First published online June 28, 2002; 10.1104/pp.001651
Plant Physiol, August 2002, Vol. 129, pp. 1763-1772
Inhibition of Phosphate Uptake in Corn Roots by Aluminum-Fluoride
Complexes1
Arnoldo Rocha
Façanha* and
Anna L.
Okorokova-Façanha
Laboratório de Biologia Celular e Tecidual and
Laboratório de Fisiologia e Bioquímica de Microrganismos,
Centro de Biociências e Biotecnologia, Universidade Estadual do
Norte Fluminense, Campos dos Goytacazes-RJ, CEP 28015-620, Brazil
F forms stable complexes with Al at conditions found in the soil.
Fluoroaluminate complexes (AlFx) have been widely described as effective analogs of inorganic phosphate (Pi) in Pi-binding sites of several proteins. In this work, we explored the possibility that the phytotoxicity of AlFx reflects their activity as
Pi analogs. For this purpose, 32P-labeled phosphate uptake
by excised roots and plasma membrane H+-ATPase activity
were investigated in an Al-tolerant variety of maize (Zea
mays L. var. dwarf hybrid), either treated or not with AlFx. In vitro, AlFx competitively inhibited
the rate of root phosphate uptake as well as the H+-ATPase
activity. Conversely, pretreatment of seedlings with AlFx in vivo promoted no effect on the H+-ATPase activity,
whereas a biphasic effect on Pi uptake by roots was observed. Although
the initial rate of phosphate uptake by roots was inhibited by
AlFx pretreatment, this situation changed over the
following minutes as the rate of uptake increased and a pronounced
stimulation in subsequent 32Pi uptake was observed. This
kinetic behavior suggests a reversible and competitive inhibition of
the phosphate transporter by fluoroaluminates. The stimulation of root
32Pi uptake induced by AlFx pretreatment was
tentatively interpreted as a phosphate starvation response. This report
places AlF3 and AlF4 among
Al-phytotoxic species and suggests a mechanism of action where the
accumulation of Pi-mimicking fluoroaluminates in the soil may affect
the phosphate absorption by plants. The biochemical, physiological, and
environmental significance of these findings is discussed.
1
This work was supported by the Conselho Nacional
de Desenvolvimento Científìco e
Tecnológico (grant no. 465918/00-0), by the
Fundação de Amparo à Pesquisa do Estado de Rio
de Janeiro (grant no. E-26/172.333/00), and by the
Fundação Estadual do Norte Fluminense. Part of this
work was presented in the 11th Workshop on Plant Membrane Biology
(Cambridge, 1998) and in the Gordon Research Conference on Water and
Salt Stress in Plants (Oxford, 1998).
*
Corresponding author; e-mail arnoldo{at}uenf.br; fax
55-22-27261514.
© 2002 American Society of Plant Physiologists
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