bluuebunny/crossref_metadata_2025 huggingface dataset:
Mycochromone decreases ATP‐driven proton translocation in plant plasma membrane‐ and tonoplast‐enriched vesicles
Authors: MACRI F. , VIANELLO A. , COCUCCI M. C.
Published: April 2006

Abstract Mycochromone, a metabolite produced by Mycosphaerella rosigena, inhibits the ATP‐dependent proton translocation and the ATP‐generated electrical potential in pea stem tonoplast‐enriched vesicles, without affecting the H+/K+ exchange induced by nigericin or an artificially imposed proton gradient. The inhibition is dependent on the time of pre‐incubation and mycochromone concentration. In addition, mycochromone inhibits the ATP‐dependent proton translocation in radish plasma membrane‐enriched vesicles, though it does not alter ATPase activity (evaluated by hydrolysis of ATP) in either type of plant vesicle. Mycochromone seems to act on the H+ channels for proton translocation of the H+‐pumping ATPase localized on plasmalemma and tonoplast, without affecting the catalytic site of ATP hydrolysis.
A microcomputer‐controlled system for the automatic measurement and maintenance of ion activities in nutrient solutions during their absorption by intact plants in hydroponic facilities
Authors: GLASS A. D. M. , SACCOMANI M. , CROOKALL G. , SIDDIQI M. Y.
Published: April 2006

Abstract A microcomputer‐based system for the measurement and maintenance of ion concentrations in hydroponic facilities is described. It is based upon the use of ion‐specific electrodes, is entirely automatic, and enables the experimenter to maintain ion concentrations as low as 25 mmol m−3 NO3− and K+ in hydroponic facilities of relatively low volume (26 dm3). The system enables the operator to store values for ambient temperature, irradiance, and any ion concentrations (including pH) which can be measured by means of ion‐specific electrodes. The components of this system are all available commercially so that the whole unit can readily be assembled. The advantages of the computer control extend to the manipulation and display of collected data.
Photoreversible association of phytochrome with membranes. I. Distinguishing between two light‐induced binding responses
Authors: NAPIER R. M. , SMITH H.
Published: April 2006

Abstract Two types of association between phytochrome and crude membrane fractions from oat (Avena sativa L.) are distinguished and compared, and that which comprises only a small fraction of the total phytochrome in extracts prepared in the absence of added divalent cations (Watson & Smith. 1982b) has been studied in detail. Extraction in the presence of phenylmethylsulphonyl fluoride shows that proteolysis of Pr (the red‐light absorbing form) probably does not account for the lower levels of membrane‐associated phytochrome measured after far‐red light than after red light. Difference spectra of soluble and membrane‐associated phytochrome indicate that the latter is much less susceptible to spectral degradation in vitro than is the soluble pool. The stoichiometry of association with the membranes is such that for each phytochrome molecule associated after far‐red light there are three associated after red light and it is argued that this stoichiometry is maintained independent of the extraction pH. The characteristics of this photo‐reversible association of phytochrome with membranes are compared to the characteristics of the widely studied light‐induced enhancement of phytochrome pelletabilily that is dependent on electrostatic interaction of phytochrome and membranes.
Photoreversible association of phytochrome with membranes. II. Reciprocity tests and a model for the binding reaction
Authors: NAPIER R. M. , SMITH H.
Published: April 2006

Abstract A series of fluence‐response curves for the binding of phytochrome to membranes in the absence of divalent cations, as described by Watson & Smith (1982), were constructed to demonstrate that the response obeys the law of reciprocity. Analysis of the binding of Pfr (the far‐red‐absorbing form of phytochrome) showed that two Pfr molecules bind to the membrane for each Pr (the form with an absorption maximum in the red) photoconverted to Pfr in the intrinsic membrane‐bound phytochrome pool. Using this stoichiometry we have been able to model the binding curve of Pr and match the binding data. Pr binding can be simulated if Pr binds only as a consequence of the binding of Pfr, i.e. when Pfr is part of a Pr: Pfr dimer. The enrichment of the membranes with Pfr as a result of the binding of Pfr was also accurately simulated. There is no binding cooperativity. Phytochrome binding is a low‐fluence response and the possibility that it has physiological significance as a mediator of phytochrome action is discussed.
Bacterial leaf symbiosis in Dioscorea sansibarensis: morphology and ultrastructure of the acuminate leaf glands*
Authors: MILLER I. M. , REPORTER M.
Published: April 2006

Abstract The symbiosis between a bacterium and the West African rain forest yam Dioscorea sansibarensis is described for the first time at the ultrastructural level. The bacteria are harboured in glands which run the entire length of the pronounced ‘drip‐tip’ leaf acumenae of the host plant. Each acumen, which may be up to 12 cm long in very large mature leaves, contains from two to six bacterial glands. The glands are kidney‐shaped in cross section and contain numerous multicellular simple trichomes which arise from the epidermis of the gland floor and project into the lumen of the gland. The bacteria are Gram‐negative and variously rod, ovoid, and coccoid in shape. The bacterial cells contain mesosomes, polyhydroxybutyrate granules and large electron‐dense bodies. Bacteria‐free plants grow more slowly and produce one yellowish‐green leaf per node in contrast to the vigorous growth habit of infected plants, with two deep green leaves per node. Infected plants exposed to a variety of atmospheres containing acetylene, both in the light and in the dark, failed to reduce acetylene to ethylene, indicating that nitrogen fixation is not a function of this symbiosis.
2‐trans‐ABA alcohol accumulation in the wilty tomato mutants flacca and sitiens
Authors: LINFORTH R. S. T. , BOWMAN W. R. , GRIFFIN D. A. , MARPLES B. A. , TAYLOR I. B.
Published: April 2006

