High temperature (HT) stress during wheat male reproductive development causes irreversible damage to the anther tapetum layer and the developing microspores it supports, resulting in reduced yield. With the frequency of pre-flowing temperature stress events likely to increase, a better understanding of the effects of high temperature stress on anther developmental regulation is required. Gibberellin (GA) signalling has been shown to regulate tapetum programmed cell death (PCD) and pollen coat formation via the transcription factor (TF) GAMYB. This project aimed to investigate the function of two putative GA-signalling components in wheat anther development and characterise the global hormonal and transcriptional anther responses to HT. RNAi and TILLInG mutants for TaGAMYB and a putative orthologue of a rice tapetum PCD component, TabHLH141, revealed that both are required for male fertility. Tagamyb mutants displayed stunted anther development with irregular tapetum vacuolisation and reduced pollen viability. An interaction between RHT-D1 and TabHLH141 suggests that GA may mediate anther development through regulation of DELLA-TF interactions. Having characterised and developed a non-destructive staging method for wheat anther development, RNA-Seq and global hormone analysis was used to investigate the response to HT stress around pollen mother cell meiosis. Significant changes in expression of tapetum metabolism and PCD annotated transcripts and anther GA, auxin and jasmonate concentrations indicates that hormonal regulation of HT-responsive transcription may contribute to defective anther development. The work in this project demonstrates that advanced functional genomics techniques can be now be applied to the dissection of complex signalling pathways in hexaploid wheat.

The plant hormone gibberellin (GA) is known to influence grain size and flour quality, flowering, development and germination in wheat. GA also induces the production of α-amylase by the aleurone layer and premature production of this enzyme during development results in degraded starch in the mature grain. While GA is proposed to have a negative effect on flour quality, it is essential for early grain development and these effects are separated both temporarily and spatially in the grain. It was the aim of this project to further understand the role GA plays in wheat grain development and in order to achieve this constructs were designed to alter GA metabolism or signalling in the seed-coat, endosperm, embryo or aleurone of developing wheat grains. In plants where GA content was manipulated in the developing endosperm it was shown that GA produced by this tissue is involved in regulating grain size and morphology. This was demonstrated by the differences observed between the transgenics and their nulls in grain size, hardness index and moisture content. Additionally, in these lines no differences were observed in the α-amylase levels, implying that GA produced by the endosperm might not be influencing the production of this enzyme. However, GA insensitivity introduced in the embryo and aleurone layers did not display the hypothesised phenotypes and was inconclusive in determining the role of GA signalling in grain development. During this project a reliable qPCR based method using TaqMan assays was also developed to determine zygosity of transgenic plants in the T1 generation. This method was successful in reducing the number of generations required to select homozygous material compared to more conventional methods.

As plants are sessile organisms, their developmental plasticity is crucial for adapting to environmental signals. Plant roots play a key role foraging resources in the soil to facilitate uptake of water and nutrients. The plant hormone auxin is a critical regulator of root growth and development, controlling root hair, branching and root angle. This thesis investigates the function of several auxin-regulated genes that control different aspects of root growth and development. It is important to maintain an appropriate auxin level in plant tissues by regulating auxin biosynthesis, transportation, conjugation and degradation pathways. In Arabidopsis thaliana, the DIOXYGENASE FOR AUXIN OXIDATION 1 (AtDAO1) gene has recently been identified to have a major function in regulating the oxidation of IAA to oxIAA. Metabolic profiling data of Atdao1 mutant lines identified that IAA level remains similar to wildtype in contrast to oxIAA and IAA congregates, revealing IAA degradation acts redundantly with the conjugate machinery. In addition, close examination of dao1 loss of function lines revealed several auxin-related phenotypes including the lengths of primary roots and root hairs. Auxin also plays a key role during lateral root branching. Bioinformatic analyses of a lateral root transcriptomic time course identified LATERAL ROOT KINASE 1 and 2 (LRK1 and LRK2, two putative LRR kinases) that exhibit the same expression dynamics during early stages of lateral root development as the auxin regulated transcription factor GATA23 that controls lateral root founder cell priming. lrk mutant analysis revealed that LRK1 and LRK2 function to controllateral root initiation. Reporter studies identified LRK1 and LRK2 are induced in root endodermal cells in the elongation zone, suggesting these genes regulate lateral root initiation indirectly. Auxin also regulates root angle. Transcriptomic profiling of a gravitropic auxin mutant arf7 arf19 identified 195differently expressed genes regulated by auxin and ARF7 ARF19. Reverse genetic studies characterised several candidates AT2G25900 (Cys3His transcription factor, TF) and AT5G47540 putative Mo25-like protein have been characterized to have function in root gravity response. Several experiments have been performed on several independent knock-out alleles to investigate the expression pattern of these two genes. The phenotyping results showed no significant differences in response to gravity stimulus, despite the original MO25 allele (mo25-2) exhibiting a strong lateral root phenotype.

