bluuebunny/crossref_metadata_2025 huggingface dataset:
The photoperceptive sites and the function of tissue light‐piping in photomorphogenesis of etiolated oat seedlings*
Authors: MANDOLI DINA F. , BRIGGS WINSLOW R.
Published: April 2006

Abstract. Responses to red light irradiation of discrete areas along the intact, etiolated oat seedling indicate that illumination of the region around the coleoptilar node results in maximal coleoptile growth stimulation and mesocotyl growth suppression. Quantitation of the fibre optic properties of these etiolated tissues shows that the amount of axially transmitted light is log linear as a function of distance for both the mesocotyl and coleoptile (plus primary leaf). Using the fibre optic properties of the tissues to predict the response of the etiolated seedling to defined illumination fields allows one to localize two sites of photoperception: although the mesocotyl response pattern can be explained by the action of a single site found near the top of the mesocotyl itself, the coleoptile response depends on irradiation of both the mesocotyl site and an additional site located just above the node. The very low‐ and the low‐fluence responses of etiolated oats independently predict similar regions of the seedling as sites of photo‐perception. The fibre optic properties of the seedling could allow the seedling to increase the effective light signal received by the photosensitive area significantly.
Osmotic adjustment to water stress in pearl millet (Pennisetum americanum[L.] Leeke) under field conditions
Authors: HENSON I. E. , MAHALAKSHMI V. , BIDINGER F. R. , ALAGARSWAMY G.
Published: April 2006

Abstract.Osmotic adjustment, a mechanism whereby plants maintain positive turgor despite low water potential (ψ), was investigated in pearl millet (Pennisetum americanum[L.] Leeke) in three types of field experiment at Hyderabad, India:

Osmotic adjustment during the growing season was evaluated by comparing solute potential (ψs) of leaves taken at midday from irrigated and droughted plots and allowed to rehydrate in the laboratory. The degree of seasonal adjustment was also estimated by comparing observed values of ψsin the field with those expected if ψsdecreased solely in proportion to water loss. Both types of assessment indicated the maximum seasonal adjustment to be about 0.2 MPa. The cultivars BJ 104 and Serere 39 differed in their capacity to adjust osmotically over the season; Serere 39 was least able to osmoregulate.

Measurements of diurnal variations in ψ and ψsinBJ104 revealed osmotic adjustment during the afternoon hours. At a given value of ψ, turgor (ψp) was about 0.1 MPa higher in irrigated, and over 0.2 MPa higher in droughted plants, in the afternoon, than in the morning.

Osmotic adjustment of different leaves within the canopy was investigated. Upper leaves had lower ψ than basal leaves. Differences in ψ were matched by gradients in ψs, so that turgor was similar for all leaf layers.
Effects of norflurazon (San 9789) on light‐increased extractable nitrate reductase activity in soybean [Glycine max (L.) Merr.]seedlings
Authors: DUKE STEPHEN O. , VAUGHN KEVIN C. , DUKE STANLEY H.
Published: April 2006

Abstract. The effects of norflurazon (San 9789) on light‐increased extractable NADH nitrate reductase activity (NRA) in soybean seedlings were studied. Continuous white light (W) increased NRA steadily in root and cotyledonary tissues over a 5 d period. Morflurazon, a pyridazinone herbicide which causes chlorophyll bleaching in W, reduced the initial NRA induction rate in roots and cotyledons. However, in cotyledons of norfiurazon‐treated plants NRA increased at a more rapid rate than in the control after 24 h of W, with activity levels reaching three times those of control seedlings after 5 d. NRA induced by W in control and norflurazon‐treated cotyledons was fluence‐rate dependent. Continuous FR induced equal amounts of NRA in control and norflurazontreated tissues, suggesting that the superinduceable NRA of norflurazon‐treated plants under W is not phytochrome induced. The FR‐induced NRA of control and norflurazon‐treated cotyledons had pH optima of 6.6, but during development under W the pH optimum of control cotyledons changed from 6.3 to between 6.6 and 7.1. The pH optimum of the norflurazon‐induced NRA of the cotyledon under W was about 7.5. The NADH/NADPH NRA ratio after 4 d of W was 1.3 in control and 2.5 in norflurazontreated cotyledons. These data indicate that photosynthelic pigments are involved only secondarily in light‐induction of NRA in this system.
Germination responses of a seed population of Taraxacum officinale Weber to constant temperatures including the supra‐optimal range
Authors: WASHITANI IZUMI
Published: April 2006

Abstract The germination responses of a nondormant fraction of a seed population of Taraxacum officinale Weber at constant temperatures in the range 7–34°C were analysed through a time‐course study. Maximal percentage germination (approximately 90%) was attained at temperatures 10–18°C, where simple linear relationships were observed between the temperature and the germination rates, i.e. the reciprocals of the time taken to germinate by subpopulations with 20–80% germination. There was a variation in the required ‘thermal times’ (θ) which characterized the linear relationships, the distribution of which could be approximated for the seed population by the following distribution function:

image

where m is the median of the distribution, and A is a shape parameter characterizing the pattern of the distribution. Final percentage germination decreased with increasing temperature from 20 to 32°C, where the final percentage germination vs. temperature plotted on a normal probability scale yielded a straight line, indicating the normality of the distribution of the upper limit temperature in the seed population. The estimated mean and standard deviation were 27.25 ± 3.75°C. The rate of germination for the subpopulation with 20–80% germination also decreased with increases in the temperature from 22 to 30°C. If the relationships between the temperature within this range and the rate for the subpopulations with 20–80% germination were approximated by the regression lines, the negative ‘thermal time’ characterizing the yielded linear relationship would have a distribution which could be approximated by the same function with the required thermal time for the relationship of suboptimal range. The parameters m and A for the negative ‘thermal time’ were determined to be 2870 K h and 1.7 × 10‐10 K‐3 h‐3.
Mathematical treatment of water movement in plant cells and tissue: a review
Authors: MOLZ FRED J. , FERRIER JACK M.
Published: April 2006