Abstract Two wilty tomato mutants, flacca and sitiens, fail to increase their endogenous ABA concentration in response to water stress. Instead, a compound accumulates which has been identified as 2‐trans‐ABA alcohol. Levels of this compound have been estimated for three wilty mutants and the control; both before and after water stress. When the compound was biosynthesized in the presence of 18O2, one atom appeared to be incorporated into the primary alcohol group. The possible implications of this for the ABA biosynthetic pathway are discussed.
The Glycine–Glomus–Rhizobium symbiosis. IV. Interactions between the mycorrhizal and nitrogen‐fixing endophytes
Authors: BAYNE H. G. , BETHLENFALVAY G. J.
Published: April 2006

Abstract Soybean (Glycine max (L.) Men) plants were grown under controlled conditions in an experiment designed as a 4 × 4 factorial. The factors were N or P nutrition, with different strains of Rhizobium japonicum or N‐fertilization as levels of the first factor and different species of vesicular‐arbuscular mycorrhizal (VAM) fungi or P fertilization as levels of the other. Organisms used were R. japonicum strains USDA 110, USDA 136, and 61A118, and the VAM fungi Glomus versiforme (Karst.) Berch, Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. and Trappe, and Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. There were 16 treatments: nine Rhizobium + Glomus combinations, three Rhizobium + V and three Glomus+ N combinations, and one non‐symbiotic set of plants supplied with N + P. The tripartite symbioses were evaluated by analysis of variance against the Rhizobium + P and Glomus + N comparison treatments for effects on root and leaf dry mass, root N and P content, nodule mass and activity, and VAM colinization. Significant to highly significant main effects and interactions were found in virtually all evaluations due to both Rhizobium strain and VAM–fungal species. We conclude that different endophyte isolates affect not only the host plant, but also the development and function of their co‐endophytes. These findings establish the existence of inter‐endophyte compatibility, an important consideration when selecting or engineering for desirable endophyte traits.
Increase in cytoplasmic calcium content in internodal cells of Lamprothamnium upon hypotonic treatment
Authors: OKAZAKI Y. , TAZAWA M.
Published: April 2006

Abstract Internodal cells of Lamprothamnium succinctum, a brackish water Characeae, regulate turgor pressure in response to changes in external osmotic pressure (turgor regulation). When internodal cells were transferred to a hypotonic medium containing 3.9 mol m−3 Ca2+, the cell osmotic pressure decreased and the original turgor pressure was recovered. During turgor regulation Ca content of the cytoplasm increased significantly. Lowering the external Ca2+ concentration from 3.9 to 0.01 mol m−3 inhibited this increase in cytoplasmic calcium content. In a hypotonic medium containing 0.01 mol m−3 Ca2+, turgor regulation was inhibited as previously reported (Okazaki & Tazawa, 1986a). Thus transient increase in cytoplasmic Ca, probably in the ionized form, induced by hypotonic treatment may play an important role in turgor regulation.
Methods for quantitative determination of ethylene in aqueous solutions for biological studies
Authors: BASSI P. K. , EASTWELL K. C. , AKALEHIYWOT T. , SPENCER MARY S.
Published: April 2006

Abstract. In many plant physiological studies, quantitative determination of ethylene in aqueous solutions is necessary. We describe two methods for such measurements based on vacuum extraction, or on stripping ethylene from solution with the carrier gas of a gas chromatograph. The gas‐stripping technique is limited by the small sample volumes that can be used, whereas the vacuum extraction technique can accommodate much larger volumes and is useful when the ethylene concentration in the solution is very low. The use of these techniques will facilitate the treatment of submerged plant tissues with known amounts of ethylene, and also the quantitative determination of ethylene from tissues grown in either static or continuous flow liquid cultures.
A systematic approach to the simulation of short‐term processes in the plant‐environment complex
Authors: CHRISTIAN K. R. , MILTHORPE F. L.
Published: April 2006

Abstract. A conceptual framework is presented for modelling short‐term processes in the plant and its environment as an integrated system. Flows of water, water vapour, heat, momentum, CO2, soluble carbohydrate and phosphorus are all described by equations of the same general type, i.e. in terms of diffusivity‐type parameters, capacities and potential gradients. A representative volume of the crop is divided horizontally into layers and vertically between crop and environment for treatment by a finite‐difference method. Vertical flow occurs in the atmosphere, soil, stems and larger roots, andilateral flow between leaves and air, and between finer roots and soil. The interception of direct sunlight and the flux densities of downward and upward diffuse radiation within layers are calculated by a step‐wise procedure.

The conversions of materials within the plant are treated as functions of appropriate state variables. Schemes for carbon and phosphorus provide for flow to and from the translocation system, and for photosynthesis, respiration and growth.

