bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of brief treatments with benzyladenine on growth and development of watermelon cotyledons
Authors: LONGO G. P. , OLGINATI M. , ROSSI G. , VALENTE M. , LONGO C. P.
Published: April 2006

Abstract Watermelon (Citrullus vulgaris Schrad.) cotyledons were excised from the seed after 24 h of imbibition and incubated for different times (ranging from 1 to 240 min) on filter paper saturated with 0.1 mM BA (benzyladenine) solution. After the incubation in BA the cotyledons were thoroughly rinsed in water and grown for 5 days in darkness on filter paper saturated with distilled water.

Continuous presence of BA is not a prerequisite for optimal growth. Several effects of the hormone (stimulation of expansion growth, acceleration of lipid breakdown, enhancement of hydroxypyruvate reductase activity, increase in carotenoid content) are more intensive if the cotyledons are treated with BA for a relatively short time and then grown in water. Maximal effects are observed after a 4 h exposure to BA. A single 1 min exposure is sufficient to elicit measurable effects on growth, hydroxypyruvate reductase and carotenoid content. The sensitivity to very short exposures is considerably different for different hormone effects. Carotenoid content and hydroxypyruvate reductase activity are enhanced much more than expansion growth.
Phytochrome control of the growth and development of Rumex obtusifolius under simulated canopy light environments*
Authors: MCLAREN J. S. , SMITH HARRY
Published: April 2006

Abstract Studies on the growth and development of Rumex obtusifolius seedlings under simulated shade conditions show that both light quantity and quality contribute to the observed responses. In the shade situation the plants have lower dry matter, lower leaf area and lower net assimilation rates. Petiole elongation occurs under shade conditions only after transfer of the plants from non‐shade environments. The effects of light quality are related to phytochrome photoequilibria set up by the increased relative photon flux in the far‐red found under vegetation canopies.
Effects of external potassium supply on stomatal closure induced by abscisic acid
Authors: WILSON J. A. , OGUNKANMI A. B. , MANSFIELD T. A.
Published: April 2006

Abstract Epidermal strips of Commelina communis with ‘isolated’ stomata were incubated on Trizma‐maleate buffer containing 0‐500 mM KCL, with or without 10−4 M ABA, for 2.5 h. The resulting stomatal apertures indicate that there is no absolute requirement for live epidermal and subsidiary cells for ABA‐mediated closure. This implies that ABA has a direct effect on influx or efflux of K+ into or out of the guard cells rather than on uptake of K+ by the subsidiary cells. The possible in vivo role of subsidiary cells in stomatal closure is discussed.
Mechanism of paraquat tolerance in perennial ryegrass
Authors: HARVEY B. M. R. , MULDOON J. , HARPER D. B.
Published: April 2006

Abstract The mechanism of paraquat tolerance was investigated in lines of perennial ryegrass (Lolium perenne L.) which had been selected for resistance to the herbicide. Uptake, metabolism and translocation of paraquat were studied. Susceptible cultivars and a tolerant line were not found to differ in uptake of radioactive paraquat applied to the leaf surface or supplied to the cut ends of excised leaves. Distribution of herbicide within leaf tissue was similar in tolerant and susceptible plants and no metabolites of 14C‐paraquat were detected in tolerant or susceptible plants treated with sub‐lethal concentrations of the herbicide. Autoradiography and quantitative determinations showed much variation in translocation of 14C‐paraquat out of treated leaves of intact plants, but the variation was not related to the degree of susceptibility to the herbicide. It is concluded that paraquat tolerance in perennial ryegrass is unlikely to depend upon reduced uptake, enhanced metabolism or altered translocation of the herbicide.
Mechanism of paraquat tolerance in perennial ryegrass
Authors: HARPER D. B. , HARVEY B. M. R.
Published: April 2006

Abstract Relative activities of superoxide dismutase, catalase and peroxidase have been determined in crude extracts of 4 paraquat‐tolerant lines and 11 paraquat‐susceptible cultivars of perennial ryegrass (Lolium perenne L.) grown under controlled conditions. Paraquat‐tolerant lines showed significantly higher activities of both catalase and superoxide dismutase than susceptible cultivars and some resistant lines exhibited in addition elevated peroxidase activity. Differences in superoxide dismutase levels in isolated chloroplasts appeared to parallel those in crude extracts. It is tentatively proposed that paraquat tolerance is due to destruction of O2−by elevated concentrations of superoxide dismutase and detoxification of the resulting hydrogen peroxide by increased levels of catalase and peroxidase.
Are developing xylem vessels the site of ion exudation from root to shoot?
Authors: LÄUCHLI A. , PITMAN M. G. , LÜTTGE U. , KRAMER D. , BALL E.
Published: April 2006

Abstract This paper describes experiments to test the suggestion that developing xylem vessels are the site of exudation of ions from the root to the shoot. Electron microscopy is used to define the stage of development of xylem vessels in young barley roots along the length of the root. The amino acid analogue p‐fluorophenyl‐alanine (FPA) is used to inhibit ion transport from the stele to the xylem vessels at varied distances from the apex. In the presence of FPA protein synthesis is not inhibited but ineffective proteins are formed. It is shown that exudation of Cl− from the root can be inhibited in this way in parts of the root where all the xylem vessels are mature. This is in contradiction to the suggestion that root exudation is due to the activity of developing vessels. The hypothesis is thus strengthened that ion transport proceeds into the xylem vessels, which are fully mature and devoid of cytoplasm, and is due to release from the xylem parenchyma cells.
Effect of temperature on ion content, ion fluxes and energy metabolism in Chara corallina
Authors: RAVEN J. A. , SMITH F. A.
Published: April 2006

Abstract Effects of temperature on the ionic relations and energy metabolism of Chara corallina were investigated. Measurements were made of the ionic content, tracer ion fluxes, and photosynthetic and dark CO2 fixation in isolated cells, and of O2 exchange in photosynthesis and respiration in isolated shoot apices.

