摘要:

The orchids are unique among angiosperms in that ovule development is initiated after successful pollination. The monandrous orchidEpidendrum ibaguensehas three placental ridges at anthesis. After pollination, mitotic activities result in the formation of a dichotomously branching system of outgrowths. The tip of each branch consists of five to six nucellar cells covered by the epidermis. A subterminal nucellar cell differentiates into the archesporial cell approximately 12 days after pollination. By day 18, it differentiates directly into a megasporocyte. The first meiotic cell division produces a dyad in which the micropylar cell begins prompt degeneration. The second meiotic cell division results in the formation of two megaspores of unequal size. The larger cell at the chalazal end will become the functional megaspore. Callose is present in the walls of the megasporocyte, the micropylar dyad cell, and the megaspore destined to degenerate. The development of the megagametophyte conforms to the Polygonum type. One of the chalazal nuclei delays its final mitotic division until fertilization, making it appear that only two antipodals are present. The mature ovules are bitegmic and have an anatropous orientation.

ISSN:0008-4026    

DOI:10.1139/b89-283

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Ungerminated spores ofFunariado not contain distinct microtubules but show diffuse antitubulin antibody fluorescence. The microtubules arise when, 24–48 h after sowing, the spores are swollen and the first germ tube begins to protrude. Initially, diffuse fluorescence and microtubules are concentrated around the nucleus. Treatment with auxin at high concentrations (5 × 10−5– 10−4 M) retards germination and cell division. Like antimicrotubule agents, such as colchicine and chloroisopropyl-N-phenylcarbamate, high auxin concentrations affect the formation of microtubules; either short, irregularly shaped microtubules and fluorescent spots arise, or there is no evidence of microtubules. The auxin effects on growth and microtubules can be reversed in less than 1 day. There is a correlation between the formation of the microtubule system and cell morphogenesis.

ISSN:0008-4026    

DOI:10.1139/b89-284

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The effect of different precursors, aromatic amino acids, or intermediates of the shikimate pathway (pathway for aromatic amino acids biosynthesis), on indole-3-acetic acid (IAA) synthesis by the ectomycorrhizal fungusHebeloma hiemalewas studied. This fungus did not release detectable amounts of IAA when cultivated on a medium containing no precursor or supplemented with 1 mM phenylalanine, 1 mM tyrosine or 1 mM shikimic acid. IAA accumulation in culture filtrates was low (0.5 μmol per flask) when the medium was supplemented with 1 mM anthranilic acid. The fungus released 1.6 μmol of IAA when cultivated on a medium containing 1 mM indole and 6.9 μmol in the presence of 1 mM tryptophan. These results were confirmed by studying the ability of crude enzyme extracts to convert these precursors to IAA. Specific IAA synthesizing activity was of the same order when indole or tryptophan were used as precursors. The comparison ofin vivoandin vitroactivity of IAA synthesizing enzymes demonstrated that a need for tryptophan concentrations higher than 0.1 mM to obtain detectable IAA synthesis is due to the low ratio of tryptophan breakdown into IAA. The inability ofH.hiemaleto synthesize IAA in the absence of precursors or in the presence of shikimic acid may be ascribed to a very poor endogenous tryptophan accumulation in the hyphae due to feed back inhibition of the anthranilate synthetase by tryptophan. These results indicate that precursor availability in root exudates is probably one of the main limiting factors for IAA release by ectomycorrhizal fungi under symbiotic association.Key words: ectomycorrhizal fungus,Hebeloma, indole-3-acetic acid, tryptophan, indole, shikimate pathway.

ISSN:0008-4026    

DOI:10.1139/b89-285

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The effects of stress conditioning with polyethylene glycol on water relations and photosynthesis in preconditioned ramets were compared with those of unconditioned black spruce (Picea marianaMill. BSP). Preconditioned plants maintained lower osmotic and water potentials and higher turgor potentials (measured as a difference between osmotic and water potentials), but photosynthetic rates were similar in both groups of plants. The conditioning treatment increased stomatal sensitivity to water stress, and stomatal conductance was lower in preconditioned plants soon after water stress was imposed. Preconditioned plants maintained significantly lower osmotic potentials during a severe water stress and were able to maintain turgor at the time when unconditioned plants wilted. Water-use efficiency was not affected by stress-conditioning treatment.

ISSN:0008-4026    

DOI:10.1139/b89-286

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

An estimate was made of the abundance of different types of mycorrhizal associations in two plant communities of conifers and hardwoods in the Harvard Forest. Lists of plant species, the coverage of their foliage in the canopy and understorey layers, and the types of mycorrhizal associations for 45 species common in these communities are presented. Of the species examined, 91 % were mycorrhizal, representing most of the known major types, viz. ectomycorrhiza, vesicular–arbuscular mycorrhiza (VAM), ericoid, and monotropoid mycorrhiza. Of the 45 species studied, 22% of the species showed ectomycorrhizal, and 71 % VAM associations. A direct spore count was a more reliable method than the most probable number method for determining VAM occurrence in the soil. Spore numbers ranged from 4.4 to 11.8 spores/g oven-dried soil. In conifer stands, ectomycorrhizae were most common, although VAM were also observed in the conifer species. In hardwood stands, VAM were more frequent than in conifer stands, but mycorrhizae were heterogeneous and included a good proportion of the ericoid type. Ectomycorrhizae were more common in communities of low diversity; VAM occurred more frequently in communities of high plant species diversity.