A model of a fully‐established lucerne crop is described and the sensitivity of model performance to changes in a number of parameter values explored. Simulation runs under varying conditions indicate realistic prediction of diurnal trends.
Photosynthetic carbon assimilation in the blue‐green alga Coccochloris peniocystis
Authors: COLEMAN J. R. , COLMAN B.
Published: April 2006

Abstract. Cells of the blue‐green alga Coccochloris peniocystis, grown at air levels of CO2, were exposed to [l4C]bicarbonate in the light for periods of 0.5 to 2.0 s followed by exposure to unlabelled bicarbonate for longer periods of time in the light. The kinetics of tracer movement during these pulse‐chase experiments demonstrate that the principal mechanism of CO2 fixation in this alga is the C3‐pathway although an appreciable amount of the C4 acid aspartate is found as one of the initial products of photosynthesis. Degradation of the labelled aspartate revealed that after 20 s of illumination, over 95% of the radioactivity was located in the β‐carboxyl of this C4 acid. This alga possesses little, if any, capacity for either the enzymatic decarboxylation of C4 acids or the regeneration of phosphoenolpyruvate (PEP) from pyruvate mediated by the enzyme pyruvate, Pi dikinase. These data further demonstrate the lack of a functional C4‐pathway in this alga.
A compartmental model of carbon allocation in the vegetative barley plant
Authors: PROSSER J. , FARRAR J. F.
Published: April 2006

Abstract. The allocation of carbon in a vegetative barley plant is described as an open, three‐compartment model; the three compartments are soluble (which exchanges material with the environment), storage, and structure (both of which exchange material with the soluble compartment). The model shows a good fit with data on 14C kinetics following 14CO2 feeding and some of its assumptions, properties and implications are discussed.
The kinetics of rehydration of detached sunflower leaves from different initial water deficits
Authors: TYREE M. T. , CRUIZIAT P. , BENIS M. , LoGULLO M. A. , SALLEO S.
Published: April 2006

Abstract. The tempo of rehydration of sunflower (Helianthus animus L.) leaves was measured after dehydration in a pressure bomb down to water potentials of −0.5 to −1.6 MPa. When rehydrated from small water deficits (−0.5 to −0.8 MPa) the plot of log rehydration rate versus time is concave. When rehydration starts from large deficits (−1.2 to −1.6 MPa) the semilog plot has a characteristic shoulder, i.e. a rehydration phase of long half‐time is followed by a phase of short half‐time. The experimental curves were fitted with parallel and series models of rehydration. In the parallel model two compartments are connected by resistances in parallel with the water source and rehydrate independently. In the series model one compartment is connected with the water source via a resistance and the second compartment is connected in series with the first by another resistance so that water entering the second compartment must pass through the first. Amongst nineteen experiments, ten could be fitted very closely by both the parallel and series models and nine could not be fitted by either model.
Nutation of growing and georsacting roots
Authors: NEY DANIEL , PILET PAUL‐EMILE
Published: April 2006

Abstract. Growth and geocurvature of the primary roots of maize (cv. LG 11) were analyzed by a filming technique allowing continuous recording, root by root. Typical nutations, in vertical growth and following the downward curvature of the roots, have been observed. The possible relations between these nutations, the elongation, the georeaction and the hormonal mechanisms which control georeaction, are discussed.
Cell‐cell communication in the leaves of Commelina cyanea and other plants
Authors: ERWEE M. G. , GOODWIN P. B. , VAN BEL A. J. E.
Published: April 2006

Abstract. The fluorescent probes 6–carboxyfluorescein and lucifer yellow CH which do not pass the plasmalemma have been used to examine cell‐to‐cell communication in the leaf of Commelina cyanea. Dye movement from cell‐to‐cell occurs in epidermal, spongy and palisade mesophyll, and vascular cells. Dye movement between these tissues was also found. Hence, the epidermis, spongy and palisade mesophyll cells, and vascular tissue are all linked in a continuous symplast. However, dye injected into the epidermal cells rarely moves into guard cells, indicating that these cells are relatively isolated from the surrounding cells. In the same way, guard cells in Vicia faba and the C4 grass Anthephora pubescens also appeared to be isolated from epidermal cells. Thus guard cell isolation from cell‐to‐cell communication appears to be a common phenomenon. Hence, the ion fluxes required for guard cell function must occur via the apoplast.
A study of the impaired growth of roots of Zea mays seedlings at low oxygen concentrations
Authors: ATWELL B. J. , THOMSON C. J. , GREENWAY H. , WARD G. , WATERS I.
Published: April 2006

Abstract. Seedlings of Zea mays L. were grown in the dark at 27°C. Four‐day‐old seedlings were then exposed for 3 days to solutions equilibrated with gas mixtures to give O2 concentrations between 0.02 and 0.25 mol m−3. Root growth was impaired just as severely at 0.06 as 0.02 mol O2 m−3 while growth at 0.16 mol O2 m−3 was about the same as in solutions in equilibrium with air (0.25 mol O2 m−3).

