RESUMEN
Phosphate (Pi) deficiency reduces nodule formation and development in different legume species including common bean. Despite significant progress in the understanding of the genetic responses underlying the adaptation of nodules to Pi deficiency, it is still unclear whether this nutritional deficiency interferes with the molecular dialogue between legumes and rhizobia. If so, what part of the molecular dialogue is impaired? In this study, we provide evidence demonstrating that Pi deficiency negatively affects critical early molecular and physiological responses that are required for a successful symbiosis between common bean and rhizobia. We demonstrated that the infection thread formation and the expression of PvNSP2, PvNIN, and PvFLOT2, which are genes controlling the nodulation process were significantly reduced in Pi-deficient common bean seedlings. In addition, whole-genome transcriptional analysis revealed that the expression of hormones-related genes is compromised in Pi-deficient seedlings inoculated with rhizobia. Moreover, we showed that regardless of the presence or absence of rhizobia, the expression of PvRIC1 and PvRIC2, two genes participating in the autoregulation of nodule numbers, was higher in Pi-deficient seedlings compared to control seedlings. The data presented in this study provides a mechanistic model to better understand how Pi deficiency impacts the early steps of the symbiosis between common bean and rhizobia.
RESUMEN
Trace metal accumulation and thiol compounds synthesis as induced by cadmium exposure was studied in the seagrass Thalassia testudinum. Shoots were exposed for 24, 48, 96 and 144 h to several CdCl(2) concentrations (0, 30, 50 and 70 microM). Levels of cadmium, cysteine, glutathione (GSH), gamma-glutamylcysteine (gamma-EC), and phytochelatin-like peptides were determined in green blades, live sheaths and root/rhizomes tissues. Metal accumulation was dependent on Cd concentration and type of tissue, with green blades showing the highest content followed by live sheaths and root/rhizomes. All tissues experienced an increase in thiol-containing compounds as a response to cadmium exposure. Live sheaths showed the highest levels of cysteine, GSH and gamma-EC. This is the first report of induction of thiol peptides, presumably phytochelatins, by a trace metal in a sea grass species.
Asunto(s)
Cloruro de Cadmio/metabolismo , Cloruro de Cadmio/toxicidad , Hydrocharitaceae/efectos de los fármacos , Compuestos de Sulfhidrilo/metabolismo , Contaminantes Químicos del Agua/toxicidad , Cromatografía Líquida de Alta Presión , Relación Dosis-Respuesta a Droga , Hydrocharitaceae/química , Proteínas de Plantas/análisis , Proteínas de Plantas/biosíntesis , Estructuras de las Plantas/química , Estadísticas no Paramétricas , Compuestos de Sulfhidrilo/análisis , Factores de Tiempo , Distribución Tisular , Contaminantes Químicos del Agua/metabolismoRESUMEN
Euglena gracilis lacks a plant-like vacuole and, when grown in Cd2+-containing medium, 60% of the accumulated Cd2+ is located inside the chloroplast. Hence, the biochemical mechanisms involved in Cd2+ accumulation in chloroplast were examined. Percoll-purified chloroplasts showed a temperature-sensitive uptake of the free 109Cd2+ ion. Kinetics of the uptake initial rate was resolved in two components, one hyperbolic and saturable (Vmax 11 nmol 109Cd2+ min(-1) mg protein (-1), Km 13 microM) and the other, linear and non-saturable. 109Cd2+ uptake was not affected by metabolic inhibitors or illumination. Zn2+ competitively inhibited 109Cd2+ uptake (Ki 8.2 microM); internal Cd2+ slightly inhibited 109Cd2+ uptake. Cadmium was partially and rapidly released from chloroplasts. These data suggested the involvement of a cation diffusion facilitator-like protein. Chloroplasts isolated from cells grown with 50 microM CdCl2 (ZCd50 chloroplasts) showed a 1.6 times increase in the uptake Vmax, whereas the Km and the non-saturable component did not change. In addition, Cd2+ retention in chloroplasts correlated with the amount of internal sulfur compounds. ZCd50 chloroplasts, which contained 4.4 times more thiol-compounds and sulfide than control chloroplasts, retained six times more Cd2+. The Cd2+ storage-inactivation mechanism was specific for Cd2+, since Zn2+ and Fe3+ were not preferentially accumulated into chloroplasts.
Asunto(s)
Cadmio/metabolismo , Cloroplastos/fisiología , Euglena gracilis/fisiología , Animales , Transporte Biológico/fisiología , Radioisótopos de Cadmio , Cloroplastos/metabolismo , Euglena gracilis/metabolismo , Hierro/metabolismo , Cinética , Temperatura , Zinc/metabolismoRESUMEN
Intracellular distribution of Cd, cysteine, glutathione, and Cd-induced thiol peptides in Euglena gracilis cultured under photoheterotrophic conditions was studied. After 3 days of culture with 0.2 mM CdCl2, 62% of the Cd accumulated by cells was equally distributed between the cytosolic and chloroplastic fractions. However, after 8 days, metal content increased in the crude chloroplastic fraction to 40% of total and decreased to 19% in the cytosol; in Percoll-purified chloroplasts the estimated content of Cd raised to 62%. Accumulation of Cd in chloroplasts could be mediated by a transporter of free Cd2+, since uptake of added CdCl2 in isolated chloroplasts exhibited a hyperbolic type of kinetics with a Km of 57 &mgr;M and Vmax of 3.7 nmol (mg protein)-1 min-1. The contents of cysteine and glutathione markedly increased in both chloroplasts (7-19 times) and cytosol (4-9 times) by exposure to Cd2+, although they were always higher in the cytosol. Thiol-containing peptides induced by Cd were mainly located in the cytosol after 3 days, and in the chloroplasts after 8 days of culture. The data suggested that Cd was compartmentalized into chloroplasts in a process that may involve the transport of free Cd and the participation of thiol-peptides.