bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abaxial and adaxial stomata from Pima cotton (Gossypium barbadense L.) differ in their pigment content and sensitivity to light quality
Authors: LU Z. , QUIÑONES M. A. , ZEIGER E. 
Published: April 2006

ABSTRACTSensitivity to light quality and pigment composition were analysed and compared in abaxial and adaxial stomata of Gossypium barbadense L. (Pima cotton). In most plants, abaxial (lower) stomatal conductances are higher than adaxial (upper) ones, and stomatal opening is more sensitive to blue light than to red. In greenhouse‐grown Pima cotton, abaxial stomatal conductances were two to three times higher than adaxial ones. In contrast, adaxial stomatal conductances were 1·5 to two times higher than abaxial ones in leaves from growth chamber‐grown plants. To establish whether light quality was a factor in the regulation of the relationship between abaxial and adaxial stomatal conductances, growth‐chamber‐grown plants were exposed to solar radiation outdoors and to increased red light in the growth chamber. In both cases, the ratios of adaxial to abaxial stomatal conductance reverted to those typical of greenhouse plants. We investigated the hypothesis that adaxial stomata are more sensitive to blue light and abaxial stomata are more sensitive to red light. Measurements of stomatal apertures in mechanically isolated epidermal peels from growth chamber and greenhouse plants showed that adaxial stomata opened more under blue light than under red light, while abaxial stomata had the opposite response. Using HPLC, we quantified the chlorophylls and carotenoids extracted from isolated adaxial and abaxial guard cells. All pigments analysed were more abundant in the adaxial than in the abaxial guard cells. Antheraxanthin and β‐carotene contents were 2·3 times higher in adaxial than in abaxial guard cells, comparing with ad/ab ratios of 1·5–1·9 for the other pigments. We conclude that adaxial and abaxial stomata from Pima cotton have a differential sensitivity to light quality and their distinct responses are correlated with different pigment content.
Long‐term effects of elevated CO2 and nutrients on photosynthesis and rubisco in loblolly pine seedlings
Authors: TISSUE D. T. , THOMAS R. B. , STRAIN B. R. 
Published: April 2006

ABSTRACTThe effects of long‐term CO2 enhancement and varying nutrient availability on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied on loblolly pine (Pinus taeda L.) seedlings grown in two atmospheric CO2 partial pressures (35 and 65 Pa) and three nutrient treatments (low N, low P, and high N and P). Measurements taken in late autumn (November) after 2 years of CO2 enrichment and nutrient addition showed that photosynthetic rates were higher for plants grown at elevated CO2 only when they received supplemental N. Total rubisco activity and rubisco content decreased at elevated CO2, but there was an increase in activation state. At elevated CO2, proportionately less N was found in rubisco and more N was found in the light reaction components. These results demonstrate acclimation of photosynthetic processes to elevated CO2 through reallocation of N. Loblolly pine grown in nutrient conditions similar to native soils (low N availability) had lower needle N and chlorophyll content, lower total rubisco activity and content, and lower photosynthetic rates than plants grown at high N and P. This suggests that the magnitude of the photosynthetic response to a future, high‐CO2 environment will be dependent on soil fertility in the system.
Natural CO2 springs in Italy: a resource for examining long‐term response of vegetation to rising atmospheric CO2 concentrations
Authors: MIGLIETTA F. , RASCHI A. , BETTARINI I. , RESTI R. , SELVI F. 
Published: April 2006

ABSTRACTIt is estimated that more than 100 geothermal CO2 springs exist in central‐western Italy. Eight springs were selected in which the atmospheric CO2 concentrations were consistently observed to be above the current atmospheric average of 354μmol mol‐1. CO2 concentration measurements at some of the springs are reported. The springs are described, and their major topographic and vegetational features are reported. Preliminary observations made on natural vegetation growing around the gas vents are then illustrated. An azonal pattern of vegetation distribution occurs around every CO2 spring regardless of soil type and phytoclimatic areas. This is composed of pioneer populations of a Northern Eurasiatic species (Agrostis canina L.) which is often associated with Scirpus lacustris L. The potential of these sites for studying the long‐term response of vegetation to rising atmospheric CO2 concentrations is discussed.
Drought‐induced leaf shedding in walnut: evidence for vulnerability segmentation
Authors: TYREE M. T. , COCHARD H. , CRUIZIAT P. , SINCLAIR B. , AMEGLIO T. 
Published: April 2006

