摘要:

The lipid bilayers of plant membranes are normally liquid crystalline, reflecting the inherent rotational motion of membrane fatty acids at physiological temperature. With the onset of senescence, the chemical composition of membrane lipids changes resulting in lipid phase separations within the bilayer. These phase changes render the membranes leaky and lead to loss of essential ion gradients and impairment of cell function. The separation of lipid phases appears to be attributable to an accumulation of lipid metabolites in the bilayer that are formed during turnover and metabolism of membrane lipids. These metabolites are normally released from membranes as lipid–protein particles found in the cell cytosol and within organelles. The lipid–protein particles also contain catabolites of membrane proteins and appear to serve as a vehicle for removing lipid and protein metabolites that would otherwise destabilize the bilayer. They bear structural resemblance to oil bodies, which are abundant in oil seeds, and have been found in leaves, cotyledons, and petals as well as in insect and animal tissue. The accumulation of lipid metabolites in senescing membranes and ensuing separation of lipid phases appear to reflect impairment of lipid–protein particle release from membranes as tissues age and to be a seminal cause of membrane dysfunction with advancing senescence.Key words: lipid bilayer, lipid phase separation, lipid–protein particles, membrane, oil body, senescence.

ISSN:0008-4026    

DOI:10.1139/b97-096

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Aquatic hyphomycete assemblages on decomposing leaf litter of the exotic speciesEucalyptus globulusLabill. were compared with those on the native riparian speciesAlnus glutinosa(L.) Gaertn. in three low-order streams of the Agüera watershed (Basque Country – Cantabria, Spain). These streams contrast by the importance of eucalypt in the riparian vegetation and by the nutrient contents in the water. Neither the total conidial production nor the number of fungal species differed between the two leaf species in any of the streams. Fungal colonization of eucalypt leaves appeared to be delayed by about 2 weeks, probably owing to their high content in inhibitory constituents. WhileFlagellospora curvulaIngold largely dominated pioneer assemblages on both leaf species, the second most important species,Lunulospora curvulaIngold, exhibited a preference for eucalypt. In the stream surrounded by eucalypt, the fungal diversity was surprisingly lower on eucalypt than on alder. In the stream with higher orthophosphate concentrations, the conidial production was similarly increased on both leaf species. The present data together with recent results from a similar investigation in Portugal suggest a minor impact of eucalypt on the activity and diversity of aquatic hyphomycete leaf-associated assemblages in southern European streams.Key words: aquatic hyphomycetes, eucalypt, alder, leaf litter, stream.

ISSN:0008-4026    

DOI:10.1139/b97-097

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A study was conducted to understand the effects of certain phenolics, terpenoids, and their equimolar mixture through agar gel and soil growth bioassays and their recovery from soils. The eight compounds selected for this study werep-hydroxybenzoic acid, ferulic acid, umbelliferone, catechin, emodin, 1,8-cineole, carvone, and betulin. Lettuce (Lactuca sativaL.) was used as test species for agar gel and soil growth bioassays. Root and shoot growth of lettuce was inhibited for all the above except emodin and catechin. However, in soils treated with different phenolics and terpenoids, only root growth of lettuce was inhibited, whereas shoot growth was promoted. Recovery ofp-hydroxybenzoic acid and umbelliferone was higher in unautoclaved soils, while that of catechin was lower. Recovery in relation to degradation of compounds and the significance of additive activities of compounds are discussed.Key words: phenolics, allelopathy, terpenoids, soil,Lactuca sativa.

