摘要:

A survey of charophycean green algal and bryophyte taxa revealed the frequent occurrence of vegetative cell walls that were characterized by a specific form of autofluorescence and resistance to high temperature acid treatment (acetolysis). The time of production and the location of resistant, autofluorescent cell walls varied among charophyte and bryophyte taxa in patterns that suggest that bryophytes inherited the capacity to produce such walls from charophyte ancestors. A number of charophytes produced resistant walls in response to desiccation stress, suggesting an evolutionarily early adaptive response.Coleochaetewas unique among charophytes, but similar to all bryophytes tested in that sexual reproduction induced autofluorescence in cell walls of well‐hydrated tissues at the placental junction. Maternal tissues in apical portions of the pseudoseta bearingSphagnumsporophytes were characterized by autofluorescent, acetolysis‐resistant cell walls similar to those observed in maternal cells adjacent toColeochaetezygotes. These observations suggest that cell–cell stimulus–response interactions regulate deposition of autofluorescent compounds in placental cell walls, and that this characteristic may have been shared by the earliest embryophytes and their charophyte ancestors. Various bryophytes deposit autofluorescent, acid‐resistant compounds at other adaptively significant sites including sporangial epidermis, spiral thickenings of elaters, rhizoids, and leaves in the special case ofSphagnummoss.Sphagnumand liverwort sporangial epidermis, which had been subjected to acetolysis or strong acid procedures commonly used to release microfossils from rock matrices, resembled published photographs of Ordovician–Devonian microfossils consisting of cellular scraps that have been attributed to earliest land plants. Our work suggests that at least some of these fossils, previously thought to represent “dispersed cuticles,” could be reinterpreted as earliest known remains of plant sporophytic tissues, and that they may be homologous with resistant sporangial epidermis of modern bryophytes. In general, the patterns of occurrence of resistant, autofluorescent cell walls in charophytes and bryophytes suggest repeated exaptation. Regulation of deposition appears to have been modified through time, so that resistant wall compounds have had a sequence of functions: desiccation resistance and/or microbial resistance in lower charophytes, a role in embryogenesis inColeochaeteand embryophytes, and finally, decay resistance in innovative structures that characterize bryophytes, such as rhizoids, sporangial epidermis, and elaters.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13908.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Tassel and ear primordia were collected from greenhouse‐grown specimens of the Mexican maize landrace Chapalote and prepared for scanning electron microscopic (SEM) examination. Measurements of inflorescence apices and spikelet pair primordia (spp) were made from SEM micrographs. Correlation of inflorescence apex diameter with number of spikelet ranks showed no significant difference between tassels and ears, except at the two‐rank level where the ear apical meristem had a significantly smaller diameter than corresponding two‐ranked tassels. Within individual inflorescences, spp in different ranks enlarged at comparable rates, although the rates from one ear to the next along the stem differed. In both tassels and ears, spp divide to form paired sessile and pedicellate spikelet primordia when the spp is 150 μm wide; ear axes are significantly thicker than tassel axes at the time of bifurcation. The similarities in growth between ear and tassel primordia lend further support to the hypothesis that both the maize tassel and ear are derived from a common inflorescence pattern, a pattern shared with teosinte. Inflorescence primordial growth also suggests that a key character difference between teosinte and maize, distichous vs. polystichous arrangement of spikelets, may be related to size of the apical dome and/or rate of primordium production by the apical meristem. There appears to be more than a single morphological event in the shift from vegetative to reproductive growth. The evocation of axillary buds (ears) is independent of, and temporally separated from, the transition to flowering at the primary shoot apex (tassel).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13909.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Aerenchyma gas spaces are important for plants that survive flooding because these spaces provide an internal pathway for oxygen transport to the root zone. The objective of this study was to characterize the development of aerenchyma gas spaces inSagittaria lancifoliaL., a dominant species in freshwater wetlands adjacent to the Gulf of Mexico. Tissue at different developmental stages was collected from hydroponically grown plants, embedded in plastic, and sections were observed with a light microscope. InS. lancifoliaroots, lysigeny (cell lysis) produced gas spaces that increased in volume from the root meristem to the most mature root tissue. Shoot aerenchyma occurred in the large petioles ofS. lancifoliaand through the blade midrib, but not in the laminar portion of the blade. In contrast to the roots, gas spaces in the petiole were formed by schizogeny (cell separation during development). Shoot initials produced cells that formed interlocking cylinders in the cortex and diaphragm cells that bridged the central portion of the cylinders. Division and expansion of both these cell types increased the diameter of the cylinders and created schizogenous gaps between diaphragm layers that produced large gas spaces in mature tissue. Therefore, aerenchyma development occurs by two different processes inS. lancifolia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13910.