摘要:

The effects of site of origin, time of seed maturation, and seed age on germination behavior, in terms of final percentage of germination and time for 50% of final germination were investigated in the widespread weedPortulaca oleraceaL. Seeds were collected in August from one population at each of three geographical regions of the Old and New Worlds representing temperate (Southern Ontario, Canada), Mediterranean (Tanta, Egypt), and subtropical (Al-Ain, United Arab Emirates (U.A.E.)) climates. The freshly harvested seeds were incubated in both light and dark at 15, 25, and 40°C. Seeds of the U.A.E. site showed little dormancy and germinated faster under a wider range of incubation conditions than did seeds from the Canadian site. To assess the effect of time of seed maturation on germination behavior, seeds were collected during the different seasons (November, February, May, and August) of the U.A.E. population. The percentage of germination was significantly higher for seeds collected in May and November and germination was significantly faster for those collected in May and August. Response of germination to light and temperature varied according to site of origin and time of seed maturation. Seeds from the Canadian site and those that matured during winter from the U.A.E. site required light and high temperature for optimal germination. The effect of seed age on percentage of germination and rate was significant at the Canadian site but not at the Egyptian and U.A.E. sites. Seed stored for 5 months at room temperature germinated significantly faster and to a higher percentage than freshly harvested seeds. Results are discussed in light of the adaptation of seed dormancy and time of germination to the prevailing environmental conditions.Key words: dormancy, geographical regions, germination, germination rate,Portulaca oleracea, seed age, site of origin, time of seed maturation

ISSN:0008-4026    

DOI:10.1139/b00-001

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The morphology and anatomy of the African monospecific genusColletoecemaE. Petit (Rubiaceae) is documented and illustrated (including wood anatomy, pollen morphology, gynoecial and exotestal structure). Morphological and anatomical comparison shows thatColletoecemadiffers in many aspects from the Psychotrieae (e.g., wood anatomy, seed structure). Consequently, the genus' provisional position in the Psychotrieae cannot be maintained. Morindeae, the second tribeColletoecemahas been associated with, has a different gynoecial structure. The oily endosperm and large embryo ofColletoecemais found in several genera that often were or still are included in the Psychotrieae or Morindeae (Trichostachys,Saldinia,Ronabea, andLasianthus). However, they differ in several other aspects, which makes a close relationship doubtful.Colletoecemaexhibits a unique combination of characters including axillary inflorescences, banded parenchyma in the wood, ovules attached around the middle of the septum, bilocular pyrenes, seeds with oily endosperm and large embryo, and verrucate exotestal thickenings, not encountered elsewhere in the Rubioideae. A cladistic analysis based on nucleotide sequence variation in therps16 intron (chloroplast DNA) confirms thatColletoecemais related neither to Psychotrieae nor to Morindeae.Colletoecemaappears as a sister genus ofOphiorrhizain a weakly supported clade among the basalmost clades of the subfamily Rubioideae, but there is very little morphological support for this relationship.Key words: anatomy, chloroplast DNA, cladistics, morphology, Psychotrieae, Rubioideae.

ISSN:0008-4026    

DOI:10.1139/b00-002

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This study examined the foliar response of putative hybrid Engelmann × white × Sitka spruce (Picea engelmanniiParry ×Picea glauca(Moench) Voss ×Picea sitchensis(Bong.) Carr) needles in relation to crown position and across three stages of development (15, 55, and 145 years). We focused on the morphological and anatomical response, and used physiological measures (photosynthesis and stomatal conductance) to emphasize the important relationship between structure and function. We found that needles from the upper outer crown position were adaptated to reduce stress from evapotranspiration. Trees from the 15- and 55-year-old stands generally responded the most, and trees from the 145-year-old stand responded the least. As they mature, these spruce trees may have reduced ability to adapt to their environment. Some of our results contradict what the literature considers "typical" for sun-shade dimorphism in temperate forests. For example, in all stands, sun needles were broader than shade needles and, in the two younger stands, sun needles were larger in area, not smaller, than shade needles. Also, in the youngest stand, stomatal pores were longer on sun needles than on shade needles. There were no definite patterns in stomatal spacing with regard to crown position. Our results are indicative of the strategies adopted to increase competitiveness in a resource-limited environment. We suggest that, in the 15-year-old stand, neither water nor light is limiting; in the 55-year-old stand, both water and light are highly limiting; and in the 145-year-old stand, water is most limiting.Key words: drought, foliar plasticity, needle anatomy, photosynthesis,Picea, stand development, sun-sh

