bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of sensitivity to ozone in seedlings and trees ofQuercus rubraL.
Authors: SAMUELSON L. J. , EDWARDS G. S. 
Published: April 2006

SUMMARYAssessments of ozone sensitivity in tree species have been based primarily on studies of Seedlings without any knowledge of the similarities between seedling and mature tree responses. To determine if seedlings and trees responded similarly to ozone, 2‐yr‐old seedlings and 30‐yr‐old trees ofQuercus rubraL. were fumigated with subambient, ambient and twice‐ambient ozone for one growing season (cumulative doses of 18, 45 and 87 ppm h−1, respectively). Carboxylation efficiency, apparent quantum yield and light‐saturated net photosynthesis of leaves from the lower canopy of the 30‐yr‐old trees were reduced by ambient and twice‐ambient ozone treatment. However, physiological characteristics of leaves from the upper canopy of trees showed no signs of ozone injury. Canopy leaf dry weight of trees was reduced by the twice‐ambient ozone treatment through reductions in leaf area rather than specific leaf weight, but bole diameter and branch growth of trees were unaffected by ozone treatment. In contrast, ozone did not influence leaf physiology of second flush leaves, stem diameter, and height and biomass growth of 2‐yr‐old seedlings. These results indicate that for deciduous hardwood species, studies of seedlings may underestimate the ozone sensitivity of larger and more physiologically mature trees. For large trees with developed canopies, leaf position within the canopy may influence the sensitivity of physiological processes to ozone.
CO2 fluxes of cryptogamic crusts
Authors: JEFFRIES D. L. , LINK S. O. , KLOPATEK J. M. 
Published: April 2006

SUMMARYThe carbon dioxide exchange of Microcoleus‐ and Scytonema‐dominated cryptogamic crusts as related to dehydration was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. The dehydration curves predicted that carboxylation and dark respiration rates for both crust types would become zero at from 4 to 5% water content (W) (approximately 16–23% soil saturation), with the water contents at which the rates became zero significantly lower in the second treatment cycle than the first. The dehydration curves predicted that net photosynthesis rates would become zero at 6.7–11.2% W (27–44% soil saturation), with the water contents at which the rates became zero significantly higher in the second cycle of treatment than the first.
Desiccation as the active principle in heat‐stimulated seed germination of Leucospermum R. Br. (Proteaceae) in fynbos*
Authors: BRITS G. J. , CALITZ F. J. , BROWN N. A. C. , MANNING J. C. 
Published: April 2006

SUMMARYA new seed biological phenomenon in the myrmecochorous, fire‐recruiting fynbos species Leucospermum cordifolium (Salisb. ex Knight) Fourcade is reported. This is the extensive breaking, following desiccation treatment, of the seed testa which in intact, soil‐stored seeds imposes dormancy on the embryo by means of oxygen exclusion. In this study the pericarps of L. cordifolium seeds were removed and seeds with intact exotestas were selected stereomicroscopically. Samples of seeds were placed in nylon bags and suspended over (cone.) H2SO4 or dried silica gel. A third series of seeds were exposed for varying periods to 40 °C, cooled and immersed in water before performing breakage tests on both the exo‐ and endotesta. All treatments resulted in extensive breaking of the exo‐ as well as the endotesta of seeds. The two ‘cool’ desiccating treatments both caused more effective breaking than heat treatments. This indicates strongly that the breakage phenomena are desiccation effects and not caused directly by heat intensity. Rehydration in air before wetting seeds completely prevented breakage effects in all treatments in the endotesta, but not in the exotesta. This further supports the conclusion that endotesta breakage is a function of desiccation plus wetting and not of heat per se. The results suggest that in nature desiccation by fire could break the exotesta and the endotesta as well, if fire is followed soon by rain. These effects amount to effective scarification of the seed and thus suggest a positive correlation, in nature, between heat intensity of fire and emergent seedling numbers.
Resistance of cowpea [Vigna unguiculata (L.) Walp.] to Striga gesnerioides (Willd.) Vatke, a parasitic angiosperm
Authors: LANE J. A. , BAILEY J. A. , BUTLER R. C. , TERRY P. J. 
Published: April 2006