No description available.

No description available.

<p>The marine environment is an important habitat where many processes occur that affect life conditions on earth. Macrophytes and planktonic oxygen evolvers are an essential component for almost all marine life forms and have developed in an environment that differs largely from the terrestrial habitats. For instance in regards to available ionic forms of inorganic carbon and moving water masses which affects incoming light. It is therefore relevant to examine the physiology of algae and marine plants to identify their unique features and differences to terrestrial plants that once orginated from algae. By using chlorophyll fluorescence measurements alone or combined with measurements of oxygen evolution and protein analysis photosynthetic strategies to withstand excess energy have been evaluated under a variety of experimental conditions. Furthermore metabolic pathways involved in energy transfer from photosynthesis to the site of active carbon uptake have been examined. The following was found:</p><p>* The ratio between photosynthetic gross oxygen evolution and estimated electron transport rate varies in <i>Ulva</i> spp depending on previous history of light and dark exposures. To obtain P/I curves with ratios close to the theoretical 1:4 value, measurements should be performed on separate pieces of tissue at each irradiance level. </p><p>* Under carbon deficient conditions, the estimated ETR is larger than the gross oxygen evolution, which may be due to the so called “water-water” cycle and absorption changes in PSII which are not corrected for in the calculation of ETR. </p><p>* Upon exposure to high irradiances (1500 µmol photons m^-2s^-1) the PSII core protein D1 is broken down with a concomittant reduction in ETR in <i>Ulva</i> <i>spp</i>. With the decrease in electron transport between PSII and PSI the acidification of the lumen decreases and the ability to dissipate excess energy as heat. At prolonged irradiance, an acclimation occurs with a lesser or no breakdown of D1 indicating an additional photo-protective strategy other than heat dissipation.</p><p>* <i>Laminaria saccharina</i> is dependent on mitochondrial respiration for active utilization of bicarbonate. By extruding protons outside the plasmalemma an acidification takes place that favors the conversion of bicarbonate into carbon dioxide that then can diffuse in to the cell. These proton pumps are driven by ATP supplied to a large degree from mitochondria, likely through the reductant NADPH produced photochemically. </p><p>* The marine angiosperm <i>Zostera marina</i> is dependent on mitochondrial respiration for utilization of bicarbonate in a manner similar to that in <i>Laminaria saccharina</i> . However, the water-water cycle may supply additional ATP to the proton pumps in <i>Zostera marina</i>. Both species exhibit a lag-phase at the onset of illumination after a dark incubation period and at least part of this lag-phase is due to a lag in an activation of mitochondrial supported bicarbonate utilization. It is clear that the marine environment holds complex plant and algae species and much is still to discover about the oxygen evolvers that grow beneath the water surface.</p>

