摘要:

The induction kinetics of chlorophyll fluorescence were measured in dark-adapted barley leaves simultaneously with O2evolution and thermal dissipation using photoacoustic spectroscopy. Significant correlations were revealed between these parameters at low and high (about 5%) CO2concentrations and different irradiances. In general, four phases were resolved in the induction curves of chlorophyll fluorescence or PA signals modulated at 35 Hz (O2-dependent component) or 400 Hz (thermal dissipation). During the first 10–15 s after onset of actinic light, a high level of reduction of the primary quinone acceptor of photosystem II (QA), a low magnitude of the O2-dependent photoacoustic signal, and a high level of heat production measured as the photoacoustic signal at 400 Hz were maintained. Further illumination led to a partial QA−reoxidation, an increased rate of O2evolution, and a decline in heat production owing to an increased energy storage at the level of the plastoquinone pool. At low CO2concentration, the steady-state level of all the above parameters was attained at the end of the first minute of illumination and remained unmodified after prolonged leaf irradiation. In contrast, the development of an additional slow peak followed by its dissipation was found for all parameters examined under high CO2concentration and strong irradiance. The position of the slow peak in the kinetics of the O2-dependent photoacoustic signal preceded the corresponding peak of chlorophyll fluorescence measured under actinic light but coincided with the position of the peak in the kinetics of photochemical quenching. The position of the slow peak in the kinetics of thermal dissipation strictly corresponded to the one of chlorophyll fluorescence. A linear correlation was found between the magnitudes of the O2-dependent component of the photoacoustic signal and the extent of photochemical quenching. The results indicate that correlations in the kinetics and magnitudes of chlorophyll fluorescence, O2evolution, and thermal dissipation are due at least in part to the dependence of the above parameters on the redox state of the acceptor side of photosystem II.Key words: photosynthesis, chlorophyll fluorescence, thermal dissipation, CO2, O2evolution, plastoquinone, photoacoustic.

ISSN:0008-4026    

DOI:10.1139/b97-854

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Nectar production and concentration were measured on male and female plants of six experimental lines ofSilene latifolia(Caryophyllaceae) that differ in disease resistance. Differences between the sexes and among the lines were found for nectar production, concentration, and total sugar production during the first 24 h of anthesis. Females produced more nectar of lower concentration than did males, and males secreted more sugar than did females during the first day of anthesis. However, nectar traits of males and females resembled one another within a line, suggesting a genetic correlation between the sexes. Further, the additive genetic basis for this trait appears weak. InS.latifoliarepeatabilities for nectar traits were low and differed between females and males, so the heritabilities must be extremely low. Groups of plant lines that are "susceptible" and "resistant" to the fungal pathogenMicrobotryum violaceumdid not differ in nectar parameters. Therefore resistance to this pollinator-borne disease does not appear to influence nectar production.Key words:Microbotryum(=Ustilago), plant – pathogen interactions, pollinator reward, anther-smut disease, dioecy, floral nectar.

ISSN:0008-4026    

DOI:10.1139/b97-855

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The time course of acetylene reduction was examined in field nodules of speckled alder (Alnus incanassp.rugosa(Du Roi) Claus.) and sweet gale (Myrica galeL.) with an open flow-through system. When detached speckled alder nodules were measured in the laboratory, there was an initial peak rate of nitrogenase activity between 2 and 3 min followed by pronounced declines to 50% of the peak rate (early summer) and 66% (late summer) at 9 min, after which there was little further change. Speckled alder nodules measured in the field while still attached to the plant also had a peak rate between 2 and 3 min. Most sweet gale nodules had a peak rate at 2–3 min and a sharp decline to 27% at 21 min followed by a partial recovery to 49% at 60 min. The time courses of field nodules of speckled alder and sweet gale were comparable with those of intact, growth chamber grown seedlings. The initial peak rate is the most accurate measure of nitrogenase activity and the only reliable way to measure this is with an open, flow-through system. We describe a simple, inexpensive, flow-through system for use in the field.Key words: acetylene-induced decline,Alnus incanassp.rugosa, actinorhizal plants,Myrica gale, nitrogen fixation, nitrogenase activity.

