Phospholipid levels were significantly increased in two parent rootstocks viz. Trifoliate orange (Poncirus trifoliata (L.). Raf.) and Carrizo citrange (Citrus sinensis (L.) Osbeck ×P. trifoliata) and one hybrid (80‐02‐08) but were otherwise unchanged by salt treatment. Free sterol levels were significantly increased by salt treatment in all of the better Cl− excluders except Carrizo citrange i.e. in Rangpur lime (Citrus reticulata Blanco var. austera hybrid?), Cleopatra mandarin (Citrus reticulata Blanco) and all hybrids except 80–05–13. In all genotypes examined, salt‐treatment resulted in a significant decrease in the ratio of sitosterol to stigmasterol reflecting, primarily, an increase in the stigmasterol level. The two poorer Cl− excluders (Trifoliate orange and hybrid 80–05–13) both underwent a significant decrease in the ratio of ‘more planar’ to ‘less planar’ sterols.

The inverse correlation between the phospholipid to free sterol ratio of control plants and leaf Cl− level of salt treated plants suggests that this ratio has the potential to be used as a biochemical marker of Cl− exclusion ability in citrus.
Seed germination in Chenopodium album L.: further evidence for the dependence of the effects of growth regulators on nitrate availability
Authors: SAINI H. S. , BASSI P. K. , SPENCER M. S.
Published: April 2006

Abstract Chenopodium album L. plants, grown under controlled environmental conditions on different levels of soil nitrate, produced seeds with proportionately different NO−3 contents. Regardless of the endogenous NO−3 content, few seeds germinated in water or upon treatment with KNO3. Ethylene promoted germination, and the extent of germination was positively correlated with the endogenous seed NO−3 content. Combined application of ethylene and KNO3 in the dark had a synergistic effect on NO−3 ‐deficient seed. The synergism between ethylene and KNO3 was attributable to the NO−3 moiety of the nitrate salt. Ethylene and light showed moderate synergism in seeds with low or high endogenous nitrate. Addition of nitrate, however, masked the interaction between ethylene and light. Gibberellic acid4+7 (GA4+7) or red light, each alone or combined with KNO3, had little effect on germination. When applied together in the dark, ethylene and GA4+7 synergistically enhanced the germination of NO−3‐deficient seed. The combined effects of the two hormones on this seed were further enhanced by the addition of KNO3. There was no synergism between ethylene and GA4+7 in NO−3‐rich seed. These interactions among GA4+7, ethylene and KNO3 were not affected by light. The results confirm and further elaborate our earlier finding that the sensitivity of C. album seeds to ethylene may depend on nitrate availability.
The nitrogen balance ofRaphanus sativusXraphanistrumplants. I. Daily nitrogen use under high nitrate supply
Authors: SCHULZE E.‐D. , KOCH G. , PERCIVAL F. , MOONEY H. A. , CHU C.
Published: April 2006

AbstractGrowth‐chamber cultivatedRaphanusplants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m−3(NO−3) in a balanced nutrient solution, the oldest leaves (eight‐leaf stage) accumulated 2.5% NO−3‐nitrogen (NO3‐N) in their lamina, and almost 5% NO3‐N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol−3m−3concentration of NO−3in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO−3uptake, NO−3fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by anin vivotest. NO−3uptake by roots and mesophyll cells was greater in the light than in the dark. The NO−3concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO−3was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty‐four per cent of the NO−3influx was turned into organic nitrogen, with the remaining NO−3accumulating in both the light and the dark.
Effects of Cr on proton extrusion, potassium uptake and transmembrane electric potential in maize root segments
Authors: ZACCHEO P. , COCUCCI M. , COCUCCI S.
Published: April 2006

