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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Some thermal relationships of tropical flowers

Patino, Sandra January 2001 (has links)
A unified approach was used to analyse the energy budgets and temperatures of flowers belonging to the families Rafflesiaceae and Convolvulacea; and some broader ecological and evolutionary implications of their thermal regimes were discussed. Rhizanthes lowii and Raflessia tuan-mudae (Rafflesiaceae) are rare parasitic plants adapted to live in the understory of the tropical rain forest in South East Asia. In the understory of the forest the ambient conditions are nearly constant (high relative humidity, low incident radiation and relatively constant air and soil temperature). These plants are parasitic on the vine Tretrastigma. They lack leaves, stems, or photosynthetic tissue and are characterised by gaseous emissions that attract the natural pollinators, carrion flies. The internal and surface temperatures of the flowers were continuously monitored with fine thermocouples in different parts of the flowers whilst radiation fluxes and microclimatic variables were recorded. In the case of Rhizanthes lowii there was evidence of both thermogenesis and thermoregulation. Endothermy was detected in young and mature buds as well as in blooming flowers and even in decaying tissues three or more days after blooming. Tissue temperatures were maintained at 7 - 9 K above air temperature. In Rafflesia tuan-mudae it was found that the internal parts of the flower were maintained a few degrees (1-6 K) above air temperature and the maximum heating was in the evening. As they are parasitic, they have the advantage over most other species as the respiratory substrate is derived from the host plant. High concentrations of CO2 may be released as the product of respiration. A fluid dynamics model was used to estimate the CO2 concentration in the reproductive cavity of Rafflesia tuan-mudae. The model suggested that the flower developed high concentrations of carbon dioxide inside the diaphragm, mainly around the central column where the cavity with the reproductive parts (anther or stigma) are located.
2

Analysis of cell wall carbohydrate composition in Eucalyptus and Arabidopsis

Gardner, Sara January 1998 (has links)
<I>Eucalyptus </I>xylem and pulp were analysed to ascertain the polysaccharides present in the wood pulp used in paper production and also the levels of these polysaccharides in the xylem of two <I>Eucalyptus </I>species (<I>E. grandis</I> and <I>E. globulus</I>). The methods used were Driselase digestion and trifluoroacetic acid (TFA) hydrolysis. Driselase digestion of cell walls produces disaccharides characteristic of some of the major cell wall polysaccharides, while hydrolysis with TFA yields monosaccharides. The analysis of the delignified xylem of the <I>Eucalyptus </I>spp. established that there was some natural variation between the species in the susceptibility of xylans to Driselase digestion, which probably reflects differences in the structure of these polysaccharides. Xylan was found to be a major contaminant of <I>Eucalyptus</I> wood pulp, making up approximately 25% of the mass of the pulp. Various genotypes (T-DNA tagged mutants and Ds mutants) of <I>A. thaliana</I> were screened for altered cell wall polysaccharide composition. As an initial screen the products of the two assays (Driselase digestion and TFA hydrolysis) were separated by paper chromatography and thin layer chromatography. HPLCA was then used to analyse lines that had shown consistent differences from the wild type in the initial screens. A small number of T-DNA tagged <I>A. thaliana </I>lines were identified that showed significant quantitative differences from the wild type in the composition of the screen products. The T-DNA tagged lines showed differences from the wild type in the amounts of cellulose, xyloglucan and xylan. Differences were also observed in the susceptibility of xylans to Driselase digestion, which probably reflect differences in the structure of these polysaccharides. The presence of xylans and glucomannans has beneficial effects on paper properties; however, xylans are believed to inhibit the removal of residual lignin from pulp. It is possible that small changes in the level and/or the composition of the xylan of the mutagenised <I>A</I>. <I>thaliana</I> lines may, once transferred to <I>Eucalyptus</I>, where xylan makes up a larger proportion of the total cell walls, affect the properties of the pulp produced from the modified trees.
3

Identification and characterisation of genes which underpin non-host disease resistance in Arabidopsis