Abstract. Over the past three decades, many contributions have been made to the development of a mathematical basis for describing water transport in plant cells and tissue. This review paper attempts to summarize the more significant contributions and to outline the concepts upon which the various mathematical analyses are founded.

The paper itself is divided into three major sections. Section I deals with the quantitative water relations of single plant cells. Basic equations are developed which describe the water statics and water dynamics of such cells. Included is a discussion of the theory and methods for measuring the various parameters (permeabilities, cell wall elastic moduli, etc.) which enter into the development. The section closes with a presentation of circuit analog models for single plant cells.

Section II is devoted to a review and development of the water relations of plant tissues which contain numerous cells in series. Following a historical overview, various existing models are derived and physical tissue properties which enter the derivation are identified. The concept of ‘local equilibrium’ is discussed and circuit analog models for single cells are generalized and applied to several cells in series.

The final section contains two example applications of water transport theory as it applies to plant tissue. One application involves radial water movement in a soybean hypocotyl while the other deals with water transport in a growing root tip. A summary at the end of the section is largely devoted to a discussion of the limitations of mathematical models dial are presently available.
Epidermal transpiration and stomatal responses to humidity: Some hypotheses explored
Authors: SHERIFF D. W.
Published: April 2006

Abstract Stomatal responses to humidity as affected by both evaporation from the epidermis and the hydraulic conductance of the transpiration stream to evaporation sites on the epidermis are discussed.

Recent estimates of evaporation from the inner walls of the epidermis are too high because the cell wall surfaces were assumed completely wet, and leaves have usually been considered isothermal.

It is suggested that a fall in humidity increases evaporation from the epidermis, and that stomata respond to the consequent fall in water potential. Cuticular transiration is inversely related to stomatal conductance. Thus, evaporation from the epidermis is dependent on the stomatal, boundary layer, and cuticular conductances, and on evaporation from the inner walls of the epidermis. Stomatal responses to humidity will change as the boundary layer conductance changes.

The conductance of the transpiration stream is a determinant of the water potential of the epidermis. Water potentials of adjacent cells will be more similar if flow is symplastic than if it is apoplastic. It is concluded that flow in living tissues is primarily symplastic over long distances, but over shorter distances it is increasingly apoplastic, and that stomatal responses to humidity are mediated by the water potential of the whole epidermis.
Voltage transients elicited by brief chilling
Authors: PICKARD BARBARA G.
Published: April 2006

Abstract Chilling auxin‐depleted, etiolated stems of Pisum sativum L. to 4°C for 60 s enhanced the production of previously described voltage transients 20‐fold. It is postulated that plasmalemmal permeability to Ca2+ is increased at low temperature, permitting influx of the ion from the apoplast to the cytosol and thereby promoting production of transients. Heating to 40°C or 45°C elicits no increase in transients, and heating to 50°C leads to loss of turgor.
The mechanism of bicarbonate assimilation by the polar leaves of Potamogeton and Elodea. CO2 concentrations at the leaf surface
Authors: PRINS H. B. A. , SNEL J. F. H. , ZANSTRA P. E. , HELDER R. J.
Published: April 2006

Abstract. Photosynthetic utilization of HCO, in leaves of Poiamogeton and Elodea occurs at the lower leaf side, with subsequent OH∼ release at the upper side. It is accompanied by transport of cations, in the present experiment K +, across the leaf. The resulting pH and K+ concentration changes near the leaf surface were recorded with miniature electrodes. From the pH and K+ concentration the concentrations of the different inorganic carbon species were calculated and compared with photosynthetic O, production. HCO−3 utilization is accompanied by a drastic increase in the free CO2 concentration near the lower epidermis. Experiments with CO2− and HCO3−free solutions showed an oscillating acidification near the lower epidermis and alkalinization near the upper epidermis. It is concluded that the acidification results from the activity of light‐dependent H+ pumps. The finding that an increase in pH at the upper side always coincided with a decrease at the lower in these experiments shows that the H+ pumps and the OH− extruding mechanism are coupled although occurring in different cell layers. Previously we have suggested that the first step in the process of photosynthetic HCO3− utilization is external conversion of HCO3−” by acidification caused by light‐dependent H+ pumps. The present results strongly support this hypothesis. Two possible pathways for the accompanying K + transport are discussed. The model presented here explains the known inhibiting effects of buffers and high pH on photosynlhetic HCO3− utilization.
Source—sink characteristics of carbon transport in Chara hispida
Authors: ANDREWS M. , BOX R. , FYSON A. , RAVEN J. A.
Published: April 2006

Abstract Rates of uptake of 14C‐labelled inorganic carbon were measured for whole Chara hispida plants, detached parts of the shoot and isolated (split‐chamber technique) apices, lateral branchlets and rhizoid—node complexes.