ISSN:0008-4026    

DOI:10.1139/b97-098

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The influence of low (70%) and high (90%) relative humidity on epiphytic growth, development, and survival ofTilletiopsis pallescens, a ballistospore-forming yeast-like fungus, on cucumber leaves was investigated. In addition, survival of the fungus in the presence or absence of powdery mildew (Sphaerotheca fuliginea) colonies was determined. Growth and development were visualized by scanning electron microscopy of the leaf surface, and survival was quantified as colony-forming units recovered on a semiselective medium. Development ofT.pallescensfrom blastospores that were applied to healthy leaves at 70% relative humidity was limited to small colonies that grew adjacent to leaf veins 7 days after application. At 90% relative humidity, extensive hyphal networks had developed within 3 days of blastospore germination, and ballistospores were produced within 7 days. Growth and sporulation ofT.pallescenswere most extensive at the base and on the surface of leaf trichomas. In the presence ofS.fuliginea,T.pallescensmycelium developed adjacent to hyphae and conidiophores of the pathogen within 3 days at both 70 and 90% relative humidity. However, at 90% relative humidity, growth ofT.pallescenswas more extensive and ballistospores were produced within 5 days, and there was visible collapse of mildew hyphae. There was no evidence of penetration of the leaf or mildew hyphae byT.pallescens. Survival ofT.pallescenswas significantly (P = 0.05) increased at 1 and 5 days postapplication at 70% relative humidity when blastospores were amended with 1% (v/v) canola oil – lecithin. Survival at 90% relative humidity was also significantly increased with canola oil – lecithin and by the presence ofS.fuliginea. The addition of liquid paraffin – lecithin or liquid paraffin – Tween had no effect on survival when compared to the control. The results from this study indicate that growth and survival ofT.pallescensare enhanced by high relative humidity and by the presence of powdery mildew, and canola oil – lecithin amendment improved survival on the leaf surface at reduced ambient humidity.Key words: antagonism, biological control, powdery mildew, yeast.

ISSN:0008-4026    

DOI:10.1139/b97-099

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Coastal dunes are very dynamic systems, particularly where the coast is rising as a result of isostatic rebound. In those environments, succession proceeds from plants highly tolerant to sand accumulation, salt spray, and low nutrient availability to less disturbance-tolerant and stress-tolerant, more nutrient-demanding, and supposedly more competitive species. In the subarctic, the regional climate exacerbates the stresses imposed by local abiotic conditions on the dunes. I hypothesized that facilitation would be particularly significant on the foredune of subarctic coastal dune systems because of intense stresses (local and regional) and frequent disturbance in the form of sand deposition. Belowground and aboveground plant biomass was sampled at three different periods during the 1990 growing season along transects perpendicular to the shoreline on a coastal dune system in subarctic Quebec (Canada). The three herbaceous perennials found on the foredune (Honckenya peploides,Elymus mollis, andLathyrus japonicus) were segregated in time during the growing season and in space along the topographical gradient. The biomass ofHonckenya, the first species encountered as one progresses from the upper part of the beach towards the foredune ridge, was not correlated to substrate physicochemistry. However, the biomass ofElymusand that ofLathyrus, the next two species to appear along the flank of the foredune, were related to pH, Mg, Na, and Cl (negatively), and to P and Ca (positively). These results suggest variable linkages between substrate physicochemistry and plant species along the foredune, possibly in relation to species-specific tolerance for abiotic conditions and requirements for substrate resources or to microscale influence of the plants themselves on substrate physicochemistry. Removal experiments carried out over 2 years revealed only one significant unidirectional interaction between these three species along the topographical gradient, and little plant control over abiotic variables (e.g., soil temperature, wind velocity, and photosynthetically active radiation). Early primary succession on subarctic coastal dunes (and elsewhere) appears to be under the control of strong limiting abiotic conditions. As plants slowly gain more control over the physical environment, interspecific interactions (positive and negative) may become more significant.Key words:Elymus mollis, facilitation,Honckenya peploides, inhibition,Lathyrus japonicus, removal experiment, succession, tolerance.