SUMMARYAn in vitro growth system was used to investigate the expression of resistance of cowpea [Vigna unguiculata (L.) Walp.] varieties B301 and 58‐57 to the angiosperm parasite Striga gesnerioides (Willd.) Vatke. Variety Blackeye was included in experiments as a susceptible control. Seeds of S. gesnerioides germinated on the roots of all varieties. Two different mechanisms of resistance were expressed in B301 and 58–57 after penetration of host roots by parasite radicles. The first mechanism was expressed in both varieties; host tissue around invading Striga radicles became necrotic in association with the early death of the parasite and lack of tubercle formation. On variety 58–57, the necrosis response was expressed only when the roots were inoculated with Striga from Burkina Faso but Striga from Mali successfully parasitized the roots of variety 58–57. The second mechanism was observed only on variety B301. Striga radicles infected cowpea roots, tubercles were formed but remained at 1–2 mm in diameter with very limited stem growth. No further development of the parasite occurred in vitro or when infected cowpeas were grown in soil or vermiculite. Similarities between the expression of resistance of cowpea to Striga and ot plants to plant pathogenic fungi are discussed.
Plasmodesmata and the supracellular nature of plants
Authors: LUCAS WILLIAM J. , DING BIAO , VAN DER SCHOOT CHRIS 
Published: April 2006

SUMMARYIn the classical formulation of Münch (1930), plasmodesmata are considered to form simple cytoplasmic bridges between neighbouring plant cells to create the symplasm. This concept has dominated, if not monopolized, the thinking of plant biologists and in particular plant physiologists over the last few decades. Recent advances in ultrastructural, physiological and molecular studies on plasmodesmata indicate that this simple view is in need of revision.Structurally, the higher plant plasmodesma has been revealed to be a supramolecular complex consisting of membranes and proteins. Functionally, evidence is at hand that this complex structure appears to have evolved not only to control the size exclusion limit for intercellular diffusion of metabolites and small molecules, but also to potentiate and regulate intercellular trafficking of macromolecules, including proteins and nucleic acids. In this regard, plasmodesmal transport may share parallel regulatory mechanisms with nucleocytoplasmic transport.Based on these findings, we advance the hypothesis that plants function as supracellular, rather than multicellular, organisms. As such, the dynamics of the plant body, including cell differentiation, tissue formation, organogenesis and specialized physiological function(s), is subject to plasmodesmal regulation. Plasmodesmata presumably accomplish such regulatory roles by trafficking informational molecules which orchestrate both metabolic activity and gene expression. Current and future studies on the evolutionary origin(s) of plasmodesmata are likely to provide valuable information in terms of the genetic and molecular basis for the supracellular nature of plants.ContentsSummary435I.Introduction436II.Plasmodesmal formation, structure and biochemistry436III.Evolution of plasmodesmata445IV.Symplasmic dynamics452V.Plasniodesmal trafficking of macromolecules: parallels with nucleocytoplasmic transport457VI.Role of plasmodesmata in plant development464VII.Concluding remarks469Acknowledgements470References470
Tansley Review No. 59 Leaf boundary layers
Authors: SCHUEPP P. H. 
Published: April 2006

Studies of heat and mass exchange between leaves and their local environment are central to our understanding of plant‐atmosphere interactions. The transfer across aerodynamic leaf boundary layers is generally described by non‐dimensional expressions which reflect largely empirical adaptations of engineering models derived for flat plates. This paper reviews studies on leaves, and leaf models with varying degrees of abstraction, in free and forced convection. It discusses implecations of finding for leaf morphology as it affects – and is affected by – the local microclimate. Predictions of transfer from many leaves in plant communities are complicated by physical and physiological feedback mechanisms between leaves and their environment. Some common approaches, and the current challenge of integrating leaf‐atmosphere interactions into models of global relevance, are also briefly addressed.ContentsSummary477I.Introduction478II.Early studies479III.The formal description of leaf transfer480IV.Effects of turbulence on idealized shapes484V.Effects of aspect ratio and inclination486VI.Leaves and leaf models in forced convection491VII.Leaves and leaf models in mixed and free convection493VIII.Interpretation of leaf shape494IX.Leaves in plant canopies499X.Synopsis and conclusions502References502
Microtubule organization and cell morphogenesis in two semi‐lobed cell types of Adiantum capillus‐veneris L. leaflets
Authors: PANTERIS E. , APOSTOLAKOS P. , GALATIS B. 
Published: April 2006

