X-ray spectra in SEM and staining with chrome azurol S show Al deposits in leaf tissues of Al-accumulating and non-accumulating plants from the cerrado

Abstract

Aims: Aluminum (Al) accumulating plants are distributed throughout the world. In the Cerrado, Al-accumulating and non-accumulating species coexist. Therefore, we anatomically/histochemically explore the sites of Al deposits in Al-accumulating species, and we also ask whether Al can be observed in non-accumulating species. Methods: The anatomical patterns of Al storage in leaf tissues of Al-accumulating [Miconia albicans, M. rubiginosa (Melastomataceae), Qualea grandiflora, and Q. parviflora (Vochysiaceae)] and non-accumulating species [(Styrax ferrugineus and S. camporum (Styracaceae)] were described using different Al indicator dyes: hematoxylin and chrome azurol S (CAS). In addition, Al-specific x-ray spectra from different regions of leaf tissues were measured and analyzed by scanning electron microscopy (SEM). Results: When compared to hematoxylin, it was confirmed by x-ray spectra in SEM that CAS was a more contrasting indicator of Al presence. Silica granules associated to Al were observed on cell walls of non-lignified leaf tissues of Al-accumulating species. However, granules were also found in leaf midribs of S. camporum. Conclusions: The anatomical description of Al accumulation in leaves and the consistent pattern of Al association with cell walls strongly suggest that Al has structural rather than physiological roles in leaves of Cerrado woody plants, and that Al is perhaps isolated from metabolism.