Ions in the soil solution traverse many layers (epidermis, exodermis, central cortex, and endodermis) within the root to reach the stele. The endodermis is present in almost all vascular plants while the exodermis is found only in majority of angiosperm roots tested. The maturation of the exodermis and the death of epidermis alter the plasma membrane surface areas (PMSA) potentially available for ion uptake. Do these changes reduce the ion uptake in proportion to the loss of absorptive surface areas? To answer this question onion (Allium cepa L cv. Wolf) adventitious root segments representing above features: Immature Exodermis Live Epidermis (IEXLEP), Mature Exodermis Live Epidermis (MEXLEP), Mature Exodermis Dead Epidermis (MEXDEP) were excised. Using a compartmental elution technique, radioactive sulphate and phosphate present in various internal compartments were quantified. Quantities of ions moved across the plasma membrane, a summation of quantities in the cytoplasm, ‘vacuole’, and ‘bound’ compartments, indicated that the maturation of the exodermis reduces the uptake of sulphate but not phosphate. In contrast, epidermal death reduced the movement of both ions across the plasma membranes. Although there is a reduction in the available PMSA with the maturation of the exodermis and death of the epidermis, these events do not necessarily reduce the ion movement into the plasma symplast. The endodermal cells of onion roots deposit suberin lamellae as secondary walls. As seen in cross-sections some cells remain without these lamellae and are known as ‘passage cells’. What is the pattern of suberin lamella deposition along the root? Is the suberin lamella a continuous layer? To answer these questions, endodermal layers isolated from onion adventitious roots were used in the present study. These layers were observed using four stains (Sudan Red 7B, Fluorol yellow 088 [Fy], berberine, and Nile red) and three microscopes (compound-white light, compound-epifluorescence and confocal scanning). In differentiating cells with and without suberin lamellae in endodermal layers Sudan Red 7B served the best results for compound-white light microscope, Fy for compound-epifluorescence microscope and Nile for confocal laser scanning microscope (CLSM). Suberin lamellae deposition initiated almost in a random manner; they continued to be deposited resulting in the production of longitudinal files alternating with files with passage cells, and were ultimately deposited in almost all cells at a distance of 255 mm from the tip. The suberin lamellae are perforated with pores, a consistent feature even as far as 285 mm from the tip. These pores may serve as portals for water, ions, and pathogen movement.

Environmental conditions affect the formation of apoplastic barriers (endodermis and exodermis) in roots. This was shown on many species in many research papers. The exodermal layer is more variable in response to stress conditions than endodermal layer. Cadmium toxicity, as many other stresses, induces faster development of apoplastic barriers. Most of research papers published so far, however characterized only the response of main root to this type of stress factor. Lateral roots, an important part of the root system absorptive surface, are neglected and there is not much information about their response to cadmium stress. The pattern of apoplastic barriers development was therefore analysed in main and also in lateral roots of various size and position on maternal root axis. We found significant differences in response to cadmium stress among these different root types. Then we summed up the differences between these types of roots. Short lateral roots were generally more responsive to cadmium stress, cadmium affected root branching as well as differentiation of apoplastic barriers in lateral roots. These results help us to better understand the response of complex roots system to environmental conditions. In the second part of this work, the role of CASP genes in exodermal development was...

Plants are able to cope with changing environmental conditions or withstand its adverse effects due to their plastic development. One way to adapt to fluctuating amounts of nutrients and water in the environment or the presence of toxic substances is to regulate the movement of substances between the plant and the environment. Beside other, this regulation is also possible at the level of the root system, by the formation of apoplastic barriers endodermis and exodermis. Some species posses endodermis only, in others exodermis in hypodrermal layers of the root can be found. These barriers differentiate in three stages and prevent free movement of coumpounds though apoplast. The transport to the symplast is the key point of regulating the uptake of substances into the plant and the endodermis is the fundamental structure. The presence of exodermis, however, affects the apoplast permeability of the surface root layers and can therefore influence the involvement of the primary cortex cells in the uptake of substances from the environment. In this work the impact of phosphate deficiency on the formation of apoplastic barriers was studied focusing on exodermis and the effect of its differentiation on the occurrence of membrane transporters and involvement of primary cortex cells in the uptake of...