AbstractProton extrusion of maize rootZea mayssegments, was inhibited by the presence of Cr (o.n. + 6; present in solution as CrO42‐, Cr2O72‐) in the incubation medium: the minimum inhibiting concentration was 2 × 10−3mol m−3and the inhibition progressively increased with Cr concentration. Cr inhibited proton extrusion. Also, when this activity was stimulated by the presence of K+or fusicoccin (FC) in the incubation medium, the K+and FC stimulating effect was still present when proton extrusion was inhibited by Cr. In addition, Cr inhibited K+uptake. This inhibition was higher (50%) at K+concentrations up to 1 mol m−3lower (15%) at higher K+concentrations. This result indicates that the system responsible for K+uptake operating at low K+concentrations is more sensitive to Cr inhibition. Cr had no effect on transmembrane electric potential (PD). The depolarizing and hyper‐polarizing effect of K+ and FC, respectively, were not affected by Cr; but Cr enhances the depolarizing effect of the uncoupler carbonylcyanidem‐chlorophenylhydrazone (CCP). These results indicate that Cr inhibited the proton translocating mechanism coupled with K+uptake, but did not change the net transport of charges through the plasmalemma. The Cr effect is discussed, taking into account the possibility of a direct effect of Cr at the membrane level or, alternatively, of an effect on some metabolic processes controlling membrane function.
Stomatal mechanism as the basis of the evolution of CAM and C4 photosynthesis
Authors: COCKBURN W.
Published: April 2006

Abstract. The similarities between the component reactions of the presently known variants of photosynthetic carbon metabolism (crassulacean acid metabolism, the acid metabolism of Tillandsia usneoides, aquatic acid metabolism, and C4 photosynthesis) when considered along with their widely scattered taxonomic distribution strongly suggest polyphyletic origins resulting from evolutionary modification of a common, universally distributed metabolic sequence. The synthesis and consumption of four‐carbon acids in the cation‐balancing reactions involved in the regulation of stomatal aperture appear to exhibit all of the characteristics likely to be displayed by such a metabolic progenitor.

The present status of the proposal that the expression of aspects of stomatal metabolism in photosynthetic mesophyll cells represents the basis for the evolution of the variant of photosynthetic carbon metabolism is discussed. The prospects of experimental approaches which may yield information relevant to the proposal are also explored.
Photosynthesis, photorespiration and nitrogen metabolism
Authors: WALLSGROVE ROGER M. , KEYS ALFRED J. , LEA PETER J. , MIFLIN BENJAMIN J.
Published: April 2006

Abstract. The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO2‐fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C3 plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions.
Photosynthetic electron transport in relation to thylakoid membrane composition and organization
Authors: ARC J. BARBER
Published: April 2006

Abstract.A review is given of the organization and properties of thylakoid membrane proteins and lipids as a basis for understanding the factors which regulate the light reactions of photosynthesis. Particular emphasis is placed on the lateral organization of the major intrinsic multipeptide complexes and on the importance of diffusional processes in controlling the kinetics of electron transport and the distribution of light energy between photosystems 1 and 2.
The uptake of inorganic carbon by freshwater plants
Authors: WALKER N. A.
Published: April 2006

Abstract. The uptake of bicarbonate for photosynthetic assimilation by charophyte plants uses a chemiosmotic mechanism involving primary outward active transport of H+ in ‘acid zones’ of the membrane, and passive H+ re‐entry in spatially separate ‘alkaline’ zones. In the process large electric currents circulate in the medium, and large local pH changes occur; bicarbonate ions, diffusing inwards across the unstirred layer of medium, encounter a number of competing mechanisms for the transfer of the carbon across the membrane. These are:

transport of H2CO3 by diffusion

transport of CO2 by diffusion; or

co‐transport of HCO3 and H+.

The decision amongst these mechanisms is not yet possible. There are parallels between the charophytes and aquatic angiosperms that are indicated, and contrasts with the chlorophytes.
Nitrate uptake into Pisum sativum L. cv. Feltham First seedlings: commonality with nitrate uptake into Chara corallina and Hordeum vulgare through a substrate cycling model
Authors: DEANE‐DRUMMOND C. E.
Published: April 2006

Abstract Net NO3−, uptake into Pisum sativum L. seedlings temporarily ceased in the presence of very low NH4 concentrations (δmmol m−3). The sensitivity to NH4+ was apparent for seedlings grown in nitrogen‐free conditions with or without NO3− pretreatment, although in the latter case the inhibitory effects were more obvious because net NO3− uptake was higher. NO3− influx, measured using 36ClO3− tracer, was unaffected by NH4+ though pretreatment with NO3− for 24 h slightly stimulated influx. The inhibitory effects of NH4+ were attributed to its effects on stimulating NOJ efflux, which, under certain conditions, was moving against its electrochemical gradient.

