Abstract
The use of fungicides containing copper (Cu) is the most effective strategy to cope with the downy mildew deses in viticulture. Their application started at the beginning of the 19th century causes Cu accumulation in the upper soil layers inducing symptoms of Cu toxicity in plants with a shallow root apparatus as young grapevines or herbaceous plants. Consequently, different strategies have been developed to reduce soil Cu concentration, but they are often environmental unfriendly and expansive. Instead, phytoremediation and Plant Growth Promoting Rhizobacteria (PGPR) are promising tools to reduce the effects of Cu toxicity on plants respecting the environment. Since plant Cu toxicity symptoms are strongly linked to rhizosphere processes, the aim of this thesis is to elucidate the rhizosphere processes involved in Cu toxicity and how they are influenced by the most promising agronomic remediation strategies. In the first work, the effects of different Cu concentrations on a Brazilian oat cultivar used in Brazil as cover crops in vineyards were assessed in hydroponic. Moreover, another oat cultivar, used in Italy, has been compared to the previous one revealing different detoxification strategies depending on the oat cultivar. The Brazilian cultivar revealed an external detoxification strategy based on exudation and Cu immobilization in root apoplast, so it was used in consociation with two grapevine rootstocks in an intercropping growing system in hydroponic in the second work. The ionomic analysis performed on different grapevine tissues revealed synergisms and antagonisms between Cu and some micronutrients. Moreover, the biomass measurement and the quantification of exudation revealed that the two rootstocks have different strategies to cope with Cu toxicity and intercropping. To unravel the molecular mechanisms causing the different strategy, the transcription of bivalent cations transporters and the analysis of root architecture was performed in the third work, which confirmed and explain the differences reported in the previous work. The intercropping strategy was then tested in a soil based experiments in the fourth work that pointed out the importance of the soil characteristics in the intercropping system. Finally, the use of a PGPR was tested in alleviating Cu toxicity in a dicotyledonous model plat (i.e. Cucumis sativus L.) in hydroponic. The study highlighted that the PGPR is able to reduce the accumulation of Cu in cucumber roots at high Cu concentrations. Moreover, this work indicated different inductions of Ferric-chelate reductase (FCR) genes depending on Cu concentration and PGPR inoculation.
Concluding, this thesis study two different Cu toxicity remediation strategies and the molecular mechanisms behind. The results increase the knowledge of using the intercropping and PGPR strategies in Cu contaminated sites. Moreover, this thesis give new insights in plant interaction mechanisms that could be a starter point for further studies.