bluuebunny/crossref_metadata_2025_split huggingface dataset:
Foraging for light: photosensory ecology and agricultural implications
Authors: BALLARÉ C. L. , SCOPEL A. L. , SÁNCHEZ R. A. 
Published: November 2003

ABSTRACTThis mini‐review is concerned with one of the facets of the sensory physiology of plants that, in the last decade, has been intensively studied using genetically altered plants and eco‐physiological techniques – the perception of the proximity of neighbouring plants through specific informational photoreceptors. We focus on the signalling mechanisms that allow individual shoots to ‘forage’ for light in patchy and highly dynamic canopy environments. We present evidence from recent experiments suggesting that the fitness of each individual plant in the population, the growth of the population as a whole, and the degree of growth inequality among neighbours are all strongly dependent on the timing and precision of foraging mechanisms controlled, at least partially, by phytochrome‐B‐like phytochromes. This evidence is discussed in the context of potential impacts on yield of agricultural crops resulting from the artificial alteration of plant sensitivity to proximity photo‐signals. Directed overexpression of phytochrome genes appears to be an interesting avenue to explore in order to alter the photomorphogenesis of specific organs (or developmental stages) without affecting the overall ability of the plants to forage for light.
Phytochrome gene diversity
Authors: MATHEWS S. , SHARROCK R. A. 
Published: November 2003

ABSTRACTThe structures and functions of the phytochrome apoprotein genes (the PHY genes), their diversity across the plant kingdom, and their evolution are central concerns in the study of red‐light sensing in plants. We summarize here recent advances in two areas relating to these topics: (1) the characteristics of the PHY gene family in Arabidopsis thaliana, the higher plant species for which the most extensive information on these genes is available, and (2) the similarity relationships, phylogeny, and evolutionary implications of PHY gene sequences and partial sequences which have been described from various plants. Together, these two areas of study, one directed at understanding in detail the phytochromes present in a single species and the other directed at a much broader understanding of PHY gene relatedness and distribution, are producing an increasingly clear picture of the diversity and evolution of plant red‐light photoreceptors. Moreover, they suggest that the complexity of the phytochrome family has increased as land plants have evolved novel morphologies.
Gravity, light and plant form
Authors: HANGARTER R. P. 
Published: November 2003

ABSTRACTPlants have evolved highly sensitive and selective mechanisms that detect and respond to various aspects of their environment. As a plant develops, it integrates the environmental information perceived by all of its sensory systems and adapts its growth to the prevailing environmental conditions. Light is of critical importance because plants depend on it for energy and, thus, survival. The quantity, quality and direction of light are perceived by several different photosensory systems that together regulate nearly all stages of plant development, presumably in order to maintain photosynthetic efficiency. Gravity provides an almost constant stimulus that is the source of critical spatial information about its surroundings and provides important cues for orientating plant growth. Gravity plays a particularly important role during the early stages of seedling growth by stimulating a negative gravitropic response in the primary shoot that orientates it towards the source of light, and a positive gravitropic response in the primary root that causes it to grow down into the soil, providing support and nutrient acquisition. Gravity also influences plant form during later stages of development through its effect on lateral organs and supporting structures. Thus, the final form of a plant depends on the cumulative effects of light, gravity and other environmental sensory inputs on endogenous developmental programs. This article is focused on developmental interactions modulated by light and gravity.
Effects of elevated CO2 on leaf gas exchange in beech and oak at two levels of nutrient supply: consequences for sensitivity to drought in beech
Authors: HEATH J. , KERSTIENS G. 
Published: November 2003

ABSTRACTBeech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were grown from seed for two whole seasons at two CO2 concentrations (ambient and ambient + 250 μmol mol−1) with two levels of soil nutrient supply. Measurements of net leaf photosynthetic rate (A) and stomatal conductance (gs) of well‐watered plants were taken over both seasons; a drought treatment was applied in the middle of the second growing season to a separate sample of beech drawn from the same population. The net leaf photosynthetic rate of well‐watered plants was stimulated in elevated CO2 by an average of 75% in beech and 33% in oak; the effect continued through both growing seasons at both nutrient levels. There were no interactive effects of CO2 concentration and nutrient level on A or gs in beech or oak. Stomatal conductance was reduced in elevated CO2 by an average of 34% in oak, but in beech there were no significant reductions in gs except under cloudy conditions (–22% in elevated CO2). During drought, there was no effect of CO2 concentration on gs in beech grown with high nutrients, but for beech grown with low nutrients, gs was significantly higher in elevated CO2, causing more rapid soil drying. With high nutrient supply, soil drying was more rapid at elevated CO2 due to increased leaf area. It appears that beech may substantially increase whole‐plant water consumption in elevated CO2, especially under conditions of high temperature and irradiance when damage due to high evaporative demand is most likely to occur, thereby putting itself at risk during periods of drought.
Interactions among stomata in response to perturbations in humidity
Authors: MOTT K. A. , DENNE F. , POWELL J. 
Published: November 2003