ISSN:0008-4026    

DOI:10.1139/b00-005

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

RhizoplacaZopf is a genus characterized by an umbilicate thallus with an upper and a lower cortex, as well as a cupulate hypothecium. It has been considered to be related toLecanoraAch., the type genus of the Lecanoraceae and, in particular, to the lobate species of this genus. The phylogeny ofRhizoplaca, the monotypicArctopeltisthuleanaPoelt, and a number of representatives of different groups ofLecanorais studied, using sequences from the nuclear ribosomal internal transcribed spacer (ITS) regions. The results suggest an origin forRhizoplacaspecies within the large genusLecanora. A well-supported monophyletic assemblage includes the umbilicate type speciesRhizoplacamelanophthalma(DC.) Leuck. & Poelt, the lobateLecanoranovomexicanaH. Magn., and five vagrantRhizoplacaspecies.Rhizoplacachrysoleuca(Sm.) Zopf andRhizoplaca subdicrepans(Nyl.) R. Sant. form a separate well-supported group andRhizoplaca peltata(Ram.) Leuck. & Poelt is more closely related toLecanora muralis(Schreb.) Rabenh. Together with data on secondary chemistry, the results show that the umbilicate thallus with a lower and an upper cortex, as well as apothecia with a cupulate hypothecium found inRhizoplacaandA. thuleana, have developed several times in independant lineages inLecanora. The thallus morphology in lecanoroid lichens is highly variable and does not necessarily reflect phylogenetic relationships.Key words:Rhizoplaca,Lecanora, Lecanorales, phylogeny, ITS.

ISSN:0008-4026    

DOI:10.1139/b00-006

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Carnitine palmitoyltransferase (EC 2.3.1.21), an enzyme that catalyses the reversible transfer of activated long-chain acyl groups between CoASH and L-carnitine, has been confirmed in pea leaf chloroplasts. This enzyme is bound to the chloroplast inner envelope membrane and has two isoforms, one bound to the outside (cytosol side) of the inner envelope and one bound to the inside (stromal side) of the inner envelope. Malonyl CoA inhibited the activity of the outer carnitine palmitoyltransferase, while stimulating the activity of the inner isoform and may be a regulator of these enzymes in vivo. Carnitine palmitoyltransferase was solubilized from the chloroplast envelope by detergent treatment and the two isoforms separated by Q-Sepharose anion exchange chromatography. Both proteins were immunochemically observed by probing Western blots of sodium dodecyl sulfate - polyacrylamide gel electrophoresis gels using an anti-beef heart mitochondrial carnitine palmitoyltransferase polyclonal antibody. The monomeric molecular mass of the protein recognized by this antibody was approximately 20 kDa. This 20-kDa protein also bound3H-carnitine. Both isoforms had broad acyl CoA substrate specificities, but showed increased activity with desaturated long-chain acyl CoAs, exhibiting a preference for linolenoyl CoA. A role for carnitine palmitoyltransferase in the shuttling of fatty acids across the chloroplast envelope is suggested.Key words:Pisum sativum, chloroplasts, carnitine palmitoyltransferase, fatty acid metabolism, eukaryotic pathway, membrane transport.

ISSN:0008-4026    

DOI:10.1139/b00-008

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The chytrids (Chytridiomycota) are morphologically simple aquatic fungi that are unified by their possession of zoospores that typically have a single, posteriorly directed flagellum. This study addresses the systematics of the chytrids by generating a phylogeny of ribosomal DNA sequences coding for the small subunit gene of 54 chytrids, with emphasis on sampling the largest order, the Chytridiales. Selected chytrid sequences were also compared with sequences from Zygomycota, Ascomycota, and Basidiomycota to derive an overall fungal phylogeny. These analyses show that the Chytridiomycota is probably not a monophyletic group; the Blastocladiales cluster with the Zygomycota. Analyses did not resolve relationships among chytrid orders, or among clades within the Chytridiales, which suggests that the divergence times of these groups may be ancient. Four clades were well supported within the Chytridiales, and each of these clades was coincident with a group previously identified by possession of a common subtype of zoospore ultrastructure. In contrast, the analyses revealed homoplasy in several developmental and zoosporangial characters.Key words: zoospore ultrastructure, Chytridiales, molecular phylogeny, Chytridiomycota, operculum.