SUMMARYProtodermal cells of Adiantum capillus‐veneris leaflets are polyhedral, displaying regularly arranged cortical microtubules transverse to the main cell axis. The nascent epidermal cells partly detach from the underlying mesophyll cells by formation of intercellular spaces, containing PAS‐positive material.In early differentiating upper epidermal cells discrete U‐like bundles of cortical microtubules form on the internal periclinal and the anticlinal walls. In contrast, microtubules are randomly scattered along the external periclinal wall. Microtubule bundles of neighbouring anticlinal walls of epidermal cells exhibit an alternating disposition but are directly opposite to those of underlying mesophyll cells. Epidermal cell wall is locally reinforced by thickenings arising under the microtubule bundles and including parallel cellulose microfibrils. The pattern of wall thickenings reflects that of the microtubule bundles. The internal periclinal epidermal cell region expands at the sectors free of wall thickenings, forming several lobes. Simultaneously, intercellular spaces open at the thickened regions of anticlinal walls, which finally become wavy. In contrast, the external periclinal wall does not form any lobes but remains smooth. As a result, epidermal cells become ‘semi‐lobed’. The lobes of lower epidermal cells are less prominent. Mesophyll cells surrounding the endodermis are also ‘semi‐lobed’. Their morphogenesis is achieved by the same mechanism. Colchicine treatment inhibits the ‘semi‐lobed’ morphogenesis of epidermal cells and mesophyll cells surrounding the endodermis and the concomitant intercellular space opening.These observations reveal that the primary event of ‘semi‐lobed’ cell morphogenesis is the organization of two different patterns of the cortical microtubule cytoskeleton in the same cell.
Occurrence of heavy metal tolerance and co‐tolerance in Deschampsia cespitosa (L.) Beauv. from European and Canadian populations
Authors: VON FRENCKELL‐INSAM BEATRIX A. K. , HUTCHINSON THOMAS C. 
Published: April 2006

SUMMARYBy sampling soils and plants from a variety of metal‐contaminated sites in Canada and Europe, heavy metal tolerance and co‐tolerance have been investigated in the grass Deschampsia cespitosa L. (Beauv.). Soils were analyzed for water extractable Ca, as well as for their heavy metal content (Cu, Ni, Zn, Pb, Cd, Co), electrical conductivity, pH and organic matter. Canadian plant material was collected from non‐contaminated areas, as well as sites contaminated by copper and nickel (Sudbury) and nickel and cobalt (Cobalt). European plants were sampled from reference sites and from zinc and lead contaminated locations (Bleikuhle, Pochsand/Germany).Using cloned material the ‘in parallel’ root elongation technique was employed to determine tolerance indices to individual metals (Cu, Ni, Zn, Pb). Among the Canadian plants, patterns of tolerances matched patterns of soil contamination. Thus, at the Cobalt sites, Cu was not present in elevated amounts, and the plants did not exhibit Cu tolerance. Also, evidence suggests that the close correlation of Cu and Ni tolerance among the Sudbury plants was not the result of Cu‐Ni co‐tolerance but occurred because ions of both metals were present in elevated amounts at these sites. In addition to the tolerances expected on soil chemistry, plants taken from metal contaminated sites exhibited enhanced tolerance also to metal ions not elevated in the soils of their origin. This is interpreted as general, non‐specific, low level co‐tolerance. Thus, most Cobalt and Sudbury plants exhibited incidental tolerance at a higher level to Zn and Pb. Correlation analysis revealed very close relations both between Zn and Pb, and especially between Ni and Zn, supporting findings from previous studies. It was concluded that among the Canadian populations tested in this study, Ni tolerance conferred Zn tolerance.Among the European plants examined, the expected tolerances to Zn and Pb were found. However, whereas some control plants from non‐contaminated sites exhibited relatively high tolerances to these metal ions, the tolerance of plants from mines was lower than expected. The Zn and Pb tolerant mine populations had no tolerance to Cu and only very low tolerance to Ni, suggesting that the enhanced Zn tolerance associated with Ni tolerance in the Canadian plants is not necessarily reversible, i.e. Zn tolerance does not necessarily confer Ni tolerance.
The demography of fine roots in response to patches of water and nitrogen
Authors: PREGITZER KURT S. , HENDRICK RONALD L. , FOGEL ROBERT 
Published: April 2006