The rates of inorganic carbon uptake by the rhizoid—node complex expressed per gram fresh weight whole plant were three to four orders of magnitude less than the uptake for the whole plant. Up to 70% of the carbon taken up by the rhizoid—node complex was translocated to the shoot. After 12 h exposure to 14C‐labelled inorganic carbon the concentration of 14C was greater in apices than in uppermost or central internodal cells and in all lateral branchlets, regardless of whether label was supplied to the whole plant or isolated rhizoid—node complexes. Measurement of inorganic carbon uptake by detached internodal cells and detached and isolated apices and lateral branchlets showed that lateral branchlets had the greatest rates of inorganic carbon uptake. During 12 h exposure to 14C, isolated lateral branchlets translocated to the attached shoot 55% of the labelled carbon taken up; for isolated apices this value was only 13%.

It is concluded that it is highly unlikely that the rhizoid of Chara hispida could acquire a significant fraction of the whole plant requirement for inorganic carbon and that apices are sink regions for photosynthate while lateral branchlets are source regions.
Comparative studies on immunological and molecular properties of phosphoenolpyruvate carboxylase in species of Sedum and Kalanchoë performing crassulacean acid metabolism (CAM)
Authors: MULLER D. , KLUGE M. , GROSCHEL‐STEWART U.
Published: April 2006

Abstract. PEP‐carboxylase was extracted and partially purified from nine species of the genus Sedum and three species of the genus Kalanchoe, all performing CAM. Immunological and molecular properties of these enzymes were compared. Molecular weight estimation with gradient slab gels showed identical molecular weights of about 232,000 for all PEP‐carboxylases. Ouchlerlony double‐diffusion analysis, immunotitralion and SDS polyacrylamide clectrophoresis indicated the presence of PEP‐c dimers consisting of monomers of MW 105,000 and 115,000. A model of PEP‐c substructure is proposed. The results are discussed in the context of CAM performance in the genus Sedum
Qualitative changes in protein synthesis in germinating pollen of Lilium longiflorum after a heat shock
Authors: HONG‐QI ZHANG , CROES A. F. , LINSKENS H. F.
Published: April 2006

Abstract Germination and protein synthesis of lily pollen subjected to a short heat shock after imbibition are strongly inhibited. The proteins synthesized after the heat shock were analysed by polyacrylamide gel electrophoresis. The patterns obtained from heat‐treated pollen are strikingly different from those of control samples. The difference is nearly completely climinated by a high concentration of proline in the incubation medium. This proline effect correlates with the protection of pollen germination from high temperature by the amino acid.
The relation between membrane lipid phase separation and frost tolerance of cereals and other cool climate plant species
Authors: HARVEY G. W. , GUPTA L. Y. , FORK D. C. , BERRY J. A.
Published: April 2006

Abstract. The temperatures at which liposomes prepared from membrane phospholipids begin to phase separate were compared to the temperatures at which intact plants were damaged. Woody perennials tolerated temperatures below which their membrane phospholipids began to phase separate. By contrast, rye and wheat seedlings were damaged about 25°C above their phase separation temperature. Differences in tolerance among cultivars pre‐hardened to frost were reflected by changes of the phase separation temperature. The results support the notion that alterations in membrane lipid composition are associated with frost hardening. A correlation between the temperature of phase separation and frost tolerance suggests that lipid properties may influence freezing tolerance of cereals; however, the lethal event is apparently not phase separation of the membrane phospholipids.
A new stem hygrometer, corrected for temperature gradients and calibrated against the pressure bomb
Authors: DIXON M. A. , TYREE M. T.
Published: April 2006

Abstract A simple stem hygrometer for attachment to a bared section of sapwood or a cross‐sectional cut end of a shoot is described. Two welded chromelconstantan thermocouples inside the chamber, one touching the sample and the other in the chamber air, allowed measurement of and correction for the temperature gradient between the sample and the dewpoint measuring junction. The instrument was attached to the cut end of an apical shoot of Thuja occidentalis L. protuding from a Scholander‐Hammel pressure bomb. Cut‐end water potential (ψhyg), measured using the stem hygrometer, was compared to xylem pressure potential (ψxp) while the latter was manipulated in the pressure bomb. After an initial equilibration time of 3–4 h, hygrometer equilibrium values were achieved within 1.5–4.0 min of changing ψxp in the pressure bomb. The half‐time (ψ1/2) for vapour pressure equilibration was 15–40 s. Stable temperature gradients between the sample and dewpoint measuring junction of 0.01–0.1°C were measured. Correcting ψhyg for the temperature gradient resulted in excellent agreement with ψxp.
Effect of temperature on phytochrome—mediated anthocyanin synthesis in red cabbage
Authors: SMALL CATHERINE J. , PECKET ROBERT C.
Published: April 2006

Abstract. A brief high temperature treatment (45 C) promoted anthocyanin synthesis in 2‐d‐old dark‐grown red cabbage seedlings. The increased effectiveness of a temperature/red light treatment as opposed to the reverse sequence suggests that an elevated temperature ‘induces’ some component which facilitates the phytochrome response.
The use of the fluorescent probe 8‐anilino‐1‐naphthalene sulphonic acid (ANS) as a histochemical stain in plant tissues
Authors: GATES P. J. , OPARKA K. J.
Published: April 2006