ISSN:0008-4026    

DOI:10.1139/b97-856

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla(Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI ≤ 0.4 and red/far red (R/FR) ratio ≤ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth.Key words: light, light quality, leaf morphology, acclimation.

ISSN:0008-4026    

DOI:10.1139/b97-857

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Small-subunit ribosomal RNA sequence data are presented forRhodogorgon carriebowensisNorris et Bucher (Rhodogorgonales, Rhodophyta) andGalaxaura marginata(Ellis et Solander) Lamouroux (Nemaliales, Rhodophyta). Data for these species were included in a matrix consisting of small-subunit ribosomal RNA sequences for 70 taxonomically diverse red algal species. Distance, parsimony, and maximum-likelihood analyses of these data all strongly support (100% of bootstrap replicates for distance and parsimony) a close alliance between the Rhodogorgonales and Corallinales. Our alignment includes 19 species representing six florideophyte orders (Acrochaetiales, Batrachospermales, Corallinales, Nemaliales, Palmariales, Rhodogorgonales) in which pit plugs are characterized by two cap layers. Distance and parsimony analyses resolve a monophyletic lineage including all "two-cap-layer" species. Our parsimony-derived molecular phylogeny was used to test a published hypothesis of pit-plug evolution. Four aspects of Pueschel's hypothesis are consistent with the results of our molecular systematic study: (i) "naked" plugs represent the ancestral type, (ii) outer cap layers are homologous structures, (iii) domed outer caps are ancestral to plate-like outer caps, and (iv) cap membranes are a derived feature within the two-cap-layer lineage. Directions for future research are discussed.Key words: Acrochaetiales, Batrachospermales, Corallinales, molecular systematics, Nemaliales, Palmariales, phylogeny, pit plug, Rhodogorgonales, Rhodophyta.

ISSN:0008-4026    

DOI:10.1139/b97-858

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The different types of tapetum found in the spermatophyta are described, along with associated characters. The characters (taken singly, pairwise, or in multiple combinations) are (i) tapetum types; (ii) cell walls, tapetum types, and loculus; (iii) tapetal cells individually, tapetum types, and loculus; (iv) number of pollen grains enveloped by tapetal cells and type of pollen dispersing unit; (v) cell types and tapetum types; (vi) number of nuclei per cell and tapetum type; (vii) cycles of hyperactivity; (viii) exine formation; (ix) orbicles; (x) peritapetal membrane; (xi) plastid differentiation; (xii) stage of pollen development in which tapetal cells degenerate and type of pollen coat; (xiii) storage vacuoles; (xiv) sporophytic proteins; and (xv) devices of tapetal origin responsible for compound pollen formation and pollination. Examples are given and an analytical key of structural and functional diversity is provided as a helpful approach to the study of the tapetum.Key words: tapetum types, activities, pollen dispersing units.

ISSN:0008-4026    

DOI:10.1139/b97-859

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Genetic variation at 32 polymorphic random amplified polymorphic DNA loci was analysed in the ascomycete canker pathogen fungusGremmeniella abietina(Lagerb.) Morelet collected from one plantation ofPinus contortaDougl. ex Loud, in northern Sweden. The genetic variability maintained in theG.abietinapopulation was high. Many different multilocus genotypes were found on each tree and in each sampling site within the plantation. The clonal fraction of the population was small, and identical genotypes were found either on the same tree or branch or on trees in the same sampling site. The finding of very few widely distributed clones suggests that the effective dispersal of asexual spores is limited to a few metres and resulted in small clusters of clones in local sites. Analysis of molecular variance revealed that 45.3% of the total variation was attributable to differences among isolates within trees, 22.5% to trees within sites and 32.3% to sampling sites differences. Allele frequencies at most of the loci varied significantly among the sampling sites and average total genetic diversity over the 32 loci was 0.27 indicating high population subdivision. The factors that could have contributed to the observed population structure were discussed.Key words:Gremmeniella abietina, genotype and clone distribution, population subdivision, RAPD.

