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Studies on fertility and crossability of species in the genus LeucadendronRhode, Adele 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The exomorphology and size of Leucadendron pollen was examined using a scanning
electron and light microscope respectively. Pollen was found to have a consistent
triangular shape with three apertures. Pollen grain size however, show difference
between species, sections and subsections on Leucadendron. Pollen of all species
examined had a woven appearance like the intertwined threads of a fabric with
orbicules present on the surface of L. chamelaea, L. elimense subsp. elimense and L.
galpinii. Pollen viability was successfully assessed using a solidified agar medium
containing 2g agar and 109 sucrose. Pollen germination for all species was found to
be above 55% viability. A diallellayout of crosses has demonstrated conclusively
that fecundity differs when crossing between species of the genus Leucadendron.
Artificial hand pollination was applied successfully on Leucadendron and showed
repeatedly that seed set following intraspecific crosses between the male and female
inflorescence of the same species gave the same high rate of seed set as found in
nature. However, seed numbers declined sharply when crossing between species of
the section 'Leucadendron'. Seed set following crosses between species of different
sections or sub-sections was the lowest and in most cross combinations there was no
seed harvested or no seed germination. The diallellayout was useful in identifying
incompatible species and for locating possible incompatibility barriers to interspecific
seed development. The morphology of the stigma was examined with a scanning
electron microscope. Stigma appearance of all species had a consistent round to oval
shape, except for L. rubrum, which had an elongated shape. Stigma surfaces of all
species were densely covered with a large number of unicellular papilar cells on the
swollen base. The aniline blue staining technique, together with the fluorescent
microscope technique was used to follow the growth of the pollen tube following compatible and incompatible cross combinations. Pollen on the stigmas of
compatible and incompatible species examined showed signs of germination. Pollen
tubes grew between the papilla cells in all directions and only the most vigorous ones
reached the upper part of the style. From the upper region of the style, yellow green
tubes grew cohesively in the middle of the style towards the ovule. In compatible
combinations a not more than 4 tubes reached the ovule region, but was difficult to
observe when they entered the micropyle for fertilization. In incompatible species a
large number of abnormalities occurred beyond the upper region of the style. / AFRIKAANSE OPSOMMING: Die morfologie en grootte van Leucadendron stuifmeel is deur middel van 'n
skandeerelektron - en ligmikroskoop bestudeer. Baie klein verskille in stuifmeel
morfologie het voorgekom. Diverse verskille in stuifmeelgrootte het wel voorgekom
tussen spesies, groepe en subgroepe van Leucadendron. Stuifmeelvorm was
deurgaans driehoekig en die oppervlakte van die stuifmeelkorrel het die voorkoms
van geweefde vesels gehad. Klein, bolvormige struktuurtjies was teen verskillende
digthede oor die stuifmeeloppervlak van L. chamelaea, L. elimense subsp. elimense en
L. galpinii versprei. Stuifmeelkiemkragtigheid is bepaal deur dit op soliede agar
medium te ontkiem en was deurgaans bo 55% kiemkragtig. Onderlings dialleliese
kruisings van Leucadendron spesies het variasie in saad set getoon. Handbestuiwing
is suksesvol uitgevoer en saadset in intraspesie kruisings hoog en soortgelyk aan
natuurlike bestuiwing. Saadset en saad ontwikkeling het drasties verswak toe verder
vewante spesies as ouers gebruik. As gevolg van hulondeurdringbare saadhuid is
neutagtige sade gewoonlik moeiliker ontkiembaar. Die diallel uitleg was ook nuttig
om verenigbare en onverenigbare kruisingskombinasies te identifiseer en om
onverenigbaarheidskanse op te spoor. 'n Skandeerelektronmiskoop is gebruik om die
morfologie van die stigma te bestudeer. Stigmas was deurgaans rond tot ovaalvormig,
behalwe die van L. rubrum wat 'n verlengde voorkoms gehad het. Die stigma bestaan
uit 'n groot aantal eensellige papilla, wat dig teen mekaar gepak is op 'n geswolle
basis. Aniline-blou fluoresserende kleurstof en 'n fluoressensie mikroskoop is
gebruik om die pad van die stuifmeelbuis in verenigbare en onverenigbare
kruisingskombinasies in Leucadendron te volg. Stuifmeelontkieming het in alle
kruisingskombinasies geskied. Stuifmeelbuise het in alle rigtings tussen die papilla gegroei en slegs die mees kiemkragtige stuifmeelbuise het die boonste deel van die
styl bereik. In die styl het die buise dig teen mekaar gegroei en was dit moeilik
telbaar. 'n Maksimum van vier buise het die vrugbeginsel bereik, maar dit was
moeilik om verder te volg nadat hulle die poortjie bereik het. In onverenigbare
kruisingskombinasies het stuifmeelbuise abnormale groeipatrone in die boonste
gedeelte van die styl getoon.
