摘要:

A quantitative light and electron microscope study of developing and degenerating mycorrhizal arbuscules ofGlomus fasciculatuminZea mayswas carried out in order to estimate three parameters during the colonization cycle. These were: 1) Vv(f,c), the fraction of the host cell volume occupied by a volume of fungus; 2) Vv(cy,c), the fraction of the host cell volume occupied by host cytoplasm; 3) Sv(pr,c), the surface‐area‐to‐volume ratio of the host protoplast to the whole host cell. Uninfected cortical cells had an Sv(pr,c) of 0.13 μm2/μm3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in protoplast Sv. The Sv(pr,c) of a cell containing a mature arbuscule is 1.275 μm2/μm3. Because of the shrinkage of the protoplast, the Svof the protoplast to its own volume rather than the original cell volume is 2.55 μm2/μm3, or almost a 20‐fold increase. Total cell size is unaffected. When the arbuscule is mature, the fungus occupies 42% of the cell, with 24% as 1‐μm‐diam branches, and 18% as trunk. Arbuscular branch formation progresses at a linear rate and is the most important factor in causing the increased host Sv. The correlation coefficient for Vv(br,c) the volume fraction for arbuscular branches, vs. Sv(pr,c) isr= 0.932 (P<0.001). Degeneration of the arbuscule is marked by a rapid decrease in branches, host Sv, and host cytoplasm. The trunk develops and degenerates at a slower rate than the branches.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12530.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Funaria hygrometricaHedw. gametophytes collected in a clearfelled and slash‐burned eucalypt forest in southern Tasmania were removed from core samples yielding high rates of nitrogen‐fixing activity (acetylene reduction) and were examined with epifluorescence optics to determine the microorganism(s) responsible for nitrogen‐fixing activity and their location on the moss gametophytes. This technique revealed heterocystous blue‐green algae (Nostocsp. andAnabaenasp.) as epiphytes on stem and leaf surfaces and within the rhizosphere. Heterocysts and akinetes were observed and could be distinguished from vegetative cells by morphology and a decrease in relative fluorescence in the case of heterocysts. Epifluorescence microscopy is a rapid and reliable method for detecting the epiphytic blue‐green algae associated withFunaria.Other examples of nitrogen‐fixing organisms associated with bryophytes are discussed in relation to the present study.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12531.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Floral surfaces of twoTheobromaspp. and one species of the allied genusHerrania(Sterculiaceae) were examined using scanning electron microscopy for reward system information of the pollinator‐adaptation syndrome. These flowers are structurally complex and have sheltered reproductive parts indicating an elaborate insect‐mediated pollination mechanism. Analysis of anther dehiscence, anthesis and pollen tube growth suggests a crepuscular pollination strategy. Suspected pollinators have been observed on floral parts of theobromas possessing stomate type nectaries and various shaped trichomes (blade of petal ligule and adaxial surface of petal hood).H. purpureahas elongate ligules devoid of stomates. Glandular clublike structures are found on the ovaries of all three spp. In numerous spp. of theobromas, exceptT. cacao,and two species ofHerrania,a conspicuous ring of multicellular trichomes occurs at the adaxial base of the sepals. A possible function for the ring may be fragrance production because of its greatly reduced condition in the faintly scentedT. cacaoand the prevalence of pronounced fragrances in these other species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12532.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Polymorphic seeds ofAtriplex triangulariswere germinated at various temperatures (5–15 C, 5–25 C, 10–20 C, 20–30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high‐day and low‐night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12533.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Selected nuclear and cytoplasmic changes of pollen grains ofHyoscyamus nigerduring normal gametophytic development and embryogenic development, induced by anther culture, were analyzed and compared ultrastructurally using stereological methods. Potentially embryogenic, uninucleate pollen could be identified within 6 hr of culture by an increased ratio of the volume density of the nucleolar granular zone to the volume density of the fibrillar zone and an increased ratio of dispersed to condensed chromatin in the nucleoplasm. Nonembryogenic pollen in vitro and in vivo possessed prominent nucleolar fibrillar zones and low ratios of dispersed to condensed chromatin. These differences may reflect changes in nuclear activity in potentially embryogenic pollen grains during early stages of culture. Following the first haploid mitosis, in potentially embryogenic pollen the generative cell maintained its large granular nucleolus and high ratio of dispersed to condensed chromatin through its first division to form a proembryoid. The volume fraction of the cytoplasm occupied by mitochondria and plastids and the area fraction occupied by RER and Golgi cisternae differed in the generative cells of potentially embryogenic and nonembryogenic pollen. Those changes only detected in generative cells of potentially embryogenic pollen include: increased area and complexity of cytoplasmic membranes, increased mitochondrial volume, and the presence of plastids at all stages of development. These results support the idea that embryogenic induction ofH. nigertakes place at the uninucleate stage of development and that subsequent nuclear and cytoplasmic changes are essential for continued sporophytic development.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12534.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Acetylene reduction by bacteria associated withTypha latifoliaL. roots and rhizomes was studied in the field and in the laboratory. In situ studies indicated that the rate of acetylene reduction in a natural cattail population was ca. 4‐fold higher than in a cultivated cattail stand. Nitrogenase activity was found to occur principally in the rhizosphere of roots and rhizomes with the greatest activity occurring in association with mature roots. Scanning electron and light microscopy, and 2, 3, 5 triphenyltetrazolium chloride reduction showed that bacterial associations were limited to the rhizoplane of this angiosperm. One diazotrophic bacterial genus was found to be associated with roots and rhizomes and was identified as the facultative anaerobeBacillus.Contribution of free‐living cyanobacteria to total nitrogen fixation in the natural stand was negligible. Calculations show that a natural stand of cattails may fix 18 kg nitrogen ha−‐1yr−‐1or ca. 8.2% of the total nitrogen present in the standing crop.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12535.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

