摘要:

Sarcandrais the only genus of Chloranthaceae hitherto thought to be vesselless. Study of liquid‐preserved material ofS. glabrarevealed that in root secondary xylem some tracheary elements are wider in diameter and have markedly scalariform end walls combined with circular pits on lateral walls. Examination of these wider tracheary elements with scanning electron microscope (SEM) demonstrated various degrees of pit membrane absence in the end walls. Commonly a few threadlike fibrils traverse the pits (perforations); these as well as intact nature of pit membranes in pits at ends of some perforation plates are evidence that lack of pit membranes does not result from damage during processing. Some perforations lack any remnants of pit membranes. Although perforation plates and therefore vessels are present inSarcandraroots, no perforations were observed in tracheary elements of stems or lignotubers. Further, stem tracheids do not have the prominently scalariform end walls that the vessel elements in roots do. Presence of vessels inSarcandraremoves at least one (probably several) hypothetical events of vessel origin that must be postulated to account for known patterns of vessel distribution in angiosperms, assuming that they are primitively vesselless. Seven (perhaps fewer) vessel origin events in angiosperms could account for these patterns; two of those events (Nelumboand monocotyledons) are different from the others in nature. Widely accepted data on trends of vessel specialization in woody dicotyledons yield an unappreciated implication: vessel specialization has happened in a highly polyphyletic manner in dicotyledons, and therefore multiple vessel origins represent a logical extension backward in time. If a group of vesselless dictyoledons ancestral to other angiosperms existed, they can be hypothesized to have had a relatively homogeneous floral plan now thatSarcandra‐likeplants no longer need be imagined within that group.Sarcandraand other Chloranthaceae show that the borderline between vessel absence and presence is less sharp than generally appreciated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08779.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Nuclear DNA of meristematic, epidermal and root cap cells from the roots of three vascular plants—the cryptogam,Equisetum hyemaleL, and the phanerogams,TradescantiaClone 02 andHordeum vulgareL.—was measured with quantitative Feulgen microspectrophotometry. Epidermal cells of all three species and root cap cells in both phanerogams contained up to 8fold the amount of nuclear DNA found in their respective meristematic telophase nuclei. In general, the large amounts of nuclear DNA parallel development and differentiation in the epidermis regardless of phylogeny, habitat, or degree of domestication. However, comparisons of the increase in nuclear DNA contents in the various epidermal cell types among these three species suggest that the mechanisms giving rise to these increases may differ phylogenetically and may represent another character in which cryptogams and phanerogams diverged in their evolution.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08780.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

