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Accueil du site → Doctorat → Allemagne → Untersuchungen zur Mikromorphologie und chemischen Zusammensetzung der Cuticularwachse bei den Gattungen Calicorema, Arthraerua und Leucosphaera (Amaranthaceae) in Namibia

University Hohenheim (2008)

Untersuchungen zur Mikromorphologie und chemischen Zusammensetzung der Cuticularwachse bei den Gattungen Calicorema, Arthraerua und Leucosphaera (Amaranthaceae) in Namibia

Dinter, Ina

Titre : Untersuchungen zur Mikromorphologie und chemischen Zusammensetzung der Cuticularwachse bei den Gattungen Calicorema, Arthraerua und Leucosphaera (Amaranthaceae) in Namibia

Investigations on the micromorphology and chemical composition of cuticular waxes of the genera Calicorema, Arthraerua and Leucosphaera (Amaranthaceae) in Namibia

Auteur : Dinter, Ina

Université de soutenance : University Hohenheim

Grade : Doctor of Philosophy PhD 2008

Résumé
Epidermal characters and especially cuticular waxes were examined in the genera Calicorema, Arthraerua and Leucosphaera (Amaranthaceae). They are chlorophyllous-stemmed shrubs of the Retama type. These drought resistant xerophytes maintain normal metabolic activity in more or less intact shoot systems even at longer lasting periods of severe dryness. Adaptations for drying delay are of crucial importance in Namibia, especially in the Namib desert which represents the dryest part of Southern Africa. Therefore, the investigations focused on the possibilities for improved water uptake, efficient water conduction, water storage, and the restriction of transpiration in the four species of Amaranthaceae. The most important adaptations for survival under drought stress serve to minimize transpiration. These are xeromorphic characters referring the interface between plants and their environment. The combined occurrence of epicuticular and intracuticular waxes, cuticular layers, and trichomes is a remarkable feature of the species examined. These properties act synergistically to optimize the surface functions. Cuticular transpiration is considerable reduced by the wax incrustation of cuticular layers. The dense arrangement of wax crystals in the epistomatal spaces minimizes stomatal transpiration without affecting gas exchange. The hydrophobic chemistry of the epicuticular waxes, their micro-roughness, and resulting unwettability cause the self-cleaning properties (so-called lotus-effect) of the surfaces to protect e.g. against pathogens. Reflectance of irradiation is a further effect of epicuticular wax crystals which prevents the plants from overheating. The mechanical protection mediated by cuticular layers (so-called thick cuticles), epicuticular wax crystals, and trichomes enables resistance to abrasion by wind-borne sand particles which turn out to increased transpiration, overheating, and infections. For the first time, epicuticular wax crystals are shown to occur in the Amaranthaceae. Intracuticular wax is also present. These wax parts are extracted separately from different shoot regions. The wax extracts contain the aliphatic substance classes of alkanes, esters, aldehydes, primary alcohols and free fatty acids. Partial solvent resistance of epicuticular wax crystals in Calicorema capitata and Arthraerua leubnitziae is indicative of polymeric aldehydes. They are insoluble at room temperature but readily dissolve in hot chloroform by cleavage of polymer bonds. A similar solubility was found in primary alcohols with the characteristic increase of amounts in hot solvent. The solvent resistance of epicuticular waxes could be explained by a co-crystallization of primary alcohols and polymeric aldehydes. The mechanical stability mediated by the chemical properties could be of considerable ecological importance in arid habitats : Increased protection against surface abrasion would reduce cuticular transpiration

Mots Clés : Amaranthaceae, Calicorema , epicuticular wax , polymeric aldehydes , xeromorphic adaptations

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Page publiée le 13 septembre 2010, mise à jour le 23 septembre 2017