Abstract. The fluorescent probe 8‐anilino‐l‐naphthalene sulphonic acid (ANS) has been evaluated as a histochemical stain for plant tissues. The wide specificity of the compound for hydrophobic binding sites limits its analytical use, but renders it of considerable value as a general fluorescent stain for use in epi‐illumination fluorescence microscopy. Used in this way it is analogous to the light‐microscope stain toluidine blue. ANS has also been found to be a sensitive vascular tracer.
Isolation of Capsicum annuum leaf nitrate reductase and characterization of the effect of adenine nucleotides and NADH on its activity
Authors: WALLACE W. , STEER B. T.
Published: April 2006

Abstract. In the preliminary purification of Capsicum leaf nitrate reductase (EC 1.6.6.1), treatment of the crude extract on Sephadex G‐25 was necessary to prevent a gelling of the extract and sedimentation of the enzyme. Its Km values for NADH and nitrate were estimated to be 9.3 and 105mmol m−3 ADP and ATP gave hyperbolic competitive inhibition, with respect to NADH, while the inhibition by AMP was linear competitive. Ki values calculated were: ADP and ATP approximately lmol m−3 and AMP 2.3 mol m−3. Inhibition by ADP was not altered by reduced glutathione.

The Capsicum nitrate reduclase was very susceptible to inhibition by NADH (in the absence of nitrate) and an in vivo assay showed that the activity of the enzyme was limited by the supply of nitrate. NADH and adenine nucleotide levels measured in the Capsicum leaf were used to estimate inhibition of nitrate reductase and a prediction was made of the nitrate reductase activity at different times in the photoperiod. This was shown to follow the same trend as the measured in vivo activity of the enzyme. Changes in adenine nucleotide levels had little effect on nitrate reductase activity.
In situ localization of the sites of paraquat action
Authors: VAUGHN KEVIN C. , DUKE STEPHEN O.
Published: April 2006

Abstract. Effects of paraquat were monitored by electron microscopic, cytochemical, and in vivo spectrophotometric procedures. Electron microscopy of paraquat‐treated pea leaf discs indicates that the chloroplasts are affected primarily with both thylakoid dilation and apparent lamellar fusions, resulting in a ‘honeycomb’ of lamellae. No ultra‐structural effects were noted when leaf discs were incubated in both DCMU and paraquat. Paraquat‐induced peroxide was located cytochemically along the stroma lamellae, on the ends of the grana stack and in the dilated thylakoids. Less destruction was noted in those samples where peroxide was precipitated by cerium chloride, indicating that peroxide or one of its products is one of the major causes of paraquat toxicily. In C4 plants mesophyll plastids exhibited much more peroxide deposition than was detected in bundle sheath plastids. No plastid peroxide depositions were noted in a photobleaching mutant that is resistant to paraquat. In situ cytochrome f oxidation‐reduction was followed during paraquat treatments and resulted in a hastening of the dark re‐reduction of cytochrome f after only 1 h of treatment. This effect was prevented by DCMU or CeCI3. Electron transport, as measured by cytochrome f oxidation‐reduction, was completely obliterated by a 24 h paraquat treatment. These in situ studies on paraquat confirm previous studies that the primary effect in the light is on the plastid and involves peroxide or further products generated by peroxide.
Effect of number and configuration of fruits, photon flux and age on the growth and dry matter distribution of fruits of Pisum sativum L.
Authors: HOLE C. C. , SCOTT P. A.
Published: April 2006

Abstract. In experiments with Pisum sativum cv. Sleaford Orbiter in a controlled environment, the effect of fruit number and position, photon flux density and developmental stage on fruit growth was studied. During early development (up to 22 d from anthesis) growth of the first fruit was unaffected by the presence of one or two additional fruits irrespective of their position. When grown to maturity in competition with fruits at the same node a small decrease in weight of this fruit was observed. Where plants retained a full complement (20‐30) of fruits the growth of the first fruit was markedly decreased at all stages of development (6‐40 d). In all instances where competition was observed, the pericarp was more affected than the seeds. This was particularly so when photon flux was decreased 18‐22 d from anthesis compared with a decrease at an earlier stage. Partition of dry matter between fruits showed a progressively increasing allocation to the later‐formed fruits with time for all treatments. The actual proportions allocated to different fruits were not changed by the number of competing fruits. Decreasing photon flux by more than two‐thirds decreased fruit growth rates but had little effect on dry matter partitioning in most cases, although where all fruits were retained, there was a tendency for fruits at the lower reproductive nodes to be less affected. These findings are discussed in relation to known sources of assimilate for fruits, assimilate transport and sink demand. It is suggested that partition of dry matter between fruits can be estimated on the basis of fruit size and the developmental trend in relative growth rate of fruits grown in the absence of competition for assimilate from other fruits.
Scanning electron microscopic aspects of short tuberized roots, with special reference to cell rhizodermis evolution under drought and rehydration
Authors: VARTANIAN N. , WERTHEIMER D. S. , COUDERC H.
Published: April 2006

Abstract. Different morphological aspects of short tuberized roots initiated during drought stress in mesophytic species, such as Sinapis alba L., were studied with the scanning electron microscopy technique of cryofixation. Specially adapted for direct and immediate observation of fresh living roots, this method has given precise information about rhizodermal organization and evolution during drought and rehydration.

