摘要:

Events associated with the release from dominance are described for internodes 1 and 2 of the axillary buds ofPisum sativum. During the inhibited state, most of the nuclei are found in the G1phase of a diploid cycle. At the release from dominance, some nuclei in the G2phase during inhibition enter into mitosis and the nuclei in G1enter into the DNA synthetic phase. Until the 3rd day, a homogeneous reaction is registered for the whole of the two first internodes. Three maxima of mitotic activity are detected in the epidermis, the cortex, and the procambium and only one in the pith. From the 3rd day, the mitoses are localized at the uppermost part of these internodes: meanwhile, elongation occurs in their basal portion. At this level, the nuclear volumes are maximal at the 6th day. After release from apical dominance, the increase in DNA content reflects the resumption of the mitotic cycle and, subsequently, the onset of differentiation, with 4C level nuclei in the cortex and 8C nuclei in the pith. The cell growth of the epidermis, the cortex, and the pith, either radial or tangential, precedes the elongation phase.

ISSN:0008-4026    

DOI:10.1139/b78-136

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

An ultrastructural study of the zoospore of the obligate plant parasitic chytridSynchytrium endobioticum(Schilb.) Perc., the causal agent of potato wart disease, is presented. The uniflagellate zoospore ofS. endobioticumis characterized ultrastructurally by (1) an even distribution of the ribosomes, (2) one large, anteriorly located lipid globule, (3) mitochondria that are gathered around the nucleus. (4) cytoplasmic microtubules associated with the functional kinetosome, (5) an extensive sheet of endoplasmic reticulum partially encapsulating most of the cellular organelles, and (6) a structure which may resemble a contractile vacuole. The ultrastructure of the zoospore ofS. endobioticumis discussed in relation to other chytridiaceous zoospores studied; it is concluded that among theChytridiales, differences in zoospore ultrastructure exist between species within the same genus (e.g.,Phlyetochytrium) that are as great as those observed between different genera and even different families.

ISSN:0008-4026    

DOI:10.1139/b78-137

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Research was initiated to determine interactions betweenDrechslera sorokinianaandCurvularia geniculatain a potential disease complex onPoa pratensis. Inoculations withD. sorokinianaresulted in the greatest disease severity at 20 and 25 °C: disease severity was minimal withC. geniculatainoculations at all temperatures. Inoculations with the combination of both organisms displayed competitive and synergistic interactions that were temperature dependent. Combination inoculations reduced disease severity below that produced byD. sorokinianaalone and increased disease severity above that produced byC. geniculataalone at 20 and 25 °C and was indicative of a competitive interaction. Inoculations with the combination of the organisms increased disease severity above that produced by either organism alone at 30 °C, indicative of a synergistic effect at higher temperatures. Reisolations of the organisms from lesions produced from inoculations with the combination of the organisms indicated thatC. geniculatacompetes more successfully for infected tissue thanD. sorokinianabut is dependent on lesions initiated byD. sorokinianato establish successfully. Competition for tissue colonization byC. geniculatais greatest at temperatures of 25 to 35 °C. It was concluded thatC. geniculatashould be recognized as a weak, high-temperature, primary-leaf infecting pathogen ofP. pratensis, that a true ‘disease complex’ relative to disease severity can exist between the organisms at 30 °C that is dependent on lesions initiated byD. sorokinianaand reflects the high-temperature aggressiveness ofC. geniculata, that tissue invaded by both organisms is more successfully colonized byC. geniculataat higher temperatures, and that the necrotic portions of lesions produced byD. sorokiniana, and on which this organism does not sporulate well, is the probable site of establishment forC. geniculatawhere the organisms are found together.

ISSN:0008-4026    

DOI:10.1139/b78-138

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Individual leaves of three bog ericads, leatherleaf (Chamaedaphne calyculata), bog laurel (Kalmia polifolia), and Labrador tea (Ledum groenlandicum), were retained for a maximum of two growing seasons in a peat bog in southern Ontario. The premature loss of mature leaves, resulting from artificial defoliation, significantly reduced the growth of new shoots ofL. groenlandicumandK. polifoliabut not ofC. calyculata. Defoliation effects were directly proportional to the normal retention time for overwintering leaves. Mature leaves probably translocate photosynthate, nitrogen, and phosphorus to other plant parts. This would explain why leaf dry weights were greatest at the start, rather than at the end, of the leaves' second growing season. Net photosynthetic rates decreased with leafage, but in terms of leaf nitrogen content, new and old leaves fixed equal amounts of carbon.

ISSN:0008-4026    

DOI:10.1139/b78-139

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

In male gametophytes of chasmogamous and cleistogamous flowers ofOxalis corniculata, the development of the tube cell at the ultrastructural level shows that gametogenesis is almost the same in both cases: the dictyosomes, in particular, go through an inactive period accompanied by an intense production of microvesicles. This rest phase, present in pollen grains of numerous Angiosperms, is thus well marked in the two types of flowers. However, the similarity between the two types of gametogenesis is less obvious with regard to cell reserves: in pollen grains of cleistogamous flowers, starch formation is slightly retarded. At maturity, they contain numerous starch grains comparable with those found in chasmogamous flowers. In both types of flowers, the generative cell of the mature gametophyte gives rise to two sperms.Earlier studies on male gametogenesis in chasmogamous and cleistogamous flowers ofStreptoearpus nobilisandViolasp. compared with results onOxalis corniculatashow that cleistogamy determines more or less strongly the ontogeny of pollen grains as well as the morphology of the vegetative and floral parts. Thus, different degrees of cleistogamy exist from very specialized states (Streptocarpus nobilis) to very little modified ones (Oxalis corniculata).