The total intracellular concentration of K+, Na+ and Cl− was the same in cells held for 5 days in non‐growing medium at 15°C (the growth temperature) as in those held at 25°C or 5°C. The tracer influx in the light of all ions tested (Rb+, Na+, CH3NH3+, Cl− and H2PO4−) was lower at 5°C than at 15°C in experiments in which cells were subjected to 5°C for less than 24 h in toto. The influx at 25°C was greater than that at 15°C for H2PO−4, there was no difference between the two temperatures for Na+, while the influx at 25°C was less than that at 15°C for Cl−, Rb+ and CH3NH3+ For Cl− and H2PO−4 similar results were found in later experiments with cells grown at 20—23°C. Photosynthetic CO2 fixation and O2 evolution, and respiratory O2 uptake, are greater at 25°C, and lower at 5°C, than they are at the growth temperature of 15°C. In longer‐term pretreatments at the different temperatures, tracer Cl− influx at 15°C and particularly at 25°C were lower than in short‐term experiments, while the influx at 5°C was higher.

It was concluded from these experiments, and from previous data on H+ free energy differences across the plasmalemma, that (1) the maintenance of internal ion concentrations involves a close balancing of influx and efflux of K+, Na+ and Cl− at all experimental temperatures; (2) the regulation of the tracer fluxes of the ions is kinetic rather than thermodynamic and (3) that the tracer fluxes at low temperatures are not restricted by the rate at which respiration or photosynthesis can supply energy to them.
Chilling injury in plants—the role of membrane lipid fluidity
Authors: WOLFE JOE
Published: April 2006

Abstract. Many authors have associated chilling injury in plants with changes in the mobility of membrane lipids but have not proposed specific mechanisms for this association.

This paper explains how the mobility of membrane lipids can affect membrane thickness, membrane permeability, the electric field, cation concentration and water ordering near a membrane and hence change the conformation (and thus activity) of a membrane‐bound enzyme. The complications in such a model due to protein‐lipid interactions and lateral phase separations are also discussed.
Transport of glutamine into isolated pea chloroplasts
Authors: BARBER D. J. , THURMAN D. A.
Published: April 2006

Abstract. Uptake of [14C] glutamine into isolated pea chloroplasts has been examined by using a centrifugal filtration technique. Competition experiments showed that glutamine uptake is mediated by a dicarboxylate carrier with Km 1.10 mM and Vmax. 118 nmol of glutamine min−1 per mg of chlorophyll. Isolated pea chloroplasts accumulated glutamine in the sucrose‐impermeable space to concentrations higher than that present in the external solution when the latter was below 0.5 mM. It is suggested that glutamine accumulation is driven by exchange (utilizing the dicarboxylate carrier) with the endogenous pool of dicarboxylates in the chloroplasts. Increasing pH stimulated glutamine uptake but inhibited that of glutamate and 2‐oxoglu‐tarate. The hypothesis is advanced that when molecules of different charge are exchanged across the chloroplast envelope via the dicarboxylate carrier, electroneutrality is maintained by transport of protons, and that this explains the observed effects of increasing pH. The low rates of glutamine transport coupled with the strong competition of other dicarboxylates for the carrier suggest that export in vivo from the chloroplast of nitrogen in the form of glutamine is not of major importance.
Plant plasma membrane water permeability and slow freezing injury
Authors: STOUT DARRYL G.
Published: April 2006

Abstract Evaluation of existing experimental evidence supports the hypothesis that, under natural or slow rates of freezing, plasma membrane permeability does not significantly limit water efflux from plant cells. Water efflux at slow freezing rates is controlled largely by the rate of heat removal from the plant cells. These conclusions are in direct contrast to the recent views of Levitt (1978).
Promoting effect of fusicoccin on Na+ efflux in barley roots: evidence for a Na+−H+ antiport
Authors: COLOMBO R. , BONETTI A. , LADO P.
Published: April 2006

Abstract. The effect of fusicoccin (FC) on the K+stimulated Na+ efflux in root cells of Na+ loaded barley roots was studied. FC (0.02 mM) stimulated Na+ efflux in the presence of K+ and its effect was synergistic with that of K+, in a similar way as its effect on proton extrusion. Decreasing the pH of the elution medium promoted Na+ efflux and partially replaced the effect of FC. As FC is known to increase the electrochemical proton gradient at the plasmalemma level, these results are consistent with the hypothesis that Na+ is extruded in exchange for H+. A further support to this view came from the finding that Na+ efflux was also promoted by a lipophilic cation, tributylbenzylammonium (TBBA +), which stimulates H + extrusion and is generally accepted not to enter the cells by means of the same carrier as K +.
Kinetics of uptake and release of Cd by potato tissue
Authors: FRANÇOIS M. , SMEYERS‐VERBEKE J. , HOOGEWIJS G. , DE JAEGEREJ R. , MASSART D. L.
Published: April 2006