The main difference from a normal lateral root grown in a well‐watered soil appears in the basal enlarged zone of the short root where all the cells show the same round and turgid aspect. In the medium zone of the short root, rhizodermis differentiation into alternating rows of short (trichoblasts) and long (atrichoblasts) cells, which characterizes the typical Sinapis root, remains clearly discernible, though not so regular as in normal lateral roots.

The turgid state of rhizodermal cells all over the short tuberized root grown in a drying soil suggests an effective regulatory mechanism for water deficit avoidance.

During the first hours of rehydration, immediate absorption of water is noticeable through the rapid swelling of some long cells which appear to protrude considerably among other rhizodermal cells. However, these protrusions will not give rise to hairs, as further observations of short roots after growth has resumed show very distinctly that progressive hair formation occurs in the medium zone of the root, and that their emergence originates from trichoblasts only.

These observations may indicate that atrichoblasts, on account of their highly vacuolated condition, are the first cells to absorb water and that they may even be stimulated, in some environmental conditions, to initiate hair formation, although they are not so well adapted to do so as the short cells in this species.
Control of plant growth by nitrogen: differences between cereals and broadleaf species
Authors: RADIN JOHN W.
Published: April 2006

Abstract. In four dicotyledonous species low levels of N strongly inhibited leaf expansion during the day but had little or no effect at night. In contrast, daytime and night‐time expansion were equally affected in four cereal species. The results support the general concept that in dicotyledons, N controls leaf expansion through its effects on hydraulic conductivity. In such N‐limited plants, water deficits generated by transpiration may inhibit daytime cell expansion. In cereals, cell expansion and transpiration occur in separate zones of the leaf and are apparently unrelated.

Growth analysis showed that low levels of N inhibited leaf area growth more strongly in dicotyledons than in cereals, but had similar effects on net assimilation rates of plants in the two groups. As a result, dry matter production was more efficient in cereals than in dicotyledons when N was limiting.
Photogeneration of a bioelectric field by red and far‐red irradiation in soybean hypocotyls
Authors: TANADA TAKLJMA
Published: April 2006

Abstract.Changes in the bioelectric field potential at the apical end of dark‐grown soybean (Glycine max)hypocotyls after exposure to several wavelengths of light have been monitored with an electrometer. A small dose of 660 nm radiation brings about a rapid positive rise in the potential. A following small dose at 760 nm prevents the increase, suggesting a phytochrome action. Pre‐irradiation with 660 nm enables a subsequent larger dose of 760 nm, which by itself is without effect, to elicit a delayed rise in the potential.

A large dose at 710 nm induces a delayed increase in the field potential. The increase is prevented by a following dose at 550 nm, but not at 660 nm.
Sources of reductant for nitrate assimilation in non‐photosynthetic tissue: a review
Authors: LEE R. B.
Published: April 2006

Abstract. Potential sources of reductant for the pathway of nitrate assimilation in non‐photosynthetic tissue are considered in terms of the intracellular distribution of the enzymes involved (relative to those of nitrate assimilation), their maximum catalytic capacity, the availability of their respective substrates, and the form in which the reductant is produced. According to these criteria, the principal sources appear to be the reactions catalysed by NAD‐glyceraldehyde‐3‐phosphate dehydrogenase, glucose‐6‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase, NAD‐malate dehydrogenase and NADP‐malic enzyme. Mitochondrial metabolism may also make a limited contribution, although the evidence is inconclusive. The capacity to generate reductant by carbohydrate oxidation within the proplastids appears insufficient to meet the demand, and an influx of reducing power from the cytoplasm in the form of dihydroxy acetone phosphate may be necessary to support nitrite reduction and the glutamate synthase reaction which occur there.
Paraquat tolerant and susceptible perennial ryegrasses: effects of paraquat treatment on carbon dioxide uptake and ultrastructure of photosynthetic cells
Authors: HARVEY BARBARA M. R. , FRASER T. W.
Published: April 2006

Abstract. Paraquat treatment of susceptible Lolium perenne seedlings (cultivar Kent Indigenous) rapidly inhibited CO2 uptake and after 1 h chloroplasts exhibited abnormal fusions of the thylakoid membranes. Further ultrastructural changes occurred within the chloroplasts until 8 h after treatment, when cytoplasmic damage also became evident. The localization of primary damage within the chloroplast differs from previous reports of paraquat toxicity in other species. Paraquat treatment of tolerant L. perenne seedlings (line PRP IX) resulted in little change in CO2 uptake and ultrastructural effects were generally confined to the gradual development of deposits in the chloroplast stroma. These observations are discussed in relation to the mechanism of action of the herbicide and the proposed mechanism of paraquat tolerance in L. perenne.
Water relations of drought hardy shrubs: osmotic potential and stomatal reactivity
Authors: HINCKLEY T. M. , DUHME F. , HINCKLEY A. R. , RICHTER H.
Published: April 2006

Abstract. Diurnal measurements of total water potential and stomatal opening were made at six sites. Pressure‐volume curves were established on parallel leaf samples. In eastern Austria, the species investigated were Cornus mas L., Cornus sanguinea L., Crateagus monogyna Jacq., Sorbus aria (L.) Crantz and Viburnum lantana L. in southern France Crateagus monogyna, and in southern Turkey Crateagus monogyna and Olea europaea L. Osmotic adjustment, defined as a change in osmotic potential larger than the passive change resulting from the loss of cell water, was relatively small from day to day or week to week in mature, non‐senescing leaves. Cornus sanguinea was an exception. A recently suggested method for the demonstration of diurnal active osmotic adjustment seems not to be reliable without further independent corroboration. Changes in the leaf water potential threshold for stomatal closure were either insignificant when the pressure‐volume characteristics of the plant material were stable, or significant when shifts in such parameters as the turgor loss point occurred (Cornus sanguinea).
Rapid development of cell suspension cultures from leaf sections of Chenopodium rubrum L.
Authors: GEILE W. , WAGNER E.
Published: April 2006