SUMMARYFine root demography was quantified in response to patches of increased water and nitrogen availability in a natural, second‐growth, mixed hardwood forest in northern Michigan, USA. As expected, the addition of water and water plus nitrogen resulted in a significant overall increase in the production of new fine roots. New root production was much greater in response to water plus nitrogen when compared with water alone, and the duration of new root production was related to the length of resource addition in the water plus nitrogen treatments; the average difference in new root length between the 20vs.40 d additions of water plus nitrogen amounted to almost 600%. Roots produced in response to the additions of water and water plus nitrogen lived longer than roots in the control treatments. Thus, additions of water and water plus nitrogen influenced both the proliferation of new roots and their longevity, with both proliferation and longevity related to the type and duration of resource supply. Results suggest that root longevity and mortality may be plastic in response to changes in soil resource availability, as is well known for root proliferation.
The susceptibility of roots to infection by an arbuscular mycorrhizal fungus in relation to age and phosphorus supply
Authors: AMIJEE BY F. , STRIBLEY D. P. , LANE P. W. 
Published: April 2006

SUMMARYAn apparatus in which plant roots may be challenged uniformly with inoculum of arbuscular mycorrhizal fungi is described. Seedlings of leek (Allium porrum L.) or clover (Trifolium repens L.) were first grown non‐symbiotically in the apparatus for 21 d at three rates of phosphorus (P) addition to soil (150 (P1), 450 (P3) and 750 (P5) mg P kg−1 soil). The positions of individual root tips were recorded, and the root systems then challenged with inoculum of Glomus mosseae (Nicol & Gerd.) Gerdemann & Trappe. Roots were excised 14 d later, and the probability of occurrence of internal infection in successive 3 mm (clover) or 5 mm (leek) sections of root was estimated in first‐order laterals (clover) or main axes (leek) from the proportion of sections at each location of replicate roots that bore internal fungal structures.Only in the region of a root proximal to the position of the root tips at inoculation could data be used to investigate change of probability of infection with cell age. Here, there were sharp declines in probability of infection with proximal distance, in both hosts and in all P treatments. The decline of probability was greater in clover: when expressed in terms of cell age at the time of challenge, there was no infection at PI in cells ≤ 10 d old in leek and none in cells ≤ 7 d old in clover.Models of the form loge, [p1/(1 –p1)] =α+β× distance, where p1 is the estimated probability of infection and a and α are constants, were fitted to these data. The odds on infection are [p1/(1 –p1)]. For leek, β was unaltered by P addition (P3 and P5 curves were parallel to P1) but from a it could be calculated that on average the odds on successful infection at any particular distance were reduced by 37% and 70% by P3 and P5 rates of P addition respectively. In clover the curves for the three P treatments were not parallel. Addition of P appeared to reduce the odds on infection of clover much more than those of leek.We conclude that the simplest explanation for the patterns of infection in leek is that P addition increased the time taken for soil inoculum of G. mosseae to infect roots: the mechanism in clover might be more complex.
Differential hyphal morphogenesis in arbuscular mycorrhizal fungi during pre‐infection stages
Authors: GIOVANNETTI M. , SBRANA C. , AVIO L. , CITERNESI A. S. , LOGI C. 
Published: April 2006