ABSTRACTTrees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87% of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water‐stress induced cavitation. These data are discussed in the context of the plant segmentation hypothesis.
Stabilizing microtubules with taxol increases microfilament stability during freezing of rye root tips
Authors: CHU B. , KERR G. P. , CARTER J. V. 
Published: April 2006

ABSTRACTWe have used double fluorescence labelling to investigate the effect of freezing on microtubules and microfilaments in root‐tip cells of rye (Secale cereale L. cv Rymin). Freezing to ‐5°C (which does not kill these cells) caused partial depolymerization of both, but microfilaments were more resistant than microtubules. When microtubules were stabilized against freeze‐induced depolymerization by pre‐treating seedlings with taxol, microfilaments exhibited enhanced stability as well. Almost all the frozen cells containing taxol‐stabilized microtubules also contained microfilaments. When seedlings were treated with the microtubule‐destabilizing drug APM prior to freezing, microfilaments became more susceptible to freeze‐induced depolymerization than in controls. These data suggest a physical interaction between microtubules and microfilaments in these cells.
Gamete orientation and induction of gametogenesis by pheromones in algae and plants
Authors: MAIER I. 
Published: April 2006

ABSTRACTThis review attempts to give a concise overview of the widespread occurrence and the significance, structure and function of pheromones in the chemical communication between individuals of the same species during sexual reproduction in algae and plants. Also included is information on the Oomyctes and the chytridiomyceteAllomyces.The terminology in respect of pheromone function and pheromone‐induced reactions is discussed.
Root demography in kiwifruit (Actinidia deliciosa)
Authors: REID J. B. , SORENSEN I. , PETRIE R. A. 
Published: April 2006

ABSTRACTA rhizotron was used to study fine‐root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty‐one per cent of the roots survived ≤28d, 69% died at an age ≤56d and only 8% survived >252d. For each year, the cumulative length of roots grown was equivalent to about 2·75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover yet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.
Blue light controls solar tracking by flowers of an alpine plant
Authors: STANTON M. L. , GALEN C. 
Published: April 2006

ABSTRACTIn at least18plant families, leaves or flowers can maintain a specific orientation with respect to diurnal movements of the sun. Previous work on heliotropic leaves has demonstrated that blue light (400–500nm) provides the cue for their tracking response. Floral heliotropism occurs in several families of arctic and alpine plants, but the spectral sensitivity of the response has not been studied previously. Moreover, no studies on the spectral sensitivity of any heliotropism have been conducted on wild plants growing in their natural habitat. Working under field conditions, we used coloured acrylic filters to determine whether heliotropism by flowers of the snow buttercup (Ranunculus adoneus) is responsive to broad‐band blue or red light. Flowers were able to orient towards the sun under boxes made entirely of blue‐transmitting filters and in red‐transmitting boxes having a single blue side that faced the sun. In these treatments, solar tracking ability was not significantly different from that observed in adjacent control flowers. In contrast, the precision of solar orientation was significantly reduced in red‐transmitting boxes and red boxes with a single blue side oriented away from the sun. In the early morning, flowers covered by red‐transmitting boxes failed to orient in the direction of sunrise, suggesting that this floral response, unlike that seen in some heliotropic leaves, lacks a residual‘memory’ for previous solar movements.
Functional aspects of secondary carotenoids in Haematococcus lacustris (Girod) Rostafinski (Volvocales). V. Influences on photomovement
Authors: HAGEN C. , BRAUNE W. , VOGEL K. , HÄDER D.‐P. 
Published: April 2006