<p>The green algae of the genus <i>Halimeda</i> Lamouroux (Chlorophyta, Bryopsidales) and the encrusting loose-lying red coralline algae (Rhodophyta, Corallinales) known as rhodoliths are abundant and widespread in all oceans. They significantly contribute to primary productivity while alive and production of CaCO₃ rich sediment materials on death and decay. Carbonate rich sediments are important components in the formation of Coral Reefs and as sources of inorganic carbon (influx) in tropical and subtropical marine environments. This study was initiated to attempt to assess their ecological significance with regard to the above mentioned roles in a tropical lagoon system, Chwaka bay (Indian Ocean), and to address some specific objectives on the genus <i>Halimeda</i> (Chlorophyta, Bryopsidales) and the loose-lying coralline algae (rhodoliths).</p><p>Four <i>Halimeda</i> species were taxonomically identified in the area. The species identified are the most common inhabitants of the world’s tropical and subtropical marine environments, and no new species were encountered. Using Satellite remote sensing technique in combination with the percentage cover data obtained from ground-truthing field work conducted in the area using quadrants, the spatial and seasonal changes of Submerged Aquatic Macrophytes (SAV) were evaluated. SAV percentage cover through ground-truthing was; 24.4% seagrass, 16% mixed <i>Halimeda</i> spp., 5.3% other macroalgae species while 54.3% remained unvegetated. No significant changes in SAV cover was observed for the period investigated, except in some smaller regions where both loss and gains occurred. The structural complexity of SAV (shoot density, above-ground biomass and canopy height) for most common seagrass communities from six meadows, dominated by <i>Thalassia hemprichii, Enhalus acoroides</i> and <i>Thalassodendron ciliatum</i>, as well as mixed meadows, were estimated and evaluated. Relative growth of <i>Halimeda</i> species was up to 1 segment tip^-1 day^-1. The number of segments produced was highest in hot season. Differences between the numbers of segments produced were insignificant between the two sites investigated. The C/N ratios obtained probably shows that <i>Halimeda</i> species experience nitrogen limitation in the area and may be a factor among others responsible for the varying growth of species obtained. However, this can be a normal ratio for calcified algae due to high CaCO₃ content in their tissues. Standing biomass of mixed <i>Halimeda</i> species averaged between 500-600 g dw m^-2 over the bay, while the mean cover in <i>Halimeda</i> meadows was about 1560 g dw m^-2. Carbonate production in <i>Halimeda</i> beds varied between 17-57 g CaCO₃ m^-2 day^-1 and for <i>H. macroloba</i> between 12-91 g CaCO₃ m^-2 day^-1. This indicates a high annual input of carbonate in the area. Decomposition of <i>Halimeda </i>using litter bag experiments at site I and II gave a decomposition rate (k) of 0.0064 and k = 0.0091 day^-1 ash-free dry weight (AFDW) respectively. Hence it would take 76-103 days for 50% of the materials to decompose.</p><p>Adding inhibitors or varying the pH significantly reduced inorganic carbon uptake, and demonstrated that the two photosynthesis and calcification were linked. Addition of TRIS strongly inhibited photosynthesis but not calcification, suggesting the involvement of proton pumps in the localized low pH acid zones and high pH basic zones. The high pH zones were maintained by the proton pumps maintaining high calcification, while TRIS was competing for proton uptake from acid zones causing photosynthesis to drop. Rhodoliths were found to maintain high productivity at a temperature of 34^oC, and even at 37^oC. It is therefore concluded that, rhodoliths are well adapted to high temperatures and excess light, a behaviour which enables them to thrive even in intertidal areas.</p>