SUMMARYRoots of host plants elicit a local change in morphology in the hyphae of arbuscular mycorrhizal fungi, prior to the formation of appressoria. The elicited hyphae switch from their original branching pattern and apical dominance to differentiate in a new irregular, septate branching pattern with reduced inter‐hyphal spacing. The extensive hyphal development associated with roots of host plants was shown to be due to the differential growth pattern described, and to precede the further cascade of events leading to appressorium formation and the development of a functional symbiosis.
Research on mycorrhizas: trends in the past 40 years as expressed in the ‘MYCOLIT’ database
Authors: KLIRONOMOS JOHN. , KENDRICK W. BRYCE 
Published: April 2006

SUMMARYA detailed analysis of MYCOLIT, a comprehensive bibliographic database of mycorrhizal research containing almost 12000 references, showed some interesting trends over the past 40 yr. During the last four decades, the average number of papers published per year were 84, 110, 214 and 488, respectively. The current rate of publication is about 700 papers per year. Much research has focused on nutrient dynamics, inoculum production, mycorrhiza formation, and morphology and physiology of both vesicular‐arbuscular mycorrhizas (VAM) and ectomycorrhizas (EM). There has been a shift of attention from EM to VAM since 1970. Very little work has been done on the other kinds of mycorrhizas. Barriers to progress in some areas, such as our inability to grow the Glomales in axenic culture, have stimulated a large number of methodological papers over the past decade, while the genetics and molecular biology, especially of VAM, have been neglected. Ecological studies were more numerous than any other kind. However, there was a bias towards laboratory studies as opposed to field studies. Within field studies, researchers focused on agricultural ecosystems, while neglecting disturbed and especially natural systems. This analysis also suggests that we may know less than we think about mycorrhizas, since we have consistently based broad hypotheses and conclusions on studies of a small number of tax. Future research should be directed towards correcting the various imbalances revealed by this analysis.
Growth and stomatal responses of birch (Betula pendula Roth.) clones to ozone in open‐air and chamber fumigations
Authors: PÄÄKKÖNEN E. , PAASISALO S. , HOLOPAINEN T. , KÄRENLAMP L. 
Published: April 2006

SUMMARYIt is evident that even outside the classical high ozone areas some plant species are at risk. In this study seedlings of five birch clones (Betula pendula Roth.) were exposed to a slightly elevated ozone level in an open‐field experiment over two growing seasons. The ozone doses were 1.2 × (1991) and 15 × (1992) higher than the ambient. The clones were also fumigated with 150 nl I1 ozone for 24 d (12 h d−1) in a chamber experiment. They were found to differ in their susceptibility to ozone: ozone fumigation decreased the height growth and leaf biomass, and increased the amount of advanced visible injury in leaves of the most sensitive clone, but did not affect the height growth or amount of visible injury of the most tolerant clone. The other three clones were intermediate with respect to their sensitivity to ozone. In all clones, elevated O3 concentrations increased diffusive resistance to water vapour but increased the stomatal density in the emerging leaves. The appearance of autumn colouring was accelerated in the field experiments. The results support the conclusion that birch populations in Finland can be negatively affected by ozone. The effect is most likely in sensitive birch individuals during ozone episodes.
Developmental biology of lichens
Authors: HONEGGER ROSMARIE 
Published: April 2006

SUMMARYLichen‐forming fungi are a large, taxonomically diverse group of nutritional specialists which acquire fixed carbon from a population of minute green algal or cyanobacterial cells. Mycobionts of foliose or fruticose lichens differ from the rest of the fungi by expressing morphologically and anatomically complex symbiotic phenotypes. The extracellularly located photobiont cell population of these macrolichens is housed and controlled by the quantitatively predominant fungal partner which competes for space above ground, secures adequate illumination and facilitates gas exchange. This review summarizes data on the ontogeny, functional morphology, growth patterns and internal thalline differentiation of macrolichens.

Contents

Summary
659

I.
Introduction
659

II.
Establishment of the lichen symbiosis
662

III.
Growth and cell turnover
669

IV.
Outlook
674

Acknowledgements
674

References
674