ISSN:0008-4026    

DOI:10.1139/b00-009

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The diagnostic characters of the genusLotusL. are a claw with a thickened infolded margin, diadelphous stamens, and a style hardened from the base. This genus contains about 100 species that are distributed throughout the world. To investigate the phylogeny of the Old World species ofLotus, subgenusEdentolotus, sectionsKrokeria,Xantholotus, andErythrolotus, a cladistic analysis was performed using 31 morphological characters. To test the phylogenetic relationships among species ofLotus-EdentolotusandDorycnium, Pedrosia,andTetragonolobus, these taxa were included as part of the ingroup. The polarity of the characters was based on the outgroup comparison method, usingAnthyllisas one outgroup andTripodionas another. The analysis withAnthyllisas outgroup yielded eight equally parsimonious trees (with all characters equally weighted), each with 62 steps, a consistency index of 0.53, and a retention index of 0.75. All trees (including the strict consensus tree from the eight initial trees) showed that genusLotus, subgenusEdentolotus, and sectionsXantholotusandErythrolotusare polyphyletic, with only sectionKrokeriaappearing as monophyletic. On the other hand, the groups of speciesLotus angustissimus,Lotus corniculatus,Lotus creticus, andLotus peregrinusare monophyletic. Identical results were derived from the data matrix usingTripodionas the outgroup. Results are compared with previous cytogenetic and biochemical evidence.Key words: cladistic analysis, Fabaceae, Loteae,Lotus, Old World species, phylogeny.

ISSN:0008-4026    

DOI:10.1139/b00-011

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Simultaneous observation of morphological and anatomical markers allowed us to reconstitute the growth pattern of the main axis in two populations of sessile oak aged 15 and 29 years, respectively. The comparison of the morphological features of annual shoots and growth units according to either their ontogenic age or their year of formation allowed us to separate endogenous trends in the development of the tree and variations resulting from the effect of annual growth conditions. Three stages of tree development were identified. The first stage is characterized by the regular production of monocyclic annual shoots with a stable mean length and is typical of young trees growing under a dense canopy. In the second stage of development, the intrinsic growth pattern expresses itself dominantly; this stage is marked by a systematic increase in the length and polycyclism rate of successive annual shoots, and by a strong differentiation between the successive growth units of polycyclic annual shoots. In the third stage, environmental factors have a stronger influence on the ontogenic growth pattern. In this stage, the length of the different growth units and annual shoots is stationary but shows important annual variations, while the differentiation between the successive growth units of bicyclic annual shoots is not systematic.Key words:Quercus petraea, sessile oak, morphology, primary growth, ontogeny.

ISSN:0008-4026    

DOI:10.1139/b00-012

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The cytological and ultrastructural modifications induced by thaxtomin A, a phytotoxin produced byStreptomyces scabies, were analyzed on mature field-grown potato tuber tissues. In tissue sampled during the first 12 h after treatment with thaxtomin A, the plasmalemma of parenchyma cells was detached from the cell wall in several places. However, the plasmalemma did not appear ruptured. The intercellular spaces between the retracted plasmalemma and the cell wall often contained fibrillar material. After a longer period of time, cells from tissues treated with thaxtomin A showed significant disorganization, such as detachment and invagination of the plasmalemma, the presence of a fibrillar-like material in the cytoplasm, and electron-dense material associated with moribund cellular features.Key words: common scab, potato, phytotoxin,Solanum tuberosum.

ISSN:0008-4026    

DOI:10.1139/b00-013

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Two cultivars of durum wheat (Triticum turgidumL.) with known, and different, grain-Cd accumulation were used to compare root tissue accumulation of Cd with root morphology. Six-day-old 'Kyle' and 'Arcola' seedlings were exposed to a range of Cd2 +concentrations (3.91 × 10-8- 3.91 × 10-7M) for 0-200 min, and root Cd contents for the two cultivars were compared with root morphological characteristics. 'Kyle' roots contained 35% less Cd per root system after 200 min of exposure and had less root surface area and fewer root tips than 'Arcola'. 'Kyle' roots also contained 30% less Cd per gram of dry weight than 'Arcola' roots after 200 min of exposure. 'Kyle' roots also had fewer root tips per unit of root dry weight and less surface area per unit of dry weight (DW) than 'Arcola'. When cadmium concentration data (µg·g-1DW) were expressed per unit of root surface area (µg·cm-2) and per number of root tips (µg·tip-1), the difference in root Cd content between the two cultivars was smaller. These results suggest that greater root Cd content of 'Arcola' than 'Kyle' can be explained by differences in morphology, specifically that a greater surface area and more root tips in 'Arcola' leads to greater Cd accumulation in root tissue.Key words: cadmium accumulation, durum wheat, root morpholog

ISSN:0008-4026    

DOI:10.1139/b00-015

出版商:NRC Research Press    

年代:2000

数据来源: NRC