ISSN:0008-4026    

DOI:10.1139/b89-287

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Multivariate analyses ofBetula cordifoliaRegel,B.populifoliaMarsh., andB. ×caeruleaBlanchard in a mixed population in northern Maine show that the latter is a hybrid between the former two species. Hybrid status ofB. ×caeruleais further supported by the fact that two putative hybrid individuals have the same chromosome number as reports for the two parental species and that all three taxa have overlapping flowering times at this site. Studies of pollen germination and stainability and seed germination show that the putative hybrids are fertile.Betula papyriferaMarsh., which is also present in this mixed population and was included in the analyses, flowers earlier thanB.cordifoliaandB.populifolia, and it apparently does not hybridize with the latter species at this site. Characters that have not been used prior to this study and that are among the best discriminators betweenB.cordifolia,B.papyrifera, andB.populifoliaare number and width of preformed staminate catkins and length and diameter of overwintering vegetative buds.

ISSN:0008-4026    

DOI:10.1139/b89-288

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

We have examined the effects of a sublethal concentration of atrazine on the incorporation of sodium-[U-14C] acetate into isolated chloroplast lipids ofLemna minor. A high level of [14C]-acetate was incorporated into diacylgalactosylglycerol (DGG) and diacylglycerol (DAG). Consequently, the conversion of phosphatide acid to DAG and that of DAG to DGG seems to be as active inL.minor(an "18:3-plant") as in "16:3-plants." Chloroplast lipids from atrazine-treated plants were more extensively labelled with [14C]-acetate than the control plants. These results are in agreement with our previousin vivostudies which suggest that sublethal concentrations of atrazine stimulate the lipid metabolism ofL.minorto form more thylakoid membranes. Furthermore, the specific radioactivity of linolenic acid was the highest in DAG and the lowest in DGG. These data suggest that desaturation of linoleic acid to linolenic acid mainly occurs before the galactosylation of DAG to form DGG inL.minor.

ISSN:0008-4026    

DOI:10.1139/b89-289

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The internal structure of mature mycelial cords ofLycoperdon pyriforme,Mutinus caninus,Steccherinum fimbriatum, andTricholomopsis platyphyllawas studied using scanning electron microscopy. Although interspecific differences in the degree of internal differentiation were observed, linear mycelial organ structure in all four species was similar, in that they consisted of a cortex of fine hyphae surrounding a medulla containing large diameter "vessel" hyphae. Based on similarities between the internal structure of rhizomorphs ofArmillaria melleaand the mycelial cords of the species considered in this study, the exclusive use of the term "rhizomorph," qualified by adjectives describing development at the growing front and the degree of internal differentiation, is proposed in describing all linear mycelial aggregates.

ISSN:0008-4026    

DOI:10.1139/b89-290

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Aluminum toxicity is an important factor limiting plant growth in soils with pH below 5.0. Because metalliferous soils are commonly acidic, understanding plant growth dynamics on such soils may require insight into the interaction between aluminum and other phytotoxic metals. To investigate potential interactions in the phytotoxicity of nickel and aluminum, seedlings ofTriticum aestivumL. cv. Neepawa were grown for 14 days in solution culture with varying concentrations of nickel (0–60 μM), with or without 40 μM aluminum. Increasing concentrations of nickel were observed in roots (232–2318 μg ∙ g−1) and leaves (25–152 μg ∙ g−1) with increasing nickel in solution, but concentrations were reduced with addition of aluminum as a second phytotoxic metal (roots: 125–1314 μg ∙ g−1; leaves: 20–108 μg ∙ g−1). Aluminum was only detectable in roots of seedlings grown with aluminum and declined with increasing nickel in the growth solution (1446–530 μg ∙ g−1). Addition of nickel to growth solutions reduced both root (0.981–0.193 g) and leaf (2.608–1.030 g) weights. Aluminum as a second phytotoxic metal further reduced root (0.698–0.194 g) and leaf (2.245–1.111 g) weights at low concentrations of nickel in solution. Analysis of variance of the root weight data indicated a significant nickel × aluminum interaction, but this may not have been indicative of a biological interaction. Root weight, both in the presence and absence of aluminum, decreased to a common minimum at high concentrations of nickel in the growth solution, possibly reflecting biomass present at the onset of experimental treatments and the lag time required for the expression of the phytotoxic growth response. When root growth relative to control was expressed as weight above the empirical minimum (the root weight index), results of the analysis of variance were different. Significant main effects of nickel were detected, while main effects due to aluminum and the nickel × aluminum interaction were not significant. Despite antagonistic effects observed with metal uptake and accumulation, such results suggest that the combined toxic effect of nickel and aluminum can be explained by a simple multiplicat

ISSN:0008-4026    

DOI:10.1139/b89-291

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The tribe Inuleae Cass. has been subject to a critical investigation. The many technical characters that are traditionally used in classification of the Inuleae are scrutinized, discussed, and analysed by means of a computerized parsimony program (PAUP). With one representative from each of the tribes Vernonieae, Liabeae, and Lactuceae as outgroups, three different analyses have been performed. Strict consensus trees for the three separate analyses are presented and discussed. A consensus tree based on the cladogram topologies obtained from all the three analyses is also presented. The taxonomic implication of the analyses is that the tribe Inuleae is an unnatural, not monophyletic group, which must be divided in better defined monophyletic tribes. Hence, three tribes are recognized and the majority of the described genera of the Inuleae are tentatively referred to one of these tribes. The tribes Gnaphalieae Rydb. (comprising the Inuleae–Gnaphaliinae and the Inuleae–Athrixiinae sensu Merxmüller et al.) and the Inuleae s.str., are accepted. Furthermore, the former subtribe Inuleae–Plucheinae Benth. is recognized and described as the new tribePlucheae(Benth.) A. Anderb.

ISSN:0008-4026    

DOI:10.1139/b89-292

出版商:NRC Research Press    

年代:1989

数据来源: NRC