Kang, Jeong-Gu January 2007 (has links)
A pathosystem using <i>Arabidopsis </i>and wheat powdery mildew, <i>Blumeria graminis </i>f. sp. <i>tritici </i>(<i>Bgt</i>), for which <i>Arabidopsis </i>is a non-host, was employed to initiate the genetic dissection of non-host resistance (NHR). The EMS mutagenised population from the <i>Arabidopsis </i>line containing the <i>GST1:LUC </i>transgene, which can facilitate a high throughput mutant screening strategy, have been screened using an ultra low light imaging camera system. Following a mutant screen of approximately 100,000 M2 plants, a number of candidates have been identified that compromise the induction of the <i>LUC </i>transgene in response to attempted <i>Bgt </i>infection. Through this screening, <i>nhr1 </i>was isolated as a putative factor for non-host pathogen recognition. This mutant showed severely compromised <i>GST1</i> induction and less hypersensitive cell death in response to <i>Bgt </i>inoculation, while exhibiting little difference against other host bacterial and fungal pathogens including <i>Pseudomonas syringae </i>p.v. tomato and <i>Hyaloperonospora parasitica. </i>In addition, <i>nhr1 </i>was sugar dependent in germination. We identified <i>ads3 </i>(<i>ACTIVATED DISEASE SUSCEPTIBILTY 3</i>), an <i>Arabidopsis </i>mutant showing drought resistant as well as disease susceptible phenotype against host and non-host pathogens. <i>ads3 </i>is <i>emf1-D </i>by enhanced expression of Embryonic Flower 1 (EMF1), which had been known as repressor of floral transition in plant. The susceptibility of <i>emf1-D </i>was recapitulated in transgenic <i>Arabidopsis </i>plants ectopically expressing <i>EMF1. </i>Conversely, conditionally decreased <i>EMF1 </i>level in the transgenic plant conveyed disease resistance. <i>emf1-D </i>was drought resistant and hypersensitive to abscisic acid (ABA). We show that ectopic expression of EMF1 modulates a ABA signalling, resulting in susceptibility to pathogens. The other plant link, which is the translationally controlled tumor protein (TCTP) over-expressing line, showed reduced NHR against <i>Bgt. </i>A leucine rich repeat receptor-like kinase (LRK) was isolated as a putative TCTP-interacting protein, and the KO line of the LRK showed less or delayed resistant response to non-host as well as host fungal pathogens. furthermore, the TCTP over-expressing line exhibited hypersensitivity towards ABA. These results suggest that ABA signalling could play a critical role in non-host resistance in plants.
4

Effects of seaweed suspensions on seed germination and seedling growth of barley (Hordeum vulgare L.) and lettuce (Lactuca sativa L.)

Möller, Michael January 1996 (has links)
Two seaweed suspensions, obtained from whole brown algae <I>Ascophyllum nodosum</I> (Linnaeus) Le Jolis (ANS), or lamina of <I>Laminaria hyperborea</I> (Gunn.) Foslie (LHS), were evaluated for their effects on seed germination and seedling growth of barley (<I>Hordeum vulgare</I> L.) and lettuce (<I>Lactuca sativa</I> L.). The seaweed suspensions (SWS) tested had mineral composition similar to that of fresh algae, and mineral concentrations at levels reflecting the dilution of the product during the manufacturing process. The activity of growth regulating substances found in the SWS were too low to be of physiological significance. When pre-germinated seeds were exposed to SWS at 10% or higher, radicle growth was inhibited both in barley and lettuce to a similar extent. The polyphenol content in ANS was found to be responsible for these effects in lettuce seedlings. For LHS unknown compound(s) were present in the supernatant, active only in the light. The compound(s) was(were) organic, heat labile above 60<SUP>O</SUP>C, degradable by microbial activity and likely not to be a protein. A growth promoting compound that increased lettuce cotyledon expansion in the light and hypocotyl elongation in the dark, was identified as potassium. Priming barley or lettuce seeds in SWS was beneficial, and adhering algal material provided additional nutrients to the seeds, compensating for leakage losses. Priming for 12 hours with a 24 hour re-drying period did not reduce seed viability, or increase the number of dead seeds or abnormal seedlings. When germinated under optimum laboratory conditions, the mean germination time of primed seeds, irrespective of initial seed vigour, was generally reduced. Priming in SWS was not superior to water treatments. However, seedling emergence and growth of barley under greenhouse conditions was promoted by priming with ANS, and was better than priming in water.
5

