摘要:

Paclobutrazol increased the tolerance of soybean (Glycine maxL. cv. AC Bravor) seedlings to elevated levels of ultraviolet-B radiation (UV-B: 280 – 320 nm). Within 3 days of exposure to elevated UV-B, nontreated seedlings were photosynthetically less efficient, and by the end of the 11th day of treatment their leaf areas and fresh masses were, respectively, 55 and 44% smaller than their counterparts not irradiated with UV-B. In contrast, paclobutrazol-treated seedlings maintained full photosynthetic efficiency throughout the duration of UV-B irradiation, and their leaf areas and fresh masses were only reduced by 30 and 22%, respectively. No changes in flavonoid composition occurred as a result of the paclobutrazol or UV-B radiation treatments, but UV-B tended to increase the quantities of photosynthetic pigments. The leaves from paclobutrazol-treated seedlings were significantly thicker than those of nontreated seedlings, and SEM analyses showed that the treated seedlings had much denser epicuticular wax layers than the controls. No significant changes in protein expression occurred during exposure to elevated UV-B and (or) paclobutrazol. Further studies with paclobutrazol-treated plants may lead to a better understanding of one or more of the mechanisms employed by plants to tolerate elevated levels of UV-B.Key words: leaf fluorescence, paclobutrazol, pigments, protein synthesis, SEM, UV-B radiation.

ISSN:0008-4026    

DOI:10.1139/b95-088

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The macrofungal Basidiomycete community of aPinus sylvestrisforest was investigated in 50 plots, 2 × 2 m, to see how vegetation composition and space influenced the distribution of saprotrophic and ectomycorrhizal fungi. Mantel tests and partial Mantel tests revealed a relationship between total cover of the field layer and mycorrhizal fungi, and total cover of the bottom layer and saprotrophic fungi. These results are consistent with the predictions that mycorrhizal fungi are mainly influenced by plant species present in the root zone, whereas saprotrophic fungi are mainly influenced by the plant species of the bottom layer. Variation in the abundance of tree species did not influence the distribution of macrofungal species at this scale. The spatial patterns of fungal distribution found in this study did not deviate significantly from a random distribution. Indirect ordination showed that the ectomycorrhizal fungi mainly responded to a gradient in cover of the field layer, whereas the saprotrophs seemed to respond to a complex gradient of cover of field and bottom layer, moisture, and paludification. A direct ordination using both vegetation and fungi descriptors indicated that some of the covariation in the saprotrophic fungi and the bottom layer might be coordinated responses to changes in the field layer. A considerably higher β diversity was found among the fungi than in the vegetation.Key words: basidiomycetes, saprotrophic fungi, mycorrhizal fungi, fungi–vegetation relationships, Mantel test, ordination.

ISSN:0008-4026    

DOI:10.1139/b95-089

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Seed mass values are given for 140 species of primary lowland rain forest and associated secondary forests in Singapore. Among shade-tolerant species of primary forest there is a trend for a decrease in mean seed mass with tall trees > woody climbers > small trees > shrubs > herbs; the differences between tall trees and small trees or shrubs or herbs, and between herbs and small trees or woody climbers are significant. There are a few light-demanding herbs or shrubs in the primary forest; among small trees, light demanders have significantly lower seed mass values than shade tolerators. In 9 out of 13 comparisons within taxa including both shade tolerants and light demanders the former had appreciably larger seeds than the latter. Two out of 13 comparisons involved very small seeded shade tolerators, and one a notably large-seed light demander. Many shade-tolerant herbs, shrubs, and trees have seed mass values much smaller than those of trees of secondary forest conventionally regarded as small seeded, and exploit moist, litter-free sites, e.g., steep microslopes. The trees of secondary forests on degraded soils do not differ significantly in seed mass from those on nondegraded soils.Key words: seed mass, light requirement, regeneration, tropical rain forest, phylogenetic analysis.