Abstract. The absorption of Cd by potato tissue was studied. No enhancement of the absorption capacity for Cd was observed by storage of the sliced potato tissue in aerated doubly distilled water for a period of 48 h. Cd absorption as a function of the external Cd concentration followed a typical hyperbolic isotherm. A two‐phase uptake process for the absorption of Cd was found: a rapid initial phase terminating after 30 min, was followed by a slower phase with a constant rate. Efflux, studied by means of compartmental analysis, of Cd showed three phases. The two first were shown to be extracellular in origin. The third phase, involving Cd remaining in the discs after efflux, probably involved Cd in different forms. Metabolic processes, however, did not seem to contribute to this phase.
Stomatal responses to light and CO2 are dependent on KCI concentration
Authors: TRAVIS A. J. , MANSFIELD T. A.
Published: April 2006

Abstract. The responses of stomata on detached epidermis of Commelina communis to light and CO2 have been shown to be strongly dependent on the concentration of KCI in the incubation medium. There was a high sensitivity to the two stimuli in 50 mM KCI, but there were much reduced responses at lower and higher concentrations. It is considered that an appropriate choice of medium is essential if useful physiological studies of stomata are to be made using epidermal strips. At lower KCI concentrations, the ability of the stomata to open is thought to be limited by the availability of K+ ions, and at higher concentrations their ability to close may be affected because of an inhibition of the net efflux of K+. The production of malate was related to KCI concentration, and was largest in the medium containing zero KCI which supported poor stomatal responses to light and CO2It is concluded that malate metabolism is unlikely to play a central part in the changes in guard cell turgor that are brought about by light and CO2.
Light and scanning electron microscopy of SO2‐induced injury to leaf surfaces of field bean (Vicia faba L.)
Authors: BLACK C. R. , BLACK V. J.
Published: April 2006

Abstract. Exposure to low concentration of SO2 increases stomatal conductance in field bean by c 20%. Microscopy of epidermal strips showed that this response was associated with extensive destruction of epidermal cells adjacent to the stomata. Guard cell survival was not affected signficantly. Collapsed epidermal cells were also observed in intact leaf samples using scanning electron miscroscopy, thus confirming that the damage seen in epidermal strips was not caused by the stripping procedure. These observations are discussed in relation to the hypothesis that the increased stomatal opening induced by low SO2 concentrations results from preferential injury to the adjacent cells.
Two phytochrome‐dependent processes in Anagallis arvensis L.: flowering and stem elongation
Authors: IMHOFF Ch. , LECHARNY A. , JACQUES R. , BRULFERT J.
Published: April 2006

Abstract Two phytochrome‐dependent processes are compared in Anagallis arvensis, an absolute long‐day plant: flowering and internode elongation. The effectiveness of red or far red radiation is different according to the length of the treatment and its position within the photoperiodic cycle: for both flowering and internode elongation, 15 h treatments with wavelengths above 700 nm are promotive, whilst wavelengths below 700 nm are inhibitory. In contrast, night breaks of 3 h red light (λ < 700 nm), given after the middle of the dark period, are promotive for flowering and inhibitory for internode elongation. These results are discussed in context with data reported in the literature on photoperiodic control of long‐day plants.
Sodium fluxes in roots of Eleocharis uniglumis, a brackish water species
Authors: SHEPHERD UNA H. , BOWLING D. J. F.
Published: April 2006

Abstract Fluxes of sodium across the plasmalemma and tonoplast of the roots of Eleocharis uniglumis have been measured using 22Na. E. uniglumis (one glumed spike rush) was collected from an estuarine habitat where it was growing in a wide range of salinities (1 mM‐50 mM Na). Compartmental analysis was used to determine sodium concentrations in the cytoplasm and the vacuole. Application of the Ussing‐Teorell equation revealed the presence of sodium pumps in the plasmalemma and the tonoplast. Active sodium transport into the cytoplasm from the bathing medium was found to occur in most of the external sodium concentrations investigated. There also appeared to be active transport of sodium into the cytoplasm from the vacuole. In contrast to halophytes, high levels of sodium appeared to be accumulated in the cytoplasm of E. uniglumis roots.
Effects of low temperatures on the loss of innate dormancy and the development of induced dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.
Authors: TOTTERDELL SUSAN , ROBERTS E. H.
Published: April 2006

Abstract It is possible to remove the innate dormancy of seeds of Rumex crispus L and Rumex obtusifolius L. by an initial period of low‐temperature stratification, providing the seeds are then transferred to a higher temperature. The lower the initial temperature within the range 1.5°‐15°C, the greater the germination; there is no stratification effect at 20°C. Although 10°C and 15°C were shown to be suitable for both stratification and for the process of germination itself, neither temperature results in any germination if given constantly: a change from a lower to a higher temperature is essential.