A theoretical model has been devised that involves NO3− cycling across the plasmalemma, with distinct parallel influx and efflux pathways, which improves the sensitivity to substrate and effectors and provides a means for control of internal pool size. The sensitivity of net flux (J) to effectors of the influx step (I) is a function of (1 +E/J), and the sensitivity of J to effectors of the efflux step (E) is a function of ‐ E/J. The model has been used to quantify the relative sensitivity of nitrate influx and efflux processes to nitrate and ammonium for Pisum sativum, Chara corallina and Hordeum vulgare. As steady state is reached, sensitivity of net flux (J) to NO3− increases, whereas sensitivity to NH4+ decreases.
Local climate, topography and plant growth in Lathkill Dale NNR. I. A twelve‐year summary of solar radiation and temperature
Authors: RORISON I. H. , SUTTON F. , HUNT R.
Published: April 2006

Abstract Data concerning the local climate experienced on the north and south slopes of a limestone dale are presented and interpreted in the form of sequences of monthly means, fitted annual and diurnal waves and tables of integrals and grand means.
Endogenous ion currents traverse growing roots and root hairs of Trifolium repens
Authors: MILLER A. L. , RAVEN J. A. , SPRENT J. I. , WEISENSEEL M. H.
Published: April 2006

Abstract The patterns of naturally growing ion currents associated with horizontally growing roots of Trifolium repens L. seedlings were measured in a simple low‐salt bathing medium using a highly sensitive vibrating electrode. Current consistently enters the main elongation zone of the root and leaves from mature, elongated tissue. This current enters and leaves with densities of ca. 4.0–11.0 mA m−2 and 4.0 mA m−2, respectively. Current was also delected entering the zone of emerging root hairs and also the root‐hair tips themselves.

These results are a further example of the involvement of self‐generated electrical fields in plant developmental processes. Possible, secondary rhizosphere‐associated effects of the extracellular loop of the developmental current are also suggested.
Structure and properties of pectin gels in plant cell walls
Authors: JARVIS MICHAEL C.
Published: April 2006

Abstract This review deals with recent advances in the structural characterization of pectins and the gels which they form, in relation to auxin‐induced extension growth, the ripening of fruit, and cellular recognition. Pectins are block polysaccharides. Heavily branched, largely methyl‐esterified blocks alternate with unbranched blocks of varying degrees of esterification. The unbranched, non‐esterified blocks can aggregate through calcium binding to form the junction zones that hold a gel together. The aggregates are of two, or possibly four, chains at low calcium levels, and larger with excess calcium. The fall in wall pH during auxin‐induced growth activates glycanase enzymes. These may attack some components of the pectic fraction, as well as xyloglucans. Pectin‐bound calcium ions may be displaced but this probably has little effect on gel strength. Pectins may be cross‐linked by diferulate esters when growth stops. The softening of ripe fruit is due to loss of cohesion in the pectin gel. In apples this results from replacement of the pectins by more esterified forms. In many other fruits it results from depolymerization by polygalacturonases, assisted by pectinesterases, so that the remaining segments are too short for effective calcium binding. Pectins have a further role in the recognition reactions between plant cells and some of their bacterial and fungal pathogens.
Use and abuse of osmo‐terminology
Authors: REED ROBERT H.
Published: April 2006

Abstract The terminology currently employed in studies concerned with the osmotic responses of plant cells is reviewed with specific reference to (1) the suitability of expressions in general use and (2) the application of such terms to experimental studies. The widely used term osmoregulation is shown to be an inappropriate and misleading expression when used to describe the adjustments in cellular solute concentration which frequently accompany changes in external salt concentration. Such usage of osmoregulation should be discouraged; more suitable expressions (e.g. osmoacclimation, osmotic adjustment, turgor/volume regulation or turgor maintenance, osmoadaptation) should be employed, depending upon the context.
Acclimation of leaf growth to low water potentials in sunflower
Authors: MATTHEWS MARK A. , VAN VOLKENBURGH E. , BOYER JOHN S.
Published: April 2006