ISSN:0008-4026    

DOI:10.1139/b95-090

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The leaf anatomy and ultrastructure of the North AmericanPhyllospadixspeciesP.serrulatusRupt. ex Aschers.,P.scouleriHook, andP.torreyiWatson are described. The unique anatomical and ultrastructural features of these species are compared with those of other seagrasses and their possible functional significance is discussed. All three species have ultrastructures similar to those in other members of the family Zosteracae. Subcuticular cavities, wall ingrowths, and numerous mitochondria and chloroplasts with well-developed grana are present in the blade epidermal cells and the adaxial sheath epidermal cells, indicating that these cells may play a major role in photosynthesis, osmoregulation, and absorption. Plasmodesmata are present occasionally between adjacent epidermal cells, and also between epidermal and mesophyll cells, suggesting that solutes can be transferred symplastically between these tissues. The vascular bundle sheath cells are not easy to recognize, as cell walls are thin and not suberized. The phloem contains both normal and nacreous-walled sieve tubes that may be functional. The walls of the phloem parenchyma cells facing nacreous-walled sieve tubes possess weak wall ingrowths, leading to speculation that these parenchyma cells may play an important role in solute translocation. The absence of suberin lamella in bundle sheath cells and the presence of a small xylem element in each vascular bundle suggest that the water flow in xylem elements in these seagrasses may be limited and that water is taken directly from the water column by leaf epidermal cells and is transported apoplastically along cell walls. The three North AmericanPhyllospadixspecies can be separated by anatomical characters such as number of vascular bundles, the shape of epidermal cells in both transverse sectional and surface views, and the distribution of fibre bundles. It is proposed thatP.serrulatusis taxonomically more closely related to the JapaneseP.iwatensisMakino than toP.scouleriandP.torreyiand that there is no detectable hybrid species occurring betweenP.scouleriandP.torreyi.Key words: anatomy, ultrastructure, seagrasses,Phyllospadix, North America.

ISSN:0008-4026    

DOI:10.1139/b95-091

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This study examines the effects of nutrient supply (three N–P–K treatments: 75, 225, and 375 kg∙ha−1; 12.5% N, 8.5% P, 16% K) on growth, allometry, and architecture ofUrtica dioicaL., an expansive clonal plant found throughout Central Europe. Biomass allocation was significantly affected by nutrient supply: higher nutrient doses resulted in less biomass allocation to belowground organs, whereas the period of intensive production of aboveground biomass was prolonged. Shoot height increases with nutrient supply. The height ratios were constant over time. Within each treatment and each harvest, inflorescence biomass was positively correlated with shoot height. Branching of the main shoots (number of lateral branches) was positively correlated with plant height and changed with time. The number of new rhizomes was affected by both treatment and harvest, especially in older plants. The results suggest that high nutrient supply increased the allocation of biomass both to reproductive organs and to vegetative organs.Key words: allometry, biomass allocation, clonal plant, nutrients, plant architecture,Urtica dioic

ISSN:0008-4026    

DOI:10.1139/b95-092

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The effects of accumulation of dead belowground plant parts (detritus) of the emergent macrophyteScirpus maritimuson the growth of this species were studied under greenhouse conditions. In the first experiment, the growth ofS. maritimusseedlings decreased when the thickness of the detritus mat, covered by a layer of sediment, was increased. The position of a 5 cm thick detritus mat in a 15-cm column filled up with sediment had only a minor effect on the growth of this species. In the second experiment, fragmentation of detritus turned out to increase the growth-reducing effects found in the first experiment. Unfertilized seedlings with the lowest dry mass proportionally allocated most dry matter to their roots. The supply of nutrients either did not or only partly compensated for differences in plant growth among substrate types. In all instances the supply of nutrients strongly reduced the proportional dry matter allocation to roots, whereas differences in nutrient concentrations in plants diminished. In most instances the soil redox potential indicated a reduction of iron, but iron concentrations in the shoots never reached toxic levels. The most likely explanations for the poor growth ofS. maritimusin its own detritus are the release of toxic compounds into the substrate and deficiency of oxygen to the roots due to reduced substrate conditions.Key words: freshwater lakes, emergent macrophytes, organic matter, degeneration.

ISSN:0008-4026    

DOI:10.1139/b95-093

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Corallorhiza trifidaChâtelain, or pale coral root orchid, is a heterotrophic, leafless, rootless, terrestrial orchid with a circumboreal distribution. Because of its relative inability to photosynthesize, the orchid obtains energy through the digestion of fungal hyphae that grow within the cells of its contorted, yellowish, coralloid rhizomes. Recently, we isolated and cultured strains of a slow-growing basidiomycete with bright yellow, clamped hyphae that are typical of the fungal cells present inC.trifidaendomycorrhizas from different treed habitats at widely distributed locations in the northern hemisphere. By inoculating the roots ofPinus contortaDouglas ex Loudon seedlings with this fungus we were able to demonstrate its ability to form distinctive ectomycorrhizas with an ectotrophic, woody plant. The formation of endomycorrhizas withC.trifidaand ectomycorrhizas withP.contortaindicates that in nature a triple symbiosis, with a circumboreal distribution, exists among certain trees, the coral root orchid, and this yellow basidiomycete that links the two and functions as a mycorrhizal symbiont in both.Key words:Corallorhiza trifida, orchid mycorrhiza, triple symbiosis, ectomycorrhiza,Pinus contorta.