Abstract. Leaf sections (1 × 1 cm) from Chenopodium rubrum L. were floated on Murashige–Skoog medium at constant 20°C and 8800 Lux white fluorescent light. During a period of 4–6 days after inoculation the leaf tissue showed rapid growth and cell division in the mesophyll. Subsequently, after 4 days on a rotary shaker the leaf tissue completely disintegrated and released a great number of single cells into suspension. This procedure, which by‐passes the callus culture stage, is well‐suited to the rapid production of standardized cell suspension cultures.
Row structure and foliage geometry as determinants of the interception of light rays in a sorghum row canopy
Authors: FUCHS M. , STANHILL G.
Published: April 2006

Abstract. The interception of light rays by the canopy of a widely spaced sorghum row crop was assessed from a series of hemispherical photographs taken on five occasions during its vegetative growth. Analysis of the photographs shows that most of the temporal and spatial variation in the canopy's interception could be accounted for by treating the row as an array of solid parallel walls with rectangular cross sections. Within the space occupied by rows, the effect of the distribution of foliage elements on interception could be assessed by the porosity of a single row. The north‐south asymmetry observed in the distribution of ray interception indicates that this sorghum canopy, grown under unirrigated, arid summer conditions, adopted a light‐avoiding growth pattern.
Photoregulation of hypocotyl growth: geotropic evidence for the operation of two photosystems
Authors: HART JAMES W. , MACDONALD IAN R.
Published: April 2006

Abstract. The rate of curvature of etiolated cress (Lepi‐dium sativum L.) hypocotyls in response to gravity (negative geotropism) was retarded by red or blue light; far‐red irradiation was without effect. The timing of the irradiation period in relation to the presentation for geostimulus markedly affected the response. When seedlings were irradiated during the 1–2 h period of geostimulus, blue light was more effective than red at retarding curvature; when seedlings were irradiated prior to geostimulus, only red light affected geocurvature. These results are interpreted as a further example of the kinetically distinct effects of red and blue light on hypocotyl development. Blue light elicited a rapid, immediate response effective only during the period of irradiation; red light induced a response characterized by a lag period and persistence in subsequent darkness. Etiolated mustard seedlings showed similar responses to light and gravity. The results are discussed in relation to the possibility that two photosystems operate in hypocotyl growth.
2H+:1 malate2−stoichiometry during Crassulacean Acid Metabolism is unaffected by lipophilic cations
Authors: LÜTTGE U. , BALL E.
Published: April 2006

Abstract.Lipophilic cations inhibit nocturnal malic acid accumulation in leaf cells of the Crassulacean Acid Metabolism plantKalanchoë tubiflora. perhaps by interacting directly or indirectly with active malic acid transport into the vacuoles. Lipophilic cations do not affect passive efflux of malic acid from the vacuoles. Membrane potentials are depolarized, oxygen uptake is stimulated by lipophilic cations and there may also be stomatal responses. Thus it is striking that lipophilic cations do not alter the stoichiometry of 2 titratable H : 1 enzymatically‐determined malate2−during diurnal malic acid oscillations of Crassulacean Acid Metabolism inKalanchoë. This suggests that coupling between protons and malate during transport into the vacuole must be tight. Transport as undissociated acid is unlikely because the dissociation equilibrium in the cytoplasm is largely on the side of malate2−. These results appear to suggest an intimate molecular interaction between a proton pump and a presumed malate2−translocator at the tonoplast of leaf cells with Crassulacean Acid Metabolism.
Purification and molecular properties of acid phosphatase from sycamore cell walls
Authors: CRASNIER MARTINE , NOAT GEORGES , RICARD JACQUES
Published: April 2006

Abstract. An acid phosphatase is isolated and purified to homogeneity from sycamore cell walls. The enzyme, which has a molecular weight close to 100,000, is a glycoprotein and is most probably made up of one polypeptide chain only. Its amino acid composition has been determined. Although homogeneous to polyacrylamide gel electrophoresis under non‐denaturing conditions, the enzyme preparation still contains protease traces that tend to split polypeptide chain in two fragments.
Germination and seedling growth under anaerobic conditions in Echinochloa crus‐galli (barnyard grass)*
Authors: KENNEDY ROBERT A. , BARRETT SPENCER C. H. , ZEE DELMAR VANDER , RUMPHO MARY E.
Published: April 2006

Abstract Although rice has long been recognized to be uniquely adapted for growth in low oxygen environments of flooded rice fields, rice weeds of the Echinochloa crus‐galli complex appear to be at least as well specialized for germination and growth under such unusual biological conditions.