Abstract Leaf growth is one of the most sensitive of plant processes to water deficits and is frequently inhibited in field crops. Plants were acclimated for 2 weeks under a moderate soil water deficit to determine whether the sensitivity of leaf growth could be altered by sustained exposure to low water potentials. Leaf growth under these conditions was less than in the controls because expansion occurred more slowly and for less of the day than in control leaves. However, acclimated leaves were able to grow at leaf water potentials (Ψ1) low enough to inhibit growth completely in control plants. This ability was associated with osmotic adjustment and maintenance of turgor in the acclimated leaves. Upon rewatering, the growth of acclimated leaves increased but was less than the growth of controls, despite higher concentrations of cell solute and greater turgor in the acclimated leaves than in controls. Therefore, factors other than turgor and osmotic adjustment limited the growth of acclimated leaves at high ψ1 Four potentially controlling factors were investigated and the results showed that acclimated leaves were less extensible and required more turgor to initiate growth than control leaves. The slow growth of acclimated leaves was not due to a decrease in the water potential gradient for water uptake, although changes in the apparent hydraulic conductivity for water transport could have occurred. It was concluded that leaf growth acclimated to low ψ1, by adjusting osmotically, and the concomitant maintenance of turgor permitted growth where none otherwise would occur. However, changes in the extensibility of the tissue and the turgor necessary to initiate growth caused generally slow growth in the acclimated leaves.
Leaf expansion in sunflower as influenced by salinity and short‐term changes in carbon fixation
Authors: RAWSON H. M. , MUNNS RANA
Published: April 2006

Abstract With a view to defining factors regulating the growth responses of sunflower to salinity, plants were grown in solution culture (0, 50 or 100 mol m−3 NaCl) and under natural light, and the areas of every leaf measured once or twice daily from 22 until 38 d after germination. During this period, carbon availability for growth was manipulated by changing light levels and by the use of a photosynthesis inhibitor, DCMU.

Salinity reduced relative leaf expansion rates per plant (RLER) by an average of 0.04 (50 mol m−3) and 0.08 (100 mol m−3) m2 m−2 d−1 compared with control plants of equivalent leaf area: the effects were found in expanding leaves regardless of age or size.

Control plants expanded faster during the day than the night, but plants grown in salt had an almost constant RLER throughout the 24 h, indicating that salt influences the rate of utilization of assimilates independently of their production. DCMU reduced RLER considerably in both control and salt‐treated plants and reduced the advantage of control plants during the day. Conditions of low light also reduced the differences in RLER between control and salt‐treated plants.

When salt was removed from the root medium of non‐DCMU plants, the expansion rates equalled that of the controls within 24 h and remained at the same levels for the following 3 d measurement period: this recovery applied to leaves of all ages. Salt‐grown plants with no photosynthesis (DCMU treatments) also increased their expansion rates upon removal of salt from the root medium, thus providing further evidence that growth was not limited by carbohydrate status, i.e. that salt influences growth primarily via its effects on the rate of utilization of stored assimilates.
Increase in calmodulin level in the early phases of radish seed (Raphanus sativus) germination
Authors: COCUCCI MAURIZIO
Published: April 2006

Abstract Calmodulin (Cam), the heat‐stable, ubiquitous, Ca2+‐dependent regulator protein, has been purified to apparent homogeneity from germinating radish seeds (Raphanus sativus). The characteristics of radish Cam‐molecular weight, absorption spectrum, Ca2+‐dependent activation of brain phosphodiesterase (PDE)‐are very similar to those described for Cam from other plant materials. Radish Cam, like other plant Cam, shows some differences to Cam of calf brain.

The total amount of Cam in radish embryos at 24 h of germination is ca. 37 μg g−1 fresh weight. Approximately 95% of the total amount of Cam is present in the soluble fraction (supernatant at 100,000 g).

The level in the embryo axis strongly increases in the first 24 h of germination (+540%); this increase is strongly reduced when the germination is inhibited by abscisic acid (ABA). In the presence of Ca2+, no ‘free’ Cam (i.e. not bound to other structures) is present in the soluble fraction, suggesting that, during early germination, Cam level is a limiting factor for the activities of Ca2+ ‐Cam‐dependent systems. These studies suggest that Cam plays an important role in the early phases of seed germination.