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Changes in the abundance and diversity of the Proteaceae over the Cainozoic in south-western AustraliaItzstein-Davey, Freea January 2003 (has links)
South-western Australia is a globally significant hotspot of plant species diversity, with high endemism and many rare plant species. Proteaceae is a major component of the south-western flora, though little is known about how its diversity developed. This prompted the present study to investigate changes in the abundance and diversity of Proteaceae, in south-western Australia, by concurrently studying three sediment sequences of different ages over the Cainozoic and a modern pollen rain study. Modern pollen-vegetation relationships in the two Proteaceae species rich nodes of the northern and southern sandplains were quantified. It was found that Proteaceous genera can contribute up to 50% of the total pollen rain. Banksia/Dryandra pollen was the most abundant with Isopogon, Petrophile and Lambertia also commonly noted. The vegetation and environmental setting during three pivotal periods of the Cainozoic: Holocene, Pliocene and Eocene, were investigated. Eocene sediment from Lake Lefroy confirmed the presence of a Nothofagus dominated rainforest in the Middle to Late Eocene. At this time Proteaceae species were at least as diverse as today, if not more so, contributing up to a maximum of 42% of the total pollen rain. Taxa recorded included: Banksieaeidites arcuatus, Propylipollis biporus, Proteacidites confragosus, Proteacidites crassus, Proteacidites nasus and Proteacidites pachypolus. Several taxa remain undescribed and unnamed. This study also identified that Proteaceae pollen representation varies across small lateral distances. Thus as samples varied spatially and temporally, single core samples are not sufficient to identify spatial patterns in Proteaceae or other low pollen producing taxa. Some 7.91 cm of laminated Pliocene sediment from Yallalie, south-western Australia, was also examined. It covers 84 years of record and confirmed other regional reports that south-western Australia was covered by a rich vegetation mosaic consisting of heathy and wet rainforest elements. Although Proteaceae species were a consistent component of the pollen counts, diversity and abundance (maximum of 5%) was low throughout the studied section. Banksia/Dryandra types were most commonly noted. A 2 m core was retrieved from Two Mile Lake, near the Stirling Ranges and provided an early Holocene vegetation history. Geochemical and palynological evidence recorded little change, suggesting the environment of deposition was relatively uniform. Proteaceae species were noted throughout the core, though in low numbers, at a maximum of 3.5 % of the total pollen rain. Banksia/Dryandra was the most abundant while Isopogon, Lambertia, Petrophile and Franklandia were also noted. A regression model was developed through the modern pollen rain study to predict the number of Proteaceae in the vegetation. This was also applied to the fossil pollen records. The estimated number of Proteaceae species in the Eocene suggests a maximum of 20 and a minimum of 10 taxa. For the Pliocene record, an estimated 7 - 9 species was found and for the Holocene pollen, between 7 - 8 were present. Thus the Eocene was similar in Proteaceae diversity to today. The results from the Pliocene and Holocene suggest that Proteaceae diversity was lower than today. Findings of this research indicate that Proteaceae species are an important and consistent component of vegetation in south-western Australia over the Cainozoic. It is likely that both changing pollination mechanisms and changes in associated vegetation are important in the determining the dispersal of Proteaceaous pollen. By understanding how the vegetation has changed and developed in south-western Australia, present vegetation can be managed to include intra-specific variation and ensure the majority of species are conserved for present and future generations to enjoy.
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