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The sporophyte‐gametophyte junction inAcaulon muticumis composed of the sporophyte foot, the surrounding gametophyte vaginula, and an intervening placental space. At an early stage of development the foot has a large basal cell, characterized by extensive wall ingrowths beginning at the lowermost tip of the basal cell and extending along its tangential walls. Sporophyte cells in contact with the basal cell develop ingrowths on their outer tangential walls and on radial walls in contact with the basal cell. All sporophyte cells at this stage are characterized by numerous mitochondria, strands of endoplasmic reticulum, and dictyosomes, particularly in the cytoplasm adjacent to areas of extensive wall development. Plastids typically contain abundant starch reserves. As development proceeds, wall ingrowths become more extensive on all walls in the sporophyte foot but are never found on the upper wall of the basal cell in contact with the remainder of the sporophyte. Plastids in the foot contain fewer starch reserves later in development. Wall ingrowths are not visible in the cells of the gametophyte vaginula until well after extensive development has occurred in the sporophyte foot. Stacks or layers of endoplasmic reticulum are characteristic of the cells of the gametophyte vaginula, along with numerous mitochondria, dictyosomes, and well‐developed plastids. Starch reserves typically are less abundant in cells of the gametophyte. The early development of extensive wall elaborations in the cells of the sporophyte foot, and particularly in the basal cell, may favor the rapid movement of water and nutrients from the gametophyte into the sporophyte at a time when rapid development in this minute, ephemeral moss is critical.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13911.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Nuclear restriction fragment length polymorphism (RFLP) analysis was used to determine the wild diploidArachisspecies that hybridized to form tetraploid domesticated peanut. Results using 20 previously mapped cDNA clones strongly indicatedA. duranensisas the progenitor of the A genome of domesticated peanut andA. ipaensisas the B genome parent. A large amount of RFLP variability was found among the various accessions ofA. duranensis, and accessions most similar to the A genome of cultivated peanut were identified. Chloroplast DNA RFLP analysis determined thatA. duranensiswas the female parent of the original hybridization event. Domesticated peanut is known to have one genome with a distinctly smaller pair of chromosomes (“A”), and one genome that lacks this pair. Cytogenetic analysis demonstrated thatA. duranensishas a pair of “A” chromosomes, andA. ipaensisdoes not. The cytogenetic evidence is thus consistent with the RFLP evidence concerning the identity of the progenitors. RFLP and cytogenetic evidence indicate a single origin for domesticated peanut in Northern Argentina or Southern Bolivia, followed by diversification under the influence of cultivation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13912.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Few integrative analyses of the structure of agamospermous plant populations have been conducted.Erigeron compositusoccurs in montane western North America and comprises both sexual and agamospermous populations. SexualE. compositushas previously been characterized as outcrossing and predominantly diploid (2n= 18). AgamicE. compositusis usually hexaploid (2n= 54), though counts herein range from 2n= 36 to 2n= 80. Starch‐gel electrophoresis, cytology, and analysis of pollen production were used to evaluate variation within and among agamospermous populations. Fifteen enzyme loci were used to identify 24 unique multilocus genotypes in seven populations, an average of 3.4 genotypes per population. Proportion of distinct genotypes per population sample size (GIN)and measures of genetic diversity (D) and evenness (E)are 0.10, 0.48, and 0.61, respectively, which indicate thatE. compositusmaintains levels of diversity similar to other agamospermous taxa. Most agamospermous populations are mosaics comprising groups of genetically distinct individuals that are frequently distinguished by cytotype and capacity for pollen production. The geographical and ecological separation of sexual and agamospermous populations make it unlikely that gene flow from sexual populations is a direct source of genetic variation in agamospermous populations. Instead, crossing between genetically distinct facultative agamosperms probably accounts for most variation. Genetic and morphological evidence document one such putative crossing event. AgamospermousE. compositusis very similar genetically to sexualE. compositus.Allozyme analysis further shows that genetic variation in agamospermous populations is partitioned among a few highly heterozygous genotypes, whereas sexual populations maintain numerous genotypes of relatively low heterozygosity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13913.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