Seeds of two varieties of E. crus‐galli germinate and grow for prolonged periods in a totally oxygen‐free environment. E. crus‐galli germinates as well as rice (Oryza sativa) under a total nitrogen atmosphere and produces as large a seedling in spite of its much smaller seed size. Like rice, the seedlings of E. crus‐galli are unpigmented, the primary leaves do not emerge from the coleoptile and no root growth occurs without oxygen. Of particular interest is the ultrastructure of mitochondria from anaerobically‐grown seedlings. Mitochondrial profiles from the primary leaf of seedlings grown continuously in nitrogen are very similar to those grown aerobically. The size and shape of the mitochondria are similar and the cristae are numerous and normal in appearance. This is in sharp contrast to previous studies of other species which have reported that mitochondria were vesiculate and tended to lose their normal fine‐structure after similar periods without oxygen.

Finally, based on ultrastructure and 14C labeling studies, anaerobically‐grown seedlings are highly active metabolically, which may explain, at least for E. crus‐galli var. oryzicola, its ability to germinate and emerge from flooded rice fields.
Characterization and comparisons of five N2‐fixing Azolla‐Anabaena associations, I. Optimization of growth conditions for biomass increase and N content in a controlled environment*
Authors: PETERS GERALD A. , TOIA ROBERT E. , EVANS WILLIAM R. , CRIST DEBORAH K. , MAYNE BERGER C. , POOLE REBECCA E.
Published: April 2006

Abstract Biomass increase, C and N content, C2H2 reduction, percentage dry weight and chlorophyll a/b ratios were determined for clones of Azolla caroliniana Willd., A. filiculoides Lam., A. mexicana Presl., and A. pinnata R. Br. as a function of nutrient solution, pH, temperature, photoperiod, and light intensity in controlled environment studies. These studies were supplemented by a glasshouse study. Under a 16 h, 26°C day at a light intensity of 200 μmol m−2 s−1 and an 8 h, 19° C dark period, there was no significant difference in the growth rates of the individual species on the five nutrient solutions employed. Growth was comparable from pH 5 to pH 8, but decreased at pH 9. Using the same photoperiod and light intensity but constant growth temperatures of 15–40°C, at 5°C intervals, the individual species exhibited maximum growth, nitro‐genase (N2ase) activity and N content at either 25° or 30°C. There was no difference in the temperature optima at pH 6 and pH 8. The tolerance of the individual species to elevated temperature was indicated to be A. mexicana> A. pinnata> A. caroliniana> A.filiculoides. At the optimum temperature, growth rates increased with increasing photoperiod at both pH 6 and pH 8 but N2ase activity was usually highest at a 16 h light period. At photon flux densities of 100, 200, 400 and 600 μmol m−2 s−1, during a 16 h light period and optimum growth temperature of the individual species, N2ase activity was saturated at less than 200 μmol m−2 s−1 and growth at 400 μmol m−2 s−1.No interacting effects of light and pH were noted for any species, nor were light intensities up to 1700 μmol m−2 s−1 detrimental to the growth rate or N content of any species in a 5 week glasshouse study with a natural 14.5 h light period and a constant temperature of 27.5°C. Using the optimum growth temperature, a 16 h light period, and a photon flux density of at least 400 μmol m−2 s−1, the Azolla species all doubled their biomass in 2 days or less and contained 5–6% N on a dry weight basis.
Temperature responses of membrane‐associated activities from spring and winter oats
Authors: THOMAS HOWARD , STODDART JOHN L. , POTTER J. F.
Published: April 2006

Abstract Two‐week old, glasshouse‐grown seedlings of spring and winter oats (Avena sativa cv. Margam and Pennal respectively) were transferred to growth rooms where the daylength was 8 h and the temperature was either 20° or 5°C. Leaves from the 20°C treatment were harvested 1 week after transfer and those from the 5°C treatment after 3 weeks. Measurements were made, at temperatures in the range 5–20°C, of the rate of senescence of excised leaf sections; the rate of in vivo tetrazolium (TTC) reduction; the NADH‐MTT tetrazolium diaphorase (NMD) activity of a membrane preparation isolated by sucrose gradient centri‐fugation; and Hill activity of isolated chloroplasts. Data from these experiments, either untransformed or plotted in accordance with the Arrhenius equation, were analysed by the method of maximum likelihood for the occurrence of rate‐temperature discontinuities. Distinct breakpoints at 14.2–16.3°C were detected for senescence, TTC reduction and NMD in winter oat leaves from the 20°C treatment, but spring oats grown at the same temperature gave a significant discontinuity only in the rate of senescent yellowing. After the hardening treatment, 3 weeks at 5°C, senescence and TTC reduction in winter oats exhibited breakpoints at 10.1–12.4°C and spring oats gave breaks at 11.8–17.3°C. No breakpoint was observed for Hill activity from either variety under either temperature treatment. The use of this approach in studies of growth at chilling temperatures and its potential as a screening method are discussed.
Reduced stomatal responses to light, carbon dioxide and abscisic acid in the presence of sodium ions
Authors: JARVIS R. G. , MANSFIELD T. A.
Published: April 2006

Abstract Responses of stomata to light and CO2 were smaller when detached epidermis of Commelina communis L. was incubated on a medium containing 50 mol m−3 NaCl than when an equimolar KCl solution was used. Although opening in the light in the absence of CO2 seemed to be the same whichever salt was present, apertures on KCl solutions were smaller in the dark or with CO2‐containing air. The response to 10−7 mol dm−3 ABA was similarly reduced in the presence of NaCl. If there is an optimal NaCl concentration for stomatal CO2 and light responses it is at or below 25 mol m−3. These findings point towards control of stomatal movements by light, CO2 and ABA at the level of cation uptake or extrusion.
Daylength change and leaf appearance in winter wheat
Authors: BAKER C. K. , GALLAGHER J. N. , MONTEITH J. L.
Published: April 2006

