摘要:

Leaf anatomy was surveyed for idioblasts inCercidium(eight to nine species) andParkinsonia(four to six species), two problematic genera of caesalpinioid legumes variously merged and separated for over a century. Leaflets from 16 accessions (11 dried and five liquid‐preserved) of ten species were cleared (protoplasts removed chemically) and stained, supplemented by resin‐embedded sections and scanning electron microscopy. FourParkinsoniaspecies had large, dimorphic, living subepidermal idioblasts (SI)—one form adaxially restricted, the other form abaxial. The fifth species,P. africana, had tiny scalelike leaflets without idioblasts. Idioblast contents are unknown but visibly different from those of adjacent cells. All fiveCercidiumspecies lacked SIs, but instead had veinlet idioblasts (VI). These large idioblasts varied in size and abundance, but inC. floridumandC. texanumthey were especially large, spheroidal to ovate, thick‐walled, and devoid of protoplasm at maturity. VIs occurred mostly as pairs or clusters, with individual cells joined by a large gap resembling a simple perforation plate. Almost all VI units abutted minor veins, but no perforation plate joined the proximal VI to a tracheary element. Cells similar to SIs occur in other Caesalpinieae genera, but VIs are unique toCercidium.The mutually exclusive distribution of SIs and VIs supports the view thatCercidiumandParkinsoniaare different.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11500.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Suppressor of sessile spikeletsl(Sos1) is a dominant mutant of maize that blocks branching of the spikelet‐pair primordium to form the sessile spikelet during ear development. As a result,Sos1mutant ears and tassels possess single spikelets as opposed to the normal condition of paired spikelets, one sessile and the other pedicellate.Sos1also causes a reduction in the number of tassel branches and the number of orthostichies (or cupule ranks) in the ear. Thesos1genetic locus maps to the short arm of maize chromosome 4. TheSos1single spikelet phenotype appears similar to the single spikelet phenotype found in teosinte, the probable progenitor of maize. This similarity invites the hypothesis thatsos1had a role in the evolution of maize from teosinte. However, genetic mapping data and a comparison of the developmental basis of the single spikelet condition in theSos1mutant and teosinte demonstrate that their similar phenotypes result from distinct genetic‐developmental mechanisms. These results indicate thatsos1was not involved in the evolution of maize and caution against drawing conclusions of homology based solely on similar adult phenotypes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11501.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Seed paternity inErythronium grandiflorumdoes not fully reflect the proportion of pollen on the stigma. When two types of pollen are simultaneously applied to the stigma, outbred seeds are produced over inbred, and seeds from more distant donors are produced over seeds from donors nearby. I looked for postfertilization causes of these previously reported patterns of differential success of pollen donors. I simultaneously pollinated stigmas with pollen from two donors and observed ovule development through a window sliced in the ovary. Pollen donor pairs were self and cross, donors 1 and 100 m from the recipient, and two donors each 100 m from the recipient. Since one donor was always the alternate homozygote from the recipient at the malate dehydrogenase locus, I could determine the paternity of developing seeds. When it appeared that ovules were aborting, I removed them and determined their paternity using starch gel electrophoresis. Ovules fertilized by self pollen were more likely to abort than ovules fertilized by cross pollen, and ovules fertilized by nearby donors were more likely to abort than ovules fertilized by distant donors. Ovules fertilized by donors 100 m from the recipient were equally likely to abort. There was not a significant relationship between the proportion of ovules fertilized by a pollen donor and the probability of those fertilized ovules developing into seeds. There was no relationship between ovule position within a fruit and ovule abortion. I manipulated available resources by removing leaves and by permitting only one fruit to develop per plant. Decreasing the amount of resources increased the proportion of aborted ovules. Abortion of ovules of lesser quality appears to release resources that can then be used to develop other offspring.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11502.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The development of pollen and ovules inArabidopsis thalianaon the space shuttle ‘Endeavour’ (STS‐54) was investigated. Plants were grown on nutrient agar for 14 days prior to loading into closed plant growth chambers that received light and temperature control inside the Plant Growth Unit flight hardware on the shuttle middeck. After 6 days in spaceflight the plants were retrieved and immediately dissected and processed for light and electron microscope observation. Reproductive development aborted at an early stage. Pistils were collapsed and ovules inside were seen to be empty. No viable pollen was observed from STS‐54 plants; young microspores were deformed and empty. At a late stage, the cytoplasm of the pollen contracted and became disorganized, but the pollen wall developed and the exine appeared normal. The tapetum in the flight flowers degenerated at early stages. Ovules from STS‐54 flight plants stopped growing and the integuments and nucellus collapsed and degenerated. The megasporocytes appeared abnormal and rarely underwent meiosis. Apparently they enlarged, or occasionally produced a dyad or tetrad, to assume the form of a female gametophyte with the single nucleus located in an egglike cell that lacks a cell wall. Synergids, polar nuclei, and antipodals were not observed. The results demonstrate the types of lesions occurring in plant reproductive material under spaceflight conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11503.