摘要:

The subalpine environment of Mount St. Helens and other southern Cascade volcanoes is characterized by porous, pyroclastic soils and summer droughts. To evaluate plant drought stress in this environment, we examined plant water relations ofEriogonum pyrolifolium, a wintergreen, shallow-rooted, rosette perennial, andPolygonum newberryi, a deciduous, deep-rooted semierect perennial (both in Polygonaceae), at a subalpine site (elevation 1575 m) on Mount St. Helens. In a very dry summer, soil moisture below 20 cm remained above −0.1 MPa, but surface tephra deposits developed soil water potentials below −4.0 MPa. Surface tephra deposits had a mulching effect on underlying pre-eruption soils. Predawn xylem pressure potentials for adults of each species were never below −0.8 MPa, but midday xylem pressure potentials were often measured near or below the estimated turgor-loss point when vapor pressure deficits were high (maximum 3.1 kPa). Compared withPolygonum,Eriogonumhad lower xylem pressure potentials, a lower turgor-loss point (mean −1.00 and −1.42 MPa, respectively), and higher conductance. In both species there was no midday depression in leaf conductance and little photosynthetic response to high evaporative demand. Thus, these species are not particularly conservative in water use and appear to rely on abundant soil moisture throughout the short growing season.

ISSN:0008-4026    

DOI:10.1139/b88-118

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Sperm cells can be isolated from maize pollen grains by gentle osmotic treatment. After the initial osmotic burst, the slurry is sieved through nylon mesh and then subjected to sucrose density gradient centrifugation to remove as much starch as possible. The isolated cells are spherical and approximately 7.2 μm in diameter, exclude Evans blue stain up to several hours at room temperature, and can be frozen and stored with reasonable retention of viability. Little alteration of the appearance of the living cells is seen after preparation for transmission electron microscopy. There is ultrastructural confirmation that maize sperm cells are protoplasts. Furthermore, there is no evidence of vegetative cell inner membrane on the outside of the sperms. Internally, there is a normal organelle complement including mitochondria, dictyosomes, protein bodies, and endoplasmic reticulum. The latter component is extensive and has associated ribosomes. Some coated vesicles occur in maize sperm protoplasts. Nuclear morphology is quite variable, including spherical, lobed, and irregular shapes.

ISSN:0008-4026    

DOI:10.1139/b88-119

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A newly developed technique was used to determine the long-term horizontal growth rate of the peat mat in Fallison Bog, a poor fen in northern Wisconsin. This technique consisted of carbon-dating material that was alive when the lake edge was at a particular location in the peatland and then measuring the distance from that location to the current lake edge. In Fallison Bog,Chamaedaphne calyculatastems currently buried at the mat peat – debris peat interface were alive when the lake edge was at that horizontal location. Radiocarbon dates of stem material from six locations in the peatland were used to estimate when the lake edge was at each location. To calculate the average long-term horizontal growth rate, the slope of the least-squares linear regression of distance from lake edge versus age of stems was computed. The estimated rate in Fallison Bog was 2.5 cm/year (95% confidence interval was 1.6–3.5 cm/year). The linear regression explained 95.6% of the variance in the data. The author suggests that this technique may be applicable in peatlands bordering acid lakes throughout northeastern North America.

ISSN:0008-4026    

DOI:10.1139/b88-120

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Silica deposition in the lower glume, lemma, and palea of wheat (Triticum aestivumL. cv. Highbury) was investigated using scanning electron microscopy and light microscopy. Silica was present in the outer walls of all the epidermal cells including prickles and papillae of the glume and lemma awns. The glume and the lemma were similar in epidermal silica deposition pattern, both having numerous silicified short trichomes and papillae on inner and outer surfaces. Epidermal long cells and short cells were also silicified. Macrohairs were restricted to isolated areas in these bracts, particularly on the inner surfaces just beneath the awns. The palea was a thin membranous structure differing markedly from the other two bracts. Most of the palea is pressed between the caryopsis and the next floret, and both surfaces are almost devoid of trichomes in these areas. However, at the apex and margins of the palea, macrohairs and papillae were abundant. The results are discussed with respect to possible taxonomic, anatomical, medical, and archaeological implications.

ISSN:0008-4026    

DOI:10.1139/b88-121

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The variability of both composition and amount of leaf surface wax from maize leaves (Zea maysL. cv. Oh 43) of different ages, and on different leaves along the plant, was studied by gas chromatography. In addition to visual comparisons of chromatograms, statistical analyses (ANOVAandPCA) were performed. For this cultivar, among the 25 hydrocarbons recognized, the dominant gas chromatography peak of the waxes from young leaves is 1-dotriacontanol, while wax from mature leaves consists predominantly of odd-numbered alkanes. The surface wax of leaves from intermediate-aged plants is a mixture of the seedling and mature waxes. In addition to age-related differences, consistent leaf-related developmental differences were detected. Furthermore, the amount of wax extracted per unit area increased during the first 20 days, declined rapidly until day 50, and declined gradually thereafter.

