Aluminum modulates the morphophysiological plasticity of Borreria latifolia (Aubl.) K. Schum. (Rubiaceae) an herbaceous hyperaccumulates this metal

Abstract We investigated the role of Aluminum (Al) as a limiting factor for the development of Borreria latifolia , analyzing morphophysiological changes, subcellular accumulation sites, and its interaction with pH on biomass increment. We evaluated biomass fluctuation under different Al concentrations of 0, 250, 500, and 750 µM, and the combined effect of Al (presence/absence) under pH 3.5, 4.5, or 5.5. The beneficial effects on both root and shoot development were dependent upon both Al concentration and medium pH. The concentration of 750 µM Al at pH 4.5 induced the highest dry mass buildup. In the absence of Al, the pH gradient did not affect plant growth, but the addition of Al (pH 4.5) promoted dry mass increases of 34% and 47% in root and shoot dry mass, respectively. Al deprivation triggered anatomical changes, root apical cell necrosis and meristem cell abnormalities. In contrast, Al-treated plants were morphologically similar to field-grown specimens. The Al was located in tissues with high metabolic activity and at subcellular level in nuclei of root meristematic cells and chloroplasts. These facts suggest the involvement of Al in vital physiological functions for the maintenance of the meristems. Regarding antioxidant enzymes, Al had a minor modulating effect, with higher activity in the leaves. We conclude that pH is a secondary factor, whereas Al plays a direct role, and its absence is considered a limiting factor for Borreria latifolia development.