摘要:

The early stages of inflorescence development inPhilodendron fragrantissimum(Hook.) G. Don are examined using scanning electron microscopy. Pistillate flowers are initiated on the lower portion of the inflorescence and staminate flowers are initiated on the distal portion. Male flowers have 6-8 stamens (sometimes 5) and female flowers have a multilocular ovary consisting of 6-10 locules. A transition zone consisting of sterile male flowers and bisexual flowers with fused or free carpels and staminodes is also present. This zone is located between the male- and female- flower zones. Generally, the portion of the bisexual flower adjacent to the male zone forms staminodes and the portion bordering the female zone develops an incomplete gynoecium with few carpels. The different floral organs of the bisexual flowers are all inserted in the same whorl. Pistillate and staminate flowers are inserted on the same contact parastichies along the inflorescence; there is no spatial discontinuity between the female zone, the bisexual zone, and the male zone. The presence of bisexual flowers is believed to correspond to a morphogenetic gradient at the level of the inflorescence as a whole. A quantitative analysis of a series of parameters (i.e., length and width of flower types and inflorescence zones) indicates that each zone of the inflorescence has its own particular nature as far as rhythm of growth and geometry are concerned. There appears to be evidence for some form of partitioning in the global development of the inflorescence. The growth of a zone seems to be more variable in size and geometry than that of individual flowers. During later stages of development, the size of the flowers of the intermediate zone, especially the sterile male flowers, increases considerably, until it exceeds that of both male and female flowers.Key words: homeosis, morphogenesis, gradient, allometry, reproduction.

ISSN:0008-4026    

DOI:10.1139/b00-030

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We investigated the soil seed bank in a subalpine ecosystem with patchy disturbance from camping. Soil cores were collected from three site types, heavily impacted, lightly impacted, and undisturbed, that differed in area of bare ground and depth of surface organic matter. We hypothesized that the density and composition of the seed bank would vary with depth of surface organic matter and distance from established vegetation. Seedling emergence was determined in the greenhouse. Seed density was significantly lower on disturbed sites, averaging 441 seeds/m2on heavily impacted sites, 1495 seeds/m2on lightly impacted sites, and 4188 seeds/m2on undisturbed sites. Seed density declined exponentially with distance from established vegetation and increased with depth of surface organic matter. The number of species present did not vary across site types, but 10 species that occurred on lightly impacted and undisturbed sites were not present on heavily impacted sites. We concluded that disturbance that causes removal of surface organic matter can affect natural revegetation by lowering the density of propagules and affecting the species represented in the seed bank.Key words: seed bank, subalpine, patchy disturbance, recreation impacts.

ISSN:0008-4026    

DOI:10.1139/b00-031

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Stomatal conductance and leaf water potential of aspen (Populus tremuloidesMichx.) were measured in response to defoliation intensity, both in the field and under controlled conditions. There was evidence of increased stomatal conductance in trees with 50 and 98% defoliation, but no change in leaf water potential. Under controlled conditions, stomatal conductance and rate of photosynthesis were measured under high and low vapour pressure deficits (VPD). Under high VPD, overall stomatal conductance and rates of photosynthesis were greatly reduced. However, in both VPD treatments, there was evidence of increased stomatal conductance and compensatory photosynthesis following defoliation. These findings may be due to increases in leaf specific hydraulic conductance following defoliation.Key words: defoliation, stomatal conductance, leaf water potential, compensatory photosynthesis.

ISSN:0008-4026    

DOI:10.1139/b00-032

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Apical dominance is advantageous in conditions favoring rapid growth in height and unbranched architecture. The cost of apical dominance, on the other hand, should be expressed in conditions where fecundity increases along with an increasing number of branches. Apical damage can be used to measure such costs: when suppressed meristems are released from apical inhibition, the vegetative and reproductive productivity of initially unbranched plants should increase owing to the regrowth and increased branch development following damage. We studied these regrowth responses in two monocarpic herbs,Erysimum strictumP. Gaertn., B. Mey., and Scherb. andRhinanthus minorL., after both apical damage (10% of the shoot cut) and more extensive damage (50 and 75% cutting). Both species tolerated apical damage, although severe damage had detrimental effects on the performance of both, especiallyR. minor. Apical damage had positive effects on most of the measured performance parameters ofErysimum. However, the success of seed germination collapsed, presumably due to delayed flowering and less successful pollination. The response was parallel inRhinanthus; apical damage affected neither the vegetative biomass nor fecundity, but heavier damage, especially 75% clipping, led to severe reductions in most performance measures. The differences in regrowth responses are presumably due to the different habitat requirements of the species.Rhinanthusprefers relatively dense vegetation and starts to branch and produce flowers after a certain threshold in height has been reached, whereasErysimumprefers gaps in vegetation. In this species, unbranched architecture may be favored in closed vegetation and branched architecture in less competitive habitats. In both species, fruit production correlated positively with the number of branches in both control and clipped plants, which is consistent with the assumption of the cost of apical dominance.Key words: apical dominance, competition, damage, meristem, overcompensation, regrowth.