Abstract In the field successive leaves of winter wheat appear at a rate which varies because it depends strongly upon temperature. When plotted against ‘thermal time’, however (temperature accumulated above a fixed base of 0°C), leaf appearance was a strictly linear function of temperature. The mean rate of leaf appearance in thermal time, R′, was faster for a spring sowing than for an autumn sowing. The variation in R′ between sowings was better correlated with the rate at which daylength was changing when the plants emerged than with the mean daylength while leaves were appearing.
Effects of CO2 concentration and irradiance on the stomatal behaviour of maize, barley and sunflower plants in the field
Authors: LOUWERSE W.
Published: April 2006

Abstract Maize, barley and sunflower plants were grown in the field, well supplied with water and nutrients. During growth, net CO2 exchange and transpiration of the crops at varying ambient CO2 concentrations and irradiance were determined by infra‐red gas analysis. In maize the net photosynthetic rate (Pn) was linearly related to the irradiance (I) and independent of the ambient CO2 concentration (Ca). The transpiration rate (ET) was also linearly related to I but decreased strongly with increasing Ca. In sunflower and barley Pn increased and ET decreased with increasing Ca. A mean stomatal conductance and intercellular CO2 concentration (Ci) were calculated. In all three species the internal CO2 concentration was independent of the irradiance. In maize it was also independent of Ca, but in sunflower and barley Ci was proportional to Ca with a ratio of 0.6.

It is concluded that differences in stomatal behaviour are only partly species‐specific and depend mainly on growing conditions. The importance of stomatal regulation for crop growth under conditions of water shortage and CO2 depletion is discussed.
Changes in starch and glucose levels in the epidermis of Commelina communis in relation to stomatal movements
Authors: DONKIN MARIA E. , MARTIN E. S.
Published: April 2006

Abstract Starch levels in Commelina communis epidermis, were shown to be higher in the dark than in the light, from plants kept under an imposed photoperiodic regime. These changes were also inversely correlated with diffusive conductance (1/diffusive resistance, 1 /R) of the leaves used. Even after advancing the photoperiod by 7 h the changes in starch levels continued for at least 1 d and were still inversely correlated with 1/R.

Corresponding changes in glucose levels were measured in the same tissue and were found to correlate with 1/R at the end of the dark period and mid photoperiod, but not at the beginning of the dark period. These changes are discussed in relation to possible mechanisms of stomatal opening and closing.
Boundary layer conductance of the leaves of some tropical timber trees
Authors: GRACE J. , FASEHUN F. E. , DIXON M.
Published: April 2006

Abstract The boundary layer conductance of brass models of leaves exposed in a wind tunnel was determined from their cooling characteristics. Conductances were generally very low, as expected from large leaves. Nusselt numbers were calculated from the rates of heat loss, so that the results could be compared with established theory. There was generally good agreement between observed and calculated values. Leaves with veins displayed an apparent transition from a laminar to a turbulent boundary layer, and so did leaves inclined at an angle from the horizontal. In still air the observed rates of heat loss by natural convection were substantially higher than those calculated.
Accumulation of carbon compounds in the epidermis of five species with either different photosynthetic systems or stomatal structure
Authors: THORPE NICOLETTE
Published: April 2006

Abstract Measurements were made of the rate and pattern of 14CO2 fixation by the attached and detached epidermis and accompanying leaf tissue of Commelina cyanea (C3), Zea mays (C4), Kalanchoë daigremontiana (CAM), Allium cepa (C3) and Paphiopedilum venustum (C3). Guard cell plastids of the last two species contain no starch and chlorophyll, respectively. The fine structure of guard cells of these species was also examined.

The epidermis of all species when detached from the leaf fixed CO2 by PEP carboxylation but at rates related to those of the underlying mesophyll. When attached to the leaf during 14CO2 feeding a much higher rate of accumulation of radioactivity in substances other than malate and aspartate was found. The results indicated that although concentrations of various metabolites in the two tissues varied greatly, there was fairly ready transport from mesophyll to epidermis. Of recently formed compounds, amino acids appeared to be most readily transported in Commelina and sugars in Zea and Kalanchoë. Epidermal cells appeared to be highly permeable, there being rapid and extensive loss of most labelled products from epidermis placed on CaSO4 solution.
The promotive effect on subsequent germination of treating imbibed celery seeds with high temperature before or during drying
Authors: BIDDINGTON N. L. , THOMAS T. H. , DEARMAN A. S.
Published: April 2006

Abstract High temperature (32°C) prevented germination of celery seeds even if given after 4 d of germination induction at 17°C in white light, but germination occurred if the seeds were then returned to 17°C. Celery seeds incubated for 3 d at 17°C in white light and then air‐dried at 20°C germinated slowly when re‐sown at 17°C in the light, achieving only 24% germination after 21 d. Exposure of such seeds to 32°C prior to and during drying resulted in 50% germination after 3.6 d at 17°C in white light, with no loss in viability, compared to 5.7 d for seeds not given a germination induction treatment. If celery seeds were dried rapidly germination was poor, an effect which could be overcome by high temperature treatment. It is suggested that the mechanism which imposes dormancy at 32°C also conditions the seed to withstand desiccation damage.