ABSTRACTThe existence of patchy stomatal closure suggests interactions among neighbouring stomata that synchronize stomatal movements in small areas of a leaf. To test for such interactions, water vapour partial pressure (ewv) for a small group of stomata was controlled independently of that for the surrounding stomata using gas flow from a small needle. The ewv for the surrounding stomata was controlled with a larger gas flow, termed the primary flow. The spatial pattern of ewv isobars caused by the needle flow was assessed experimentally and theoretically. Stomatal apertures were monitored following perturbations in ewv of the primary flow and the needle flow. When ewv of the primary flow was perturbed and that of the needle flow held constant, stomata for which there was little or no perturbation in ewv responded similarly to stomata experiencing the perturbation. When the ewv of the needle flow was perturbed and that of the primary flow held constant, many stomata experiencing little or no perturbation responded similarly to those experiencing a large perturbation. The results are discussed in relation to a mechanism for stomatal interactions that has been proposed in a previous study [Haefner, Buckley & Mott (1997) Plant, Cell and Environment 20, 1087–1097, this issue].
Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field
Authors: TISSUE D. T. , THOMAS R. B. , STRAIN B. R. 
Published: November 2003

ABSTRACTForest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long‐term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size‐dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60–130% increase) than in the winter (14–44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non‐structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy‐level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.
Mannitol inhibits growth of intact cucumber but not pea seedlings by mechanically collapsing the root pressure
Authors: STAHLBERG R. , COSGROVE D. J. 
Published: November 2003

ABSTRACTThe positive xylem pressure (Px) in cucumber hypocotyls is a direct extension of root pressure and therefore depends on the root environment. Solutions of the electrolyte KCl (0.10 osm) reduced the hypocotyl Px transiently (biphasic response), while the Px reduction by mannitol solutions was sustained. The amplitudes of the induced Px reduction depended directly, and the degree of Px restoration after stress release depended indirectly, on the size of the initial positive Px, indicating that mannitol released the root pressure by a mechanical rather than osmotic mechanism. Mannitol treatment and other means of root pressure reduction revealed two separate growth responses in the affected cucumber hypocotyls. Only steep Px drops (following root excision or root pressure release in mannitol) directly cause a rapid, transient drop in growth rate (GR). Both rapid and slow (after root incubation in KCN or NEM) decreases in root pressure, however, led to a sustained growth inhibition of cucumber hypocotyls after about 30 min. This delay characterizes the growth response as an indirect consequence of the Px change. Pea seedlings, which lacked root pressure and had a negative Px throughout, showed extremely small changes in epicotyl Px and GR after root incubation in mannitol. It is apparent that the higher sensitivity of cucumber growth to mannitol depended on the presence and release of root pressure.
Impact of gas transport through rice cultivars on methane emission from rice paddy fields
Authors: BUTTERBACH‐BAHL K. , PAPEN H. , RENNENBERG H. 
Published: November 2003

