Salinity usually reduces plant growth in terms of height and biomass, but can increase secondary metabolite production. This frequently reported observation in guayule (Parthenium argentatum Gray, Asteraceae) was investigated for possible mechanisms.Osmotic and specific ion effects of four chloride salts (CaCl2, MgCl2, KCl, and NaCl) on leaf anatomical and plant physiological parameters were studied. One-year-old plants of guayule line AZ 2 were grown under two salt concentrations (750 ppm and 1500 ppm) for each salt type (plus a control) in sand culture (semi-hydroponic) for eight weeks under controlled greenhouse conditions in Tucson, Arizona.Growth in height decreased with increasing salt concentration. Shoot dry weight, rubber, and resin contents, however, showed no significant differences between treatments, indicating no effect from either salt concentration or salt type. There was a trend for increasing rubber content with increasing salt concentration, although not statistically significant. At the same time, net CO2 gas exchange rates decreased significantly with increasing salinity.With increasing salt concentration, guayule showed osmotic effects in terms of height, indicating a lower hydraulic conductivity. Although plants of higher salt concentrations utilized significantly less water, they had the same shoot dry weights, rubber, and resin contents. Salt-stressed plants therefore achieved higher water use efficiencies. The diurnal net CO2 gas exchange rates were significantly reduced with increasing salinity; the nocturnal net CO2 gas exchange rates showed no significant difference between the treatments.Anatomically, it was found that the stomata were raised or elevated above the epidermis, and supported by upwardly curving cells. When guayule was grown under salt treatments, the trichomes were found to include deposits of material. Trichomes might act as a detoxification repository for excess ions. Although the physiological significance of raised stomata is unknown, it is hypothesized that the unique combination of raised stomata, indumentum, and multiple layers of palisade parenchyma allows for an overall high photosynthetic capacity and performance. During stress conditions such as salinity or drought, guayule might activate an internal CO2 concentrating mechanism, i.e., bicarbonate/CO2 pump, internal CO2 recycling, or PEP carboxylation activity.

La formation d’un squelette de CaCO3 par les coraux Scléractiniaires est à la base de l’édification des récifs coralliens. Nombre de ces coraux constructeurs de récif vivent en symbiose avec des Dinoflagellés photosynthétiques. Ces deux processus reposent sur le transport et l’utilisation de carbone inorganique (Ci) provenant de l’eau de mer pour la photosynthèse, et du métabolisme animal pour la calcification. Cette thèse s’est intéressée à l’étude moléculaire et physiologique des mécanismes, permettant l’utilisation de ce carbone inorganique.Malgré l’importance des transports de HCO3-, aucun transporteur n’a été caractérisé à cejour et leur implication dans la physiologie des coraux n’est que suggérée par la pharmacologie. Durant cette thèse nous avons cloné un gène codant pour un transporteur deHCO3- chez le corail Acropora sp. La conversion de ce HCO3- en CO2 pour la photosynthèse est facilitée par l’acidification de l’environnement proche du Dinoflagellé dans la cellule animale. Cette acidification est causée par une H+-ATPase de type P que nous avons caractérisée. Ce gène est le premier à montrer une expression dépendante de la vie en symbiose chez le symbiote.Nous avons aussi cloné et localisé deux anhydrases carboniques (AC). L’une impliquée dans la calcification et l’autre dans la régulation du pH intracellulaire et l’équilibre entre leCO2 et HCO3-. Une étude pharmacologique de ces deux AC, a identifié des molécules inhibitrices et activatrices qui ont permis des expériences de physiologie in vivo. Celles-ci permettent une analyse plus discriminante du rôle des AC dans la calcification. / Coral reefs edification is based on the formation of a calcium carbonate skeleton byscleractinian corals. Many of these reef-building corals establish a symbiotic association with photosynthetic Dinoflagellates. Both processes involve the transport and utilization of inorganic carbon (Ci) coming from seawater for photosynthesis, and from animal metabolismfor calcification. This work focused on the molecular and physiological study of poorlyknown mechanisms that allow the utilization of Ci.Despite the importance of bicarbonate transport, no transporter has been characterized and their role in coral physiology is only suggested by pharmacological experiments. We have cloned a gene encoding a bicarbonate transporter in the coral Acropora sp. The conversion of this bicarbonate into CO2 for photosynthesis is mediated by the acidification of the are asurrounding the Dinoflagellate in the animal cell. This is performed by a P type H+-ATPasethat we characterized here. This is the first gene with a symbiosis-dependent expression in the symbiont.This work also allowed the cloning and the localization of two carbonic anhydrases (CA).The first one is involved in calcification, the second one plays a role in the intracellular pHregulation and the CO2 / HCO3- equilibrium. A pharmacological study of these two enzymes identified inhibitor and activator compounds that have been then used in physiology experiments. This last approach represents a more accurate study of the role of CAs incalcification.