摘要:

The role and metabolism of sucrose in cultured tassels ofZea mayscv. Oh43 were investigated. Although cultured tassels required 0.3 M (10% w/v) sucrose for "normal" development, they consumed less than 50% of it by day 21 of culture. The substitution of sucrose with mannitol inhibited both tassel growth and spikelet development. Sucrose served, therefore, mainly as an energy source and not as an osmoticum for cultured tassels during the first 15 days. However, from 15 days of culture onwards, tassels were shown to be capable of CO2fixation and consumed negligible amounts of sucrose until day 21 of culture. Nevertheless, the presence of sucrose was shown to be essential for differentiation of "normal" spikelets.

ISSN:0008-4026    

DOI:10.1139/b89-031

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Systematic studies of vegetation on 18 salt marshes along the coast of Maine show that the vegetation is highly variable in species composition, species richness, and zonation pattern. Marshes with high species richness are found in relatively stable geologic settings, while unstable marshes at the base of erodible bluffs have low species richness. Species composition is influenced by freshwater input. Salt-marsh zonation varies greatly in both the number of zones present per marsh and the species assemblages within zones. With a few notable exceptions, the vegetation of salt marshes in southern Maine is similar to that of marshes in southern New England. Salt-marsh vegetation in northeastern Maine is more similar to that of marshes in the Bay of Fundy region.Key words: tidal marsh, salt marsh, Maine, vegetation, New England, Bay of Fundy.

ISSN:0008-4026    

DOI:10.1139/b89-032

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The organization and ontogeny of microtubular structures associated with cell division in the green algaAphanochaete magnahave been analyzed using indirect immunofluorescence and transmission electron microscopy. The cortical cytoskeleton lining the longitudinal cell walls in dividing apical and side branch initiating cells depolymerizes at prophase, has completely disappeared at anaphase, and starts to repolymerize in the apex of the cell at the transition of mitosis and cytokinesis. At prophase, astral microtubule systems develop from the nuclear pole associated centriole complexes, and the nucleus becomes ensheathed by centriole-interconnecting astral microtubules. The asters disappear at metaphase–anaphase, reappear at telophase, and finally depolymerize at posttelophase. A star-shaped phycoplast develops at telophase, transforms into a planar array at posttelophase, and becomes associated with the new cross wall, while the cortical cytoskeleton lining the longitudinal cell walls reforms (resulting in the coexistence of two wall-lining microtubule assemblages having different origins). Finally, the phycoplast microtubules depolymerize. The presence of astral microtubule systems at prophase in green algae is discussed and the behaviour of the cortical cytoskeleton at cell division is compared with that in other plant cell systems.

ISSN:0008-4026    

DOI:10.1139/b89-033

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Addition of the cytokinins, benzylaminopurine,N6-Δ-(2-isopentenyl)-adenine, kinetin, zeatin, and zeatin riboside to a basal medium containing mineral salts and sucrose induced characteristic changes in pollen embryogenesis in cultured anthers and anther segments ofHyoscyamus niger. In anthers cultured in media containing 0.01–10.0 mg/L of each cytokinin, there was a progressive delay in the appearance of plantlets outside the anther locule and in the morphology of plantlets formed. Among the cytokinins tested, only zeatin riboside promoted anther efficiency; however, all compounds reduced pollen efficiency by as much as 40–60% of the control even in the lowest concentration tested. The effects of cytokinins were particularly noticeable in the failure of pollen grains to form embryoids by the division of the generative cell and in the decrease in the number of embryoids formed by the division of both generative and vegetative cells. At the morphogenetic level, embryoids formed in media containing cytokinins displayed various abnormalities such as precocious elongation of the root apex, cotyledon expansion, and callus formation on the cotyledons, hypocotyl, and root. During their subsequent growth, calluses induced on embryoids by benzylaminopurine,N6-Δ-(2-isopentenyl)-adenine, zeatin, and zeatin riboside formed somatic embryos that recapitulated stages of zygotic embryogenesis. Globular and heart-shaped embryoids, which did not develop further, were frequently observed on kinetin-induced pollen callus; the callus also regenerated leafy shoots by organogenesis. Addition of adenine to the medium did not have any effect on pollen embryogenesis in cultured anthers ofH.niger.

