摘要:

Spore wall morphogenesis ofEquisetum arvensewas observed by transmission electron microscopy. The spore wall ofE. arvenseconsists of four layers: intine, exine, middle layer, and elater. The exine is formed after meiosis and consists of two distinct layers. The inner portion of the exine is formed in advance of the outer layer of the exine. The middle layer is deposited after the exine. The elater can be subdivided into two distinct layers. The inner layer comprises longitudinal microfibrils that surround the spore in spiral fashion. The elater appears as thin beltlike structures at the beginning of development. Numerous microtubules were observed on the inner surface of the plasmodial plasma membrane opposite the inner layer of the elater, suggesting that these microtubules are involved with the synthesis of inner elater microfibrils. The matrix of the outer elater is formed by discharge of granules from the plasmodial cytoplasm. The intine is the last component of the sporoderm to be formed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15074.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Stereological principles were used to study epidermal cell redifferentiation during the post‐genital tissue union in the developing flowers ofCatharanthus roseus.Volume densities of ultrastructural components at three separate stages of cell differentiation were analyzed and compared. Nuclear volume density decreased and vacuolar volume density increased throughout the period studied. The only other components whose volume densities changed significantly were plastids, mitochondria, and dictyosomes. For each of these organelles, the mean relative volume was greatest at the time of fusion. By 12 hr after fusion, however, the mean relative volume of each fell to a level significantly lower than its volume in the prefusion cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15075.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

