摘要:

Development of anthers in three subfamilies of Orchidaceae was studied anatomically to examine homology hypotheses for pollinium number characters and to produce a model of pollinium development for the family. Serial sections of plastic‐embedded embryonic inflorescences revealed that anther primordia were either flattened or ovoid; subsequent expansion of thecae and their inward (adaxial) reorientation (“rotation”), achieved by differential cell division and elongation in the connective, result in a mature anther with strongly introrse morphology and pollinia oriented side by side (juxtaposed). Strongly introrse anthers occur in at least some members of all subfamilies and are probably the basal state for the family. All anthers examined (from Orchidoideae, Spiranthoideae, and Epidendroideae) showed a single meristematic region, which would later give rise to pollen, per theca at earliest stages; septation of each of these regions resulted in four or eight pollinia per anther, while lack of septation in some members of the Epidendroideae gave two pollinia. In contrast, the two bipartite pollinia found in many Spiranthoideae and Orchidoideae were produced by adherence of the contents of two locules at a late ontogenetic stage, and should be recognized as a distinct character state. Eight pollinia result from partitioning by two longitudinal septa or a longitudinal and a transverse septum; these two morphologies may also represent separate character states.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12773.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The ultrastructure of cells of mung bean (Vigna radiataL. var. Wilczek) in suspension culture was studied during chilling. During such treatment, three kinds of injured cells were observed: swollen cells, cells with broken vacuolar membranes, and cells with shrunken plasma membranes. Swelling was observed from the early stages of chilling, and in most cells during chilling. The other two types of cells were observed at the late stages of chilling. At the early stage of chilling, whorls of rough endoplasmic reticulum that surrounded clear regions of cytoplasm were observed. At the same time, markedly rough vacuolar membranes, plastids and mitochondria with vacuoles, enlargement of Golgi vesicles, and dilation of the ER were seen. These changes preceded the swelling of cells. These ultrastructural features of chilling injury are discussed in terms of biochemical observations. The disruption of the vacuolar membrane and the shrinking of the plasma membrane are discussed in terms of destruction of the cytoskeleton.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12774.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Changes in normalized cell length (NCL) and tissue volume densities (Vv) of five trap tissues were studied during reopening of fully closed traps of Venus's flytrap (Dionaea muscipulaEllis). Four trap‐reopening stages were identified based on morphological changes observed in time‐lapse video: (1) Sealed—the last stage of trap closure before the trap began to reopen; (2) Deappressed—characterized by a convex bulge in the upper region of the trap; (3) Release—in which the bulge region moved closer to the trap margins initiating lobe separation while the marginal tynes remained interdigitated; (4) Fully opened—the trap lobes assumed a morphology similar to that of a nonstimulated trap. Morphological changes associated with trap reopening occurred as a series of relatively fast (l‐5h) and slow (10‐15 h) movements and appeared to be a reversal of the morphologies observed during trap closure. However, comparison of changes in NCL of trap tissues during closure and reopening showed very little statistical correlation indicating that the tissue dynamics associated with trap closure were not simply reversed during reopening. Although the precise cell movements that provided driving force for trap morphological change were not delineated in this study, comparison of NCL data suggested that tissues in the trap lobe were alternately “active” and “quiescent” in temporally and regionally complex patterns. Changes in the NCL of analogous tissues on opposite sides of the mid‐trap tissues within a trap region showed high positive correlation values, which indicated the possibility of coordinated activity in opposing tissues.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12775.