Effects of root cooling on leaf growth and the significance of abscisic acid in mediating the responses

Seraphin, Eliane Stacciarini January 1992 (has links)
The effects of root cooling treatments on leaf growth of seedlings of <i>Phaseolus vulgaris</i> L. were examined. Plants were germinated in vermiculite and then grown with their root systems cooled to 10<SUP>o</SUP>C or 15<SUP>o</SUP>C, or kept at the same temperature as the serial parts (23<SUP>o</SUP>C). Leaf elongation rates, recorded continuously using Rotary Variable Displacement Transducers, were shown to be very sensitive to root cooling treatments, and at 10<SUP>o</SUP>C, elongation rates fell to zero growth within 10 min after start of treatment. When root systems were returned to 23<SUP>o</SUP>C, leaf elongation rates increased almost immediately to overshoot the control rates within 5-10 min, subsequently declining to control values over the next 50-60 min. Leaf turgor pressure fell at the beginning of the root cooling treatment and was believed to cause the instantaneous growth reduction, and to trigger abscisic acid (ABA) synthesis in leaves. Recovery in bulk leaf turgor occurred within 3-4 h from the commencement of root cooling and remained virtually constant throughout the experiment. No detectable changes in leaf turgor were observed when root systems were returned to 23<SUP>o</SUP>C. A rise in abscisic acid occurred in rapidly expanding leaves of <i>Phaseolus vulgaris, Hordeum vulgare</i> L. and <i>Helianthus annuus</i> L. Root cooling treatment did not lead to a rise in leaf ABA content in the fully expanded first leaf of <i>H.vulgare</i>. In <i>H.annuus</i> as well as in <i>H.vulgare</i> the levels of abscisic acid declined as leaves aged. Analysis of abscisic acid present in xylem sap of <i>P.vulgaris</i> seedlings showed that the amount of this hormone coming from the roots was insufficient to account for the observed rise in leaf ABA. However, the responses involving high concentration of abscisic acid in the leaves, may be indirectly mediated by ABA coming from the root systems.
6

Changes in protein during differentiation

Tulett, Mavis January 1967 (has links)
No description available.
7

The effects of light and gibberellic acid on development of the mainstem apex of barley (Hordeum vulgare L.)

Cottrell, Joan Elizabeth January 1980 (has links)
The major objective of this project was to obtain detailed information regarding the effect of daylength on the development of the mainstem apex in barley and to determine whether its effects are exerted through a change in the levels of endogenous plant growth regulators, particularly gibberellins. In long days, spikelet initiation in the cultivar Clipper was rapid but extended over a short period. In short days, initiation was slower, as was the rate of spikelet development, but occurred over a much longer period. It appeared that spikelet initiation stopped following the appearance of stamen initials, and large numbers of spikelets resulted when development was slow in relation to initiation. Applied GA3 had its greatest effect in short days where treatment led to an increase in the rate of initiation and a reduction in the final number of spikelets. In long days, GA did not affect the rate of initiation but reduced final spikelet number. In both daylengths, reductions in spikelet number were associated with increased rates of development in relation to initiation. The effects of applied GA3 on spikelet initiation and development were long lived and it is proposed that this was the result of an autocatalytic effect of applied GA on the endogenous synthesis of gibberellins. It is suggested that the spikelets are sources of gibberellin which is transported upwards to accelerate the development of the younger spikelets and to bring about the osbserved trend towards the synchronization of spikelet development along the ear. Promotion of the development of the basal spikelets by exogenous GA3 may therefore have increased the source of endogenous gibberellins so that the rate of development was enhanced long after the original application. On this interpretation the levels of gibberellins in the developing ear should rise between the beginning and end of spikelet initiation. Estimates using the barley endosperm bioassay indicated that, at least in long days, more gibberellin was present in the ear at stamen initiation than double ridge formation. During normal development, the apical dome was initially small, elongated to a maximum, then decreased in size until initiation ceased, after which it elongated slightly then died. In short days, the apical dome of GA3-treated plants continued to elongate by an increase in cell number and reached massive proportions. This extension was followed by renewed production of spikelet primordia close to the tip of the dome. Death of the apical dome is not therefore an inevitable consequence of the cessation of initiation. There is some evidence to suggest that the most advanced spikelets produced inhibitors which prevented the initiation of new spikelets and may eventually have risen to prevent the growth of dome as well. Continued extension of the dome in the GA3-treated plants suggests that inhibitor may not have reached sufficiently high concentrations in the dome to curtail growth.
8