An increase in nuclear DNA, without an increase in chromosome number, has been found to occur as a result of anther culture inNicotiana tabacumL. The objective of this study was to determine the cytological consequences of this DNA amplification in F1hybrids between a doubled haploid that had undergone a substantial increase in DNA and the cultivar from which that doubled haploid was derived. Mitotic and meiotic analyses were performed on plants obtained from reciprocal crosses ofN. tabacumcv. NC95 and NC95 SCDHL 12, a doubled haploid line that has 41% more DNA than the parental cultivar. While no cytological abnormalities were observed in either parental line, numerous abnormalities were seen in both somatic and meiotic tissues of the F1hybrid. Chromosome losses, which appeared to result from spindle errors, were observed in these tissues. It is speculated that the spindle errors may be the result of a genetic unbalance caused by combining genomes with widely differing amounts of DNA. In addition to the spindle errors, a quadrivalent with an atypical morphology was observed in meiotic diplotene and metaphase I cells of the hybrid. The quadrivalent configuration was interpreted to represent pairing between amplified homologous regions in homeologous chromosomes. Further investigations of additional doubled haploid × cultivar lines is required before the significance of these findings to the anther culture process inN. tabacumcan be fully assessed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15076.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Study of an in situBothrodendron punctatumcommunity in a strip mine in Bear Valley, Shamokin Quadrangle, Pennsylvania, provides new insights into the ontogeny of Middle Pennsylvanian arborescent lycopods and into the ecological and environmental characteristics of lycopod‐dominated clastic‐swamp communities.Bothrodendron punctatumbegan growth as a monocaulous stem. The first branches developed when the stem attained a minimum height of 5 m. Lateral branches bore terminal cones and were determinate and deciduous. They grew to a maximum length of 1 m, and became smaller and more closely spaced with increasing stem height. The branch scars were not disrupted by secondary stem growth indicating that the branches stayed attached until the stem attained its determinate growth limit. The plant grew to a height of 25 m. ThoughB. punctatumis an uncommon component of Euramerican floras, the plant could become locally dominant under favorable environmental and edaphic conditions. The upper canopy was formed byB. punctatumand contained emergents ofLepidodendron aculeatumand aSigillariaspecies. The understory contained pteridosperms and rareCalamites. Bothrodendron punctatumseems to have preferred environments transitional between clastic and peat swamp conditions. It was sensitive to local inhomogeneity in microhabitat characteristics, as well as to regional climatic fluctuations (drought stress). Both these variables produce specifically attributable effects on branch size and separation trends.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15077.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Seed collections from 72 rubber rabbitbrush populations occupying a range of habitats in western North America were incubated at 3 C in the laboratory. Collections from warm desert habitats required less than 2 weeks to achieve 90% relative germination under these conditions, while collections from montane habitats showed delayed germination requiring up to 20 weeks. When 13 representative collections were incubated at constant temperatures from 5 to 30 C, all germinated completely at 30 C within 4 weeks. Collections from warm desert habitats germinated rapidly over the whole range of temperatures. Montane collections sometimes exhibited dormancy at intermediate temperatures (15 and 25 C) even though they were ultimately able to germinate at lower temperatures. Results suggest that dormancy is conditional and temperature‐dependent in this species. Chilling the seeds extends the temperature range for germination downward to include the chill temperature itself. Germination response to temperature and its variation as a function of habitat are of apparent adaptive significance, serving to time germination so that the probability of seedling survival is maximized in each habitat. Within populations, response to temperature varied as a function of year of harvest and of within‐year harvest date, indicating that germination patterns are probably not under rigid genetic control but represent an integration of genetic and environmental factors.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15078.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Small, anatomically preserved ovules are described from specimens collected at Fremouw Peak in the central Transantarctic Mountains. The ovules occur within a silicified peat in the upper part of the Fremouw Formation, which is considered to be Early to Middle Triassic. Ovules are radially symmetrical and ovoid, with an integument that consists of a narrow endotesta and a complex sclerotesta. The bilayered nucellus has a characteristic scalloped appearance and is attached to the integument only at the base. Of 43 ovules examined, 50 to 60% contain cellular megagametophyte tissue. One specimen contains a possible archegonium with embryo. Although the ovules have not been found attached, their possible affinities are discussed in relation to the known flora from this locality and other, comparable‐aged floras from Gondwana.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15079.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Mature staminate flowers of giant ragweed (Ambrosia trifidaL.; Asteraceae, tribe Heliantheae) are about 2 mm long. Each of the five fused petals is traversed for most of its length by a prominent polyacetylene‐filled reservoir (PAR). PAR'S have a biseriate epithelium and, except for their short length of about 1.5 mm, seem identical to the much longer PAR's of leaf and stem. Study of sections of resin‐embedded flowers at different developmental stages showed that corolla PAR's appear with a full complement of epithelial cells, and occupy their full relative length, in flowers only 150μm in length. As the flower enlarges, the original epithelial cells also enlarge and elongate, and secrete into the lumen, which opens simultaneously for its entire length when the flower is nearly 300μm long. PAR's in mature flowers have only their original epithelial cells, which remain alive. Corolla PAR's seem anatomically to be representative of the canals and ducts that have been described elsewhere in Asteraceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15080.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Young gametophytes ofBotrychium dissectumproduce a mucopolysaccharide coating on the external surface of the proximal cell. Scanning electron microscopy reveals deposition of the mucilage, which initially has a patchy distribution, in the shape of a thick triangular ring. Young gametophytes in the hydrated condition have a thin coating of mucilage over the other areas of the proximal cell wall. Histochemical staining indicates that the mucilage contains sugars with vicinal hydroxyl groups, carboxylated sugars, and small amounts of sulfated sugars. Protein and phenolic materials are also found in the mucilage. Lipids,β, 1‐3 glucans andβ,1‐4 glucans are not present. Fluorescein labelled lectin binding shows the presence of terminal galactose and terminal fucose units. Germinating spores in the presence of the microtubule inhibitors CIPC (3‐chloro‐N‐phenyl isporopyl carbamate) and griesiofulvin cause abnormal mucilage secretion. The inhibitor CIPC prevents mucilage secretion whereas griesiofulvin disrupts the pattern of deposition. Several functions of the mucilage are postulated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15081.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The patterns of variability in the production of staminate inflorescences, pistillate flowers, and fruits forCarya ovata(Mill.) K. Koch andC. tomentosa(Poir.) Nutt. at Hutcheson Memorial Forest (Somerset County, New Jersey) were examined over a four‐year period. We sought to determine 1) the patterns of variability in flowering and fruiting (within‐trees, among‐trees, and between‐years), 2) if variable flowering might account for observed nut‐bearing patterns, and 3) what were the relative contributions of intrinsic (genetic) and/or extrinsic (environmental) factors in determining flower production and fruit set. In general, our fine‐scale analysis of shoots within canopies did not reveal a distinct mast fruiting pattern. While the number of male and female flowers varied significantly (among trees and between years), fruit set was not markedly affected. Variability of flowering and fruiting among shoots within trees was low. Both flowering and fruiting were observed to have a strong genetic and/or microenvironmental basis; however, flowering appeared more plastic and thus more sensitive to yearly environmental vagaries than did fruiting. Favorable environmental conditions at the time of flower differentiation may result in increased flower production; but, this does not necessarily result in increased fruit set. Many pistillate flowers abscise around the time of pollination and fertilization, apparently adjusting fruit set to available shoot resources. Approximately 50% of the pistillate flowers of both species fail to set fruit. Overall, individual trees exhibit their own flowering and fruiting schedules, suggesting the need to account for this level of variability in future studies of mast fruiting.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15082.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Ponderosa pine from California (Pinus ponderosavar.ponderosa) were crossed to one another and also to individuals from the Rocky Mountains (P. p.var.scopulorum). All crosses involved a single mother and a single pollen donor. Patterns of inheritance of electrophoretically‐detectable loci followed Mendelian expectations with one exception. Shikimate dehydrogenase showed unpredictable banding patterns in intervarietal crosses. Variability at these biochemical loci was compared to variability at 14 morphometric characters. The relationship between these two levels of variation is complex and permits only one generalization: variability at one level is not a good predictor of variability at the other level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15083.x

出版商:Wiley    

年代:1989

数据来源: WILEY