Growth of young seedlings at low O2 concentrations was inhibited to the same extent in nutrient solution and 0.5 ml m−3 CaCl2, showing that the adverse effect of O2 deficits on growth was not due to less uptake of inorganic nutrients. Furthermore, at low O2 concentrations neither exposure of the shoots to a relative humidity of 100% (26.0 g H2O m−3) nor excision of the entire shoot enhanced root growth relative to that in plants with shoots at a relative humidity of 50% (13.0 g H2O m−3). Therefore, for these seedlings growing in the dark, impairment of root growth at low O2 concentrations was not a consequence of water deficits in the shoot or of other shoot‐root interactions.

Total soluble sugars and amino acid concentrations were generally greater at low (0.02–0.06 mol O2m−3) than at high O2 concentrations (0.16–0.25 mol O2 m −3). This applied specifically to the root apices (0–2 mm) and expanding (2–15 mm) tissue except in some experiments where sugar concentrations in expanding tissue were slightly greater at high than at low O2 concentrations.

Critical O2 pressures for respiration of excised root segments were approximately 0.117 and 0.065 mol O2 m−3 in the expanding and expanded zones of the roots, respectively. In contrast, the critical O2 pressure exceeded 0.20 mol O2 m−3 in the apex, suggesting that O2 supply for metabolic processes is most likely to be sub‐optimal in this zone. Our results show clearly that the adverse effects of low O2 concentrations are unlikely to be a consequence of substrate shortage for either respiration or synthesis of macromolecules; low rates of ATP regeneration in growing root tissues are the logical cause for impaired growth in young seedlings while they are being sustained by seed reserves.
The effect of short‐term H2S fumigation on water‐soluble sulphydryl and glutathione levels in spinach
Authors: DE KOK L. J. , BOSMA W. , MAAS F. M. , KUIPER P. J. C.
Published: April 2006

Abstract. Short‐term fumigation of Spinacia oleracea with 380 μg m−3 H2S (250 ppb) resulted in a rapid accumulation of water‐soluble SH‐compounds in the shoots. After 1 h exposure a substantial increase in the SH‐content was already detectable and maximal accumulation, three‐ to four‐fold that in control plants, was observed after 24 h of exposure. Irradiation during H2S exposure only slightly affected the rate and level of SH‐accumulation. H2S fumigation did not affect the water‐soluble SH‐content of the roots. Glutathione was the sole water‐soluble SH‐compound accumulating upon exposure to H2S. It was calculated that during the first hour of exposure to 380 μg m−3 H2S 39% of the possible absorbed H2S was converted into glutathione. The SH‐content of the water‐soluble proteins of the shoots was not affected by H2S exposure. When fumigation was stopped, a rapid decrease in glutathione content was observed and after 48 h the content was comparable to that of the control plants. Contrary to H2S, SO2 fumigation did not result in a rapid accumulation of glutathione in spinach shoots. The possible role of glutathione accumulation during H2S fumigation is discussed.
Some observations on the spectral distribution characteristics of short‐wave radiation within Pinus radiata D. Don canopies
Authors: MORGAN D. C. , WARRINGTON I. J. , ROOK D. A.
Published: April 2006

Abstract. Measurements of the photosynthetic photon flux density (400–700 nm) and of the spectral distribution of photon flux density across the 370–800 nm waveband, were made under both clear and overcast sky conditions above and at various positions within two Pinus radiata canopies of different stocking but similar leaf area indices. The spectra obtained for the daylight conditions (i.e. above forest canopy) were generally similar to those published previously. The spectra for shadelight within the forest canopy showed no blue peak which was characteristic of previously reported measurements which were restricted to the diffuse radiation component. There was almost neutral absorption within the 400–700 nm waveband, and typical lower attenuation in the 700–800 nm waveband. The blue: red ratio was largely unchanged by either canopy type or sky conditions and varied between 0.57 and 0.81. The red: far‐red ratio in shadelight was between 0.22 and 0.41 under clear sky and between 0.68 and 0.95 under overcast sky conditions. Values for daylight were between 1.16–1.22. Calculated phytochrome photoequilibrium values in shadelight were approximately 0.35 under clear sky and 0.46 under overcast sky conditions. In each case there appeared to be no differences between the two canopies with respect to these minimum values.
A simple method for determining the boundary layer resistance in leaf cuvettes
Authors: PARKINSON K. J.
Published: April 2006

Abstract. A new method is described for determining the boundary layer resistance over wet filter paper exposed within a leaf cuvette, based on the energy balance of the filler paper. The boundary layer resistance is calculated by an iterative procedure from measurements of the relative humidity and temperature of the air in the cuvette. Comparisons between the new and the conventional method, involving measurement of the filter paper temperature, show close agreement.

To simplify the method further, a graph has been constructed for the relationship between boundary layer resistance and cuvette relative humidity at temperatures from 15 to 35°C, determined at one value of the ratio of the flow rate through the cuvette to the filter paper area.