Growth and development during germination of the pea seed

McNair, David J. January 1966 (has links)
No description available.
9

Interactions in stomatal function

Aphalo, Pedro Jose January 1991 (has links)
(1) What is the relationship between stomatal responses and the rate of photosynthesis? The COa flux density and stomatal conductance are closely correlated, but there is not a simple causal link between them. This relationship is complex, and depends on both parallel but independent responses to light of stomata and photosynthesis, and indirect response of stomata mediated by photosynthesis. This indirect response occurs through CO2 depletion in the air spaces of the mesophyll and stomatal response to CO2- No evidence was found in favour of the proposed effect of photosynthesis on stomata through an unknown messenger. (2) What is the nature of the interaction between stomatal responses to humidity and temperature? The hypothesis that these responses are brought about by a single response to relative humidity at the leaf surface was tested, and shown to be incompatible with the responses of Hedera helix. It is suggested that the most appropriate variable for expressing humidity is, in this context, the water vapour deficit at the leaf surface. (3) What is the role of the boundary layer in the control of stomatal opening? Real world and simulation experiments were used to show that responses to bulk air vapour and COa mol fractions are both dependent on stomatal responses to CO2 and humidity. It is also shown that a feedforward response to humidity requires feedback through another variable for stability under natural conditions. Response to wind speed is due to changes in humidity and CO2 mol fraction at the leaf surface. (4) Are our current knowledge, and the resulting models, good enough for predicting short-term stomatal responses to changes in the environment? The need for a careful analysis of simulation models is stressed. Ball's empirical model of stomatal conductance was analysed. The original interpretation was found to be flawed, and a new one was proposed. The new interpretation views the model as a description of the relationship between COj flux rate and stomatal conductance, rather than of stomatal conductance alone. It is shown that this model is useful for describing the behaviour of the intercellular COj concentration. The model, was tested against data from the experiments. It was found that the responses to temperature and humidity are not treated in a satisfactory way. The response of the model to other variables is realistic. A modification to the model is described and tested. It is concluded that the model is a good starting point for the development of simulation models to be used as submodels in canopy and regional models.
10

The growth and physiology of tropical forest tree seedlings in relation to light

Kamaluddin, Mohammed January 1991 (has links)
This work reports the results of the experiment on the growth and physiology of tropical forest tree seedlings in relation to light. The experiments were carried out in a controlled environment simulating forest light conditions. The species studied were <i>Anthocephalus chinensis</i> (Lamk.) Rich. ex Walp., <i>Bischofia javanica</i> Blume, and <i>Hopea odorata</i> Roxb. from the moist forests of tropical Asia. The main aim of this study was to characterise the responses of seedlings in relation to (a) irradiance and nutrient supply, (b) shadelight quality, red to far-red (R:FR) ratio or low proportion of blue light, and (c) changing light availability. The species displayed differential growth responses when their seedlings were grown at different levels of irradiance and nutrient supply. Growth of gap species <i>Bischofia</i> was more plastic than that of the climax species <i>Hopea</i>. The growth of the former was substantially restricted when the nutrient supply was low at the higher irradiances. Pioneer species <i>Anthocephalus</i> responded to a low R:FR ratio by a large increase in stem extension growth with concomitant increase in allocation of dry matter to stem at the expense of leaf development. The effect of R:FR ratio on extension growth was independent of a low proportion of blue light. Very small amounts of blue light in the shadelight restricted leaf expansion in <i>Anthocephalus</i> and <i>Bischofia</i>, and increased specific stem length in the former. The climax species <i>Hopea</i> was relatively unresponsive to the R:FR ratios or the different proportions of blue light in the shadelight.

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