摘要:

Nitrogen‐fixing activity in the phyllosphere of 12 species ofTillandsiafrom different Mexican habitats was evaluated by the acetylene reduction assay, and nitrogen‐fixing microorganisms were isolated and characterized. The leaves from eight of the 12Tillandsiaspecies examined exhibited nitrogenase activity in enrichment cultures. Among the microorganisms implicated—Agrobacterium, Bacillus, Erwinia, Pseudomonas, Rahnella, Vibrio, andXanthomonas—onlyBacillus megatheriumreduced acetylene in pure culture. Our findings suggest that nitrogen fixation in the phyllosphere of the sampled epiphytes occurs under suitable conditions and that most of the bacteria involved are primarily soil and water inhabitants. The results also suggest a relationship between the composition of the nitrogen‐fixing microbial communities grown on the leaf and the different development of the leaf area inTillandsiadue to the aerial components (wings) of the trichomes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13646.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Trembling aspen (Populus tremuloidesMichx.), a clonal angiosperm, is the most geographically widespread tree in North America. It is generally thought that most extant populations in the western interior of Canada and the United States became established shortly after glacial retreat, but sexual recruitment then effictively ceased owing to inimical climatic conditions. Six populations of trembling aspen were studied in the prairie and montane environments of Waterton Lakes National Park, Alberta. Vegetative tissues were analyzed for electrophoretically detectable variation in 13 enzymes encoded by 14 polymorphic loci and three monomorphic loci. All populations maintained high levels of inter‐ and intrapopulation diversity (P= 0.891;H= 0.319;A= 2.4). The mean fixation index,F, was ‐0.102, indicating some deviation from Hardy‐Weinberg expectations. Genetic differentiation (FST= 3.0) was apparent in this ecologically diverse, but geographically small‐scale, spatial setting. It is suggested that the maintenance of diversity in the absence of frequent modern‐day recruitment, and resistance to further geographic differentiation in this spatially heterogeneous environment reflect occasional seedling establishment through “windows of opportunity” and more importantly, the species' clonal morphology. The phalanx growth form and concomitant physiological integration between ramets combine to spread the risk of death and buffer the effects of selection over time and space.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13647.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Interest in the potential consequences of stratospheric ozone depletion has led to numerous studies that have evaluated the effects of ultraviolet‐B (UV‐B) radiation on plant growth and productivity. However, few studies have been conducted on plants from natural ecosystems. Differences in solar UV‐B radiation along latitudinal or elevational gradients may have resulted in plants from diverse habitats developing contrasting sensitivities to UV‐B radiation. In this study, seeds were collected along a 3,000‐m elevational gradient in Hawaii and then germinated and grown in an unshaded greenhouse with either no UV‐B radiation or one of two daily UV‐B irradiances, 15.5 or 23.1 kj m2. Seedlings were grown for 12 weeks and harvested to determine whether UV‐B radiation altered plant biomass. The responses to UV‐B radiation varied among species, but, in general, sensitivity to UV‐B radiation was reduced as the elevation of seed collection increased. Of the 33 species tested, UV‐B radiation significantly reduced plant height in 14 species and biomass in eight species. Biomass increased in four species grown under UV‐B radiation. This study provides clear evidence that natural plant populations exhibit wide variation in UV‐B radiation sensitivity and that this variation is related to the natural (ambient) UV‐B radiation environment in which these plants grow.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13648.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

