摘要:

Several workers have suggested that species with restricted ranges and few individuals are more likely to be self‐compatible and to exhibit low levels of inbreeding depression than are geographically widespread congeners. To investigate these predicted patterns, controlled pollinations were performed in the field on populations of two restricted and two widespread species ofAstragalus.All four species are xerophytic perennials which have similar floral size and morphology. Both restrictedA. linifoliusand restrictedA. osterhoutiare self‐compatible, andA. linifoliusis moderately autogamous. WidespreadA. lonchocarpusis self‐compatible, but widespreadA. pectinatusis essentially self‐incompatible. Neither the restricted nor the widespread species exhibited evidence of fecundity components of inbreeding depression (as measured by percent seed set and percent embryo abortion). Seedlings ofA. linifoliusandA. lonchocarpusthat had been produced by self‐ and cross‐fertilization were grown in a growth chamber to investigate progeny viability components of inbreeding depression. In contrast to the predicted patterns, inbreeding depression was detected in progeny of restrictedA. linifolius, but not in progeny of widespreadA. lonchocarpus.These patterns emphasize the importance of studying inbreeding depression in additional restricted and widespread species at several stages of the life cycle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11319.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Amelanchier bartramiana, which has been shown to be sexual and self‐incompatible, andA. laevis, in which apospory and self‐compatibility occur, grow in a mixed population in western Maine. Also present there is the putative interspecific hybrid,A. × neglecta.Principal components and canonical discriminant analyses of seven morphological characters from 96 parental and putative hybrid individuals substantiate morphological intermediacy of the hybrids. A Nomarski differential interference microscopy study of megasporogenesis and megagametogenesis in five hybrid plants shows a predominantly aposporous mode of reproduction, and controlled pollinations indicate that seed formation betweenA. bartramianaandA. laevisis possible and that the hybrids are self‐compatible. The hybrids, which are tetraploids (n= ca. 34) like both parents in Maine, produce viable pollen and seed, but there is little evidence for backcrossing with either parent.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11320.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