<p>Waste products from the forest industry are to be spread in forests in Sweden to counteract nutrient depletion due to whole tree harvesting. This may increase the bioavailability of calcium (Ca) and heavy metals, such as cadmium (Cd), copper (Cu) and zinc (Zn) in forest soils. Heavy metals, like Cd, have already been enriched in forest soils in Sweden, due to deposition of air pollutions, and acidification of forest soils has increased the bioavailability of toxic metals for plant uptake. Changes in the bioavailability of metals may be reflected in altered accumulation of Ca and heavy metals in forest trees, changes in tree growth, including wood formation, and altered tree species composition. This thesis aims at examining: A) if inter- or intra- specific differences in sensitivity to Cd occur in the most common tree species of Sweden, and if so, to study if these can be explained by the uptake and distribution of Cd within the plant: B) how elevated levels of Ca, Cd, Cu and Zn affect the accumulation and attachment of metals in bark and wood, and growth of young Norway spruce (<i>Picea abies</i>): C) how waste products from the forest industry, such as wood ash, influence the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce.</p><p>Sensitivity to Cd, and its uptake and distribution, in seedlings of <i>Picea abies</i>, <i>Pinus sylvestris</i> and <i>Betula pendula</i> from three regions (southern, central and northern parts) of Sweden, treated with varying concentrations of Cd, were compared. Differences in root sensitivity to Cd both among and within woody species were found and the differences could to some extent be explained by differences in uptake and translocation of Cd. The root sensitivity assays revealed that birch was the least, and spruce the most, sensitive species, both to the external and to tissue levels of Cd. The central ecotype of the species tested tended to be most Cd resistant. </p><p>The radial distribution, accumulation and attachment of, and interactions between Ca and heavy metals in stems of two-year-old Norway spruce trees treated with elevated levels of Cd, Cu, Zn and/or Ca, were investigated. Further, the influence of these metals on growth, and on root metal content, was examined. Accumulation of the metals was enhanced in wood, bark and/or roots at elevated levels of the metal in question. Even at low levels of the metals, similar to after application of wood ash, an enhanced accumulation was apparent in wood and/or bark, except for Cd. The increased accumulation of Zn and Cu in the stem did not affect the growth. However, Cu decreased the accumulation of Ca in wood. Higher levels of Cu and Cd reduced the stem diameter and the toxic effect was associated with a reduced Ca content in wood. Copper and Cd also decreased the accumulation of Zn in the stem. On the other hand, elevated levels of Ca increased the stem diameter and reduced the accumulation of Cd, Cu, Zn and Mn in wood and/or bark. When metals interacted with each other the firmly bound fraction of the metal reduced was in almost all cases not affected. As an exception, Cd decreased the firmly bound fraction of Zn in the stem. </p><p>The influence of pellets of wood ash (ash) or a mixture of wood ash and green liquor dregs (ash+GLD), in the amount of 3000 kg ha^-1, on the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce in the field was examined. The effect of the treatments on the metal content of bark and wood was larger after 3 years than after 6 years. Treatment with ash+GLD had less effect on the heavy metal content of bark and wood than treatment with ash alone. The ash treatment increased the Cu and Zn content in bark and wood, respectively, after 3 years, and decreased the Ca content of the wood after 6 years. The ash+GLD treatment increased the Ca content of the bark and decreased the Zn content of bark and wood after 3 years. Both treatments reduced, or tended to decrease, the Cd content in wood and bark at both times.</p><p>To conclude, small changes in the bioavailability of Ca, Cu, Cd and Zn in forest soils, such as after spreading pellets of wood ash or a mixture of wood ash and green liquor dregs from the forest industry, will be reflected in an altered accumulation of metals in wood and bark of Norway spruce. It will not only be reflected in changed accumulation of those metals in which bioavailability in the soil has been enhanced, but also of other metals, probably partly due to interactions between metals. When metals interact the exchangeable bound fraction of the metal reduced is suggested to be the main fraction affected. The small alterations in accumulation of metals should not affect the growth of Norway spruce, especially since the changes in accumulation of metals are low, and further since these decrease over time. However, as an exception, one positive and maybe persistent effect of the waste products is that these may decrease the accumulation of Cd in Norway spruce, which partly may be explained by competition with Ca for uptake, translocation and binding. A decreased accumulation of Cd in Norway spruce will probably affect the trees positively, since Norway spruce is one of the most sensitive species to Cd of the forest trees in Sweden. Thus, spreading of waste products from the forest industry may be a solution to decrease the accumulation of Cd in Norway spruce. In a longer perspective, this will decrease the risk of Cd altering the tree species composition of the forest ecosystem. An elevated bioavailability of Ca in forest soils will, in addition to Cd, probably also decrease the accumulation of other less competitive heavy metals, like Zn and Mn, in the stem. </p>

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Plant Physiology" Title from author supplied metadata (automated record created on Feb. 23, 2007.) Vita. Abstract. Includes bibliographical references.

