Estrés per metalls pesantsrespostes fisiològiques induïdes per Cd i Ni en arròs (Oryza sativa L).

Abstract

Some physiological responses of rice plants to two heavy metals, Cd and Ni, have been studied during the first stages of their development, with the following specific objectives: - Characterization of Cd and Ni effects on plasma membrane functionality. - Study of the effects of these heavy metals on energetic metabolism, which supplies the energy needed for membrane transport. - Evaluation of the changes induced by Cd and Ni in the production of ethylene, the hormone most directly related to variations in membrane stability under stress conditions. The possible interactions of these metals with other hormones have also been studied. The results obtained in these investigations indicate that: - Cd induces rapid and drastic effects on membrane permeability and transmembrane potential difference (Em). However, the effect is transient, possibly due to the existence of inducible detoxifying mechanisms. - Contrastingly, Ni treatments do not affect membrane permeability at the short term, but causes strong losses of K+ at the long term, which may be related with the reduced water content measured in Ni-treated plants. - Both metals affect drastically the photosynthetic performance, which is reflected in a strong decrease in plant growth. - At the whole plant level, respiration is not altered by any of these metals. However, a differential effect of Ni on roots and shoots is observed, indicating a change in the distribution of the energy between growth and maintenance of the tissues. - Both metals induce a decrease in ethylene production, even at metal concentrations which do not alter plant growth. - GA3, but not ABA, interacts with the inhibitory effect of the metals, causing an increase in ethylene production up to values similar to those of controls. - All the effects observed may be reverted, at least partially, by elimination of the metals from the external medium.