The optimum period for stratification depends on two separate processes which occur during the treatment–a rapid loss of innate or primary dormancy and a slower development of induced or secondary dormancy. Within the range 1.5°‐15°C the rate of loss of innate dormancy appears to be independent of light and is probably independent of temperature. In contrast, the rate of induction of secondary dormancy increases with increase in temperature, and is more rapid in the dark than the light. The rate of induction of secondary dormancy during stratification is greater in R. crispus than in R. obtusifolius. As a consequence, maximum germination was obtained in both species after stratification at 1.5°C in the light, the optimum period of treatment being about 4 weeks in R. Obtusifolius and 6 weeks in R. crispus, while the maximum germination obtained and the optimal period of stratification decrease in both species with increase in stratification temperature.
Bulbing of onions (Allium cepa L.): The role of endogenous ethylene*
Authors: LEVY DAVID , GOLDSCHMIDT ELIEZER E. , KEDAR NAHUM
Published: April 2006

Abstract Bulbing of onions under naturally increasing daylengths was typically associated with elevated rates of ethylene evolution (10−20 mm3× 103 g−1h−1) during the initial stages of bulbing, followed by a decline to very low rates (1 mm3× 103 g−1h−1) towards bulb maturation. However, detailed comparisons conducted under controlled photoperiodic conditions showed only slight differences in the course of ethylene evolution between inductive and non‐inductive lighting regimens. Bulbing was not prevented by hypobaric ventilation or by treatments with the ethoxy analogue of rhizobitoxine, but Ag+ interfered with bulbing. Although exogenous ethylene induces bulbing under non‐inductive photoperiodic conditions, the role of endogenous ethylene in the natural process requires further clarification.
Sites of acid phosphatase in the differentiating root protophloem of Nymphoides peltata (S.G. Gmel.) O. Kuntze.
Authors: OPARKA K. J. , JOHNSON R. P. C. , BOWEN I. D.
Published: April 2006

Abstract Sites of acid‐phosphatase activity were found in the differentiating root protophloem of Nymphoides peltata by lead‐salt and by azo‐dye methods. Different substrates revealed different subcellular locations of the enzyme. The substrates β‐glycerophosphate (β‐GP) and naphthol ASBI phosphate revealed enzyme activity at similar sites within the sieve element. These sites included plasmodesmata, dictyosomes and small vacuoles in the cytoplasm. The substrate p‐nitrophenylphosphate (p‐NPP), however, revealed additional sites of acid‐phosphatase activity which were not detectable by either naphthol ASBI phosphate or β‐GP. For example, the inner region of the wall in mature sieve elements showed conspicuous acid‐phosphatase activity only when p‐NPP was used as substrate. The significance of the different locations of acid phosphatase within the sieve element is discussed.

The convoluted ER, characteristic of immature sieve elements of N. peltata, failed to show acid‐phosphatase activity whichever substate was used. By contrast, the stacked ER found in the parietal layer of mature sieve elements showed prominent acid‐phosphatase activity regardless of the substrate used. The demonstration of acid‐phosphatase activity in the stacked ER, and by both lead‐salt and azo‐dye methods, suggests that this organelle is a true site of acid‐phosphatase activity.

The onset of acid‐phosphatase activity in the ER in later stages of sieve‐element differentiation is compatible with the view that stacked ER plays a role in the final autolysis of the sieve‐element protoplast.
Relationship of the cell cycle to xylem cell differentiation: A new model
Authors: DODDS JOHN H.
Published: April 2006

Abstract. Conflicting data have appeared in the literature concerning the necessity for DNA synthesis prior to xylem cell differentiation. In some systems DNA synthesis is not required before differentiation, while in other systems DNA synthesis appears to be an absolute necessity. The construction of a model for the cell cycle in which the G1 phase is subdivided into a separate ‘early’ and ‘late’ phase can resolve this apparent conflict.
Respiration rates of apple trees, estimated by CO2‐efflux measurements
Authors: BUTLER D. R. , LANDSBERG J. J.
Published: April 2006

Abstract. Measurements of the efflux of CO2 from 5–6 year old container grown apple trees, in the dark at a range of temperatures (T), indicated that respiration rate (R) can be described by the equation R = SL e kT. The temperature coefficient k, was the same at all times of the year and for all components of the trees, but the values of a varied. At the same temperature respiration rates were low when the trees were dormant, rose rapidly to a peak in spring (before full bloom) and then declined steadily through the season. When respiration was expressed as a flux density, rates for different components of the tree were usually similar. Differences were sometimes statistically significant but no clear pattern emerged. The results obtained are similar to those published for other plants and the equation can be used in the calculation of the carbon balance of apple trees.
Plasmalemmasomes in cotyledon leaves of germinating Vigna radiata L. (mung beans)
Authors: HARRIS N.
Published: April 2006

Abstract. Storage parenchyma, vascular parenchyma and phloem companion cells are found adjacent to sieve tubes in the vascular bundles of cotyledon leaves of mung bean (Vigna radiata L.) seedlings. The paramural bodies of storage parenchyma cells are characterized by flask shaped invaginations of the plasmalemma whereas the plasmalemmasomes of the adjacent vascular parenchyma and companion cells consist of numerous finger‐like evaginations which are not enclosed in plasmalemma pockets. Phloem associated transfer cells are not present and it is suggested that the fine tubular plasmalemmasomes may act as the interface between apoplast and symplast in the transport of rapidly mobilized reserves during germination. Tubular structures observed within the protoplasts of storage cells close to vascular tissue were also observed in vascular parenchyma and companion cells between the plasmalemmae and cell walls.
The effect of salinity on the yield and composition of Diplachne fusca (Kallar grass)
Authors: SANDHU G. R. , ASLAM Z. , SALIM M. , SATTAR A. , QURESHI R. H. , AHMAD N. , WYN JONES R. G.
Published: April 2006