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Using RAPD markers and one morphological marker, we studied the among‐ and within‐population structure in a selfing annual plant species,Medicago truncatulaGAERTN. About 200 individuals, sampled from four populations subdivided into three subpopulations each, were scored for 22 markers. It was found that the within‐population variance component accounted for 55% of the total variance, while the among‐population variance component accounted for 45%. Eighteen percent of the total variance was due to within‐population structure (i.e., among subpopulations). Thus, 37% of the total variance was within subpopulations. Using a multilocus approach, it was found that no multilocus genotype was common to two populations. Two of the four studied populations were composed of few (≤6) multilocus genotypes, whereas the other two had many (≥15) multilocus genotypes. In the most polymorphic population (37 genotypes), only one genotype was found to be common to two subpopulations. Resampling experiments show that, depending on the population, three to 16 polymorphic loci were necessary and sufficient to score all multilocus genotypes in the population. When these data are compared to published results, it appears that on some occasions, the number of genotypes per population of selfing species might be larger than would be expected from the sole consideration of effective population size. The large within‐subpopulation genetic variance observed in some populations could be explained by either small neighborhood sizes within subpopulations, or by outcrossing following migration through seed and/or pollen.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12776.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Intraspecific variation in seed dispersion provides the initial context for frequency‐dependent and density‐dependent processes affecting seed/seedling survival. We examined intraspecific variation in seed dispersion in a ballistically dispersed herbaceous annual,Lepidium campestre, in both the presence/absence of vegetation to determine the magnitude of variation in seed dispersion among parents, the relationship of this variation to parental architecture, and the effect of the presence of vegetation both on the variation and on its relationship to parental architecture. We quantified seed dispersion by placing concentric rings of traps around individual parents out to a distance of 2 m in the presence/absence of vegetation in an old‐field plant community. In the absence of vegetation, parents differed in the distance and direction that their seeds traveled. Parental height and infructescence length explained a significant proportion of the variation in mean and standard deviation of seed dispersal distance, as well as skewness and kurtosis of the distribution of seed number as a function of distance. The mean direction that seeds traveled was correlated with all architectural traits. When plants dispersed their seeds in sites with dense vegetation, mean dispersal distance and standard deviation in distance decreased, and dispersal distributions were more right‐skewed and leptokurtic. The presence/absence of vegetation explained some of the variation among parents in the moments of the distance distribution, but architectural traits also contributed to these descriptive models. Directional components of dispersal were not affected by vegetation. Correspondence analysis, a multivariate technique that examined distance and direction simultaneously, revealed that architectural attributes related to variation in dispersion were different from analyses of distance alone. These results suggest that architectural attributes of the parent contribute not only to the distance that seeds travel, but also to other axes of variation, i.e., skewness and kurtosis of the distance distribution or multivariate axes of seed dispersion. Surrounding vegetation alters seed dispersion, but parental attributes can still explain some of the residual variation. This variation in seed dispersion among parents creates the opportunity for selection on parental dispersal traits.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12777.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Racemose inflorescences were investigated organographically and ontogenetically in three species ofCampylotropis.An additional phyllome was found to be borne at the base of the pedicel inC. hirtellaandC. giraldiibut not inC. polyantha.Organographic observations revealed that the additional phyllome is the prophyll on the reduced lateral branch borne in the axil of the phyllome on the central inflorescence axis, and that the additional phyllome subtends the pedicel terminating in a flower. The flower presents its abaxial side to the additional phyllome in accordance with the organographic observations. Ontogenetic observations, moreover, revealed the presence of a rudimentary apex of the reduced branch in earlier stages of development. On the basis of such evidence, the central inflorescence axis ofCampylotropisis interpreted as being composed of reduced lateral branches each of which usually bears only one flower in the additional phyllome axil. The inflorescence structure is kept in spite of the loss of the additional phyllome. In comparison with allied genera, the inflorescence ofCampylotropisis regarded as a reduced pseudoraceme. An evolutionary trend in the inflorescence structure of the genus is inferred.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12778.