An analysis of errors suggests that the new method is less sensitive than the conventional to errors in temperature and humidity.
Location and distribution of symbiotic bacteria during floral development in Ardisia crispa
Authors: MILLER I. M. , DONNELLY A. E.
Published: April 2006

Abstract. The location and distribution of symbiotic bacteria during floral development in Ardisia crispa (Thunb.) A.DC., a species characterized by bacterial leaf nodules, has been studied using light, scanning and transmission electron microscopy. During early floral development, bacteria in mucilage derived from host plant trichomes, become enclosed in a small conical chamber on top of the placenta, as a result of the closure and fusion of the carpel initials. The placental epidermal cells, which appear to be secretory in nature, become detached apically in places forming a network of grooves which traverse the placental surface. The symbiotic bacteria are preferentially located in these grooves. As growth and development of the placenta proceed, the grooves widen and deepen to form channels. The cells lining these channels secrete a mucilaginous material. The network of channels covers the entire placental surface and terminates at the placental margins surrounding the ovules. Bacteria are found within the channels, at the ends of the channels near the margin of the placenta, on the surface of the ovules and in the micropyle. It is suggested that these mucilage‐filled channels are responsible for, and a prerequisite of, ensuring that the bacterial partner is efficiently transmitted from one host generation to the next by providing a mechanism by which the bacteria arc accurately placed within the developing seed.
Physiological effects of sulphur dioxide. 1. The effect of SO2 on photosynthesis and stomatal regulation of Vicia faba L.
Authors: KROPFF M. J.
Published: April 2006

Abstract. The effect of short‐term SO2 fumigation on photosynthesis and transpiration of Vicia faba L. was measured at different irradiances and SO2 concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO2 and the magnitude of the reduction was linearly related to the rate of SO2 uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.

The effect of SO2 on photosynthesis was measured at different CO2 concentrations to analyse the contribution of stomatal and non‐stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO2 diffusion increased as a result of SO2 exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO2 fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO2 concentration.

Analysis of gas‐exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO2 exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO2 than for O2.
Measurement of mass flow of water in the stems of herbaceous plants
Authors: BAKER J. M. , VAN BAVEL C. H. M.
Published: April 2006

Abstract. Heat balance methods of stem flow measurement offer the opportunity to measure directly the mass flow rate of water in plants. We have tested one such approach; the constant power heat balance method of Sakuratani (1981). The results supported his statement of an approximate accuracy of 10% when measuring the transpiration rate of herbaceous plants. The response to sudden changes in stem flow rate is not instantaneous, but investigation of the time constant shows that it decreases as stem flow increases, to the extent that, at flow rates typical of daytime conditions the system is capable of accurately tracking changes in stem flow within 5 min or less.

We describe a new gauge design that is relatively rugged, simple to use with an appropriate digital datalogger and suitable for field use over prolonged periods of time. It does not injure or penetrate the stem, is amenable to continuous and direct recording of the mass flow rate of water in the stem and requires no calibration. A further refinement, which should improve both the accuracy and the dynamic response of the system, is proposed.
The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don
Authors: CONROY JANN P. , KÜPPERS M. , KÜPPERS B. , VIRGONA J. , BARLOW E. W. R.
Published: April 2006

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well‐watered or water‐stressed conditions at CO2 concentrations of either 330 or 660mm3 dm−3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO2concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm3 CO2 dm−3 (plants grown and measured at the same CO2 concentration). Water stress reduced growth and foliar surface area at both CO2 concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO2 where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO2 was higher in the periodically water‐stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO2 enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO2 were generally in the same direction as those at the whole plant level. If the atmospheric CO2 level reaches the predicted concentration of 660 mm3 dm−3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought‐affected regions but total water use is unlikely to be reduced.
Comparative ultrastructural properties of pallisade tissue and spongy tissue chloroplasts from normal and mutant leaves of Pisum sativum L.*
Authors: SCHWARZ H. P.
Published: April 2006

Abstract. The ultrastructure of chloroplasts from palisade and spongy tissue was studied in order to analyse the adaptation of chloroplasts to the light gradient within the bifacial leaves of pea. Chloroplasts of two nuclear gene mutants of Pisum sativum (chlorotica‐29 and chlorophyll b‐less 130A), grown under normal light conditions, were compared with the wild type (WT) garden‐pea cv. ‘Dippes Gelbe Viktoria’. The differentiation of the thylakoid membrane system of plastids from normal pea leaves exhibited nearly the same degree of grana formation in palisade and in spongy tissue. Using morphometrical measurements, only a slight increase in grana stacking capacity was found in chloroplasts of spongy tissue. In contrast, chloroplasts of mutant leaves differed in grana development in palisade and spongy tissue, respectively. Their thylakoid systems appeared to be disorganized and not developed as much as in chloroplasts from normal pea leaves. Grana contained fewer lamellae per granum, the number of grana per chloroplast section was reduced and the length of appressed thylakoid regions was decreased. Nevertheless, chloroplasts of the mutants were always differentiated into grana and stroma thylakoids. The structural changes observed and the reduction of the total chlorophyll content correlated with alterations in the polypeptide composition of thylakoid membrane preparations from mutant chloroplasts. In sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE), polypeptide bands with a relative molecular mass of 27 and 26 kilodalton (kD) were markedly reduced in mutant chloroplasts. These two polypeptides represented the major apoproteins of the light harvesting chlorophyll a/b complex from photosystem II (LHC‐II) as inferred from a comparison with the electrophoretic mobility of polypeptides isolated from the LHC‐II.
The compatibility of osmotica in cyanobacteria
Authors: WARR S. R. C. , REED R. H. , STEWART W. D. P.
Published: April 2006