A new genus and speciesGordoniopsis polyspermaand two new species ofGordonia(Gordonieae, Camellioideae, Theaceae) are described based on fossil fruit and seed remains. These specimens are part of a large flora consisting of various plant organs from the middle Eocene Claiborne Formation in western Kentucky and Tennessee.Gordoniopsisis a five‐valved loculicidally dehiscent capsule similar to capsules ofGordoniabut differing in having unwinged seeds and a greater number of seeds per locule. The twoGordoniaspecies are among the earliest unequivocal records of the genus and two of only four fossilGordoniaspecies known with in situ seeds. Two extinct genera,GordoniopsisandAndrewsiocarpon, and the extant genusGordoniain the tribe Gordonieae are known from the middle Eocene Claiborne flora, suggesting an early radiation within the tribe. Based on a survey of Recent fruits and seeds we concur with Keng's proposal to mergeLaplaceawithGordonia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13649.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Silicified leaves, dwarf shoots, pollen cones, and seed cones ofPinusfrom a Late Miocene chert bed within the Yakima Basalt Formation near Yakima, Washington are interpreted as coming from a single new species,P. foisyi.The needles and dwarf shoots are those of a three‐needle pine. The needles contain two to four medial resin canals, a biform hypodermis, and endodermal cells with uniformly thickened walls. The pollen cones are ellipsoidal and about 1 cm long, and many contain bisaccate pollen grains. The seed cones are at least 6 cm long and are slightly asymmetrical. The cone axis has a broad sclerotic outer cortex, and the seed wing extends from a thick parenchymatous base. The scale apex bears a conspicuously swollen projection. The foliage and seed cones are identifiable with the SubgenusPinus, SectionPinus, SubsectionOocarpaeindependently of one another, and together indicate a fossil species related to the modem Californian closed cone pines.Pinus foisyirepresents one of the earliest occurrences of cone asymmetry associated with this group. However, cone serotiny characteristic of the modem species appears to have evolved after the Late Miocene.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13650.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Type II callus cultures were initiated from immature tassels of a maize genotype with an A188/B73 genetic background using N6 medium containing 1.0 mg/liter 2,4‐D, 100 mg/liter casamino acids, 25 mM proline, and 0.2% phytagel™. Inclusion of 10 μM AgNO3in this medium significantly increased the frequency and vigor of the type II callus response. Friable calli emerged from these explants after two consecutive 2‐week subculture intervals. Tassels from 10 to 30 mm long were capable of producing type II cultures. The plants regenerated from these cultures were green and indistinguishable from plants regenerated from immature embryo‐derived calli.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13651.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The effects of waterlogging and salinity (25 or 325 mol m3NaCl) stressors on the anatomy and metabolism of the marsh grasses 5.alternifloraLoisel. and S.patensAiton (Muhl.) were investigated in aVfactorial greenhouse experiment over 30 d. Waterlogging and salinity in combination resulted in anatomical and metabolic responses in both species. Waterlogging reduced soil redox potential and decreased root‐specific gravity significantly in both species. The inadequacy of aerenchyma development under hypoxia to support aerobic root respiration inS. patenswas indicated by significant increases in root alcohol dehydrogenase (ADH) activity of 1,752% and 420%, respectively, in the low and high salinity treatments. ADH activity was not increased significantly by flooding ofS. alterniflora.Proline concentrations in roots and leaves were low at low salinities and increased significantly at high salinities in both species, but only under drained conditions. Decrease in leaf elongation by high salinity occurred in drained, but not flooded treatments in both species. Under flooded conditions, leaf elongation was significantly greater inS. alterniflorathanS. patens.Greatest leaf elongation occurred in flooded low salinityS. alternifloraplants that had the least proline. Although both species are adapted to waterlogging and salinity,S. alternifloraappears to be more tolerant of reducing soil conditions and less responsive to higher salinity thanS. patens.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13652.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Neither colchicine nor ultracentrifugation, singly or in sequence, significantly alters the normal Rabl distribution of interphase or prophase telomeres in root tip cells ofAllium cepaL. The position of telomeres was determined by C‐banding, which stainsA. cepachromosomes only at the telomeres. Centrifugation displaces mitotic figures toward one side of the cell, but otherwise their mitotic configurations are little changed. These light microscope results are interpreted to show that a) interphase and prophase telomeres are attached strongly to some component of the nuclear envelope; b) a colchicine‐sensitive component apparently does not attach interphase and prophase telomeres to the nuclear envelope; and c) chromosomes at all stages of the cell cycle are attached to some structure, nuclear envelope, and/or spindle fibers.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13653.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

We have monitored by in situ hybridization the cell‐ and tissue‐specific expression of a rice histone H3 gene during anther and pollen development in henbane (Hyoscyamus niger). Autoradiographic silver grains generated by hybridization of35S‐labeled antisense probe were present in more or less the same density in all the cells of the anther primordium. During later development of the anther, there was a sequential accumulation of histone mRNA beginning in the epidermis on the outside and ending in the tapetum inside. These changes in transcript abundance in the sporophytic cells of the anther were also related to the stage of microsporogenesis. Transcript level increased during sporogenesis and reached a maximum in mature pollen grains collected from open flowers.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13654.x

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

High night temperatures during floral development induce male sterility in cowpea (Vigna unguiculata[L.] Walp.). The objectives of this study were to determine: the possible causes of the male sterility; the stage of floral development when damage due to heat stress occurs; and whether specific tissues are damaged during the period of sensitivity to heat. Plants were grown under controlled temperatures in both greenhouses and growth chambers in separate experiments. Floral development was normal under a night temperature of 20 C, whereas flowers developed under high night temperature (30 C) set no pods due to low pollen viability and anther indehiscence. Anthers developed under 33/30 C day/night temperatures did not exhibit endothecial formation, whereas anthers developed under 33/20 C day/night temperatures exhibited normal development of the endothecial layer. Reciprocal transfers of plants between chambers with high or optimum night temperature demonstrated that the stage of floral development most sensitive to heat stress occurs 9 to 7 d before anthesis. Anthers developed under either optimal or high night temperatures were compared cytologically. Development was similar through meiosis, but after tetrad release, which occurred 8 d before anthesis, the tapetal layer degenerated prematurely under high night temperature. Premature degeneration of the tapetal layer and lack of endothecial development may be responsible for the low pollen viability, low anther dehiscence, and low pod set under high night temperatures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1992.tb13655.x

出版商:Wiley    

年代:1992

数据来源: WILEY