Abstract. Aspects of the response of Kallar grass (Diplachne fusca) to root salinity have been studied. Field observation on the high level of tolerance of this species have been mirrored in pot trials and a 50% yield (dry matter) was obtained at ECe 22.3. While salt stress led to Na and Cl uptake, most of these ions appeared to be secreted selectively from the leaves. The shoot K+ content on a tissue water basis remained unaffected by salt stress and the shoot tissue had a high K+ selectivity. Osmotic adaptation was mainly brought about by tissue dehydration and not net salt accumulation although the compatible solute glycinebetaine was accumulated in fairly high concentrations.

The organic and inorganic chemical composition of the shoots, including the trace elements Zn, Fe, Cu and Mn, is such as to make this species a highly promising plant for the exploitation of saline soils which might otherwise not be amenable to agriculture use.
Light measurement and the terminology of low
Authors: BELL C. J. , ROSE D. A.
Published: April 2006

Abstract. This paper (i) considers the measurement of light in terms of the flow of radiant energy or of particles in a vector field; (ii) derives terminology and units for the specification of light as a flow of radiant energy or of photons which satisfy both the requirements of SI and are physically consistent and (iii) recommends that this terminology is adopted by all plant scientists to avoid ambiguity, confusion and the proliferation of synonyms when reporting light measurements.
Analysis of growth during light‐induced hook opening in cress
Authors: MACDONALD IAN R. , HART JAMES W. , GORDON DENNIS C.
Published: April 2006

Abstract. Growth in various regions of the hypocotyls of dark‐grown cress seedlings before and after exposure lo continuous white light has been analysed by time‐lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle.
Analysis of growth during phototropic curvature of cress hypocotyls
Authors: HART JAMES W. , GORDON DENNIS C. , MACDONALD IAN R.
Published: April 2006

Abstract. Growth rates throughout an organ curving phototropically under continuous, unilateral while light were monitored by lime‐lapse photography of cress hypocotyls marked into 1 mm sections by two rows of ion‐exchange beads. Curvature resulted from an integrated sequence of changes in growth rate on each side of the organ, but the actual patterns of change and, therefore rales of curvature, differed within even this one species, depending upon the immediate pretreatment of the seedlings. Transference of seedlings from darkness to unilateral irradiation gave immediate growth inhibition on both sides of the organ. Curvature resulted from differential recovery of growth rate, being seen first on the shaded side, most prominently in the apical regions; only 2h after initial exposure to light did growth recover on the lit (lower) side. On the other hand, transfer of seedlings from omnilateral to unilateral irradiation of the same intensity resulted in simultaneous growth inhibition on the irradiated side and stimulated growth on the shaded side: this growth stimulation of the shaded side was greater than occurred in totally darkened control plants.
Ultrastructure and membrane permeability in cowpea seeds
Authors: THOMSON W. W. , PLATT‐ALOIA K.
Published: April 2006

Abstract.The leakage of electrolytes and the localization of chloride within the cells of NaCl‐imbibed seeds indicates the plasmalemma is quite permeable during the early stages of imbibition. However, lanthanum is not able to penetrate the plasmalemma, suggesting that the plasmalemma is not entirely porous. Freeze‐fracture microscopy indicates that the plasmalemma is highly convoluted but reveals a fairly normal fracture plane. These observations suggest the membrane is a bilayer and leakiness may be more related to the degree of order within the bilayered membrane than to a primary restructuring and/or reorganization of the membrane components in the dry state.
Ozone‐induced ultrastructural changes in the plasma membrane of Chlorella sorokiniana
Authors: SWANSON ELIZABETH S. , TOIVIO‐KINNUCAN MARIA , HEATH ROBERT , CUNNINGHAM WILLIAM P.
Published: April 2006

Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm−3(140 p.p.m.) O3 for 30 min. Sixty‐eight per cent of the cells were plasmolysed after 15 min O3 exposure with disruption of organelles similar to that previously described in higher plants. Freeze‐fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O3for short periods. After 20 min O3 90% of the cells cross‐fracture, which indicates a change in molecular interactions in the membrane exposed to O3 The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O3 Changes in 86Rb influx occur during a similar time. After more extended exposure to O3 the plasma membrane P face shows regions of lipid phase transition to the crystalline state.
A survey of the reciprocity characteristics of responses to end‐of‐day irradiations in oat, sunflower, and mung bean*
Authors: GORTON HOLLY L. , BRIGGS WINSLOW R.
Published: April 2006