Abstract. The solutes accumulated by cyanobacteria in response to hyper‐osmotic stress include Na+, K+, sucrose, trehalose, glucosyl‐glycerol, glyeine betaine and glutamate betaine. The compatibility of several of these solutes with glutamine synthetase activity has been examined using cell‐free extracts from a range of freshwater, marine and halotolerant cyanobacteria. All of the solutes tested were compatible with (i.e. non‐inhibitory to) enzymic activity at physiological concentrations and the results demonstrate a rank order of compatibility which correlates with the concentrations at which the organic solutes occur in cyanobacteria, i.e. glycine betaine > polyol‐derivatives > disaccharides and with the upper salinity limit for growth. The protection against inhibition by NaCl (halo‐protection) afforded by these solutes to enzymic activity was also examined. Only glycine betaine was found to exert a significant halo‐protective effect and this may be explained by differences in the mechanism of compatible solute function between small charged molecules and sugars/polyols.
Phototropism and geotropism in hypocotyls of cress (Lepidium sativum L.)
Authors: HART JAMES W. , MACDONALD IAN R.
Published: April 2006

Abstract. The phototropic and the geotropic sensitivities of cress hypocotyls differed in etiolated and in green seedlings. In etiolated seedlings, phototropism was poorly developed and geotropism seemed to be the dominant orientation mechanism. In green seedlings, although geotropic sensitivity was slightly greater, phototropic responses were markedly enhanced, such that photo‐signals could over‐ride, or even reverse, geocurvature. The ‘de‐etiolation’ light pretreatments required to bring about these changes in the photo‐and geo‐systems were different. The slight enhancement of geocurvature could be achieved by short‐term exposure to red light and was reversed by far‐red irradiation. The marked stimulation of photocurvature required extensive irradiation pretreatments.
Changes in sensitivity of Amaranthus retroflexus L seeds to ethylene during preincubation. II. Effects of alternating temperature and burial in soil
Authors: SCHONBECK MARK W. , EGLEY G. H.
Published: April 2006

Abstract. The effects of diurnally alternating temperatures and of prolonged burial in the soil on germination response of redroot pigweed (Amaranthus retroflexus L.) seeds to ethylene were investigated. Percentage germination in a 12 h/12 h, 23° C/35° C temperature regime roughly equalled that observed at constant 35° C, and greatly exceeded that observed at 30°C. Preincubation for 61 d in alternating temperatures, which were gradually increased to simulate soil warming in spring, caused little germination in the absence of ethylene, but considerably enhanced sensitivity to ethylene. Seeds kept in soil in the same temperature regime failed to show the response to ethylene, and the soil itself removed ethylene from the soil atmosphere.

After burial in a field plot either over winter or during the summer, seeds had a very low ethylene response threshold (0.01−0.05 cm3 m−3) and strong response to ethylene (70–95% germination at 51 cm3 m−3 compared to 1–20% without ethylene). Germinability of seeds buried overwinter declined between 10 May (85%) and 24 May (7%), and 90% of those recovered on or after 24 May had a visible rupture in the seed coat. Apparently, germination had begun during burial, but was arrested by unknown causes in an early phase and was followed by seed deterioration.

Although the role of ethylene in germination of buried seeds remains uncertain, the greatly enhanced sensitivity to ethylene observed in pigweed seeds after burial deserves further investigation.
Diurnal changes in the regulatory properties of PEP‐carboxylase in Crassulacean Acid Metabolism (CAM)
Authors: KLUGE M. , BRULFERT J. , QUEIROZ O.
Published: April 2006

Abstract. The CAM plants Kalanchoe tubiflora and K. blossfeldiana were grown under photoperiodically controlled conditions (short days). In these plants, phos‐phoenolpyruvate carboxylase capacity and the sensitivity of the enzyme to the effectors L‐malate (inhibitor) and glucose‐6‐phosphate (activator) were measured throughout the diurnal CAM cycle. In K. tubiflora, enzyme capacity was higher if measured at pH 7.0 than at pH 8.0 and displayed a rhythmical behavior with highest values at the end of the light period. As reported earlier, in K. blossfeldiana PEP‐C capacity was higher during the night. It was more pronounced when plants were kept in CO2‐free air during the dark period. In both plants, the sensitivity of the enzyme to the effectors showed very clear diurnal changes: inhibition by malate and activation by glucose‐6‐phosphate were strikingly higher during the day than during the night; the effect depended on PEP concentration. The changing activation of the enzyme by glucose‐6‐phos‐phate reflects diurnal changes of the Km for PEP which was found to be higher during the day than during the night. Manipulations of malate accumulation by nocturnal application of CO2‐free air did not influence these effects. The results are discussed in context with the metabolic control of CAM.
Membrane potential measurements of marine macroalgae:Porphyra purpureaandUlva lactuca
Authors: REED ROBERT H. , COLLINS JULIAN C.
Published: April 2006