To investigate temporal changes occurring during tissue maturation and loss of organogenic competence, embryos ofPinus ponderosaLaws, were excised from seed and placed horizontally on medium in sterile culture. On a hormone‐free basal medium, cotyledons differentiated and failed to form multiple buds. When placed on a benzyladenine (BA)‐containing medium, the lower cotyledons in contact with the medium formed multiple buds while those elevated above the medium did not. Cotyledons became incompetent to form buds when embryos were initially placed on basal medium for 2 days before being transferred to the BA‐supplemented medium. In order to initiate buds, cotyledons of newly excised embryos had to be exposed to BA for at least 3 days. Exposure to BA for longer than 7 days did not significantly increase the number of cotyledonary buds. Cotyledons elevated above the BA‐supplemented medium retained organogenic competence to form buds for up to 14 days but did not form buds unless the cotyledons were placed in contact with the medium. The presence of BA is required to retard cotyledon maturation and sustain tissue competence to initiate buds.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11321.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The pressure chamber and the thermocouple psychrometer often provide different values when used to estimate plant water potential. One hypothesis to explain the discrepancy between instruments is that water movement between the xylem and symplast occurs during pressurization in the pressure chamber. Pressure chamber and thermocouple psychrometer measurements ofPinus ponderosa(Laws.) seedling shoots and matureQuercus agrifolia(Nee) shoots showed that the discrepancy is greater forQuercus.It was hypothesized that the xylem water content‐water potential relationship of these species would explain the magnitude of the discrepancy between instruments. The xylem water holding capacity alone, however, does not explain the difference between species. The larger discrepancy inQuercusis likely due to a greater volume of water held in the xylem relative to the volume held in the symplast.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11322.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The effects of disturbance on reproduction and plant and seed bank dynamics in the perennial herbBonamia grandiflorawere studied by comparing populations in recently burned, mechanically disturbed, and undisturbed habitats in central Florida over a 3‐year period. Plant densities, seed production, and the occurrence of herbivory and predispersal seed predation varied considerably between sites and between years, with recently disturbed sites supporting the densest and most dynamic populations. Death of established plants was rare in all sites. In each site, the soil seed bank was several‐fold larger than single season seed rains suggesting thatB. grandifloraseeds are long‐lived and accumulate in the soil. There was no evidence that postdispersal predation or pathogens have any significant influence on the seed bank dynamics. Fire resulted in large increases in stem densities due to both increased clonal stem production and new genet recruitment from seed. Burning also caused significant increases in the percentage of flowers producing seed and the numbers of capsules and seeds per plant. The seed rain was ten to thirty times greater in the burned site relative to adjacent unburned site during the 3 years after burning. However, additions to the seed bank from the postfire seed rain were balanced by equivalent losses due primarily to seed mortality during fire, and to a much lesser extent due to germination and new genet establishment. As a result, the subsequent densities of seeds stored in the soil in these two sites were similar, indicating that fire results in a significant turnover in the seed bank population but no immediate change in its size. These effects on seed bank dynamics, in addition to new genet recruitment, suggest that periodic fires may play an important role in the maintenance of genetic variability as well as the size of these populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11323.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Physiological and morphological differences betweenPlantago majorL. (Plantaginaceae) growing in full sunlight and shaded conditions were examined. Photosynthesis of isolated leaves was saturated by irradiance around 300μE m−‐2sec−‐1and 170μE m−‐2sec−‐1, respectively. In contrast to previous studies of sun/shade leaf responses, initial slopes of curves from shaded plants are significantly less than those taken from full‐sun plants. Within the 400–500 nm and 600–700 nm ranges, leaves 5.0 cm or longer are essentially opaque, transmitting less than 1.25% of incident light. Chlorophyll content per unit leaf area is nearly equivalent for leaves from plants growing under the two extremes in light levels. Morphometric comparisons indicate shaded plants bear fewer leaves, have less leaf overlap, lower total leaf area, and longer petioles than full‐sun plants. Leaf elongation rates are lower and the duration between the emergence of successive leaves is longer in shaded plants. Computer analyses of both types of rosette morphology reveal shaded plants have an equal or greater capacity to intercept light than full‐sun plants, principally because of the minimization of leaf overlap and the large variation in the deflection angles of leaves in shaded rosette morphologies. Simulations, calculated on the basis of light interception, and taking into account the transition between photosynthate‐importing and ‐exporting leaves, predict relative growth rates for full‐sun and shaded rosette morphologies that are in reasonable agreement with empirically determined leaf growth rates. However, the data indicate that significant physiological and morphological differences exist among leaves from a single rosette, and among developmentally comparable leaves from rosettes growing under different ambient light environments. Differences among leaves on a single plant must be accommodated in computerized techniques attempting to simulate light interception and its consequences on potential growth rates.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11324.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Senecio flavus(Decne.) Schultz‐Bip. of the Saharo‐Arabian and Namibian deserts andSenecio mohavensisGray of the Mojave and Sonoran deserts form a pair of closely related disjunct annual taxa. The two species exhibit slight morphological differences and have different ploidy levels: all North American populations examined are tetraploid, while African and Asian populations are diploid.Senecio flavuscomprises two morphologically and geographically distinct subspecies, subsp.flavusand subsp.breviflorusKadereit. Electrophoretic examination of 13 enzymes revealed that the subsp.breviflorushas two additional isozymes relative to subsp.flavus, and that 5.mohavensishas four additional isozymes relative to subsp.breviflorus. Senecio flavussubsp.breviflorusandS. mohavensisare identical at 20 of the 21 (I= 0.952) remaining homologous loci. This value is much higher than the genetic identity values observed in other taxa with disjunct intercontinental distributions such as members ofAgastache, Datisca, Liriodendron, andStyrax.This suggests that theSeneciodisjunction may be of recent origin.Senecio flavussubsp.flavusfrom North Africa and Namibia has lower genetic identity values withS. mohavensis(0.857 and 0.805, respectively), implicatingS. flavussubsp.breviflorusas the progenitor of 5.mohavensis.The complete lack of heterozygosity confirms that the plants are highly autogamous, and thus could have attained their disjunct distribution through long distance dispersal.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11325.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Fungal sporocarps are described from Triassic silicified peat deposits from Antarctica. Sporocarps possess a two‐layered wall and contain a single spore. The outer layer is mycelial; the inner layer, noncellular. The combination of primitive and advanced features suggests that this fungus is intermediate in complexity between the lower and evolutionarily more advanced fungi. The Antarctic fungus and morphologically similar fossils resemble extant members of the Endogonaceae, but appear to have been saprophytes rather than mycorrhizal symbionts.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11326.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Embryo enlargement and plant formation via in ovulo embryo culture was studied in stenospermic grapes. Genotypes, culture media and their interactions significantly affected embryo enlargement, whereas culture dates did not. Genotype P60‐58, when compared to cv. Thompson Seedless, had the greatest number of enlarged embryos after 3 months in culture. P60‐58 ovules cultured on Cain's basal medium plus L‐serine or L‐glutamine and cv. Thompson Seedless ovules cultured on Cain's basal medium plus L‐cysteine or L‐asparagine produced the greatest number of enlarged embryos. Viable embryos and morphologically normal‐appearing plants were obtained. Polyembryony was observed in cultured zygotic embryos.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11327.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

A mature, quiescent, primary axillary bud on the main axis of a floweringNicotiana tabacumcv. Wisconsin 38 plant, when released from apical dominance and before forming its terminal flower, produced a number of nodes which was dependent upon its position on the main axis. Each bud produced about one more node than the next bud above it. The total number of nodes produced by an axillary bud was about 6 to 8 greater than the number of nodes present above this bud on the main axis. At anthesis of the terminal flower on the main axis, mature, quiescent, primary axillary buds had initiated 7 to 9 leaf primordia while secondary axillary buds, sometimes present in addition to the primary ones, had initiated 4 to 5 leaf primordia. When permitted to grow out independently, primary and secondary axillary buds located at the same node on the main axis produced the same number of nodes before forming their terminal flowers. In contrast, immature primary axillary buds which had produced only 5 leaf primordia and which were released from apical dominance prior to the formation of flowers on the main axis produced only as many nodes as would be produced above them on the main axis by the terminal meristem, i.e., “extra” nodes were not produced. Therefore, it is the physiological status of the plant and not the number of nodes on the bud at the time of release from apical dominance that influenced the node‐counting process of a bud. When two axillary buds were permitted to develop on the same main axis, each produced the same number of nodes as single axillary buds developing at these nodes. Thus, the counting process in an axillary bud of tobacco is independent of other buds. Axillary buds on main axes of plants that had been placed horizontally produced the same number of nodes as identically‐positioned axillary buds on vertical plants, indicating that gravity does not play a major role in the counting, by an axillary bud, of the nodes on the main axis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11328.x

出版商:Wiley    

年代:1989

数据来源: WILEY