An analysis of 23 species ofTrichomaness. 1. indicates that the presence of C‐glycosylflavones, especially mono‐C‐glycosylflavones, may be a basic characteristic for this genus. Except for the morphologically uniqueCardiomanes reniforme, this feature appears to delimit the species ofTrichomaness. 1. from those ofHymenophyllums. 1. Several species, primarily those classified withinDidymoglossum(according to both Copeland and Morton), synthesize flavone‐O‐glycosides in addition to their C‐glycosylflavone profiles. Two species,T. birmanicumandT. radicans, appear to be unique in synthesizing the di‐C‐glycosylflavones violanthin and isoviolanthin; five species(T. collariatum, T. scandins, T. birmanicum, T. bicorne, andT. alatum) appear to synthesize di‐C‐glycosylflavones but lack mono‐C‐glycosylflavones. Based on this and other studies, it may be appropriate to consider these C‐glycosylflavone‐producing plants as representing primitive leptosporangiate stock.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13914.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Meiotic behaviors and reproductive modes of JapaneseIsoeteswere studied. The hexaploid (2n =66) and the octaploid (2n =88) ofI. japonicaconsistently formed 33 and 44 bivalents, respectively, at diakinesis and/or metaphase I in both micro‐ and megaspore mother cells. The tetraploid (2n= 44) ofI. sinensisformed 22 bivalents and its hexaploid made 33 bivalents in both types of spore mother cells. At diakinesis and/or metaphase I of microspore mother cells inI. asiaticawith 2n =22, 11 bivalents were detected. Because behaviors of meiosis in all cytotypes mentioned above were quite regular and plants yielded normal‐appearing spores, they should reproduce sexually. Aneuploids ofI. japonicawith 2n =87 formed 43 bivalents and one univalent, andI. sinensiswith 2n= 65 formed 32 bivalents and one univalent in microspore mother cells. Meiosis of both cytotypes was almost regular and yielded microspores of normal appearance. In the heptaploid (2n= 77) ofI. japonica, a configuration of 22 bivalents and 33 univalents was detected in micro‐ and megaspore mother cells, and various irregularities were observed throughout the meiotic divisions. Therefore, the genomic formula of the heptaploid is symbolized as AABBCDE, and the heptaploid is a sterile F, hybrid between the hexaploid (AABBCC) and the octaploid (AABBDDEE) ofI. japonica.Since diploid and even‐numbered polyploids regularly formed bivalents and odd‐numbered ones displayed irregularities, allopolyploidy should act as a significant speciation mechanism in this genus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13915.x

出版商:Wiley    

年代:1996

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13916.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Within‐panicle flowering, exsertion, and seed ripening were investigated in four clones ofP. maximum.Flowering, exsertion, and seed ripening were fast processes (<;10 d for each process). Dates and timing were stable within each clone and should allow definition of the harvest date for each genotype and for each harvest method. Clones showed two main flowering patterns differing in the number of flowered spikelets at the date of maximal flowering and in the time of flowering. Seed set was similar to that of allogamous and anemophilous plants. It was nevertheless lower in clones with a high degree of flowering‐shedding overlap. In the absence of flowering‐shedding overlap, the time for a panicle to flower and to produce seeds was shorter than the time between two emergences of panicles on a tiller. Reproduction timing seemed controlled to minimize competition between panicles on a tiller.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb13917.x

出版商:Wiley    

年代:1996

数据来源: WILEY