Waste products from the forest industry are to be spread in forests in Sweden to counteract nutrient depletion due to whole tree harvesting. This may increase the bioavailability of calcium (Ca) and heavy metals, such as cadmium (Cd), copper (Cu) and zinc (Zn) in forest soils. Heavy metals, like Cd, have already been enriched in forest soils in Sweden, due to deposition of air pollutions, and acidification of forest soils has increased the bioavailability of toxic metals for plant uptake. Changes in the bioavailability of metals may be reflected in altered accumulation of Ca and heavy metals in forest trees, changes in tree growth, including wood formation, and altered tree species composition. This thesis aims at examining: A) if inter- or intra- specific differences in sensitivity to Cd occur in the most common tree species of Sweden, and if so, to study if these can be explained by the uptake and distribution of Cd within the plant: B) how elevated levels of Ca, Cd, Cu and Zn affect the accumulation and attachment of metals in bark and wood, and growth of young Norway spruce (Picea abies): C) how waste products from the forest industry, such as wood ash, influence the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce. Sensitivity to Cd, and its uptake and distribution, in seedlings of Picea abies, Pinus sylvestris and Betula pendula from three regions (southern, central and northern parts) of Sweden, treated with varying concentrations of Cd, were compared. Differences in root sensitivity to Cd both among and within woody species were found and the differences could to some extent be explained by differences in uptake and translocation of Cd. The root sensitivity assays revealed that birch was the least, and spruce the most, sensitive species, both to the external and to tissue levels of Cd. The central ecotype of the species tested tended to be most Cd resistant. The radial distribution, accumulation and attachment of, and interactions between Ca and heavy metals in stems of two-year-old Norway spruce trees treated with elevated levels of Cd, Cu, Zn and/or Ca, were investigated. Further, the influence of these metals on growth, and on root metal content, was examined. Accumulation of the metals was enhanced in wood, bark and/or roots at elevated levels of the metal in question. Even at low levels of the metals, similar to after application of wood ash, an enhanced accumulation was apparent in wood and/or bark, except for Cd. The increased accumulation of Zn and Cu in the stem did not affect the growth. However, Cu decreased the accumulation of Ca in wood. Higher levels of Cu and Cd reduced the stem diameter and the toxic effect was associated with a reduced Ca content in wood. Copper and Cd also decreased the accumulation of Zn in the stem. On the other hand, elevated levels of Ca increased the stem diameter and reduced the accumulation of Cd, Cu, Zn and Mn in wood and/or bark. When metals interacted with each other the firmly bound fraction of the metal reduced was in almost all cases not affected. As an exception, Cd decreased the firmly bound fraction of Zn in the stem. The influence of pellets of wood ash (ash) or a mixture of wood ash and green liquor dregs (ash+GLD), in the amount of 3000 kg ha-1, on the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce in the field was examined. The effect of the treatments on the metal content of bark and wood was larger after 3 years than after 6 years. Treatment with ash+GLD had less effect on the heavy metal content of bark and wood than treatment with ash alone. The ash treatment increased the Cu and Zn content in bark and wood, respectively, after 3 years, and decreased the Ca content of the wood after 6 years. The ash+GLD treatment increased the Ca content of the bark and decreased the Zn content of bark and wood after 3 years. Both treatments reduced, or tended to decrease, the Cd content in wood and bark at both times. To conclude, small changes in the bioavailability of Ca, Cu, Cd and Zn in forest soils, such as after spreading pellets of wood ash or a mixture of wood ash and green liquor dregs from the forest industry, will be reflected in an altered accumulation of metals in wood and bark of Norway spruce. It will not only be reflected in changed accumulation of those metals in which bioavailability in the soil has been enhanced, but also of other metals, probably partly due to interactions between metals. When metals interact the exchangeable bound fraction of the metal reduced is suggested to be the main fraction affected. The small alterations in accumulation of metals should not affect the growth of Norway spruce, especially since the changes in accumulation of metals are low, and further since these decrease over time. However, as an exception, one positive and maybe persistent effect of the waste products is that these may decrease the accumulation of Cd in Norway spruce, which partly may be explained by competition with Ca for uptake, translocation and binding. A decreased accumulation of Cd in Norway spruce will probably affect the trees positively, since Norway spruce is one of the most sensitive species to Cd of the forest trees in Sweden. Thus, spreading of waste products from the forest industry may be a solution to decrease the accumulation of Cd in Norway spruce. In a longer perspective, this will decrease the risk of Cd altering the tree species composition of the forest ecosystem. An elevated bioavailability of Ca in forest soils will, in addition to Cd, probably also decrease the accumulation of other less competitive heavy metals, like Zn and Mn, in the stem.