RESUMEN
Nod factor [NodRm-IV(Ac,S)], isolated from the bacterium Rhizobium meliloti, induces a well-known depolarization in Medicago sativa (cv Sitel) root hairs. Analysis of this membrane response using the discontinuous single-electrode voltage-clamp technique (dSEVC) shows that anion channel, K+ channel and H+-ATPase pump currents are involved in young growing root hairs. The early Nod-factor-induced depolarization is due to increase of the inward ion current and inhibition of the H+ pump. It involved an instantaneous inward anion current (IIAC) and/or a time-dependent inward K+ current (IRKC). These two ion currents are then down-regulated while the H+ pump is stimulated, allowing long-term rectification of the membrane potential (Em). Our results support the idea that the regulation of inward current plays a primary role in the Nod-factor-induced electrical response, the nature of the ions carried by these currents depending on the activated anion and/or K+ channels at the plasma membrane.
Asunto(s)
Canales Iónicos/efectos de los fármacos , Canales Iónicos/metabolismo , Lipopolisacáridos/farmacología , Medicago sativa/efectos de los fármacos , Medicago sativa/metabolismo , Señalización del Calcio/efectos de los fármacos , Cinética , Medicago sativa/microbiología , Potenciales de la Membrana/efectos de los fármacos , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/metabolismo , Raíces de Plantas/microbiología , Canales de Potasio/efectos de los fármacos , Canales de Potasio/metabolismo , Bombas de Protones/efectos de los fármacos , Bombas de Protones/metabolismo , Sinorhizobium meliloti/metabolismoRESUMEN
In Hevea, rubber synthesis is confined to the cytosol of the highly differentiated laticifer cells. Agronomic and biochemical studies showed that this process uses high amounts of sugars that are efficiently imported into the laticifer. A H(+)-sugar symport system located in the plasma membrane is involved in sugar uptake into laticifers. Laticifer protoplasts were prepared and used in electrophysiological and labeling experiments to test the capacity of this system to transport a variety of sugars such as oligosaccharides from the raffinose family, trace compounds in rubber. Translocation of sugars known to be transported with different efficiency across the plasma membrane of plant cells was also tested. A 1 mM sucrose affinity was found for the symport. All the sugars tested, except palatinose induce membrane depolarization indicating that they were actively absorbed by the laticifer network. This reveals the wide capacity of this peculiar sink for the uptake of sugars.