A study of developing transmitting tissue ofLilium Leucanthumpistils was undertaken in order to correlate structure with function. Lining the stylar canal are stigmatoid cells which contain a secretory zone consisting of a labyrinth of wall ingrowths characteristic of transfer cells. The functional feature of the labyrinth is a high surface‐to‐volume ratio that facilitates an intensive transmembrane flux of solutes. Stigmatoid cells in various stages of development and maturation have been investigated with the aid of electron and light optics in conjunction with cytochemical techniques. During development of the secretory zone, vesicles, formed by hypersecretory dictyosomes, fuse with the plasma membrane and contribute their contents to the growing wall. The pattern of secretory zone development is basipetal and is associated with initiation of chemotropism. In a mature pistil large crystals, having a basipetal pattern of development, and sensitive to protease, can be observed in the cytoplasm of stigmatoid cells. At anathesis, degradation of the crystal can be observed in the cells of the stigma surface and progresses basipetally as the pistil ages. The role of the crystal is uncertain. Immature pistils cultured in the presence of labeled proline take up the label which at maturity of the pistil is transferred to the canal of the pistil. The label is found in the crystals and the secretory zone of the stigmatoid cells. Pollen tubes growing in the canal of a labeled pistil take up the label.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12536.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Chromosome number determinations from 118 populations of eight species of the aster genusVirgulusare reported for the first time. Based on these counts and literature reports the geographic distributions of diploids and tetraploids inV. concolor, V. novae‐angliae, V. oblongifolius,andV. patenshave been determined. In the first three species, diploids were widely distributed, while tetraploids were more restricted. InV. patens,diploids were restricted to the southwestern portion of the species’ range, while tetraploids were found throughout the range. BothV. adnatusandV. walteriwere found only at the tetraploid level throughout their ranges. Two other species with restricted distributions were consistently found to be high level polyploids:V. georgianuswith 2n= 50,V. grandifloruswith 2n= 60. The following new combinations are listed:Virgulus georgianus(Alexander ex Small) Semple;Virgulussubsect.Brachyphylli(Torr.&Gray) Semple; andVirgulussect.Polyliguli(Semple&Brouillet) Semple.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12537.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Ontogeny of the secondary fruit of navel orange (Citrus sinensis[L.] Osbeck) was studied using flower buds and fruit from groves in north central Florida. The secondary fruit, or navel, develops as a whorl of secondary‐carpel primordia within the primary‐carpel whorl when the flower bud is 1.5 to 2.0 mm in length. A complete secondary gynoecium with fused ovary but separate styles and stigmas develops within the primary gynoecium before anthesis. The stigma and style of secondary carpels are not as distinct as those of primary carpels. Three types of tissue protrusions from the secondary fruit into primary‐fruit locules were abnormal placentae, free secondary carpels, and secondary‐carpel outgrowths, the last being the most common. An abscission layer is present in the central axis of the primary fruit near the base of the secondary ovary. This layer is indistinguishable from adjacent tissues prior to commencement of secondary fruit abscission. Parenchyma cells in the abscission layer, however, contain large numbers of starch grains during abscission. Secondary and primary fruit have similar sigmoid growth patterns; however, onset of the cell‐enlargement stage is approximately 2 wk later in secondary fruit.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12538.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Seed dimorphism influenced the germination behavior ofSalicornia europaeaL., with small seeds being more dormant and less salt tolerant than large seeds. All of the large less dormant seeds ofS. europaeagerminated prior to May, and all seedlings produced after this time were from small seeds. A persistent seed bank was maintained by the small dormant seeds. Survivorship was relatively constant during the normal germination season, but increasing salinity stress at any time during the spring reduces the chance of seedling survival. Little germination occurred from July through September because of the high surface soil salinities during this period.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12539.x

出版商:Wiley    

年代:1984

数据来源: WILEY