RESUMO

Two species of perennial Phyllanthus (Euphorbiaceae) (Phyllanthus orbicularis and Phyllanthus discolor, both endemic to ultramafic areas of Cuba, and their natural hybrid, Phyllanthus xpallidus) were selected for metal localization microanalysis. Different plant tissues were analyzed by X-ray fluorescence, inductively coupled plasma-atomic emission spectroscopy, and scanning electron microscopy coupled with an energy-dispersive X-ray probe. All of the studied taxa are nickel (Ni) hyperaccumulators and significant concentrations of this element were found in different leaf and stem tissues. The highest Ni content was found in the laticifer tubes, whereas leaf epidermis Ni content resulted to be much more relevant in terms of total metal storage. Calcium and magnesium were found more evenly distributed in leaf and stem tissues.

Assuntos

Euphorbiaceae/metabolismo , Níquel/metabolismo , Solo , Álcalis , Cuba , Euphorbiaceae/ultraestrutura , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura

RESUMO

Extraordinary uptake of nickel (Ni), reaching concentrations of 0.1-5.0%, c. 1000 times greater than those usually found in flowering plants, has been observed previously in c, 190 species that grow on Ni-rich serpentine soils derived from ultramafic rocks in various parts of the world. These so-called hyperaccumulators of Ni include c. 50 species from the rich ultramafic flora of New Caledonia and c. 80 species from the Brassicaceae of Mediterranean Europe and Turkey. A study of a limited part (the families Buxaceae and Euphorbiaceae) of the very large ultramafic flora of Cuba has now identified this as the home of at least 80 hyperaccumulators, the largest number jet found in any one country. The more frequent incidence here of this unusual form of plant behaviour is linked to the very long period (r. 10-30 million years) during which some of the Cuban ultramafic substrata are believed to have been continuously available for colonization; the distribution of Ni hyperaccumulators between older and younger ultrarnafic soils in Cuba mirrors the overall incidence of endemic species in these areas.