Abstract. Fluence‐response and reciprocity data were collected for response to end‐of‐day FR in several light‐grown plants. Coleoptile elongation in oat and hypocotyl elongation in sunflower and mung bean are stimulated by end‐of‐day FR, and anthocyanin accumulation in mung bean hypocotyls is decreased by the same treatment. All responses have threshold fluences at about 200μmol m−2 and saturation fluences between 4000 and 10,000 μmol m−2 Responses to end‐of‐day FR were reversible by subsequent R with threshold fluences between 2.0 and 3.0 μmol m−2 and saturation fluences between 300 and 1000 μmol m2 Rapid, reverse reciprocity failure which could not be explained by escape from photoreversibility was observed only for stimulation of oat coleoptile elongation by end‐of‐day FR. Oats also showed apparent reverse reciprocity failure for R, but it was entirely explainable by escape. Rapid, reverse reciprocity failure is not a ubiquitous phenomenon for responses to end‐of‐day irradiations.
A comparative study of low‐temperature‐induced ultrastructural alterations of three species with differing chilling sensitivities
Authors: WISE ROBERT R. , McWILLIAM J. R. , NAYLOR AUBREY W.
Published: April 2006

Abstract. The effects of light and water stress upon chilling injury of chloroplasts have been assessed by electron microscopy in seedlings of three species known to differ in their chilling susceptibility. Chilling injury to chloroplasts was first manifested by distortion and swelling of thylakoids, reduction in starch granule size, and the formation of small vesicles of the envelope, called the peripheral reticulum. More prolonged treatment produced accumulations of lipid droplets, increased staining of the stroma, disintegration of the envelope, and mixing with cytoplasmic contents. Cotton, a notably chilling‐sensitive plant, and bush bean, a somewhat less sensitive plant, showed damage within 6 h when exposed to both light and water stress at chilling temperatures (5°C). Even collard, a chilling‐resistant species, exhibited signs of chilling injury to chloroplasts after 6 h when exposed to both light and water stress but the plastids remained intact throughout the 48 h of treatment. Comparable chilling injury does not occur in cotton until around 72 h if the plants are exposed to water stress or light separately. Bush bean was affected less by separate treatments of light and water stress. The least chilling injury occurred in all three species when they were kept in the dark at a high humidity.
The effect of CO2on potassium transport byChlorella fusca
Authors: TROMBALLA H. W.
Published: April 2006

Abstract.The effect of CO2on net K+uptake byChlorella fuscagrown on high CO2levels was examined by passing 1.5% CO2through algal suspensions gassed previously with air or CO2‐free air Addition of CO2in the light caused a large net uptake of K+(initial velocity 4.2–9.2 mmol s−1m−3cells) which decreased the concentration of K+in the supernatant from 0.1–0.2 mol m−3to 3–10 mmol m−3. In the dark and in the presence of 30 mmol m−3DCMU, no effects were found.

Measurement or the unidirectional K+fluxes by using86Rb+as a label showed that in the presence of 1.5% CO2, influx of K+was increased by a factor of 2–4 while efflux was inhibited completely.

CO2hyperpolarized the membrane potential (determined through TPP+uptake) from –120mV to –130 mV which could not explain the more than 15,000‐fold K+accumulations.

In the light, CO2lowered the intracellular pH (determined with DMO) by 0.5 units. In the dark and in the presence of DCMU only, a small acidification of 0.1 units was found.

During the first 15 min after addition of CO2the malate content of the cells increased from 0.7 to 1.5 mol m−3packed cells.

On the basis of these and earlier results, CO2‐induced net K+uptake is interpreted as a stimulation of an electroneutral ATP‐dependent K+/H+exchange at the plasmalemma. This exchange acts as a ‘pHstat’ by reducing the intracellular acidification caused by production of acidic assimilation products.
Diurnal course of the temperature in aLithopssp. (Mesembryanthemaceae Fenzl) and its surrounding soil
Authors: ELLER BENNO M. , NIPKOW ANDRÉ
Published: April 2006

Abstract.The embedding ofLithopsplants into the soil could be an adaptation to protect the plants from critical low or high temperatures. Thermoelectric measurements onLithops leslieiN.E. Br andL. turbiniformis(Haw.) N.E. Br. were made to determine whether the temperatures of the plant tissues at various depths differ from those in the soil close to the plant. The environmental conditions of their habitat were simulated in a growth chamber equipped with a cold sky to simulate the net radiation loss during a cool and clear night. The effects of microclimatic conditions resulting in dew or hoar‐frost formation on the plant were investigated, as well as the temperature range where freezing occurs.

The results provide no evidence that the embedding of aLithopsplant into the soil yields advantages to the plants in respect of critical low or high temperatures. Plant temperatures are always very close to the soil temperatures at the same depth, but heat fluxes from the bottom or the plant and its surrounding soil to the top of the plant can occur if the plant freezes. No positive effect on the temperature relations could be detected when dew or hoar‐frost is formed on the top of the plant.Lithopsis frost hard to at least –3°C.
The influence of NaCI concentration on the amino acid and neutral soluble carbohydrate content of Dunaliella
Authors: GINZBURG MARGARET E. , BROWNLEE COLIN , JENNINGS DAVID H.
Published: April 2006

Abstract. Two strains of Dunaliella, both grown at 25°C were analysed for their α‐amino acid and neutral soluble carbohydrate content. Glycerol was found as a major cell constituent in both varieties; the amount was roughly proportional to the outside NaCI concentration between 0.5 and 3 kmol m−3, and varied from 3.4% to 45% of the total dry weight of packed cells. The sum of sugars and α‐amino acids did not amount to more than 2% of the total dry weight at any NaCI concentration.
Significance of inhibition of seed germination under the leaf canopy in ash coppice
Authors: PONS T. L.
Published: April 2006

Abstract. The effect on seed germination of the red/far‐red ratio of light (ζ) as modified by a leaf canopy was studied. The artificial light sources used and daylight filtered through leaves appeared to have identical effects in tests with lettuce seed.

