摘要:

Fossil plant compressions belonging to Isoetales have been discovered, for the first time, in clay from the Lower Cretaceous of Merbah el Asfer, Tataouine area (south Tunisia). The study of leafy corms and sporophylls has permitted us to attribute the fossils to the genusIsoetitesMünster. The comparison between the known Mesozoic material leads to the description of a new species :I. daharensisnov.sp. Its affinities withIsoetesand with Triassic species show that the Isoetales were differentiated before the beginning of the Mesozoic era, and since then this lineage has shown little morphological variation. The good preservation of fossils is evidence of short transportation in a deltaic plain with sufficient moisture to permit the growth and development of these plants.Key words: Isoetales,Isoetites, Lower Cretaceous, Tunisia, phylogeny, palaeoecology

ISSN:0008-4026    

DOI:10.1139/b98-209

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

To determine the dominant fungal endophytes of the Japanese beech (Fagus crenataBlume) and to monitor their isolation frequency, we isolated fungi from symptomless organs of beech including leaves, petioles, and current and old (1- to 5-year-old) twigs after surface sterilization. Of the 13 fungal taxa obtained, 3 were isolated most often. An unidentified species ofDisculaand an unidentified sterile fungus, Lb, were isolated frequently from leaves, and an unidentified species ofPhomopsiswas isolated most frequently from twigs. The isolation frequency over the growing season varied for the two dominant fungal species in the leaves,Disculasp. and Lb. These two species had similar patterns of isolation, even in petioles and current-year twigs, although isolation frequencies of a given species varied with organs. An organ-specific distribution of the fungal species in the host plant was apparent. The three fungal species noted above were considered to be the dominant endophytes of the Japanese beech.Key words: fungal endophyte,Fagus crenata, isolation frequency, organ specificity.

ISSN:0008-4026    

DOI:10.1139/b98-220

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The giant columnar cactusNeobuxbaumia tetetzo(Coulter) Backeberg is the dominant species of a vegetation type locally called "tetechera" that occupies ca. 400 km2in the Tehuacán Valley. As a way to analyse the role of biotic interactions on the population dynamics of this species, we conducted an elasticity analysis, using matrix models elaborated from field data, to determine the finite rate of increase and the critical stages of the life cycle that were related to the biotic interactions occurring during these stages. Although the estimated finite rate of increase did not differ from unity there were significant differences between the actual and predicted size distributions. Elasticity analysis showed that survivorship was the most important life-history parameter to the finite rate of increase. Because survivorship depends on the presence of nurse plants, our results emphasise the importance of positive interactions on the population dynamics of long-lived columnar cacti.Key words: biotic interactions, Cactaceae, deserts, matrix models, population dynamics

ISSN:0008-4026    

DOI:10.1139/b98-207

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

All species in the genusCyperus(Cyperaceae) that occur in temperate eastern North America were assigned to either the C3or C4photosynthetic pathway using leaf anatomical characteristics and stable carbon isotope ratios. Of the 39 species in the study area, 32 had C4photosynthesis while 7 had C3. The numbers of C3, C4, and totalCyperusspecies were significantly and positively correlated with both summer precipitation and mean annual temperature. However, the proportional abundance of C4species withinCyperuswas not significantly related to either climatic variable. The highestCyperusdiversity was found on the Atlantic Coastal Plain, a pattern that remained after climatic differences between regions were accounted for. All the C3species and the majority of the C4species were restricted to wetlands or damp soil habitats; 13 of the 32 C4species occurred in dry, sandy habitats. Given that the C3pathway is ancestral in the genusCyperus, it appears that C4photosynthesis evolved in a wetland context for this genus. We suggest that the high nitrogen use efficiency associated with the C4pathway is largely responsible for the evolution and ecological success of C4Cyperusspecies in infertile, temperate wetlands.Key words: C3and C4photosynthetic pathways,Cyperus, Cyperaceae, eastern North America, stable carbon isotopes.

ISSN:0008-4026    

DOI:10.1139/b98-216

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The architecture resulting from the iteration of modules during plant growth affects resource capture. Phalanx and guerrilla growth forms have been described as ends of a continuum regarding the spacing of modules in plants. In this study we investigated the growth form of the perennial, tussock-forming grassSchizachyrium scopariumMichx. var.littoralis(Nash) Hitchc. in three dune microhabitats at El Morro de la Mancha, southeastern Mexico: a mobile, a semi-mobile, and a stabilized site. We followed the growth of 15 genets at each site for two consecutive years and found that daughter-tussock formation was more frequent in the stabilized than in the semi-mobile or the mobile sites. Individual tussocks had a higher number of tillers in the mobile site than in the other two. Tiller production occurred within parental tussocks in the mobile site and in the form of daughter tussocks in the stabilized site. Reciprocal transplants suggested that phenotypic plasticity was responsible for the differences observed. Fertilization enhanced tiller production within parental tussocks but did not affect daughter tussock formation. Clearing experiments resulted in enhanced tiller production within tussocks. In these experiments, daughter-tussock production did not occur directionally towards nutrient-rich microsites. It appears thatS. scopariumtillers are spaced at longer distances when resources are scarce and intraclonal competition is severe.Key words: clonal growth, growth form, nutrient availability, phalanx-guerrilla continuum.