ISSN:0008-4026    

DOI:10.1139/b97-100

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Histological studies on crosses between distantly relatedAlstroemeriaspecies revealed post-fertilization crossing barriers. Developmental events between normal developing seeds (after self-fertilization) and aborting seeds (after cross-fertilization) during 0–32 days after pollination were compared. In both cases the pollen tube remained as a swollen structure inside the micropyle during eight days, and thereafter degenerated. The first division of the zygote occurred within four days after pollination and resulted in a polar two-celled proembryo with a large basal cell and a small apical cell. The self-fertilized embryos developed a polar structure with suspensor and a globular embryo eight days after pollination according to the monocotyledonous type. The cross-fertilized zygotes showed retardation and deviation in plane of the cell plate in the second and third divisions, resulting respectively in linear three-celled and eight-celled proembryos 4–6 days after pollination. Differentiation in suspensor and globular stage embryos proper was not found in the cross-fertilized ovules but in stead aberrant undifferentiated embryos were observed, which formed two groups of cells in later stages. Endosperm development was quite similar in both cases till 12 days after pollination, when the coenocytic endosperm of the self-fertilized ovules formed cell walls around the nuclei, whereas cell wall formation was completely absent in the cross-fertilized ovules. The chalazal nucellus of the cross-fertilized ovules started to degenerate six days after pollination, and presumably restricted the flow of carbohydrates to the developing embryo and endosperm. Subsequently, a loss of contact between the endospermic transfer wall and the chalazal nucellus occurred after twelve days of development. Finally the cross-fertilized embryos aborted after they had lost their contact with the micropylar side of the former embryo sac. Thus, a number of events occurred from the second division of the hybrid zygote onwards, all leading to the abortion of the embryo 18–22 days after pollination. It seemed that during the early cell divisions of the zygote the fate of the embryo was already determined. Embryo abortion was associated with retarded embryo growth and early degeneration of sporophytic tissue.Key words:Alstroemeriaspp., interspecific hybridization, embryogenesis, embryo abortion, endosperm degeneration, chalazal nucellus degeneration.

ISSN:0008-4026    

DOI:10.1139/b97-101

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Under natural conditions, wild and cultivated pearl millet,Pennisetum glaucum(L.) R.Br., exchanged genes for millenia and, nevertheless, maintain high morphological differentiation. Under experimental conditions in the Sahel, hybridization between wild and cultivated pearl millet was measured using isozymic markers and interpreted in relation to the phenology of the plants. Gene flows were asymmetric, engendering 8% of hybrids in the progeny of the wild phenotype, 45% in that of the cultivated phenotype, and 39% in that of the intermediate "shibra" phenotype; these last two phenotypes constitute the sample of cultivated pearl millet. The proportion of hybrids in the progeny of the wild sample was time dependent during the flowering phase of cultivated pearl millet. The proportion of hybrids produced by the cultivated pearl millet was not time dependent. In the seeds produced by the cultivated phenotype along its reproductive phase, the proportion of viable seeds was negatively correlated with the frequency of hybrids. Likewise, the speed of germination of seeds produced by the cultivated or the shibra phenotypes was negatively correlated with the frequency of the hybrids that they contained. The effects of balancing among genetic intermixing, isolation and reproduction barriers, and differential anthropic and natural selection pressures are discussed to better understand the evolution and the maintenance of the polymorphism ofPennisetum glaucum.Key words: pearl millet, wild pearl millet,Pennisetum glaucum, gene flow, domestication, hybrid.