The sensitivity of the seeds to ζ varied with the environmental conditions during pretreatment and during the actual germination test. Freshly harvested and dry‐stored seeds of Cirsium palustre were strongly inhibited at low ζ; after stratification, the inhibition was much less. The fact that C. palustre emerges mainly after the coppice is felled could not be explained from these results combined with field data on ζ and the response of germination to temperature.

The ecological significance of inhibition at low ζ is to be found directly after dispersal. Seed germination will then be delayed until the following spring or later.

Geum urbanum showed primary dormancy, which was released by a stratification treatment. No inhibition of germination at low ζ was found in the spring and seeds germinated in light and darkness at low temperatures. These results explain why the species emerges early in spring regardless of the presence of the ash canopy.
Accumulation and conversion of sugars by developing wheat grains. 3. Non‐diffusional uptake of sucrose, the substrate preferred by endosperm slices
Authors: RIJVEN A. H. G. C. , GIFFORD R. M.
Published: April 2006

Abstract. Starch synthesis by developing wheat endosperm slices incubated in liquid media was more rapid, at optimum concentration, from sucrose as external substrate than from glucose and/or fructose. Fructose inhibited conversion of sucrose or glucose. The results are consistent with the hypothesis that sucrose is not hydrolysed in the apoplast before uptake.

Besides a diffusional influx and efflux of labelled sucrose there was a non‐diffusional influx; it was inhibited by dinitrophenol, potassium arsenate, potassium iodide, and parachloromercuribenzene sulphonate (PCMBS). PCMBS inhibited both uptake and conversion of label from 150 molm−314C‐sucrose by 75%. Uptake and conversion of sucrose were stimulated by lowering pH and by fusicoccin, a promoter of proton extrusion.

Extracellular solutes like raffinosc and polyethylene glycol stimulated net uptake of label from 14C‐sucrose — the larger molecule being more effective — this being due to a non‐specific inhibition of diffusional efflux. At too high an osmotic concentration such solutes reduced net uptake; the larger the molecule the lower this transitional concentration.

In conclusion, wheat endosperm is better equipped to convert apoplastic sucrose rather than the hydrolysis products to starch; active loading of sucrose possibly involves proton co‐transport; and large molecules in the extracellular solution reduce the diffusional elllux of loaded substrate.
Fate of chloramphenicol in tobacco tissue culture under various light regimes
Authors: BARG R. , UMIEL N. , NITZAN Y.
Published: April 2006

Abstract. Non‐differentiated tissue cultures (calli) and differentiated tissues (shoots) of tobacco were found to differ in their sensitivity to chloramphenicol (CAP). This phenomenon is especially manifested in darkness and in an illumination regime lacking u.v. and blue light. When the latter are included, CAP's photodegradation products are shown to appear. It seems that one of the main photodegradation pathways is through the production of p‐nitro‐benzaldehyde (p‐NBA) which is further degraded. The possibility that either acetylation or physiological nitration of CAP is the cause for the differential tolerance was eliminated. The chromatographic and radiographic results indicate that in vivo degradation of CAP occurs both in calli and in shoot cultures. One of the in vivo degradation products is CAP‐base.
Effects of light on the catabolism of [2‐14C]‐3‐indole acetic acid in protoplasts, a chloroplast‐rich fraction, and a crude cytoplasmic preparation from barley (Hordeum vulgare L)
Authors: SANDBERG GÖRAN , JENSEN EINAR , CROZIER ALAN
Published: April 2006

Abstract. Combined gas chromatography‐mass spectrometry has been used to identify 3‐indole acetic acid in an extract from protoplasts of barley. In addition, a study has been made of the effect of light on the rate of catabolism of [2‐14C]‐3‐indole acetic acid by protoplasts, a chloroplast‐rich fraction and a crude cytoplasmic preparation from barley leaves. While light enhanced the rate of catabolism of [2‐14C]‐3‐indok acetic acid by protoplasts and, to a lesser degree, by the chloroplast‐rich fraction, it did not affect the catabolic activity of the crude, cytoplasmic fraction. These findings, when considered along with the data of Sandberg, Jensen & Crozier (1983), imply that the rate of turnover of 3‐indole acetic acid, in both protoplasts and chloroplasts, is more rapid in light than it is in darkness.
Interaction between light and chilling temperature on the inhibition of photosynthesis in chilling‐sensitive plants*
Authors: POWLES STEPHEN B. , BERRY JOSEPH A. , BJÖRKMAN OLLE
Published: April 2006

Abstract. Fully expanded leaves of 25°C grown Phaseolus vulgaris and six other species were exposed for 3 h to chilling temperatures at photon flux densities equivalent to full sunlight. In four of the species this treatment resulted in substantial inhibition of the subsequent quantum yield of CO2 uptake, indicating reduction of the photochemical efficiency of photosynthesis. The extent of inhibition was dependent on the photon flux density during chilling and no inhibition occurred when chilling occurred at a low photon flux density. No inhibition occurred at temperatures above 11.5°C, even in the presence of the equivalent of full sunlight. This interaction between chilling and light to cause inhibition of photosynthesis was promoted by the presence of oxygen at normal air partial pressures and was unaffected by the CO2 partial pressure present when chilling occurred in air. When chilling occurred at low O2 partial pressures, CO2 was effective in reducing the degree of inhibition. Apparently, when leaves of chilling‐sensitive plants are exposed to chilling temperatures in air of normal composition then light is instrumental in inducing rapid damage to the photochemical efficiency of photosynthesis.
Comparative ecophysiology of C3 and C4 plants
Authors: PEARCY R. W. , EHLERINGER J.
Published: April 2006