ISSN:0008-4026    

DOI:10.1139/b98-212

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Here we report the partial purification and characterization of wheat mitochondrial ATP (CTP):tRNA nucleotidyltransferase (EC 2.7.7.25). Our purification scheme involves ammonium sulfate fractionation and chromatography on anion-exchange, hydroxyapatite, and affinity columns. Our results indicate that the enzyme is stable over a broad range of temperatures with highest activity at 37°C. High activity is seen at alkaline pH with a maximum at pH 9. The enzyme exhibits maximal activity in the presence of 10 mM MgCl2and is inhibited by (at least) 100 mM NaCl. We also show that a second form of this enzyme exists in the wheat cytosolic fraction. This enzyme shares many features with the mitochondrial enzyme but differs from the mitochondrial enzyme in its elution profile from hydroxyapatite and in its response to manganese.Key words: tRNA nucleotidyltransferase, wheat, mitochondria

ISSN:0008-4026    

DOI:10.1139/b98-206

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Allenrolfea occidentalis(S. Wats.) Kuntze, a halophytic perennial shrub in the family Chenopodiaceae, is widely distributed in inland salt marshes and salt playas of western North America. Experiments were conducted to determine the effects of NaCl, light, and temperature on seed germination and their recovery of germination from saline conditions after being transferred to distilled water. Seeds ofA. occidentaliswere germinated at various temperatures (5:15, 10:20, 10:30, 15:25, 20:30, and 25:35°C (night:day)) and salinities (0, 200, 400, 600, 800, and 1000 mM NaCl) in a 12 h light : 12 h dark photoperiod and in 24 h darkness. Increases in NaCl concentration progressively inhibited seed germination, and this inhibition was greater in the dark than in light. No seeds germinated at concentrations higher than 800 mM NaCl. Cooler temperatures significantly inhibited germination in all treatments, while regimes of high night (25°C) and high day (35°C) temperatures showed higher germination. Rate of germination decreased with an increase in salinity. Germination rate was higher at 25:35°C and lower at 5:15°C. Seeds were transferred from salt solutions to distilled water after 20 days, and those from high salinities recovered quickly at all temperature regimes. Recovery germination percentages at higher salinities varied from 51 to 100% at various temperatures, but recovery of germination of seeds from salt stress was significantly affected by temperature regime.Key words:Allenrolfea occidentalis, halophyte, light, recovery of seed germination, salt playas, thermoperiod,

ISSN:0008-4026    

DOI:10.1139/b98-204

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

During a survey of fungi associated with bark beetles in Germany, an undescribed species ofOphiostomawas isolated that differs from the other species of the genus by having pigmented, aseptate, convergent ostiolar hyphae, cucullate, sheathed ascospores, and aHyalorhinocladiellaanamorph. The species is described asOphiostoma neglectumKirschner & Oberwinkler. It is rarely associated with primary bark beetles but often associated with secondary bark beetles mainly infesting Norway spruce.Key words:Ophiostoma neglectum,Hyalorhinocladiella, secondary bark beetles,Picea abies,Pinus sylvestris, conidial development.

ISSN:0008-4026    

DOI:10.1139/b98-196

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The lifetime of many plant organs does not exceed a few weeks or a few months. These organs separate from the plant at the level of specialized abscission zones. The observation of xylem vasculature in abscission zones, a largely neglected subject, revealed original features when a vessel casting method was used. In all species of dicotyledons examined so far, flower and leaf abscission zones possessed heterogenous metaxylem vessels adjoining protoxylem and secondary xylem vessels with homogenous patterns of lignified thickenings. Heterogenous metaxylem vessel thickenings were helical, reticulate, or scalariform elements when in the abscission zone and pitted elements on the proximal and the distal sides. The origin and possible role of these vessels are considered. Data obtained on the flower abscission zone of tomato (Lycopersicon esculentumMill.) suggest that formation of heterogenous vessels results from localized changes in the rhythm of cell differentiation and cell maturation inside the procambium-cambium continuum.Key words: abscission zone, cambium, differentiation, heterogenous vessels, procambium, vessel cast.

ISSN:0008-4026    

DOI:10.1139/b98-213

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A relationship was developed between phenological stages of inflorescence expansion and the internal development of pollen within the anther ofAmelanchier alnifoliaNutt. flowers. The major microscopic events associated with microsporogenesis and microgametogenesis were correlated with seven stages of external inflorescence development in both natural buds and those forced from dormancy in different concentrations of gibberellin at various times of the year. In fall and early spring, it was found that gibberellin at a concentration of 2.5 mg/L forced buds to produce inflorescences that most resembled those from natural field populations. However, it was not possible to force flower buds to develop all the way to anthesis. Flower bud development stopped when the pollen was at the binucleate stage. Despite this limitation, the ability to force buds increases the time frame for the study of many aspects of the reproductive biology ofA. alnifolia.Key words: microsporogenesis, microgametogenesis, gibberellin, GA, flowering.

ISSN:0008-4026    

DOI:10.1139/b98-211

出版商:NRC Research Press    

年代:1999

数据来源: NRC