ISSN:0008-4026    

DOI:10.1139/b00-033

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We investigated whether the deposition ofCastillejalinariaefolia(Pursh) V. Grant pollen on flowers ofIpomopsisaggregata(Benth.) in DC. reducedI.aggregata's seed set.Ipomopsisflowers were hand-pollinated with either pure conspecific pollen (the control) or withC.linariaefoliapollen applied prior to, simultaneously with, or following conspecific pollen. Flowers that were simultaneously givenC.linariaefoliaandI.aggregatapollen received 39% less conspecific pollen than flowers in the control, but did not set fewer seeds per fruit. Flowers that were givenC.linariaefoliapollen first received 30% less conspecific pollen and set 38% fewer seeds per fruit than the control. These results suggest that there is a priority effect; deposition ofC.linariaefoliapollen onI.aggregataflowers results in competition, but only whenC.linariaefoliapollen is deposited first. Unlike pollen of another competitor ofI.aggregata(DelphiniumnelsoniiGreene. Per.),C.linariaefoliapollen caused competition without inducing an increased rate of stigma closure. Only 12% ofI.aggregata's stigmas closed whenC.linariaefoliapollen was deposited, and seed set ofI.aggregatawas reduced relative to the control whether their stigmas closed or not. The low rate at whichC.linariaefoliapollen induces closure ofI.aggregata's stigmas could be an adaptation to reduce the negative effects of competition.Key words:Castillejalinariaefolia, competition, hand pollination, hummingbirds,Ipomopsisaggregata, pollination.

ISSN:0008-4026    

DOI:10.1139/b00-034

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The production, accumulation, and in situ location of pectin methylesterase (EC 3.1.11) was examined in ripening fruit of the processing tomato cv. UC82B. Pectin methylesterase detected with a monoclonal antibody (PME-1) first appeared adjacent to seeds in immature green fruit and was later detected only in tissue adjacent to the cuticle (i.e., exopericarp) during ripening. Enzyme-linked immunosorbant assay and Western blot analysis using PME-1 demonstrated that the fresh-market cultivars Celebrity and Better Boy accumulated lower levels of this immunologically detectable pectin methylesterase during maturation than did processing cv. UC82B, and that the immunologically detected pectin methylesterase and the total detectable pectin methylesterase activities of 'Celebrity' and 'Better Boy' increased throughout ripening. In contrast, processing cv. UC82B displayed a total detectable pectin methylesterase activity profile that peaked during the breaker stage, a finding supported immunologically by tissue-printing. To correlate pectin methylesterase expression during ripening to the degree of methylesterification of pectins in exopericarp cell walls, we subjected exopericarp tissue from 'UC82B' fruit to an immunocytochemical and ultrastructure study. Esterified pectin decreased in some regions of the exopericarp cell walls during fruit development but persisted in some regions as well. Less-esterified pectin was localized in the middle lamella of exopericarp cell walls during preripe stages, while in ripe fruit, this labeling was largely absent.Key words: pectin methylesterase (PME), immunocytochemistry, tissue-print, pectin esterification,Lycopersicon esculentum.