ABSTRACTSecondary carotenoids are suspected to modulate photomovement in Haematococcus lacustris [Girod] Rostafinski (Volvocales). To investigate the influence of these extrachloroplastic ketocarotenoids on phototactic and photophobic responses in the flagellate stage of the green alga, flagellate suspensions differing in the content of secondary carotenoids were grown from green and red aplanospores. Photo‐orientation of these flagellates induced by unilateral irradiation was investigated using a computer‐aided system for microscopic image analysis. Results were hypothetically summarized as follows:(1) Diminution of precision of the positive phototaxis was found in red flagellates. This might be due to cellular shading of the blue‐light‐sensitive photoreceptor by secondary carotenoids.(2) Red flagellates exhibited an increase in the photophobic response. This finding is discussed in relation to an adaptive increase of the photoreceptor sensitivity, thought to be a result of the higher optical density of the corresponding cell suspension in the blue wavelength region.
Applications of a thermal imaging technique in the study of the ascent of sap in woody species
Authors: ANFODILLO T. , SIGALOTTI G. B. , TOMASI M. , SEMENZATO P. , VALENTINI R. 
Published: April 2006

ABSTRACTWe present applications of infrared thermograph to the direct observation of water transport in stems of woody species. Presently, the method gives only qualitative information on the path of sap movement along the stem, and therefore, does not replace any of the common quantitative methods of sap flow measurement. Nevertheless, the thermal imaging technique provides a novel approach to the study of the ascent of sap and could have a role in supporting more quantitative methods. Thermography permits visualization of the thermal variations of a fairly large area of the stem in real time, and hence, is well suited for spatial analysis of sap movement. Three experiments were carried out during the summers of 1991 and 1992, with the following objectives: to define the sap flow distribution in the active annual rings; to identify grain anomalies in the sap wood; and to study the consequences of induced embolism on the path of sap flow. Altogether, we tested more than 10 woody species (broad‐leaves and conifers) either in natural conditions or in the nursery. We found considerable differences in the spatial distribution of sap flow not only between species and individuals but also within a single tree. Grain anomalies or embolized zones in the xylem, which are easily demonstrated, often further modify the path of sap flow. The irregularity of sapwood dimensions and of sap flow among tree rings requires careful evaluation of the positioning of the probes when using methods for quantitative measurements.
Cellular differentiation in root caps of Zea mays that do not secrete mucilage
Authors: MOORE R. , MILLER I. 
Published: April 2006

ABSTRACTWe quantified the structural changes accompanying cellular differentiation in root caps of Zea mays cv. Ageotropic to determine the developmental basis for the nongraviresponsiveness of their primary roots. Cells of the calyptrogen and columella of primary roots of the ageotropic mutant have structures indistinguishable from those of caps of primary roots of Z. mays cv. Kys the graviresponsive, wild‐type parent of Z. mays cv. Ageotropic. However, the relative volumes of dictyosomes, dictyosome‐derived vesicles and starch in the outermost peripheral cells of wild‐type roots were significantly lower than were those in peripheral cells of mutant roots. This corresponds to a dramatic accumulation of starch and mucilage‐filled vesicles in peripheral cells of mutant roots. Cellular differentiation in root caps of graviresponsive seminal roots of the Ageotropic mutant resembled that of primary and seminal roots of the wild‐type cultivar, and differed significantly from that of primary roots of the mutant. We conclude that the mutation that blocks secretion of mucilage from peripheral cells of Ageotropic roots: (1) expresses itself late in cellular differentiation in root caps; (2) is expressed only in primary (but not seminal) roots of the Ageotropic mutant; and (3) is consistent with malfunctioning dictyosomes and dictyosome‐derived vesicles being the cellular basis for agravitropism of primary roots of this mutant.
Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses
Authors: MUNNS R. 
Published: April 2006

ABSTRACTRecent progress in improving the salt tolerance of cultivated plants has been slow. Physiologists have been unable to define single genes or even specific metabolic processes that molecular biologists could target, or pinpoint the part of the plant in which such genes for salt tolerance might be expressed. While the physiological might be expressed. While the physiological processes are undoubtedly complex, faster progress on unraveling mechanisms of salt tolerance might be made if there were more effort to test hypotheses rather than to accumulate data, and to integrate cellular and whole plant responses. This article argues that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme. Rather, the build‐up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growth.
Feedback limitation of photosynthesis of Phaseolus vulgaris L grown in elevated CO2
Authors: SOCIAS F. X. , MEDRANO H. , SHARKEY T. D. 
Published: April 2006