ABSTRACTTwo Italian rice (Oryza sativa var. japonica) cultivars, Lido and Roma, were tested in the field for methane production, oxidation and emission. In two consecutive years, fields planted with the rice cultivar Lido showed methane emissions 24–31% lower than fields planted with the cultivar Roma. This difference was observed irrespective of fertilizer treatment. In contrast to methane emissions, differences in methane production or oxidation were not observed between fields planted with the two cultivars. Plant‐mediated transport of methane from the sediment to the atmosphere was the dominating pathway of methane emission. During the entire vegetation period, the contribution of this pathway to total methane emission amounted to c. 90%, whereas the contribution of gas bubble release and of diffusion through the water column to total methane emission was of minor significance. Results obtained from transport studies of tracer gas through the aerenchyma system of rice plants demonstrated that the root–shoot transition zone is the main site of resistance to plant‐mediated gas exchange between the soil and the atmosphere. The cultivar Lido, showing relatively low methane emissions in the field, had a significantly lower gas transport capacity through the aerenchyma system than the cultivar Roma. Thus, the observed differences in methane emissions in the field between the cultivars Lido and Roma can be explained by different gas transport capacities. Apparently, these differences in gas transport capacities are a consequence of differences in morphology of the aerenchyma systems, especially in the root–shoot transition zone. It is, therefore, concluded that identification and use of high‐yielding rice cultivars which have a low gas transport capacity represent an economically feasible, environmentally sound and promising approach to mitigating methane emissons from rice paddy fields.
dr and spr/sr mutations of Chlamydomonas reinhardtii affecting D1 protein function and synthesis define two independent steps leading to chronic photoinhibition and confer differential fitness
Authors: HEIFETZ P. B. , LERS A. , TURPIN D. H. , GILLHAM N. W. , BOYNTON J. E. , OSMOND C. B. 
Published: November 2003

ABSTRACTThe effects of introduced chloroplast gene mutations affecting D1 synthesis, turnover and function on photosynthesis, growth and competitive ability were examined in autotrophic cultures of Chlamydomonas reinhardtii (Chlorophyta) adapted to low or high irradiance. Few discernible effects were evident when the mutants were grown in low light (LL, 70 μmol m−2 s−1). The herbicide‐resistant psbA mutation Ser264→ Ala (dr) slowed electron transfer and accelerated D1 degradation in cells grown under high light (HL, 600 μmol m−2 s−1). The maximum rate of light‐and CO2‐saturated photosynthesis, cell growth rate and competitive ability in the dr mutant were reduced compared to wild type under HL. However, the wild‐type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. In spr/sr cells grown under HL, D1 synthesis was reduced by 40–60% compared to wild type and D1 degradation was accelerated, leading to a 4‐fold reduction in D1 pool size. The reduced D1 levels were accompanied by an elevation of Fo and a decline in Fv/Fm, quantum yield and maximum rate of CO2‐saturated photosynthesis. Chemostat experiments showed that the growth rate and competitive ability of spr/sr were reduced against both wild type and dr.
Kinetics of nitrate and ammonium absorption and accompanying H+fluxes in roots ofLolium perenneL. and N2‐fixingTrifolium repensL.
Authors: HØGH‐JENSEN H. , WOLLENWEBER B. , SCHJOERRING J. K. 
Published: November 2003

ABSTRACTKinetic parameters for NH4+and NO3−uptake were measured in intact roots ofLolium perenneand actively N2‐fixingTrifolium repens.Simultaneously, net H+fluxes between the roots and the root medium were recorded, as were the net photosynthetic rate and transpiration of the leaves. A Michaelis–Menten‐type high‐affinity system operated in the concentration range up to about 500 mmol m−3NO3−or NH4+. InL. perenne, theVmaxof this system was 9–11 and 13–14 μmol g−1root FW h−1for NO3−and NH4+, respectively. The corresponding values inT. repenswere 5–7 and 2 μmol g−1root FW h−1. TheKmfor NH4+uptake was much lower inL. perennethan inT. repens(c.40 compared with 170 mmol m−3), whileKmvalues for NO3−absorption were roughly similar (around 130 mmol m−3) in the two species. There were no indications of a significant efflux component in the net uptake of the two ions. The translocation rate to the shoots of nitrogen derived from absorbed NO3−‐N was higher inT. repensthan inL. perenne, while the opposite was the case for nitrogen absorbed as NH4+.Trifolium repenshad higher rates of transpiration and net photosynthesis thanL. perenne.Measurements of net H+fluxes between roots and nutrient solution showed thatL. perenneabsorbing NO3−had a net uptake of H+, whileL. perennewith access to NH4+andT. repens, with access to NO3−or NH4+, in all cases acidified the nutrient solution. Within the individual combinations of plant species and inorganic N form, the net H+fluxes varied only a little with external N concentration and, hence, with the absorption rate of inorganic N. Based on assessment of the net H+fluxes inT. repens, nitrogen absorption rate via N2fixation was similar to that of inorganic N and was not down‐regulated by exposure to inorganic N for 2 h. It is concluded thatL. perennewill have a competitive advantage overT. repenswith respect to inorganic N acquisition.
Freezing exposure releases bud dormancy in Betula pubescens and B. pendula
Authors: RINNE P. , HÄNNINEN H. , KAIKURANTA P. , JALONEN J. E. , REPO T. 
Published: November 2003