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Odors of pollen and whole flowers were compared in taxonomically unrelated species that offer pollen as the only food reward to pollinators. Volatiles were collected using headspace adsorption and analyzed by gas chromatography and mass spectrometry. The odor of pollen was found to be chemically distinct from the total flower odor, and this pollen‐odor distinctness varied among the three species. InPapaver rhoeas(Papaveraceae), the contrast between pollen and whole‐flower odors was most subtle, with differences observed only in the proportions of individual volatiles (almost exclusively aliphatic hydrocarbons). InFilipendula vulgaris(Rosaceae), pollen volatiles were fewer than in the flowers (comprising mainly benzenoids and fatty‐acid derivatives) and their relative proportions produced an odor dominated by 2‐heptadecanone that contrasted strikingly with the flower odor dominated by 2‐phenyl ethanol. InLupinus polyphyllus(Fabaceae), the pollen odor contained fewer volatiles and in differing proportions than the flower fragrance (comprising almost exclusively isoprenoids). The findings add to earlier chemical evidence of odor contrasts between pollen and other flower parts in two other species. Drawing on information from pollination studies of these various species, it is suggested that pollen odor is used by pollen‐foraging insects both to discriminate between plant species and to assess reward availability in individual flowers, and that it might in addition serve a protective function against destructive flower‐feeding insects and pathogens.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12779.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Previous field experiments have shown that, for the annual herbVicia sativa, leaf area lost to herbivory results in reduced number of fruit (pods) produced per plant as well as fewer seeds per pod. We conducted a controlled garden experiment to determine the precise relationship between level of defoliation and various measures of maternal fitness through fruit and seed. We employed manual clipping of individual leaflets of newly produced leaves to 25% increments of damage (from 0% to 100%) over the entire period of development and flowering of these annual herbs, harvesting pods when filled but not dehisced. We found significant reduction in number of pods, number of seeds, total seed mass, and individual seed mass with leaf area lost. Even with the highest levels of defoliation over the life of the individual, plants still produced a substantial number of pods and seeds. Seeds produced by plants in all treatment groups showed similar percentages of germination and time to germination.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12780.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Progeny arrays ofOcotea tenera(Lauraceae), a gynodioecious tree endemic to Costa Rica, were electrophoretically surveyed for allozyme variation to estimate the outcrossing rate in the overall population and to test for differences in outcrossing rates between hermaphroditic and female trees. Multilocus outcrossing rate estimates across 3 yr indicatedO. tenerapredominantly outcrosses. However, significant heterogeneity in single‐locus outcrossing rates was found among loci. Two loci (Fe1, Fe2) gave high outcrossing estimates, and a third locus (Gdh) gave much lower outcrossing estimates. Heterogeneity inGdhpollen allele frequencies, consanguineous matings, and selection against homozygous zygote genotypes at theFe1andFe2loci are factors contributing to the discrepancy in outcrossing rate estimates among loci. There were no differences in the mating systems of hermaphroditic and female trees, which suggests that factors beyond prevention of self‐fertilization may have also promoted the evolution of gynodioecy inO. tenera.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12781.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The influence of the sequence of maternal tissue development inBetula pendulaupon the potential for male gamete selection was investigated, and the timing of the fixed abortion of one of the two ovules was determined. We used scanning electronic microscopy, confocal laser scanning microscopy, and blue light microscopy. The stigmas remain fresh throughout male anthesis, and may also last after its end, depending on ambient temperatures. The presence of germinated pollen does not induce stigmatic necrotization, and grains may arrive at different times. The pollen tube tips remain within the stigma base until the end of female anthesis. The ovules will not develop until after necrotization of the stigmas. The pollen tubes thus have a fair start to the ovules, regardless of their different arrival times and of the original positions of the pollen grains at the stigma surface. Therefore, competition among different microgametophytes is possible, in spite of low pollination intensity. Our results indicate that when the first pollen tube penetrates an ovule, this ovule starts to outgrow the other one, and even if the other is also penetrated, its vascular support soon atrophies and the megagametophyte will shrivel. Fertilization of both ovules was never seen in this study.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12782.x

出版商:Wiley    

年代:1996

数据来源: WILEY