ISSN:0008-4026    

DOI:10.1139/b88-122

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Growth of triazine-resistant and -susceptible biotypes ofSolanum nigrumwas studied over a range of temperatures to test whether resistant biotypes show reduced performance under high temperatures. Each biotype was represented by parental lines and reciprocal F1crosses. Resistant biotypes were inferior in growth relative to susceptible biotypes. Temperature had no differential effect on the relative performance of resistant and susceptible biotypes. Our results withSolanum nigrumdo not support the hypothesis that the infrequent occurrence of the resistant biotypes in southern regions is explained by their decreased growth at high temperatures.

ISSN:0008-4026    

DOI:10.1139/b88-123

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

At Mount Albert, Quebec, many taxa are found exclusively on either serpentine or amphibolite contiguous formations. This exclusivity is clearly more noticeable within the saxicolous lichens than within the other groups. Serpentine seems to be an unfavourable substratum for the growth of saxicolous lichens. There are more infrequent taxa on serpentine than on amphibolite. The saxicolous, muscicolous, and terricolous lichen flora and the lichenicolous fungi of the plateau include 202 taxa, most of which have an arctic affinity. Of these taxa, 36 are recorded for the first time in Quebec, 16 in Canada and, 11 in North America. The ecological influence of serpentine on the lichens is, in many aspects, similar to that observed on vascular plants.

ISSN:0008-4026    

DOI:10.1139/b88-124

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The effect of an acute ozone dose applied to eastern cottonwood (Populus deltoidesBartr.) on subsequent lesion production of the leaf spot fungusMarssonina brunnea(Ell. et Ev.) P. Magn. was investigated. Two cottonwood clones were exposed to 393 μg∙m−3(0.20 ppm) ozone for 5 h and then inoculated with conidia ofM.brunneain leaf-disk and whole-plant assays on leaves of different ages (according to the leaf plastochron index (LPI)). There was no significant difference in lesion production on ozone-treated or control foliage, and significantly more lesions were produced on LPI 5 leaves compared with LPI 3, 7, and 9 leaves, irrespective of clone or treatment. These results show that infection of plants by facultative parasites will not necessarily increase when plants are exposed to air pollutants. In another study, urediospore production by an obligate parasite, the cottonwood leaf rust fungus (Melampsora medusaeThum.), was shown to decrease on cottonwood plants treated with an acute ozone dose in comparison with control plants. Thus, we hypothesize that ozone exposure of cottonwoods may have the potential to alter the relative destructive potential and abundance of members of the cottonwood pathogen community by differentially altering host susceptibility to different pathogen

ISSN:0008-4026    

DOI:10.1139/b88-125

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

By matching serial sections from the flagellum to the kinetosome in selected species of chytrids (Chytridiales), the kinetosome triplets have been assigned numbers that correspond to the numbers given by general convention to the flagellum doublets. The various organelles in the zoospore are located in nine longitudinal segments that lie proximal to the kinetosome. Each segment is delineated by the cartwheel spokes of the kinetosome; segment 1 lies between subfibers A of triplets 1 and 2. InRhizophydium chlorogoniiJaczewski,R.granulosporumScherffel,Chytridium confervae(Wille) Minden, andChytriomyces hyalinusKarling, the rootlet extends from between kinetosome triplets 1 and 2, but at different angles in each species. InCatenochytridium hemicystiKnox the rootlet extends from the triplet 1, and inAllochytridium luteumBarr & Désaulniers between triplets 9 and 1. In all species the center of the rumposome is located in segments 8, 9, or 1, and the nucleus in segments on the opposite side. The nonfunctional centriole is connected by fibers that extend from kinetosome triplets 6–7 in all species and also from triplets 5 and 8 in some species.

ISSN:0008-4026    

DOI:10.1139/b88-126

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Coelomomyces stegomyiae(Chytridiomycetes, Blastocladiales) infection in adult femaleAedes aegypti(Diptera, Culicidae) is located primarily in the ovaries. Fungal hyphae do not penetrate the germaria or follicles but instead lie between the tunica propria and epithelial sheath within each ovariole and between the epithelial sheath and the peritoneal sheath of the ovary.Aedes aegyptiis an anautogenous mosquito requiring a blood meal for egg development; similarly, fungal hyphae in infected ovaries will not differentiate to form resting sporangia until after the mosquito has taken a blood meal. The fungus restricts receptor-mediated endocytosis of vitellogenin by the plasma membrane of the oocyte so that few, if any, vitellin yolk granules form. Thick-walled resting sporangia have formed 72 h after the blood meal has been taken and these will be oviposited by the females in place of the aborted eggs.

ISSN:0008-4026    

DOI:10.1139/b88-127

出版商:NRC Research Press    

年代:1988

数据来源: NRC