Abstract.Accumulation of the lipophilic cation tri‐phenylmethylphosphonium (TPMP+) has been used to estimate the plasmalemma potential (Φm) of Porphyra purpurea (Rhodophyta, Bangiales) and Ulva lactuca (Chlorophyta, Ulvales). Values of Φm obtained using the Nernst equation were −61 mV and −54 mV respectively; these values compare well with those obtained using glass microelectrodes. A trend of hyperpolarization of Φm in P. purpurea was observed with decreasing external salinity. This hyperpolarization was shown to be primarily due to changes in external K+concentration. Varying external Na+concentration was found to have little effect on Φm. The present data suggest that the membrane potential of P. purpurea is not wholly due to a K+diffusion potential, but may have an electrogenic component.
Optimization of red light‐induced elongation in Avena coleoptile sections and properties of the phytochrome‐mediated growth response*
Authors: SHINKLE J. R. , BRIGGS W. R.
Published: April 2006

Abstract Optimal conditions for studying the elongation response to a 1 mmol m−2, 2‐min pulse of red light in subapical coleoptile sections from dark‐grown oat (Avena sativa L. ev. Lodi) seedlings have been determined. A technique for obtaining standard‐length coleoptile sections without exposing either seedlings or sections to any light has been developed, and is described. The optimal conditions found were: sampling time, 12 h after irradiation; buffer conditions, 5 mol m−3 potassium phosphate with 5% (w/v) sucrose (pH 5.9). The optima were determined by obtaining the time course for light‐induced growth under various conditions. The red light‐induced growth response is linear until 12 h after irradiation, when it undergoes an interruption. Optimal incubation conditions were determined by varying the buffer contents systematically and measuring the responses at the optimal lime determined. The results indicate a distinct difference between auxin‐induced and light‐induced growth responses. Even with variations of basal growth rate and several incubation conditions, the red light‐induced elongation appears to be of a constant magnitude, to persist for a constant time period. and to exhibit a constant lag period between irradiation and the onset of response.

The use of sections that were produced and handled in complete darkness yielded an unusual response to fusicoccin. A linear, high growth rate in response to I mmol m−3 FC was observed for more than 12 h, both in the irradiated sections and in the dark controls.
A novel approach and a fully automated microcomputer‐based system to study kinetics of NO−3, NO−2, and NH+4 transport simultaneously by intact wheat seedlings
Authors: GOYAL S. S. , HUFFAKER R. C.
Published: April 2006

Abstract A 16‐channel fully automated microcomputer‐based system was designed to measure the disappearance of NO−3 NO−2 and NH+4 simultaneously from uptake solutions. The analyses were done using high‐performance liquid chromatography. Statistical procedures were used to generate transport kinetics and interactions amongst NO−3, NO−2 and NH+4 by intact wheat seedlings. The simultaneous analysis of NO−3, NO−2 and NH+4 at real‐time; the accommodation of varying sampling intervals; the capability to study up to 16 experimental units in synchrony; and the analysis of the data with a microcomputer, make this a powerful system for studying transport kinetics and interactions.
Comparative ultrastructure and gas exchange characteristics of the C3–C4 intermediate Neurachne minor S. T. Blake (Poaceae)
Authors: HATTERSLEY P. W. , WONG SUAN‐CHIN , PERRY S. , ROKSANDIC Z.
Published: April 2006

Abstract Ultrastructural and physiological characteristics of the C3‐C4 intermediate Neurachne minor S. T. Blake (Poaceae) are compared with those of C3 and C4 relatives, and C3‐C4Panicum milioides Nees ex Trin. N. minor consistently exhibits very low CO2 compensation points (τ: 1.0, usually 0.3–0.6 Pa) yet has C3‐like δ13C values. CO2 assimilation rates (A) respond like those of C3 plants to a decrease in O2 partial pressure (2 × 104–1.9 × 103 Pa) at ambient CO2 levels, but this response is progressively attenuated until negligible at very low CO2. By contrast, other species of the Neurachneae are clearly either C4 (two spp.) or C3 (seven spp.). For plants grown and measured at different photon flux densities (PFDs), τ for N. minor and P. milioides increases from 0.5 to 1.0, and from 1.0 to 2.1 Pa, respectively, as PFD is decreased from 1860 to 460 μmol m−2s−1. In N. minor, the O2 response of τ is either biphasic as in P. milioides, but much diminished and with a higher transition point, or is very C4‐like. As in C4 relatives, inner sheath cells contain numerous chloroplasts. Their walls possess a suberized lamella, which may make them more CO2‐tight than bundle sheath cells of P. milioides, contributing to the almost C4‐like τ characteristics of N. minor. The biochemical basis of C3‐C4 intermediacy is considered.
Extensin—a major cell wall glycoprotein
Authors: WILSON L. G. , FRY J. C.
Published: April 2006

Abstract The structure of extensin is described in detail. It has a hydroxyproline‐rich backbone, which contains repeating peptides glycosylated by short side chains and it adopts a polyproline II helical conformation. The glycoprotein is synthesized intracellularly and soluble precursors are secreted to the wall, where they are bound, perhaps, by the formation of isodityrosine cross‐links. The various hypotheses, including the most recent ‘warp and weft’ model, which have been suggested to explain the attachment of extensin to the other wall polymers are discussed. The possible functions of extensin in defence and in the control of extension growth are described in addition to its probable structural role. Other glycoproteins which resemble extensin are also mentioned.
Comparative effects of light during growth on the photosynthetic properties of NADP‐ME type C4grasses from open and shaded habitats. I. Gas exchange, leaf anatomy and ultrastructure*
Authors: WARD D. A. , WOOLHOUSE H. W.
Published: April 2006

