Mapping the Functional Roles of Cap Cells in the Response of Arabidopsis Primary Roots to Gravity1

The cap is widely accepted to be the site of gravity sensing in roots because removal of the cap abolishes root curvature. Circumstantial evidence favors the columella cells as the gravisensory cells because amyloplasts (and often other cellular components) are polarized with respect to the gravity vector. However, there has been no functional confirmation of their role. To address this problem, we used laser ablation to remove defined cells in the cap of Arabidopsis primary roots and quantified the response of the roots to gravity using three parameters: time course of curvature, presentation time, and deviation from vertical growth. Ablation of the peripheral cap cells and tip cells did not alter root curvature. Ablation of the innermost columella cells caused the strongest inhibitory effect on root curvature without affecting growth rates. Many of these roots deviated significantly from vertical growth and had a presentation time 6-fold longer than the controls. Among the two inner columella stories, the central cells of story 2 contributed the most to root gravitropism. These cells also exhibited the largest amyloplast sedimentation velocities. Therefore, these results are consistent with the starch-statolith sedimentation hypothesis for gravity sensing.

Peder Månssons Skrifter på svenska; efter handskrifter i Sockholm, Uppsala och Linköping, med en inledning utgifna

The originals (if any) of the 5th and 7th-12th treatises are unknown. cf. Inledning.

Federici Bonaventurae Vrbinatis Anemologiae pars prior : id est De affectionibus, signis causisque ventorum ex Aristotele, Theophrasto ac Ptolem[a]eo tractatus ... adiectus est index locorum, [et] quaestionum quae explicantur ...

Contiene con portada propia y paginación independiente: Claudii Ptolemaei Inerrantium stellarum aparitiones ac significationum collectio ... / a Federico Bonaventura Vrbinate latinitate donatus ... ; item libelli duo, alter ex Columella, alter ex Plinio excerpti De inerrantium stellarum significationibus. - Federici Bonauenturae Vrbinatis De causa ventorum motus : Peripatetica disceptatio ... - Federici Bonauenturae Vrbinatis Pro Theophrasto, atque Alexandro Aphrodisiensi, de vero tempore ortus, atq[ue] occasus Orionis, apologia : tribus libris distincta ...

Supplementary papers of the American School of Classical Studies in Rome. v. 1-2 ...

Papers of the school were ordinarily published in the American Journal of Archaeology, 2d. ser.; supplementary volumes wre authorized when material for publication either exceeded the space available in the journal, or when it was of such a nature as to make a different mode of publication advisable. (cf. v. 1, Prefatory note) The present volumes form the only collection of papers issued separately by the school in Rome. (Lists of the papers published in other journals, 1898-1907, may be found in the Supplementary papers, v. 1-2, Prefatory note) From 1909-12, the reports, etc., of the school were published in the Bulletin of the Archaeological Institute of America. On January 1, 1913, the American School of Classical Studies in Rome became a part of the American Academy in Rome.

L'économie rurale de Columelle,

Mode of access: Internet.

Scriptores rei rusticae veteres latini e recensione Jo. Matth. Gesneri cum ejusdem praef. et Lexico rustico...

Half-title. v. 1: Scriptores rei rusticæ veteres latini: Cato, Varro, Columella, Palladius, quibus accedit Vegetius De mulomedicina, et Gargilii Martialis fragmentum.

Cell Fate Specification and the Regulation of RNA-dependent DNA Methylation in the Arabidopsis Root Meristem

The Arabidopsis root apical meristem (RAM) is a complex tissue capable of generating all the cell types that ultimately make up the root. The work presented in this thesis takes advantage of the versatility of high-throughput sequencing to address two independent questions about the root meristem. Although a lot of information is known regarding the cell fate decisions that occur at the RAM, cortex specification and differentiation remain poorly understood. In the first part of this thesis, I used an ethylmethanesulfonate (EMS) mutagenized marker line to perform a forward genetics screen. The goal of this screen was to identify novel genes involved in the specification and differentiation of the cortex tissue. Mapping analysis from the results obtained in this screen revealed a new allele of BRASSINOSTEROID4 with abnormal marker expression in the cortex tissue. Although this allele proved to be non-cortex specific, this project highlights new technology that allows mapping of EMS-generated mutations without the need to map-cross or back-cross. In the second part of this thesis, using fluorescence activated cell sorting (FACS) coupled with high throughput sequencing, my collaborators and I generated single-base resolution whole genome DNA methylomes, mRNA transcriptomes, and smallRNA transcriptomes for six different populations of cell types in the Arabidopsis root meristem. We were able to discover that the columella is hypermethylated in the CHH context within transposable elements. This hypermethylation is accompanied by upregulation of the RNA-dependent DNA methylation pathway (RdDM), including higher levels of 24-nt silencing RNAs (siRNAs). In summary, our studies demonstrate the versatility of high-throughput sequencing as a method for identifying single mutations or to perform complex comparative genomic analyses.

The role of FMT and FIS1A in mitochondrial morphology and salt stress in Arabidopsis thaliana

Salt stress is known to have severe effects on plant health and fecundity, and mitochondria are known to be an essential part of the plant salt stress response. Arabidopsis thaliana serves as an excellent model to study the effects of salt stress as well as mitochondrial morphology. Arabidopsis contains several homologues to known mitochondrial proteins, including the fission protein FIS1A, and FMT, a homologue of the CLU subfamily. We sought to examine the effects of salt stress on knockout lines of FIS1A and FMT, as well as a transgenic line overexpressing FMT (FMT-OE) in columella cells in the root cap of Arabidopsis. fmt mutants displayed defects in both root and leaf growth, as well as a delay in flowering time. These mutants also showed a pronounced increase in mitochondrial clustering and number. FMT-OE mutants displayed severe defects in germination, including a decrease in total germination, and an increase in the number of days to germination. fis1A mutants exhibited shorter roots and slightly shorter leaves, as well as a tendency towards random mitochondrial clustering in root cells. Salt stress was shown to affect various mitochondrial parameters, including an increase in mitochondrial number and clustering, as well as a decrease in mitochondrial area. These results reveal a previously unknown role for FMT in germination and flowering in Arabidopsis, as well as insight into the effects of salt stress on mitochondrial morphology. FMT, along with FIS1A, may also help to regulate mitochondrial number and clustering, as well as root and leaf growth, under both control and salt-stressed conditions. This has implications for both FMT and FIS1A in whole-plant morphology as well as the plant salt stress response.