La peridermis és una estructura complexa que protegeix els òrgans vegetals madurs (secundaris) i les zones que han sofert ferides de la pèrdua d'aigua i dels patògens. Aquesta funció barrera és deguda al fel·lema o súber, un teixit format per cèl·lules suberificades. Tant el fel·lema com la suberina són crucials per la vida de les plantes terrestres, però pràcticament no es coneix res dels processos moleculars que regulen la seva formació, probablement degut a la manca de models adequats. En aquesta tesi s'han identificat i caracteritzat gens induïts al fel·lema mitjançant la combinació de dues plantes models. L'escorça d'alzina surera (Quercus suber) s'ha utilitzat per aïllar gens candidats de la formació del fel·lema i per investigar el comportament d'alguns d'aquests gens durant l'estació de creixement, mentre que la pela de la patata (Solanum tuberosum) s'ha utilitzat en estudis de genètica reversa per demostrar la funció d'alguns gens reguladors al fel·lema. / The periderm is a complex structure that protects plant mature (secondary) organs and wounded tissues from water loss, injuries and pathogens. This barrier capacity is accomplished by the cork layer of the periderm, a tissue made of dead cells with suberin deposited into cell walls. Although cork and suberin are critical for the survival of land plants, very few is known about the molecular processes involved in their biosynthesis and differentiation, probably due to the lack of appropriate plant models. Here we developed a strategy to identify and characterize cork candidate genes using a combination of two model plants for periderm studies. The bark of cork oak (Quercus suber) was used to identify candidate genes and to analyze the seasonal behaviour of some of these genes. The potato (Solanum tuberosum) tuber was used to demonstrate the role of some selected candidates in the regulation of cork by reverse genetic analyses.

Chez les plantes, la subérine est un biopolymère constitué de composés aliphatiques etaromatiques déposés au niveau de la paroi des cellules de plusieurs tissus comme l’endodermeet le périderme des racines ou encore le manteau des graines. La subérine forme une barrièrehydrophobe permettant entre autres de contrôler les flux d’eau et de solutés, et de protéger laplante de stress environnementaux comme la sécheresse ou les pathogènes. Grâce à desanalyses en LC-MS/MS et en GC-MS, nous avons pu montrer que la majorité des alcools grasprésents dans la fraction soluble de racines d’Arabidopsis thaliana est sous forme d’alkylcaféates et d’alkyl coumarates. De plus, nous avons montré que ces cires associées aupolymère de subérine sont présentes dès les premiers stades du développement de la racine.Une étude de la distribution des chaînes acyles des racines nous a permis de mettre enévidence la contribution majeure des alcools gras dans la composition de la subérine ainsi quel’importance de la subérine dans le métabolisme lipidique des racines. Afin d’identifier desacteurs impliqués dans l’export des précurseurs de la subérine vers l’espace extracellulaire,nous avons mené une approche de génétique inverse en utilisant des lignées mutées pour desgènes codant notamment pour des ABCG transporteurs co-exprimés avec des gènes connuspour participer à la biosynthèse de la subérine. Les résultats de ces analyses ont confirmé quele processus d’export fait intervenir plusieurs protéines pouvant avoir des fonctionsredondantes et ont suggéré l’implication d’un nouveau transporteur dans l’export desprécurseurs de subérine. / In plants, suberin is a complex biopolymer made of aliphatic and aromatic compounds.It is deposited in the cell wall of tissues such as the endoderm and the periderm of roots or thecoat of the seeds. Suberin forms a hydrophobic barrier controlling the flow of water andsolutes, and protecting the plant from environmental stresses such as drought or pathogens.Through LC-MS/MS and GC-MS analyses, we have shown that the majority of the fattyalcohols present in the soluble fraction of Arabidopsis roots is in the form of alkyl caffeatesand alkyl coumarates. Such waxes, most probably associated with the suberin polymer, arealready detected at early stages of root development. A study of the distribution of all acylchains present in roots allowed us to highlight the major contribution of fatty alcohols in thecomposition of suberin and the importance of suberin in the global lipid metabolism of theroots. To identify proteins involved in the export of suberin precursors to the extracellularspace, we conducted a reverse genetic approach using lines mutated in genes coding forseveral ABCG transporters which were co-expressed with genes known to participate in thebiosynthesis of suberin. The results of these analyses confirmed that the export processinvolves several proteins that can have redundant functions, and supported the involvement ofa new transporter in the export of the suberin precursors.

