Effects of aluminum on the external morphology of root tips in rice

Acid soils with elevated aluminum (Al) saturations are worldwide distributed and harm the crop production in most of the tropical and subtropical regions. The initial and most dramatic symptoms of Al toxicity are changes on the external morphology and inhibition of elongation of roots. These changes have served as a marker for level of Al toxicity and the ability of plants tolerate this metal. Therefore, the goal of this study was to evaluate the Al effects on the growth root and the external morphology of root tips in two rice genotypes: Fernandes (CNA-1158) and Maravilha (CNA-6843-1), tolerant and sensitive to Al, respectively. The genotypes were treated with 0 and 1 mM of Al in Clark’s solution for different times (3, 6 and 9 days). The contents and the distribution of Al in root tips, as well as its morphology, were analyzed. After Al exposure, the content of this metal was higher in Al-sensitive genotype leading to inhibition of root length and decrease in root dry matter production, after the sixth day of treatment. Additionally, Al accumulation in the root tips (0–3 mm) of both genotypes was detected mainly in root cap cells. We also observed damage in the external micromorphology of the root tips, especially in the Al-sensitive Maravilha genotype. Al accumulation in root tips of this genotype induced cellular disorganization in the root cap cells, resulting in the peeling of the superficial layers. Overall, our findings evidenced the higher tolerance of one of genotypes (genotype Fernandes) to Al.