ISSN:0008-4026    

DOI:10.1139/b00-035

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The thermal, kinetic, and electrophoretic properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were analyzed in plants from two ecotypes of barnyard grass (Echinochloa crus-galli(L.) Beauv.: Poaceae) originated from sites of contrasting climates in Quebec (QUE) and Mississippi (MISS). The thermostability, cold inactivation, the apparent energy of activation (Ea), the Michaelis-Menten constant (Km), andVmax/Kmratios for phosphoenolpyruvate (PEP) and Mg2+were analyzed with desalted Sephadex G-25 crude PEPC extracts, with partially purified PEPC from the polyethylene glycol (PEG) 13% fraction and with purified PEPC obtained after elution from DEAE-Sepharose affinity chromatography. PEPC from illuminated leaves from both ecotypes consisted of one isomorph with the same electrophoretic mobility in polyacrylamide gels, similar molecular masses for the native enzyme (400 kDa) and for each subunit of the tetramer (100 kDa), and a same isoelectric point (pI) of 4.95. The only kinetic property for PEPC for which differences of physiological importance among ecotypes were observed at the three levels of purification wasKmfor PEP for which values for QUE plants were significantly lower at low assay temperatures. Differences among ecotypes for thermostability were only observed in assays with crude and partially purified PEPC extracts, while no differences were found for cold inactivation rates,Km(Mg2+) estimates at any level of purification or forVmax/Kmratios (PEP or Mg2+) from purified PEPC. Significant differences among the two ecotypes were found for catalytic constant (Kcat) estimates obtained with purified PEPC. However, results show higher catalytic efficiency for PEPC from MISS plants at high assay temperatures but no indication of an improved catalytic efficiency for PEPC from QUE plants at low assay temperatures. The lack of ecotypic differences for most thermal and kinetic properties observed with purified PEPC casts doubts about the evolutionary interpretations of results obtained in previous kinetic comparative analyses, which were based on crude or partially purified enzymatic preparations of PEPC extracted fromE. crus-galliplants.Key words: phosphoenolpyruvate carboxylase, enzyme kinetics, thermal adaptation, barnyard grass, electrophoresis,Echinochloa crus-galli.

ISSN:0008-4026    

DOI:10.1139/b00-036

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Terra Nova National Park, located on the east coast of Newfoundland, has a vascular flora of 535 taxa, including 33 rare species and 94 introduced taxa. About 75% of the native flora of the Park is composed of hemicryptophyte and cryptophyte species. Phanerophytes and nanophanerophytes represent only 13% of the flora, but the percentages of occurrence of these life forms reaches 31%. The flora of the Park is mainly boreal (56%), composed mainly of Boreal North American, Boreal Eastern North American, and Circumboreal elements. Arctic-alpine species are infrequent. We report two species as new to Newfoundland:Festuca richardsoniiHooker (Poaceae) andCarex communisL.H. Bailey var.communis(Cyperaceae). Significant positive and negative associations between (i) life forms and (ii) phytogeographical elements, and the distribution of species within the habitats of the Park were established using the Fourth Corner Method. Distribution of life forms and phytogeographical elements within habitats of the Park appears to be explained more by ecological characteristics of species than by their history.Key words: life form, biogeography, biodiversity, Terra Nova National Park, Newfoundland, Canada.

ISSN:0008-4026    

DOI:10.1139/b00-040

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Wheat genotypes susceptible to different races of a pathogen,Puccinia striiformis, were planted in pure stands and in three different 1:1 mixtures, in both the presence and absence of disease, in two sites, and over 3 years. Using analyses of variance, we tested whether disease and intergenotypic competition influenced a genotype's fitness and whether significant interactions existed between the effects of disease and competition on genotype fitness. Seed weight, number of inflorescences per seed planted, seeds per inflorescence, and absolute fitness were estimated for each genotype in each treatment. Absolute fitness was determined as the number of seeds collected per seed planted. Disease reduced seed weight. The other fitness measures were influenced by either disease or competition, and the impact of each factor often varied among site-year combinations. In general, interactions between the effects of disease and competition on genotype fitness were not significant. The few significant interactions indicated a less than additive effect of competition and disease on genotype fitness. The overall lack of interaction may be, in part, due to lesser disease levels in mixed as compared with pure stands, or reduced level of competition under diseased conditions.Key words: pathogens, competition, plant fitness, stripe rust, wheat.

ISSN:0008-4026    

DOI:10.1139/b00-037

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Two species ofChamaecyparisand six cultivars each ofJuniperus chinensisL. andJuniperus scopulorumSarg. (Cupressaceae) were subjected to random amplified polymorphic DNA (RAPD) analysis using seven primers. Unweighted pair group method with averages (UPGMA) and principal component analyses of genetic distances between cultivars showed that 42 polymorphic RAPD bands could distinguish among all cultivars and properly group them by species and genera. Where the origin of a specific juniper cultivar is uncertain, analysis of genetic distance can pinpoint close relatives. For example, we were unable to trace the origin ofJ. chinensis'Alps', and we initially thought it was a mislabeledJ. chinensis'Blue Alps'. However, we found 'Alps' to be closer toJ. chinensis'Fairview' and 'Mountbatten' than to 'Blue Alps'. Similarly, 'Wichita Blue' has an unknown origin, but it had the highest genetic similarity with 'Medora'.Key words: juniper, cedar, RAPD, cultivars, phylogenetics.

ISSN:0008-4026    

DOI:10.1139/b00-046

出版商:NRC Research Press    

年代:2000

数据来源: NRC