摘要:

The nucleolus is sensitive to cold-protective media and to low temperatures. Nucleolar changes observed in the leaf primordia of wheat seedlings were related to the impregnation medium (distilled water or a mixture of glycerol, dimethyl sulfoxide, and sucrose), to the temperature (20 or 2 °C), and to the duration of the pretreatment (1 to 12 days). The cryoprotective agent generated the formation of nucleoli "with a diffuse granular zone." If the impregnation was done at 2 °C, characteristic nucleoli "with an indented aspect" occurred. The longer the duration of the impregnation and the more intense the subsequent freezing, the more important were the nucleolar changes. On rewarming the seedlings the various transformations were shown to be reversible.

ISSN:0008-4026    

DOI:10.1139/b85-084

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A study of the effects of fire on the regrowth of beaked hazel (Corylus cornutaMarsh.) and wild red raspberry (Rubus strigosusMichx.) was carried out in Elk Island National Park, Alberta. Shrubs growing under an aspen stand were subjected to five levels of fire severity by artificially adjusting the fuel load on small plots within a larger prescribed fire. Effects studied included mortality, number of stem sprouts, height growth of sprouts, and number of leaves per sprout, all during the first growing season, and biomass after the second season. Generally, fire killed the shrub stems at all severity levels. Variation in fire severity had little significant effect on regrowth, except that lower levels seemed to favor higher numbers of hazel sprouts and increased raspberry height growth.

ISSN:0008-4026    

DOI:10.1139/b85-085

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Alcohol extraction was made from seedlings ofUlmus americanaL. first inoculated with either a nonaggressive or an aggressive strain ofOphiostoma ulmi(Buisman) Nannf. and cross-inoculated 2 weeks later. The content of mansonones A,C,E,F, and G, phytoalexins inU.americana, was determined weekly for 1–6 weeks after the first inoculation. Inoculation with the nonaggressive strain led to greater levels of mansonones than did inoculation with the aggressive strain. The aggressive strain counteracted the effect of the nonaggressive strain in cross-inoculated seedlings. Mansonones F and E were the two quantitatively most important mansonones, representing 40.0 and 32.4%, respectively, whereas mansonones G,C, and A represented 15.2, 8.7, and 3.7%, respectively, of the total quantities of mansonones A,C,E,F, and G present in each sample.

ISSN:0008-4026    

DOI:10.1139/b85-086

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The mycosymbiont ofPertusaria pertusawas cultivated from ascospores or conidiospores. On Sabouraud agar, a nematothallus forms a multilobed, conidia-producing vesicle. Some mycelian filaments grow away from it and initiate "sclerotial structures." On maltea 2%, only a mycelian sheet was obtained. On the Lilly and Barnett medium such a mycelian sheet generates a hollow structure. The mycosymbiont of theXanthoria parietinawas cultivated from one ascospore or from conidiospores. On maltea 2%, a mycelian sheet is formed, then a nematothallian structure, generating a swollen, hollow, conidiogenous formation. On the Lilly and Barnett medium, the hollow structure is progressively filled with new hyphae. On the Sabouraud agar, the vesiculous structure becomes more structured; it can bear young apothecial primordia. It gives rise to small tongue-shaped lobes resembling young thallus lobes. The mycosymbiont oftheLecidea parasemacould be cultivated on Sabouraud agar. A mycelium is formed which is then transformed into a nematothallus. On it appear concentric crown-shaped protuberances. The cultures ofLobaria pulmonariaandLobaria laetevirensform a mycelian sheet which is transformed into a nematothallus. On Sabouraud agar this generates a vesiculous structure. Under intense light a sclerotic structure is formed. So, the mycosymbiont of the lichens has a great morphogenic plasticity; the phycosymbiont plays a fundamental role in the symbiotic union, leading to the formation of a pseudocladomian lichen thallus.

ISSN:0008-4026    

DOI:10.1139/b85-087

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Leaf water potential, osmotic potential, and leaf conductance were measured on corn (Zea maysL.) under water stress in the field and the greenhouse. Field-grown plants were subjected to several cycles of moderate water stress during vegetative growth, while greenhouse plants were well watered until just before the measurement period began following tasselling. In both the field and the greenhouse, leaf water potential declined at midday. Comparison of leaf water potential and osmotic potential measurements indicated that in both environments, the midday decline in leaf water potential was accompanied by a decline in osmotic potential. Since the decline in osmotic potential was greater than that accounted for by predicted volume changes resulting from normal daily dehydration, it was assumed to indicate osmotic adjustment. Despite these similarities, field-grown plants showed a greater response to water stress. Field plants underwent larger daily changes in leaf water potential and these were accompanied by larger changes in osmotic potential. As a result of this greater osmotic adjustment in the field, conductivity was higher at equivalent leaf water potentials and the critical leaf water potential was lower than in greenhouse-grown plants. In both environments, osmotic adjustment maintained leaf turgor (or pressure potential) in a narrow positive range. Although there was no direct relation between turgor potential and leaf conductivity, we hypothesize that the maintenance of a positive turgor potential during daylight hours is significant for growth since it may allow the moisture- and temperature-sensitive process of leaf expansion to proceed during the warmer daylight hours, even under moderate water stress.

