The genetic and molecular basis of natural variation for plant growth and related traits in Arabidopsis thaliana

Plant growth is a complex quantitative trait of which the (eco)physiological aspects have been researched in great detail. In contrast, little is known about the genetic basis and molecular basis of plant growth. Most of what is known today has been discovered by using reverse genetic approaches that target single genes. Forward genetics using naturally occurring variation provides the possibility to investigate genetic effects within the context of the genetic background. This thesis describes the results of a study that aimed at elucidating the genetic basis and the underlying molecular basis of natural genetic variation for plant growth and related traits in Arabidopsis thaliana. A set of over 30 growth related traits has been quantified in two Arabidopsis RIL populations, derived from crosses between the accessions Landsberg erecta (Ler) x Kashmir-2 and Landsberg erecta x Shakdara (Sha) respectively. The projected rosette area (PRA) and Feret diameter of each plant was measured repeatedly during its growth using digital image analysis and. A logistic model and a linear model were fitted to the PRA data for quantification of plant growth rate. The dimensions of the largest rosette leaves, plant hight and chlorophyll content index were measured. Furthermore, flowering time and leaf numbers were recorded. A selection of 15 traits was used to perform a multi-trait QTL analysis using mixed-model methodology. A total 19 QTL were detected of which some art similar locations in both populations. QTL important for flowering time were also found to explain nearly half of the genetic variance for plant growth rate. These QTL mainly mapped to similar locations in both populations indicating a common genetic basis for the affected traits in the studied accessions. However, population specific QTL with no effect on flowering time accounted for the remaining genetic variance explained for plant growth. These QTL were chosen for follow-up studies in order to elucidate the underlying molecular basis. The detected QTL effects were validated in a selected set of near isogenic lines (NILs). These NILs will provide the opportunity to fine-map the QTL in order to identify the genes, and in particular the DNA polymorphisms responsible for these effects. For a single QTL fine-mapping could be advanced efficiently, currently down to 151 genes, due to particularly penetrant effects on plant morphology. QTL that also affected flowering time were not the main interest of these studies because they mapped to positions of genes that were already described for their role in the regulation of this trait. However, although the relation between flowering time and plant growth of such QTL had been described in literature, no distinction between pleiotropy and closely linked QTL could be made so far. A QTL that effected flowering time and plant growth rate, among other traits, located on the bottom end of chromosome 5 has been fine-mapped and cloned using NILs with introgressions of Sha in the genetic background of Ler. Fine-mapping achieved a resolution at which it could be proven that the cluster of MAF2-MAF5 (MADS affecting flowering) genes was underlying the detected QTL effects on flowering time. The effects on plant growth were fine-mapped to a slightly larger region this included an additional 3 genes. Although it was known that these genes affect flowering time, their role in natural variation for this trait had not been directly shown before. Sequence analysis of the cluster showed that Sha carried a fusion consisting of the 5’ portion of MAF2 and the 3’ portion of MAF3. An intact MAF3 gene was not found in this accession. Recently it was shown that such MAF2/MAF3 fusions are relatively common among Arabidopsis accessions but the loss of MAF3 makes Sha unique. Genomic complementation indicated that neither MAF2, MAF3 nor MAF4 can explain the QTL effects by itself. The current hypothesis is therefore that both MAF2 and MAF3 are required in the regulation of flowering time to reconstitute the phenotypical value of Ler in a NIL

Land vehicle antennas for satellite mobile communications

The RF performance, size, pointing system, and cost were investigated concepts are: for a mechanically steered 1 x 4 tilted microstrip array, a mechanically steered fixed-beam conformal array, and an electronically steered conformal phased array. Emphasis is on the RF performance of the tilted 1 x 4 antenna array and methods for pointing the various antennas studied to a geosynchronous satellite. An updated version of satellite isolations in a two-satellite system is presented. Cost estimates for the antennas in quantities of 10,000 and 100,000 unites are summarized

Quantum Monte Carlo calculations of electroweak transition matrix elements in A = 6,7 nuclei

Green's function Monte Carlo calculations of magnetic dipole, electric quadrupole, Fermi, and Gamow-Teller transition matrix elements are reported for A=6,7 nuclei. The matrix elements are extrapolated from mixed estimates that bracket the relevant electroweak operator between variational Monte Carlo and GFMC propagated wave functions. Because they are off-diagonal terms, two mixed estimates are required for each transition, with a VMC initial (final) state paired with a GFMC final (initial) state. The realistic Argonne v18 two-nucleon and Illinois-2 three-nucleon interactions are used to generate the nuclear states. In most cases we find good agreement with experimental data.Comment: v2: minor corrections to text and figure

Quantum Monte Carlo calculations of excited states in A = 6--8 nuclei

A variational Monte Carlo method is used to generate sets of orthogonal trial functions, Psi_T(J^pi,T), for given quantum numbers in various light p-shell nuclei. These Psi_T are then used as input to Green's function Monte Carlo calculations of first, second, and higher excited (J^pi,T) states. Realistic two- and three-nucleon interactions are used. We find that if the physical excited state is reasonably narrow, the GFMC energy converges to a stable result. With the combined Argonne v_18 two-nucleon and Illinois-2 three-nucleon interactions, the results for many second and higher states in A = 6--8 nuclei are close to the experimental values.Comment: Revised version with minor changes as accepted by Phys. Rev. C. 11 page

Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes

In semiconductor manufacturing, contamination due to particulates significantly decreases the yield and quality of device fabrication, therefore increasing the cost of production. Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and in plasma deposition processes. Dust particles suspended within such plasmas will acquire an electric charge from collisions with free electrons in the plasma. If the ratio of inter-particle potential energy to the average kinetic energy is sufficient, the particles will form either a liquid structure with short range ordering or a crystalline structure with long range ordering. Otherwise, the dust particle system will remain in a gaseous state. Many experiments have been conducted over the past decade on such colloidal plasmas to discover the character of the systems formed, but more work is needed to fully understand these structures. The preponderance of previous experiments used monodisperse spheres to form complex plasma systems

Tensor Forces and the Ground-State Structure of Nuclei

Two-nucleon momentum distributions are calculated for the ground states of nuclei with mass number $A\leq 8$, using variational Monte Carlo wave functions derived from a realistic Hamiltonian with two- and three-nucleon potentials. The momentum distribution of $np$ pairs is found to be much larger than that of $pp$ pairs for values of the relative momentum in the range (300--600) MeV/c and vanishing total momentum. This order of magnitude difference is seen in all nuclei considered and has a universal character originating from the tensor components present in any realistic nucleon-nucleon potential. The correlations induced by the tensor force strongly influence the structure of $np$ pairs, which are predominantly in deuteron-like states, while they are ineffective for $pp$ pairs, which are mostly in $^1$S$_0$ states. These features should be easily observable in two-nucleon knock-out processes, such as $A(e,e^\prime np)$ and $A(e,e^\prime pp)$.Comment: 4 pages including 3 figure