Abstract
One of the major limitations to plant growth and yield in acidic soils is the prevalence of soluble aluminum ions (Al3+) in the soil solution, which can irreversible damage the root apex cells. Nonetheless, many Al-tolerant species overcome Al toxicity and are well-adapted to acidic soils, being able to complete their life cycle under such stressful conditions. At this point, the complex physiological and biochemical processes inherent to Al tolerance remain unclear, especially in what concerns the behavior of antioxidant enzymes and stress indicators at early plant development. Since rye (Secale cereale L.), is considered the most Al-tolerant cereal, in this study we resort to seedlings of two genotypes with different Al sensitivities in order to evaluate their oxidative metabolism after short term Al exposure. Al-induced toxicity and antioxidant responses were dependent on rye genotype, organ and exposure period. Al affected biomass production and membrane integrity in roots and leaves of the sensitive (RioDeva) genotype. Catalase was the primary enzyme involved in H2O2 detoxification in the tolerant (Beira) genotype, while in RioDeva this task was mainly performed by GPX and POX. Evaluation of the enzymatic and non-enzymatic components of the ascorbate–glutathione cycle, as well the oxalate content, revealed that Beira genotype coped with Al stress by converting DHA into oxalate and tartarate, which posteriorly may bind to Al forming non-toxic chelates. In contrast, RioDeva genotype used a much more ineffective strategy which passed through ascorbate regeneration. So, remarkable differences between MDHAR and DHAR activities appear to be the key for a higher Al tolerance.
Highlights
30–40% of the world’s potentially arable lands are acidic soils, on which Al is the main factor that limits plant growth and crop production (Kochian et al, 2004)
Negative controls of selected parameters were performed in a second group of plants grown on the same conditions stated before, but without Al in order to differentiate between Al toxicity effects and development effects
Our results suggest that biological membranes are one of the targets of oxidative stress in rye under Al short-term exposure
Summary
30–40% of the world’s potentially arable lands are acidic soils, on which Al is the main factor that limits plant growth and crop production (Kochian et al, 2004). Observing that some plant species exhibited natural tolerance to Al toxicity in fields, producers started to ask for the development of new crop varieties with similar characteristics that would allow them to direct future agricultural expansion onto acid soils. Since a great inter- and intraspecific variability has been observed for Al tolerance, several efforts are in progress in order to identify major genes and associated biochemical and physiological processes underlying Al resistance in Al-tolerant genotypes. This will provide important resources for further improvement of crop resistance for Al toxicity trough breeding programs. Uncovering the genetic, molecular and physiological mechanisms involved in rye Al tolerance will provide vital information that can be used to increase Al tolerance in other cereals, such as wheat and Triticale
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