Soil organic matter (SOM) contains about twice the amount of carbon in the atmosphere. With global changes, the potential shifts in SOM quantity and quality are a major concern. Due to its heterogeneity, SOM remains largely unknown in terms of its molecular composition and responses to climatic events. Traditional bulk soil analysis cannot depict the structural changes in SOM. This thesis applies two complementary molecular-level methods, i.e., SOM biomarker gas chromatography/mass spectrometry (GC/MS) and nuclear magnetic resonance (NMR) spectroscopy, to examine the origin and degradation of various SOM components in grassland and temperate forest soils, and to investigate the shifts in microbial community and SOM composition with both laboratory- and field-simulated global changes, such as frequent freeze-thaw cycles, increasing soil temperatures, elevated atmospheric CO2 levels, and nitrogen (N) deposition. This thesis has several major findings. First, as the most active component in soil, microbial communities were sensitive to substrate availability changes resulting from prolonged soil incubation, freeze-thaw-induced cell lyses, N fertilization and increased plant inputs under elevated CO2 or soil warming. Microbial community shifts have direct impacts on SOM decomposition patterns. For instance, an increased fungal community was believed to contribute to the enhanced lignin oxidation in an in situ soil warming experiment as the primary degrader of lignin in terrestrial environments. Second, contrast to the conventional belief that aromatic structure was recalcitrant and stable in SOM, ester-bond aliphatic lipids primarily originating from plant cutin and suberin were preferentially preserved in the Canadian Prairie grassland soil profiles as compared with lignin-derived phenols. Cutin- and suberin-derived compounds also demonstrated higher stability during soil incubation. With an increased litter production under elevated CO2 or global warming, an enrichment of alkyl structures that had strong contributions from leaf cuticles was observed in the Duke Forest Free Air CO2 Enrichment (FACE) and soil warming experiments, suggesting an accumulation of plant-derived recalcitrant carbon in the soil. These results have significant implications for carbon sequestration and terrestrial biogeochemistry. Overall, this thesis represents the first of its kind to employ comprehensive molecular-level techniques in the investigation of SOM structural alterations under global changes.

Soil organic matter (SOM) contains about twice the amount of carbon in the atmosphere. With global changes, the potential shifts in SOM quantity and quality are a major concern. Due to its heterogeneity, SOM remains largely unknown in terms of its molecular composition and responses to climatic events. Traditional bulk soil analysis cannot depict the structural changes in SOM. This thesis applies two complementary molecular-level methods, i.e., SOM biomarker gas chromatography/mass spectrometry (GC/MS) and nuclear magnetic resonance (NMR) spectroscopy, to examine the origin and degradation of various SOM components in grassland and temperate forest soils, and to investigate the shifts in microbial community and SOM composition with both laboratory- and field-simulated global changes, such as frequent freeze-thaw cycles, increasing soil temperatures, elevated atmospheric CO2 levels, and nitrogen (N) deposition. This thesis has several major findings. First, as the most active component in soil, microbial communities were sensitive to substrate availability changes resulting from prolonged soil incubation, freeze-thaw-induced cell lyses, N fertilization and increased plant inputs under elevated CO2 or soil warming. Microbial community shifts have direct impacts on SOM decomposition patterns. For instance, an increased fungal community was believed to contribute to the enhanced lignin oxidation in an in situ soil warming experiment as the primary degrader of lignin in terrestrial environments. Second, contrast to the conventional belief that aromatic structure was recalcitrant and stable in SOM, ester-bond aliphatic lipids primarily originating from plant cutin and suberin were preferentially preserved in the Canadian Prairie grassland soil profiles as compared with lignin-derived phenols. Cutin- and suberin-derived compounds also demonstrated higher stability during soil incubation. With an increased litter production under elevated CO2 or global warming, an enrichment of alkyl structures that had strong contributions from leaf cuticles was observed in the Duke Forest Free Air CO2 Enrichment (FACE) and soil warming experiments, suggesting an accumulation of plant-derived recalcitrant carbon in the soil. These results have significant implications for carbon sequestration and terrestrial biogeochemistry. Overall, this thesis represents the first of its kind to employ comprehensive molecular-level techniques in the investigation of SOM structural alterations under global changes.