Inhibition of Phosphate Uptake in Corn Roots by Aluminum-Fluoride Complexes

Abstract

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 AlFxin 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 root32Pi 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.

Germinação de sementes de Erythrina speciosa Andr., Eugenia brasiliensis Lam. e Cucumis sativus L. em meio ácido

“…Apesar de terem sido realizados alguns estudos avaliando efeitos tóxicos da salinidade em sementes (Santos et al 1992, Torres et al 2000, Fonseca & Perez 2001, pouco ainda se conhece efetivamente sobre o efeito do cloro, justificando o desenvolvimento de pesquisas com esse objetivo específico. Por outro lado, vários estudos demonstraram os efeitos tóxicos do Al 3+ na germinação das sementes e, principalmente, no desenvolvimento inicial das plântulas (Rout et al 2001), como os observados no presente trabalho, frequentemente empregando o cloreto de alumínio como fonte deste último (Taylor et al 2000, Ma et al 2001, Miyasaka & Hawes 2001, Façanha & Okorokova-Façanha 2002, Ma & Furukawa 2003, Tamás et al 2004, Wang et al 2004, Tamás et al 2006.…”

“…O cloreto de alumínio é freqüentemente adotado em estudos que visam a analisar o efeito tóxico do Al sobre as espécies vegetais (Taylor et al 2000, Ma et al 2001, Miyasaka & Hawes 2001, Façanha & Okorokova-Façanha 2002, Ma & Furukawa 2003, Tamás et al 2004, Wang et al 2004, Tamás et al 2006, não havendo descrição sobre possíveis efeitos do cloro (Cl) destas soluções sobre a germinação das sementes ou sobre o desenvolvimento vegetal.…”

Aluminum impairs morphogenic transition and stimulates H+transport mediated by the plasma membrane ATPase ofYarrowia lipolytica

“…The P-type H 1 -ATPase is modulated in plants by Al (Façanha & Okorokova-Façanha, 2002;Shen et al, 2005). The P-type H 1 -ATPase is modulated in plants by Al (Façanha & Okorokova-Façanha, 2002;Shen et al, 2005).…”

“…Next, the effect of Al on plasma membrane H 1 -ATPase was analyzed. The P-type H 1 -ATPase is modulated in plants by Al (Façanha & Okorokova-Façanha, 2002;Shen et al, 2005). Additionally, extracellular pH is among the key factors involved in the regulation of dimorphism in Y. lipolytica (Ruiz-Herrera & Sentandreu, 2002;Szabo & Štofaniková, 2002).…”

Impact of Calcareous Amendments on Rye Production and the Exchange Complex in a Palexerult in Northwestern Spain

“…Thus, Al 3+ is widely regarded as the most rhizotoxic species after the highly toxic polynuclear tridecamer species Al 13 (Kochian 1995). Mononuclear Al hydroxides such as Al(OH) 2+ and Al(OH) 2 + are also seemingly toxic (Facana and Okorokova 2002;Cory 2004). In the presence of sulfate ions, Al forms ion pairs of little or no toxicity (Kinraide 1997), and in that of fluoride ions, for which Al exhibits a high affinity, the metal forms Al x F (3-x) complexes (Elrashidi and Lindsay 1986).…”