Kinetics of phosphate absorption byStylosanthesspp. in the presence of aluminium

Abstract

The mechanisms of action by which aluminium affects phosphate absorption were evaluated in Stylosanthes guianensis (aluminium-sensitive)and Stylosanthes macrocephala (aluminium-tolerant), through kinetic studies with aluminium in pre-and co-treatment. Multiphasic and cooperative models of ions absorption were tested. In the absence of aluminium, S. guianensis, a specie which normaly requires more phosphorus, showed lower rates of phosphate absorption, which was attributed to slower turnover of the carrier. In S. guianensis, the higher rates of absorption may be related to higher turnover and/or higher concentration of the carrier in the roots. Both species showed negative correlation in the absorption of phosphate, but it was more pronounced in S.guianensis. The effect of aluminium seems to be related to the decreased capacity of the carrier to associate with the ion. There may also be a reduction in the turnover of the carrier, which appears to be more pronounced in the tolerant species, reducing phosphate absorption. In the presence of aluminium, the association becomes positive or approaches Michaelis-Menten kinetics in both species.However, the absorption of phosphate is not increased since there is also a reduction in the capacity of the carrier to bind to the ion.

Effects of aluminum, nitrate and ammonium on the growth, potassium content and composition of amino acids in Stylosanthes

“…One toxic effect of the aluminum in plants is the interference in absorption of minerals, especially phosphorus (Foy et al, 1978;Machado et al, 1992;Marschner, 1995). The studies of the absorption kinetics in Stylosanthes, Machado et al (1992) concluded that the reduction in the absorption rate of phosphorus by aluminum cannot elucidate the physiological mechanism that grants some plants differential tolerance to this element, but a generalized action of aluminum in plasmalemma entail changes in phosphate transport system.…”