Morfoanatomía de semillas de Nothofagus alessandrii y su uso en la variabilidad de poblaciones

Nothofagus alessandrii is an endangered species that is endemic to the Mediterranean area of Chile. There is no information on the anatomical structure of its seeds and there are few studies on the morphometric and germination differences between its populations. Therefore, the purpose of this study was to describe the morpho-anatomical structure of seeds of N. alessandrii in order to compare the morphology and germination four geographically distinct populations. This was done by selecting seeds of four different origins covering the entire latitudinal distribution of the species and measuring their size, shape, dry weight and germination in order to perform a comparative analysis. Results showed that the anatomical structure of N. alessandrii seeds is similar to that of other species of the Fagaceae family such as Fagus sylvatica. No differences were found between seeds from the four different origins in morphological characteristics or germinative power. Thus, it was not possible to demonstrate the existence of clinal variation, although the southernmost population showed differences in length and weight, suggesting that it may belong to a different ecotype.Nothofagus alessandrii es una especie endémica del área Mediterránea de Chile, de la cual no se cuenta con información sobre la estructura anatómica de sus semillas. Existen muy pocos estudios sobre la variabilidad morfológica y de germinación entre sus poblaciones. El objetivo de este estudio fue describir la estructura morfoanatómica de semillas de N. alessandrii con el fin de comparar la morfología y la germinación entre cuatro poblaciones geográficamente separadas. Se seleccionaron semillas de cuatro orígenes geográficos a lo largo de la distribución latitudinal de la especie, y se midieron el tamaño, la forma, el peso seco, y la germinación. Los resultados mostraron que las semillas de N. alessandrii tienen una estructura anatómica similar a la de otras especies de la familia Fagaceae como Fagus sylvatica. No se encontraron diferencias significativas en las características morfológicas de los lotes estudiados, ni tampoco en el poder germinativo, por lo que no se ha observado una variación clinal entre poblaciones, aunque la población localizada más al sur presentó variaciones en longitud y peso, sugiriendo la posibilidad de ecotipo diferenciado

Mitochondrial Na+ controls oxidative phosphorylation and hypoxic redox signalling

All metazoans depend on O2 delivery and consumption by the mitochondrial oxidative phosphorylation (OXPHOS) system to produce energy. A decrease in O2 availability (hypoxia) leads to profound metabolic rewiring. In addition, OXPHOS uses O2 to produce reactive oxygen species (ROS) that can drive cell adaptations through redox signalling, but also trigger cell damage1–4, and both phenomena occur in hypoxia4–8. However, the precise mechanism by which acute hypoxia triggers mitochondrial ROS production is still unknown. Ca2+ is one of the best known examples of an ion acting as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential and collaborating in ion transport10. Here we show that Na+ acts as a second messenger regulating OXPHOS function and ROS production by modulating fluidity of the inner mitochondrial membrane (IMM). We found that a conformational shift in mitochondrial complex I during acute hypoxia11 drives the acidification of the matrix and solubilization of calcium phosphate precipitates. The concomitant increase in matrix free-Ca2+ activates the mitochondrial Na+/Ca2+ exchanger (NCLX), which imports Na+ into the matrix. Na+ interacts with phospholipids reducing IMM fluidity and mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III, generating a redox signal. Inhibition of mitochondrial Na+ import through NCLX is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ import into the mitochondrial matrix controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences in cellular metabolism