ISSN:0008-4026    

DOI:10.1139/b95-094

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The cellular interaction between the smut fungusUstacystis waldsteiniaeand its hostWaldsteinia geoideswas analyzed by serial-section electron microscopy using chemically fixed and high-pressure frozen – freeze-substituted samples. After penetration, each haustorium extends a short distance into the host cell where it often forms up to three short lobes. The haustorium is wholly ensheathed by a prominent matrix. The matrix is a complex structure, differing significantly from that known of other fungal plant parasites: it is filled with amorphous, electron-opaque material in which membrane-bounded, coralloid vesicles are embedded. During the contact phase of the hypha with the host cell wall, vesicles with electron-opaque contents accumulate in the contact area of the hypha where they appear to fuse with the fungal plasma membrane and extrude their contents. Subsequently, the host cell wall increases in electron opacity and matrix material becomes deposited between host plasma membrane and host cell wall exactly at the ends of the altered areas in the host cell wall. The coralloid vesicles within the matrix, however, are of host origin: exocytosis of Golgi products into the matrix results in the formation of coralloid vesicular buds in the host plasma membrane. Subsequently, the buds seem to detach from the host plasma membrane to flow as coralloid vesicles into the matrix. Matrix development continues during penetration and after penetration at the haustorial tips. After host wall penetration, the fungal cell wall comes in contact with the matrix. The fungal component of the matrix may play a key role in the inducement of these transfer cell-like compartments in host cells responding to infection.Key words: freeze substitution, haustoria, high-pressure freezing, host–parasite interaction, smut fungi,Ustacystis waldsteiniae.

ISSN:0008-4026    

DOI:10.1139/b95-095

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

We examined the population genetic structure of the ectomycorrhizal fungusLaccaria bicolor(Maire) Orton using single spore homokaryotic cultures from 33 basidiomes collected in northern Minnesota in association with red pine (Pinus resinosaAit.), jack pine (Pinus banksianaLamb.), and trembling aspen (Populus tremuloidesMichx.) of three age-classes (0–20 years, 21–40 years, and > 41 years). Mating competence between cultures of isolates, as determined by the presence of clamp connections, revealed the presence of two subpopulations that were not freely interbreeding, one composed of 29 dikaryons, the other of 3 dikaryons. Phenetic cluster analysis using random amplified polymorphic DNA markers did not reveal differentiation between these subpopulations. Clustering failed to reveal genetically distinct groups based on incompatibility group, tree host species, or geographic origin of isolates.Key words: heterogenic incompatibility, RAPD, population genetics.

ISSN:0008-4026    

DOI:10.1139/b95-096

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Symbiotic relationships between wheat plants and mycorrhizal fungi may play an important role in the growth and productivity of wheat as a crop. Wheat cultivars differ in their ability to form such relationships, but little is known concerning the genetic basis of such differences. A set of intervarietal substitution lines having individual chromosomes from 'Cheyenne' (nonresponsive to mycorrhizae) substituted into 'Chinese Spring' (nonresponsive to mycorrhizae) were tested for mycorrhizal response in greenhouse experiments. Chromosomes 1A, 5B, 6B, 7B, 5D, and 7D of 'Cheyenne' had positive effects on the trait, with homologous groups 5 and 7 in the B and D genomes having the largest effects. Chromosome 5B of 'Hope', a nonresponsive cultivar, also had a positive effect in a 'Chinese Spring' background. In addition, the mycorrhizal responsiveness of a range of other cultivars and ancestors was tested to expand information on the trait in wheat and its relatives. Data on chromosome location of mycorrhizal-response genes and genotypic responsiveness will permit more effective genetic manipulation of this trait.Key words: pathogenesis, growth response, vesicular–arbuscular mycorrhizae.

ISSN:0008-4026    

DOI:10.1139/b95-097

出版商:NRC Research Press    

年代:1995

数据来源: NRC