Aluminium Tolerance Mechanisms in Brachiaria sp.

Abstract

This thesis considers the differential responses to Al toxicity of three contrasting Brachiaria species in order to contribute to a better understanding of the Al resistance mechanisms in these economically important fodder grasses. _x000D_ The research was divided into 5 chapters. In the first one, we evaluated the response of three Brachiaria species to aluminium toxicity. Brachiaria decumbens, B. brizantha and B. ruziziensis were grown in low ionic strength nutrient solution and pH acid. Root elongation and the ability to maintain adequate nutrient homeostasis under Al stress was evaluated by mineral analysis of roots._x000D_ In the second chapter we used different staining methods to analyse toxic effects and distribution of Aluminium in the root apex of the Brachiaria species. Localization of Al in Brachiaria roots was performed using confocal fluorescence microscopy of lumogallion or morin stained roots. In B. decumbens more efficiently excluded Al from the roots and in this species Al was localized mainly in root hair initials that developed close to the apex. These sites with high Al accumulation seem to contribute to low Al accumulation in sensitive root zones._x000D_ In the third chapter Al-induced alterations on root surface structure of two Brachiaria species were observed. SEM-EDX and TEM techniques were used for better characterizing the time dependent responses to Al in B. decumbens and B. brizantha. We found that Al induced structural and ultrastructural alterations in both Brachiaria species. However, in the Al resistant B. decumbens root recovered after 96 h exposure to Al. These results indicate the inducible character of the Al tolerance mechanism in B. decumbens_x000D_ In the fourth chapter we explored the possible implication of phenolic substances in the differential Al tolerance of B. decumbens and B. brizantha in order to contribute to a better understanding of this hyperresistance to Al in B. decumbens. The phenolics change in the presence of Al-toxicity._x000D_ Once characterize the most Al tolerant species (B. decumbens) in the last chapter the proteomic study was focused on this species. We conducted proteomic analysis of B. decumbens roots under Al stress after different exposure two times using 2-D-DIGE and MALDI-TOF analysis. A relative small number of only 11 proteins were found to be specifically up or down regulated during the first 96h of exposure to Al. Among those PAL (phenylalanine ammonia lyase) was found to be down regulated after 24 h exposure to Al, but recovered after 96 h.

Date of Award	12 Jul 2012
Original language	English
Supervisor	Charlotte Poschenrieder (Director) & Roser Tolra Perez (Director)