Aluminum bioaccumulation and tolerance in Plantago algarbiensis Samp. and Plantago almogravensis Franco, assessed by using in vitro cultures and micropropagated plants

摘要

This thesis aims to understand the aluminum (Al) bioaccumulation capacity, toxicityeffects and tolerance mechanisms in two rare species endemic from Portugal, Plantagoalgarbiensis Samp. and Plantago almogravensis Franco. Firstly, two protocols weredeveloped to propagate in vitro these species (Chapter 2). Afterwards it wasinvestigated the influence of low pH on in vitro growth (Chapter 3). The seedgermination requirements and the effects of Al on the germination and earlydevelopment of seedlings were then evaluated in Chapters 4 and 5, respectively. Theimpact of low pH and Al on physiological responses, oxidative stress status andcapacity for Al accumulation in micropropagated shoots and plantlets was investigatedin the subsequent chapters (Chapters 6, 7 and 8). Finally, in Chapter 9 the possibleimplications of organic acids in Al detoxification were evaluated.Both species were successfully micropropagated showing high shoot multiplicationrates and rooting frequencies and the micropropagated shoots of both species were ableto tolerate and grow in low pH conditions. The seeds of both species germinate readilyat 15 ºC and Al showed no impact on the germination percentage in either species butoxidative stress during early seedling development was detected. Although, both speciesaccumulated considerable Al amounts and showed to be moderately tolerant to low pHand Al, P. almogravensis appeared to be more able to manage the oxidative stress and,therefore, adapted to maintain cellular physiology and growth under these stressconditions. Results suggested that Al detoxification in P. almogravensis implies bothsecretion of organic acids from roots and Al intracellular chelation by organic acids,while in P. algarbiensis only the internal mechanism seems to be involved. Thisresearch contributes to the understanding of the mechanisms underlying P. algarbiensisand P. almogravensis adaptation to acidic Al-rich conditions.