ABSTRACTThe capacity for photosynthesis is often affected when plants are grown in air with elevated CO2 partial pressure. We grew Phaseolus vulgaris L. in 35 and 65 Pa CO2 and measured photosynthetic parameters. When assayed at the growth CO2 level, photosynthesis was equal in the two CO2 treatments. The maximum rate of ribulose‐1,5‐bisphosphate (RuBP) consumption was lower in plants grown at 65 Pa, but the CO2 partial pressure at which the maximum occurred was higher in the high‐CO2‐grown plants, indicating acclimation to high CO2. The acclimation of RuBP consumption to CO2 involved a reduction of the activity of RuBP carboxylase which resulted from reduced carbamylation, not a loss of protein. The rate of RuBP consumption declined with CO2 when the CO2 partial pressure was above 50Pa in plants grown under both CO2 levels. This was caused by feedback inhibition as judged by a lack of response to removing O2 from the air stream. The rate of photosynthesis at high CO2 was lower in the high‐CO2‐grown plants and this was correlated with reduced activity of sucrose‐phosphate synthase. This is only the second report of O2‐insensitive photosynthesis under growth conditions for plants grown in high CO2.
Effects of atmospheric CO2 enrichment on early growth of Vivia faba, a plant with large cotyledons
Authors: RADOGLOU K. M. , JARVIS P. G. 
Published: April 2006

ABSTRACTSeedlings of Vicia faba L. were grown in open‐top growth chambers at present (P=350μmol−1) and at elevated (E=700μmol mol−1) atmospheric CO2 concentration. The effects of CO2 enrichment on the first phase of growth after germination were examined over 45 d. There were no positive effects of CO2 enrichment on growth of the seedlings during this early phase. No differences were observed in leaf area or in total dry weight. No differences were found in morphology or anatomy of the leaves. The numbers of stomatal and epidermal cells, thickness of leaf, of epidermis and of mesophyll cell‐layers were unaffected by CO2 enrichment. Also, no differences were observed in leaf concentrations of chlorophyll, reducing carbohydrates or starch. These results contrast markedly with results from similar experiments on poplar hybrids and Phaseolus vulgaris obtained in the same growth facility. It seems that the intitial growth is under internal control such that the atmospheric CO2 concentration has no effects. The lack of response in this case may be attributed to the presence and longevity of the large cotyledons which provided available substrate for growth.
Intensity of hydrostimulation for the induction of root hydrotropism and its sensing by the root cap
Authors: TAKAHASHI H. , SCOTT T. K. 
Published: April 2006

ABSTRACTRoots of Pisum sativum L. and Zea mays L. were exposed to different moisture gradients established by placing both wet cheesecloth (hydrostimulant) and saturated aqueous solutions of various salts in a closed chamber. Atmospheric conditions with different relative humidity (RH) in a range between 98 and 86% RH were obtained at root level, 2 to 3mm from the water‐saturated hydrostimulant. Roots of Silver Queen corn placed vertically with the tips down curved sideways toward the hydrostimulant in response to approximately 94% RH but did not respond positively to RH higher than approximately 95%. The positive hydrotropic response increased linearly as RH was lowered from 95 to 90%. A maximum response was observed at RH between 90 and 86%. However, RH required for the induction of hydrotropism as well as the responsiveness differed among plant species used; gravitropically sensitive roots appeared to require a somewhat greater moisture gradient for the induction of hydrotropism. Decapped roots of corn failed to curve hydrotropically, suggesting the root cap as a major site of hydrosensing.
Wall‐to‐membrane linkers in onion epidermis: some hypotheses
Authors: PONT‐LEZICA R. F. , McNALLY J. G. , PICKARD B. G. 
Published: April 2006