ISSN:0008-4026    

DOI:10.1139/b78-140

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A protoplasmodium ofEchinostelium minutumde Bary forms a single fruiting body consisting of a globose mass of whitish spores mounted at the apex of a tapering acellular stalk within 24 to 48 h of the time that it is deprived of a microbial food supply. Sporulation is normally completed within. Phase-contrast microscopy indicates that a single, synchronous, intranuclear division occurs during the progressive, centripetal cleavage of the sporangium. This contention is supported by the observation that the number of uninucleate protospores is invariably twice the number of dividing nuclei present in the immature sporangium. Binucleate protospores are occasionally formed by the incorporation of nondividing, pycnotic nuclei.

ISSN:0008-4026    

DOI:10.1139/b78-141

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The chromosome numbers of individuals from 48 sites in southern Ontario and 12 sites in the eastern U.S.A. were determined. Twenty-one populations in Ontario ofAster pilosusvar.pringleiwere found to be hexaploid with 2n = 48 (first report for taxon). Sixteen populations ofAster pilosusvar.pilosuswere tetraploid 2n = 32 (first report for this ploidy level) and 11 populations were hexaploid 2n = 48. In southwestern Ontario, hexaploids of var.pilosuswere found concentrated in one region on glacial sand, till soils, and coarse gravel fill, while tetraploids were only found on finer textured silt plains and limestone outcropping. In Ontario, the two varieties are nearly allopatric, only growing in close proximity on Presqu'ile Point on Lake Ontario. Both tetraploid and hexaploid plants of var.pilosuswere found in the United States. The hexaploids were common near the Great Lakes but rare further south.Aster pilosusvar.demotuswas treated as a synonym of var.pilosus, since nearly glabrous plants produced pilose shoots when transplanted to the greenhouse at the University of Waterloo.

ISSN:0008-4026    

DOI:10.1139/b78-142

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Male plants ofSilene albaare found to possess one of two pollen types, distinguished by the ektexine structure. In one type, found in 58% of the plants examined, the ektexine is punctate with spinulose and tubuliferous elements, whereas the other type has a reticulate–spinulose ektexine. Associated with the ektexine features are differences in grain diameter, wall thickness, and pore number. In the related speciesS. noctifloraandS. dioica, all of the pollen examined had a reticulate–spinulose ektexine. No evidence could be found for the possibility that the reticulate ektexine inS. albamight be due to introgression fromS. dioica. Pollen dimorphism has not hitherto been reported in the Caryophyllales (Centrospermae), nor has it previously been established in a dioecious species. This appears also to be the first report of genetically controlled pollen dimorphism in a species that does not exhibit heterostyly.

ISSN:0008-4026    

DOI:10.1139/b78-143

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Experiments have been performed to induce callus formation and organogenesis in anther culture of cassava (Manihot esculentaCrantz). Callusing was achieved on a modified Murashige and Skoog medium (MSB) supplemented with 4.44 μM6-benzylaminopurine (BAP) and 4.52 μM2,4-dichlorophenoxyacetic acid (2.4-D). No callus was formed from anthers pretreated at 4 °C for more than 48 h or on a medium containing 4g/ℓ activated charcoal. Callus on MSB with 4.44–8.88 μMBAP alone formed roots only. BAP (8.88 μM) in combination with α-naphthalene acetic acid (NAA) (10.74 μM) resulted in chlorophyll formation in callus. Abscisic acid (ABA) acted as an antagonist to NAA in reducing the frequency of callus greening when the latter was applied jointly with BAP. Chromosome counts of mitotic figures from callus cells ranged from 34 to 38 indicating that the calli were derived from the somatic tissues of the anther

ISSN:0008-4026    

DOI:10.1139/b78-144

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Nuclear DNA from wheat, rye, andTriticaleplantlets was isolated and purified. Purity of the samples was tested spectrophotometrically. Tm values and hyperchromicities were determined for the three DNA samples. The DNA(s) were denaturated and annealed under controlled conditions. Cot curves were carried out for total DNA on the three samples and for the repetitive DNA fractions.The analysis of those curves indicated that the genomes of wheat and rye are made of highly repetitive, intermediate, and unique DNA fractions. The highly repetitive fraction (107) is suggested as corresponding to palindrome areas in the genome.TheTriticalegenome showed a similar pattern to the parents, except for the highly repetitive DNA fraction which showed different orders of repetitiveness.

ISSN:0008-4026    

DOI:10.1139/b78-145

出版商:NRC Research Press    

年代:1978

数据来源: NRC