Abstract. In this review we relate the physiological significance of C4 photosynthesis to plant performance in nature. We begin with an examination of the physiological consequences of the C4 pathway on photosynthesis, then discuss the ecophysiological performance of C4 plants in contrasting environments. We then compare the performance of C3 and C4 plants when they occur together in similar habitats, and finally discuss the distribution of C4 photosynthesis with respect to the physical environment, phylogeny, and life form.
Grain or coleoptile tip as the source of IAA in cereal shoots?
Authors: JACKSON D. L. , McWHA J. A.
Published: April 2006

Abstract. Current opinion is divided on whether the free IAA in cereal shoots is derived from the coleoptile tip or from the grain. To date these hypotheses have been considered to be mutually exclusive. In this paper the idea is advanced that both sources may function in the supply of IAA in the shoot. Critical review of the literature shows that such an explanation best fits all the available evidence. It is argued that the relative importance of each source may vary between species of the Gramineae, with the supply of IAA in Avena shoots being derived predominantly from the grain, whereas in Zea the coleoptile tip is the more important source.
CAM and carbon isotope composition: Origin of the constitutive carbon in young leaves of Bryophyllum daigremontianum Berger
Authors: DELEENS E. , QUEIROZ O.
Published: April 2006

Abstract. The export of assimilates from mature leaves towards the young leaves was investigated: 100% and 65% of constitutive matter of leaves of rank 0 (the youngest leaves at the top of the plant) and of rank 1, respectively, originated from other parts of the plant. Photosynthesis of a particular leaf covers the total carbon requirement of that leaf only when it reaches about two‐thirds of its mature size. When pairs of mature leaves were excised, the young leaves increased their own autotrophic growth while the level of assimilates exported by the remaining leaves remained unchanged. The existence of permanent pools in the leaves that export the assimilates was demonstrated; about 50% of the carbon, both in the soluble and insoluble fractions of mature and senescent leaves (ranks 5 to 8 from the apex), was not renewed by turnover. It is shown that the 13C‐enrichment of the components of the starch‐malate sequence in young leaves results, at least in part, from the incorporation of imported carbon chains. The significance of the δ13C diagnosis in CAM determination is discussed in relation to the origin of the constitutive carbon of the leaves.
Calcium fluxes at plasmalemma and tonoplast
Authors: MACKLON A. E. S.
Published: April 2006

Abstract. An account is given of the characterization of calcium fluxes across plasmalemma and tonoplast membranes of root cortical cells, using compartmental analysis. Some of the assumptions associated with the method are discussed. Recent evidence regarding the concentration of free Ca2+ in plant cells, and the mechanisms driving active calcium transport across cell membranes, is reviewed. It is proposed that the evidence from whole cell studies and work at the molecular level is mutually supportive, and some speculation is ventured about the general pattern of calcium transport in higher plant cells.
Calcium in fungi
Authors: PITT D. , UGALDE U. O.
Published: April 2006

Abstract. Recently much experimental evidence has accumulated concerning intracellular calcium and its fundamental role as a regulator in eukaryotic cells. The literature relating to Ca2+ in fungi is large and diverse and this paper draws together the available information and discusses the particular functions of the ion in this group of organisms.

Uptake mechanisms in fungi are considered with special reference to the effect of Ca2+ on permeability and the systems responsible for transport of ions, sugars and amino acids. Discussion of the subcellular locations and distribution of Ca2+ is accompanied by a critique of methodology used in determination of subcellular sites of Ca2+ in fungi. The role of Ca2+ in morphogenesis in fungi is considered with particular reference to selected groups.
Effect of salt and soil water status on transpiration ofSalsola kaliL.
Authors: ESHEL AMRAM , WAISEL YOAV
Published: April 2006

AbstractTranspiration ofSalsola kaliL. plants, grown in small pots under controlled environmental conditions, was followed through a drying cycle of the soil. Three different nutrient solutions were used during the preconditioning growth period: control (C), half‐strength Hoagland's nutrient solution; C plus 150mol m−3NaCl; and C plus 150mol m−3KCl. Soil water content at saturation at the beginning of the drying cycle was 20% (w/w). Both NaCl and KCl treatments modified the plants' response to changes in soil water status. The control plants transpired twice as much (per unit leaf dry weight) as the salt‐treated plants, even when the soil was at maximal water capacity. Transpiration of the control plants remained high, until the soil water content declined to 5%. After that stage the stomata of these plants closed abruptly. Transpiration of the salt‐treated plants started decreasing when the soil water content was approximately 16%, and did so gradually until all the available water was depleted. When transpiration was plotted against soil water potential a sharp decline in the transpiration of control plants was observed with the soil water potential decreasing from ‐0.04 to ‐1.2MPa. Transpiration of the salt‐treated plants decreased gradually over a wide range of soil water potential (−0.8 to −7.0MPa).