InHordeum vulgareL., the nucleus of differentiating root hairs contains amplified, extrachromosomal DNA sequences. Cytophotometry shows that the nuclei of trichoblasts and root hairs grown under normal conditions contain up to 50% more DNA than those grown in 200 mM salt. Although the root hairs develop and differentiate under salt stress, amplification of their nuclear DNA is suppressed. From this, we conclude that amplification is not necessary for differentiation at the cellular level. Characterization of the amplified nuclear DNA of the root hair is based on the physical/chemical nature of the DNA. The amplified sequences separate as a satellite band when total nucleic acids are centrifuged on CsCl gradients. Enzyme restriction of the satellite and main bands with Msp I and Hpa II followed by agarose gel electrophoresis shows that the satellite band is not more highly methylated than the main band. Restriction of the root hair DNA with EcoRI reveals repetitive DNA sequences not seen in similarly restricted whole root, leaf or salt‐stressed root hair preparations. While these unique, repetitive sequences in the 2–6 kb region of the gel do not hybridize with ribosomal, chloroplast, or mitochondrial DNAs, RNA hybridization shows that some of them are transcribed. We believe that the amplified sequences are extrachromosomal based on their selective degradation during root hair senescence, their separation as a satellite band and their restriction patterns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08781.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Effects of plant water content, previous desiccation, photon flux density, and temperature on rate of net photosynthesis were measured in the common species in the assemblage of desiccationtolerant mosses that dominates the flora on granitic boulders at a semiarid site in the inland chaparral of San Diego County, California. Species differed significantly in their responses to water content, desiccation, and light. Species previously found to occur in microsites of lower water availability attained maximum net photosynthesis at lower water contents and showed greater ability to recover from prolonged desiccation. Species found in microsites of lower light availability had higher rates of net photosynthesis at low photon flux density. Results suggest that differences in potential rates of net photosynthesis partly determine relative ability of these species to colonize xeric or dark microsites, but that other factors also determine microdistribution.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08782.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The mature male gametophyte ofGinkgo bilobacan be divided into two regions: a large saccate structure that is suspended within the fertilization chamber above the archegonia, and a pervasive, highly branched haustorial system that ramifies through the intercellular air spaces of the apex of the nucellus. This morphology appears to differ in many ways from the simpler more typical male gametophytes of most other groups of seed plants.Growth and development of the male gametophyte ofGinkgo bilobawere studied using computer reconstruction techniques to generate images of the gametophyte from data derived from serial sections through the ovule. These investigations reveal that morphological development of the male gametophyte ofGinkgo bilobais divided into three distinct phases: 1) Germination, characterized by an initial brief period of diffuse growth. This phenomenon has not been described for any other seed plant male gametophyte; 2) Initiation of tip growth and the formation of a tubular body, as typifies all seed plant male gametophytes. InGinkgo, this is accompanied by a high degree of branching, giving rise to an extensively branched haustorial system; 3) Late swelling of the proximal unbranched portion of the gametophyte resulting in formation of the saccate structure that is characteristic of the mature gametophyte. This process appears to be very similar to late development in cycad male gametophytes.Thus, despite the seemingly anomalous morphology of the mature male gametophyte ofGinkgo biloba, specific patterns of growth and development are in many ways similar to growth processes expressed by the male gametophytes of some or all major groups of seed plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08783.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Morphogenesis in the morphologically complex male gametophyte of the seed plantGinkgo bilobawas investigated in vitro. These studies reveal that although development in vitro is far more variable than in vivo, it is still characterized by the sequential expression of three distinct patterns of growth: initial diffuse growth of the tube cell, initiation and establishment of tip growth (which may be accompanied by branching), and radial swelling of the gametophyte. Time lapse photography shows that branching of the male gametophyte results from two distinct types of initiation events: one apical (“primary branching”), and the other subapical (“secondary branching”). Experimental manipulation of the growth medium indicates that exogenous sucrose levels strongly influence the likelihood of expression of normal morphogenetic processes. High levels of sucrose tend to inhibit both the initiation of tip growth following initial diffuse growth, as well as branching of the gametophyte. Low sucrose levels appear to promote a normal pattern of early establishment of tip growth and subsequent branching of the gametophyte, similar to development of the gametophyte in vivo.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08784.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Pontederia cordatais a tristylous, self‐incompatible emergent aquatic. Measurements of reproductive organs in mature flowers and developing buds and analysis of relative growth rates of the styles, filaments, and floral tube were used to analyze the developmental processes that result in reciprocal positioning of reproductive parts among the style morphs. Flowers are trimerous with two series of three tepals, two series of three stamens, and a tricarpellate ovary with a single ovule. Each flower has stamens of two lengths, but the two lengths correspond to upper vs. lower position in the zygomorphic flowers, not to the two series initiated in the primordium. Morph‐dependent variation in stigma height depends on differences in style length, not ovary length. Differences among morphs in anther height result from differences in the position of filament insertion on the floral tube and differences in filament length. Styles of the three morphs develop to different lengths as a result of two distinct processes. Styles of L and M morphs develop at different rates with the L style growing more rapidly than the M style, whereas styles of the S morph have a brief period of rapid growth followed by early inhibition. Stamen growth in the S morph also differs qualitatively from that in the L and M morphs, which are distinguished from each other by quantitative differences in growth rates. Results indicate that the developmental processes that result in the complementary arrangements of organs in different morphs are morph‐specific. An attempt is made to integrate the findings of this study with the model for genetic control of tristyly.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08785.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Ultrastructural changes during omniaperturate pollen development inTrillium kamtschaticumPall, was examined using transmission electron microscopy. The pollen mother cells are not enveloped within a thick callosic wall. The microspores resulting from successive meiosis are divided by scanty deposition of callosic wall in the tetrad. A primexine/exine template is not recognizable within the tetrad during formation of exinous components. Preexinous globules, originating from vesicles in the callosic wall, accumulate electron‐dense materials and develop into exinous globules. The preexinous globules have ca 10 nm wide contacts with tilted and invaginated plasma membrane of the microspore within the callosic wall. After dissolution of the callosic wall, the microspores separate and mitosis subsequently leads to the formation of a generative cell and vegetative cell encased in a loose aggregation of developing exinous globules. When the generative cell is at the pollen grain surface, the channeled zone is initiated at the opposite side of the microspore on the surface of the vegetative cell. Just before pollen maturity, a new layer develops under the channeled zone. Thus, development of the omniaperturate pollen grains ofT. kamtschaticuminvolves some processes that are distinct from those ofCannaandHeliconiaand some that are similar.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08786.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The examination of several taxa from various tropical regions of the world, previously classified asPhyllanthus urinariaL., indicates that they do not belong to a single species. On the basis of morphology, cytology, genetics, and biometry, a new classification is presented in which the collective speciesP. urinaria, or “urinariacomplex,” is elevated to the subsection level:PhyllanthussubsectionUrinaria.Within the subsection, two subgroups may be recognized on the basis of seed coat ornamentation. Each of these lines is represented by two species which differ from each other in chromosome number:P. embergerinov. spec. (2n =100) andP. nozeraniinov. spec. (2n= 50) in the “spiraled” line,P. hookeriMuell. Arg. (2n= 100) andP. urinariaL. (2n= 50) in the “radiated” line. In the latter species, which has undergone diversification, two subspecies may be distinguished:P. urinaria urinariaandP. urinaria nudicarpussubspec. nova.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08787.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Intact roots ofLepidium sativumwere photographed at 1.5‐ to 6‐min intervals before and after being tilted from a vertical to a horizontal position. Relative extension rates were calculated for segments of the root by measuring the rate of movement of charcoal particles on the surface of the root. Curvature was measured at points separated by 0.8 mm, from the tip to the root hair zone. For the first hour after the root was tilted to a horizontal position, the relative extension rate for the side of the root producing the outer side of the curve is higher than that during straight growth. The relative rate for the inner side falls to near zero during the first hour in the horizontal position. There is thus a positive gradient in extension rate from the inner to the outer side of the curve. For most of the second hour, the two sides have approximately equal relative rates of extension. In the last 12 min of the second hour, as the root tip is moving the final distance to a vertical position, the rate on the inner side shows a high extension rate. The gradient in extension rate from the inner to the outer side of the curve has thus become negative during the second hour. This reversal in the extension gradient is necessary to prevent the root from continuing to grow in a circle past the point where the root tip is vertical. Curvature reaches maximal values of 0.7 mm‐1to 1.2 mm‐1for the inner side and 0.5 mm‐1to 0.7 mm‐1for the outer side. (Units express reciprocals of the radius of curvature in mm.) Two locations where curvature is highest are separated by a flatter region. The charcoal particles marking specific locations on the root surface move away from the tip at the same rate as the features of the curvature pattern.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08788.x

出版商:Wiley    

年代:1987

数据来源: WILEY