ISSN:0008-4026    

DOI:10.1139/b85-088

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effect of chilling temperatures on the porphyrin pathway leading to chlorophyll was studied in Seneca Chief hybrid sweet corn. One-week-old seedlings grown at 28 °C in a 14 h light: 10 h dark photoperiod synthesize negligible amounts of chlorophyll when exposed to 12 °C for a subsequent 6 d. When the chilled plant is then brought back to 28 °C, chlorophyll synthesis is restored to control levels. Little difference in carotenoid content was detected between chill-stressed and control tissue even after 4 d of stress. Small differences in the chlorophyll content per 106chloroplasts could be detected between stressed and control seedlings. Etiolated seedlings synthesize negligible amounts of chlorophyll or its precursors when illuminated at 12 °C. Incubation of tissue with aminolevulinic acid at various temperatures from 12 to 22 °C resulted in an accumulation of precursors comparable to 28 °C control tissue. The ability of etiolated tissue to accumulate aminolevulinic acid was negligible when illuminated at 12 °C as compared with that in tissue illuminated at 28 °C.

ISSN:0008-4026    

DOI:10.1139/b85-089

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Accumulation of chlorophyll, the carotenoids (β-carotene, lutein, violaxanthin, and neoxanthin), and the benzoquinones (plastoquinone A and α-tocopherol) were monitored in 'Puma' rye as a function of leaf ontogeny at warm and cold-hardening temperatures. Although the kinetics of accumulation differed among the leaves of warm-grown plants, the initial and maximum levels of the pigments and benzoquinones expressed on a leaf area basis did not differ significantly among the first four leaves of the main culm. In contrast, the third and fourth leaf of cold-grown plants, which developed completely at the low temperature, generally exhibited initial and maximum pigment and benzoquinone levels 60–300% greater than was observed for leaf 1 and 2 of cold-grown plants, which were completely or partially developed at the warm temperature regime. This resulted in pigment and benzoquinone levels which were 1.6- to 3-fold greater in the plants grown at cold-hardening temperatures than those grown at the warm temperature, when expressed on a per unit leaf area basis. However, when pigment accumulation was calculated on a chlorophyll basis, the benzoquinone content of leaves that developed solely at cold-hardening temperatures exhibited a 1.7-fold increase over the same leaves developed at warm temperatures. Carotenoids did not exhibit this trend. Calculations based on chlorophyll/carotenoid content and dry weight accumulation indicated that leaves that were developed at cold-hardening temperatures appeared to produce more dry matter per unit of photosynthetic pigments than the same leaves that were developed at nonhardening temperatures.

ISSN:0008-4026    

DOI:10.1139/b85-090

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The genetic composition ofPinus contortavar.latifoliaas determined by isozyme analysis was examined in terms of its variation over space and time. Four populations of lodgepole pine consisting of approximately 125 trees each were sampled along an elevational gradient spanning a distance of 2 km in the Front Range of the Rocky Mountains in Colorado. Four isozymes were electrophoretically resolved from needle tissue removed from each tree. Ages were estimated from ring counts of either a tree core or a basal cross section of each tree. Gene frequencies were submitted to two-way analyses of variance using a subsampling procedure to generate multiple estimates within each cell. Analyses were performed to examine the variation in gene frequencies for each of the seven alleles resolved, using site (spatial) and age (temporal) as the independent factors. The results indicated that spatial heterogeneity contributes more to variation in genetic composition of lodgepole pine than does temporal heterogeneity. These results support theoretical proposals that spatial environmental heterogeneity under certain conditions can have more effect on variation in genetic composition than does temporal heterogeneity. It is further concluded that under certain conditions the analysis of variance procedure can be a useful analytic tool for examining gene frequency differences.

ISSN:0008-4026    

DOI:10.1139/b85-091

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The two intersterile chromosomally differentiated groups hitherto included inMedicago murexwere found to exhibit overlapping variation for 18 morphological characteristics. However, discriminant analysis showed that three of these characters in combination could be used to readily separate them. The nameM.murexWilld. was found to be applicable to the 2n = 14 species. The 2n = 16 form is recognized in this paper as a new species,M. lesinsiiE. Small.

ISSN:0008-4026    

DOI:10.1139/b85-092

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Material of the diploid (HBD) and tetraploid (HBT)Hordeum bulbosumcollected in the Mediterranean and Near East areas was examined for 14 morphometric characters. Exploratory data analysis revealed that cilia on the margins of the glumes of the central spikelets may or may not be present in HBT but are never present in HBD. The data were submitted to various kinds of discriminant analysis in which group assignment was based on ploidy level. When presence–absence of cilia on glume margins is used in combination with the resulting linear discriminant functions (DF) there is about 91% probability of correct identification; with DF alone there is about 81% probability. The results of discriminant analysis provided justification, in the opinion of the authors, to regard HBD and HBT as separate taxa at the level of subspecies, namelyH. bulbosumsubsp.bulbosumandH. bulbosumL. subsp.nodosum(L.) Baum.

ISSN:0008-4026    

DOI:10.1139/b85-093

出版商:NRC Research Press    

年代:1985

数据来源: NRC