Plant development is complex and highly regulated. Tens of thousands of genes have been sequenced for the model plant <em>Arabidopsis thaliana</em>, yet few have been functionally annotated and characterized. This thesis describes the expression analysis and characterization of four genes in <em>Arabidopsis</em>. Three of these belong to the eukaryotic translation initiation factor 5A (eIF5A) gene family, and the fourth encodes diacylglycerol acyltransferase 1 (DGAT1). Putative roles for these genes in the development of <em>Arabidopsis thaliana</em> are described. <br /><br /> eIF5A is the only known protein to contain the amino acid hypusine. It has been demonstrated previously that eIF5A acts as a shuttle protein, moving specific mRNAs from the nucleus to the cytoplasm for translation. In <em>Arabidopsis thaliana</em> (At), there are three isoforms of eIF5A, and it is clear from the present study that they each have a unique temporal and spatial expression pattern. AteIF5A-1 and -2 are up-regulated during natural senescence and wounding/pathogenesis, respectively, and it is proposed that they regulate the onset of programmed cell death during these events. AteIF5A-3 is up-regulated in elongating meristem of the root, and it is proposed that this isoform is involved in cell growth. <br /><br /> Over-expression of the individual <em>AteIF5A</em> isoforms <em>in planta</em> resulted in pleiotropic phenotypes. When <em>AteIF5A-1</em> or <em>AteIF5A-2</em> was over-expressed, the phenotypes observed were indicative of their putative roles in the translation of proteins required for programmed cell death. When <em>AteIF5A-3</em> was over-expressed, the phenotypes were indicative of a role for this protein in the regulation of cell and tissue elongation. <br /><br /> Lipid analysis of rosette leaves from <em>Arabidopsis thaliana</em> revealed an accumulation of triacylglycerol with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of triacylglycerol in <em>Arabidopsis</em> is catalyzed by DGAT1. When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the <em>Arabidopsis</em> EST clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of triacylglycerol. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the triacylglycerol of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, triacylglycerol isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that DGAT1 plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into triacylglycerol.

Plant development is complex and highly regulated. Tens of thousands of genes have been sequenced for the model plant <em>Arabidopsis thaliana</em>, yet few have been functionally annotated and characterized. This thesis describes the expression analysis and characterization of four genes in <em>Arabidopsis</em>. Three of these belong to the eukaryotic translation initiation factor 5A (eIF5A) gene family, and the fourth encodes diacylglycerol acyltransferase 1 (DGAT1). Putative roles for these genes in the development of <em>Arabidopsis thaliana</em> are described. <br /><br /> eIF5A is the only known protein to contain the amino acid hypusine. It has been demonstrated previously that eIF5A acts as a shuttle protein, moving specific mRNAs from the nucleus to the cytoplasm for translation. In <em>Arabidopsis thaliana</em> (At), there are three isoforms of eIF5A, and it is clear from the present study that they each have a unique temporal and spatial expression pattern. AteIF5A-1 and -2 are up-regulated during natural senescence and wounding/pathogenesis, respectively, and it is proposed that they regulate the onset of programmed cell death during these events. AteIF5A-3 is up-regulated in elongating meristem of the root, and it is proposed that this isoform is involved in cell growth. <br /><br /> Over-expression of the individual <em>AteIF5A</em> isoforms <em>in planta</em> resulted in pleiotropic phenotypes. When <em>AteIF5A-1</em> or <em>AteIF5A-2</em> was over-expressed, the phenotypes observed were indicative of their putative roles in the translation of proteins required for programmed cell death. When <em>AteIF5A-3</em> was over-expressed, the phenotypes were indicative of a role for this protein in the regulation of cell and tissue elongation. <br /><br /> Lipid analysis of rosette leaves from <em>Arabidopsis thaliana</em> revealed an accumulation of triacylglycerol with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of triacylglycerol in <em>Arabidopsis</em> is catalyzed by DGAT1. When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the <em>Arabidopsis</em> EST clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of triacylglycerol. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the triacylglycerol of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, triacylglycerol isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that DGAT1 plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into triacylglycerol.

Forest stands may act as important carbon storage places - sinks, due to carbon allocation into both the plant biomass in the process of photosynthesis and the soil. Enhancement of CO2 concentration affects a whole range of plant physiological processes and, thus, it is necessary to study its effect on photosynthetic apparatus - leaf anatomical structure and chloroplast ultrastructure. The first aim of the Thesis was to evaluate changes in chloroplast ultrastructure of common beech (Fagus sylvatica L.) under the effects of both elevated CO2 concentration and different irradiance. The second aim was to evaluate if the anatomical parameters obtained from the middle part of the leaf are representative for the whole leaf blade. The trees were grown in glass domes at the Bílý Kříž experimental site in the Beskids Mountains (Czech Republic), owned by the CzechGlobe Institute. Leaves were sampled in 2010 from juvenile trees, which were planted in 2005 being 5-year old and cultivated since then in ambient (AC; 390 micromol/mol) and elevated (EC; 700 micromol/mol) CO2 concentrations. The EC effect was recorded to be an increased proportion of starch grains in the chloroplast median section and decreased proportion of of intergranal thylakoids (IGT) while the ratio of granal to intergranal thylakoids...