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Considerable effort has been spent documenting correlations between dioecy and various ecological and morphological traits for the purpose of testing hypotheses about conditions that favor dioecy. The data analyzed in these studies, with few exceptions, come from local floras, within which it was possible to contrast the subsets of dioecious and nondioecious taxa with regard to the traits in question. However, if there is a strong phylogenetic component to the presence or absence of dioecy, regional sampling may result in spurious associations. Here, we report results of a categorical multivariate analysis of the strengths of various associations of dioecy with other traits over all flowering plants. Families were scored for presence of absence of monoecy or dioecy, systematic position, numbers of species and genera, growth forms, modes of pollination and dispersal, geographic distribution, and trophic status. Seven percent of angiosperm genera (959 of 13,500) contain at least some dioecious species, and ≈6% of angiosperm species (14,620 of 240,000) are dioecious. The most consistent associations in the data set relate the presence of dioecy to monoecy, wind or water pollination, and climbing growth. At both the family and the genus level, insect pollination is underrepresented among dioecious plants. At the family level, a positive correlation between dioecy and woody growth results primarily from the association between dioecy and climbing growth (whether woody or herbaceous) because neither the tree nor the shrub growth forms alone are consistently correlated with a family's tendency to include dioecious members. Dioecy appears to have evolved most frequently via monoecy, perhaps through divergent adjustments of floral sex ratios between individual plants. Monoecy itself is related to abiotic pollination and climbing growth as revealed by multivariate analysis. Dioecy and monoecy are concentrated in the less advanced superorders of Thorne (1992) and subclasses of Cronquist (1988). The frequency of dioecy found in a local flora therefore reflects the level of dioecy in its particular pool of families as much as, or more than, local selective factors. The positive associations of dioecy with abiotic pollination and monoecy are related to floral developmental and morphological attributes, as is the negative association with bird and bat pollination; the positive association of dioecy with climbing growth is tentatively explained in terms of differential selection for optimal resource allocation to sexual function. If rapid upward growth is at a premium in climbers and if fruit set at least temporarily inhibits growth or requires the production of thicker, more slowly growing stems to support heavy fruits, it might be advantageous to postpone femaleness. If the effect is strong, this may favor male plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11504.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The phenological pattern of flowering at the community level was studied in a Greek phryganic ecosystem near Athens for 4 consecutive years. Flowering is strongly seasonal: 80% of the insect‐pollinated flora, which consists of 133 species, blooms between February and June. There is a variably expressed secondary flowering period in autumn. The pollinating fauna follows a strongly correlated pattern of abundance. Two types of plants were distinguished: pauciflorous species bearing<10 flowers that are large compared to the plant body, and multiflorous species with many small flowers. Pauciflorous species flower in the winter half of the year, while multiflorous species flower mainly in the summer half. The mean flower life spans are 9 and 3 days, respectively. The duration of flowering (DF) for each species is 55 days on average, which is long compared to other communities. The DF shows year‐to‐year variations, concomitant with the vicissitudes of the climate. The start of flowering of a species is statistically correlated with the temperature in the previous month, not with rainfall; its end date of flowering only partly compensates for the time gained or lost. DF is maximal in winter. The average flower life span of species flowering at any given date varies strongly and independently of the average DF. We tested the hypothesis that flowering phenology is set by phylogenetic and life form constraints. This could not be corroborated for phylogeny, evidently because of the overriding influence of the mediterranean climate, and probably also for biogeographical reasons. In contrast, life forms and multiflorous and pauciflorous species show strong differences. Many (51) of the species are therophytes; we tested the hypothesis that because of their annual habit they would be more dependent on pollination than perennials. Thus we anticipated that therophytic species would be differentiated from perennials in their flowering phenologies. This is not corroborated. We therefore conclude that the seed bank plays a role that is analogous to that of a perennial plant body.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11505.