Abstract
In acidic soil, aluminum (Al) ionizes into trivalent cation and becomes highly toxic to plants. Thus, the objectives of this work were (i) to evaluate the Al concentration and identify sites of Al toxicity and its effect on the structure on rice root tips and (ii) to elucidate the adjustments involved in the activities/contents of enzymes/compounds in the roots against Al. For this, two genotypes with contrasting Al tolerance were used. Our results showed that the root length of the tolerant genotype was not affected after Al exposure. We also observed that both the genotypes used strategies to avoid Al uptake, such as the overlap of P and Al in the tolerant genotype and the presence of border cells in the sensitive genotype, which proved inefficient. In the tolerant genotype, other external Al detoxification mechanisms may have contributed to the lower Al concentration in roots and lower fluorescence of the Al-lumogallion complex. Additionally, both genotypes present the activation of key enzymes to decrease oxidative stress, such as CAT, POX, APX, and DHAR, and a more reducing redox environment, mainly due to the increase in the AA/DHA ratio. However, higher total ascorbate, AA, total glutathione, and GSH contents associated with higher SOD, GPX, and GR activities contributed to the reduction of oxidative stress in the tolerant genotype after Al exposure. Furthermore, there was a strong association between the sensitive genotype to Al concentration, O(2) (•-) content, and MDA amount; therefore, these traits can be used as sensitivity indicators in Al studies.