ABSTRACTBud dormancy in woody plants is released by long‐term exposure to non‐freezing chilling temperatures, whereas freezing temperatures have been considered to have little or no effect. However, the present results demonstrate that short‐term exposure to freezing can release bud dormancy in Betula pubescens (Ehrh.) and B. pendula (Roth). Short‐term freezing during the dormancy induction phase improved the release of bud dormancy only if an adequate level of dormancy had been reached. In fully dormant or chilled plants both the percentage and the speed of bud‐burst increased, the more so the lower the temperature. Our results rule out the possibility that endogenous abscisic acid could be directly involved in the physiological control of bud dormancy release. The fast, easily applicable method presented here for bud dormancy release could further investigations into the biochemical and biophysical background to the process. The mechanisms of bud dormancy release and its relationship to cold acclimation are discussed in the light of these results, as also are the implications of the findings for modelling of bud dormancy.
Effects of ozone on the plasma membrane proteins in Arabidopsis thaliana (L.) leaves
Authors: TOKARSKA‐SCHLATTNER M. , FINK A. , CASTILLO F. J. , CRESPI P. , CREVECOEUR M. , GREPPIN H. , TACCHINI P. 
Published: November 2003

ABSTRACTThe protein pattern of leaf plasma membranes from Arabidopsis thaliana (L.) Landsberg erecta was analysed in order to detect changes induced by acute short‐term ozone treatment. Plasma membranes were isolated 0, 3 and 8 h after the end of a 2 h fumigation of the plants with 500 nmol mol−1 of O3. Proteins extracted from plasma membranes were separated by high‐performance two‐dimensional polyacrylamide gel electrophoresis. Eight hours after the end of fumigation, one new protein appeared and the amounts of two other proteins increased significantly. The reported study is a first step towards the identification of plasmalemma proteins altered by ozone and to a more detailed characterization of structural changes occurring in the plasma membrane after ozone exposure.
Water use efficiency of two succulents with contrasting CO2 fixation pathways
Authors: ELLER B. M. , FERRARI S. 
Published: November 2003

ABSTRACTTwo succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C3 pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled‐environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO2 fixation was similar in the two species. This result confirms that the daily CO2 fixation of CAM plants is as high as that of morphologically similar C3 plants adapted to the same habitat. As expected, both species reduced CO2 fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol−1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better ‘water saver’ than a C3 plant does not necessarily hold for CAM and C3 plants with similar growth forms growing under the same environmental conditions.
Influence of ozone on transgenic tobacco plants expressing reduced quantities of Rubisco
Authors: WIESE C. B. , PELL E. J. 
Published: November 2003

ABSTRACT RbcS‐antisense transformed tobacco plants (Nicotiana tabacum cv. Petit Havana) expressing reduced quantities of Rubisco protein were used to examine the role of Rubisco quantity in determining ozone (O3) sensitivity. Transformed and wild‐type plants were exposed to O3 in the greenhouse and in the field. Stomatal conductance, net photosynthesis and Rubisco protein quantity were measured at various times. Antisense‐transformed genotypes responded to O3 by exhibiting rapid, severe foliar necrosis. The wild‐type plants responded more slowly, exhibiting limited injury. Decreases in stomatal conductance, net photosynthesis or Rubisco quantity in plants exposed to O3 were not observed in asymptomatic leaves. Total biomass was lower for the transformed genotypes and decreased in both genotypes after exposure to O3. Shoot–root ratio and specific leaf area were higher in the transformed genotypes and increased in both genotypes with exposure to O3. Measurements of intercellular airspace demonstrated the presence of larger intercellular spaces in the transformed plants. The indirect effects of the rbcS antisense transformation, including morphological changes in the leaf, probably rendered the transformed plants more sensitive to the oxidant. The decreased quantity of Rubisco is not thought to be directly related to increased O3 sensitivity in the transformed plants.