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Life history trade‐offs among clonal growth, storage, and sexual reproduction were investigated in the perennial grassAmphibromus scabrivalvisin relation to soil nutrients. This species exhibits clonal growth by producing rhizomes and stores reserves in the form of basal corms; seeds are matured in cleistogamous spikelets on panicles enclosed within the leaf sheaths along each culm. Ten seed‐derived genotypes (clones) were separated into 72 ramets and planted in the greenhouse. Control ramets received only water while the remainder received fertilizer applied every 2 wk. Twenty‐four ramets were harvested per clone at 11, 20, and 26 wk. The dry mass of corms, rhizomes, roots, shoots, and seeds were recorded. Biomass partitioning to rhizomes provided a measure of carbon allocation to clonal growth, partitioning to corms provided a measure of allocation to storage, and partitioning to seeds provided a measure of allocation to sexual reproduction. Allocation to most organs was significantly influenced by clone identity; fertilizer significantly increased allocation to corms and seeds at 20 wk, but never affected rhizome allocation at any age. Corm allocation increased from 2% at 11 wk to 27% at 26 wk; rhizome allocation decreased from 10% at 11 wk to 3% at 26 wk. Significant negative relationships were detected for rhizome vs. seed and corm vs. rhizome allocation in fertilized clones at 20 wk. This suggests an age‐dependent physiological life history trade‐off between clonality and sexual reproduction and between clonality and storage. In contrast, a significant positive relationship was consistently noted for corm vs. seed allocation in fertilized and unfertilized clones at 20 and 26 wk. The absence of a trade‐off between storage and sexual reproduction may indicate that these two processes are not necessarily mutually exclusive components of life history.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11506.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Aster macrophyllus, a temperate forest understory species of the northeastern United States, inhabits a broad range of light habitats. Plants receiving several minutes of direct sun in canopy gap and forest edge habitats occasionally wilt, a response indicative of water stress. We compared two alterative scenarios for patterns of evaporative load and stomatal conductance for plants in large (0.15 ha) tree canopy gaps and small (3 m2) herbaceous subcanopy gaps: 1) evaporative loads are typically moderate and stomatal conductance is largely governed by light intensity; or 2) evaporative loads are often substantial, mandating stomatal closure to prevent excessive transpiration. In all cases evaporative loads were elevated by light intensity above 25% of full sun. This was accompanied by substantial stomatal closure. Transitions from low to moderate light intensity (<13% full sun) caused little increase in leaf evaporative load, and stimulated increases in stomatal conductance. Very brief periods of high light also stimulated stomatal opening. Light environments in the small herbaceous subcanopy gaps differ greatly in their patterns of evaporative load from day to day.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11507.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Spatial and temporal dynamics of barrier island shrub thickets were investigated on Hog Island, a barrier island along the Eastern Shore peninsula of Virginia. The island thickets are dominated by the actinorhizal shrub,Myrica cerifera.On the accreting, northern half of the island, thickets expanded as swale area increased. Analysis of aerial photographs revealed that total thicket area increased by nearly 400% from 1949 to 1989, paralleling a substantial increase in area for the northern portion of the island. Thicket characteristics varied with the age and position of the three field sites on Hog Island. At the youngest site examined (20 yr), recruitment and shrub growth were high. Shrub growth remained high and recruitment continued in the stable central portions of the island (50 yr). However, at the oldest site near a bay side salt marsh (≈130 yr), recruitment was not evident, shrub growth was reduced, and mortality was most apparent. Several “life stages” for shrub thickets were identified relative to island accretion. After the stabilization of new land, seedlings establish and grow rapidly to form a thicket. Once established, a thicket rapidly expands in the relatively protected, mesic swale environment. Thicket decline follows, characterized by an increase in vine growth on and around the shrubs and the formation of gaps as the thicket breaks up. Spatial variation inM. ceriferathickets on Hog Island is related to length of time soils have been stabilized and, especially, to time since thicket establishment.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11508.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Karyotypes of six species (in ten populations) of the genusSerjaniaand one species of the genusUrvilleawere studied using root tip mitotic metaphases. All species ofSerjaniawere diploids with 2n= 24 chromosomes and the species ofUrvilleawas octoploid with 2n =86 chromosomes. Analysis of the karyotypes ofSerjaniashowed that the species are differentiated by chromosomic structural changes. Chromosome lengths showed great differences among the species that may be explained by chromosomal deletion or addition. The basic chromosomic number isx= 12 forSerjaniaandx= 11 forUrvillea.InUrvilleathe evolutionary trend may be toward polyploidy followed by reductional aneuploidy. The Giemsa (C‐band) staining technique was applied inSerjania; however, no clear blocks of heterochromatin were observed. This result agrees with the presence of semireticulate nuclei. The Nucleolar Organizing Region (NOR‐banding) technique was applied inS. communisandS. laruotteana, which showed one and two pairs stained, respectively. Variation in the number of nucleoli was observed among the different populations ofSerjania.This variation could be explained by the presence of small nucleolar organizer regions that occur scattered along the genome and are not detected by the silver staining methodology.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11509.x

出版商:Wiley    

年代:1995

数据来源: WILEY