Vol.:(0123456789) 1 3 Brazilian Journal of Botany (2020) 43:413–418 https://doi.org/10.1007/s40415-020-00620-9 PHYSIOLOGY AND BIOCHEMISTRY - SHORT COMMUNICATION Efects of aluminum on the external morphology of root tips in rice Danielle Santos Brito 1  · Roberto Neri‑Silva 1  · Karla Veloso Gonçalves Ribeiro 2  · Paulo Henrique Pereira Peixoto 3  · Cleberson Ribeiro 1 Received: 6 April 2020 / Accepted: 16 June 2020 / Published online: 25 June 2020 © Botanical Society of Sao Paulo 2020 Abstract 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 morphol- ogy 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 efects 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 sensi- tive to Al, respectively. The genotypes were treated with 0 and 1 mM of Al in Clark’s solution for diferent 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 superfcial layers. Overall, our fndings evidenced the higher tolerance of one of genotypes (genotype Fernandes) to Al. Keywords Acid soils · Energy-dispersive X-ray spectrometry · Oryza sativa · Root cap · Root growth · Scanning electron microscopy 1 Introduction Aluminum (Al) is the most abundant metal and the third most common element in the Earth’s crust (Yang et al. 2017a). When soils become acidic (pH < 5.0), Al ionizes producing the phytotoxic trivalent cation (Al 3+ ), that is readily absorbed by plant roots. In such soils, the toxicity caused by this metal is one of the main factors that limit plant growth and development (Zhang et al. 2018). The cell wall is the frst Al-target where negative charges of the carboxyl groups present in the pectin contribute to the binding of this metal (Nagayama et al. 2019). The Al can remain linked to the cell wall or be absorbed and accumu- late within the cells inducing structural and/or physiologi- cal changes to roots, such as a reduction in length of lateral roots and root hairs, color change, thickening, atrophy, roots curvature, and accumulation of organic acids (Čiamporová 2002). Studies have shown that the root tip is the major percep- tion site of Al toxicity which accumulates preferentially in the distal transition zone (DTZ) and promotes rapid inhi- bition of root elongation and reduction in cell division (Kopittke et al. 2015; Singh et al. 2017; Kusunoki et al. 2018; Nagayama et al. 2019). The inhibition of root elonga- tion is followed by changes in its architecture, callose pro- duction, and lignin deposition, which reduce the ability of a plant to uptake water and nutrients, and consequently limit the growth (Kochian 1995; He et al. 2012). Since the dam- age intensity induced by Al depends on the plant develop- ment stage, metal concentration and plant tolerance as well as between genotypes from the same species (Tahara et al. * Cleberson Ribeiro cleberson.ribeiro@ufv.br 1 Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, Minas Gerais 36570-900, Brazil 2 Núcleo de Microscopia e Microanálise, Universidade Federal de Viçosa, Viçosa, Minas Gerais 36570-900, Brazil 3 Departamento de Botânica, Universidade Federal de Juiz de Fora, Juiz De Fora, Minas Gerais 36036-900, Brazil