ISSN:0008-4026    

DOI:10.1139/b97-102

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Peroxidase (EC 1.11.1.7) and laccase (EC 1.10.3.1) activities were determined in mycorrhizal and non-mycorrhizal main and lateral roots ofPicea abies(L.) Karst. (Norway spruce) andLarix deciduaMill, (larch) and in mycelia of the ectomycorrhizal fungusLaccaria amethystea(Bull.) Murr. grown under axenic conditions. Peroxidase isozyme patterns were identified after isoelectric focussing. In both tree species, mycorrhizae contained the lowest, and laterals of noninoculated plants the highest, peroxidase activities. Pure mycelia ofLaccaria amethysteacontained considerable laccase activity but no peroxidase activity. Laccase activity was barely detected in noninoculated laterals of spruce, but was present in noninoculated laterals of larch and in main roots of Norway spruce and larch. Highest laccase activities were found in mycorrhizae of both tree species, indicating that most of the activity was derived from the fungus. Laterals of Norway spruce contained eight, and those of larch five, acidic peroxidase isozymes. In mycorrhizae of Norway spruce and larch, specific peroxidase isozymes with pI values of 4.5 and 6.2 and 5.8 and 6.0, respectively, were almost completely suppressed. The specific suppression of peroxidase suggests that the fungal symbiont is able to modify the host defence response in mature mycorrhizae.Key words: defence mechanism, laccase, mycorrhiza, peroxidase (isozymes), plant–fungus interaction.

ISSN:0008-4026    

DOI:10.1139/b97-103

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This paper focusses on the survivorship pattern of seedlings ofRumex obtusifoliusL. in the irrigated alfalfa crops (Medicago sativaL.) in central Catalonia (NE Spain). The relationship between this pattern and seasonal environmental change was evaluated by monitoring seedling cohorts that had germinated at different times of the year for 31 months. Paired comparisons of cohort survivorship curves were performed over their life-spans and for their coexistence period, using Peto and Peto's log rank test. The significance of intrinsic variables such as age and size in determining seedling survival was tested using hierarchical log-linear analysis applied on a three-way contingency table and by means of Goodman and Kruskal's association coefficients. Results showed that seedling cohorts emerging at different times in the year exhibited a similar Deevey type III survivorship pattern. Therefore, survivorship was scarcely affected by seasonal environmental variation. However, since age had little effect on seedling survival compared with size, this age-specific survivorship pattern was, in fact, a consequence of both size-dependent mortality and changes in size distribution with age. In the first weeks of life, cohort size distribution was greatly skewed to the smallest classes, with the highest mortality rates, and therefore the risk of death in the cohort was high. Afterwards, the frequency of the largest size classes increased with age, thus reducing the risk of death of the cohort.Key words:Rumex obtusifolius, seedling survivorship pattern, size versus age dependency, survival analysis.

ISSN:0008-4026    

DOI:10.1139/b97-104

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Simultaneous measurements were made of O2exchange, inorganic carbon (Ci) accumulation and assimilation, and chlorophyllafluorescence of the cyanobacteriumSynechococcusUTEX 625. The addition of Cito cells at the CO2compensation point resulted in quenching of chlorophyllafluorescence in the presence or absence of the CO2fixation inhibitor, iodoacetamide. The magnitude of quenching was related to electron flow to terminal electron acceptors such as CO2and O2. When photosynthetic CO2fixation was allowed, the rate of electron transport, as expressed by (F*m– F)/F*m, was highly correlated with the onset of photosynthesis. When CO2fixation was inhibited by the addition of iodoacetamide, the observed fluorescence quenching was consistent with the enhanced rate of O2photoreduction that occurred when Ciwas added. There was a close correlation (r = 0.98) between the magnitude of O2-dependent fluorescence quenching and the amount of O2photoreduction. The degree of stimulation of electron flow to O2photoreduction was dependent on the inorganic carbon concentration. The K1/2(Ci) for extracellular Ciwas 1.36 ± 0.13 μM (mean ± SD,n = 3) and K1/2(Ci) for the intracellular Cipool was 1.4 ± 0.18 mM (mean ± SD,n = 3). The reduction ofN,N-dimethyl-p-nitrosoaniline was also stimulated by the addition of Ci, whereas the addition of Cihad no effect on the reduction of 2,6-dimethylbenzoquinone and ferricyanide. The results suggest that Cistimulates electron flow in photosystem I.Key words: cyanobacteria, O2photoreduction, fluorescence, Ciconcentrating mechanism, inorganic carbon pool, linear electron transport, kinetic study.

ISSN:0008-4026    

DOI:10.1139/b97-105

出版商:NRC Research Press    

年代:1997

数据来源: NRC