An inhibitor of the Ca2+‐Cam‐dependent phosphodiesterase is present in the soluble fraction from radish embryos; this substance decreases during germination. A possible role of this inhibitor during the early germination phases is hypothesized.
Differential effects of ecotoxicological substances on lipid peroxidation of plant cell protoplasts
Authors: SCHNABL H. , KÜNNE J. , FLORSCHÜTZ K. , YOUNGMAN R. J.
Published: April 2006

AbstractThe determination of ethane formation in the light and dark in the presence and absence of SHAM provides a memthod for the elucidation of the mechanism of membrane destruction in plant cell protoplasts, induced by chemical treatment. Accordingly, PCP is postulated to act via radical and enzymic‐mediated lipid peroxidation. In contrast, HgCl2appears to inhibit the enzymic pathway, and causes damage to the membranes via a radical mediated mechanism alone.
Abscisic‐acid‐induced turion formation in Spirodela polyrrhiza L. IV. Comparative ion flux characteristics of the turion and the vegetative frond and the effect of ABA during early turion development
Authors: SMART CHERYL C. , TREWAVAS ANTHONY J.
Published: April 2006

Abstract Using the method of compartmental analysis, the ion fluxes and compartment concentrations of Ca2+, K+ and Cl‐ have been compared in the untreated vegetative frond and the abscisic acid (ABA) induced turion of Spirodela polyrrhiza. The ABA‐induced turion is characterized by reduced Ca2+ exchange across the tonoplast and low vacuolar Ca2+ concentration relative to the vegetative frond. In addition the turion exhibits a higher plasmalemma flux with a correspondingly high Ca2+ concentration in the cytoplasm. The concentration of K+ and Cl‐ is much lower in the cytoplasm of the ABA‐induced turion than in the vegetative frond with the influx/efflux ratio at both the plasmalemma and the tonoplast being less than 1, a finding exhibited also in dormant storage tissue.

Treatment of vegetative fronds with ABA for 18 h resulted in a reduced K+ plasmalemma efflux relative to untreated vegetative fronds and a concomitant increase in the cytoplasmic concentration. There was no rapid effect of ABA on Ca2+, K+ or Cl‐ fluxes through either membrane. These results are consistent with the notion that drastic changes in ion fluxes and concentrations in the turion are a secondary consequence of ABA‐induced development, possibly due to prior regulation by ABA of enzymes inherent to processes involved in membrane transport.
Time course of photosynthetic temperature acclimation in Carex eleocharis Bailey
Authors: VERES JOHN S. , WILLIAMS GEORGE J.
Published: April 2006

Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo‐synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf.
Long‐term culturing of plants with aseptic roots Determination of rape root exudates
Authors: HÄGGQUIST MAJ‐LIS , SVENNINGSSON HELEN , OLSSON STEFAN , SUNDIN PETER , ODHAM GÖRAN , LILJENBERG CONNY
Published: April 2006

Abstract A plant culture system allowing growth of aseptic roots has been designed. One version of the system comprises vessels developed for plant root‐microorganism interaction studies in series. A second version has been built for measurements of different physiological parameters of the shoot and root system during growth periods of at least 2 months. The system was tested by determining soluble organic carbon glucose and sucrose in the root exudates of rape plants (Brassica napus L.) grown for 3 weeks in the culture system. The plants were cultivated with a sterile or a non‐sterile root system, or with a root system infected with Verticillium dahliae Kleb.
Catabolism of indole‐3‐acetic acid in chloroplast fractions from light‐grown Pisum sativum L. seedlings
Authors: BROWN B. H. , CROZIER A. , SANDBERG G.
Published: April 2006

Abstract The catabolism of indole‐3‐acetic acid was investigated in chloroplast preparations and a crude enzyme fraction derived from chloroplasts of Pisum sativum seedlings. Data obtained with both systems indicate that indole‐3‐acetic acid undergoes decarboxylative oxidation in pea chloroplast preparations. An enhanced rate of decarboxylation of [1′‐1C]indole‐3‐acetic acid was obtained when chloroplast preparations were incubated in the light rather than in darkness. Results from control experiments discounted the possibility of this being due to light‐induced breakdown of indole‐3‐acetic acid. High performance liquid chromatography analysis of [2′‐14C]indole‐3‐acetic acid‐fed incubates showed that indole‐3‐methanol was the major catabolite in both the chloroplast and the crude enzyme preparations. The identification of this reaction product was confirmed by gas chromatography‐mass spectrometry when [2H5]indole‐3‐methanol was detected in a purified extract derived from the incubation of an enzyme preparation with 32H5]indole‐3‐acetic acid.