ABSTRACTWall‐to‐wall linkage may help maintain cell integrity and polarity, and focus mechanical stress from wall to mech‐anotransductive ion channels within the plasm a lemma. When cells of onion bulb scale epidermis shrink during plasmolysis with CaCl2, the plasmalemma remains attached to the cell wall by Hechtian strands which we hypothesize might possibly be drawn out from linkages fulfilling the above functions. We show that at least many of the attachment loci are independent of the plasmodesmata. A priori, wall glycoproteins seem good candidates for the wall‐to‐membrane linkers; therefore, we investigated the distribution in wall and plasmalemma of antigen recognized by antibody to hydroxyproline‐rich glycoprotein (HRGP). Using fluorescent secondary antibodies, we showed that polyclonal antibodies prepared against wall HRGP from soybean bind to the onion walls (following mild depectination), but also bind to the plasmalemma after the wall is enzymatically digested. The distribution of the antibodies is punctate. On the plasmalemma, the points tend to be scattered more or less uniformly, but can cluster at termini of large streaming strands (which rarely form in wall‐constrained cells.) These streaming strands can be seen to exert tension on the membrane. We hypothesize that (1) the antigen on the surface of the protoplast may correspond to the antigen in the walls, (2) such antigen may be responsible for adhesion of membrane to wall at the linkage sites visualized by CaCl2 plasmolysis, and (3) the linkage sites may be transmembrane proteins to which cytoskeleton can attach at the inner surface.
Nodule growth and activity may be regulated by a feedback mechanism involving phloem nitrogen*
Authors: PARSONS R. , STANFORTH A. , RAVEN J. A. , SPRENT J. I. 
Published: April 2006

ABSTRACTWe present a mechanism of regulation of growth and activity of legume root nodules which is consistent with published experimental observations. The concentration of reduced nitrogen compounds, probably amino acids, flowing into the nodules from the phloem, is sensed by the nodules; growth and activity of the nodules is adjusted accordingly. In many legumes this response may involve changes in the oxygen diffusion resistance of the nodule cortex. A straightforward feedback mechanism in which nodule activity is lowered when reduced N in the phloem is high and increased when it is low is envisaged. Almost all import into nodules is via the phloem sap originating in the lower leaves. As a plant develops, these mature leaves no longer utilize nitrogen delivered in the xylem and so export it in the phloem. In plants with an adequate nitrogen supply (from nodules or combined nitrogen in soil), a high concentration of nitrogen containing compounds in the phloem from the lower leaves may inhibit nodule growth as well as activity. This suggestion is an alternative to the hypotheses of carbohydrate deprivation or nitrate inhibition which are commonly used to explain the effects of combined nitrogen on nodule growth and activity.
Plant growth modelling without integrating mechanisms
Authors: CHEESEMAN J. M. 
Published: April 2006

ABSTRACTThe integration of root and shoot activity for resource acquisition and allocation is a central problem both in experimental physiology and in mathematical growth modelling. A key feature in all proposed solutions is the mechanism by which roots and shoot communicate their resource status, their needs or their demands. In experimental studies, chemical messengers (hormones or nutrients) have been central. In mathematical models, partitioning or productivity functions of one form or another have been incorporated to fill a similar role. In this paper, the central hypothesis is that growth and resource allocation can be based solely on local, internal, non‐structural resource concentrations and local kinetic rules, without the need for additional mechanisms to integrate activities at the organis‐mal level. The specific objective was to develop a formal model using the classical two‐compartment, two‐resource framework which did not include direct intercompartmental coordinating or communicating mechanisms or resource partitioning functions. The formalization effort was successful based on two criteria. First, the ‘plants’ grow at steady and balanced rates when ‘growth conditions’ are constant; and second, challenged with experimental manipulations such as pruning or limitations in resource acquisition, their growth responses mimic those of real plants. Analysis of the results indicates that the complex integrated growth patterns of the modelled plants are emergent properties – having no direct or indirect mechanistic basis – of the simple system. They imply that similar ‘mechanism‐less’ integration is possible in real plants as an emergent property of strictly local, cellular‐level activities.