The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, Picea abies, a representative of the gymnosperm group of seed plants. The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage. Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms. Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic Arabidopsis plants. Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns. The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.

<p>This work describes the regulation of drought stress responses in <i>Arabidopsis thaliana</i> and adresses the roles of the homeodomain-leucine zipper (HD-Zip) transcription factors in this regulation. The characteristics of <i>ATHB6</i> and <i>ATHB7</i>, two genes encoding class I HD-Zip transcription factors were analysed. </p><p>Expression of <i>ATHB6</i> and <i>ATHB7</i> was transcriptionally activated in plants subjected to water deficit or exogenous treatment with abscisic acid (ABA).</p><p>Transgenic plants constitutively expressing the <i>ATHB7</i> gene displayed a delayed elongation growth of the main inflorescence stem after transition to reproductive development. This phenotype is consistent with ATHB7 acting as a negative regulator of growth and development of the elongating stem in response to water availability.</p><p>Transgenic <i>abi1-1</i> mutant plants constitutively expressing the <i>ATHB7</i> gene displayed a reduced wiltiness as compared to monogenic <i>abi1-1</i> mutants. These data are consistent with the ATHB7 protein having a central role in the drought stress response, regulating the water balance of the plant, and acting downstream to <i>ABI1</i>. Furthermore, the data is consistent with ATHB7 acting as a positive regulator of the drought stress response.</p><p>The ABA-induced expression of the <i>ATHB7</i> gene displayed a dependence on the phytochrome system, suggesting an interplay between light and osmotic stress signaling in the regulation of the <i>ATHB7</i> gene.</p>

<p>The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, <i>Picea abies</i>, a representative of the gymnosperm group of seed plants.</p><p>The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage.</p><p>Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms.</p><p>Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic <i>Arabidopsis</i> plants.</p><p>Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns.</p><p>The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.</p>

This work describes the regulation of drought stress responses in Arabidopsis thaliana and adresses the roles of the homeodomain-leucine zipper (HD-Zip) transcription factors in this regulation. The characteristics of ATHB6 and ATHB7, two genes encoding class I HD-Zip transcription factors were analysed. Expression of ATHB6 and ATHB7 was transcriptionally activated in plants subjected to water deficit or exogenous treatment with abscisic acid (ABA). Transgenic plants constitutively expressing the ATHB7 gene displayed a delayed elongation growth of the main inflorescence stem after transition to reproductive development. This phenotype is consistent with ATHB7 acting as a negative regulator of growth and development of the elongating stem in response to water availability. Transgenic abi1-1 mutant plants constitutively expressing the ATHB7 gene displayed a reduced wiltiness as compared to monogenic abi1-1 mutants. These data are consistent with the ATHB7 protein having a central role in the drought stress response, regulating the water balance of the plant, and acting downstream to ABI1. Furthermore, the data is consistent with ATHB7 acting as a positive regulator of the drought stress response. The ABA-induced expression of the ATHB7 gene displayed a dependence on the phytochrome system, suggesting an interplay between light and osmotic stress signaling in the regulation of the ATHB7 gene.

Homeodomain leucine zipper (HDZip) proteins constitute a large family of transcription factors characterised by the presence of a DNA-binding homeodomain and an adjacent leucine zipper motif, which mediates protein-dimer formation. The HDZip genes of Arabidopsis have been divided into four classes, HDZip I-IV. This thesis describes the characterisation and phylogeny of the class I HDZip genes and focuses on the expression and function of four HDZip I genes, ATHB5, -6, -7 and -16. The phylogenetic analyses of the 17 HDZip I sequences defined six subclasses, supported by the intron patterning and the traced duplication history of the genes. The members within each subclass showed diversification in expression, suggesting that the cis regulatory regions of the closely related genes have undergone evolutionary changes. However, similarities in the gene expression patterns between genes also exist and external factors like the availability of water and quality of light directs the expression of a subset of HDZip I genes. Expression analyses revealed that the plant hormone abscisic acid (ABA) is involved as a systemic signal for the salt or osmoticum induced ATHB7 expression, whereas light signals mediated through the blue light photoreceptors was found to direct the expression of ATHB6. Phenotypic analyses of plants with altered levels of ATHB6 or ATHB16 suggested that these paralogous genes encode proteins with very similar functions. ATHB16 was shown to act as a negative regulator of leaf cell expansion, as a suppressor of the flowering time sensitivity to photoperiod and as a positive regulator of blue light dependent inhibition of hypocotyl growth. A similar role for ATHB6 in the regulation of hypocotyl elongation was recorded. Further, analyses of multiple loss-of-function plants demonstrated that ATHB5, -6 and -16 function at least in part redundantly in mediating light effects on hypocotyl elongation.

<p>In the present work the regulation of environmentally induced cell death and signaling of systemic acquired acclimation (SAA) in <i>Arabidopsis thaliana</i> is characterized. We used the <i>lesion simulating disease1</i> (<i>lsd1</i>) mutant as a model system that is deregulated in light acclimation and programmed cell death (PCD). In this system we identify that redox status controlling SAA and cell death is controlled by the genes <i>LSD1</i>, <i>EDS1</i>, <i>EIN2</i> and <i>PAD4</i> which regulate cellular homeostasis of salicylic acid (SA), ethylene (ET), auxin (IAA) and reactive oxygen species (ROS). Furthermore we propose that the roles of <i>LSD1</i> in light acclimation and in biotic stress are functionally linked. The influence of SA on plant growth, short-term acclimation to high light (HL), and on the redox homeostasis of <i>Arabidopsis</i> leaves was also assessed. SA impaired acclimation of wild-type plants to prolonged conditions of excess excitation energy (EEE). This indicates an essential role of SA in acclimation and regulation of cellular redox homeostasis. We also show that cell death in response to EEE is controlled by specific redox changes of photosynthetic electron transport carriers that normally regulate EEE acclimation. These redox changes cause production of ET that signals through the<i> EIN2 </i>gene and regulon. In the<i> lsd1</i> mutant, we found that propagation of cell death depends on the plant defence regulators <i>EDS1 </i>and <i>PAD4</i> operating upstream of ET production. We conclude that the balanced activities of <i>LSD1</i>, <i>EDS1</i>, <i>PAD4</i> and <i>EIN2 </i>regulate chloroplast dependent acclimatory and defence responses. Furthermore, we show that <i>Arabidopsis</i> hypocotyls form lysigenous aerenchyma in response to hypoxia and that this process involves H₂O₂ and ET signalling. We found that formation of lysigenous aerenchyma depends on <i>LSD1</i>, <i>EDS1</i> and <i>PAD4</i>. Conclusively we show that <i>LSD1</i>, <i>EDS1</i> and <i>PAD4</i>, in their functions as major plant redox and hormone regulators provide a basis for fundamental plant survival in natural contitions.</p>

<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>

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.