Aluminum: an essential element for the growth and development of Borreria latifolia (Aubl.) K. Schum (Rubiaceae).

Main conclusion: We demonstrated that Al is essential for the growth and development of Borreria latifolia, as it is a crucial element to ensure the activity of the apical meristems. This study is the first to indicate Al as an essential element for a herbaceous plant native to the Cerrado. Although aluminum (Al), in the form of the trivalent cation (Al³⁺), is toxic to most plants, the benefits of this metal have already been highlighted for some species in acidic soils. Here, through morphophysiological evaluations of individuals grown in the absence and presence of Al, we aimed to understand the role of this metal in Borreria latifolia (Aubl.) K. Schum. (Rubiaceae), an Al-hyperaccumulator species found in the Brazilian savanna. We subjected plants to the absence of Al (T0) throughout the experiment (57 days) and the absence of Al for 40 days, followed by the addition of 500 µM Al for 17 days (T0 + 500) in hydroponic culture. We performed morphoanatomical, nutritional, and growth analyses, as well as evaluations of malondialdehyde concentration, electrolyte leakage, SPAD index, and Al histolocalization using light and confocal microscopy. Nutritional and oxidative stress in the T0 individuals led to the appearance of leaf chlorosis and necrosis, death of the apical meristems, and gelatinization of the roots. Consequently, the plants showed a reduced biomass, while growth and development ceased. After Al supplementation (T0 + 500), we stimulated meristematic activity with the formation of new roots and adventitious buds in the stem, and both plant growth and development were restored. We were then able to identify new sites of Al accumulation, such as vessel elements and colleters in B. latifolia. It is evident that the absence of Al leads to the cessation of meristematic activity and the occurrence of necrosis in the root and stem apices, thereby impeding growth and development of the plants.