ISSN:0008-4026    

DOI:10.1139/b97-860

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Yellow starthistle (Centaurea solstitialisL.), a diploid annual native to the Mediterranean region, has rapidly colonized a variety of disturbed habitats in the western United States since its accidental introduction in the mid-19th century. Population genetic attributes were investigated in association with the species' colonizing success. Allozyme electrophoretic surveys were conducted for a total of 22 populations from California, Washington, and Idaho, including the southern and northern extremes of its distribution in the Pacific states. High levels of allozyme variation exist within populations, on average 43% of loci were polymorphic, with 2.88 alleles, a heterozygosity of 0.38, and gene diversity of 0.35 per polymorphic locus. At the species level, 56% of loci were polymorphic, with 2.85 alleles per locus, and the total gene diversity was 0.172. With the exception of a marginal population San Diego, the level of genetic diversity was similarly high in all regions. Lack of interpopulation genetic divergence (GST = 0.095) suggests that majority of the colonial populations were founded by a large number of genotypes and that high levels of gene flow may exist between local populations (Nm = 2.38). Information on genetic structure of the weed populations may aid our understanding of the species' colonizing ability in North America and is important for predicting the effectiveness of biological control program.Key words: allozyme variation,Centaurea solstitialis, population genetics, weed colonization, yellow starthistle.

ISSN:0008-4026    

DOI:10.1139/b97-861

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Two species of trichomycetous fungi,Asellaria armadillidii(Asellariales) andParataeniella armadillidii(Eccrinales), were found attached to the hindgut lining of the pill bug,Armadillidium vulgare. In the former fungus, the thallus was composed of a basal cell bearing an apical whorl of many lateral branches. Electron micrographs in ultrathin sections showed that an electron-opaque holdfast substance surrounded the rhizoidal projections of the basal cell. The cross wall of the thallus was the typical bifurcate type of septum, i.e., the wall flared at the central perforation which was occluded by an electron-opaque plug. This is the third report of this type of septum in the order Asellariales. The bifurcated structure of the septal wall was found to remain at the distal portion of the mature arthrospore cell wall. InP.armadillidii, both primary and secondary infestation sporangiospores were examined in ultrathin sections. A number of electron-transparent pits, 40–50 nm in diameter, were found in the basal portion of the cell wall of secondary infestation sporangiospores which were still contained inside the sporangium.Key words:Asellaria, bifurcate septum,Parataeniella, Trichomycetes.

ISSN:0008-4026    

DOI:10.1139/b97-862

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Pathogenicity and random amplified polymorphic DNA (RAPD) markers were used to assess genetic diversity among 93 highly virulent isolates ofLeptosphaeria maculans(Desm.) Ces. & de Not. collected from two oilseed rape (Brassica napusL.) fields located 20 km apart in southern Ontario. Using three differential host cultivars ofB.napus(Westar, Quinta, and Glacier), isolates were separated into three pathogenicity groups (PG). Eighty percent of the isolates were in PG4, virulent on all cultivars, and 11% were in PG3, virulent on two cultivars. The remaining 9% were tentatively placed into a new PG, PG5, because they showed intermediate virulence on the three cultivars. There was no relationship between RAPD pattern and either PG or isolate collection site. Cluster analysis of RAPD patterns, based on estimates of genetic distance, grouped isolates into two populations, corresponding to the field of collection. Analysis of molecular variance attributed 45.5% of the total variance to differences between populations and 54.5% to differences among isolates. Every isolate was genetically distinct, suggesting that the populations of the fungus were produced mostly by sexual reproduction. We conclude that inoculum in the two fields consisted principally of ascopores, derived almost equally from sources that were common to both fields and sources that were distinct for each field.Key words: highly virulent,Leptosphaerla maculans, random amplified polymorphic DNA (RAPD), genetic variation.

ISSN:0008-4026    

DOI:10.1139/b97-863

出版商:NRC Research Press    

年代:1997

数据来源: NRC