AbstractMaximum photosynthetic rate (PmaxinZea maysL. was reduced to a much greater extent by neutral shading during growth than in the shade‐adapted C4grassPaspalum conjugatumBerg., although under a high light regime thePmaxofZ. mayswas two‐fold higher than that ofP. conjugatum.In both species the shade‐induced reductions ofPmaxwere not of stomatal origin since the intercellular CO2concentration (Ci) was not decreased by growth under low light levels. TheCiofP. conjugatum(∼200 μPa Pa−1) measured at air levels of CO2and high photon flux densities was 30% greater than that ofZ. maysand, concomitantly, leaf water use efficiency was less. As withPmax, specific leaf weight, leaf thickness and chlorenchyma volume were reduced to a greater extent by shading inZ. maysthan inP. conjugatum.In contrast toZ. mays, bundle sheath chloroplasts ofP. conjugatumcontained well‐defined stacks of grana. Mesophyll chloroplasts ofP. conjugatumdeveloped under a high light regime also contained large amounts of starch. This was not the case withZ. mays.
Comparative effects of light during growth on the photosynthetic properties of NADP‐ME type C4 grasses from open and shaded habitats. II. Photosynthetic enzyme activities and metabolism*
Authors: WARD D. A. , WOOLHOUSE H. W.
Published: April 2006

Abstract The influences of shading during growth upon the activities of several photosynthetic enzymes were examined in NADP‐ME type C4 grasses from open (Zea mays L.) and shaded (Paspalum conjugation Berg.) habitats. The substantial species‐difference in maximum photosynthetic rate observed under a high light regime was correlated with large differences in both enzyme activities and leaf protein contents. With the exception of RuBP carboxylase activity, other photosynthetic enzyme activities in Z. mays were reduced by shading to a similar extent as maximum photosynthetic rate. In contrast, only PEP carboxylase and pyruvate, Pi dikinase activities were decreased by shading in P. conjugatum. As with maximum photosynthetic rate, other photosynthetic enzyme activities in P. conjugatum were relatively insensitive to irradiance during growth. Under a low photon flux density of photosynthetically active radiation (50 μmol m−2 s−1), the flow of [14C] label through photosynthetic intermediates in intact, shade‐grown leaves of P. conjugatum was typical of C4 metabolism. This provides incontrovertible proof for the occurrence of C4 photosynthesis in shaded habitats.
Chloroplast‐ultrastructure and chlorophyll content in leaves fromQuercusbranches with and without epiphytic lichen thalli
Authors: ASCASO C. , RAPSCH S.
Published: April 2006

AbstractThe effect that the massive presence of lichen thalli growing on the branches ofQuercus pyrenaicaandQ. rotundifolialeaves has on their chloroplasts been studied. In both species there were significant decreases in the amount of chlorophylls in the leaves of twigs with a dense cover of lichens in comparison with the leaves from thallus‐free twigs. The areas and perimeter of chloroplasts in leaves from twigs with epiphytes did not differ significantly from those in leaves without epiphytes. However, in leaves with epiphytes the percentage of chloroplast area occupied by starch was higher. InQ. pyrenaicathe number of grana per chloroplast section and per μm2, the percentage of chloroplast stroma occupied by grana, the average number of thylakoids forming grana and the grana width was significantly smaller in leaves near lichen populations. These results are discussed and related to the great chelating capacity of the lichen's substances.
The kinetics of photoinhibition of the photosynthetic apparatus in pea chloroplasts
Authors: BRADBURY M. , BAKER N. R.
Published: April 2006

Abstract The kinetics of a range of chlorophyll fluorescence parameters, non‐cyclic electron transport and the capacity of the thylakoids to bind Atrazine were examined during photoinhibition treatment of intact pea chloroplasts. Parameters of fluorescence induction of chloroplasts in the presence and absence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea at 20 °C and at 77 K were determined. The contributions of photochemical and non‐photochemical quenching processes to the loss of fluorescence during photoinhibitory treatment were assessed. Two distinct phases of photoinhibitory damage were observed. During the initial 5 min period of exposure to light the minimal fluorescence level (Fo) increased, whilst the maximal fluorescence level (FP) decreased, both coupled and uncoupled non‐cyclic electron transport to methyl viologen decreased and the ability to bind Atrazine to the thylakoids decreased. Fluorescence analyses demonstrated that during this period thylakoids were becoming increasingly less efficient at generating and maintaining a transmembrane proton electrochemical gradient. Photoinhibitory damage that occurred at later times between 5 and 20 min was of a very different nature. Both Fo and FP declined, a loss of coupled and uncoupled non‐cyclic electron transport was observed together with a loss of the capacity to photo‐oxidize water. However, no further loss of Atrazine‐binding was associated with such changes. A consistent decrease in the quantum yield of non‐cyclic electron transport was also observed throughout photoinhibition treatment. The possibility of two distinct mechanisms of photoinhibitory damage to the photosynthetic apparatus is discussed.