ISSN:0008-4026    

DOI:10.1139/b89-034

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The behavior of the fungusPythium coloratumVaartaja on onion (Allium cepaL.) roots with a hypodermis of long and short cells was studied. Frequency of encystment adjacent to long versus short cells was compared in live and heat-killed roots. To determine whether the state of suberization of hypodermal cells was correlated with the number of zoospores encysting next to the cell, roots on which zoospores had encysted were stained with toluidine blue to quench most autofluorescence except that caused by lamellar suberin. Penetration of fluorescent long cells, nonfluorescent long cells, and nonfluorescent short cells was compared. Encystment of zoospores on the onion epidermis was more frequent adjacent to short cells of the hypodermis than could be expected for random encystment. More zoospores encysted next to short cells on heat-killed roots than on live roots. Encystment was more frequent over nonfluorescent long cells than over fluorescent long cells. Penetration by the fungus was more frequent into short cells and nonfluorescent long cells than into fluorescent long cells.

ISSN:0008-4026    

DOI:10.1139/b89-035

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

β-1,3-Glucanase activity was assayed over a 14-day period in leaves of three maize (Zea maysL.) near-isogenic inbred lines with differing susceptibilities to the fungal pathogenExserohilum turcicum(Pass.) Leonard and Suggs. Crude leaf extracts of β-1,3-glucanase activity had a pH optimum of 4.5 and required a sulfhydryl reagent for maximal activity. One half of the plants of each inbred line were inoculated with race 2 ofE.turcicumat the beginning of the experiment. β-1,3-Glucanase activity increased with inoculation in all isolines, but was highest 14 days after inoculation in line B37Ht2, with an allele conferring specific resistance to race 2. Isoline B37HtN, with a nonspecific allele for resistance, displayed an intermediate increase in β-1,3-glucanase activity. Susceptible line B37 had the lowest β-1,3-glucanase activity. β-1,3-Glucanase activity appeared to be induced in maize and was not a result of increased enzyme activity in the pathogen.

ISSN:0008-4026    

DOI:10.1139/b89-036

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Three species of fungi that attack microscopic animals are described as new.Verticillium coronatum(Hyphomycetes) produces conidia that have a cluster of small, apical appendages. The appendages function in attaching the conidia to the cuticle of the host nematode in the initial stages of infection.Diheterospora humicola(Hyphomycetes) was found to attack bdelloid rotifers in soil. Infection of the host is initiated by ingestion of conidia.Lagenidium oviparasiticum(Oomycetes) is an aggressive parasite of the eggs ofAdinetarotifers. Zoospores of the fungus encyst on the egg shell, penetrate, and transfer their contents into the egg to initiate infection.

ISSN:0008-4026    

DOI:10.1139/b89-037

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

When suitable stages of rachilla tissues derived from coconut palm were selected as an explant source, a higher frequency of callus induction was observed in medium containing activated carbon and 20–30 ppm 2,4-dichlorophenoxyacetic acid (2,4-D).

ISSN:0008-4026    

DOI:10.1139/b89-038

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The species composition and abundance of viable seed in organic forest floor and surface mineral soil from two high-latitude jack pine dominated and two white spruce dominated stands were determined by enumerating germinants from samples placed on moist peat-moss beds. Estimated seed density ranged from 500 to 2600 seeds/m2, representing 13 species of trees, shrubs, and forbs. About half of the species in the seed bank were present as mature plants in each stand. The high seed densities recorded are inconsistent with the previously proposed poleward decline in the abundance of buried seed. The role of buried viable seed differed among species in relation to inherent seed dispersal capabilities and seed longevity. Several species were recorded that are considered to have a very short period of viability in the soil. It is suggested that even a short residence in the seed bank may be adaptive in areas where spring burning accounts for a large proportion of the total area burned annually.

ISSN:0008-4026    

DOI:10.1139/b89-039

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Etiolated cucumber seedlings grown from seeds pretreated with 5 μg∙mL−1triadimefon (1-(4-chlorophenoxy)-3,3 dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone) exhibited a marked reduction in both ethylene (C2H4) production and endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) levels. Most of this reduction could be accounted for by a twofold drop in C2H4production and fivefold drop in ACC content of root tissue. Roots of control seedlings efficiently converted exogenous ACC to C2H4, but the ability of triadimefon-treated roots to convert ACC to C2H4was impaired. However, triadimefon-treated shoots and cotyledons were nearly twice as efficient in utilizing exogenous ACC and metabolizing it to C2H4as control tissue

ISSN:0008-4026    

DOI:10.1139/b89-040

出版商:NRC Research Press    

年代:1989

数据来源: NRC