RESUMO
Amine fungicides are widely used as crop protectants. Their success is believed to be related to their ability to inhibit postlanosterol sterol biosynthesis in fungi, in particular sterol-Δ(8),Δ(7)-isomerases and sterol-Δ(14)-reductases, with a concomitant accumulation of toxic abnormal sterols. However, their actual cellular effects and mechanisms of death induction are still poorly understood. Paradoxically, plants exhibit a natural resistance to amine fungicides although they have similar enzymes in postcicloartenol sterol biosynthesis that are also susceptible to fungicide inhibition. A major difference in vacuolar ion homeostasis between plants and fungi is the presence of a dual set of primary proton pumps in the former (V-ATPase and H(+)-pyrophosphatase), but only the V-ATPase in the latter. Abnormal sterols affect the proton-pumping capacity of V-ATPases in fungi and this has been proposed as a major determinant in fungicide action. Using Saccharomyces cerevisiae as a model fungus, we provide evidence that amine fungicide treatment induced cell death by apoptosis. Cell death was concomitant with impaired H(+)-pumping capacity in vacuole vesicles and dependent on vacuolar proteases. Also, the heterologous expression of the Arabidopsis thaliana main H(+)-pyrophosphatase (AVP1) at the fungal vacuolar membrane reduced apoptosis levels in yeast and increased resistance to amine fungicides. Consistently, A. thaliana avp1 mutant seedlings showed increased susceptibility to this amine fungicide, particularly at the level of root development. This is in agreement with AVP1 being nearly the sole H(+)-pyrophosphatase gene expressed at the root elongation zones. All in all, the present data suggest that H(+)-pyrophosphatases are major determinants of plant tolerance to amine fungicides.
RESUMO
La energía derivada de especies leñosas, esto es, mejor denominada como ENERGIA BIOMASICA, es un elemento importante en áreas en donde el acceso de la electricidad es restringida por diferentes razones. Alrededor de 2.000 millones de seres en los países subdesarrollados satifacen sus necesidades en un 90 por ciento con el uso de la leña y el carbón vegetal, mostrando la importancia de este tema en el mundo de hoy. Costa Rica, pese a su ejemplar desarrollo hidroenergético, tiente muchas comunidades pobres, suburbanas, urbanas y rurales, en donde la leña es el único medio para preparar los alimentos. No obstante, la situación es mucho peor en los demás países del Istmo centroamericano. Paralelamente a la importancia que tiene la leña como recurso energético, es preciso indicar que no observasre ciertas medidas preventivas, el sistema en sí puede convertirse (y de hecho ha sucedido) en un enemigo doméstico de la salud de sus usuarios. Escasa ventilación, leña o poco seca y constante exposición al humo cada día, son factores que provocan la aparición de enfermedades bronco pulmonares.